Trimethylsilylating agents

Acids likewise inhibit the formation of trimethylsilyl derivatives, and thus the acid in hydrolyzates must be carefully neutralized. In cases where deproteinization is necessary, acidic conditions should be avoided.137,138 High concentrations of urea, as in urine samples, also interfere with the trimethylsilylation reaction, and should be eliminated by treatment with urease,138 although some authors have reported successful results without use of this step,118 Various reagents other than hexamethyldisilazane and chlorotri-methylsilane have been recommended for trimethylsilylation. These differ in their effectiveness as trimethylsilylating agents, their stability to water, or both. 

Despite the fact that the differencies in the rates of reaction of sterically hindered and unhindered hydroxyl groups towards various trimethylsilylating agents are well established [396-398], the numer of preparative partial trimethylsilylation results is very low in carbohydrates. The ethers are too susceptible to solvolysis in protic media and, consequently, partial silylation is not easily controlled, the results can vary from run to run [399]. 

Still another calixarene derivative of interest and utility is the trimethylsilyl ether. The hexa-trimethylsilyl ealix[6]arenes and octa-trimethylsilyl calix[8]arenes can be prepared 23) by using standard trimethylsilylating agents such as hexamethyldisilazene and chlorotrimethylsilane. The tetra-trimethylsilyl ethers of the calix[4]arenes, however, do not form under these conditions and require the use of the very reactive N,0-i (trimethylsilyl (acetamide 109). 

Identification of N-acetyl-g-(p-tolyloxy)alanine in the urine of rats treated with 3-(p-tolyloxy)-l,2-propanediol. The Mephenesin analogue, 3-( -tolyloxy)-l,2-propanediol was administered to rats and urinary metabolites were identified by GC-MS. In the alkaline extracts, the unchanged substance was the major component. Fig. 1 (top) shows the gas chromatographic patterns of acidic extracts from the urine of rat treated with 3-( -tolyloxy)-1,2-propanediol. For derivatization, hexamethyldisilazane was used as the trimethylsilylating agent. The column temperature was programmed from 200 C at 3 C/min. The large peak pointed by a small arrow was identified as B-( -tolyloxy)-lactic acid. 

A new trimethylsilylating agent for alcohols, (46), is said to be more efficient than AO-bistrimethylsilyl acetamide. Quaternary ammonium alkoxides are the... 

A large number of silylating agents exist for the introduction of the trimethylsilyl group onto a variety of alcohols. In general, the sterically least hindered alcohols are the most readily silylated, but these are also the most labile to hydrolysis with either acid or base. Trimethylsilylation is used extensively for derivatization of... 

Trimethylsilyl trifluoromethanesulfonate. This is an extremely powerful silylating agent, but probably is more useful for its many other applications in synthetic chemistry... 

A solution of trimethylsilyl lithium (10 mmol) in HMPA (CAUTION— CANCER SUSPECT AGENT) (5 ml) and ether (10 ml, from the MeLi) prepared as above was cooled to 0°C and diluted with THF (20 ml). Copper(i) cyanide (5 mmol) was added in one portion, and the resulting black mixture was stirred at 0°C for 20min. 

To a stirred suspension of NaH or KH (20 mmol) in HMPA (CAUTION— CANCER SUSPECT AGENT) was added hexamethyldisilane (10 mmol) slowly with stirring. A clear yellow-brown solution of trimethylsilyl potassium was obtained immediately mild heating at 30-40 °C is necessary to prepare trimethylsilylsodium. 

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