Petasis reaction of activated quinoline and isoquinoline with various boronic acids

Petasis reactions of activated forms of quinolines and isoquinolines with electron sufficient boronic acids such as 2-benzofuranboronic acid, trans-2-phenylvinylboronic acid etc in DCM proceeded smoothly at room temperature to provide the corresponding dihydroquinolines and dihydroisoquinolines in good to high yields.     

New investigation of Vilsmeier-type reaction using pyrazolones with various amides

New investigation of Vilsmeier-type reaction was evaluated to realize the solvent effect by using pyrazolones to react with various of amides, including formamide, N-methylformamide, N-propylformamide, N-tert-butylformamide, N,N-dimethylformamide (DMF), N,N-diethylformamide (DEF), N,N-dipropylformamide (DPF), N,N-diisopropylformamide, N,N-dibutylformamide, piperidine-1-carbaldehyde, and pyrrolidine-1-carbaldehyde, in the presence of phosphorous oxychloride POCl₃. The unexpected resulting products were observed in this work according to the difference chemoseletivities of substituted amides. The plausible reactive pathways were proposed to explain the experimental result.     

Quantum chemical investigation on the reaction mechanism of tertiary phosphines with unsaturated carboxylic acids: An insight into kinetic data

The structures of intermediates and transition states in the reaction of tertiary phosphines with unsaturated carboxylic acids have been calculated at the B3LYP level of theory using the 6‐31+G(d,p) basis set. Analysis of the results shows that [1,3]‐intramolecular migration of carboxylic proton to carbanionic center of generated zwitterionic intermediate is strongly kinetically unfavorable, and external proton‐donor source is essential to complete quaternization. A molecular cluster of the intermediate with one molecule of water has been modeled for intermolecular reaction pathway, but even in this case, the proton transfer remains to be the rate‐determining step that is in a good agreement with previous kinetic investigations on this reaction. The data obtained for this reaction have much in common with recent studies on the mechanisms of the Morita–Baylis–Hillman reaction and phosphine‐catalyzed [3+2] cycloaddition, which revealed paramount importance of proton‐transfer steps. © 2013 Wiley Periodicals, Inc.     

Application of radiochemical technique in the investigation of chemical reaction at low temperature

Radiochemical technique was used to investigate cryogenic chemical reaction. By introducing reactants of H and T into liquid ³H through ³He(n,p)T reaction, behaviors of H+T→HT and T+T→T₂ were investigated under pressurized condition. Within saturated vapor pressure upto 0.61 Mpa, the isotope ratio of HT/T₂ changed. It was suggested that the change of HT/T₂ was attributed to bubble formation and chemical potential in liquid helium.     

Quantum chemical investigation of the mechanism of the reaction of pyridines with trichloromethylarenes

Models of the major end products and intermediate products, pre viously detected in a study of the mechanism of the interaction of trichloromethylarenes with pyridines, were calculated by a semiem pirical quantum chemical MNDO method. Models of some putative unstable intermediates of the key redox step of the process under consideration — the aromatization of 4-chloro- or 4-pyridino-substituted 1-(,-dichloroarylmethyl)-1,4-dihydropyridines with transfer of hydrogen from the 4-position of the dihydropyridine ring to the benzyl dichloromethylene group and the formation of N-(-chloroarylmethyl)-4-cliloropyridiniuni chlorides of N-(-chloroarylmethyl)-4-pyridinopyridinium dichlorides, were also calculated.N. D. Zelinksii Institute of Organic Chemistry, Russian Academy of Sciences, Moscow 117913. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1551–1558, November, 1995. Original article submitted November 13, 1995     

Automated determination of carboxylic acids in biological and geochemical samples by means of a chemical reaction detector

Rapid evaluation of carboxylic acids by means of an automated spectrophotometric determination in a continuous-flow system is described. The system was applied to food and soil extracts either as a stand-alone device or as a chemical reaction detector coupled to a chromatographic separation column. Calibration in the automated system was performed with citric acid as a reference standard in the concentration range 4.76 × 10^?5?4.76 × 10^?3 mol l^?1. The molar calibration equation was A=64x ? 6.7 × 10^?5 (x=concentration ) with a correlation coefficient of 0.9997 ( six points). The sample volume was 0.5 ml. In addition to the semi-quantitative evaluation of carboxylic groups, it is shown that the system is also applicable to species analyses.     

Artificial neural network model for the evaluation of chemical kinetics in thermally induced solid-state reaction

The artificial intelligence technique is utilized to improve evaluation of thermally induced solid-state reaction kinetics. A general regression neural network (GRNN) model was applied to directly determine the kinetic triplets, i.e., activation energy, pre-exponential factor, and mechanism model. The effect of number of heating rate on prediction performance of the GRNN model was assessed based on the estimation indictors. The obtained kinetic triplets based on the triple heating rates were considered to be accepted. The prediction ability of the GRNN model was very robust at more than three heating rates. The relative errors for kinetic parameters derived from five heating rates were within ±?4%, and the cognition rates for mechanism models were up to 99.6%. The developed GRNN model was successfully applied in the high-temperature synthesis of Li₄Ti₅O₁₂/C composites. It is expected that the model also could be extended to estimate the kinetics of other solid-state reactions.

     

Determination of fumaric and maleic acids with stacking analytes by transient moving chemical reaction boundary method in capillary electrophoresis

The paper presents an on-line transient moving chemical reaction boundary (MCRB) method for simply but efficiently stacking analytes in capillary electrophoresis (CE). The CE technique was developed for a rapid determination of fumaric and maleic acid. Based on the theory of MCRB, Effects of several important factors such as the pH and concentration of running buffer and the conditions of stacking analytes were investigated to acquire the optimum conditions. The optimized separations were carried out in a 20 mmol/L sulphate neutralized with ethylenediamine to pH 6.0 electrolytes using a capillary coated with poly (diallyldimethylammonium chloride) and direct UV detection at 214 nm. The optimized preconcentrations were carried out in 50 mmol/L borax (pH 9.0). The calibration curves were linear in the concentration range of 1.0 × 10⁻⁷–1.0 × 10⁻⁴ mol/L and 5.0 × 10⁻⁷–1.0 × 10⁻⁴ mol/L for fumaric and maleic acid with correlation coefficients higher than 0.9991. The detection limits were 5.34 × 10⁻⁸ mol/L for fumaric acid and 1.92 × 10⁻⁷ mol/L for maleic acid. This method was applied for determination of fumaric acid in apple juice and of fumaric and maleic acid in dl-malic, the recovery tests established for real samples were within the range 95–105%. This work provided a valid and simple approach to detect fumaric and maleic acid.     

Mechanism of the chemical conversions of amino acids with various chain lengths on a dehydrated silica surface

The joint use of methods of IR spectroscopy and mass spectrometry with bombardment by fast atoms to identify products of chemisorption of --amino acids on a dehydrated silica surface is described. It was established that amino acids undergo multistage chemical conversions in this case, with the formation of various products of intra- and intermolecular condensation — lactams, linear and cyclic peptides. The composition of the condensation products depends on the chain length of the amino acids.Translated from Teoreticheskaya i Éksperimental/naya Khimiya, Vol. 26, No. 5, pp. 628–633, September–October, 1990.     

The chemical bonding in phosphonic acids

The P—O stretching force constants of the phosphonic acids of the type CH_xCl_3-xPO₃H₂, in which x varies from 0 to 3, and their anions are interpreted in terms of (d_π—p_π)—bonding. The behaviour of the P—C stretching force constants in these compounds is also discussed.     

Synthesis of proline derivatives of bile acids and their evaluation as organocatalysts in the asymmetric direct aldol reaction

A new family of bile acid derived organocatalysts was obtained by linking l- or d-proline to amino derivatives of cholic and deoxycholic acids, which were used to promote the asymmetric direct aldol reaction between acetone and 4-nitrobenzaldehyde. Both the activity and enantioselectivity of the organocatalytic systems were dependent not only on the position of the proline moiety on the cholestanic backbone and its absolute configuration, but also on the presence of free hydroxyl group on the steroidal skeleton. The cholic acid derivative bearing a d-prolinamide moiety at the 12-position and free hydroxyl groups at the 3- and 7-positions emerged as the best organocatalytic system giving complete conversion of the substrate, even when using only 2% of catalyst loading and ee up to 80%.     

A chemical investigation of pasternoside

Summary 1. The new flavonoid glycoside pasternoside has the structure of isorhamnetin 3--D-glucopyranoside 4--L-rhamnopyranoside.2. The enzymatic hydrolysis of pasternoside has given the monoglycoside deglucopasternoside, which has been shown to be isorhamnetin 4--L-rhamnopyranoside.Khimiya Prirodnykh Soedinenii, Vol. 2, No. 1, pp. 20–26, 1966     

Intermediate carbene formation in the reaction of thioamides with phosphorus (III) derivatives: Quantum chemical investigation

The reactions of perfluoroalkyl thioamides with trimethyl phosphine, trimethyl phosphite, and tris(dimethylamino)phosphine have been analyzed by means of quantum chemical (DFT and MP2) calculations. The reaction seems to proceed via the nucleophilic attack of the electrophilic carbon atom by the phosphorus lone pair with the formation of cyclic or acyclic adducts. The latter releases the thiophosphate molecule forming perfluoroalkylaminocarbene as the short‐lived intermediate. The reaction of the carbene with the second molecule of trialkyl phosphite yields phosphorus ylide. The ylide undergoes a migration of fluorine from carbon to phosphorus. The reactions of perfluoroalkyl thioamides with phosphines and tris(dimethylamino)phosphine probably proceeds differently. Using alkyl thioamides or amides instead of perfluoroalkyl thioamides also makes the reaction less favorable. The only combination of perfluoroalkyl thioamides with trialkyl phosphite fulfills both the kinetic requirements (moderate activation energies and relative energies for intermediates) and the thermodynamic aspects (higher stabilities of the reaction products compared with the starting materials). © 2013 Wiley Periodicals, Inc.     

Symmetry numbers and chemical reaction rates

This article shows how to evaluate rotational symmetry numbers for different molecular configurations and how to apply them to transition state theory. In general, the symmetry number is given by the ratio of the reactant and transition state rotational symmetry numbers. However, special care is advised in the evaluation of symmetry numbers in the following situations: (i) if the reaction is symmetric, (ii) if reactants and/or transition states are chiral, (iii) if the reaction has multiple conformers for reactants and/or transition states and, (iv) if there is an internal rotation of part of the molecular system. All these four situations are treated systematically and analyzed in detail in the present article. We also include a large number of examples to clarify some complicated situations, and in the last section we discuss an example involving an achiral diasteroisomer.