Hicham H. Dib

Chemistry of 2-arylhydrazonals: utility of substituted 2-arylhydrazono-3-oxoalkanals as precursors for 3-oxoalkanonitriles, 3-aminoisoxazole and 1,2,3- and 1,2,4-triazoles

Efficient routes to 2-arylhydrazono-3-oxoalkanonitriles, 1,2,3- and 1,2,4-triazoles, and 3-aminoisoxazole utilising the oximes of the title hydrazones are reported. The behaviour of the oximes on pyrolysis in the gas phase and by flash vacuum is analysed. X-ray crystallography were used to confirm the structure of the triazole 10b and the 3-oxoalkanonitrile 12f.

Gas-phase pyrolytic reactions of N-ethyl, N-isopropyl, and N-t-butyl substituted 2-aminopyrazine and 2-aminopyrimidine

The rates of gas-phase elimination of N-ethyl (1), N-isopropyl (2), N-t-butyl (3) substituted 2-aminopyrazine and N-ethyl (4), N-isopropyl (5), and N-t-butyl (6) substituted 2-aminopyrimidine have been measured. The compounds undergo unimolecular first-order pyrolytic reactions. The relative rates of the primary:secondary;tertiary alkyl homologues at 600 K are 1:14.4:38.0 for the pyrazines and 1:20.8:162.5 for the pyrimidines, respectively. The reactivities of these compounds have been compared with those of the alkoxy analogues and with each other. Product analyses, together with the kinetic data, were used to outline a feasible pathway for the elimination reaction of the compounds under study.

Gas-phase pyrolytic reactions of esters of 2-pyridine and 8-quinoline sulfonic acid

The rates of gas-phase thermal elimination reaction of esters of 2-pyridine sulfonic acid and 8-quinoline sulfonic acid have been measured over at least 50° for each compound. The relative rates of the first-order unimolecular decomposition at 500 K for the primary:secondary esters suggest that CO bond breaking is kinetically more significant than CH bond breaking, leading to a transition state of carbocationic character. This is consistent with the electron-donating effect provided by the methoxy substituent in 2-p-methoxyphenylethyl of 2-pyridine and 8-quinoline sulfonate esters stabilizing the carbocation center.