Neopentyl bromide, hydrolysis

We have already noticed (p. 86) that the SN2 hydrolysis of 1-bromo-2,2-dimethylpropane (neopentyl bromide, 24) is slow due to steric hindrance. Carrying out the reaction under conditions favouring the Sjyl mode can result in an increased reaction rate but the product alcohol is found to be 2-methylbutan-2-ol (26) and not the expected... 

The nucleophilic displacement of halogens by fluorine can be successfully carried out by reaction with potassium fluoride under several conditions. Primary and secondary alkyl halides 1 are converted to the corresponding fluorides 2 by heating with a saturated aqueous solution of potassium fluoride in the presence of catalytic amounts of hexadecyltributylphosphonium bromide.56 Small amounts of the corresponding alcohol and the olefinic elimination product are formed as side products. While neopentyl bromide does not react at all, polyhaloalkanes give only products of elimination or hydrolysis. Chlorocyclohexane gives only the elimination product.56... 

The first-order hydrolysis of neopentyl bromide gives mixtures of sec-amyl alcohol and some neopentyl alcohol. While this does not establish the stability of a bridged carbonium ion intermediate, it does indicate the passage through such a state. The reaction is otherwise very difficult to picture. The postulated carbonium ion mechanism is... 

It is interesting to note that while the neopentyl-type bromide (30) undergoes rearrangement during SN hydrolysis, no such rearrangement takes place with its phenyl analogue (31) ... 

The expected reaction would be the formation of a primary alcohol by hydrolysis of the primary bromide. Nevertheless, the hindered neopentylic nature of the bromide causes the unexpected formation of a tertiary alcohol... 

---

See also in sourсe #XX -- [ , ]

---