User:Mickey Boray/Hunsdiecker reaction

Reaction with α, β-Unsaturated Carboxylic Acids

Synthesis of β-arylvinyl halide by microwave-induced Hunsdiecker reaction.

Chowdhury and Roy noted several drawbacks of using Hunsdiecker reaction, namely that some reagents, such as molecular bromine and salts of mercury, thallium, lead, and silver, are inherently toxic and that reactions with α, β-unsaturated carboxylic acids result in low yield. Regarding reactions using α, β-unsaturated carboxylic acids, Kuang et al. modified the reaction with using a new halogenating agent, N-halosuccinimide, and lithium acetate as the catalyst, which resulted in higher yield of β-Halostyrenes. They found that using the microwave irradiation could synthesize (E)-β-arylvinyl halide much quicker with higher yields. This is useful because synthesizing (E)-vinyl bromide in general is not very practical due to the complexity of alternative reagents (e.g. organometallic compounds), longer reaction times, and lower yields. Using microwave irradiation also allows the synthesized arylvinyl halide to carry electron-donating groups (in addition to electron-withdrawing groups), which is not possible with alternative synthetic methods. While tetrabutylammonium trifluoroacetate (TBATFA) could be used as an alternative catalyst for a metal-free reaction, it was noted that lithium acetate resulted in higher yields compared to other relatively complex catalysts, including tetrabutylammonium trifluoroacetate. An alternative method using micelles was found, with green characteristics. Micelles generally facilitate reactions thanks to their solublization capability and here, it was found that a reaction with α, β-unsaturated aromatic carboxylic acids and N-halosuccinimide catalyzed by cetyl trimethyl ammonium bromide (CTAB), sodium dodecyl sulfate (SDS), and Triton-X-100 in dichloroethane (DCE) carried out under reflux conditions of 20-60 minutes formed β-Halostyrenes in excellent yields with high regioselectivity.