Trimethylsilyl deriv high volatility

For volatile materials vapor phase chromatography (gas chromatography) permits equilibration between the gas phase and immobilized liquids at relatively high temperatures. Tire formation of volatile derivatives, e.g., methyl esters or trimethylsilyl derivatives of sugars, extends the usefulness of the method.103104 A method which makes use of neither a gas nor a liquid as the mobile phase is supercritical fluid chromatography.105 A gas above but close to its critical pressure and temperature serves as the solvent. The technique has advantages of high resolution, low temperatures, and ease of recovery of products. Carbon dioxide, N20, and xenon are suitable solvents. 

The increasing use of mass spectroscopy and gas-liquid chromatography in the identification of organic molecules has stimulated the synthesis of new, highly volatile derivatives. Their use permits lower operational temperatures, and results in decreased breakdown of the substituted molecules. An almost quantitative yield (80%) of the (trimethylsilyl) ether was obtained by the dropwise addition of chlorotrimethylsilane to a pyridine solution of D-fructose. ... 

Silyl ethers are formed with carbohydrate hydroxyl groups by reaction with chlorotrimethylsilane in pyridine with hexamethyldizilazane. Trimethylsilyl ethers are stable in neutral and basic condition but are hydrolyzed in aqueous acidic conditions [18]. The major uses of the silyl ethers is the formation of highly volatile carbohydrate derivatives that can be used in gas chromatography and gas chromatography/mass spectrometric analysis [19,20]. 

Even isolated mono- and disaccharides are capable of extensive hydrogen bonding, which results in extremely low vapor pressures. Attempts at vaporization of these materials results in decomposition. Volatile derivatives must be prepared and the approaches are similar to those described for amino acids. The most common derivatives are methyl or trimethylsilyl ethers and acetyl or trifluoroacetyl esters. A highly detailed review of applications of GLC to carbohydrates including over 1000 references concerning derivatization and types of columns used has been written by Dutton (69,70). 

GC and thin layer chromatography (TLC) are used less frequently than HPLC for the analysis of flavonols.79-90 104 To accomplish analysis by GC, flavonols must first be hydrolyzed and converted into trimethylsilyl (TMS) derivatives to increase their volatility and thermal stability. Although this method provides high resolution and low detection limits, it should be noted that TMS derivatives can form with more than one hydroxyl group as they possess different reactivities. This often results in the production of several derivatives, which can complicate quantification. Thus, the... 

For gas chromatography volatile derivatives such as the methyl ester of ABA (27, 29, 30) or trimethylsilylated ABA (20, 28) must be prepared. ABA is a molecule with a high electron affinity so that the methyl ester can be measured with a gas chromatograph equipped with an electron capture detector. Injections of as little as 5 pg of Me-ABA cause a detector response (27). Metabolites of ABA such as phaseic and dihydro-phaseic acid can also be measured by this method (33). 

In the Croteau and Fogerson study, the triperpenic alcohols and sterols were derivatized into their trimethylsilyl ether derivatives using bis-trimethylsilylacetamide. The isopropanol-chloroform extract contained higher amounts of sterols and triteipenic alcohols such as p-sitosterol and amyrin compared to the SF extract. This could be due to the high polarity of the extracting liquid solvent as opposed to the supercritical fluid, and the increased volatility of the silylated sterols and triteipenic compounds relative to our fatty acid methyl esters, in addition to these compounds, the isopropanol-chloroform extract reported earlier also contained ursolic acid, a polar triteipenic acid, which was not extracted with pure CO2. 

Trialkylsilyl halides show a great propensity to react with the oxygen rather than the carbon of enolate anions. Stork showed that 0-alkylation allows enolates to be trapped as the trialkylsilyl enol ether, which is most useful for kinetic enolates in which a lithium enolate (such as the kinetic enolate derived from 2-methyl-cyclohexanone and LDA) is reacted with trimethylsilyl chloride to give an isolable intermediate, 112. jjig enolate is trapped with high efficiency, and conversion to the enolate is readily accomplished by treatment with methyllithium, which generates the kinetic enolate (113) and the volatile trimethylsilane (Me3SiH). This... 

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