Catalytic Cracking of Aliphatic Sulfides on Silica-Alumina Catalysts

Abstract

The catalytic cracking of various aliphatic sulfides on the silica-alumina catalyst by the use of a pulse reactor was investigated. The cracking reactivity of these sulfides increased in the following order.
CH₃SCH₃<C₂H₅SC₂H₅<C₃H₇SC₃H₇<n-C₄H₉SC₄H₉ This order is in accordance with that of the electron donability of alkyl group adjacent to sulfur atom in the sulfide molecule, because a linear relationship was observed between the logarithms of the apparent first order rate constants of this reaction and the Taft σ which is the measure of the electron donability of alkyl group in the molecule.
On the other hand, the cracking activity of the silica-alumina catalyst decreased when the effective acid sites on the catalyst surface were poisoned by treating it with KOH solution in the range of 0 to 0.14 meq/g. However, the observed apparent activation energy did not change by this treatment. Aliphatic sulfides were also decomposed in the presence of solid phosphoric acid catalyst having predominantly Brönsted acid sites and the order of the cracking reactivity was nearly similar to silica-alumina.
From these results, it was concluded that the cracking of aliphatic sulfides on silica-alumina catalyst proceeds on the Brönsted acid sites.