P.M.R. Spectroscopy of Trimethylsilyl Derivatives of Hydroxy Acids

Abstract

Del~(rrt1~~nt o l ' C h e~n i s t r~~. Tlre U~l i r e r s i t~of British Colrr~tlbia, Va~tcolcrer 8 . British Colrrmbia Received July 24, 1972 P.m.r. spectroscopy at 60 MHz of trimethylsilyl ethers and esters, prepared from hydroxy acids, gives well resolved sharp singlets in the range T 9.8-9.9. These signals may be used to determine the ratio of hydroxyl to carboxyl groups in a molecule. Measurements may be made directly on fractions isolated by gas-liquid chromatography. The influence of the solvent on the resolution is demonstrated.La spectroscopie r.m.n. (60 MHz) des ethers et esters trimCthylsilyl, derives des acides hydroxyies, donne des pics bien resolus (T 9.8--9.9). On peut utiliser ces signaux pour determiner le rapport entre les groupements hydroxyles et carboxyles dans une molCcule. On peut faire les mesures directement sur les fractions isolees par chromatographie en phase gaseuse. L'influence du solvant sur la rCsolution des pics est demontree.Canadian Journal of Chemistry, 50. 3913 (1971) Trimethylsilyl derivatives have been prepared from many different types of compounds and the silylation reaction has been reviewed (1). These derivatives are commonly prepared mainly for the purpose of separations by gasliquid chromatography and also for mass spectrometry (1). In contrast to the wealth of literature available on these two applications of trimethylsilyl derivatives much less has been reported on the physical properties of such compounds and, in particular, their uses in p.m.r. spectroscopy.We have shown recently that the protons of the -OSi(CH,), group in trimethylsilyl ethers give a sharp singlet in the range T 9.8 and that non-equivalent ethers have distinct chemical shifts (2). Thus, the trimethylsilyl ether of glycerol gives two such singlets (integral ratio 1 : 2), and the derivatives of methyl a-D-galactopyranoside and of a-D-glucopyranose give four and five well resolved signals of equal magnitude, respectively. Carboxylic acids readily form trimethylsilyl esters and thus hydroxy acids give derivatives which are both trimethylsilyl ethers and esters. The present note shows how p.m.r. spectroscopy of these derivatives may be used to determine the relative numbers of carboxyl and hydroxyl groups per molecule and, in certain cases, the absolute number.Trimethylsilyl (TMS) derivatives were prepared by reaction of the hydroxy acid in pyridine with hexamethyldisilazane (HMDS) alone or For personal use only.

Polar functional group analysis of mixtures by silicon-29 nuclear magnetic resonance

“…The methods utilized in the past for the determination of 1-NP in a complex matrix, including diesel particulate extracts, are liquid chromatography with fluorescence detection (HP-LC) (2,2) or gas chromatography with some variation of mass spectrometric detection (3)(4)(5)(6)(7). These methods can require extensive sample preparation, followed by quantitation using expensive instrumentation.…”

“…and numerous synthetic procedures (1). In combination with proton NMR, trimethylsilylation enhances the accuracy of quantitation of polar groups (2)(3)(4)(5). Proton chemical shifts of the trimethylsilyl group are, however, not sufficiently sensitive to variations of molecular structure, and so differentiation of various polar functions in polyfunctional compounds or in mixtures is usually not possible by NMR spectroscopy.…”