The kinetics and product distribution have been measured for the pyrolysis of 3-methyl-3-carbomethoxy-1-pyrazoline (1) and its 4,4-d2 and 5,5-d2 analogues in tetralin, n-butyl phthalate, nitrobenzene, and formamide. The isotope effect k,/kD for 1-5,5-d2 of 1.22 and for 1-4,4-L& of 1.36 isconsistent with a mechanism involving migration of the C-4 hydrogen concerted with loss of nitrogen.
Canadian Journal of Chemistry, 47, 3975 (1969)The use of deuterium isotope effects as a probe of mechanisms is well known. As a further evaluation of the mechanism of the pyrolysis of pyrazolines we have investigated the kinetics of this reaction for a series of pyrazolines and their deuterated analogues.
ExperimentalMaterials 3-Methyl-3-carbomethoxy-1-py~azoline (1) and 3-methyl-3-cyano-1-pyrazoline (2) have been prepared previously (1,2). T h e 3-methyl-3-carbon~ethoxy-1-pyrazoline-5,5-dz was prepared using dideuterated diazoniethane (prepared by exchange with D,O using potassium carbonate) and analysis showed it to contain 80% deuterium at C-5. In a similar way 3-methyl-3-cyano-1-pyrazoline-5,5-dz was prepared and contained over 95% deuterium at C-5. Methyl methacrylate-3,3-d, was prepared by the Mannich reaction from methyl hydrogen methylmalonate and a 30% solution of formaldehyded, in water (Merck Sharp and Dohme of Canada, Ltd.). Yields of only 12% were obtained compared to 50% for trial runs in which methyl methacrylate was made from formalin solution. 3-Methyl-3-carbomethoxy-1-pyrazoline-4,4-d, was prepared from the methyl methacrylate-3,3-d2 with diazomethane.
Kinetic Measurei~~ei~tsThe rates of decomposition of the pyrazolines studied were determined by volumetric measurement of the rate of formation of nitrogen using an apparatus similar to that described by Peterson and co-workers (3). The reaction flask was heated in an oil bath (Dow Corning silicon fluid DC-550) and the reaction solution was stirred by a magnetic stirrer. The bath temperature was controlled to 10.05" and measured by a thermometer calibrated against an N.B.S. calibrated thermonleter. The solvents used were all reagent grade and twice distilled at reduced pressure.For the kinetic runs standard solutions of the pyrazolines were prepared in a 5 or 10 ml volumetric so that 'Taken in part from the P1i.D. thesis of I. M. Masters,
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.