Alcohols - Study Notes PDF

ALCOHOLS Alcohols are compounds which contain one hydroxyl group called monohydric alcohols, while those of two hydroxyl groups called dihydric alcohold. Alcohols of three hydroxyl groups called trihydric alcohols. Monohydric alcohols : The monohydric alcohols have a general formula R-OH where R...

ALCOHOLS Alcohols are compounds which contain one hydroxyl group called monohydric alcohols, while those of two hydroxyl groups called dihydric alcohold. Alcohols of three hydroxyl groups called trihydric alcohols. Monohydric alcohols : The monohydric alcohols have a general formula R-OH where R is an alkyl group , these alcohols have a general molecular formula Cn H2n+2 O and the are divided into three classes: a- Primary alcohols R-CH2-OH b- Secondary alcohols (R)2-CH-OH c- Tertiary alcohols (R)3-C-OH Nomenclature of alcohols 1-IUPAC system: alcohols have a name derived from the corresponding alkane by changing " e " of " ane " to " ol" and alcohols of more than two carbon atoms must be numbered starting from carbon atom which is nearest to the hydroxyl group, where the alcohol take the number of carbon atom in which the hydroxyl group is attached to it. 2-Alkyl system: in which the word alcohol is coupled with the name of alkyl group. 3-Carbinol system: where the simplest alcohol ( CH3OH ) called carbinol and the other alcohols can be considered as a derivatives from carbinol  CH3OH CH 3CH2OH CH 3CH2CH2OH methnaol ethanol n-propanol( 1-propanol) methyl alc. ethyl alcohol n-propyl alcohol carbinol methyl carbinol ethyl carbinol CH3 CH3 CHCH 3 CH3 C CH3 CH3CH2CH2CH2OH OH OH n-butanol(1-butanol) isopropanol(2-propanol) ter.butanol isopropyl alcohol ter.butyl alcohol n-butyl alcohol dimethyl carbinol n-propyl carbinol trimethyl carbinol CH3-CH-CH2-CH3 CH3-CH-CH2-OH OH CH3 sec.butanol( 2-butanol) iso-butanol sec.butyl alcohol iso-butyl alcohol ethyl methyl carbinol isopropyl carninol Methods of preparation 1-Hydrolysis of alkyl halides with aqueous alkali ( NaOH, KOH ) : R-X + NaOH R-OH + NaX e.g.: CH3CH2Cl + NaOH CH3CH2OH + NaCl ethyl chloride ethanol 2-Indirect hydration of olefins: H.OH CH3CH CH2 + H.HSO 4 CH3 CH CH3 propene HSO4 CH3 CH CH3 + H2SO4 OH isopropanol 3-Reduction of carbonyl compounds with lithium aluminum hydride (LiAlH 4) or H2 in presence of a catalyst; where aldehydes give primary alcohols , ketones give secondary alcohols while the reduction of the fatty acids ,esters, acid anhydride and acid chlorides give primary alcohols. a-reduction of aldehydes: LiAlH4 R C O R CH2OH H e.g.: CH3 LiAlH4 C O CH3CH2OH H acetaldehyde ethanol b-reduction of ketones LiAlH4 R C O R C R` R` OH LiAlH4 e.g.: CH3 C O CH3C CH3 CH3 OH acetone isopropyl alcohol  c- reduction of fatty acids: LiAlH4 R C O R CH2OH + H2O OH LiAlH4 e.g.: CH3 C O CH3CH2OH + H2O OH acetic acide d-reduction of acid chloride: LiAlH4 R C O R CH2OH + HCl Cl LiAlH4 e.g.: CH3 C O CH3CH2OH + HCl Cl acetyl chloride e- reduction of acid anhydride: R-CO O = LiAlH4 2 RCH2OH R-CO acid anhydride CH3-CO O + LiAlH4 2CH3CH2OH CH3CO acetic acid 4- Action of Grignard'reagenrs on: a- formaldehyde gives primary alcohols: H.OH OH RMgX + C O R-CH2OMgX R-CH2OH +Mg X H H.OH CH CH OH +Mg OH CH3MgI + CH2O CH3CH2OMgI 3 2 I methyl mag.iodide ethanol aldehydes rather than formaldehyde give secondary alcohols -c H H OH H.OH RMgX + R` C O R-COMgX R-C-R` + Mg H R` OH X H H H.OH CH3MgI + CH3CH2CHO CH3 CH2COMgI CH3 CH2CCH3 propionaldehyde CH3 OH sec.butanol c- ketones give tertiary alcohols: R OH OH H.OH RMgX + R` C O R-COMgX R-C-R` +Mg X R R` R CH3 CH3 H.OH CH3MgI + CH3CCH3 CH3 COMgI CH3CCH3 acetone O CH3 OH ter.butanol e-ethylene oxide gives primary alcohol : Ag2O RMgX H.OH CH2 CH2 CH2 CH2 RCH 2CH2OMgX O R-CH2CH2OH + Mg X OH H2O CH3MgBr + CH2 CH2 CH3CH2CH2OMgBr O ethylene oxide CH3CH2CH2OH + Mg Br OH n-propanol 5-Alkaline hydrolysis of esters give alcohols and fatty acids ( their salts): H2O RCOOR' R'OH + RCOONa NaOH NaOH CH3CO2C2H5 C2H5OH + CH3CO2Na H2O ethylacetate ethanol sod. acetate 6-Action of nitrous acid on primary amines: R-CH2NH2 + HONO R-CH2OH + N2 + H2O 10 amine nitrous acid CH3CH2NH2 + HNO2 CH3CH2OH +N 2 +H2O ethanol ethyl amine  Properties of alcohols Isomerism in alcohols: 1- Position isomerism which depends on the position of the functional group in the molecule. e.g.: CH3CH2CH2CH2OH CH3CH2CHCH 3 OH 1-butanol 2-butanol 2- Chain isomerism, which depends on the shape of carbon chain( straight or branched ). e.g.: CH3CH2CH2CH2OH CH3CH-CH 2OH CH3 n-butanol iso-butanol 3-Optical isomerism, present in alcohols which contain asymmetrical carbon atom, where the molecule in this case has two isomers called " enantiomers" which they are optical active ( i.e. rotate the plane of polarized light in spectrometer).e.g.: sec-butanol can has this configuration in the space: CH3 CH3CH2CH2CH2OH CH3 CH CH2OH n-butanol iso-butanol Hydrogen Bonding: The relative low volatility of alcohol is due to the association of the molecules in the liquid state, through the hydrogen bond, these hydrogen bonds could be broken by the action of heat and this explain the high boiling points of alcohols. R H etc. R R O O H O R O H H hydrogen bonding Chemical properties of alcohols: 1-Reaction with alkali metals such as Na, and K; form salts which are called alkoxides with liberation of H2: R--OH + Na R-ONa + 1/2 H2 CH3CH2OH + Na CH3CH2ONa + 1/2 H2 ethanol sodium ethoxide 2-Action of hydrogen halides ( HX) give alkyl halides (R-X) : ROH + HX RX + H2O HBr CH3CHCH3 CH3CHCH3 + H2O OH Br iso-propanol iso-propyl bromide 3-Action of phosphorouspentachloride (PCl5) or thionyl chloride ( SOCl2) give alkyl chlorides: CH3CH2OH + PCl5 CH3CH2Cl + POCl3 + HCl ethanol ethyl chloride CH3OH + SOCl2 CH3Cl + SO2 + HCl methanol methyl chloride 4-Dehydration by the action of heated alumna( Al2O3) or concentrated sulfuric acid give olefins -H2O CH3CH2OH + H.HSO 4 CH3CH2.HSO4 ethyl hydrogen sulfate o 140 C 170oC C2H5OH CH3CH2OCH 2CH3 CH2 CH2 + H2SO 4 diethyl ether ethylene The formation of ether proceeds according to Williamson continuos etherification method, where the heating of ethylhydrogen sulfate at 140C in presence of an excess of alcohol led to the formation of ether according to the following mechanism. H -H2O HOCH 2CH3 CH3CH2OH CH3CH2OH2 CH3CH2 -H CH3CH2-O-CH2CH3 CH3CH2-O-CH2CH3 H HSO4 dietyl ether if there is no adjacent -C-H , the dehydration takes place with rearrangement  CH3 CH3 CH3 H -H2O CH3-C-CH2OH CH3-C-CH2OH2 CH3-C-CH2 CH3 CH3 CH3 2,2-dimethyl-1-propanol rearrangement -H CH3-C-CH2 CH3 CH3-C CHCH 3 CH3 CH3 2-methyl-2-butene Also dehydration of 2,3-dimethyl-butanol can be represented as follow: CH3 H CH3 H -H2O CH3 C C CH3 CH3 C C CH3 H+ CH3 OH CH3 secondary carbonium ion ( less stable ) CH3 H E1 CH3 C C CH3 CH2 C CH CH3 + B-elimination CH3 CH3 CH3 ter- carbonium ion ( minor ) CH3 CH3 ( more stable ) CH3 C C CH3 ( major ) 5-Esterification: Fisher method: by the reaction of alcohol with organic acid in presence of )a dehydrating agent such as hydrochloric acid in gaseous state or conc. sulfuric acid:  H2SO4 R-CO2H + R`OH RCO2R` + H2O H2SO4 CH3CO2H + CH3OH CH3CO2CH3 + H2O methanol conc. methyl acetate Mechanism: OH R`OH OH H R-C OH R-C OH R-C OH O O-R` OH O H H -H2O -H R-C OH2 R-C R-C -OR` OR` OR` O b-reaction with acid chloride: - O R-C-Cl + HOR` R-C-OR` + HCl O e.g.: CH3COCl + C2H5OH CH3CO2C2H5 +HCl acetyl chloride ethyl acetate c- Reaction of alcohol with acid anhydrides: (RCO)2O + R'OH RCOOR' + RCOOH acid anhydride alcohol ester acid (CH3CO)2O + C2H5OH CH3COOC2H5 + CH3COOH acetic anhydride ethanol ethyl acetate acetic acid 6- Dehyrogenation: Dehydrogenation is carried out by passing the vapor of alcohol over heated copper ( 350C) : a- Primary alcohols give aldehydes:  Cu /350o e.g.: CH3CH2OH CH3CHO +H2 acetaldehyde b-Secondary alcohols give ketones: OH O Cu /350o CH3-CH-CH3 CH3C-CH3 + H2 acetone isopropanol c-Tertiary alcohols give olefins: OH Cu /350o CH3-C-CH3 CH3-C CH2 ter.butanolCH3 isobutene CH3 7- Oxidation: Oxidation with potassium permanganate or potassium dichromate: a) 10 alc. ( O) ( O) aldehyde acid (O) (O) R CH2 OH R CHO R CO2H KMnO 4 KMnO 4 (O) b) sec. alc. ketones (O) R CH R' R C R' OH O c) ter. alcohols resist the oxidation under this conditions 8- Haloform reaction: Alcohols which have CH3 CH OH group in the presence of halogen ( X2 ) and NaOH give Haloform: 3 I2 NaOH I2 CH 3CH 2OH CH 3CHO CI 3 CHO oxidation substitution iodal ethanol acetaldehyde CHI 3 + HCOONa chloroform sod.formate Differentiation between primary, secondary and tertiary alcohols: Oxidation ( as mentioned before ) Dehyrogenation ( as mentioned before ) Victor- Mayer's method: a- Primary alcohol: AgNO3 R CH2OH + PC l 5 R CH2Cl HONO NaOH R C NO 2 red colour (NaNO2/HCl) N OH b) Secondary alcohols: AgNO 3 R CH R' + PCl5 R CH R' R CHNO 2 OH Cl R' R' HONO NaOH R C NO 2 blue colour (NaNO2/HCl) N O c) Tertiary alcohols: R" R" R" PCl5 AgNO3 HNO2 R C R' R C R' R C R' OH Cl NO2 HNO2 no reaction  Dihydric Alcohol e.g. Ethylene glycol CH2(OH) - CH2(OH) Methods of preparation: 1- Hydrolysis of vic-dihalides CH2 CH2 + NaOH CH2 CH2 Cl Cl OH OH ethylene chloride 2-By passing ethylene into cold dilute alkaline permanganate (O) CH2 CH2 CH2 CH2 KMnO 4 OH OH Chemical reactions: 1- Glycols condense with aldehydes or ketones to give cyclic acetals or cyclic ketals O CH3 CH2 OH CH3 CH2 + O C C CH2 OH CH3 CH2 CH3 O 2-With hydrochloric acid (HCl): The products depends on the reaction's temperature. CH2 Cl HCl CH2 OH HCl CH2 Cl CH2 OH 160o CH2 OH 200o CH2 Cl 2-Oxidation with nitric acid gives glycollic and oxalic acids: with nitric acid, ethylene glycol can be oxidized finally to oxalic acid through different oxidative steps: CHO ( O ) C O2H CH2 OH (O) CH2 OH glycollic CH2 OH CH2 OH acid (O) (O) CHO (O) C O2H (O) C O2H CHO C O2H CHO glyoxal oxalic glyoxalic acid acid Trihydric Alcohols e.g. Glycerol ( propane-1,2,3-triol ) CH2(OH)CH(OH)CH2(OH) Glycerol occurs in almost all animal and vegetable oils and fats as the glyceryl ester of palmitic, stearic and oleic acids. Preparations: 1- Glycerol is prepared for industrial uses by the hydrolysis of fats and oils with water under pressure at 220 C CH2 O-CO-R CH2 OH NaOH CH O-CO-R + 3 H2O CH OH + 3 RCO 2Na CH2 O-CO-R CH2 OH triglyceride glycerol soap 2- From propene: Cl2/400oC HOCl CH3 CH CH2 Cl-CH2-CH CH2 soda lime CH2 CH CH2 CH2 CH CH2 hyd. -HCl Cl O Cl Cl OH CH2 CH CH2 OH OH OH 3- From acrolein: H2O2 CH2 CH CHO H2/Pt CH2 CH CH2 CH2 CH CHO OH OH OH OH OH Chemical reactions: 1-Action of conc. H2SO4 gives acrolein. CH2 OH CH2 OH CHO CHO conc. -H2O CH OH CH CH CH H2SO4 H2SO4 CH2 OH CH2 OH CH2 OH CH2 2-Action of HI. CH2 OH CH2 I CH2 CH2 3HI -I2 HI HI CH OH CH I CH CH CH2 OH CH2 I CH2I CH3 CH3 CH CH3 allyl iodide I isopropyl iodide 3- Conversion to citric acid: CH2 OH CH2 Cl CH2 Cl CH2 Cl 2HCl (O) HCN CH OH CH OH C O CH (OH)CN CH2 OH CH2 Cl CH2 Cl CH2 Cl CH2 CN CH2 CO2H hyd. 2 KCN CH (OH)CN CH (OH)CO2H CH2 CN CH2 CO2H citria acid 4-Nitration: CH2 OH CH2 O NO2 conc. CH OH CH O NO2 HNO 3 /H2S O 4 CH2 OH CH2 O NO2 glyceryl trinitrate 5-Oxidation: With dilute nitric acid , it gives glyceric acid. CH2 OH CO2H dilute CH OH CH OH HNO 3 CH2 OH CH2 OH glyceric acid  Aromatic Alcohols Aromatic alcohols are hydroxy compounds in which the hydroxyl groups are attached to a side chain of benzene ring, for example benzyl alcohol C6H5CH2OH which can be considered as a phenyl derivative of methanol, therefore it resembles aliphatic alcohols in its preparations and its chemical reactions. Benzyl alcohol C6H5CH2OH Methods of preparations: 1-In industry: it can be prepared by the alkaline hydrolysis of benzyl chloride with sodium bicarbonate solution. CH2Cl CH2OH Na2CO3 solution 2-From Canizzaro’s reaction: CHO CO2Na NaOH CH2OH 2 + 3-By reduction of benzaldehyde with sodium amalgam. CHO CH2OH Na /Hg 4-From Grignard’s reagent: by the action of phenylmagnesium iodide on formaldehyde. MgI 1) CH2 O CH2OH 2)H2O Chemical reactions: Na C6H5CH2ONa + H2 HCl or C6H5CH2Cl PCl5 CH3COCl or C6H5CH2OCOCH3 C6H5CH2OH (CH3CO)2O benzylacetate [O] O C6H5CHO C6H5CO2H HNO3 HI / P C6H5CH3 conc. H2SO4 C6H5CH2OCH2C6H5 - H2O dibenzyl ether  Phenols Phenols characterized by the presence of one or more hydroxyl group ( OH ) are directly attached to the benzene nucleus. They are classified as monohydric, dihydric, trihydric or polyhydric phenols according to the number of the hydroxyl groups which are attached to benzene nucleus. OH OH OH OH OH CH3 CH3 NO2 CH3 Phenol p-nitrophenol o-methylphenol m-methylphenol p-methylphenol ( o-cresol ) ( m-cresol ) ( p-cresol ) OH OH OH OH OH OH OH OH Catechol resorcinol quinol alph naphthol beta naphthol Methods of preparations 1-Fusion of sodiumbenzenesulphonate with sodium hydroxide gives sodium phenoxide which can be easily hydrolyzed to give phenol. SO3Na ONa OH NaOH HCl fusion This method is important in conversion of benzene to phenol.  2-From diazonium salts: by boiling it in water. N2Cl OH H2O + N2 + HCl boil 3- From Grignard’s reagent: Br MgBr OMgBr OH Mg O H2O ether 4- Hydrolysis of aromatic halogen compounds : by heating with alkali such as NaOH at high temperature and pressure in presence of a catalyst such as copper. Cl OH ONa NaOH H2CO3 P Physical properties: Simplest phenols are liquid compounds , phenol itself is solid in low temperature but in relatively high temperature become liquid, it characterized by characteristic odor and is partially soluble in water.  Chemical Properties of Phenols Phenols are acidic in nature and the greater acidity of phenols rather than aliphatic alcohols is due to the delocalization of the lone pair of electrons on the oxygen atom with the π electrons cloud of benzene ring. Such delocalization creates a partial positive charge on the oxygen atom, therefore it facilitate the removal of H as H+. OH OH OH OH OH Beside the above reason, the acidity of phenols can be also attributed to the fact that the phenoxide ion is more stabilized by the resonance than phenol molecule. O O O O O Hybrid structure The presence of OH group in phenol increase the electron delocalization on the benzene ring by +R effect, i.e activates the benzene ring towards the electrophiles which will attack the ring on o- and p- positions. The chemical reactions of phenol may be divided into: 1- Reactions involving the O-H bond. 2- Reactions involving the C-O bond. 3- Reactions involving the aromatic ring.  [A] Reactions involving the O-H bond. 1-Formation of metallic salts: due to the acidity of phenol as mentioned before, phenols soluble in aqueous alkali solutions to give phenoxides. ONa OH NaOH sodium phenoxide The acidity of phenols can be increased by introducing of an electron attracting group especially in o- and p- positions as the nitro group ( NO2 ) which has –R effect i.e this group will increases the positive charge on the oxygen atom of the hydroxyl group i.e facilitate its removal as H+. OH OH OH OH N N N N O O O O O O O O While in case of p- cresol the acidity is less than that of phenol due to the + I effect of methyl group in p- position. H3C OH p- cresol  2-Methylation with diazomethane: it gives anisole. CH2N2 OH OCH3 anisole 4- Formation of ester: Schotten-Baumann reaction. Reaction of phenol with acid chloride or anhydrides in presence of a base such as NaOH gives ester. CH3COCl OH OCOCH3 or (CH3CO)2O phenylacetate C6H5COCl OH OCOC6H5 NaOH phenylbenzoate 5-Formation of ethers: phenol reacts with alkyl halides in presence of a base such as NaOH to give phenyl alkyl ether. CH3Cl OH OCH3 NaOH phenylmethyl ether ( anisole ) 6-Formation of thiophenol: phenols react with phosphorus pentasulphide P2S5 to give thiophenol. P2S5 OH SH  [B] Reactions of C- O bond: Due to the resonance, oxygen atom has a partial positive charge and therefore the C-O bond has a double bond character, therefore the tendency of OH group to be replaced by a halogen atom through the action of PCl5 or HX as in aliphatic alcohols is so difficult. However, the replacement of the hydroxyl group ( OH ) by halogens or by an amino group ( NH2 ) must be carried out under drastic conditions. 1-placement of ( OH ) group by amino group. When phenol is heated with NH3 under pressure and in presence of a catalyst such as ZnCl2 it gives aniline. NH3 OH NH2 + H2O ZnCl2 / 2-Replacement by hydrogen: reduction. By passing the vapor of phenol over zinc it will be reduced to benzene. OH + H2O Zn /  [C] Reaction of the aromatic ring: 1-Reimer-Tiemann reaction: Phenol reacts with chloroform CHCl3 in presence of NaOH to give salicylaldehyde. OH OH CHCl3 CHO NaOH The Mechanism of reaction: OH CHCl3 CCl2 carbene - H2O O O O H H CCl2 CCl2 OH O O CHCl2 CHCl2 CHO hydrolysis 2-Kolb’s reaction: Heating of sodium phenoxide with carbon dioxide at high temperature and pressure gives salicylic acid. ONa OCOONa OH OH COONa CO2H CO2 HCl p/  Mechanism of the reaction: O O O O H H C O COONa OH OH CO2Na HCl CO2H [ D ] Substitution by electrophilic reagents: The high electron density on benzene ring in phenol ( due to the delocalization of lone pair of electrons from oxygen atom to the  electrons of benzene ring ) result in the rapid substitution by electrophiles compared with benzene i.e benzene ring in case of phenol is more reactive than benzene towards electrophiles. 1-Halogenation: Phenol reacts with bromine solution rapidly to give a white precipitate from 2,4,6- tribromophenol. OH OH 3 Br2 Br Br Br But if the bromination is carried out in anhydrous carbon disulphide CS2 it gives a mixture from o- and p-bromophenol. OH OH OH Br2 Br + Br  b- Sulphonation: Phenol can be easily sulphonated by concentrated H2SO4 to give a mixture from o- and p- phenolsulphonic acid. OH OH OH conc. SO3H + H2SO4 SO3H Nitration: I ) In dilute nitric acid , phenol can be nitrated by the action of dilute HNO3 to give a mixture from o- and p- nitrophenol. OH OH OH dilute NO2 + HNO3 NO2 ii) In concentrated nitric acid, phenol is nitrated to give 2,4,6-trinitrophenol ( picric acid ). OH OH conc. HNO3 NO2 NO2 2,4,6-trinitrophenol NO2 ( picric acid )  d- Nitrosation: Phenol reacts with nitrous acid to give p- nitrosophenol. OH CH2OH (NaNO2/HCl) HNO2 NO e- Coupling reactions: Diazonium salts couple with phenol in alkaline medium at the para position, but if the para position is occupied, the coupling occurs in ortho position giving a red dye. OH N2Cl N N OH NaOH p-hydroxyazobenzene f-Hydroxymethylation: Phenol condenses with formaldehyde at low temperature to give p-hydroxybenzyl alcohol as a major product and a small amount from o-hydroxybenzyl alcohol. OH OH OH CH2O CH2OH + NaOH CH2OH