Aldehydes and Ketones Chapter 27 PDF

1255 60 Aldehydes and Ketones Chapter E3 27 Aldehydes and Ketones ID Introduction Carbonyl compounds are of two types, aldehydes and ketones. Both have a carbon-oxygen double bond often called as carbonyl group. O Preparation of carbonyl compounds C D YG Carbonyl group U (1) From alcohols OH Both al...

1255 60 Aldehydes and Ketones Chapter E3 27 Aldehydes and Ketones ID Introduction Carbonyl compounds are of two types, aldehydes and ketones. Both have a carbon-oxygen double bond often called as carbonyl group. O Preparation of carbonyl compounds C D YG Carbonyl group U (1) From alcohols OH Both aldehyde and ketones possess the same general formula Cn H 2n O. Structure : Carbonyl carbon atom is joined to three atoms by sigma bonds. Since these bonds utilise (i) By oxidation. O | || Mild oxidising R  CH  R '    R  C  R ' Secondary alcohol agents O || Mild oxidising R  CH 2  OH    R  C  H agents Primary alcohol Mild oxidising agents are (a) X 2 (Halogen) (b) (e) Sarret reagent (f) MnO 2 ST U apart. The carbon-oxygen double bond is different than carbon-carbon double bond. Since, oxygen is more electronegative, the electrons of the bond are attracted towards oxygen. Consequently, oxygen attains a partial negative charge and carbon a partial positive charge making the bond polar. The high values of dipole  C O (2.3 – 2.8D) cannot be explained only on the basis of inductive effect and thus, it is proposed that carbonyl group is a resonance hybrid of the following two structures. C  O  120° 120° C 120°  C O -bond O  -bond Fenton reagent  (c) K 2 Cr2 O7 / H  Aldehy de ( FeSO 4  H 2 O2 ) sp 2 -orbitals, they lie in the same plane and are 120° moment, Ketone (d) Jones reagent (g) Aluminium [ Al(O  C(CH 3 )3 )3 ] tertiary butoxide  When the secondary alcohols can be oxidised to ketones by aluminium tert-butoxide, [(CH 3 )3 CO]3 Al the reaction is known as oppenauer oxidation. Unsaturated secondary alcohols can also be oxidised to unsaturated ketones (without affecting double bond) by this reagent.  The yield of aldehydes is usually low by this methods. The allylic alcohols can be converted to aldehydes by treating with oxidising agent pyridinium chloro-chromate (C 5 H 5 NH  CrO 3 Cl  ). It is abbreviated as PCC and is called Collin's reagent. This reagent is used in non-aqueous solvents like CH 2 Cl 2 (dichloro methane). It is prepared by mixing pyridine, CrO3 and HCl in dichloromethane. This is a very good reagent because it checks the further oxidation of aldehydes to carboxylic 1256 Aldehydes and Ketones acids and is suitable method for preparing ,unsaturated aldehydes. (ii) Dehydrogenation of 1° and 2° alcohols by Cu/300° or Ag/300°C. O || R  CH 2 OH   R  C  H  H 2 OH R  C  OH  R COO H  R  C  R  CO 2  HOH Ketone Carboxy lic acid (3) From gem dihalides : Gem dihalides on hydrolysis give carbonyl compounds  || X (2) From carboxylic acids  (RCOO )2 Ca  (R ' COO )2 Ca  2 R  C  R' 2CaCO 3 Thus in the product, one alkyl group comes from one carboxylic acid and other alkyl group from other carboxylic acid. X  This method is not used much since aldehydes are affected by alkali and dihalides are usually prepared from the carbonyl compounds. (4) From alkenes (i) Ozonolysis : Alkenes on reductive ozonolysis give carbonyl compounds (i) O3 R  CH  CH  R   R  CHO  RCHO Alkene R   | O+CaCO3 O (i) O3 O O || ||   R  C  R  R '  C  R ' (ii) H O / Zn 2 R' Alkene U O  This method is used only for aliphatic carbonyl compounds. D YG O      || Distillation   O  C  (CH 2 )5  COO  Ca      R' CC R Cyclopropanone (ii) H 2O / Zn ID Calcium salts of dibasic acid (1, 4 and higher) on distillation give cyclic ketones. HOH / O H E3 O || ||  R  C  R ' (ii) R  C  R '    || || O  | (i) Distillation of Ca, Ba, Sr or Th salts of monobasic acids O Aldehy de Gemdihalid e Cu / 300 C R  CH  R '    R  C  R '  H 2 C H2  C O Distillation Ca      | CH 2  C  O || MnO / 300 C HOH / O H (i) R  CHX 2   R  CHO O | O || 60 Cu / 300 C O Cyclohexanone (ii) Decarboxylation or Dehydration of acids by MnO/300°C. (a) This reaction takes place between two molecules of carboxylic acids. Both may be the same or different. U (b) If one of the carboxylic acids is HCOOH then this acid undergoes decarboxylation because this acid is the only monobasic acid which undergoes decarboxylation even in the absence of catalyst. (ii) Oxo process CO 2 (CO )8 R  CH  CH 2  CO  H 2   R  CH 2  CH 2  CHO 150 C , 300 atm  Oxo process is used only for the preparation of aldehydes. (iii) Wacker process PdCl 2 / HOH   CH 3  CHO (a) CH 2  CH 2  air / Cu 2Cl 2 Ethene O ||  R  C  CH 3 (b) R  CH  CH 2  PdCl 2 / HOH air/Cu 2 Cl 2 Alky l ethene (5) From alkynes O ST Case I : When both molecules are HCOOH O || H  C  OH  H COO H formic acid H2O/HgSO4 /H2SO4 O ||  CO 2  HOH  H  C  H MnO 300 C formaldehyde R–CC–H (i) SiO2 BH3 Case II : When only one molecule is formic acid. O O || || MnO / 300 C R  C  OH  H  COO H   R  C  H  CO 2  HOH Carboxy lic acid formic acid R – C – CH3 R – CH2 – CHO  (ii) H2O2/ OH (6) From Grignard reagents Aldehy de O Case III : When none of the molecule is formic R' – C – Cl acid. HCOOC2H5 O R' – C – R O (Only ketone) H – C – R (Aldehyde) O R' COOC2H5 R – MgX (Excess) R–C– R' O (Ketone) Aldehydes and Ketones 1257 DMSO R  CH 2 Cl    R  CHO ; Cl O | || R  C H  R   R  C  R DMSO DMSO or (i) (CH 2 )6 N 4 C 6 H 5  CH 2 Cl          C 6 H 5  CHO (ii) H 2 O / H or Cu ( NO 3 )2 or Pb ( NO 3 )2 (11) From nitro alkanes : Nitro alkanes having at least one  -hydrogen atom give carbonyl compounds on treatment with conc NaOH followed by 70% H 2 SO 4. 60 The reaction is known as Nef carbonyl synthesis. O OH O H2 NaOH R  CH 2  N   R  C H  N Tautomeris ation O O (Aciform)  R  CHO 70 % H 2SO 4 || || R ' 2 Cd R  C  Cl    R  C  R ' O O || || R  C  Cl  R  C  R' E3 R D YG H 2 / Pd  BaSO 4  CaCO 3 R  C  Cl   R  C  H Xy lene || O || H 2 / Pd  BaSO 4  CaCO 3 || ST U (Only used for aldehydes) (8) From cyanides (i) Stephen aldehyde synthesis : Conversion of cyanides into aldehydes by partial reduction with SnCl 2 / HCl , followed by hydrolysis, is known as C6H5 – CH3 Toluene Aldehy de O C6H5 CHO C6H5 – CH2Cl C6H5CH O Pb(NO3)2/ C6H5 – CHO C6H5 – CHO (3) Gattermann – Koch formylation : This reaction is mainly given by aromatic hydrocarbons and CHO halobenzenes. || HIO4 CO/HCl /Anhy. ZnCl2 /Cu2Cl2 | R Pb(OCOCH 3 )4 also Air/MnO Cu(NO3)2/ R  CH  C  R  RCHO  R  C  R  H 2 O  C6H5 CHO (ii) H2O (i) (CH2)6N4 / (ii) H2O (Only used for aldehydes) C6H5CHO (2) From chloro methyl R  C  N   R  CHO | (i) CrO2Cl2 (ii) HOH (Etard's reaction) (i) CrO3 /(CH3CO)2O/CH3COOH 500°C (i) SnCl 2 / HCl / ether | || Preparation of only aromatic carbonyl compounds (1) From methyl arenes Stephens aldehyde synthesis. (9) From vic diols OH OH Ketone (ii) H 2 SO 4 (ii) HOH / H Xy lene (ii) H 2O /  or steam distillati on O (Iso- nitro alkane) Ar  C  Cl        Ar  C  H Alky l cy anide || (12) Reaction with excess of alkyl lithium : Carboxylic acids react with excess of organo lithium compound to give lithium salt of gem diols which on hydrolysis give ketones. O O || O O (i) NaOH   R  C  R (i) R  Li (excess) R'  C  OH   R'  C  R (Only used for the preparation of ketones) In this method product is always ketone because R  H and also R'  H. (ii) Rosenmunds reduction : This reduction takes place in the presence of Lindlars catalyst. O O || Aldehy de O CH  N U R ' 2 CuLi R ID (7) From acid chloride (i) Acid chlorides give nucleophilic substitution reaction with dialkyl cadmium and dialkyl lithium cuprate to give ketones. This is one of the most important method for the preparation of ketones from acid chlorides. O O gives similar oxidation products. (10) From Alkyl halides and benzyl halides Benzene CH3 Benzaldehyde CH3 CHO CO/HCl /Anhy. ZnCl2 /Cu2Cl2 Toluene Cl CH3 + o-methyl benzaldehyde Cl CHO p-methyl benzaldehyde Cl 1258 Aldehydes and Ketones (6) Reimer – Tiemann reaction : Phenol gives oand p- hydroxy benzaldehyde in this reaction. OH OH OH CHO + (i) CHCl3 /Alc.KOH/ (ii) H2O/H+ 60 phenol (major) CHO (Minor) Physical properties of carbonyl compounds CH3 CH3 CHO (i) Zn(CN)2 /HCl gas + o-methyl benzaldehyd e Toluene OH OH CHO (i) Zn(CN)2 /HCl gas (ii) H2O/ CHO p-methyl benzaldehyd e OH U (ii) H2O/ ID CH3 D YG + oCHO salicylaldehyd pe salicylaldehyd Phenol OCH3 OCH3 e OCH3 CHO (i) Zn(CN)2 /HCl gas (ii) H2O/ + o-methoxy benzaldehyde U Anisol CHO p-methoxy benzaldehyde ST (5) Houben – Hoesch reaction : This reaction is given by di and polyhydric benzenes. OH OH (i) RCN/HCl gas/Anhy.ZnCl 2 (ii) H2O OH Resorcino l OH COR 2,4-dihydroxy ketone OH OH OH Phloroglucinol HO  + – + + O + – C O H H O=C With the increase in the size of alkyl group, the solubility decreases and the compounds with more than four carbon atom are practically insoluble in water. All aldehydes and ketones are, however, soluble in organic solvents such as ether, alcohol, etc. The ketones are good solvents themselves. (4) Boiling points : The boiling points of aldehydes and ketones are higher than those of non polar compounds (hydrocarbons) or weakly polar compounds (such as ethers) of comparable molecular masses. However, their boiling points are lower than those of corresponding alcohols or carboxylic acids. This is because aldehydes and ketones are polar compounds having sufficient intermolecular dipoledipole interactions between the opposite ends of C  O dipoles.       C  O C  O C  O  (i) RCN/HCl gas/Anhy.ZnCl 2 (ii) H2O HO (1) Physical state : Methanal is a pungent smell gas. Ethanal is a volatile liquid, boiling points 294 K. Other aldehydes and ketones containing up to eleven carbon atoms are colourless liquids while higher members are solids. (2) Smell : With the exception of lower aldehydes which have unpleasant odours, aldehydes and ketones have generally pleasant smell. As the size of the molecule increases, the odour becomes less pungent and more fragrant. In fact, many naturally occurring aldehydes and ketones have been used in blending of perfumes and flavouring agents. (3) Solubility : Aldehydes and ketones upto four carbon atoms are miscible with water. This is due to the presence of hydrogen bonding between the polar carbonyl group and water molecules as shown below : – E3 (4) Gattermann formylation : This reaction is mainly given by alkyl benzenes, phenols and phenolic ethers. OH COR 2,4,6-trihydroxy ketone However, these dipole-dipole interactions are weaker than the intermolecular hydrogen bonding in alcohols and carboxylic acids. Therefore, boiling points Aldehydes and Ketones CH 3 CH 3.. CO:.. CO: CH 3 H Acetone   2.88 D b.pt  329 K Acetaldehyde   2.52 D b.pt.  322 K (5) Density : Density of aldehydes and ketones is less than that of water. Chemical properties of carbonyl compounds (3) Oxidation (5) Reactions due to -hydrogen D YG (6) Condensation reactions and (7) Miscellaneous reactions (1) Nucleophilic addition reactions (i) Carbonyl compounds give nucleophilic addition reaction with those reagents which on dissociation give electrophile as well as nucleophile. (ii) If nucleophile is weak then addition reaction is carried out in the presence of acid as catalyst. U (iii) Product of addition reactions can be written as follows, H ||   OH | R  C  R '  H  Nu  R  C  R ' ST  Addition R CO > H Formaldehy de R Aldehy de Ketone (b) Stearic effect : The size of the alkyl group is more than that of hydrogen. In aldehydes, there is one alkyl group but in ketones, there are two alkyl groups attached to the carbonyl group. The alkyl groups are larger than a hydrogen atom and these cause hindrance to the attacking group. This is called stearic hindrance. As the number and size of the alkyl groups increase, the hindrance to the attack of nucleophile also increases and the reactivity of a carbonyl decreases. The lack of hindrance in nucleophilic attack is another reason for the greater reactivity of formaldehyde. Thus, the reactivity follows the order: | Nu Adduct In addition reactions nucleophile adds on carbonyl carbon and electrophile on carbonyl oxygen to give adduct. (iv) Relative reactivity of aldehydes and ketones : Aldehydes and ketones readily undergo nucleophilic addition reactions. However, ketones are less reactive than aldehydes. This is due to electronic and stearic effects as explained below: (a) Inductive effect : The relative reactivities of aldehydes and ketones in nucleophilic addition reactions may be attributed to the amount of positive CH 3 H CH 3 CO > H CO H Form aldehy de CO > > CH 3 Acetaldehyde Acetone (CH 3 )2 CH (CH 3 )3 C CO CO > (CH 3 )2 CH (CH 3 )3 C Di- tert. buty l ketone Di- isopropy l ketone  O CO U (4) Reduction R ID Chemical reactions of carbonyl compounds can be classified into following categories. (2) Addition followed by elimination reactions H CO > Carbonyl compounds give chemical reactions due to carbonyl group and -hydrogens. (1) Nucleophilic addition reactions 60 Among the carbonyl compounds, ketones have slightly higher boiling points than the isomeric aldehydes. This is due to the presence of two electrons releasing groups around the carbonyl carbon, which makes them more polar. charge on the carbon. A greater positive charge means a higher reactivity. If the positive charge is dispersed throughout the molecule, the carbonyl compound becomes more stable and its reactivity decreases. Now, alkyl group is an electron releasing group (+I inductive effect). Therefore, electron releasing power of two alkyl groups in ketones is more than that of one alkyl group in aldehyde. As a result, the electron deficiency of carbon atom in the carbonyl group is satisfied more in ketones than in aldehydes. Therefore, the reduced positive charge on carbon in case of ketones discourages the attack of nucleophiles. Hence ketones are less reactive than aldehydes. Formaldehyde with no alkyl groups is the most reactive of the aldehydes and ketones. Thus, the order of reactivity is: E3 of aldehydes and ketones are relatively lower than the alcohols and carboxylic acids of comparable molecular masses. 1259 In general, aromatic aldehydes and ketones are less reactive than the corresponding aliphatic analogues. For example, benzaldehyde is less reactive than aliphatic aldehydes. This can be easily understood from the resonating structures of benzaldehyde as shown below: : O.. H C..– : O.. H C..– : O.. H C   I II III 1260 Aldehydes and Ketones..– : O.. H All types of aldehydes give addition reaction with this reagent. O H C OH O C || | O   || H or OH or R  C  H   R  C  H    R  C  H  HSO 3 Na | HCHO SO 3 Na Adduct; white cry stalline in nature It is clear from the resonating structures that due to electron releasing resonance effect of the benzene ring, the magnitude of the positive charge on the carbonyl group decreases and consequently it becomes less susceptible to the nucleophilic attack. Thus, aromatic aldehydes and ketones are less reactive than the corresponding aliphatic aldehyde and ketones. The order of reactivity of aromatic aldehydes and ketones is, C6 H 5 CHO > C6 H 5 COCH 3 > C6 H 5 COC 6 H 5 Acetopheno ne Some important addition reactions Addition of HCN O nucleophilic | OH R  C  H  HCN   R  C  CN C 6 H 5  C  H  HCN  OH | C 6 H 5  C  CN | D YG H Benzaldehy de cy anohy drin U  Because HCN is a toxic gas, the best way to carry out this reaction is to generate hydrogen cyanide during the reaction by adding HCl to a mixture of the carbonyl compound and excess of NaCN.  Benzophenone does not react with HCN.  Except formaldehyde, all other aldehydes gives optically active cyanohydrin (racemic mixture).  This reaction is synthetically useful reaction for the preparation of -hydroxy acids, -amino alcohols and -hydroxy aldehydes. OH  ST H2O/H/  - Hy droxy acid (If R is CH3 then product is lactic acid) H2/Pt | OH | R  C(i) H  CH 2  NH 2  - Amino alcohol SnCl /HCl (ii) 2HOH/ OH | R  C H  CHO  -hy droxy aldehy de Addition of sodium bisulphite HCHO Colourless cry stalline product  This reagent can be used for differentiation between aromatic and aliphatic methyl ketones, e.g. || CH 3  CH 2  C  CH 2  CH 3 and O || O || CH 3  CH 2  C  CH 3 and  This reagent can be used for the separation of aldehydes and aliphatic methyl ketones from the mixture, e.g. CH 3  CH 2  CHO and O || CH 3  CH 2  C  CH 2  CH 3 These two compounds can be separated from their mixture by the use of NaHSO3. Higher aliphatic ketones and aromatic ketones do not react with NaHSO3. Addition of alcohols : Carbonyl compounds give addition reaction with alcohols. This reaction is catalysed by acid and base. Nature of product depends on the catalyst. | R  C H  COOH OH R  CH  CN | C6 H 5  C  CH 3 OH Benzaldehy de || U  H or OH or SO 3 Na || Cy anohy drin || O   | R  C  CH 3   R  C  CH 3    R  C  H HSO 3 Na O | H O addition CH 3  CH 2  CH 2  C  CH 3 OH  || of OH give O Benzopheno ne examples O || ID Benzaldehy de Only aliphatic methyl ketones reaction with sodium bisulphite. 60 V E3 IV Case I : Addition catalysed by base : In the presence of a base one equivalent of an alcohol reacts with only one equivalent of the carbonyl compound. The product obtained is called hemiacetal (in case of aldehyde) and hemiketal (in case of ketone). The reaction is reversible. There is always equilibrium between reactants and product. O ||   CH 3  C  H  CH 3  O  H  HO OH | CH 3  C  H | OCH 3 Hemiacetal Aldehydes and Ketones || CH 3  C  CH 3  CH 3  O  H OH  HO | CH 3  C  CH 3 | OCH 3 Hemiketal and hemiketals -alkoxy are Case II : Addition catalysed by acid : In the presence of an acid one equivalent of carbonyl compound reacts with two equivalents of alcohol. Product of the reaction is acetal (in case of aldehyde) or ketal (in case of ketone). O || R  C  H  2CH 3 OH | | || R  C  R  H 2O R  C  R  2CH 3 OH | OCH 3 O Ketal || C O   H OCH 3  H 2O (ii) Acetals compounds. and ketals are gem dialkoxy (iii) High yield of acetals or ketals are obtained if the water eliminated from the reaction is removed as it formed because the reaction is reversible. (iv) Acetals and ketals can be transformed back to corresponding aldehyde or ketone in the presence of excess of water. O U OCH 3  | || H R  C  R  H 2 O  R  C  R  2CH 3 OH | OCH 3 OH | R  C  R' | Ketone OH Gemdiol U H  O  CH 3 OCH 3 OH | R' – CH – R 2°alcohol OH | R' – C – R' 3°-alcohol | R Gem diols are highly unstable compounds hence equilibrium favours the backward direction. The extent to which an aldehyde or ketone is hydrated depends on the stability of gem diol. D YG R R  C  R '  HOH ID (i) Formation of acetals and ketals can be shown as follows: H  O  CH 3 R – CH2OH 1°-alcohol Addition of water : Carbonyl compounds react with water to give gem diols. This reaction is catalysed by acid. The reaction is reversible reaction. OCH 3 C (i) R' – C – R'  (ii) HOH/H | Acetal R RMgX Grignard reagent R  C  H  H 2O O R (i) R' – C – H  (ii) HOH/H O OCH 3  H OCH 3 R (i) H – C – H  (ii) HOH/H O E3 Hemiacetals alcohols. Addition of Grignard reagents : Grignard reagents react with carbonyl compounds to give alcohols. Nature of alcohol depends on the nature of O carbonyl compound. 60 O 1261 (Excess) ST Ketal This reaction is very useful reaction for the protection of carbonyl group which can be deprotected by hydrolysis. Glycol is used for this purpose. Suppose we want to carry out the given conversion by LiAlH 4. Stability of gem diols depend on the following factors: (i) Steric hindrance by +I group around -carbon decreases the stability of gem diols. +I group decreases stability of gem diol and hence decreases extent of hydration. (ii) Stability of gem diols mainly depends on the presence of –I group on -carbon. More is the –I power of the group more will be stability of gem diols. (iii) Intramolecular hydrogen bonding increases stability of gem diols. –I groups present on carbon having gem diol group increases strength of hydrogen bond. More is the strength of hydrogen bond more will be the stability of gem diol. Addition of terminal alkynes : This reaction is known as ethinylation.  O || LiAlH 4   CH 3  C  CH 2  COOC 2 H 5    || ONa | R  C  C Na  R '  C  R   R  C  C  C  R " Sod. salt of alky ne O || CH 3  C  CH 2  CH 2 OH This can be achieved by protection of group and then by deprotection O CO | R' O R–C– 1262 Aldehydes and Ketones OH  |   R  C  C  C  R " HOH / H | R' alky nol  R  HOH R  C  R    CNZ | N HZ.. D YG An imine Different Imine formation with NH 2  Z is given below U O || C 6 H 5  C  CH 3  CH 3  C  NH  C 6 H 5 (i) PCl 5 || N OH (ii) H 2 O N - pheny lacetamide Acetopheno xime O || CH 3  C  C 6 H 5  C 6 H 5  C  NH  CH 3 (i) PCl 5 (ii) H 2 O N - methy l acetamide In short product of the rearrangement can be obtained as follows: R R' C An imine R The overall reaction can be shown as follows R R .. H C  O  N H 2  Z  H 2O  C N R R R ST etc.) U | (PCl 5 , SOCl 2 , PhSO 2 Cl, RCOCl , SO 3 , BF3 N OH  OH Lewis acids || .. H R  C  R  H  N H  Z  || and ID O Beckmann rearrangement : Ketoxime when treated with acid at 0°C it undergoes rearrangement known as Beckmann rearrangement. Thus acid catalysed conversion of ketoximes to Nsubstituted amides is called Beckmann rearrangement. Acid catalyst used are proton acids (H 2 SO 4 , HCl, H 3 PO 4 ) 60 (i) In nucleophilic addition reactions poor nucleophile such as ammonia and ammonia derivatives requires acid as catalyst. (ii) If the attacking atom of the nucleophile has a lone pair of electrons in the addition product, water will be eliminated from the addition product. This is called a nucleophilic addition elimination. Primary amines and derivatives of ammonia react with carbonyl compounds to give adduct. In adduct nucleophilic group has lone pair of electrons. It undergoes elimination to give product known as imine. An imine is a compound with a carbon-nitrogen double bond. E3 (2) Addition followed by elimination reactions : This reaction is given by ammonia derivatives (NH 2  Z). || N OH O || R ' C  O  H  R '  C  NH  R Tautomeris ation || RN (3) Oxidation of carbonyl compounds (i) Oxidation by mild oxidising agents : Mild oxidising agents oxidise only aldehydes into carboxylic acids. They do not oxidises ketones. Main oxidising agents are: (a) Fehling solution : It is a mixture of two Fehling solution: Fehling solution No. 1 : It contains CuSO 4 solution and NaOH. Fehling solution No. 2 : It contains sodium potassium tartrate. (Roschelle salt). (b) Benedict's solution : This solution contains CuSO 4 , NaOH and sodium or potassium citrate.  Reacting species of both solutions is Cu   oxidation no. of Cu varies from 2 to 1.  These two oxidising agents oxidise only aliphatic aldehydes and have no effect on any other functional groups Benedict's solution and Fehling solutions are used as a reagent for the test of sugar (glucose) in blood sample. Aldehydes and Ketones (c) Tollens reagent : Tollens reagent is ammonical O ||  [O ] CH 2  CH 2  CH 3   CH 3  CH 2  CH 2  C  C=7 COOH COOH CH 3  CH 2  CH 2  COOH  CH 3  CH 2  COOH silver nitrate solution. Its reacting species is Ag.  It oxidises aliphatic as well as aromatic aldehydes. C 4 Redox R  CHO  Ag     RCOOH  Ag (as reaction Thus number of carbons in any product is less than the number of carbons in ketone. multiple bond. CH 2  CH  CHO  Ag   CH 2  CH  COOH  Ag In this reaction the oxidation no. of Ag varies Case II : Oxidation of unsymmetrical ketones : In case of unsymmetrical ketones -carbon whose bond breaks always belongs to the alkyl group which has more number of carbons. This rule is known as Popoff’s rule. from +1 to 0. O  Glucose, fructose give positive test with Tollen's reagents and Fehling solution. C  O (keto) group yet give (d) Reaction with mercuric chloride solution : Case III : Oxidation of cyclic ketones : Formation of dibasic acid takes place from cyclic ketones. In this case the number of carbons in ketone and dibasic O carboxylic acid is always same.   || O O U R  C  H  HgCl 2  H 2 O  R  C  OH  HCl  Hg 2 Cl 2 () || D YG (Black) || O CH 3CHO colourless solution    pink colour restored (In cold). (ii) Oxidation by strong oxidising agents : Main KMnO 4 / H / , agents K 2 Cr2 O 7 / H  are / KMnO 4 / OH and conc  / , HNO3 / . U These agents oxidise aldehydes as well as ketones. (a) Oxidation of aldehydes oxidised into corresponding acids. O : Aldehydes H ST  KMnO 4 / O H /  C6 H 5 CHO    C6 H 5 COOH (b) Oxidation of ketones : Ketones undergo oxidation only in drastic conditions. During the oxidation of ketones there is breaking of carbon-carbon bond between -carbon and carbonyl carbon. In this process both carbons convert into carboxylic groups. This leads to the formation of two moles of monocarboxylic acids. H CH 3 |  2-Methyl COOH  (CH 2 )3  CH  COOH cyclohaxanone  - Methy l adipic acid (iii) Miscellaneous oxidation (a) Haloform Reaction O  || (i) X2 / OH R  C  CH 3    RCOOH  CHX 3  methy l carbony l  (ii) H (b) Oxidation at -CH2 or CH3 by SeO2 : SeO2 oxidises   CH 2  group into keto group and   CH 3  group into aldehydic group. In this oxidation reactivity of CH 2 is more than the CH 3 group and Oxidation is regio selective in nature. 2 CH 3  CHO  CHO  CHO ; SeO Gly oxal O || Case I : Oxidation of symmetrical ketones CH3 [O ] are C n  H [O ] RCHO   RCOOH C n Adipic acid  If both -carbons are not identical then bond breaking takes place between carbonyl carbon and the carbon which has maximum number of hydrogens. SO 2 (e) Schiff's reagent : Megenta solution    [O ]   COOH  (CH 2 )4  COOH (White) R  C  H  Hg 2 Cl 2  H 2 O  R  C  OH  HCl  Hg() oxidising COOH [O ]   CH 3  CH 2  COOH  CH 3  CH 2  COOH ID positive test with Fehling solution due to presence of hydroxyl keto group. Tollens reagent also gives positive test with terminal alkynes and HCOOH. C  CH 2  CH 3 COOH Gluconic acid Fructose contain || E3 CH 3  CH 2  CH 2 C5 H11 O5 CHO  Cu 2 O (or) Ag 2 O  C5 H11 O5 COOH || 60  This reagent has no effect on carbon-carbon O C 3 Total number of C  4  3 7 silver mirror) strong 1263 O || 2 CH 3  C  CH 3  CH 3  C  CHO SeO Methy lgly oxal 1264 Aldehydes and Ketones (i) LiAlH4 R  CHO   R  CH 2 OH (c) Oxidation by organic peracids : Organic peracids oxidise aldehydes into carboxylic acids and ketones into esters. This oxidation is known as Baeyer – Villiger oxidation. O O O OH || (ii) NaBH 4 (iii) Aluminium isopropoxi de || C6 H 5 COOOH   R  C  O  R  R  C  R   || NaBH 4 is regioselective reducing agent because it reduced only. CHO in the presence of other reducible group. Example : NaBH 4 CH 3  CH  CH  CHO   CH 3  CH  CH  CH 2 OH Crotonalde hyde during reduction. Example O || C6 H 5 COOOH R  C  C  R    R  C  O  C  R || Crotonyl alcohol Hydride ion of NaBH 4 attack on carbonyl carbon E3 In case of aldehyde there is insertion of atomic oxygen (obtained from peracid) between carbonyl carbon and hydrogen of carbonyl carbon. In case of ketone, insertion of oxygen takes place between carbonyl carbon and -carbon. Thus the product is ester. This is one of the most important reaction for the conversion of ketones into esters.  Vic dicarbonyl compound also undergo oxidation and product is anhydride. O O || : OD || | NaBD 4 CH 3  C  CH 3    CH 3  C  CH 2  CH 3 | D2 O 2-Butanone D OH | NaBD4 CH3 – C – CH2 – H2 O CH3 O || | CH 3  C  CH 3  D OD 2 Butanone | NaBH4 CH3 – C – CH2 – D2 O CH3 | H (iii) Reductive amination : In this reduction CO  group converts into CH  NH 2 group ID O O  Popoff's rule : Oxidation of unsymmetrical ketones largely take place in such a way that the smaller alkyl group remains attached to the CO group during the formation of two molecules of acids. This is known as Popoff's rule Example : | R  C  R '  R  CH  R ' (i) LiAlH 4 60 || (ii) NaBH 4 (iii) Aluminium isopropoxi de U [O ] CH 3  CO  CH 2  CH 3   CH 3  COOH  HOOCCH 3 (d) Baeyer- villiger oxidation : H | H  C  H  O  O  C  H  H  C  OH || || O O D YG || O H | CH 3  C  H  O  O  C  H  CH 3  C  OH || || || O O O  Reaction will be held if the oxidising agent is performic acid. U (4) Reduction of carbonyl compounds O || (i) Reduction of – C – group into –CH2 – group : Following three reagents reduce carbonyl group into CH 2  groups: (a) HI / P /  (b) Zn / Hg / Conc. HCl and R R C  O  NH 3  R R ST R – CH2 – R' Zn/Hg/Conc. HCl  O || NH2 – NH2 /OH  || | | | | R  C  C  R   R  C  C  R || || R R (i) Mg / Hg (ii) HOH R R Vic cis diol (pinacol) When this reaction is carried out in the presence of Mg / Hg / TiCl4 , the product is vic trans diol. n reduction) 2 O R – CH2 – R' (Wolff-kishner reduction) carbonyl compounds (ii) Reduction of into hydroxy compounds : Carbonyl group converts into and CHOH  group by LiAlH 4 , NaBH 4 , Na / C2 H 5 OH aluminium isopropoxide. OH OH O R – CH2 – R' (Clemmenso  Primary amine (iv) Reduction of ketones by Mg or Mg/Hg : In this case ketones undergo reduction via coupling reaction and product is vic cis diol. (c) NH 2  NH 2 / OH. O || R–C– R' CH  NH 2 R Imine  HI/P/ R H 2 / Ni C  NH    Cyclohexanone (i) Hg – Mg – TiCl4HOH (ii) HO OH Vic trans diol (v) Reduction of benzaldehyde by Na/C2H5OH : Benzaldehyde undergoes reduction via coupling reaction and product is vic diol. Aldehydes and Ketones carbanion is stabilised by delocalisation of negative charge. O O || | | C6 H 5  C  C  C6 H 5  (i) Na/C 2 H 5 OH (ii) HOH H H OH OH | O CH 3  C  R | C6 H 5  CH  C H  C6 H 5 vic diol (Bouveault-blanc reaction)  Aldehydes are reduced to 1° alcohols whereas ketones to 2° alcohols. If carbon – carbon double bond is also present in the carbonyl compound, it is also reduced alongwith. However, the use of the reagent 9-BBN (9– borabicyclo (3, 3, 1) nonane) prevents this and thus only the carbonyl group is reduced Example : | CH 2  C  R  CH 2  C  R Enolate ion (more stable) (c) The acidity of -hydrogen is more than ethyne. pKa value of aldehydes and ketones are generally 19 – 20 where as pKa value of ethyne is 25. (d) Compounds having active methylene or methyne group are even more acidic than simple aldehydes and ketones. O || C6 H 5  CH 2  C  CH 3  CH  CH  CHO   HOCH 2CH 2 NH 2 pKa  15.9 E3  - pheny l acetone O Cinnamaldehy de O || Carbanion (less stable)  9 BBN  O  Base || 60 || 1265 O  || CH  CHCH 2OH || C6 H 5  C  CH 2  C  CH 3 pKa  8. 5  - benzoy l acetone Cinnamyl (ii) Halogenation : Carbonyl compounds having -hydrogens undergo halogenation reactions. This ID alcohol  If reducing agent is NaH, reaction is called Darzen's reaction, we can also use LiAlH4 in this reaction.  If reducing agent is aluminium iso propoxide (CH 3  C H  O )3 Al. Product will be alcohol. This | || U CH 3 reaction is catalysed by acid as well as base. (a) Acid catalysed halogenation : This gives only monohalo derivative. O O D YG reaction is called Meerwein – pondorff verley reduction (MPV reduction).  The percentage yield of alkanes can be increased by using diethylene glycol in Wolf Kishner reduction. Then reaction is called Huang – Millan conversion. (vi) Hydrazones when treated with base like alkoxide give hydrocarbon (Wolf – Kishner reduction). N. NH 2 O || || CH 3  C  CH 3 23   CH 3  C  CH 2 Br Br / CH COOH   bromo acetone Acetone (b) Base catalysed halogenation : In the presence of base all -hydrogens of the same carbon is replaced by halogens.   O   || CH 3  CH 2  C  CH 2  CH 3 – X2/OH Excess || NH 2 NH 2 RONa R  C  R'    R  C  R'    R  CH 2  R Hy drazone U (vii) Schiff's base on reduction gives secondary amines. R ' NH 2 H 2 / Ni R  CH  O    R  CH  NR '    R  CH 2 NHR Aldehyde Schiff's base Secondary amine ST (5) Reactions due to -hydrogen (i) Acidity of -hydrogens : (a) -hydrogen of carbonyl compounds are acidic in character due to the presence of the electron withdrawing CO  group. -Hydrogen is acidic due H O | || –C–C– | Carbon to strong –I group; – CO –. (b) Thus carbonyl compounds having -hydrogen convert into carbanions in the presence of base. This O X O  || || | | X X | CH 3  CH 2  C  C  CH 3 CH 3  CH  C  CH  CH 3 | X Carbonyl compounds having three -hydrogens give haloform reaction. O  || O  ||    RCOO  CHX 3 R  C  CH 3  R  C  CX 3 OH X 2 / OH (iii) Deuterium exchange reaction : Deuterium exchange reaction is catalysed by acid (D  ) as well as  base (OD). In both the cases all the hydrogens on only one -carbon is replaced by D. O || O  || R  C  CH 2  R   R  C  CD2  R ; O || D2 O / OD  O || R  C  CH 2  R  R  C  CD2  R D2 O / D 1266 Aldehydes and Ketones ||  | || | H or C6 H 5  C  C  C 2 H 5    C6 H 5  C  C  C 2 H 5 |  | H OH H 2  methy l-1 - pheny l -1 - one Racemic mixture CH 3 O | ||  C 2 H 5  C  C  C6 H 5 |   CH 3  CH  CHO , CH 3  NO 2 , |  CH 3  CH 2  CN CH 3  If substrate and reagent both are carbonyl compounds then one should have at least one -hydrogen and other may or may not have -hydrogen. Condensation reaction always takes place in the presence of acid or base as catalyst. Best result is obtained with base at lower temp. OH O  || | H or R  C  R  CH 3  Z    R  C  C H 2  Z 60 (iv) Racemisation : Ketones whose -carbon is chiral undergo Racemisation in the presence of acid as well as base. O CH 3 O CH 3  H  | OH R Condensation is carried out at lower temperature ( 20 C ) because product of the reaction is alcohol which has strong –I group at -carbon. best result is obtained with CH 3  X. Other halides Such type of alcohols are highly reactive for dehydration. They undergo dehydration in the presence of acid as well as base even at 25°C. They also undergo elimination even on strong heating. O CH 3 LDA (Bulky base) || | (i) Aldol condensation CH 3 || CH 3 D YG CH 3 (Main product) Ethy l- isopropy l ketone (vi) Wittig reaction : Aldehyde and ketones undergo the wittig reaction to form alkenes. Ph 3 P  CH 2   C  O   C  CH 2  Aldehy de or ketone alkene Ph 3 P  O Tripheny l Phosphoniu m oxide Ph3 P  CHR 1  CHR 2  Ph3 P   CHR 1  || | O CHR 2 O U Ph 3 P  CHR 1  Ph 3 P  CHR 1 | | || O  CHR 2 || O CHR 2 ST (6) Condensation reaction of carbonyl compounds : Nucleophilic addition reaction of compounds having carbonyl group with those compounds which have at least one acidic hydrogen at -carbon is known as condensation reaction. In this addition reaction : Substrate is always an organic compound having a carbonyl group, e.g. O O O O || || H  C  H , C6 H 5  C  H , || Dehy dration β CH 3 (Main product) CH 3 I   CH 3 CH 2  C  CH || O  | R O R  C  H, R C  CH  Z R (a) This reaction takes place between two molecules of carbonyl compounds; one molecule should have at least two -hydrogen atoms. In this reaction best result is obtained when U  CH 2  C  CH  | HO/  R  C  CH 2  Z    CH 3  C  C  CH 3 | CH 3 OH ID undergo elimination in the presence of strong base. O O CH 3 CH 3 || ||  NaH CH 3 I CH 3  C  CH   CH 3  C  C   (Small base) Carbanion CH 3 CH 3 E3 (v) Alkylation : Carbonyl compounds having hydrogens undergo alkylation reaction with RX in the presence of base. This reaction is S N 2 reaction. The || Both molecule are the same or One should have no -hydrogen atom and other should have at least two -hydrogens. (b) These reactions are practical when base is NaOH and reaction temperature is high ( 100 ). (c) The reaction is two step reaction. First step is aldol formation and second step is dehydration of aldol. OH   |   CH 3  CHO  CH 3  CHO   CH 3  CH  CH 2  CHO        NaOH / OH Dehydration   CH 3  CH  CH  CHO a,   unsaturate d aldehyde Due to hyper-conjugation in crotonaldehyde further condensation give conjugated alkene carbonyl compound. CH3 – CH = CH – CHO + CH3 – CH = CH – CHO R  C  R etc. Addition always takes place on the carbonyl group. Reagents of the condensation reaction are also organic compounds having at least one hydrogen on carbon and -carbon should have –I group, e.g. NaOH OH | CH3 – CH = CH – CH – CH2 – CH = CH – CHO  –H2O CH3 – CH = CH – CH = CH – CH = CH – CHO CH3 – (CH = CH –)3 – CHO Condensed compound Aldehydes and Ketones 1267 Intra molecular aldol condensation : One molecule Intramolecular condensation give aldol compounds Example : OH  O  CH  (CH 2 )5  CHO   di. NaOH OH /  Mechanism : C 6 H 5  CHO  CH 3  CHO  CHO C6 H 5  CH  CH  CHO  HOH O  | | H Step III : OH | D YG | H C6 H 5  CH  CH  CHO  C6 H 5  CH  CH  CHO  HOH | H  OH In aldol condensation, dehydration occurs readily because the double bond that forms is conjugated, both with the carbonyl group and with the benzene ring. The conjugation system is thereby extended. ST U Crossed aldol condensation : Aldol condensation between two different aldehydes or two different ketones or one aldehyde and another ketone provided at least one of the components have -hydrogen atom gives different possible product dil NaOH (a) CH 3 CHO  CH 3  CH 2  CHO    Ethanal Test | However crossed aldol condensation is important when only it the components has -hydrogen atom.  CH 2 O  CH 3 CHO  CH 2  CH 2  CHO  CH 2  CH  CHO  H 2O | OH (3 - hy droxy propanal) (Acrolein) Ketones No colour. With Fehling's solution Give precipitate. No precipitate is formed. With Tollen's reagent Black precipitate or silver mirror is formed. No black precipitate or silver mirror is formed. With saturated sodium bisulphite solution in water Crystalline compound (colourless) formed. Crystalline compound (colourless) is formed. With 2, 4dinitrophenyl hydrazine Orange-yellow or red well defined crystals with melting points characteristic of individual aldehydes. Orange-yellow or red well defined crystals with melting points characteristic of individual ketones. With sodium hydroxide Give brown resinous mass (formaldehyde does not give this test). No reaction. With sodium nitroprusside and few drops of sodium hydroxide A deep red colour (formaldehyde does not respond to this test). Red colour which changes to orange. OH CH 3 | Aldehydes Give pink colour. Propanal CH 3  CH  CH  CHO  CH 3  CH 2  CHOH  CH 2  CHO Table : 27.1 With Schiff's reagent U C6 H 5  C  CH 2  CHO  C6 H 5  C  CH 2  CHO  OH HOH || ID OH | O OH Test of aldehydes and Ketones (Distinction) | H   || 4  Pheny l 3  buten - 2 - one Step II : C6 H 5  C  CH 2  CHO  O O C6 H 5 CHO  CH 3  C  CH 3    C6 H 5  CH  CH  C  CH 3 100 C  || 60    O O   || | HOH  CH 2  C  H  CH 2  C  H        (ii) Claisen – Schmidt reaction : Crossed aldol condensation between aromatic aldehyde and aliphatic ketone or mixed ketone is known as Claisen – Schmidt reaction. Claisen – Schmidt reactions are useful when bases such as sodium hydroxide are used because under these conditions ketones do not undergo self condensation. Some examples of this reaction are : E3  Step I : HO  H  CH 2  CHO red is Some commercially important aliphatic carbonyl compounds 1268 Aldehydes and Ketones Formaldehyde : Formaldehyde is the first member of the aldehyde series. It is present in green leaves of plants where its presence is supposed to be due to the reaction of CO 2 with water in presence of sunlight and chlorophyll. (1) Preparation Formaldehy de K 2 Cr2 O7 CH 3 OH  [O]   HCHO  H 2 O 60 (i) By oxidation of ethyl alcohol with acidified potassium dichromate or with air in presence of a catalyst like silver at 300°C. Cu or Ag (ii) CH 3 OH    HCHO Formaldehy de Heat (iii) Ca(HCOO ) 2   HCHO Formaldehy de (ii) By dehydrogenation of ethyl alcohol. The vapours of ethyl alcohol are passed over copper at 300°C. (iv) CH 2  CH 2  O3   HCHO H2 Pd Formaldehy de Mo- oxide   HCHO (v) CH 4  O 2  Methane Catalyst Formaldehy de E3 Calcium formate prepared by Scheele in 1774 by oxidation of ethyl alcohol. given below H 2 SO 4 300  400 C Acetaldehyde is the second member of the aldehyde series. It occurs in certain fruits. It was first (1) Preparation : It may be prepared by any of the general methods. The summary of the methods is Platinised asbestos (i) 2CH 3 OH  O 2   HCHO 300  400 C Acetaldehyde (iii) By heating the mixture of calcium acetate and calcium formate. (vi) CO  H 2   HCHO Elec. discharge Formaldehy de (iv) By heating ethylidene chloride with caustic soda or caustic potash solution. ID (2) Physical properties (i) It is a colourless, pungent smelling gas. (ii) It is extremely soluble in water. Its solubility in water may be due to hydrogen bonding between water molecules and its hydrate. (iii) It can easily be condensed into liquid. The liquid formaldehyde boils at – 21°C. (iv) It causes irritation to skin, eyes, nose and throat. D YG U (v) By the reduction of acetyl chloride with hydrogen in presence of a catalyst palladium suspended in barium sulphate (Rosenmund's reaction). (v) Its solution acts as antiseptic and disinfectant. (3) Uses (i) The 40% solution of formaldehyde (formalin) is used as disinfectant, germicide and antiseptic. It is used for the preservation of biological specimens. U (ii) It is used in the preparation of hexamethylene tetramine (urotropine) which is used as an antiseptic and germicide. (iii) It is used in silvering of mirror. ST (iv) It is employed in manufacture of synthetic dyes such as para-rosaniline, indigo, etc. (v) It is used in the manufacture of formamint (by mixing formaldehyde with lactose) – a throat lozenges. (vi) It is used for making synthetic plastics like bakelite, urea-formaldehyde resin, etc. (vii) Rongalite – a product obtained by reducing formaldehyde sodium bisulphite derivative with zinc dust and ammonia and is used as a reducing agent in vat dyeing. (vi) By the reduction of CH 3 CN with stannous chloride and HCl in ether and hydrolysis (Stephen's method). (vii) By hydration of acetylene with dil. H 2 SO 4 and HgSO 4 at 60°C. (viii) By ozonolysis of butene-2 and subsequent breaking of ozonide. (ix) Laboratory preparation : Acetaldehyde is prepared in the laboratory by oxidation of ethyl alcohol with acidified potassium dichromate or acidified sodium dichromate. K 2 Cr2 O7  4 H 2 SO 4  K 2 SO 4  Cr2 (SO 4 )3  4 H 2 O  3[O] [CH 3 CH 2 OH  O  CH 3 CHO  H 2 O]  3 K 2 Cr2 O7  3CH 3 CH 2 OH  4 H 2 SO 4  Potassium dichromate Ethyl alcohol Sulphuric acid K 2 SO 4  Cr2 (SO 4 )3  3 CH 3 CHO  7 H 2 O Potassium sulphate Chromic sulphate Acetaldehyde Water To recover acetaldehyde, the distillate is treated with dry ammonia when crystallised product, acetaldehyde ammonia, is formed. It is filtered and washed with dry ether. The dried crystals are then Aldehydes and Ketones distilled with dilute sulphuric acetaldehyde is collected. acid when pure 1269 (i) Acetaldehyde is a colourless volatile liquid. It boils at 21°C. OH (ii) It has a characteristic pungent smell. | CH 3 CHO  NH 3 CH 3  CH  NH 2  H 2 SO 4 Acetaldehyde ammonia CH 3 CHO  ( NH 4 ) 2 SO 4 Acetaldehyde (x) Manufacture : Acetaldehyde can manufactured by one of the following methods: be (iii) It is soluble in water, chloroform, ethyl alcohol and ether. Its aqueous solution has a pleasant odour. In water, it is hydrated to a considerable extent to form ethylidene diol. CH 3 CHO  H 2 O  CH 3 CH (OH )2 60 (3) Uses : Acetaldehyde is used : (a) By air oxidation of ethyl alcohol (i) In the preparation of acetic acid, acetic anhydride, ethyl acetate, chloral, 1,3-butadiene (used in Ag 2CH 3 CH 2 OH  O2   2CH 3 CHO  2 H 2 O 300 C (b) By dehydrogenation of alcohol rubbers), dyes and drugs. CH 3 CH 2 OH   CH 3 CHO Cu E3 (ii) As an antiseptic inhalent in nose troubles. 300 C (iii) In the preparation of paraldehyde (hypnotic and sporofic) and metaldehyde (solid fuel). (c) By hydration of acetylene HgSO 4 ,(1 %),60 C CH  CH  H 2 O   CH 3 CHO H 2 SO 4 (40 %) (a ID (d) From ethylene (Wacker process) (iv) In the preparation of acetaldehyde ammonia rubber accelerator). PdCl 2 ,CuCl 2 H 2 C  CH 2  O 2     H 3 C  CHO H 2O (2) Physical properties Reaction Similarities 1. 2. Formaldehyde HCHO Acetaldehyde CH3CHO D YG S.No. U Table : 27.2 Comparative study of formaldehyde and acetaldehyde Addition of hydrogen (a) H2 in presence of catalyst, Ni, Pd or Pt (b) LiAlH 4 (ether) Forms methyl alcohol Forms ethyl alcohol HCHO  H 2  CH 3 OH CH 3 CHO  H 2  CH 3 CH 2 OH Forms methyl alcohol Forms methane Forms ethyl alcohol Forms ethane (c) Amalgamated zinc + conc. HCl (Clemmenson reduction) Addition of NaHSO 3 solution HCHO  4 H  CH 4  H 2 O CH 3 CHO  4 H  C 2 H 6  H 2 O Forms bisulphite addition product Forms product U HCHO  NaHSO 3  CH 2 (OH )SO 3 Na 4. Addition of HCN Addition of Grignard followed by hydrolysis addition CH 3 CHO  NaHSO 3  CH 3CH (OH )SO 3 Na ST 3. bisulphite Forms formaldehyde cyanohydrin HCHO  HCN  CH 2 (OH )CN Forms cyanohydrin acetaldehyde CH 3 CHO  HCN  CH 3CH (OH )CN reagent Forms ethyl alcohol HCHO  CH 3 MgI  CH 2 Forms isopropyl alcohol OMgI CH 3  CH 3 CH 2 OH H 2O  Mg(OH ) I CH 3 CHO  CH 3 MgI  H 2O CH 3  C HOMgI   | CH 3  Mg(OH ) I 1270 Aldehydes and Ketones CH 3 CH  OH | CH 3 6. With hydroxylamine NH 2 OH With hydrazine (NH 2 NH 2 ) Forms formaldoxime Forms acetaldoxime  H 2O CH 2  O  H 2 NOH     H 2O CH 3 CH  O  H 2 NOH    CH 2  NOH CH 3 CH  NOH Forms formaldehyde hydrazone Forms acetaldehyde hydrazone  H 2O CH 2 O  H 2 N NH 2     H 2O CH 3 CH  O  H 2 NNH 2    CH 2  NNH 2 7. With phenyl (C6 H 5 NHNH 2 ) hydrazine 60 5. CH 3CH  NNH 2 Forms formaldehyde hydrazone phenyl E3  H 2O CH 2  O  H 2 NNHC 6 H 5    Forms acetaldehyde phenyl hydrazone CH 3 CH  O  H 2 NNHC 6 H 5  H 2O    CH 3 CH  NNHC 6 H 5 CH 2  NNHC 6 H 5 8. With (H 2 NNHCONH 2 ) semicarbazide Forms semicarbazone formaldehyde CH 2  NNHCONH 2  H 2O    CH 3 CH  NNHCONH 2 2 With alcohol (C2 H 5 OH ) in presence Forms ethylal of acid H 2 C  O  2C 2 H 5 OH  HCl U 9.  H 2O    ID CH 2  O  H 2 NNHCONH Forms acetaldehyde semicarbazone CH 3 CH  O  H 2 NNHCONH 2 Forms acetal acetaldehyde diethyl HCl CH 3 CHO  2C 2 H 5 OH   OC 2 H 5 D YG CH 2 OC 2 H 5 OC 2 H 5 10. With thioalcohols (C 2 H 5 SH ) in CH 3 CH OC 2 H 5 Forms thio ethylal H 2 C  O  2C 2 H 5 SH  presence of acid Forms acetaldehyde thioacetal diethyl CH 3 CH  O  2C 2 H 5 SH  SC 2 H 5 CH 2 SC 2 H 5 U SC 2 H 5 CH 3 CH SC 2 H 5 Oxidation with acidified K2Cr2O7 Forms formic acid HCHO  O  HCOOH Forms acetic acid CH 3 CHO  O  CH 3 COOH 12. With Schiff's reagent Restores pink colour of Schiff's reagent Gives black precipitate of Ag or silver mirror Ag 2 O  HCHO  2 Ag  HCOOH Restores pink colour of Schiff's reagent Gives black precipitate of Ag or silver mirror Ag 2 O  CH 3 CHO  ST 11. 13. 14. With Tollen's reagent With Fehling's Benedict's solution 2 Ag  CH 3COOH solution or Gives red precipitate of cuprous oxide 2CuO  HCHO  Cu 2 O  HCOOH Gives red precipitate cuprous oxide 2CuO  CH 3 CHO  Cu 2O  CH 3COOH 15. Polymerisation Undergoes polymerisation Evaporatio n Room temp. heat Undergoes polymerisation H2SO4Conc. dil. H2SO4. distill H2SO4Conc. dil. H2SO4. distill of Aldehydes and Ketones (HCHO )n Paraformaldehy de nHCHO 3 HCHO (HCHO )3 1271 3CH 3CHO (CH 3 CHO )3 Paraldehy de Metaformaldehy de 4 CH 3CHO (CH 3 CHO )4 Metaldehy de Dissimilarities 16. With PCl5 Forms ethylidene chloride 60 No reaction Cl CH 3 CHO  PCl 5  CH 3 CH Cl With chlorine No reaction 18. With SeO2 No reaction 20. With dil. alkali (Aldol condensation) 21. With conc. NaOH (Cannizzaro's reaction) No reaction U Iodoform reaction (I2+NaOH) 3 HCl Forms glyoxal CH 3 CHO  SeO 2  CHO.CHO Se  H 2 O Forms iodoform CH 3 CHO  3 I2  4 NaOH  CHl 3  HCOONa  3 NaI  3 H 2 O No reaction Forms aldol CH 3 CHO  HCH 2 CHO  D YG 19. Forms chloral CH 3 CHO  3 Cl 2  CCl 3 CHO ID 17. E3  POCl 3 CH 3 CH (OH )CH 2 CHO Forms sodium formate and methyl alcohol 2HCHO  NaOH  HCOONa Forms a brown resinous mass CH 3 OH With ammonia ST U 22. Forms hexamethylene tetramine (urotropine) 6 HCHO  4 NH 3 (CH 2 )6 N 4  6 H 2 O Forms addition product, acetaldehyde ammonia CH 3 CHO  NH 3  OH CH 3 CH NH 2 23. With phenol Forms bakelite plastic No reaction 24. 25. With urea Condensation in presence of Ca(OH )2 Forms urea-formaldehyde plastic Form formose (a mixuture of sugars) No reaction No reaction Inter conversion of formaldehyde and acetaldehyde (1) Ascent of series : Conversion of formaldehyde into acetaldehyde (i) H 2 / Ni PCl 5 Alc. HCHO   CH 3 OH   CH 3 Cl   Formaldehy de Methy l alcohol Methy l chloride KCN NaNO 2 Na / Alcohol CH 3 CN   CH 3 CH 2 NH 2   Methy l cy anide Ethy l amine H 2 SO 4 (dil.) CH 3 CH 2 OH   CH 3 CHO Ethyl alcohol K 2 Cr2 O7 Acetaldehyde HCl 1272 Aldehydes and Ketones  The acetone thus obtained is purified with the help of sodium bisulphite. CH 3 MgI H3O HCHO   CH 3 CH 2OMgI    Formaldehy de Ether Cu CH 3 CH 2OH   CH 3 CHO 300 C Ethyl alcohol (iii) Acetaldehyde (ii) It is inflammable liquid. It boils at 56 o C. Ca (OH )2 7 HCHO 2 2   HCOOH   K Cr O Formaldehy de Formic acid H 2 SO 4 (CH 3 COO )2 Ca (HCOO )2 Ca   CH 3 CHO heat Calcium formate (2) Descent of series acetaldehyde into formaldehyde : (2) Physical properties : (i) It is a colourless liquid with characteristic pleasant odour. Acetaldehyde Conversion (iii) It is highly miscible with water, alcohol and ether. (3) Chemical properties Reduction H2, Ni, CH 3 CHOHCH 3 Pd Isopropy l alcohol Amalgamated or LiAlH4 Zn of 60 (ii) K 2 Cr2 O7 NH 3 (i) CH 3 CHO    CH 3 COOH   Acetaldehyde H 2 SO 4 Br2 / KOH Heat CH 3 COONH 4   CH 3 CONH 2    Amm.acetate Formaldehy de K 2 Cr2 O7 NaOH (ii) CH 3 CHO    CH 3 COOH    CH 3 COONa Acetaldehyde H 2 SO 4 Acetic acid Sod.acetat e Cl 2 AgOH Sodalime   CH 4   CH 3 Cl    hv Methane HCN Acetone cy anohy drin CH3MgI 300 C NH2OH (CH 3 )2 C  NOH (CH 3 )2 C  NNH 2 Acetone hy drazone C6H5NHNH2 U D YG Acetoxime NH2NH2 Formaldehy de Acetone It is a symmetrical (simple) ketone and is the first member of the homologous series of ketones. In traces, it is present in blood and urine. (1) Preparation : (i)  (CH 3 COO )2 Ca  (CH 3 )3 COH Tertiary buty l alcohol Ether CH 3 OH   HCHO Cu OH CN (CH 3 )2 C ID heat (CH 3 )2 C(OH )SO 3 Na Acetone sodium bisulphit e derivative E3 300 C HCl Propane NaHSO3 Acetamide NaNO 2 Cu CH 3 NH 2   CH 3 OH   HCHO Methyl amine CH 3 CH 2 CH 3 + conc. HCl Acetic acid (CH 3 )2 C  NNHC 6 H 5 Acetone pheny l hy drazone H2NNHCONH2 (CH 3 )2 C  NNHCONH PCl5 Cl Cl (CH 3 )2 C calcium acetate (ii) 500 C 2CH 3 CHOHCH 3  O2    Isopropyl alcohol (iii) Cu CH 3 CHOHCH 3   300 C 2 propanol (iv) (a) CH 3 CH  CH 2  PdCl 2  H 2 O propene (b) CH 3 CH  CH 2  H 2 SO 4 CH3COCH3 U propene CH 3CH (HSO 4 )CH 3 Isopropy lidene chloride Cl2 CH 3 COCCl 3 Trichloro acetone I2 +NaOH CHI 3 Iodoform CH3 CH3COCH3 (Acetone ) C Conc. H2SO4 CH CH H2O Cu CH 3 CH (OH )CH 3   ST CH3 Zn (CrO 2 ) (v) 2C3 H 5 OH  H 3 O    500 C (vi) catalyst 2CH  CH  3 H 2O    420 C (vii) From pyroligneous acid : Pyroligneous acid containing acetic acid, acetone and methyl alcohol is distilled in copper vessel and the vapours are passed through hot milk of lime. Acetic acid combines to form nonvolatile calcium acetate. The unabsorbed vapours of methanol and acetone are condensed and fractionally distilled. Acetone distills at 56 o C. C C 300 C Isopropyl alcohol 2 Acetone semicarbazone CaOCl2 (Bleaching powder) heat K2Cr2O7 + H2SO4 CHCl3 CH3 CH Mesitylene (1, 3, 5-trimethyl benzene) CHCl 3 Chloroform CH 3 COOH  CO 2  H 2 O (CH 3 )2 C(OH )CCl 3 Chloretone Ba(OH)2 (CH 3 )2 C(OH )CH 2 COCH 3 Diacetone alcohol HNO2 CH 3 COCH  NOH (Oximino acetone) NH3 (CH 3 )2 C(NH 2 )CH 2 COCH 3 Diacetone amine Mg–Hg + H2O OH | OH | (CH 3 )2 C — C (CH 3 )2 Schiff's reagent Tollen's Pinacol No reaction Aldehydes and Ketones 1273 CH 3 | HOH / H      CH 3  C  CH 2 Br    Zn  OH   | | OH COOC 2 H 5  - hy droxy esters CH 3 |  CH 3  C  CH  COOC 2 H 5 (4) Uses (i) As a solvent for cellulose acetate, cellulose nitrate, celluloid, lacquers, resins, etc. three moles of acetone undergoes condensation polymerisation and form a compound called ‘Phorone’. (ii) For storing acetylene. CH 3 | CH 3  C  O 3 (iii) In the manufacture of cordite – a smoke less powder explosive. | CH 3  C  CH H (iv) In the preparation of chloroform, iodoform, sulphonal and chloretone. CH E3 CH 60 If acetone would be in excess in ketal condensation or catalyst (ZnCl 2 / dry HCl ) is used then H 3 | CH 3  C  O H (vi) In the preparation of an artificial scent (ionone), plexiglass (unbreakable glass) and synthetic rubber. CH 3  C  CH CH ID CH | CH 3 H (v) As a nailpolish remover. CO ZnCl 2    C = O dry. HCl (5) Tests Acetone (3 phoron molecule) Molecular mass of phorone = 3 mole of acetone – U 2 mole of H 2 O (i) Legal's test : When a few drops prepared sodium nitroprusside and sodium solution are added to an aqueous solution of wine colour is obtained which changes to standing. Reformatsky reaction: This reaction involves the treatment of aldehyde and ketone with a bromo acid ester in presence of metallic zinc to form  -hydroxy ,  - D YG ester, which can be easily dehydrated into unsaturated ester.  Benzene  Br  Zn CH 2 COOC 2 H 5 (a) BrCH 2 COOC 2 H 5  Zn  Organo zinc compound (b) Addition to carbonyl group CH 3 Zn Br | of freshly hydroxide acetone, a yellow on (ii) Indigo test : A small amount of orthonitrobenzaldehyde is added to about 2 ml. of acetone and it is diluted with KOH solution and stirred. A blue colour of indigotin is produced. (iii) Iodoform test : Acetone gives iodoform test with iodine and sodium hydroxide or iodine and ammonium hydroxide. CH 3 | C  O  CH 2 COOC 2 H 5  CH 3  C  CH 2 CH 2 COOC 2 H 5 | CH 3 U OZn Br Table : 27.3 Comparison between Acetaldehyde and Acetone ST Reaction Acetaldehyde Acetone Similarities 1. Reduction with Forms ethyl alcohol Forms isopropyl alcohol and Ni or LiAlH 4 CH 3 CHO  H 2   CH 3 CH 2 OH CH 3 COCH 3  H 2  CH 3 CHOHCH 3 2. Clemmensen's reduction Forms ethane (an alkane) Forms propane (an alkane) CH 3 CHO  4 H  CH 3 CH 3  H 2 O CH 3 COCH 3  4 H  CH 3 CH 2 CH 3  H 2 O Forms acetaldehyde cyanohydrin Forms acetone cyanohydrin H2 Ni (Zn/Hg and conc. HCl) 3. Addition of HCN 1274 Aldehydes and Ketones OH OH CH 3 CHO  HCN  CH 3 CH (CH 3 ) 2 CO  HCN (CH 3 ) 2 C CN 4. Addition of NaHSO 3 CN White crystalline derivative White crystalline derivative OH OH CH 3 CHO  NaHSO 3  CH 3 CH (CH 3 ) 2 CO  NaHSO 3 (CH 3 ) 2 C SO 3 Na Forms isopropyl alcohol Forms tertiary butyl alcohol CH 3 CHO  CH 3 MgI (CH 3 )2 CH  OMgI (CH 3 ) 2 CO  CH 3 MgI (CH 3 )3 COMgI 60 5. Grignard reagent followed by hydrolysis SO 3 Na  CH 3 CHOHCH 3 H 2O 7. With (NH 2 NH 2 ) hydrazine 8. With phenyl hydrazine (C6 H5 NHNH 2 ) Forms acetoxime (an oxime) CH 3 CHO  H 2 NOH  CH 3 CH  NOH (CH 3 ) 2 CO  H 2 NOH  (CH 3 ) 2 C  NOH Forms acetaldehyde hydrazone Forms acetone hydrazone E3 (NH 2OH ) Forms acetaldoxime (an oxime) CH 3 CHO  H 2 NNH 2  CH 3 CH  NNH 2 (CH 3 ) 2 CO  H 2 NNH 2  (CH 3 ) 2 C  NNH 2 Forms acetaldehyde phenylhydrazone Forms acetone phenyl hydrazone CH 3 CHO  H 2 NNHC 6 H 5  (CH 3 ) 2 CO  H 2 NNHC 6 H 5  ID 6. With hydroxylamine H 2O   (CH 3 ) 3 COH CH 3 CH  NNHC 6 H 5 (CH 3 )2 C  NNHC 6 H 5 9. With semicarbazide Forms acetaldehyde semicarbazone Forms acetone semicarbazone (H2 NNHCONH 2 ) CH 3 CHO  H 2 NNHCONH (CH 3 ) 2 CO  H 2 NNHCONH 2  U CH 3 CH  NNHCONH 2 Forms ethylidene dihalide) chloride D YG 10. With PCl5 (Gem 2  (CH 3 )2 C  NNHCONH Forms isopropylidene dihalide) chloride (CH 3 )2 CO  PCl 5 (CH 3 )2 C Cl Cl 12. With alcohols Forms chloral (Gem trihalide) Forms trichloro acetone (Gem trihalide) CH 3 CHO  Cl 2  CCl 3 CHO CH 3 COCH 3  Cl 2  CCl 3 COCH 3 Forms acetal (a diether) Forms ketal (a diether) U OC 2 H 5 OC 2 H 5 (CH 3 )2 CO  2C 2 H 5 OH (CH 3 )2 C CH 3 CHO  2C2 H 5 OH  CH 3 CH OC 2 H 5 OC 2 H 5 Forms glyoxal Forms methyl glyoxal CH 3 CHO  SeO 2  CHOCHO  Se  H 2 O (CH 3 )2 CO  SeO 2  CH 3 COCHO  Se  H 2 O Forms iodoform Forms iodoform 15. Bleaching powder Forms chloroform Forms chloroform 16. Aldol condensation with mild alkali Forms aldol Forms diacetone alcohol 2CH 3 CHO  CH 3 CHOHCH 2 CHO 2CH 3 COCH 3 (CH 3 )2 C(OH )CH 2 COCH 3 17. Polymerisation Undergoes polymerisation Does not undergo polymerisation but gives condensation reaction 18. With NH 3 Forms acetaldehyde ammonia Forms diacetone ammonia ST 13. With SeO 2 (Gem Cl Cl CH 3 CHO  PCl 5  CH 3 CH 11. With chlorine 2 14. Iodoform reaction (I2  NaOH ) Aldehydes and Ketones 1275 (CH 3 )2 CO  NH 3  OC(CH 3 )2  OH CH 3 CHO  NH 3  CH 3 CH (CH 3 )2 C(NH 2 )CH 2COCH 3 NH 2 19. With conc. NaOH Forms brownish resinous mass No reaction 20. With HNO2 No reaction Forms oximino acetone CH 3 COCH 3  HNO 2  CH 3 COCH  NOH 21. With chloroform No reaction Forms chloretone OH 60 (CH 3 )2 CO  CHCl 3 (CH 3 )2 C CCl 3 sodium Deep red colour Red colour changes to yellow on standing 23. With sodium nitroprusside + Pyridine Blue colour No effect 24. Boiling point 21 o C E3 22. With alk. nitroprusside 56 o C Dissimilarities Pink colour 26. With solution Fehling's Gives red precipitate 27. With reagent Tollen's Gives silver mirror No reaction U K2Cr2O7 with No reaction Easily oxidised to acetic acid Oxidation occurs with difficulty to form acetic acid CH 3 CHO  O  CH 3 COOH D YG 28. Oxidation acidified Does not give pink colour ID 25. With Schiff's reagent CH 3 COCH 3  O  CH 3 COOH  CO 2  H 2 O Aromatic Carbonyl Compounds Aromatic aldehydes are of two types : The compounds in which CHO group is attached directly to an aromatic ring, e.g., benzaldehyde, C6 H 5 CHO. Those in which aldehyde (CHO ) group is U attached to side chain, e.g., phenyl acetaldehyde, C6 H 5 CH 2 CHO. They closely resemble with aliphatic Benzaldehyde is the simplest aromatic aldehyde. It occurs in bitter almonds in the form of its glucoside, amygdalin (C20 H 27 O11 N ). When amygdalin is boiled with dilute acids, it hydrolyses into benzaldehyde, glucose and HCN CN | C 6 H 5 CHOC 12 H 21 O10  2 H 2 O  C 6 H 5 CHO  Amy gdalin aldehydes. ST Aromatic ketones are compounds in which a carbonyl group (  C  O) is attached to either two aryl groups or one aryl group and one alkyl group. Examples are : CHO COCH 3 COC 6 H 5 OH CHO Benzaldehy de Acetopheno ne Benzopheno ne Salicylald ehyde (M ethyl phenyl (Diphenyl ketone) ketone) CHO Benzaldehy de 2C 6 H 12 O 6  HCN Glucose Benzaldehyde is also known as oil of bitter almonds. (1) Method of preparation (i) Laboratory method : It is conveniently prepared by boiling benzyl chloride with copper nitrate or lead nitrate solution in a current of carbon dioxide. heat 2C 6 H 5 CH 2 Cl  Cu ( NO 3 )2   2C 6 H 5 CHO  CuCl 2  2 HNO 2 Benzy l chloride or Pb ( NO 3 )2 CO 2 Benzaldehy de [2 HNO 2  NO  NO 2  H 2 O] Benzaldehyde, C6 H 5 CHO or (ii) Rosenmund reaction : 1276 Aldehydes and Ketones Pd / BaSO 4 C6 H 5 COCl  H 2   C6 H 5 CHO  HCl xylene CHO Benzaldehy de (iii) By dry distillation of a mixture of calcium benzoate and calcium formate O O CH Ca  Ca CH || C 6 H 5 COO O O Calcium benzoate Benzene Benzaldehy de  heat   2C 6 H 5 CHO  2CaCO 3 Benzaldehy de (Major product) HC  N  HCl  AlCl 3  H C  NH  AlCl 4 ;   C 6 H 5 H  HC  NH  C 6 H 5 CH  NH 2 Calcium formate Benzene (iv) By oxidation of benzyl alcohol : This involves the treatment of benzyl alcohol with dil. HNO 3  C6 H 5 CH  NH 2  H 2 O  AlCl 4  C6 H5 CHO  NH 3  AlCl 3  HCl or acidic potassium dichromate or chromic anhydride in acetic anhydride or with copper catalyst at 350 o C. Benzyl alcohol CHO Benzaldehy de CHO Ca (OH )2 Benzaldehy de D YG (vi) By oxidation of Toluene Aldimine complex H 2O   2C 6 H 5 CHO (xi) By ozonolysis of styrene O V O 350 o C toluene  H 2O benzaldehyde Commercially the oxidation of toluene is done with air and diluted with nitrogen (to prevent complete oxidation) at 500 o C in the presence of oxides of Mn, Mo or Zr as catalyst. U Partial oxidation of toluene with manganese dioxide and dilute sulphuric acid at 35 o C , also forms benzaldehyde. H /H O 3 2 C6 H 5 CH 3  C6 H 5 CH (OCOCH 3 )2   ST CrO (CH 3 CO )2 O Benzy lidene acetate C6 H5 CHO  2CH 3COOH (vii) Etard's reaction : C6 H 5 CH 3  2CrO2 Cl 2  C6 H 5 CH 3 2CrO2 Cl 2 2 C6 H 5 CHO Brown addition product H O Benzaldehy de (viii) Gattermann-koch aldehyde synthesis : Benzene is converted into benzaldehyde by passing a mixture of carbon monoxide and HCl gas under high pressure into the ether solution of benzene in presence of anhydrous aluminium chloride and cuprous chloride. H 2O CH 2   Viny l benzene O CHO 2 5  O 2   Toluene Ether O3 C6 H 5 CH  CH 2   C6 H 5 – CH This is also an industrial method. CH 3 Phenyl cyanide U Intermedia te (unstable)  NH 4 Cl (x) Stephen's reaction : Benzaldehyde is obtained by partial reduction of phenyl cyanide with stannous chloride and passing dry HCl gas in ether solution followed by hydrolysis of the aldimine stannic chloride with water. HCl / SnCl 2 C6 H 5 C  N  [C6 H 5 CH  NH ]2 H 2 SnCl 6 ID This method is used for commercial production of benzaldehyde. (v) By hydrolysis of benzal chloride : OH CHCl 2 CH OH ( H 2 O ) NaOH      CHO AlCl 3  HCN  HCl  H 2 O    Thus, E3 [O ] CH 2 OH   Benzal Chloride  HCl (ix) Gattermann reaction || C 6 H 5 COO AlCl 3  CO  HCl   60 Benzyl chloride O C6 H 5 CHO  HCHO  H 2 O2 (xii) Grignard reaction O O || Br || HCOC 2 H 5  BrMgC 6 H 5  C 6 H 5 C  H  Mg Ethy l formate Benzaldehy de OC 2 H 5 Other reagents like carbon monoxide or HCN can also be used in place of ethyl formate. (xiii) From Diazonium salt N  N  Cl  HCH  NOH Formaldoxi me CH  NOH + HCl + N2 Benzaldoxi me H2O CHO Benzaldehy (2) Physical properties de (i) Benzaldehyde is a colourless oily liquid. Its boiling point is 179 o C. (ii) It has smell of bitter almonds. (iii) It is sparingly soluble in water but highly soluble in organic solvents. (iv) It is steam volatile. (v) It is heavier than water (sp. gr. 1.0504 at 15 o C ). (vi) It is poisonous in nature. (3) Chemical properties Aldehydes and Ketones (i) Addition reaction: The carbonyl group is polar as oxygen is more electronegative than carbon,  C O Thus, The positive part of the polar reagent always goes to the carbonyl oxygen and negative part goes to carbonyl carbon. OH H   C 6 H 5 CH C 6 H 5 CH H 2O CN COOH Benzaldehy de cy anohy drin Mandelic acid SO 3 Na Benzaldehy de sodium bisulphit e (White solid) OMgI (Benzaldehy de) CH3MgI C 6 H 5 CHO  Ag 2 O  2 Ag  C 6 H 5 COOH OH H 2O CH 3 1-Pheny l-1-ethanol (vi) Schiff's reaction: It restores pink colour to Schiff's reagent (aqueous solution of p-rosaniline hydrochloride decolourised by passing sulphur dioxide). (2 o alcohol) Benzy l alcohol H 2O C6 H 5 CH  CH  C6 H 5 | D YG | OH OH Hy drobenzo in (ii) Reactions involving replacement of carbonyl oxygen H2NNH2 C6 H 5 CH  NNH 2  H 2 O Benzaldehy de hy drazone C6 H 5 CH  N. NHC 6 H 5  H 2 O Benzaldehy de pheny l hy drazone CHO C6 H 5 CH  NOH  H 2O U H2NOH 2 ST (Benzaldehyd e) H2N.NHCONH H2NC6H 5 PCl5 2CH3OH HCl : On heating intermolecular oxidation and reduction (like aliphatic aldehydes) to form acid and alcohol respectively as such and react to produce benzyl benzoate (an ester). U However on reduction with sodium amalgam and water, it gives hydrobenzoin, Na  Hg C6 H 5 CH  O  2 H  O  CHC 6 H 5   H2N.NHC6H5 reaction benzaldehyde with aluminium alkoxide (ethoxide) and a little of anhydrous AlCl 3 or ZnCl 2 , it undergoes an C 6 H 5 CH 2 OH LiAlH4 Tischenko ID (vii) 2[H] Benzoic acid HCl  CH 3 nitrate solution (Tollen's reagent) to give silver mirror but does not reduce Fehling's solution. Zn  Hg C 6 H 5 CHO  4 H    C 6 H 5 CH 3  H 2 O H   C 6 H 5 CH C 6 H 5 CH (iv) Reducing properties : Benzaldehyde is a weak reducing agent. It reduces ammonical silver (v) Clemmensen's reduction : With amalgamated zinc and conc. HCl, benzaldehyde is reduced to toluene. C 6 H 5 CH CHO and dilute HNO 3 can be used as oxidising agents for oxidation. Benzaldehy de OH NaHSO3 Acidified K 2 Cr2 O7 , alkaline KMnO 4 60 OH HCN [O ] C 6 H 5 CHO   C 6 H 5 COOH E3  1277 Benzaldoxi me C6 H 5 CH  NNHCONH 2  Benzaldehy de semicarbazone H 2O Al(OC 2 H 5 )3 2C 6 H 5 CHO    C 6 H 5 CH 2 OOCC 6 H 5 Benzaldehy de Benzyl benzoate (ester) (viii) Reactions in which benzaldehyde differs from aliphatic aldehydes (a) With fehling's solution : No reaction (b) Action of chlorine : Benzoyl chloride is formed when chlorine is passed through benzaldehyde at its boiling point in absence of halogen carrier. This is because in benzaldehyde there is no  -hydrogen atom present which could be replaced by chlorine. o 170 C C 6 H 5 CHO  Cl 2    C 6 H 5 COCl  HCl  KOH (c) Cannizzaro's reaction : 2C6 H 5 CHO   Benzaldehy de C6 H 5 CH  NC 6 H 5  H 2 O C6 H 5 CH 2 OH  C6 H 5 COOK Benzy lidine aniline (Schiff's base) Benzy l alcohol C 6 H 5 CHCl 2  POCl 3 Benzal chloride Potassium benzoate The possible Mechanism is First step is the reversible addition of hydroxide OCH 3 | C 6 H 5 CH ion to carbonyl group.  H 2O | OCH 3 Methy l acetal of benzald ehy de H C 6 H 5  C  O  OH  (Fast ) | H (iii) Oxidation : Benzaldehyde is readily oxidised to benzoic acid even on exposure to air. | C6 H 5  C  O  | OH Anion (I) Second step is the transfer of hydride ion directly to the another aldehyde molecule, the latter is thus 1278 Aldehydes and Ketones reduced to alkoxide ion and the former (ion I) is oxidised to an acid. | H | Hy dride C 6 H 5 C  O  C 6 H 5 C  O    C 6 H 5 C  O   C 6 H 5 C  O | ion transfer (slow) OH | | H OH | + (H exchange) + | C 6 H 5  C  OH  C 6 H 5  C  O H O Benzy l alcohol || O O Benzil (e) Perkin's reaction H | || Py ridine H 2O O Benzoin –H | || OH acid Alkoxide ion H CuSO 4 C 6 H 5  CH  C  C 6 H 5  [O]    C 6 H 5  C  C  C 6 H 5 C 6 H 5 CH O  H 2 CHCOOCOCH Benzaldehy de CH COONa 3 3     H 2O Acetic anhydride 60 H | H Benzoin can be readily oxidised to a diketone, i.e, benzil. C6 H 5 CH  CHCOOCOCH  Benzoate ion 3 H O So one molecule of aldehyde acts as hydride donor and the other acts as hydride acceptor. In other words, Cannizzaro's reaction is an example of self reduction and oxidation. Cinnamic acid | H 2 C  CO C6 H 5 CH  O  heat Sod. formate Benzyl alcohol Aldehyde which do not have  - hydrogen ( C6 H5  CHO, CCl 3 CHO, (CH 3 )3 C  CHO, CH 2O etc.) D YG undergoes Cannizzaro’s reaction. Intramolecular cannizzaro reaction CHO CHO CH2OH Propionic anhydride CH 3 | C6 H 5 CH  C  COOH  CH 3 CH 2 COONa  - Methyl cinnamic acid U Formaldehy de Benzaldehy de (f) Claisen condensation [Claisen-schmidt reaction] | CH 3 NaOH C 6 H 5 CHO  H 2 C  CHO    Propionald ehy de CH 3 |      C6 H 5 CH  C  CHO  H 2O   -Methyl cinnamic aldehyde H / H 2O CH2OH COOH (d) Benzoin Condensation H O | ||  C  C | H H O | ||  C  C U || O Alc. KCN    | NaOH (Dil.) C6 H 5 CHO  H 2CHCOCH 3   Acetone C6 H 5 CH  CHCOCH 3  H 2 O Benzylidene acetone  hydroxy (  (g) ketone) Knoevenagel reaction OH Two molecules of benzald ehy de Benzoin (An aldol)   hy droxy ketone COOH Pyridine C6 H 5 CH  O  H 2 C  COOH ST Benzoin can also be reduced to a number of C6 H 5  CHOH  CHOH  C6 H 5 Na-Hg/C2H5OH OH O | | H [H] Zn-Hg/HCl Benzoin C6 H 5 CH  CHCOOH  CO 2  H 2O Cinnamic acid Hydrobenzoin (h) Reaction with aniline : Benzaldehyde reacts with aniline and forms Schiff's base OH || C6 H 5  C  C  C6 H 5 | Warm H |  H 2O C 6 H 5  CH  CH  C 6 H 5   C6 H 5 CH  O  H 2 NC 6 H 5   C6 H 5 CH  NC 6 H 5 Aniline ( H 2 O ) C6 H 5 CH  CHC 6 H 5 Stilbene Reaction with Dimethylaniline H2 H2/Raney Ni  Malonic acid product i.e., [H] (Dil.) COOH NaOH / 100  C CHO CHO CH CH COONa 3 O  2 CH 3  CH 2 CO C6 H 5 CHO  HCHO   C6 H 5 CH 2 OH  HCOONa NaOH Acetic acid CH 3 ID  Two different aldehydes each having no  hydrogen atom, exhibit crossed Cannizzaro's reaction when heated in alkaline solution. 2 C6 H 5 CH  CHCOOH  CH 3 COOH E3 Third Step is exchange of protons to give most stable pair alcohol and acid anion. C 6 H 5  CH 2  CH 2  C 6 H 5  2 H 2 O Dibenzyl Benzylidene aniline (Schiff' s base) Aldehydes and Ketones N (CH 3 ) 2 Conc. H 2 SO 4      H CH ( H 2 O ) N (CH 3 ) 2 N (CH 3 ) 2 Dimethyl aniline Tetramethy l diamino triphenyl methane (Malachite green) (i) Reaction with Ammonia : Benzaldehyde reacts with ammonia to form hydrobenzamide aldehyde other than CH 2O give aldehyde ammonia while CH 2 O forms CH  C6 H 5 C 6 H 5 CHCH 2 COOC 2 H 5  C 6 H 5  CH  CH 2 COOC 2 H 5 OH  -hy droxy ester (k) Reaction of benzene ring   O CCH 3 || O || 2 C 6 H 5 CCH 3  2 CaCO 3 Acetopheno ne methylation of benzaldehyde with C6 H 5 CHO  CH 2 N 2  C6 H 5 COCH 3  N 2 U CHO NO2 (iv) By treating benzoyl chloride with dimethyl cadmium. D YG CHO H2SO4 SO3H m  Benzaldehy de Sulphonic acid Cl2 Ca  Ca Calcium acetate (iii) By diazomethane. m  Nitrobenza ldehy de fuming || O CCH 3 ID | Benzaldehy de (ii) By distillation of a mixture of calcium benzoate and calcium acetate. O O Bromo ethylaceta te H 2O CHO Acetopheno ne C6 H 5 COO Calcium benzoate  C6 H 5 CH  O  Zn  Br C H 2 COOC 2 H 5  H2SO4 (conc.) Acetyl chloride C6 H 5 COO (j) Reformatsky reaction HNO3(conc.) (1) Method of preparation (i) Friedel-Craft's reaction : Acetyl chloride reacts with benzene in presence of anhydrous aluminium chloride to form acetophenone. AlCl Hydrobenza mide OZnBr Acetophenone, C6H5COCH3, Acetyl Benzene Benzene C6 H 5  CH  N C6 H 5  CH  N | precipitate of benzoic acid on cooling. 3 C 6 H 5 H  Cl COCH 3   C 6 H 5 COCH 3  HCl urotropine. C 6 H 5  CHO H 2 NH O  CH  C 6 H 5    C 6 H 5  CHO H 2 NH Benzaldehy de (v) Benzaldehyde on treatment with alkaline KMnO 4 and subsequent acidification gives a white 60 CH  O  N (CH 3 ) 2 E3 H 1279 2C6 H5 COCl  (CH 3 )2 Cd  2C6 H5 COCH 3  CdCl 2 (v) By Grignard reagent (a) CH 3 C  N  C6 H 5 MgBr  CH 3 C  NMgBr H2O | C6 H 5 C6 H 5 COCH 3  NH 3  Mg(OH )Br CHO FeCl3 Cl m Chlorobenz aldehy de O || (b) C 6 H 5 MgBr  H 5 C 2 O C CH 3  Ethyl acetate U (4) Uses : Benzaldehyde is used, O || C 6 H 5 C CH 3  Mg (i) In perfumery (ii) In manufacture of dyes (vi) Commercial preparation : Ethylbenzene is ST (iii) In manufacture of benzoic acid, cinnamic acid, cinnamaldehyde, Schiff's base, etc. (5) Tests : (i) Benzaldehyde forms a white precipitate with NaHSO 3 solution. (ii) Benzaldehyde forms a yellow precipitate with 2 : 4 dinitrophenyl hydrazine. (iii) Benzaldehyde gives pink colour with Schiff's reagent. (iv) Benzaldehyde forms black precipitate silver mirror with Tollen's reagent. Br OC 2 H 5 or oxidised with air at 126 o C under pressure in presence of a catalyst manganese acetate. CH 2 CH 3 COCH 3 Catalyst  O2   H 2O 126 o C pressure (2) Physical properties : It is a colourless crystalline solid with melting point 20 o C and boiling point 202 o C. It has characteristic pleasant odour. It is slightly soluble in water. Chemically, It is similar to acetone. (3) Chemical properties : OH | HCN C 6 H 5  C  CH 3 | CN Acetopheno ne cy anohy drine CH 3 H2NOH | Rearrangement C 6 H 5  C  NOH   Acetopheno ne oxime or (Methy lpheny l ketoxime) H 2 SO 4 1280 Aldehydes and Ketones  Acidified K2Cr2O7 i.e., chromic acid sulphuric acid 60 mixture is known as Jone’s reagent. When used as an oxidising agent unlike acidified KMnO4 it does not K2Cr2O7/H2S diffect a double bond. O4 CH2 =CHCH2OH CH2=CHCHO  Vilsmeyer reaction : this reaction involves the E3 conversion of aromatic compounds to aldehydes in the presence of a 2o amino and formic acid. CHO (CH3)2 NH + HCOOH+POCl3 Oxidation C 6 H 5 COCHO SeO2  Benzaldehyde although reduces Tollen’s reagent. It does not reduce Fehling or Benedict solution. C 6 H 5 CCl 2 CH 3 PCl5 (It is C 6 H 5 COCH 2 Cl harmless C6H5COCH3 relatively but powerful lachrymator or tear gas and is used by police to disperse C 6 H 5 COONa  CHI 3 mobs.) Iodoform CH 3 O | || C 6 H 5  C  CH  C  C 6 H 5 D YG I2/NaO H Aldol type condensation Al-terbutoxide Dy pnone (It is used as hy pnotic) Nitratio NO 2 C 6 H 4 COCH 3 n 3/H2SO HNO m -Nitroaceto phenone 4 U Phenacy l chloride (Used as a tear gas) Iodoform reaction ID 2, 2-Dichloroethy lbenzene Cl2 (Acetophenone) Benzane Pheny l gly oxal conc. H2SO4 HSO 3 C 6 H 4 COCH 3 Acetopheno ne m  sulphonic acid (4) Uses : It is used in perfumery and as a sleep producing drug. Benzophenone, C6H5COC6H5 U (1) Method of preparation (i) From alkyl benzenes HNO 3 C 6 H 5  CH 2  C 6 H 5  2O    C 6 H 5 COC 6 H 5 ST (2) Physical properties : It is a colourless, pleasant smelling solid. (3) Chemical properties : It shows the characteristic properties of keto group but does not give bisulphite compounds. (i) Reduction : Na  Hg C 6 H 5 COC 6 H 5  2 H    C 6 H 5.CHOHC 6 H 5 Diphenyl carbinol (ii) Clemmenson reduction : Zn / Hg C6 H 5 COC 6 H 5    C6 H 5 CH 2 C6 H 5  H 2 O HCl Diphenyl methane (iii) Fusion with KOH : Fuse C6 H 5 COC 6 H 5  KOH   C6 H 5 COOK  C6 H 6 Pot. tert. Butoxide C6 H 5 COC 6 H 5  H 2 O    C6 H 5 COOH  C6 H 6 Ether Benzoic acid