Roland Szalay

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.

Total synthesis of isotopically enriched Si-29 silica NPs as potential spikes for isotope dilution quantification of natural silica NPs.

A new method was developed for the preparation of highly monodisperse isotopically enriched Si-29 silica nanoparticles ((29)Si-silica NPs) with the purpose of using them as spikes for isotope dilution mass spectrometry (IDMS) quantification of silica NPs with natural isotopic distribution. Si-29 tetraethyl orthosilicate ((29)Si-TEOS), the silica precursor was prepared in two steps starting from elementary silicon-29 pellets. In the first step Si-29 silicon tetrachloride ((29)SiCl4) was prepared by heating elementary silicon-29 in chlorine gas stream. By using a multistep cooling system and the dilution of the volatile and moisture-sensitive (29)SiCl4 in carbon tetrachloride as inert medium we managed to reduce product loss caused by evaporation. (29)Si-TEOS was obtained by treating (29)SiCl4 with absolute ethanol. Structural characterisation of (29)Si-TEOS was performed by using (1)H and (13)C nuclear magnetic resonance (NMR) spectroscopy and Fourier-transform infrared (FTIR) spectroscopy. For the NP preparation, a basic amino acid catalysis route was used and the resulting NPs were analysed using transmission electron microscopy (TEM), small angle X-ray scattering (SAXS), dynamic light scattering (DLS) and zeta potential measurements. Finally, the feasibility of using enriched NPs for on-line field-flow fractionation coupled with multi-angle light scattering and inductively coupled plasma mass spectrometry (FFF/MALS/ICP-MS) has been demonstrated.

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.

The effect of carboxylic acids on the oxidation of coated iron oxide nanoparticles

Abstract57Fe Mössbauer spectroscopy, XRD, and TEM were used to investigate the effect of mandelic- and salicylic acid coatings on the iron oxide nanoparticles. These two carboxylic acids have similar molecules size and stoichiometry, but different structure and acidity. Significant differences were observed between the Mössbauer spectra of samples coated with mandelic acid and salicylic acid. These results indicate that the occurrence of iron microenvironments in the mandelic- and salicylic acid-coated iron oxide nanoparticles is different. The results can be interpreted in terms of the influence of the acidity of carboxylic acids on the formation, core/shell structure, and oxidation of coated iron oxide nanocomposites.