Date of Award

1-1-1981

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Abstract

High temperature-high pressure reactions were done with N,N-dimethylaniline and related compounds to study the cleavage of the aromatic and aliphatic C-N bonds, for denitrogenation under coal liquefaction conditions. Reactions were run in a pair of 250-ml Hastelloy 'C' autoclaves and in 12-ml stainless steel autoclaves designed in our laboratory. The range of temperatures studied was 425(DEGREES)C-450(DEGREES)C and that of pressure was 0-1500 psi (initial).The mechanism of the cleavage of both the aromatic C-N bond and the alkyl C-N bond have been postulated. The two sets of conditions studied were; (i) those which excluded any form of sulfur and (ii) those which included some form of sulfur. In the first set of conditions, benzene and toluene were the major products, and in the second set of conditions aniline and N-methylaniline were the major products.When hydrogen alone was used as a reducing gas, maximum yields of toluene and benzene were obtained, resulting from the cleavage of the aromatic C-N bond. Here the N-methylene radical is postulated to be formed which undergoes rearrangement at the 'ipso' position to form the N-methylbenzylamine radical. In partial confirmation of this hypothesis, N-methylbenzylamine was found in the reaction mixture. N-Methylbenzylamine was found to readily cleave to give benzene and toluene under these conditions.When elemental sulfur or hydrogen sulfide was used, high yields of aniline were obtained resulting from the cleavage of the aliphatic C-N bond. Sulfur was found to be a better promotor for this cleavage than hydrogen sulfide. The dealkylation process was found to be stepwise. N-Methylaniline was demonstrated as an intermediate in the formation of aniline via the use of a time study. Methane, hydrogen sulfide and carbon dioxide were formed in the ratio 1:2:1.A mechanistic pathway has been proposed to explain the formation of aniline from N,N-dimethylaniline under sulfur-containing conditions.

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