Fuel instability studies: The reaction of 3-methyl indole with aryl sulfonic acids

Incompatibility reactions in middle distillate fuels can be ascribed to the presence of specific polar heteroatomic compounds or species containing oxygen, 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 addition 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-methyl indole with aryl sulfonic acids. The results of this study were accomplished by identifying the nature and the structure of the sediments formed using elemental analysis and various instrumental techniques.