Gas-solid hydrohalogenation

Table III. Gas-solid hydrohalogenation of ethyl trana-cinnamate in...

Table II shows the results for the gas-solid hydrohalogenation of the a-and fi-CD complexes with styrene at 25 C. Both the CD complexes produced racemic 8a and 9 in 30-50% yields (8a 9 = 1 1) under hydrobromination for 3 h, and no 9 but racemic 8b in 30-40% yields under hydrochlorination for 20 h.

ABSTRACT The gas-solid halogenation and hydrohalogenation using micro-crystalline cyclodextrin complexes are found to be efficient for production of the optical active halides of ethyl trans-cinnamate in moderate optical yields On exposure to HBr at 2QOC for 15-20 hr, the cinnamate in solid a- and S-cyclodextrin complexes yields ethyl R-(+)-3-bromo-3-phenylpropanoate in 46% e.e., and S-(-)-enantiomer in 31% e.e., respectively. No addition nor substitution products are obtained with HCl vapor at 0-50°C for 15-65 hr. Bromination of the B-cyclodextrin complex results in the formation of optical active ethyl erz/t/zrc>-2,3-dibromo-3-phenylpropanoate, while chlorination gives the optical active mixture of trans and cis addition products, ethyl erythro- and threo-2,3-di-chloro-3-phenylpropanoates in 60-80% yields. Mechanism of chiral induction in the present gas-solid reaction has been proposed on the basis of the crystal structure of the complex. 

Fig. 3. Products from the gas-solid halogenation and hydrohalogenation of styrene in the crystalline cyclodextrin complexes.

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