Carboxamide

Carboxylic acid amides are derivatives of ammonia, and primary and secondary amines in which one or more hydrogen atoms are substituted on the nitrogen by carboxylic acid radicals (R -CO-). They are a sub-group of the amides. Carboxylic acid amides include reaction products of carboxylic acid chlorides or carboxylic acid anhydrides with ammonia or amines. Carboxylic acids themselves react with ammonia or amines to give the corresponding ammonium salt, but not to carboxamides.

Nomenclature

Carboxamides with a distinction in accordance with the number of carboxy groups on the nitrogen atom between primary ( a carboxy group, two hydrogen atoms ), secondary ( two carboxy groups, a hydrogen atom ) and tertiary ( three carboxy groups is not a hydrogen atom ) amides. Amides with one or two alkyl groups on the nitrogen atom is called N- alkylamides or N, N- dialkylamides. Cyclic amides are called lactams. Secondary amides of dicarboxylic acids are called imides. Peptides and proteins are made - linked by amide bonds - amino acids. This type of bond is often called a peptide bond. Technically very important are the polyamide fibers nylon and Perlon.

Structure

Since the carbonyl carbon and the nitrogen atom are sp2 - hybridized, all three atoms of the amide bond -CO-N = and the neighboring atoms in one plane. Further, since the CN bond is much shorter (132 pm ) than in other carbon-nitrogen compounds (147 pm ), must be assumed that a conjugated system in which by delocalization of π - electrons present a partial double bond character. Because of the sp2 hybridization of the nitrogen lone pair of electrons which is not protonisable n- electron pair, but (as eg in pyrrole ) a contributing to conjugate π - electron pair, so amides are not basic.

Representative

Representation

Amides are obtained mainly from the reaction of carboxylic acid derivatives with ammonia or an amine. In the simplest case, it is at the carboxylic acid derivative is a carboxylic acid chloride. The released hydrogen chloride ( HCl) react with the amine to give a hydrochloride, so that the amine has to be used in a double amount of:

Aminolysis of carboxylic acid esters and carboxylic acid amides, alcohols provides:

Carboxylic acids themselves react with amines to form the corresponding salts:

In case of strong heating the salts dissociate but partially amine and carboxylic acid, which then result in the elimination of water, the amide:

Other important methods for the synthesis of amides are the Ritter reaction, the hydrolysis of nitriles, the Beckmann rearrangement and the Haller -Bauer cleavage.

• Substance Group
• Carboxamide