Pentyl alcohols, dehydration

Pillai and Pines (84) found that neopentyl alcohol, mixed with 10% by weight of piperidine and passed over alumina prepared from aluminum isopropoxide, yielded 2-methyl-l-butene and 2-methyl-2-butene, in a maximum ratio of 3, and small amounts of 1,1-dimethylcyclo-propane. However, lert-pentyl alcohol yielded these two olefins in a maximum ratio of only 1.4, and none of the cyclopropane was produced (Table VI). Because of these facts a carbonium ion mechanism which is applicable to ferf-pentyl alcohol is not adequate to explain the rearrangement taking place during the dehydration of neopentyl alcohol,... 

Dehydration of Neopentyl Alcohol and terl-Pentyl Alcohols" over Alumina ... 

The different nature of the intermediate in the dehydration of primary and tertiary alcohols, is substantiated by the contrasting dehydration behaviour of neopentyl and -pentyl alcohols . The carbonium ion mechanism for the tertiary alcohol leads only to 2-methyl-1-butene (57%) and 2-methyl-2-butene (42%), but neopentyl alcohol gives different proportions of these olefins (64-73% 23-32%) along with small amounts of 1,1-dimethylcyclopropane. These latter facts are accommodated better in terms of a concerted mechanism for the dehydration of neopentyl alcohol, viz-... 

Several reagents reduce aldehydes preferentially to ketones in mixtures of both. Very high selectivity was found in reductions using dehydrated aluminum oxide soaked with isopropyl alcohol and especially diisopropylcarbinol [755], or silica gel and tributylstamane [756]. The best selectivity was achieved with lithium trialkoxyalumimm hydrides at —78°. In the system hexanal/ cyclohexanone the ratio of primary to secondary alcohol was 87 13 at 0° and 91.5 8.5 at —78° with lithium tris(/er/-butoxy)aluminum hydride [752], and 93.6 6.4 at 0° and 99.6 0.4 at —78° with lithium tris(3-ethyl-3-pentyl-oxy)aluminum hydride [752],... 

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