Understanding the pathways of improved chlorohydrination of allyl chloride with HCl and H2O2 catalyzed by titanium-incorporated zeolites

Abstract

Chlorine based olefin chlorohydrination reaction is one of the most hazard and polluted processes for manufacturing epoxy compounds. To solve these drawbacks, we have exploited a totally novel allyl chloride chlorohydrination route, using HCl and H2O2 as raw materials, catalyzed by hollow titanium silicate (HTS) zeolite. Under optimal parameters, almost 100% allyl chloride conversion and over 98.0% dichloropropanol (DCP) selectivity have been achieved, and HTS zeolite displays pretty high stability in strong acidic solution for over 25days. UV-Raman spectroscopy directly reveals the formation of Cl2 and its derivates, but this chlorohydrination is also competitively dominated by an epoxidation-ring opening mechanism, especially in high catalyst dosage. That is because allyl chloride is much easier to be epoxidized to epichlorohydrin (ECH) under HTS catalyst, rather than reacts with Cl-containing species generated via the HCl oxidation with H2O2. Meanwhile, ECH is highly active to react with HCl to form 1,3-DCP catalyzed by H+ ions, thus the epoxidation process can be significantly promoted by ring-opening reaction, due to the pushing of chemical balance. Importantly, this study provides a novel viewpoint on developing green chemical processes, on the basis of their fundamental reaction mechanisms.