Long-chain phenols: XX. Synthesis of oxidative degradation products from the methylated component phenols ofAnacardium occidentale and other phenolic lipids: Confirmation of the structure of the parent phenols and of a related material

A general procedure for the determination of the first double bond position in the side-chain of a phenolic lipid has been investigated and, in the first place, the phenols of natural cashew nut-shell liquid (Anacardium occidentale) have been examined. An improved oxidative degradation procedure has been applied consisting of methylation by the phase transfer procedure, hydroxylation with performic acid and oxidation of the mixture of vicinal diols with periodic acid (Malaprade reaction) followed by reduction of the aldehyde fragments with sodium borohydride. The aromatic moieties from the 15∶1, 15∶2 and 15∶3 constituents of cardanol methyl ether, cardol dimethyl ether and dimethyl anacardate were shown to be 8-(3-methoxyphenyl)octan-1-ol, 8-(3,5-dimethoxyphenyl)octan-1-ol and 6-(8-hydroxyocyl)salicylate methyl ether, respectively. The first two octanols were identical to synthetic materials, thus confirming the 8-position for the first double bond in the side-chain of cardanol methyl ether and cardol dimethyl ether constituents. Methyl 6-(8-hydroxyoctyl)salicylate relationship in a series of synthetic reference materials of log (retention time) to the methylene chain length. The synthetic acids 8-(3-methoxyphenyl)octanoic acid, 8-(3,5-dimethoxyphenyl)octanoic acid and 6-(7-carboxyheptyl)salicylic acid methyl ether have been obtained pure for the first time and correspond to the oxidation products of the aromatic aldehyde fragments from the Malaprade reaction stage. The unsaturation in peladjauol, 17∶1-bishomocardanol methyl ether, fromPentaspadon officinalis was confirmed to be at the 8-position by the identity of the anilides of synthetic 8-(3-methoxyphenyl) octanoic acid and of the oxidative degradation product. For part XIX, see ref. 1.