Carbonyl Compounds PDF

# **Carbonyl Compounds** ## **Carbonyl Compounds include** 1. Aldehydes & Ketones 2. Carboxylic acids 3. Carboxylic acid derivatives (Acid halides, Acid anhydrides, Esters & Amides) ### **The study of each class** * Nomenclature * Classification * Synthesis * Reactions * Physical characters # **A...

# **Carbonyl Compounds** ## **Carbonyl Compounds include** 1. Aldehydes & Ketones 2. Carboxylic acids 3. Carboxylic acid derivatives (Acid halides, Acid anhydrides, Esters & Amides) ### **The study of each class** * Nomenclature * Classification * Synthesis * Reactions * Physical characters # **Aldehydes and Ketones** ## **1. Aldehydes and Ketones** * They are characterized by the presence of an acyl group: * An aldehyde: $R-C(=O)-H$ * A Ketone: $R-C(=O)-R$ * They are bonded to a H or alkyl groups: * Formaldehyde: $H-C(=O)-H$ * Aldehyde: $R-C(=O)-H$ * Ketone: $R-C(=O)-R'$ ## **1. Nomenclature (IUPAC)** ### **A. ALDEHYDES** 1. When naming the parent, replace the final -e in the alkane with an -al. * Pentanal: $CH_3CH_2CH_2CH_2C(=O)H$ * Butanal: $CH_3CH_2CH_2C(=O)H$ * Hexanal: $CH_3(CH_2)_4C(=O)H$ 2. When numbering the parent chain of an aldehyde, the aldehydic carbon is assigned No. 1, despite the presence of alkyl substituents, $\pi$-bonds, or hydroxyl groups. 3. When attached to a ring system, they are named substitutively by adding the suffix Carbaldehyde. * Benzenecarbaldehyde: $C_6H_5C(=O)H$ * Cyclohexanecarbaldehyde: $C_6H_{11}C(=O)H$ * 2-Naphthalenecarbaldehyde: $C_{10}H_7C(=O)H$ * The common name benzaldehyde is more frequently used than benzene carbaldehyde. ### **Examples:** * Propanal: $CH_3CH_2C(=O)H$ * 5-Chloropentanal: $ClCH_2CH_2CH_2CH_2C(=O)H$ * Cyclohexanecarbaldehyde: $C_6H_{11}C(=O)H$ * Benzenecarbaldehyde, Benzaldehyde: $C_6H_5C(=O)H$ * Cyclopentanecarbaldehyde: $C_5H_9C(=O)H$ * Some have common names that are still retained by the IUPAC system. * Formaldehyde: $H-C(=O)-H$ * Acetaldehyde: $CH_3-C(=O)-H$ * Methanal: $H-C(=O)-H$ * Ethanal: $CH_3-C(=O)-H$ * Given below are the common names and structural formulas of a few aldehydes. Provide an alternative IUPAC name? * a) $CH_3CH(CH_3)C(=O)H$ (isobutyraldehyde) * b) $H-C(=O)-CH_2CH_2CH_2- (-O)-H$ (glutaraldehyde) * c) $CH_3-CH=CH-CHO$ (crotonaldehyde) * d) $CH_3-CH=CH-C(=O)-H$ (cinnamaldehyde) * e) $HOC_6H_4(OCH_3)CH_2-C(=O)-H$ (vanillin) * Some aromatic aldehydes obtained from natural sources have very pleasant fragrances. Provide an alternative IUPAC name? * Benzaldehyde: $C_6H_5C(=O)H$ (from bitter almonds) * Vanillin: $HOC_6H_4(OCH_3)C(=O)H$ (from vanilla beans) * Salicylaldehyde: $HOC_6H_4C(=O)H$ (from meadowsweet) * Cinnamaldehyde: $C_6H_5CH=CHC(=O)H$ (from cinnamon) * Piperonal: $C_8H_6O_3$ (made from safrole; odor of heliotrope) ## **1. Nomenclature (IUPAC)** ### **A. Ketones** 1. Ketones, like aldehydes, are named using the same three-step procedure. When naming the parent, the suffix "-one" indicates the presence of a ketonic group. * In aliphatic ketones, replace the -e in the corresponding alkane with -one giving the C=O the least numbering. * Butane: $CH_3CH_2CH_2CH_3$ * Butanone: $CH_3CH_2C(=O)CH_3$ ### **Examples:** * Acetone: $CH_3C(=O)CH_3$ (propanone or dimethyl ketone) * Acetopheneone: $C_6H_5C(=O)CH_3$ (1-phenylethanone or methypheyl ketone) * Benzophenone: $C_6H_5C(=O)C_6H_5$ (diphenylmethanone or diphenyl ketone) * 2-Butanone: $CH_3CH_2C(=O)CH_3$ (ethyl methyl ketone) * 2-Pentanone: $CH_3C(=O)CH_2CH_2CH_3$ (metyl propyl ketone) 2. Some common names retained in the IUPAC system. ### **Examples:** * Ethyl propyl ketone. 3. Although rarely used, IUPAC rules also allow simple ketones to be named as alkyl alkyl ketones. For example. * *Note that:* Ketonic group (C=O) may be named as prefix called (oxo) * 4-Oxopentanoic acid: $CH_3CH_2CH(C=O)CH_2COOH$ (levulinic acid) * Which is the correct name? * 3-methylcyclohexanone * 5-methylcyclohexanone * Give the best IUPAC name? ## **A. Nomenclature of Aldehyde and Ketones (IUPAC)** * When the $R-C(=O)-$ are named as substituents they are called alkanoyl or acyl gps. e.g. * Methanoyl or formyl: $H-C(=O)-$ * Ethanoyl or acetyl: $CH_3-C(=O)-$ * 2-Methanoylbenzoic acid (o-formylbenzoic acid): $HOC_6H_4(C=O)H$ * 4-Ethanoylbenzenesulfonic acid (p-acetylbenzenesulfonic acid): $CH_3C(=O)C_6H_4SO_3H$ * 1,3-diphenyl-2-propanone: $C_6H_5CH_2C(=O)CH_2C_6H_5$ * 3-Hexanone: $CH_3CH_2CH_2C(=O)CH_2CH_3$ (not 4-hexanone) * 4-Methyl-2-pentanone: $CH_3CH(CH_3)CH_2C(=O)CH_3$ (not 2-methyl-4-pentanone) * 4-Methylcyclohexanone: $CH_3C_6H_9C(=O)$ * 4,4'-Dimethylpentanal: $(CH_3)_2CHCH_2CH(CH_3)C(=O)H$ * 5-Hexenal: $CH_2=CHCH_2CH_2CH_2C(=O)H$ * 2-Phenylpropanedial: $C_6H_5CH_2CH(C=O)C(=O)H$ * Cyclopentanecarbaldehyde: $C_5H_9C(=O)H$ * 1-Naphthalenecarbaldehyde: $C_{10}H_7C(=O)H$ * **Challenging Quiz 2** * I-Give the IPUAC substitutive names for the seven isomeric Aldehydes and Ketones with the formula (M.F.) $C_8H_{10}O$. * 2- Give the structures and names (common or IUPAC substitutive names) for all the aldehydes and ketones that contain a benzene ring and have M.F. $C_8H_8O$. * **Challenging Quiz 3** * 3- CONVERT EACH OF THE FOLLOWING COMMON KETONIC COMPOUNDS NAMES TO IUPAC: * A) DIBENZYL KETONE. * B) ETHYL ISOPROPYL KETONE. * C) METHYL 2,2'-DIMETHYL PROPYL KETONE. * D) ALLYL METHYL KETONE. ## **2. Synthesis of Aldehydes & Ketones** ### **A. Synthesis of Aldehydes** 1. Aldehydes by oxidation of 1^o alcohols. 2. Aldehydes by reduction of acyl chlorides, esters, and nitriles. 3. Aldehydes from acyl chlorides, ### **1-Oxidation of Primary Alcohols to Aldehydes:** * Using pyridinium dichromate (PDC) or pyridinium chloro chromate (PCC) in anhydrous media such as, dichloromethane. * Oxidize 1^o alcohols to aldehydes while avoiding over oxidation to C.As. * $PCC = CrO_3(C_5H_5N)_2$ * $PDC = CrO_2(C_5H_5N)_2$. * $R-CH_2OH \longrightarrow^{PCC or PDC, CH_2Cl_2} R-C(=O)-H$ ### **Examples:** 1. $RCH_2OH \longrightarrow^{PDC or PCC, CH_2Cl_2} R-C(=O)-H$ 2. $CH_3(CH_2)_8CH_2OH \longrightarrow^{PDC, CH_2Cl_2} CH_3(CH_2)_8C(=O)H $ (Decanal (98%)) 3. $CH_3(CH_2)_5CH_2OH \longrightarrow^{C_3H_5NH CrO_3Cl, CH_2Cl_2} CH_3(CH_2)_5C(=O)H$ (Heptanal (93%)) ### **Note that:** The oxidation state of aldehydes lies between that of 1° alcohols and carboxylic acids. * $R-CH_2OH \longrightarrow^{[O]} R-C(=O)-H \longrightarrow^{[O]} R-C(=O)-OH$ ### **A. Synthesis of Aldehydes** * So, How to obtain the aldehyde from c. acids? * It's not helpful to use a stoichiometric amount of LiAlH4!! Why? * So, the use of derivatives of C.A and we use aluminum hydride derivatives that are less reactive than LiAlH4. * Lithium tri-tert-butoxy aluminum hydride: $Li[HAl(OC(CH_3)_3)_3]$ * Diisobutylaluminum hydride (abbreviated -i-Bu₂AIH or DIBAL-H): $HAl(CH_2CH(CH_3)_2)_2$ ### **Examples of synthesis of aldehydes from acid derivatives** * $R-C(=O)-Cl \longrightarrow^{(1) LiAlH(Ot-Bu)_3, -​78°C \\ (2) H_2O} R-C(=O)-H$ * $R-C(=O)-OR' \longrightarrow^{(1) DIBAL-H, hexane, ​ -​78°C \\ (2) H_2O} R-C(=O)-H$ * $R-C\equiv N \longrightarrow^{(1) DIBAL-H, hexane \\ (2) H_2O} R-C(=O)-H$ * Transfer of hydride ion ($H^-$) from Al atom to the C=O carbon of the acyl chloride, subsequent hydrolysis frees the aldehydes. * $R-C(=O)-Cl \longrightarrow^{LiAlH_4, ether \\ H_2O, -​78°C} R-C(=O)-H$ * **Suggest the mechanism for the Reduction of an Acyl Chloride???** ### **A. Synthesis of Aldehydes** * **3- From Terminal Alkynes** * $CH_3C\equiv CH \longrightarrow^{(BH_3)_2,THF} CH_3CH_2CH(OH)_2 \longrightarrow^{H_2O,-​HO} CH_3CH_2CH(OH)-OH \longrightarrow^{H_2O,-​HO} CH_3CH_2C(=O)H$ * Borane is added anti-Markownikove's ($BH_3$ is added to less substituted carbon and H is added to highly substituted carbon) * **Suggest the role of the **THF**???* * **Markovnikov’s # anti–Markovnikov’s** rule ### **B. Synthesis of Ketones** 1. Ketones by oxidation of 2^o alcohols. 2. Ozonolysis of Alkenes 3. Hydration of alkynes 4. Friedel-Crafts acylation ### **Ketones by oxidation of 2^o alcohols** * $R-C(=O)-R' \longrightarrow^{Cr(VI)} R-C(=O)-R'$ * $CH_3CH(OH)CH_2CH_2CH_2CH_3 \longrightarrow^{CrO_3,acetic acid-water} CH_3C(=O)CH_2CH_2CH_2CH_3$ (1-Phenyl-1-pentol -> 1-Phenyl-1-pentanone (93%)) * *Many oxidizing agents are available for converting secondary alcohols to ketones.* * *PDC or PCC may be used, as well as other Cr (VI)-based agents such as chromic acid or potassium dichromate and sulfuric acid.* ### **2- Ozonolysis of Alkenes** * $R-C(=O)-C(=O)-R' \longrightarrow^{(1) O_3 \\ (2) H_2O, Zn} R-C(=O)-R + R'-C(=O)-H$ * $CH_3CH=CHCH_2CH_2CH_3 \longrightarrow^{(1) O_3 \\ (2) ​H_2​, Zn} ​ CH_3C(=O)CH_3+ CH_3CH_2CH_2CH(C=O)H$ (2,6-Dimethyl-2-octene -> Acetone + 4-Methylhexanal (91%)) * *Hydrolysis of the ozonide intermediate in the presence of zinc (reductive workup) permits aldehyde products to be isolated without further oxidation.* * *Break the double bond, replace with two carbonyl groups.* ### **3-Hydration of alkynes** * $RC\equiv CR' + H_2O \longrightarrow^{H_2SO_4, HgSO_4} RCCH_2R’$ (Alkyne -> ​ Ketone) * $HC\equiv C(CH_2)_5CH_3 + H_2O \longrightarrow^{H_2SO_4, HgSO_4} CH_3C(CH_2)_5CH_3$ (1-Octyne -> 2-Octanone (91%)) * Markovnikov addition of H2O to triple bond where reaction is catalyzed by strong acids and Hg2+ ion with the formation of vinylic alcohol which usually unstable and rearranges rapidly to a ketone. ### **4- Friedel-Crafts Acylation of Aromatic Compounds.** * Acyl chlorides and carboxylic acid anhydrides acylate aromatic rings in the presence of aluminum chloride. * $ArH + RC(=O)-Cl \longrightarrow^{AlCl_3} Ar-C(=O)-R + HCl$ * $ArH + (RC(=O))_2O \longrightarrow^{AlCl_3} Ar-C(=O)-R + R-C(=O)-OH$ * $CH_3OC_6H_5 + CH_3C(=O)OCCH_3 \longrightarrow^{AlCl_3} CH_3OC_6H_4C(=O)CH_3$ (​Anisole + Acetic anhydride -> ​ p-Methoxyacetophenone (90-94%)) * *The reaction is one of electrophilic aromatic substitution in which acylium ions are generated and attack the ring.* * **Summary of aldehyde synthesis** * **Summary of ketone preparation** ## **3. Physical Properties of Aldehydes & Ketones** ### **A. STRUCTURE AND BONDING** 1. Aldehydes and Ketones are polar compounds, containing a dipole moment along the carbon-oxygen double bond. 2. Because of the high electronegativity of $O_2$, the electron density in both $\sigma$ and $\pi$ components of C=O double bond is displaced toward $O_2$. The C=O group is polarized so that the C is partially +ve and the $O_2$ is partially -ve. * The Carbonyl gp and the atoms attached to it all lie in the same plane and the angles between them are close to 120° e.g. formaldehyde is a planar molecule. * Bonding in formaldehyde can be described as an SP2 hybridization model analogous to that of ethylene. * The presence of C=O makes aldehyde and ketones rather polar. * The molecular dipole moments, are substantially larger, than those compounds containing double​ bond C=C. * 1-Butene: $CH_3CH_2CH=CH_2$ D.m 0.3D * Propanal: $CH_3CH_2CH=O$ D.m. 2.5D * In resonance terms, electron delocalization in the C=O group is represented by contribution from two principal resonance forms. ### **B. Boiling Point** The structural effect on C=O group stability are an important factor in the relative reactivities of aldehydes and ketones. The C=O group is a polar group i.e. aldehydes and ketones have higher B.Ps than hydrocarbons of the same M.W. * Butane: $CH_3CH_2CH_2CH_3$ * Propanal: $CH_3CH_2C(=O)H$ * Acetone: $CH_3C(=O)CH_3$ * 1-Propanol: $CH_3CH_2CH_2OH$ * Aldehydes and ketones can't have strong interriblecular hydrogen bonding between their molecules, so they have low B.ps than the corresponding alcohols. * Which compound in each of the following pairs listed has the higher B.P? * a) Pentanal or 1-pentanol * b) 2-Pentanone or 2 pentanol * c) Pentane or pentanal * d) Acetophenone or 2-phenylethanol * e) Benzaldehyde or benzyl alcohol. * **Physical properties of aldehydes and ketones** | Formula | Name | Mp (°C) | bp (°C) | Solubility in water | |:-------------|:--------------------|--------:|--------:|:----------------------:| | HCHO | Formaldehyde | -92 | -21 | very soluble | | CH3CHO | Acetaldehyde | -125 | 21 | unlimited | | CH3CH2CHO | Propanal | -81 | 49 | very soluble | | CH3(CH2)2CHO | Butanal | -99 | 76 | soluble | | CH3(CH2)3CHO | Pentanal | -91.5 | 10 | sl. soluble | | CH3(CH2)4CHO | Hexanal | -51 | 2 | sl. soluble | | C6H5CHO | Benzaldehyde | -26 | 13 | sl. soluble | | C6H5CH2CHO | Phenylacetald. | 33 | 1 | sl. soluble | | CH3COCH3 | Acetone | -95 | 17 | unlimited | | CH3COCH2CH3 | Butanone | -86 | 8 | very soluble | | CH3COCH2CH2CH3 | 2-Pentanone | -78 | 19 | ​soluble | | CH3CH2COCH2CH3 | 3-Pentanone | -39 | 3 | soluble | | CH3COC6H5 | Acetophenone | 21 | 56 | insoluble | | C6H5COC6H5 | Benzonphenone | 48 | 1 | insoluble | * **END OF PART ONE**