Hydroxy acids, determination

Peldszus, S., Huck, P. M., and Andrews, S. A., Determination of short-chain aliphatic, oxo- and hydroxy acids in drinking water at low microgram per liter concentrations, /. Chromatogr. A, 723, 27, 1996. 

Kinetic studies of the oxidation of some a-hydroxy acids with pyridinium dichromate (PDC) are consistent with a mechanism involving the loss of H2O from the pro-tonated substrate in the rate-determining step. The oxidation of 8-hydroxyquinoline (oxine) by PDC has been studied. The intermediacy of an acetochromate ion in the oxidation of some acetophenone oximes with PDC is suggested. 

The influence of a cream containing 20% glycerin and its vehicle on skin barrier properties has been investigated. Recent studies have shown that polymers offer several advantages and can be used in skin care products. Phase diagrams were determined for lactic and isohexanoic hydroxy acids as well as salicylic acid with water, a nonionic surfactant and a paraffinic oil, to outline the influence of hydroxy acids on the structure in a model for a skin lotion. The results showed the influence of the acid to be similar to that of the oil but that the difference in chain length between the two alpha acids had only insignificant influence. The results are discussed from two aspects the structures involved in the lotion as applied, and the action of the lotion residue on the skin after the evaporation of the water. 

No Walden inversion was found to take place when amino acids were converted into the corresponding hydroxy acid by the action of nitrous acid. It was therefore possible to determine the relationship of serine to glyceric acid d-serine was converted by nitrous acid into a glyceric acid which Neubei and Silbermann regarded as 1-glyceric acid on account of its relationship to 1-tartaric acid, but which Neuberg, a little later, stated required confirmation. 

Like amino acids, the optical purity of sterically hindered a-substituted a-hydroxy acids can be determined by H NMR after reaction with (5)-2-chloropropanoyl chloride58. 

The formation of oxazolidines 54 or oxazolidinones 55 is currently utilized to assign the absolute stereochemistry of diastereomers of 1,2-amino alcohols, based on H NMR analysis of the H4 and H5 protons of these heterocycles. In the case of y-amino-p-hydroxy acids, the internally cyclized pyrrolidinone 56 is also suitable for determination of the relative configurations of the y-amino and p-hydroxy groups (Scheme 23). 

As a rule, qualitative and quantitative determinations of fatty acids are performed by g.l.c. of their methyl esters, obtained by treating the glycolipid with HC1 in methanol.160 To raise the volatility of the methyl esters of a-hydroxy acids, they are methylated161 or trimethylsilylated.162... 

From the sea anemone M. senile was isolated j3-glucopyranosyl-( 1 - l)-ceramide, the structure of which was determined by mass spectrometry, H-n.m.r. spectroscopy, and chemical splitting. The major sphingosine in the cerebroside is a new base containing two double bonds and branching at one double bond, namely, 2-amino-D-eryf/jro-l,3-dihydroxy-9-methyl-( , E)-octadeca-4,8-diene. The major fatty acids are Ci6 0 and C20 o a-hydroxy acids.133... 

When Michael additions of chiral enolates to nitroalkenes were studied, it was found that lithium enolates (132) of l,3-dioxolan-4-ones (131), derived from the corresponding a-hydroxy acids, afford the adducts (133) with high diastereoselectivity (Scheme 50).144 Recrystallization leads, in general, to diastereomerically pure products, which in turn can efficiently be converted to homochiral compounds like (134), (135) or (136). A number of other chiral enolates (137M140) were also shown to undergo highly selective additions to nitroalkenes however, product configurations were not determined in these cases. 

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