Zeolite-catalyzed chlorination of toluene by sulfuryl chloride: The role of sulfuryl chloride decomposition in chlorination

The catalytic decomposition of sulfuryl chloride was studied over dried sodium forms of zeolites ZSM-5, L, and Y. NaZSM-5 did not catalyze the decomposition, whereas NaKL and NaY did. During the chlorination of aromatic hydrocarbons using NaKL or NaY, the chlorinating agent sulfuryl chloride must compete with molecular chlorine produced by its own decomposition. The rate of reaction with molecular chlorine alone is much faster than that with sulfuryl chloride. In the presence of sulfuryl chloride, however, the rate of chlorination by molecular chlorine is greatly reduced. Both chlorinating agents use Lewis acid sites, suggesting that these sites are predominantly covered by sulfuryl chloride. Sulfuryl chloride is slightly more selective for para-chlorotoluene than is molecular chlorine. NaZSM-5 catalyzes chlorination using either molecular chlorine or sulfuryl chloride alone, but the latter reactant is not simultaneously decomposed by NaZSM-5. The decomposition may require a basic site adjacent to the Lewis acid site, and NaZSM-5 may not possess basic sites of sufficient strength.