Aldehydes,Ketones and Carboxylic Acids

and Ketones ketones or a mixture of both depending on the substitution pattern of the alkene (Unit , Class XI). ( ii ) By hydration of alkynes: Addition of water to ethyne in the presence of H SO and HgSO gives acetaldehyde. All other alkynes give ketones in this reaction (Unit , Class XI). .

From acyl chloride (acid chloride) Acyl chloride (acid chloride) is hydrogenated over catalyst, palladium on barium sulphate. This reaction is called Rosenmund reduction . . From nitriles and esters Nitriles are reduced to corresponding imine with stannous chloride in the presence of hydrochloric acid, which on hydrolysis give corresponding aldehyde.

This reaction is called Stephen reaction . Alternatively, nitriles are selectively reduced by diisobutylaluminium hydride, (DIBAL-H) to imines followed by hydrolysis to aldehydes: . . Preparation of Similarly, esters are also reduced to aldehydes with DIBAL-H.

. From hydrocarbons Aromatic aldehydes (benzaldehyde and its derivatives) are prepared from aromatic hydrocarbons by the following methods: (i) By oxidation of methylbenzene Strong oxidising agents oxidise toluene and its derivatives to benzoic acids. However, it is possible to stop the oxidation at the aldehyde stage with suitable reagents that convert the methyl group to an intermediate that is difficult to oxidise further. The following methods are used for this purpose.

(a) Use of chromyl chloride (CrO Cl ): Chromyl chloride oxidises methyl group to a chromium complex, which on hydrolysis gives corresponding benzaldehyde. This reaction is called Etard reaction . (b) Use of chromic oxide (CrO ): Toluene or substituted toluene is converted to benzylidene diacetate on treating with chromic oxide in acetic anhydride. The benzylidene diacetate can be hydrolysed to corresponding benzaldehyde with aqueous acid.

(iii) By Gatterman – Koch reaction When benzene or its derivative is treated with carbon monoxide and hydrogen chloride in the presence of anhydrous aluminium chloride or cuprous chloride, it gives benzaldehyde or substituted benzaldehyde. (ii) By side chain chlorination followed by hydrolysis Side chain chlorination of toluene gives benzal chloride, which on hydrolysis gives benzaldehyde. This is a commercial method of manufacture of benzaldehyde. This reaction is known as Gatterman-Koch reaction.

. From acyl chlorides Treatment of acyl chlorides with dialkylcadmium, prepared by the reaction of cadmium chloride with Grignard reagent, gives ketones. . .

Preparation of Ketones . From nitriles Treating a nitrile with Grignard reagent followed by hydrolysis yields a ketone. Give names of the reagents to bring about the following transformations: (i) Hexan- -ol to hexanal Cyclohexanol to cyclohexanone (iii) p -Fluorotoluene to Ethanenitrile to ethanal p -fluorobenzaldehyde (v) Allyl alcohol to propenal (vi) But- -ene to ethanal (i) C H NH + CrO Cl - (PCC) Anhydrous CrO (iii) CrO in the presence (Diisobutyl)aluminium of acetic anhydride/ hydride (DIBAL-H) . CrO Cl .

HOH (v) PCC (vi) O /H O-Zn dust and Ketones Structure Common name IUPAC name HCOOH Formic acid Methanoic acid CH COOH Acetic acid Ethanoic acid CH CH COOH Propionic acid Propanoic acid CH CH CH COOH Butyric acid Butanoic acid (CH ) CHCOOH Isobutyric acid -Methylpropanoic acid HOOC-COOH Oxalic acid Ethanedioic acid HOOC -CH -COOH Malonic acid Propanedioic acid HOOC -(CH ) -COOH Succinic acid Butanedioic acid HOOC -(CH ) -COOH Glutaric acid Pentanedioic acid HOOC -(CH ) -COOH Adipic acid Hexanedioic acid HOOC -CH -CH(COOH)-CH -COOH Tricarballylic acid Propane- , , - or carballylic acid tricarboxylic acid Carboxylic Acids Carbon compounds containing a carboxyl functional group, –COOH are called carboxylic acids. The carboxyl group, consists of a carbonyl group attached to a hydroxyl group, hence its name carboxyl . Carboxylic acids may be aliphatic (RCOOH) or aromatic (ArCOOH) depending on the group, alkyl or aryl, attached to carboxylic carbon. Large number of carboxylic acids are found in nature.

Some higher members of aliphatic carboxylic acids (C – C ) known as fatty acids , occur in natural fats as esters of glycerol. Carboxylic acids serve as starting material for several other important organic compounds such as anhydrides, esters, acid chlorides, amides, etc. Since carboxylic acids are amongst the earliest organic compounds to be isolated from nature, a large number of them are known by their common names. The common names end with the suffix – ic acid and have been derived from Latin or Greek names of their natural sources.

For example, formic acid (HCOOH) was first obtained from red ants (Latin: formica means ant), acetic acid (CH COOH) from vinegar (Latin: acetum , means vinegar), butyric acid (CH CH CH COOH) from rancid butter (Latin: butyrum, means butter). In the IUPAC system, aliphatic carboxylic acids are named by replacing the ending – e in the name of the corresponding alkane with – oic acid . In numbering the carbon chain, the carboxylic carbon is numbered one. For naming compounds containing more than one carboxyl group, the alkyl chain leaving carboxyl groups is numbered and the number of carboxyl groups is indicated by adding the multiplicative prefix, dicarboxylic acid , tricarboxylic acid, etc.

to the name of parent alkyl chain. The position of –COOH groups are indicated by the arabic numeral before the multiplicative prefix. Some of the carboxylic acids along with their common and IUPAC names are listed in Table . .