D. Knausz

Trimethylsilylated N- alkyl-substituted carbamates I.preparation and some reactions

Abstract Trimethylsilyl N-monoalkyl- and N, N-dialkyl-carbamates have been made in 85–95% yields by silylation of the corresponding ammonium carbamates with trimethylchlorosilane. Trimethylsilyl N N-dimethylcarbamate can be used for silylation of alcohols,phenols, and carboxylic acids. The silycarbamates react with carboxylic acid halides to give the corresponding acide amides. The reaction of trimethylsilyl carbamates with carboxylic anhydrides give the corresponding silyl carboxylate and acid amide, while the reaction with dicarboxylic anhydrides give the trimethylsilyl monoamide of the corresponding dicarboxylic acid, i.e. Me3SiO2-C CONR1R2.

Simultaneous gas-liquid chromatographic determination of sugars and organic acids as trimethylsilyl derivatives in vegetables and strawberries

Abstract The simultaneous determination of organic acids (succinic, malic, pimelic, tartaric, shikimic, citric, quinic, cafeeic and chlorogenic acids), sorbitol and sugars (arabinose, rhamnose, fructose, galactose, glucose, sucrose, maltose and raffinose) as trimethylsilyl (TMS)-oxime and TMS derivatives in a single solution has been developed. The optimum conditions for the simultaneous derivatization and the rapid quantitative evaluation of the nineteen compounds by capillary gas—liquid chromatography are reported in this paper. Reproducibility data reveal that ⪖0.02 μg of acids in the presence of ⪕12 μg of sugars can be determined with a relative standard error (R.S.E.) of ⪕11.2%, whereas the m ain constituents are determined with an R.S.E. of ⪕3.6%.

N-Substituted trimethylsilylcarbamates as silylating and/or methoxime derivatizing reagents for gas chromatographic analysis

N-Substituted trimethylsilylcarbamates were tested as derivatizing reagents for gas chromatographic analysis. N,N-Dimethyltrimethylsilylcarbamate was found to be a suitable agent for direct trimethylsilylation of the salts of alkaloids without previous liberation of the bases. N-Methoxy-N,O-bistrimethylsilylcarbamate was found to react simultaneously and quantitatively with the hydroxy and keto groups of steroids, resulting in the corresponding methoxime trimethylsilyl derivatives.

Trimethylsilylated N-alkyl-substituted carbamates: III. Structure of trimethylsilyl-N,N-diisopropyl carbamate in solid phase and in solution☆

Abstract The conformers of trimethylsilyl- N , N -diisopropyl carbamate were studied by 1 H NMR spectroscopy. The barriers to rotation by isopropyl groups and to the rotation around the amide bond, and the population of the conformers were determined from the coalescence temperature of the methyne signal. Single crystal X-ray diffraction studies revealed that the crystal had formed from preferred conformer in solution. The mirror symmetric conformer is stabilized by an intramolecular CH ⋯ O hydrogen bond and by an intramolecular O ⋯ Si donor-acceptor interaction.

Preparation, crystal structure and thermal decomposition study of some trimethylsilyl esters of dicarbamic acids

Some new trimethylsilylated dicarbamic acid esters 1–9 and 10 were prepared. Their thermal decomposition was studied in n-alkanes as media. The reactions were monitored by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS), respectively. Some N-silylated cyclic ureas 11–15 were also prepared from the corresponding esters 2–6 by thermolysis. The crystal structures of 2, 5 and 8 are also discussed. The crystal and molecular structures of 2 and 5 have very similar characteristics. Both molecules are sited via their molecular centre of symmetry on crystallographic inversion centres. The Carbamate groups are planar in all three cases as expected. An analysis of the data showed that the force due to SiO conjugation which constrains the Si atom into the plane of the carbamate group is comparable to the crystal packing forces with a small out-of-plane movement being not unfavourable.

New N-hydroxy carbamic acid trialkylsilyl derivatives: preparation and thermal reactions

Abstract New N-siloxy- or N-alkoxy-carbamic acid derivatives have been prepared. The crystal structure of N-siloxy-O-tert-butyl carbamate was determined. The thermal behaviour of these compounds was studied in the absence and in the presence of other reaction partners. The reaction products were identified by gas chromatography, gas chromatography-mass spectroscopy, IR spectroscopy and NMR. The experimental results can be explained by the formation of a radical-type transition state (carboxynitrene), detected by mass spectroscopy.

Synthesis and reactions of silylcarbamates with bulky substituents

Abstract New silylcarbamates containing bulky substituents were synthesized in order to study their reactivity with nucleophilic agents as lactones and chloroformates. We suggest a mechanism for these reactions.

Two N-Aryl-Substituted Silyl Carbamates

Trimethylsilyl N-(4-bromophenyl)carbamate, C10H14BrNO2Si, and trimethylsilyl N-tert-butyl-N-phenylcarbamate, C14H23NO2Si, are both important silylating agents. The structures of both molecules are dominated by a plane containing a remarkably large number of atoms. The planes are organized by delocalization around the carbamate moiety. A quasi-pentacoordination of the Si atom in both compounds is also described.

Preparation and solvolysis kinetics of trimethylsilyl N-alkyl-N-phenyl-carbamates

Abstract Some trimethylsilyl esters of N- phenyl -N- alkyl- (methyl-, ethyl -, n propyl -, i propyl -, n butyl -, t butyl -) carbamic acids were prepared by a novel method. Their solvolysis with isopropanol was studied. UV spectrophotometry was used to monitor the reaction and the pseudo first order rate constants were determined.A reaction mechanism is suggested on the basis of the dependence of rates on the ionic strength, on the temperature, on the isotope effect and on the concentration of various additives (sodium isopropoxide, sodium hydroxide, triethylamine and its hydrochloride, respectively).

Solvolysis kinetics of trimethylsilyl esters of aromatic N-carboxylic acids

Abstract Some new trimethylsilyl esters of cyclic and/or aromatic N -carboxylic acids were prepared. Their solvolysis reactions with isopropanol were studied by gas chromatography and by UV spectrophotometry respectively. The pseudo-first-order rate constants, the salt effects and the activation parameters were determined.