Syntheses of alkylthiophenes, dithialkanes and thiacyclohexane derivatives of known structure
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Some time ago the staff of the Department of Chemistry at Texas Woman's University became interesting in determining the structure of organic sulfur compounds in petroleum. The method employed was an indirect one in that the properties of compounds of known structure, synthesized by accepted procedures, were compared with the properties of pure sulfur compounds isolated from petroleum fractions. In the vent all the properties investigated were the same, it could be concluded that the structures of the two compounds were identical. Interest was directed toward these sulfur constituents in petroleum for many reasons. Firstly, there was a purely academic interest in that one is naturally curious about the chemical nature of all natural products. In this particular case it was felt that further knowledge on the structure of the constituents in petroleum would also shed some light on the origin of this most important natural resource. Secondly, the petroleum industry is vitally interested in the nature of these sulfur constituents in petroleum for economic reasons. Thirdly. preparation of additional sulfur compounds would contribute a great deal to the fundamental knowledge of organic sulfur chemistry. It is a well-known fact that the sulfur compounds in petroleum, particularly the refined products obtained therefrom, are obnoxious and detrimental. The problem is further complicated because of the difficulties associated with the removal of the sulfur components during the refining processes. As a matter of fact, in the past many of the oil fields which had a high sulfur content were by-passed. However, with the increased uses of petroleum in our highly mechanized civilization, it is necessary to utilize all kinds of petroleum fields, even those which present problems. It is believed by many authorities on petroleum refining that more efficient methods of removing the harmful sulfur impurities could be achieved if the chemical structure of the sulfur constituents were known. Consequently the major objective of this investigation was to prepare a series of organic sulfur compounds of known structure to serve as reference standards in the identification of sulfur compounds isolated from petroleum. The first type of sulfur compounds prepared in the Texas Woman's University laboratories were thiophene derivatives. Interest was initially focused on this type structure because many earlier investigators had obtained evidence that some structures of this type were present in petroleum. Of course, only a very few of the many thousands of possible structures could be made in the course of time involved in this research work. The compounds of this type prepared in a high degree of purity by this investigator were 2-propylthiophane, 2-pentylthiophane, 2-propyl-2-isoamylthiophane and 2-pentyl-5-hexylthiophane. Some attention was directed toward effecting a synthesis of thiacyclohexans and its alkyl derivatives. It was anticipated that many of the higher boiling sulfur constituents in petroleum were cyclic in nature or even polycyclic. Therefore, methods were sought to prepare, at first, some of the simplest of the thiacyclohexane derivatives. Many problems were encountered. Thiacyclohexane and its 4-methyl derivatives were prepared but unfortunately neither in a high degree of purity nor in good yields. This synthetic problem needs further investigation. When difficulty is encountered in the preparation of thiacyclohexane, it was deemed wise to follow a sideline that presented itself during the synthesis of thiacyclohexane. An intermediate in the attempted preparation of thiacyclohexane by one procedure was 1,5-dithiapentane. This compound was readily alkylated with n-propyl bromids to yield dithialkane, namely, 4,10-dithiatridecane, Another dithialkane prepared was 4,7-dithiadecane. All the compounds produced were investigated in the Texas Woman's University Microbiological Research Laboratory. These results will be compiled and presented in a separate thesis.