Hydroxyl groups kinetic method

The products are formed in kinetically controlled reactions, except in those instances, considered in the next subsection, where ethers result from the addition of a hydroxyl group to an activated alkene. The analytical method of Spurlin266 has often been used in order to evaluate relative rate-constants for reaction at the hydroxyl groups. 

Ikeda, T., Sasaki, M., and Yasunaga, T. (1982a). Kinetics of the hydrolysis of hydroxyl groups on zeolite surfaces using the pressure-jump relaxation method. J. Phys. Chem. 86, 1678-1680. 

Polymeric supports can also be used with advantage to form monofunctional moieties from difunctional (Hies. Leznoff has used this principal in the synthesis of sex attractants on polymer supports (67). Starting from a sheap symmetrical diol he blocked one hydroxyl group by the polymer. Functionalization of cross-linked polymers is mostly performed by chloromethylation (65). A very promising method to introduce functional groups into crosslinked styrene-divinylbenzene copolymers is the direct lithiation with butyllithium in presence of N,N,N, N -tetramethyl-ethylenediamine (TMEDA) (69, 70). Metalation of linear polystyrene with butyl-lithium/TMEDA showed no exchange of benzylic hydrogen and a ratio of attack at m/p-position of 2 1 (71). In the model reaction of cumene with amylsodium, a kinetic control of the reaction path is established. After 3h of treatment with amyl-sodiuni, cumene is metalated 42% in a-, 39% m-, and 19% p-position. After 20h the mixture equilibrates to affort 100% of the thermodynamically more stable a-prod-uct (72). 

We hope that our survey of the important methods for reduction has shown you that, by choosing the right reagent, you can often react the functional group you want. The chemoselectivity you obtain is kinetic chemoselectivity—reaction at one functional group is simply faster than at another. Now look at the acylation of an amino alcohol (which is, in fact, a synthesis of the painkiller isobu-caine) using benzoyl chloride under acid conditions. The hydroxyl group is acylated to form an ester. Yet under basic conditions, the selectivity is quite different, and an amide is formed. 

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