Kinetics of the gas‐phase thermal elimination of N‐alkyl‐pyrazoles

Abstract

The kinetic study of the gas-phase thermal elimination reactions of N-ethyl-3,5 dimethyl-pyrazole ( I ) , N-ethyl-pyrazole ( I I 1, N-sec-butyl-pyrazole ( I I I 1, and N-tert-butyl-pyrazole (IV) using a flow system is reported. After obtaining activation parameters for I we carried out competitive reactions with II, III and IV using I as internal standard to obtain their E,. The values of A(AH,") calculated for II, ZII and ZV agree with the little differences in E , experimentally found.

An experimental (flash vacuum pyrolysis) and theoretical study of the tautomerism of pyrazolinones at high temperatures

“…10 m/z (30 eV): 160 (M ϩ ). 3(5)-Methoxy-5(3)-phenylpyrazole (3) was prepared by methylation of 2 by diazomethane in diethyl ether, following the technique described by Vogel. 9b Yield 55%, mp 109-110 ЊC, lit.…”

“…For several years we have been interested in the flash vacuum pyrolysis (FVP) of pyrazoles and indazoles (benzopyrazoles). [1][2][3][4][5][6][7] Pyrazolinones have four tautomers, two of which, 1c and 1d, are 5-and 3-hydroxypyrazole derivatives: 8 As a natural extension of our work, we decided to subject some pyrazolinones to FVP and to calculate theoretically the effect of the temperature on the equilibria between the above represented tautomers of 1. In addition, we determined experimentally the variation of K T with the temperature by 1 H NMR in solution for a model compound.…”

Kinetics of the gas‐phase thermal elimination of (β‐chloro ethyl)‐pyrazole

“…However, the activation energy for the latter should be higher than the former according to our results [2,3], and the activation parameters reported for alkyl chlorides [lo]. The FVP of V between 600-660°C afforded pyrazole and vinyl chloride as products.…”

“…To obtain E,, we took an k l / k 2 average and applied it to eq. (21, as we did in the previous work [3]. Results are shown in Table 111.…”

“…The uncertainty in E, obtained from the Arrhenius plot of ln(kl/k2) vs 1/T is about 4 kcal/mol. AcAH;) calculation for the reactions of N-ethyl pyrazole (1) and (0 From the calculation for 11 we replaced the groups where chlorine is involved [3].…”