Advancements and Applications of trans-Cinnamic Acid in Modern Chemistry

Trans-cinnamic acid is a white crystalline compound that is slightly soluble in water, and freely soluble in many organic solvents.Classified as an unsaturated carboxylic acid, it occurs naturally in a number of plants.

Property

β-trans-Cinnamic acids do not usually photodimerise in fluid solution, owing to their short excited lifetimes; only cis-trans isomerisation is known to occur. Photodimers were isolated from the solid state (which can display three different crystalline modifications) in which the mutual arrangement of molecules controls the reactivity (topochemistry). Thus crystals of α-form 11α give rise only to α-truxillic acid 12 whereas β-truxinic acid 13 is isolated from the β modification (11β). The crystals are photostable owing to the large distance (>4A) between the reactive centres.

Synthesis of trans-Cinnamic Acid

Trans-cinnamic acid is a central intermediate in the biosynthesis of a myriad of natural products including lignols (precursors to lignin and lignocellulose), flavonoids, isoflavonoids, coumarins, aurones, stilbenes, catechin, and phenylpropanoids. Its biosynthesis involves the action of the enzyme phenylalanine ammonia-lyase (PAL) on phenylalanine.1

Applications of trans-Cinnamic Acid

Trans-cinnamic acid is used in flavorings, synthetic indigo, and certain pharmaceuticals. A major use is as a precursor to produce methyl cinnamate, ethyl cinnamate, and benzyl cinnamate for the perfume industry. Cinnamic acid is a precursor to the sweetener aspartame via enzyme-catalysed amination with phenylalanine. Cinnamic acid can dimerize in non-polar solvents resulting in different linear free energy relationships.

[1]Vogt, T. (2010). "Phenylpropanoid Biosynthesis". Molecular Plant. 3 (1): 2–20.