Rearrangement of Acetals of 2-Bromoproplophenone as a Test Reaction to Characterize the Lewis Sites in Large Pore Zeolites

Rearrangement of dimethyl and cyclic ethylene acetals of 2-bromopropiophenone to 2-phenylpropanoates (3) can be catalyzed in the liquid phase at 130°C in the presence of metal ion exchanged large pore zeolites, including a novel crystalline structure. IR Spectroscopic characterization of the sites and comparison of the results achieved with the HY, LaNaY and the rest of the samples have shown that Brönsted acid sites and hard Lewis sites are responsible for the hydrolysis of the acetal, the major side reaction. On the other hand, an increase of the softness of the Lewis site tend to favour the competitive 1,2-alkoxy migration leading to dihydro-1,4-dioxin or 2-methoxypropiophenone versus the 1,2-phenyl shift giving 3. Finally, a small extent of debromination through a radical mechanism has also been observed.