Isobutyl alcohol rearrangement

Carbocation rearrangements occur in the reactions of some secondary alco hols with DAST, thus isobutyl alcohol gives a mixture of isobutyl fluoride and tert-hxAy] fluonde [95] (Table 6), and both bomeol and isoborneol rearrange to the same 3-fluoro-2 2,3-tnraethylbicyclo[2 2 IJheptane (72-74%) accompanied by camphene [95]... 

Because salicylic acid contains the deactivating meta-directing carboxyl group, Friedel-Crafts reactions are generally inhibited. This effect is somewhat offset by the presence of the activating hydroxyl group. Salicylic acid reacts with isobutyl or /-butyl alcohol in 80 wt % sulfuric acid at 75°C to yield 5-/-butylsalicylic acid [16094-31-8], In the case of isobutyl alcohol, the intermediate carbonium ion rearranges to (CH3)3C+. 

Isobutyl halides and other isobutyl compounds rearrange readily to tert-butyl compounds for the older literature see Whitmore and Lux.869 However, PBr3 (see page 223) converts isobutyl alcohol into isobutyl bromide in good yield with less than 1% of tert-butyl bromide.869... 

When the reduction is carried out with an IiAlHi/AlCl3 mixture, howeva epoxide rearrangement precedes reduction and isobutyl alcohol becomes the major product. This rearrangement was confirmed by a deutraium-labeling experiment in which an LiAlD AICI3 mixture was used. Where was the deuterium located in the isobutyl alcohol product ... 

The dehydration of isobutyl alcohol over Si02—AI2O3 yields a mixture of butenes in which the fraction of n-butene is 33%. Since the rate of skeletal isomerization of isobutene to n-butenes is significandy lower than the rate of formation of a-butenes in dehydration, n-butenes must be primary products. This indicates that the reaction proceeds via the 1 mechanism. Formation of n-butenes is associated with the formation of the least stable isopropyl carbenium ions, which are readily rearranged by hydride or methyl transfer to form more stable tertiary or secondary carbenium ions. 

Certain classical work is in accordance with this view. Thus Palmer and Constable (102) showed that the five alcohols, ethyl, propyl, butyl, isobutyl, and isoamyl, had the same rates of dehydrogenation on a copper catalyst under the same conditions. The energy of activation was about 22 kcal. They supposed that the alcohols were adsorbed ivith their chains vertical to the catalyst surface, and that the rate determining step was the removal of a hydrogen atom from the hydroxyl group (103). The rearrange-... 

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