The Positional (18O) Values of Extracted and Synthetic Vanillin

Abstract

The positional δ(18O) values of vanillin (1) of different origins have been determined from the global values of 2-methoxy-4-methylphenol (4), obtained from 1 upon Clemensen reduction, and of 3-methylanisole (5), obtained from 4 by removal of the phenolic O-atom. By these means, it is possible to differentiate samples of 1 of synthetic origin from those extracted from Vanilla plants or produced from lignin by chemical oxidation. The main difference between the samples derived from guaiacol and those possessing the aromatic moiety of natural origin is in the enrichment values of the O-atoms at C(3) and C(4), while the extractive materials from the pods are distinguished from the product from lignin on the basis of the carbonyl oxygen δ(18O) values, ranging from +25.5 and +26.2 in the natural material to +19.7‰ in the lignan-based sample. The values for the phenolic O-atom vary from +8.9 and +12‰ of the synthetic materials to +6.5, +5.3, and +6.3‰, respectively, of the sample from lignin and the two samples from Vanilla pods,whereas the MeO O-atoms show the following values for the same compounds: −2.9, −3.2, +3.5, +3.1, and +2.3‰, respectively. This study indicates the significance of the positional δ(18O) values of polyoxygenated compounds for the definition of their origin.