Functional derivatives of carboxylic acids

There are some problems associated with the use of functional derivatives of carboxylic acids. Long-chain acid anhydrides are not commercially available, and one half of the acylation reagent is not utilized. Acyl chlorides require the use of tertiary base catalysts, whose double role has been explained before. Some of the intermediate acyl ammonium compounds formed are, however, insoluble in the solvent system. Examples include RCO - N+EtsCL in LiCl/DMAc, where RCO refers to the propionyl, hexanoyl, and stearoyl moiety, respectively. Hexanoyl- and stearoyl-pyridinium chlorides are also insoluble in the same solvent system [185]. 

Closely related to the carboxylic acids and to each other are a number of chemical families known as functional derivatives of carboxylic acids acid chlorideSy anhydrides, amides, and esters. These derivatives are compounds in which the —OH of a carboxyl group has been replaced by —Cl, —OOCR, —NH2, or —OR. ... 

Functional derivatives of carboxylic acids are recognized by their hydrolysis— under more or less vigorous conditions—to carboxylic acids. Just hkh kind of derivative it is is indicated by the other products of the hydrolysis. 

Cyanoformamidines, exhibiting nucleophilic and electrophilic properties in the 1,3-positions, react with hexafluoroacetone forming five-membered heterocycles (86CB2127). This ability to form five-membered heterocycles is the major characteristic of hexafluoroacetone, which is also inherent in some perfluorinated and partially fluorinated ketones, aldehydes, and imines in their reactions with a-functional derivatives of carboxylic acids, as well as w-amino, a-N-alkylamino,... 

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