Gas-phase kinetics of elimination reactions of pentane-2,4-dione derivatives. Part ii [1]. Thermolysis of derivatives and analogues of 3-phenylhydrazonopentane-2,4-dione

Abstract

Six analogues and derivatives (1-6) of 3-phenylhydrazonopentane-2,4-dione (7) were subjected to gas-phase thermolysis. The Arrhenius log A and Ea (kJ ) of the Ϫ1 Ϫ1(s ) mol analogues (1-5) are, respectively: 10.42 and 140.8 for 1-cyano-1-phenyl-hydrazonopropanone (1), 11.19 and 135.4 for 1-cyano-1-(p-nitrophenylhydrazono)-propanone (2), 10.68 and 144.9 for 1-cyano-1-(p-methoxyphenylhydrazono)propanone (3), 11.76 and 137.8 for 1-cyano-3-phenyl-1-phenylhydrazonopropanone (4), and 11.29 and 145.9 for 1-cyano-1-phenylhydrazonobutanone (5). The corresponding values for ethyl 3-oxo-2-phenylhydrazonobutanoate (6) are 11.90 and 143.3 kJ The rates of reaction at are compared with those of Ϫ1 Ϫ1 s mol . 600 K the title diketone (7) and of pentane-2,4-dione (8) and rationalized in terms of a plausible elimination pathway involving a semiconcerted six-membered transition state.

Theoretical Study on the Pyrolysis of Sulphonyl Oximes in the Gas Phase

“…The experimental work reported by Al-Awadi et al 2 suggested that the thermal elimination of oximes passes through a six-membered ring transition state irrespective of substituents and presented the reaction rate coefficients k and Arrhenius activation energies Ea for a series of sulphonyl oximes (Y = OCH 3 , CH 3 , H, and Cl). Discussions about the structures of stationary points on the potential energy surface, energetics, and nature of reaction mechanism in this study will be given for these compounds for the purpose of comparison.…”

“…Polar substituent effects are investigated extensively in kinetic investigations of reaction mechanism. In this work, several substituents Y=OCH 3 , CH 3 , H, Cl, NO 2 , are chosen at the para position in the Yphenyl rings. We take a series of oximes as an example to study the effect of the substituents of Y-ring on the reactivity and properties of molecules.…”

“…1,2 Some similar reactions have also been studied for 3-phenylhydrazonopentane-2,4-dione, 3 ethyl (hetero) arylcarboxylate esters, 4 and heterocyclic hydrazone 5 systems experimentally. The common character of these reactions is that they were found to be homegeneous and unimolecular, and follow firstorder rate law.…”

“…2 In this work, we theoretically study the molecular mechanism of the pyrolysis of sulphonyl oximes (Y = OCH 3 , CH 3 , H, Cl, NO 2 ) in gas phase using HF/3-21G, ONIOM methods. The effects of substituent in Y-ring on the reactivity of these oximes are investigated.…”

Kinetics and mechanism of gas‐phase pyrolysis of N‐aryl‐3‐oxobutanamide ketoanilides, their 2‐arylhydrazono derivatives, and related compounds

“…In these studies the proposed mechanisms were concerted asynchronous processes involving a cyclic six‐membered TS (Scheme ), and molecular reactivities were reported to be a function of the H‐bond donor acidity of the HX bond (i), the polarity of the AB bond (ii), the protophilicity of the YZ multiple bond (iii), or an effect combining two or all of the three bonds (Scheme ). Reactivity might additionally be subject to the thermodynamic stability of the incipient elimination fragments 8,16.…”