Answer to Question #178447 in General Chemistry for Cristy

Question

1.     Briefly describe the 5 ways of preparing carboxylic acids, showing examples of reaction equations where relevant.  (10 marks)

2.     Explain briefly about esters being hydrolyzed. Draw an example reaction equation to illustrate your explanation. (5 marks) 

Answer 1

1.a) By using primary Alcohols and Aldehyde

We will notice that the primary alcohol gets oxidized to carboxylic acid when oxidizing agents are added such as potassium permanganate (KMnO4) in an acidic, alkaline or neutral medium. On using a mild oxidizing agent we can get carboxylic acids from aldehydes.

b) From Alkylbenzenes

We can get aromatic carboxylic acids after vigorous oxidation of alkylbenzenes with chromic acid. Irrespective of the length of the chain the whole side chain is oxidized to a carbonyl group. The oxidation of primary and secondary alkyl groups can be done in this manner while the tertiary group is unaffected.

c) From Nitriles and Amides

Amides are prepared by the hydrolysis of nitriles and then is converted to acids in the presence of catalysts (H+ or OH-1). In order to stop the reaction at the amide stage, mild reaction conditions are used.

d) By using Grignard Reagents

When Grignard reagent reacts with carbon dioxide its forms salts of carboxylic acids which after some time gives corresponding carboxylic acid after the acidification with any mineral acid. We can prepare Grignard reagents as well as nitriles from alkyl halides. These methods are very useful for the conversion of alkyl halides into corresponding carboxylic acids which has one carbon atom more than what is present in alkyl halides.

e) By Acyl Halides and Anhydrides

When acid chloride is hydrolysed with water than carboxylic acid is produced and it is more readily hydrolysed with aqueous base and gives corresponding carboxylic ions which on further acidification gives the carboxylic acid.

2.The alkoxy (OR′) group of an ester is replaced by another group. One such reaction is hydrolysis, literally “splitting with water.” The hydrolysis of esters is catalyzed by either an acid or a base. ... The ester is heated with a large excess of water containing a strong-acid catalyst.