Plant‐polyphenols and related compounds. A mass‐spectrometric study of the trimethylsilyl derivatives of hydroxy‐ and/or methoxy‐substituted cinnamic acids and of their methyl esters

Abstract

AbstractThe low resolution 70 eV mass spectra of the TMS (Trimethylsilyl) derivatives of eight naturally occurring hydroxy‐ and/or methoxycinnamic acids are presented in detail. The TMS derivatives studied are I, of o‐coumaric acid; II, of m‐coumaric acid; III, of p‐coumaric acid; IV, of isoferulic acid; V, of ferulic acid; VI, of 3,4‐dimethoxycinnamic acid; VII, of sinapic acid; VIII, of caffeic acid; Ia to Va, VIIa, of the corresponding methyl esters; and VIa, methyl 3,4‐dimethoxycinnamate.The derivatives studied show a high degree of stability under conditions of electron‐impact. The major fragmentation processes for the free acid TMS derivatives begin with methyl radical loss from either the ester or ring TMS group. The spectra of the methyl ester TMS derivatives have enabled the site of initial methyl loss to be determined. Accurate mass measurements and analysis of the second field‐free region metastable peaks provide support for suggested fragmentation schemes. The spectra are sufficiently different to permit identification except between compounds IV and V (and IVa and Va) where the major fragmentation process involves a common ion, thought to be the silicon analogue of an acetonide.