Flash vacuum thermolysis of the l‐alkyl‐pyrazoles (I) yields the pyrazoles (II) and the alkenes (III).

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.

The gas‐phase pyrazole elimination of N‐alkyl pyrazoles has been studied using MNDO semi‐empirical molecular orbital (MO) theory with complete geometry optimization of all stationary points. We found that the activation energies (Ea) of the concerted processes are around 80 kcal/mol, 25 Kcal/mol higher than experimental values. But the differences in Ea between compounds with different substituents are in good agreement with the experimental ones.

Flash vacuum pyrolysis of (p-chloro ethyl)-pyrazole was studied. Pyrazole elimination and vinyl chloride formation were found. Competitive reactions with (p-chloro ethyl)-pyrazole were carried out using N-ethyl-3,5-dimethyl pyrazole as internal standard to obtain the kinetic parameters (Ea). A(bHf") for this reaction was calculated.

Flash Vacuum Pyrolysis of (a-phenylethyl) and (P-phenylethy1)-pyrazole were studied. Pyrazole and Styrene were found as only products of both reactions. The kinetic parameters obtained reinforce the results previously found about the poor influence of the substitutents on the LY and p carbons of the ethyl group in the FVP of N-alkyl pyrazoles and (p-haloethyl) pyrazoles.