Substitution reactions of carboxylic acids

Carboxylic acids can be brominated at the a-position by reaction with bromine and phosphorus tribromide (PBr3) in the Hell-Volhard-Zelinsky reaction. The reaction, which proceeds via an acid bromide, leads to the substitution of an a-hydrogen atom by a bromine atom. 

PBrs can also be used to convert an alcohol into a bromoalkane (Section 5.2.2) 

The mechanism of hydrolysis of an acid bromide is analogous to the hydrolysis of an acid chloride (Section 9.5) 

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Nucleophilic Acyl Substitution Reactions of Carboxylic Acid Derivatives (Chapter21)... 

We don t expect you to be satisfied with the bland statement that tetrahedral intermediates are formed in these reactions of course, you wonder how we know that this is true. The first evidence for tetrahedral intermediates in the substitution reactions of carboxylic acid derivatives was provided by Bender in 1951. 

Using pKaH to predict the outcome of substitution reactions of carboxylic acid derivatives... 

Acid catalysts catalyse substitution reactions of carboxylic acids... 

Summary of the Nucleophilic Substitution Reactions of Carboxylic Acids and Their Derivatives... 

The familiar substitution reactions of derivatives of carboxylic acids with basic reagents illustrate nucleophihc substitution at aliphatic sp carbons. (Substitution reactions of carboxylic acids, and their derivatives, with acidic reagents are covered in Chapter 4.) The mechanisms of these reactions involve two steps (1) addition of the nucleophile to the carbonyl group and (2) elimination of some other group attached to that carbon. Common examples include the basic hydrolysis and aminolysis of acid chlorides, anhydrides, esters, and amides. 

Many nucleophilic acyl substitution reactions of carboxylic acids are acid-initiated. For example, in esterification, the carbonyl group is protonated, alcohol attacks to form the tetrahedral intermediate, proton transfers occur, and water leaves. 

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