Vol 483, No 2 (2018)

The acylative kinetic resolution of racemic 2-methyl-1,2,3,4-tetrahydroquinoline and 3,4-dihydro-3-methyl-2H-[1,4]benzoxazines with acyl chlorides of N-naphthaloyl-(S)-alanine and N-naphthaloyl-(S)-phenylalanine has been studied. It has been shown that diastereoselective acylation of racemic amines with N-naphthaloyl (S)-amino acyl chlorides results in the predominant formation of (R,S)-amides, whereas acylation of the same amines with N-phthaloyl (S)-amino acyl chlorides proceeds with the opposite diastereoselectivity. The parallel kinetic resolution of racemic 3,4-dihydro-3-methyl-2H-[1,4]benzoxazine using a mixture of acylating agents derived from a single precursor, (S)-phenylalanine, was carried out.

The effect of carbon nanotubes (CNTs) on the catalysis of combustion of high energy propellants was studied. Carbon nanotubes increased the burning rate of a propellant in the presence of a catalyst to a much higher extent than carbon black. The structure and composition of quenched propellant samples were studied by scanning electron microscopy and electron probe X-ray microanalysis. In the presence of CNTs, a higher carbon frame was formed virtually over the whole combustion surface and the accumulation of the catalyst particles on it was much more pronounced than in the case of carbon black. The obtained results unambiguously indicate that CNTs are more efficient in the catalyzed propellant combustion.

The kinetics of sintering of nanosized (20 nm) and microsized (0.7–0.9 μm) hydroxyapatite (HA) powders with continuously increasing temperature at a constant rate was studied by dilatometry. The sintering of the HA micropowders within the temperature range 1100–1300°C occurred by the mechanism of diffusion-viscous flow of crystalline particles. The kinetics of the process was described by a power-law function of time; i.e., the process rate depended on current shrinkage. The shrinkage of the nanopowders within the sintering temperature range was directly proportional to temperature, occurred by the law of viscous flow of amorphous particles, and was independent of the temperature increase rate. The apparent sintering activation energies of the studied micro- and nanopowders were 180 and 60 kJ/mol, respectively.

Copper nanoparticles were produced by a chemical metallurgical method and by the thermal decomposition of copper citrate and formate. It was shown that the copper nanopowder obtained from copper citrate is not pyrophoric. Combustion of this copper nanopowder can be initiated by an external source, and the combustion wave velocity is 1.3 ± 0.3 mm/s. The specific surface area (45 ± 5 m²/g) of the copper nanopowder obtained from copper citrate is almost four times as large as that of the nanopowder produced by a chemical metallurgical method. The former nanopowder contains almost no oxides and is stable in atmospheric air, whereas the latter nanopowder is pyrophoric and, therefore, requires passivation, but its passivation gives rise to noticeable amounts of copper oxides. The combustion velocities of the passivated and unpassivated copper nanopowders are almost equal and are 0.3 ± 0.04 mm/s. The dynamics of the temperature fields in ignition and combustion of the copper nanopowders obtained by different methods was studied.