Potassium glycidate

Potassium (R)-(+)-2,3-epoxypropanoate (Potassium glycidate). The crude acid from the preceding step (74.5 g, 0.44 mol) is dissolved in absolute ethanol (300 mL) and cooled to -20°C. Under N2, a filtered solution of potassium hydroxide (86%, 55.5 g, 0.85 mol) in absolute ethanol (300 mL) is slowly added. After 2 hr, the mixture is allowed to warm to 0°C and stirred at this temperature for 14 hr. The solution is filtered to remove precipitated salts. Half of the solvent is removed by rotary evaporation without warming and an additional crop of salt (2-4 g) is isolated by filtration. The combined salts are dried under vacuum to give 105 g of a 1 1 mixture of KBr and potassium glycidate. 

The amount of potassium bromide remaining in the recrystallized potassium glycidate is determined by potentiometric titration using a silver electrode. 

Methyl 2,3-epoxypropanoate can be prepared by reaction of potassium glycidate with dimethyl sulfate and one equivalent of benzyltriethylammonium chloride in methylene chloride at room temperature (65% yield).14 The reactions of this ester with organolithium or organomagnesium reagents at low temperature afford optically pure epoxy ketones14 that may be transformed via reductive amination to anti amino epoxides.15... 

This procedure describes an efficient method for the synthesis of >99% enantiomerically pure ethyl glycidate from L-serine. Although preparation of potassium glycidate via cyclization of 3-bromo-2-hydroxypropionic acid,2 and from 3-chloro-2-hydroxypropionic acid (obtained by microbial reduction of chloropyruvic acid)3 was previously reported, the corresponding ethyl ester was never described. An enantioselective synthesis of the 2,3-epoxy acid by oxidation of 2,3-epoxypropanol has also been reported.4... 

Epoxides (see also a,(3-Epoxy alcohols, etc., Glycidic acids, esters, nitriles) From alkenes by epoxidation Dimethyldioxirane, 120 Fluorine-Acetonitrile, 135 Potassium peroxomonosulfate, 259 From carbonyl compounds Alumina, 14... 

Glycidic esters are prepared by the reaction of an aldehyde or ketone with an a-haloester in the presence of base (sodium ethoxide, sodamide, finely divided sodium or potassium t-butoxide) (the Darzens glycidic ester condensation). 

A two-phase solid-liquid transfer catalytic system has been developed for aromatic aldehydes and for aliphatic aldehydes which are branched at the a-carbon.116 The aldehyde and the a-chloroester are stirred in dimethylformamide in the presence of solid potassium carbonate and triethylbenzylammonium chloride. The isolated yield of glycidic ester compares favourably with that of the procedure above. 

If desired, glycidic esters can be derived from a,3-dihydroxy esters, such as (110), by either of two methods. In one method, reaction of the diol with an arenesulfonyl chloride is regioselective, producing the a-arenesulfonate (111) in preference to the 3-sulfbnate. Treatment of (111) with an equivalent of base produces the erythro-glycidic ester (112) in good yield. In the second method, the diol is converted to a bromohydrin (114) via the acetoxy bromide (113). The brotmhydrin (114) affords the threo-g ycidic ester (115) on exposure to potassium caitxHiate in methanol. 

In contrast to this result, Zimmerman and Ahramjian have reported that treatment of the halohydrin (9 a single diastereomer, unknown relative stereochemistry) with potassium f-butoxide in the presence of m-nitrobenzaldehyde affords only the glycidic ester (10 equation 4), indicating that in this case the rate-limiting step is cyclization. ... 

Normally, the Darzens reaction of simple a-halo esters is carried out under anhydrous conditions, since in aqueous media or under phase-transfer catalysis conditions the esters are prone to hydrolysis. Saponification can be largely prevented by using r-butyl esters, but this strategy also poses potential problems, as hydrolysis of the resulting glycidic ester is often the next stage of a synthetic process. Recently, a procedure has been developed in which a-chloro esters are deprotonated by treatment with potassium... 

Usually only a small portion of the sample is water-soluble (chlorides, nitrates, nitrites, sulphates, alkali metals — when unbound in silicates, glycides, fatty acids, humic substances). The extract for the determination of nutrients (nitrogen, phosphorus, potassium, trace elements) is prepared with the use of leaching solutions 1% citric acid, 1% potassium sulphate, 1% hydrochloric acid, calcium lactate, etc. 

The usual Darzen s reaction consists of the reaction of aldehydes or ketones with a-haloester or a-halonitriles in presence of a base like potassium tertiarybutoxide to give glycidic esters or nitriles, respectively (Scheme 20). 

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