Spectrophotometric determination of aliphatic amines by acylation with cinnamic anhydride

Abstract

A simple, sensitive method for the determination of primary and secondary aliphatic amines is based upon their conversion to N-substituted cinnamides by reaction with trans-cinnamic anhydride. After acylation of the amine in acetonitrile solution, the excess anhydride is hydrolyzed, the cinnamide is extracted into chloroform, and the amide is measured spectrophotometrically. The method is applicable to amine samples in the 1-5 pmole range; the standard deviation is 0.5-1.0%. Water and methanol do not interfere. The kinetics of the acylation and hydrolysis reactions have been studied, and a correlation can be demonstrated between acylation rate and basicity for many primary amines; sterically hindered amines react more slowly than would be anticipated from their basicity.

Precise kinetic measurements for identifying organic compounds

“…From the data presented in references (9)(10)(11)(12)(13)(14)(15)(16)(17)(18) it is apparent that reaction rate constants can be useful in the identification of organic compounds. However, this is not the only benefit from such studies, since the approach also represents a valuable teaching mechanism.…”

“…An incidental benefit from these studies is the accumulation of extensive rate data for related compounds under identical conditions. Utilization of these data for analytical design, structure-activity relationships, and mechanistic implications has, to some extent, already been attempted (IS,15,16).…”

Kinetics of trans-Cinnamic Anhydride Reactions Catalyzed by Pyridine, 4-Dimethylaminopyridine, and N-Methylimidazole

“…A quantitative method for aliphatic amines (1,2) is based on their reaction with trans-cinnamic anhydride to give the corresponding cinnamamides. These reactions are rapid and quantitative, but aromatic amines and alcohols, which are relatively weak nucleophiles, react too slowly for practical use of the published procedure.…”