Incompatibility reactions in middle distillate fuels can be ascribed to the
presence of specific polar heteroatomic compounds or species containing ox
ygen, sulfur, and nitrogen. It has been proposed that the observed sediment
and/or gum formation results from the interaction of heteroatomic species
with the acids contained in fuels. Recent studies have shown that the addit
ion of non-basic nitrogen heterocycles such as indoles to a fuel increases
deposit formation dramatically. Therefore, an attempt was made to identify
the structure of the sediment. This paper reports on the reaction of 3-meth
yl indole with aryl sulfonic acids. The results of this study were accompli
shed by identifying the nature and the structure of the sediments formed us
ing elemental analysis and various instrumental techniques.