Theoretical investigations on the synthesis mechanism of cyanuric acid from NH3 and CO2.

In the synthesis of cyanuric acid from NH3 and CO2, urea and isocyanic acid OCNH are two pivotal intermediates. Based on density functional theory (DFT) calculations, the synthesis mechanism of cyanuric acid from NH3 + CO2 was investigated systematically. Urea can be synthesized from NH3 and CO2, and cyanuric acid can be obtained from urea or NH3 + CO2. In the stepwise mechanism of cyanuric acid from urea or NH3 + CO2, the energy barriers are relatively high, and the condition of high pressure and temperature does not decrease the energy barriers. Our theoretical model shows that cyanuric acid is actually acquired from OCNH via a one-step cycloaddition reaction.

4-Nitro-benzoic acid-2,2'-biimidazole (2/1).

In the title adduct, C(7)H(5)NO(4)·0.5C(6)H(6)N(4), the complete biimidazole molecule is generated by a crystallographic inversion centre. In the crystal, N-H⋯O and O-H⋯N hydrogen bonds connects the 4-nitro-benzoic acid and 2,2'-biimidazole units, affording multi-dimensional frameworks with graph-set descriptor R(2) (2)(9).

Diethyl 4-(4-cyano-phen-yl)-2,6-dimethyl-1,4-dihydro-pyridine-3,5-dicarboxyl-ate.

In the title compound, C(20)H(22)N(2)O(4), the dihedral angle between the roughly planar dihydro-pyridine ring (r.m.s. deviation = 0.092 Å) and the benzene ring is 87.09 (6)°. One of the eth-oxy side chains is disordered over two orientations in a 0.669 (14):0.331 (14) ratio. In the crystal, mol-ecules are linked by N-H⋯N hydrogen bonds, generating chains.

Thixotropic properties of aqueous suspensions containing cationic starch and aluminum magnesium hydrotalcite-like compound.

The rheological properties of aqueous suspensions consisting of cationic starch (CS) and positively charged aluminum magnesium hydrotalcite-like compound (HTlc) were investigated. Special emphasis was placed on the thixotropic phenomena. With the increase of mass ratio (R) of HTlc to CS, the equilibrium viscosity (eta(eq)) and the consistency coefficient (m) values of the suspensions increase in the range of neutral and alkaline pH (higher than 6.5) while decrease in the range of acid pH (lower than 6.5). With the increase of pH value, the eta(eq) and m values of the suspensions in the R range of 0-0.08 studied increase initially and then decrease, appearing a maximum value at about pH 7.41+/-0.25. The CS/HTlc suspensions display viscid character and the yield point of the suspensions was not observed except the suspension with R=0.08 in the pH range of 7.66-9.70, which showed a yield point and viscoelasticity. The CS/HTlc suspensions may display different thixotropic types: negative, complex or positive thixotropy, depending on pH and R value. The thixotropic type of the CS/HTlc suspension may be transformed from negative (pure CS solution), through complex (R=0.02), into positive thixotropy (R=0.05 and 0.08) with the increase of R in the studied R range of 0-0.08, and the thixotropic strength of the suspensions increases initially and then decreases with pH value in the pH range studied. The mechanism of the thixotropic phenomenon is discussed.