Aromatic Amines in Organic Synthesis Part III; p-Aminocinnamic Acids and Their Methyl Esters

Fifteen amine derivatives of cinnamic acid were synthesized by reaction of the corresponding benzaldehydes and malonic acid. The selected acids were then converted into methyl esters. Three esterification methods were tested with (1) thionyl chloride in methanol, (2) sulfuric acid in methanol, and (3) dimethyl sulfate in acetone. The latter method turned out to be the best, both in terms of reaction efficiency and product purity. The chemical structure and purity of all the synthesized compounds were verified by elemental analysis, 1H and 13C NMR, and IR spectroscopy. The cinnamic acids and their esters, thanks to an extensive system of conjugated double bonds compared to analogous benzoic acids, can be used to obtain dyes for various applications, including non-linear optics and optoelectronics. Therefore, their basic spectroscopic properties are presented as well.