Pyrazolines. VII. Concerning the formation of olefins from the pyrolysis of pyrazolines

McGreer, Donald E.; Wu, Weh-Sai

doi:10.1139/v67-080

Cited by 32 publications

(19 citation statements)

References 13 publications

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“…An attractive approach to interpreting these results is to consider separate paths for the formation of the olefin and cyclopropane products. This possibility has been suggested earlier (6). Isotope effects for both paths can be calculated by making use of the product distributions given in Table If The isotope effect k,/k, for the olefin forming reaction thus becomes 1.94 and that for the cyclopropane forming reaction becomes 1.20.…”

Section: Prod~rct Analysesmentioning

confidence: 92%

“…Isotope effects for both paths can be calculated by making use of the product distributions given in Table If The isotope effect k,/k, for the olefin forming reaction thus becomes 1.94 and that for the cyclopropane forming reaction becomes 1.20. We envisage the olefin forming reaction to involve an intermediate such as 3 (6). A primary isotope effect for the hydrogen on C-4 is expected with a magnitude of between 1.41 and 2.36 based on studies by Rabinovitch and co-workers (7,8) and Blades (9) for the isomerization of cyclopropane to propylene.…”

Section: Prod~rct Analysesmentioning

confidence: 98%

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Pyrazolines X. Kinetics for the pyrolysis of some deuterated 1-pyrazolines in solution

McGreer¹,

Masters²

1969

Can. J. Chem.

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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,

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Section: Prod~rct Analysesmentioning

confidence: 92%

Section: Prod~rct Analysesmentioning

confidence: 98%

Pyrazolines X. Kinetics for the pyrolysis of some deuterated 1-pyrazolines in solution

McGreer¹,

Masters²

1969

Can. J. Chem.

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“…Ea=32.4 kcal rno1-I and AS* = -2.6 cal K -I mo1-'[7'l. A transition state such as (32) in which N2 .N3 bond has suffered more extensive heterolytic cleavage than N4 C5 was proposed by Baldwin et al on the basis of Hammett p values of + 1.16 and -0.23 for 2-aryl-5-phenyl-and 5-aryI-2-phenyltetrazoles, respe~tively1~'l.…”

Section: Nitrile Iminesmentioning

confidence: 99%

1,3‐Dipolar Cycloreversions

Bianchi

Micheli

Gandolfi

1979

Angew. Chem. Int. Ed. Engl.

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The 1,3-dipolar cycloreversion reaction represents a general scheme of fragmentation of pentaatomic heterocycles to produce 1,3-dipolar systems and dipolarophiles. This review summarizes cycloreversions which give rise to octet-stabilized 1,3-dipoles. The reaction can be either thermal or photochemical or electron impact induced. The aim of the article is to survey the published results, to emphasize the synthetic potential of this reaction, and to stimulate the study of its several not yet unambiguously defined mechanistic aspects. Scheme 1. 1.3-Dipolar cycloadditions and cycloreversions. Above: reactions with 1,3-dipoles of ally1 type. Below: Reactions with 1,3-dipoles of propargyl-allenyl type. In the reactant shown at top left of scheme, all [5-.3+2]-fragmentations are apriori possible. (a)-(e), see text.

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“…During the course of this investigation it became evident that these reactions provide a facile new method for the synthesis of 1,3-diaroylureas. Unlike several previously reported methods (3)(4)(5)(6), which are either inconvenient or of untested generality, the present procedure utilizes readily available starting materials and appears to be quite general in scope.…”

mentioning

confidence: 96%

“…Evidence has been presented that indicates that this reaction is both acid-and base-catalyzed (2). Aromatization occurs in preference to the elimination of nitrogen and formation of cyclopropane and olefin products (3). We have prepared the stereoisomers of 4-bromo-3-methyl-3-carbomethoxy-1-pyrazoline (1 and 2) in the hope that double substitution at C-3 would favor the reaction leading to loss of nitrogen.…”

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confidence: 99%

Pyrazolines VIII. Migration of a carbomethoxy group in a bromopyrazoline to pyrazole conversion

McGreer¹,

Wigfield²

1969

Can. J. Chem.

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Pyrazolines. VII. Concerning the formation of olefins from the pyrolysis of pyrazolines

Cited by 32 publications

References 13 publications

Pyrazolines X. Kinetics for the pyrolysis of some deuterated 1-pyrazolines in solution

Pyrazolines X. Kinetics for the pyrolysis of some deuterated 1-pyrazolines in solution

1,3‐Dipolar Cycloreversions

Pyrazolines VIII. Migration of a carbomethoxy group in a bromopyrazoline to pyrazole conversion

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