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

The positional delta(O-18) 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 delta(O-18) values, ranging from + 25.5 and + 26.2 in the natural material to + 19.7 parts per thousand in the lignan-based sample. The values for the phenolic O-atom vary from + 8.9 and + 12 parts per thousand of the synthetic materials to + 6.5, + 5.3, and + 6.3 parts per thousand, respectively, of the sample from lignin and the two samples from Vanilla pods, whereas the MeO O-atoms show the following values significance of the positional delta(O-18) values of polyoxygenated compounds for the definition of their origin.