Further complicating the Wacker process mechanism is questions about the role of copper chloride. Most theories assumed copper does not play a role in the olefin oxidation mechanisms. Yet, experiments by Stangl and Jira found chlorohydrin formation was dependent on copper chloride concentrations. Work by Hosokawa and coworkers yielded a crystallized product containing copper chloride, indicating it may have a non-innocent role in olefin oxidation. Finally, an ab initio study by Comas-Vives, "et al." involving no copper co-catalyst found anti-addition was the preferred pathway. This pathway was later confirmed by copper-free experiments by Anderson and Sigman. A different kinetic rate law with no proton dependence was found under copper-free conditions, indicating the possibility that even small amounts of copper co-catalysts may have non-innocent roles on this chemistry. While these works complicate the picture of the Wacker process mechanism, one should probably infer that this and related chemistry can be sensitive to reaction conditions, and multiple different reaction pathways may be in play.