Polymerization Mechanism of Nitrogen-Containing Heteroaromatic Compound Under High-Pressure and High-Temperature Conditions.

Hydrogenated carbon nitride is synthesized by polymerization of 1,5-naphthyridine, a nitrogen-containing heteroaromatic compound, under high-pressure and high-temperature conditions. The polymerization progressed significantly at temperatures above 573 K at 0.5 GPa and above 623 K at 1.5 GPa. The reaction temperature was relatively lower than that observed for pure naphthalene, suggesting that the reaction temperature is considerably lowered when nitrogen atoms exist in the aromatic ring structure. The polymerization reaction largely progresses without significant change in the N/C ratio. Three types of dimerization are identified; naphthylation, exact dimerization, and dimerization with hydrogenation as determined from the gas chromatograph-mass spectrometry analysis of soluble products. Infrared spectra suggest that hydrogenation products were likely to be formed with sp3 carbon and NH bonding. Solid-state 13C nuclear magnetic resonance reveals that the sp3/sp2 ratio is 0.14 in both the insoluble solids synthesized at 0.5 and 1.5 GPa. Not only the dimers but also soluble heavier oligomers and insoluble polymers formed through more extensive polymerization. The major reaction mechanism of 1,5-Nap was common to both the 0.5 and 1.5 GPa experiments, although the required reaction temperature increased with increasing pressure and aromatic rings preferentially remained at the higher pressure.

Decomposition and oligomerization of 2,3-naphthyridine under high-pressure and high-temperature conditions.

The chemical reaction of 2,3-naphthyridine, a nitrogen-containing aromatic compound, was investigated at pressures ranging from 0.5 to 1.5 GPa and temperatures from 473 to 573 K. A distinct decrease in the amount of residual 2,3-naphthyridine was observed in the samples recovered after reaction at ˃523 K at 0.5 and 1.0 GPa, and ˃548 K at 1.5 GPa. The formation of o-xylene and o-tolunitrile accompanied a decreasing N/C ratio of the reaction products, indicating decomposition of the aromatic ring and release of nitrogen. Precise analysis of the reaction products indicated the oligomerization of decomposed products with the residual 2,3-naphthyridine to form larger molecules up to 7mers. Nitrogen in the aromatic ring accelerated reactions to decompose the molecule and to oligomerize at lower temperatures than those typically reported for aromatic hydrocarbon oligomerization. The major reaction mechanism was similar between 0.5 and 1.5 GPa, although larger products preferentially formed in the samples at higher pressure.

Chiral gas chromatography of 2,5-diketopiperazines following a ring-opening derivatization method for complete isomeric separation.

2,5-Diketopiperazines (DKPs) are widely recognized as chiral molecules with great potential in medicinal chemistry. Complete separation of DKP stereoisomers is very important for efficiently investigating the chemical characteristics of DKPs. The combination of esterification and acylation caused the enantiomers of cyclo(d-Ala-d-Ala) and cyclo(l-Ala-l-Ala) to ring-open and generate their dipeptide derivatives. These derivatives were completely separated by chiral gas chromatography (GC), and the determined isomer ratios were the same as the original isomer ratios. The derivatization also caused the ring-opening of cyclo(l-Asp-l-Phe) and cyclo(l-Met-l-Pro), and their derivatives were determined by the chiral GC method. The present study is the first report of the complete separation of cis-DKPs using chiral GC. This separation procedure can substantially contribute to the development of the chemistry of chiral DKPs.

Hydrogen and Hydrocarbon Gases, Polycyclic Aromatic Hydrocarbons, and Amorphous Carbon Produced by Multiple Shock Compression of Liquid Benzene up to 27.4 GPa.

Phase diagrams of benzene have been reported on the basis of data mainly obtained from static compression at various pressure-temperature, P-T, conditions. However, there are few data in the high-pressure and high temperature-region of the phase diagram. To understand the physical and chemical behavior of benzene in that region, multiple shock compression of benzene was evaluated by a recovery experimental system that directly analyzed the shocked samples. The shocked samples were composed of the remaining benzene, gases (H2, CH4, C2H4, C2H6, C3H6, and C3H8), polycyclic aromatic hydrocarbons with molecular weights from 128 (naphthalene) to 300 (coronene), and amorphous carbon. The abundances of these chemical species varied according to the P-T conditions induced by shock compression. Samples in the lower-pressure and lower-temperature region of the a-C:H phase in the phase diagram contained a significant amount of benzene as well as amorphous carbon. In the higher-pressure and higher-temperature region of the a-C:H phase, benzene was mostly converted into amorphous carbon (H/C = 0.2), H2, and CH4. Therefore, the amorphous carbon in the present study was produced by a different pathway than that in previous studies that have detected hydrogenated amorphous carbon (H/C = 1). For earth sciences, the present study can provide basic information on the delivery to the early earth of extraterrestrial organic materials related to the origin of life.

Pressure-induced oligomerization of alanine at 25 °C.

Pressure-induced oligomerization was found from high-pressure experiments at 25 °C on alanine powder soaked in its saturated aqueous solution. The oligomerization to alanylalanine occurred at 5 GPa. The maximum yields of alanylalanine and trialanine were, respectively, 1.1 × 10(-3) and 1.3 × 10(-4) at 11 GPa.