H₂S‐promoted thermal isomerization of butene‐2 CIS to butene‐1 or butene‐2 trans around 500°C

Abstract

H2S increases the thermal isomerization of butene-2 cis (B,) to butene-1 (B1) and butene-2 trans (Bt) around 500°C. This effect is interpreted on the basis of a free radical mechanism in which buten-2-yl and thiyl free radicals are the main chain carriers. B1 formation is essentially explained by the metathetical steps: RICHARD, BOIVEAUT, AND MARTIN the latter being in agreement with values given in a previous work. Lastly, the activation energy of the addition process:(4) HS + B, -CdHsSH is shown to be Ed N 3.5 f 2 kcal/mol, of the same order as the activation energy of the corresponding metathetical step.

ChemInform Abstract: THERMAL REACTION OF HYDROGEN‐BUTENE‐2‐CIS MIXTURES AT 500°: HYDROGENATION, HYDROGENOLYSIS, AND THERMAL REACTION OF THE OLEFIN

“…Under these conditions, the presence of hydrogen cannot modify the rates of processes (ml) and (mz) at low extent of reaction. As we actually do not observe any hydrogen effect on the initial formation rates of Bt or butadiene-1,3, we conclude that the free-radical part of these hydrocarbons is negligible as compared to their molecular part, as this has already been observed [11, 12,14]. By contrast, hydrogen increases the formation rates of hydrogenolysis products.…”

“…By contrast, the thermal reactions of butene-2 have been extensively studied, either pure or in the presence of ethanal [12], of dimethyl mercury [13], of hydrogen sulfide [14], but never in the presence of hydrogen. Choosing therefore butene-%cis as a model molecule, we decided to study the thermal coreaction of hydrogen-butene-2-cis mixtures around 500°C and at low extent of reaction.…”

The reactions of hydrogen atom with organosulfur compounds

“…This interpretation of the results, however, should be viewed with caution for the following reasons: i) SH radicals have been shown to be effective in causing the geometrical isomerization of alkenes [66,67] via reversible addition; ii) the sulfur atoms formed in the SH + SH ÷ H2S + S(3p) reaction have been shown [68] to react with thiiranes to give the corresponding alkene; therefore a significant fraction of the butenes could have been produced via the S(3p) + dimethylthiirene + S 2 + butene reaction; iii) it has also been shown [69] that triplet thiiranes, formed in addition reactions of S(3p) atoms to alkenes, are capable, via reversible addition to alkenes, of inducing geometrical isomerization.…”