Patent Watch

October 7, 2013

pH control is the key to allyl chloride epoxidation. Dow Chemical, in partnership with BASF, developed process technology for producing propylene oxide (PO) by epoxidizing propylene with H2O2 as the oxidant. For this process to be economically competitive, the selectivity to PO based on consumed H2O2 must be high because H2O2 is a relatively costly feedstock. To accomplish this goal, the pH of the reaction medium must be carefully controlled.

Inventor H. L. Crampton explored a similar method for converting allyl chloride to epichlorohydrin, also by using H2O2 as the oxidant. To control the pH of the reaction medium, she found that supported bases are very effective and lead to high epichlorohydrin selectivities.

In one example, Crampton prepared a prereaction solution of 52.3 wt% allyl chloride, 5 wt% MeOH, 23.3 wt% 1,2-dichlorobenzene, and 1.4 wt% TS-1 catalyst. (TS-1 is a titanium silicalite zeolite.) Separately, a 30% aq H2O2 solution was stirred with enough Amberlyst A-21 resin to adjust the pH of the solution to 5.7.

The H2O2 solution was slowly added to the allyl chloride solution at 40 ºC for 60 min. The H2O2 conversion was 99.4%, and H2O2 selectivity to epichlorohydrin was 93.4%. The only byproducts reported in the patent were 1-chloro-3-methoxy-2 propanol (1.0 %), 1-chloro-2,3-propanediol (0.4%), and 0.44% higher–molecular weight materials. Other supported bases that gave good results included poly(4-vinylpyridine), Lewatit MP-62, and Dowex MWA-1. (Dow Global Technologies [Midland, MI]. US Patent 8,524,926, Sept 3, 2013; Jeffrey S. Plotkin)