Researches on the chemistry of coal-Part IV. The oxidation of the residue from the benzene-pressure-extraction process

Abstract

Since publishing the last paper of this series, in which was described our process of extracting coals with benzene under pressure up to 700 lb. per square inch, and of fractionating the crude extracts thereby obtained, we have turned our attention to the “residues” resulting from it, which in the case of most bituminous coals usually form about 90 per cent, of the actual coal substance. And in this paper the results of our experiments during the past eighteen months upon their oxidation by means of an alkaline solution of potassium permanganate are briefly described. It was decided to publish these results a t this stage of the investigation because of the recent publication by Mr. W. Francis and Prof. R. Y. Wheeler of an account of their work upon “The Properties and Constitution of Coal Ulmins,” in the course of which they oxidised, with either hydrogen peroxide or 30 per cent, nitric acid, what they termed the “regenerated ulminsfrom coals,” obtaining good yields of oxalic and succinic acids together with small quantities of other acids, among which picric acid, and certain benzene polycarboxylic acids were mentioned. They state ( loc . cit ., p. 2245) “symmetrical benzene tetracarboxylic acid (m. p. 264° with decomposition) has been isolated in a pure form by slow crystallisation from acetic acid, and its methyl ester (m. p. 138°) formed. The tricarboxylic acid appears to be trimellitic acid, but it has not yet been obtained in a sufficiently pure crystalline form to identify.” No ultimate analyses of these acids were, however, published.