On the origin of alkylbenzenes in geochemical samples

Abstract

In 1978, Stuermer and Harvey reported the isolation of a series of C₁₀- C₁₄ alkyl-substituted benzenes after high-pressure hydrogenation and ether cleavage reactions on a Sargasso Sea fulvic acid. Mass spectra of the multiple homologues indicated that the phenyl group was substituted on every possible secondary position of the alkyl chain. The presence of this series of compounds in the reaction products was interpreted as evidence that the basic structural units had been part of the original fulvic acid and that the severe reactions employed had cleaved them out of the main structure. More recently, Harvey et al. (1983) used this observation in partial support of a proposed marine fulvic acid structure resulting from the oxidative crosslinking of polyunsaturated lipids. There now appears to be a more likely origin for these particular alkyl benzenes isolated from a marine fulvic acid reaction mixture; we believe they are the C₁₀- C₁₄ linear alkyl benzenes (LAB) which are the precursors in the commercial production of linear alkyl benzene sulfonate (LAS) surfactants widely used in detergents. We present this evidence now so as to avoid a similar situation of a decade ago with the phthalate plasticizers which were reported by many workers to be widely distributed natural products (Mathur, 1974; Mayer et al., 1972).