Carboxylic Acids. Esters, Chlorides, Anhydrides, Amides, and Nitriles

2 Carboxylic Acids, Esters, Chlorides, Anhydrides, Amides, and Nitriles The C=0 

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Carboxylic Acids, Ester, Chlorides Anhydrides, Amides and Nitriles ... 

This chapter concerns the preparation and reactions of acyl chlorides acid anhydrides thioesters esters amides and nitriles These com pounds are generally classified as carboxylic acid derivatives and their nomenclature is based on that of carboxylic acids... 

Carboxylic acids are prepared hy the hydrolysis of acid chlorides and acid anhydrides, and acid- or hase-catalysed hydrolysis (see Section 5.6.1) of esters, primary amides and nitriles (see Section 5.6.1). 

Functional groups containing n-bonds are more reactive because ir-bond is weaker and can be easily broken, e.g. aromatic rings, alkenes, alkynes, aldehydes and ketones, carboxylic acids, esters, amides, acid chlorides, acid anhydrides, nitriles, etc. 

Carboxylic acids (511) and their chlorides, anhydrides, amides, esters and nitriles, condense with o-aminothiophenols (507) or their zinc salts, affording 2-substituted benzothiazoles (513), the only exception being acetic acid. The intermediate o -acylaminothioph-enols (512) could be isolated and readily cyclized. The activation of carboxylic acids in... 

Table 4.16 Shift Positions for the C=0 group and other carbon atoms of carboxylic acids, esters, Icatones, chlorides, anhydrides, amides, carbamates, and nitriles (ppm from TMS)...

We did not see a method for directly converting a carboxylic acid into either an amide or a nitrile. All other carboxylic acid derivatives (acid chlorides, acid anhydrides, and esters) can be made directly from a carboxylic acid. 

The high oxidation state of carhon in which there are three bonds to electronegative atoms is the characteristic of carboxylic acids and the related acid chlorides, anhydrides, esters, ortho esters, amides, and nitriles. The transformations may involve oxidation from hydrocarbons or other partially oxidized substrates or exchange among various electronegative atoms on the carbon. 

Carboxylic acid derivatives are compounds that possess an acyl group (R—C=0) linked to an electronegative atom, e.g. —Cl, —CO2 R, —OR or —NH2. They can be converted to carboxylic acids via simple acidic or basic hydrolysis. The important acid derivatives are acid chlorides, acid anhydrides, esters and amides. Usually nitriles are also considered as carboxylic acid derivatives. Although nitriles are not directly carboxylic acid derivatives, they are conveniently hydrolysed to carboxylic acids by acid or base catalysts. Moreover, nitriles can be easily prepared through dehydration of amides, which are carboxylic acid derivatives. 

Esters arc most commonly prepared by the reaction of a carboxylic acid and an alcohol with Lhc elimination of water. Esters are also formed by a number of other reactions utilizing acid anhydrides, acid chloride s, amides, nitriles, unsaturated hydrocarbons, ethers, aldehydes, ketones, alcohols, and esters (via ester interchange). 

Name an aromatic compound, a phenol, an aldehyde, a ketone, a carboxylic acid, an acid chloride, an anhydride, an ester, an amide, a nitrile, and a carboxylic acid salt. (Problems 12.21, 12.31, and 12.33)... 

Thermal dehydration of o- (acylamino)phenols is the method of choice for the preparation of benzoxazoles (equation 96) and other annulated oxazoles. 0,iV-Diacyl derivatives of o-aminophenols cyclize at lower temperatures than do the monoacyl compounds. The synthesis is often carried out by heating the aminophenol with the carboxylic acid or a derivative, such as the acid chloride, anhydride, an ester, amide or nitrile. The Beckmann rearrangement of oximes of o-hydroxybenzophenones leads directly to benzoxazoles (equation 97). 

Lithium aluminium hydride is highly reactive and can also reduce carboxylic acids, acid chlorides, anhydrides, esters, lactones, amides, lactams, imines, nitriles and nitro group. For example, -COCI, -CO2H, -C02Et, -CHO and >CO are reduced to -CH2OH or >CHOH, provided the correct solvent is used. 

L22,13 and L24.12,14 Many carboxylic acid derivatives such as esters, amides, and chlorides or anhydrides may also be used. The same reaction conditions can be applied to the condensation reaction of aromatic nitriles with o-phenylenediamine for the synthesis of H2L8,15 H2L13, and L13a.16,17... 

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