Oxygen Exchange into 2-Butanol and Hydration of 1-Butene Do Not Proceed through a Common Carbocation Intermediate

Article abstract of DOI:10.1021/ja00241a024

The acid-catalyzed isomerization of the 4-methyl group of 1,1,1,2,3,3-hexadeuteriated 2-butanol between the 1- and 4-positions occurs faster than dehydration to 2-butene, as measured by hydrogen incorporation from water into the 3-position of 2-butanol.The rate constants for these processes are k_isom = 1.1E-6 s^-1 and k_hyd = 5.6E-7 s^-1, respectively, in 0.55 M HClO4 at 100 deg C.These results require that isomerization occurs by hydride transfer from C-3 to C-2, as well as by the formation and hydration of 2-butene.The 6percent initial yield of isomerized product in the acid-catalyzed hydration of <4-14C>-1-butene, before there is significant accumulation of 2-butene (Manassen, J.; Klein, F.J.Chem.Soc. l960, 4023), shows that hydride transfer is also significant in this reaction.Comparison of the product yields from 1-butene and the rate constants for isomerization and oxygen exchange of <4-14C>-2-butanol in the earlier work shows that the two reactions do not occur through a common carbocation intermediate.The preferential formation of cis-2-butene from 1-butene and trans-2-butene from 2-butanol confirms this conclusion.