1.2- Diols s. Glycols

Kpoxicles are cleaved by treatment with acid just as other ethers are, but under much milder conditions because of ring strain. As we saw in Section 7.8, dilute aqueous acid at room temperature is sufficient to cause the hydrolysis of epoxides to 1,2-diols, also called vicinal glycols. (The word vicinal means "adjacent," and a glycol is a diol.) The epoxide cleavage takes place by S v 2-like backside attack of a nucleophile on the protoiiated epoxide, giving a /mm-l,2-diol as product. 

S)-2-hydroxy propionic acid (lactate)11321 and for the kinetic resolution of racemic 2-hydroxy acids[127, 131], but also for selective oxidations of 1,2-diols such as ethylene glycol (Fig. 16.2-30). 

Mcthyltrioxotechnetium(VII), CH3TCO3, is also capable of adding olefins such as cyelohexene and forming the glycolate complex of Tc(V) that releases, by hydrolysis in the presence of acids, the 1,2-diols. When cyelohexene was added, the stereospecific production of c/s-l,2-cyclohcxanediol was observed [31]. 

The U.S. production of ethylene oxide is over 2 5 Mt, of which about 65% is hydrolysed to ethylene glycol (ethane-1,2-diol). Nearly 60% of the glycol is used in the production of polyethylene terephthalate and the rest in antifreeze. Di- and triethylene glycols are used in resins and for gas drying ethanolamines are used in detergents and for gas separations. 

The presence of a phenyl group on one or both carbon atoms of an olefin alters the situation by causing cleavage of the epoxide ring with retention of configuration at the phenylated carbon atom with production of the c/s-glycol. A recent example reported by Riviere" is that hydroxylation of 1-phenylcycloheptene (1) with performic acid gives the cis-diol (2), identical with the product of hydroxylation with... 

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