GEOSYNTHESIS OF ORGANIC-COMPOUNDS .3. FORMATION OF ALKYLTOLUENES AND ALKYLXYLENES IN SEDIMENTS

Heating ortho-undecyltoluene with an acidic clay catalyst and hexameth ylbenzene as a methylating agent resulted in the formation of hydrocar bon mixtures containing undecyltoluenes and dimethylundecylbenzenes. A t short heating times, methylation at ring positions 4 and 5 forming 2 ,4- and 2,5-dimethylundecylbenzene s occurred predominantly, while at longer heating times, methylation and isomerization/transalkylation re actions resulted in higher concentrations of more stable alkylxylene i somers. The distributions of undecyltoluenes and dimethylundecylbenzen es in two mature crude oils were also compared to those formed in the laboratory heating experiments. One crude oil derived from carbonate s ediments was shown to have a predominance of ortho-undecyltoluene and 2,4- and 2,5-dimethylundecylbenzenes, similar to the reaction products formed from short-term laboratory heating experiments. The other crud e oil, derived from elastic sediments containing abundant clays, was s hown to contain a mixture of the undecyltoluenes and dimethylundecylbe nzenes similar to the reaction products generated from longer-term hea ting experiments. These observations suggest that alkylxylenes in crud e oils result from sedimentary methylation of ortho-alkyltoluenes, as the ortho-alkyltoluenes isomers are often the most abundant isomers in low maturity sediments. The initial products formed under kinetic con trol then undergo clay-catalyzed isomerization/transalkylation reactio ns to yield mixtures with higher abundances of the more thermodynamica lly stable isomers.