2- Ethyl-2-methylsuccinic acid

The optical purity is usually, but not always, equal to enantiomer excess. In order for the two to be equal, it is necessary that there be no aggregation. It is possible, for example, that a homochiral or heterochiral dimer (see Glossary, Section 1.6, for definitions) would refract the circularly polarized light differently than the monomer (or each other). In 1968 [19] Krow and Hill showed that the specific rotation of (S)-2-ethyl-2-methylsuccinic acid (85% ee) varies markedly with concentration, and even changes from levorotatory to dextrorotatory upon dilution. In 1969 [20], Horeau followed up on Krow and Hill s observation, and showed that the optical purity (at constant concentration) and enantiomer excess of (5)-2-ethyl-2-methylsuccinic acid were unequal except when enantiomerically pure or completely racemic. This deviation from linearity is known as the Horeau effect, and its possible occurence should be remembered when determining enantiomeric purity by polarimetry. 

Acetoxy-2-methylbutyric acid, A32.17 2-Acetoxy-2-methylbutyric acid, A33.8 2-Ethyl-2-methylsuccinic acid, A55.5 2-Ethyl-3-methylsuccinic acids, A31.12, A31.20 Lactic acid, O-acetyl, ethyl ester, A1.9 2-Propylsuccinic acid, A28.9, A"36 2-Ethylglutaric acid, A32.il... 

Heating the reaction for shorter periods gave erratic results. At this point the semisolid mixture can be diluted with 200 ml. of water, extracted with benzene, and the benzene extract fractionally distilled to give ethyl 2,3-dicyano-3-methylpentanoate, b.p. 146.0-147.5° (2.5 mm.), m27d 1.4429 (highly purified ester has b.p. 138.5-141.5° (2 mm.), 25d 1.4432). The overall yield of a-ethyl-a-methylsuccinic acid is decreased by about 5% when the dicyano intermediate is isolated. 

Scheme 2. Nonequivalence of optical purity (op) and enantiomeric excess (ee) for 1-ethyl-l-methylsuccinic acid in chloroform.

Butanone, conversion to a-ethyl-a-methylsuccinic acid, 44, 59 Butenolides from aryl aldehydes and y-keto adds, 43, 5 7-(-Butoxynorbornadifne, 44,12... 

Active methylene groups undergo Mitsunobu reactions with alcohols. Thus, when ethyl cyanoacetate is reacted with ethyl L-lactate, diethyl 2-cyano-3-methylsuccinate (113) is formed in 61% yield [42]. Acidic hydrolysis furnishes (5)-( — )-methylsuccinic acid (114) in 29% yield with an optical purity of 99% [43]. 

Fig. 14.2 Chromatogram of organic acids extracted using ethyl acetate and diethyl ether and separated as their methyl esters (diazomethane) on 5 per cent OV-1 using temperature programming from 70°C to 300°C at 4°C min Peak identifications are 1, ethylmalonate 2, methylsuccinate 3, adipate 4, hexanoylglycine 5, hippurate 6, n-pentadecanoate (internal standard). (Redrawn with modifications from Mantagos et al., 1979)...

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