1976 Volume 49 Issue 12 Pages 3437-3440
Elimination reactions of 2-bromobutane and 2,3-dibromobutane over silica gels in which silanol protons on the surface were exchanged with bivalent ions such as Ba(II), Ca(II), Mg(II), and Ni(II) have been investigated. Dehydrobromination of 2-bromobutane was found to proceed mainly with syn elimination. Debromination by anti mode and non-stereospecific dehydrobromination were observed for 2,3-dibromobutane. The catalytic activities of these silica gels exhibit reversed volcano-type patterns when they are plotted against the electronegativity of metal ion together with those of alkali-ion exchanged silica gels. Reaction intermediates consistent with the stereochemistry observed are a s-butyl cation and a bromonium ion, respectively for 2-bromobutane and 2,3-dibromobutane.
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