Synthesis and heteroelectrocyclization of unsymmetrically substituted diazomalonamides

A selective procedure was developed for the synthesis of 1,2,3-triazoles and unsymmetrically substituted diazomalonamides. Cyclization of unsymmetrically substituted diazomalonamides to 1,2,3-triazoles was studied by the method of intramolecular competitive reactions. The kinetic and thermodynamic characteristics of the process were determined. Quantum-chemical calculations for the monorotatory electrocyclic and nonrotatory heteroelectrocyclic mechanisms of cyclization were carried out. N-Aryldiazomalonamides undergo cyclization according to the heteroelectrocyclic mechanism, whereas cyclization of N-alkyldiazomalonamides proceeds by the monorotatory mechanism. The experimental constant of competition between these processes is (1.3—8.3)·10³ (DMSO-d₆) and (45.2—72.4)·10³ (CD₃OD).     

A numerical method for the minimax solution of the Bellman equation in the Cauchy problem with additional restrictions

A new numerical method is suggested for constructing the value function in optimal control problems of prescribed duration with positional running cost along motions of controlled dynamical systems. The algorithm is based on a backward procedure involving characteristics of the Bellman equation. Estimations of the approximation are provided. Results of simulations for a model example are exposed.     

Synthesis and properties of glycidyl methacrylate copolymers with side chromophore groups

A number of styrylquinoline chromophores with carboxyl groups have been prepared through the interaction of 2-methylcinchonic acid with aromatic aldehydes of various chemical structures. The copolymer of glycidyl methacrylate and methyl methacrylate carrying side epoxide groups has been synthesized, and the chemical modification of the copolymer with the above chromophores has been performed. The thermal, spectral, and nonlinear optical properties of the chromophores and modified polymers have been studied.     

Mechanical characteristics of films based on comb-shaped poly(amidoimides) with different contents of side chromophoric groups

For films based on poly(amidoimide) with a comb-shaped structure and long side chains, the specific features of the mechanical and thermomechanical behavior and their dependence on the concentration of the above chains are studied. With variation of the composition of the material, changes in the mechanical characteristics show a nonmonotonic character. Comparison of the results of mechanical tests and densimetric measurements allows certain conclusions to be drawn about the character of variations in the structural organization of films with an increase in the concentration of side fragments in macrochains. The role of plasticization in the behavior of the above materials during heating is demonstrated. The advantages of the practical use of the above phenomena for the optimization of the regimes of thermally stimulated polarization of films are discussed.     

Polyamidoimides with side chromophoric groups

A new method was elaborated for the introduction of chromophores into the side chains of polymers by esterification of polyamidoimides containing side carboxy groups with glycidyl ethers of dyes, 4-(4-nitrophenylazo)phenol and 4-(6-nitrobenzothiazol-2-ylazo)phenol. The optimum modification conditions were found that made it possible to esterify 15, 30, 50, and 90% of the carboxy groups. The synthesized polymers possess valuable physicomechanical properties (E = 2.8–3.3 GPa, σ_u = 69–90 MPa, ε_u = 38–77%) and glass transition temperatures of 115–125 °C, depending on the degree of esterification. After chromophore orientation in the corona discharge, all the polymers demonstrate nonlinear optical properties of the second order. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1438–1444, June, 2005.     

IR Spectroscopic Study of Alkane Interaction with the Brønsted Acid Sites of Hydrogen-Exchanged Zeolites

Diffuse-reflectance IR spectroscopy is used to study the interaction of C₃ and C₆ alkanes (propane, n-hexane, 3-methylpentane, and cyclohexane) with the Brønsted acid sites of hydrogen-exchanged mordenite, ferrierite, ZSM-5, and faujasite. It is found that a shift of the absorption band of the stretching vibrations of acidic Si(OH)Al groups toward lower frequencies (OH) due to the formation of a hydrogen bond with adsorbed alkanes increases in the following series: OH(propane) < OH(n-hexane) = OH(3-methylpentane). The accessibility of Si(OH)Al groups to alkane molecules is determined by the dimension of rings through which molecules enter zeolite channels and cavities. It follows from the measured OH values that the strength of Brønsted acid sites decreases in the following series: HZSM-5 > H-mordenite H-ferrierite HY. The difference between the three high-silica zeolites is not great. The results obtained are compared with the published IR data on Si(OH)Al groups of zeolites with adsorbed alkanes and other weak bases.     

On two alternative mechanisms of ethane activation over ZSM-5 zeolite modified by Zn2+ and Ga1+ cations

The activation of ethane over zinc- and gallium-modified HZSM-5 dehydrogenation catalysts was studied by diffuse reflectance infrared spectroscopy. Hydrocarbon activation on HZSM-5 modified by bivalent Zn and univalent Ga cations proceeds via two distinctly different mechanisms. The stronger molecular adsorption of ethane by the acid-base pairs formed by distantly separated cationic Zn2+ and basic oxygen sites results already at room temperature in strong polarizability of adsorbed ethane and subsequent heterolytic dissociative adsorption at moderate temperatures. In contrast, molecular adsorption of ethane on Ga+ cations is weak. At high temperatures dissociative hydrocarbon adsorption takes place, resulting in the formation of ethyl and hydride fragments coordinating to the cationic gallium species. Whereas in the zinc case a Br?nsted acid proton is formed upon ethane dissociation, decomposition of the ethyl fragment on gallium results in gallium dihydride species and does not lead to Br?nsted acid protons. This difference in alkane activation has direct consequences for hydrocarbon conversions involving dehydrogenation.