Meso-butane-2,3-diol

McFeeters (11) separates, in 22 min, numerous analytes of wine, including ethanol, (/ )- or (5 )-butane-2,3-diol and the meso-butane-2,3-diol with a Phenomenex Resex organic acid column... 

Such an A2 mechanism (A stands for acid, 2 indicates a bimolecular rate-determining step) results in a stereospecific reaction. Thus ( )-butane-2,3-diol is formed from cz.s-2,3-dimethyloxirane and meso-butane-2,3-diol from ra 5-2,3-dimethyloxirane. The oxirane obtained by epoxidation of cyclohexene is ra .s -cyclohexane-l,2-diol. 

If X is weakly nucleophihc (e.g., X = S04 or Cl04 ), the protonated oxirane is attacked by H2O and 1,2-diols are formed. For symmetrically substituted systems like ds-and trans-2,3-dimethyl oxirane or cyclohexene oxide, the acid-catalyzed hydrolysis follows a bimolecular SN2-hke mechanism, as indicated by its stereospecific outcome Products are rac-butane-2,3-diol, meso-butane-2,3-diol, and trans-cyclohexane-l,2-diol, respectively. 

Butane-1,3-diol (C H q02) rac-Butane-2,3-diol (C H q02) meso-Butane-2,3-diol (C H2 q02)... 

Fig. 8.—Separation of Alditol Acetates. (Key (A) tetra-O-acetylerythritol (B) penta-0-acetylribitol (C) penta-0-acetylxylitol (D) hexarO-acetjdallitol (E) hexa-0-acetyl-D-iditol (F) hepta-O-acetyl-meso-jij/cero-ollo-heptitol (G) hepta-O-acetyl-D-(//j/cero-D-monno-heptitol (H) hepta-O-acetyl-n-jlycero-D-ffluco-heptitol and (I) octa-0-acetyl-D-erylAro-L-po/ocIo-octitol. Conditions column (120 x 0.5 cm.) of a 1 1 (v/v) mixture of the two following packings (1) 1 1 (w/w) mixtures of (a) 20% w/w butane-diol succinate on Chromosorb W, 60-80 mesh, and (b) 20% w/w Apiezon M grease on silver-coated Chromosorb W, 60-80 mesh, with (2) 0.3% w/w Apiezon M grease on silver-coated glass-beads, 60-plus mesh 213° 200 ml. of argon/min. /3-ionization detector.)...

In addition to the butane diols, degradation afforded dibutyl-ene glycols. Comparison of these fractions with model dibutylene glycols provided confirmatory evidence that the polymers were diisotactic. This is because the dibutylene glycol fraction from crystalline poly (fm s-2,3-epoxybutane) was largely the meso-dibutylene glycol with -dd-dd- and -ll-ll- carbon sequences. 

ANSWER (a) The meso compound, cw-2,3-dimethyloxirane (Fig. 11.1), yields on hydrolysis (2/ ,3/ )-2,3-butane-diol and (2S,3S)-2,3-butanediol. These products are enantiomers. Since the attack by water at either carbon [path (a) or path (b) in Fig. 11.1] occurs at the same rate, the product is obtained in a racemic form. 

Values of the rate coefficients and k have been determined for ethane-l,2-diol andmethyl-substituted ethane-l,2-diols (Buisteta/. ). The general effect of methyl substitution is to decrease k . For meso- and ( )-butane-2,3-diols the values of kf are practically identical, although the equilibrium constant for forming the diester is much larger for the latter. This result suggests that formation of a monoester as an intermediate is rate determining, viz. 

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