Nucleophilic substitution reactions of carboxylic acids

Good leaving groups are neutral molecules or stable anions 

Nucleophilic substitution of the OH group of a carboxylic acid (RCO2H) is difficult to achieve because of competing deprotonation (see Section 9.3.2). In order for substimtion to occur, the OH group needs to be converted into a good leaving group (e.g. Cl). 

Thionyl chloride also reacts with alcohols to form chloroalkanes (Section 5.2.2) 

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

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

A. Nucleophilic acyl substitution reactions of carboxylic acids (Section 21.3). 

Because nitriles have no leaving group, they do not undergo nucleophilic substitution reactions like carboxylic acid derivatives. Because the cyano group contains an electrophilic carbon atom that is part of a multiple bond, a nitrile reacts with nucleophiles by a nucleophilic addition reaction. The nature of the nucleophile determines the structure of the product. 

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. 

H Nucleophilic Acyl Substitution Reaction of Carboxylic Acids... 

Some nucleophilic acyl substitution reactions of carboxylic acids. 

In addition to sulfonic acid groups, carboxylic acid groups as ring substituents results in self-doping of polyaniline and influence properties such as solubility, pH dependent redox activity, conductivity, thermal stability, etc. Sulfonated polyanilines are typically obtained by postpolymerization modifications such as electrophilic and nucleophilic substitution reactions. However, carboxylic-acid-functionalized polyanilines are typically synthesized directly by chemical and electrochemical polymerization of monomer in the form of homopolymer or copolymer with aniline. In contrast to sulfonated polyaniline, very few monomers are available for the synthesis of carboxyl acid functionalized polyaniline. Anthranilic acid (2-aminobenzoic acid) is an important monomer and is often used for the synthesis of carboxyl acid functionalized polyanilines. 

This chapter will discuss methods for the preparation of esters, acid chlorides, anhydrides, and amides from carboxylic acids, based on acyl substitution reactions. Acyl substitution reactions of carboxylic acid derivatives will include hydrolysis, interconversion of one acid derivative into another, and reactions with strong nucleophiles such as organometallic reagents. In addition, the chemistry of dicarboxylic acid derivatives will be discussed, as well as cyclic esters, amides, and anhydrides. Sulfonic acid derivatives will be introduced as well as sulfate esters and phosphate esters. Finally, nitriles will be shown to be acid derivatives by virtue of their reactivity. 

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