2-Methylpropene oxide, polymerization

In the presence of H3O, 2-methylpropene oxide undergoes chain-growth polymerization such that nucleophilic attack occurs at the more substituted end of the epoxide. Draw a stepwise mechanism for this process, and explain this regioselectivity. 

The most complex type of behavior is exhibited by 2-methylpropene which polymerizes, rearranges, cyclizes, and oxidizes. Although the dominant alkenyl cation has not been completely identified, it is known to be a cyclopentenyl cation with methyl groups at C-1, C-2, and C-3 (XII) (Deno et al., 1964). 

Methylpropene can be removed from the reaction mixture by distillation and easily is made the principal product by appropriate adjustment of the reaction conditions. If the 2-methylpropene is not removed as it is formed, polymer and oxidation products become important. Sulfuric acid often is an unduly strenuous reagent for dehydration of tertiary alcohols. Potassium hydrogen sulfate, copper sulfate, iodine, phosphoric acid, or phosphorus pentoxide may give better results by causing less polymerization and less oxidative degradation which, with sulfuric acid, results in the formation of sulfur dioxide. 

Problem 12.35. Give the equation for each of the following reactions. If there is more than one product, indicate which is the major product(s) and which the minor. If there is no reaction, state No Reaction. (a) 1-Butene-1-NaOH, (ft) 1-methylcyclohexeneHCl, (c) 1,3-butadiene-I-excess CI2, (d) polymerization of 2-methylpropene, (e) oxidation of 2-pentene with hot, acidic K2Cr207, (/) combustion of 2-pentene, (g) 1-methylcyclohexene -t- H2O in the presence of an acid catalyst. 

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