Hydrogenation of 4-methylcinnoline


The rapid expansion of knowledge of cinnoline chemistry since 1941 has not included the hydrocinnolines. Not one catalytic hydrogenation of a fully aromatic cinnoline had been reported. This thesis is an effort to enlarge knowledge of this particular area of cinnoline chemistry. The work is a natural outgrowth of that done at Brigham Young University on decahydroquinoxaline, both the cis- and trans- isomers having been prepared and characterized. 4-Methylcinnoline, prepared by the method of Jacobs, et.al., was hydrogenated in neutral and acidic ethanolic solutions at 2000-3000 psig. hydrogen pressure and 100-266°. The catalysts used were 5% palladium on alumina, ruthenium oxide, 5% palladium on activated charcoal, 5% rhodium on activated charcoal, and platinum oxide. The filtered reaction mixtures were either vacuum-distilled or made basic, extracted, and then vacuum-distilled. Both the average and median material recoveries were 66 weight per cent. Seven different products were variously obtained (in order of decreasing total yield): o-amino-β-methylphenethylamine, octahydroskatole, 1-ethyloctahydroskatole, 2, 3-dihydroskatole, 4-methyl-3, 4-dihydrocinnoline, 4-methyl- 1, 2, 3, 4-tetrahydrocinnoline, and an unknown compound. 4-Methyl-3, 4-dihydrocinnoline and 4-methyl- 1, 2, 3, 4-tetrahydrocinnoline also were obtained by reduction of 4-methylcinnoline in acidic solution at 60 psig. hydrogen pressure and room temperature. The catalysts were 5% rhodium on alumina and platinum oxide, respectively. The structures of octahydroskatole, 1-ethyloctahydroskatole, and 4-methyl-1, 2, 3, 4-tetrahydrocinnoline were proven by comparison with authentic samples, aided by infrared spectra and elemental analyses. The structures of 2, 3 -dihydroskatole and 4-methyl-3, 4- dihydrocinnoline were assigned on the basis of infrared spectra, elemental analyses, and, in the case of the latter, hydrogen absorption. o-Amino-β-methylphenethylamine, a new composition of matter, was so designated on the basis of its infrared spectrum, elemental analyses, and chemical properties. Diazotization of the diamine in concentrated hydrochloric acid yielded 4-methylcinnoline. Diazotization in dilute aqueous sulfuric acid solution gave 2-(o-amino-phenyl)- 1-propanol (a new composition of matter), based on infrared absorption data and elemental analysis. The results of the diazotization reactions support the structure assignment for the diamine. With all compounds, the preparation of such derivatives as the hydrochloride, picrate, and picrolonate served mainly to provide more easily purified samples for elemental analyses. Determinations of pKa values and nonaqueous titrations were of limited value in structural assignment. Hydrogenation of 4-methylcinnoline in neutral ethanolic solution with either 5% rhodium on activated charcoal or platinum oxide gave mainly o-amino-β-methylphenethylamine. In acidic solution the main product was octahydroskatole. o-Amino-β-methylphenethylamine was the main product from the hydrogenation of 4-methylcinnoline with 5% palladium on activated charcoal in both neutral and acidic ethanolic solutions. Hydrogenation of 4-methylcinnoline with ruthenium oxide in neutral ethanolic solution gave 1-ethyloctahydroskatole. In acidic solution octahydroskatole was the main product; an unknown compound was also isolated. Low-temperature ( < 132°) reductions of 4-methylcinnoline in acidic or neutral ethanolic solutions with 5% rhodium on alumina gave mainly o-amino-β-methylphenethylamine, while high temperatures (200°) favored formation of octahydroskatole.



College and Department

Chemistry and Biochemistry



Date Submitted


Document Type





Chemistry, Organic, Hydrocinnoline



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