Activation of nitriles by trifluoroacetic acid in exchange reactions of functional groups

A strong catalytic effect of trifluoroacetic acid in reactions of nitriles with carboxylic acids and their amides has been found. The formation of stable intermediates in reactions with aliphatic carboxylic acids has been studied. Kinetic data permit to suggest that nitriles in TFA solutions form stable n-complexes.

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. . , n-.

     

Kinetics of OH reactions with aliphatic thiols

The kinetics of OH reactions with 1–4 carbon aliphatic thiols have been investigated over the temperature range 252–430 K. OH radicals were produced by flash photolysis of water vapor at λ > 165 nm and detected by time-resolved resonance fluorescence spectroscopy. All thiols investigated react with OH at nearly the same rate; k(298 K) = 3.2–4.6 × 10^?11 cm³ molecule^?1 s^?1, -E_act = 0.6–1.0 kcal/mol, A = 0.6–1.2 × 10^?11 cm³ molecule^?1 s^?1. CH₃SH and CH₃SD react with OH at identical rates over the entire temperature range investigated. We conclude that the dominant reaction pathway is addition to the sulfur atom.     

Kinetics of proton exchange between semiquinone radicals and hydrochloric acid

The mechanism of proton exchange between semiquinone neutral radicals 3,6-di-tert-butyl-2-hydroxyphenoxyl (1), 6-tert-butyl-3-chloro-2-hydroxy-4-triphenylmethylphenoxyl, and hydrochloric acid in toluene solutions has been studied. The rate of proton exchange with hydrochloric acid is less than that with acetic acid owing to the higher thermodynamic stability of the radical cation formed upon semiquinone radical protonation by hydrochloric acid. The formation of radical cations and their dimers has been proven by spectroscopy.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No 1, pp. 84–87, January, 1993.     

1,3-cycloaddition of substituted benzonitrile oxides to aliphatic nitriles. The kinetic effect of substituents

A previous study of the reaction of aromatic nitrile oxides with simple aliphatic nitriles, with the formation of 3,5-disubstituted 1,2,4-oxadiazoles, has been extended to a larger number of nitrile oxides. Sixteen new oxadiazole derivatives have been prepared and characterized. Cycloaddition rates have been measured in the temperature range from 50 to 80°. When considering the effect of substituents on the aromatic ring, roughly V-shaped Hammett plots have been obtained, as already observed for other concerted 1,3-cycloadditions.     

Synthesis of substituted 2-aminoquinoline-3-carboxylic acid amides

Substituted 3-(2-nitrophenyl)-2-cyanoacrylic acid amides were synthesized by the Knoevenagel reaction and were then reduced with iron in acetic acid to the corresponding 2-aminoquinoline-3-carboxylic acid amides.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1515–1517, November, 1988.     

Polyaniline doped by a new class of dopants,benzoic acid and substituted benzoic acid: synthesis and characterization

This work reports on a new class of dopants, benzoic acid and substituted benzoic acids such as 2‐hydroxybenzoic acid, 2‐chlorobenzoic acid, 4‐nitrobenzoic acid, 2‐methoxybenzoic acid, 3‐methylbenzoic acid, 4‐methylbenzoic acid, 3‐aminobenzoic acid and 4‐aminobenzoic acid, for polyaniline. Benzoic acids can be used to dope polyaniline by mixing benzoic acid (or a substituted benzoic acid) with polyaniline in the common solvent 1‐methyl‐2‐pyrrolidone. Properties of benzoic acid doped polyaniline salts are studied using Fourier transform infra‐red, X‐ray diffraction spectroscopy, scanning electron microscopy, thermogravimetric analysis and conductivity measurements. The conductivity of polyaniline‐benzoic acid salt was found to be high (10⁻² S/cm) when compared to polyaniline‐substituted benzoic acid salts (10⁻³–10⁻⁵ S/cm). Copyright © 2005 John Wiley & Sons, Ltd.     

Kinetics of metal ion exchange between citric acid and serum transferrin

The exchange of Fe(3+), Tb(3+), In(3+), Ga(3+), and Al(3+) between the C-terminal metal-binding site of the serum iron transport protein transferrin and the low-molecular-mass serum chelating agent citrate has been studied at pH 7.4 and 25 degrees C. The removal of Ga(3+), In(3+), and Al(3+) follows simple saturation kinetics with respect to the citrate concentration. In contrast, removal of both Fe(3+) and Tb(3+) shows a combination of saturation and first-order kinetic behavior with respect to the citrate concentration. The saturation component is consistent with a mechanism for metal release in which access to the bound metal is controlled by a rate-limiting conformational change in the protein. The first-order kinetic pathway is very rapid for Tb(3+), and this is attributed to a direct attack of the citrate on the Tb(3+) ion within the closed protein conformation. It is suggested that this pathway is more readily available for Tb(3+) because of the larger coordination number for this cation and the presence of an aquated coordination site in the Tb(3+)-CO(3)-Tf ternary complex. There is relatively little variation in the k(max) values for the saturation pathway for Tb(3+), Ga(3+), Al(3+), and In(3+), but the k(max) value for Fe(3+) is significantly smaller. It is suggested that protein interactions across the interdomain cleft of transferrin largely control the release of the first group of metal ions, while the breaking of stronger metal-protein bonds slows the rate of iron release. The rates of metal binding to apotransferrin are clearly controlled in large part by the hydrolytic tendencies of the free metal ions. For the more amphoteric metal ions Al(3+) and Ga(3+), there is rapid protein binding, and the addition of citrate actually retards this reaction. In contrast, the nonamphoteric In(3+) ion binds very slowly in the absence of citrate, presumably due to the rapid formation of polymeric In-hydroxo complexes upon addition of the unchelated metal ion to the pH 7.4 protein solution. The addition of citrate to the reaction accelerates the binding of In(3+) to apoTf, presumably by forming soluble, mononuclear In-citrate complexes.     

Rearrangement reactions of the molecular ions of some substituted aliphatic oxiranes

The fragmentation reactions of glycidic methyl ester (1) and of its derivatives (2–6) substituted by one, two and three methyl groups, respectively, at the oxirane ring, of the corresponding glycidols (7–12), and of the glycidyl ethers (13–16) in the 70 eV mass spectra have been studied using isotopic labelling and mass-analysed ion kinetic energy spectrometry. It is shown that the typical reaction of these aliphatic oxirane radical cations carrying a nucleophilic methoxy group and hydroxy group, respectively, at the side chain corresponds under high-energy conditions to a rearrangement by a methoxy group or a hydroxy group migration to the β-carbon atom of the oxirane moiety. This rearrangement is very likely mediated by the isomerization of the molecular ions into distonic ions via C? C bond cleavage within the oxirane ring.     

Kinetics of the reactions of hydroxyl radical with aliphatic aldehydes

Rate coefficients for OH reactions with the 2–5 carbon aliphatic aldehydes have been measured under pseudo first-order conditions in OH. OH was generated by flash photolysis of H₂O at wavelengths greater than 165 nm and its concentration monitored using time-resolved resonance fluorescence spectroscopy. Two reactions were studied only at 298 K while five reactions were studied over the temperature range 250–425 K; negative activation energies were observed for all five reactions. Aldehyde reactivity toward OH is nearly independent of the identity of the hydrocarbon side chain. Our results are compared with those obtained in previous studies of OH-aldehyde reaction kinetics and their mechanistic implications are discussed.     

Kinetics of self-decomposition and hydrogen atom transfer reactions of substituted phthalimide N-oxyl radicals in acetic acid

Kinetic data have been obtained for three distinct types of reactions of phthalimide N-oxyl radicals (PINO(.)) and N-hydroxyphthalimide (NHPI) derivatives. The first is the self-decomposition of PINO(.) which was found to follow second-order kinetics. In the self-decomposition of 4-methyl-N-hydroxyphthalimide (4-Me-NHPI), H-atom abstraction competes with self-decomposition in the presence of excess 4-Me-NHPI. The second set of reactions studied is hydrogen atom transfer from NHPI to PINO(.), e.g., PINO(.) + 4-Me-NHPI <=> NHPI + 4-Me-PINO(.). The substantial KIE, k(H)/k(D) = 11 for both forward and reverse reactions, supports the assignment of H-atom transfer rather than stepwise electron-proton transfer. These data were correlated with the Marcus cross relation for hydrogen-atom transfer, and good agreement between the experimental and the calculated rate constants was obtained. The third reaction studied is hydrogen abstraction by PINO(.) from p-xylene and toluene. The reaction becomes regularly slower as the ring substituent on PINO(.) is more electron donating. Analysis by the Hammett equation gave rho = 1.1 and 1.8 for the reactions of PINO(.) with p-xylene and toluene, respectively.     

One-pot high-temperature synthesis of polyimides in molten benzoic acid: Kinetics of reactions modeling stages of polycondensation and cyclization

For aromatic and aliphatic diamines of significantly different basicities, the kinetics of acylation with phthalic anhydride in glacial acetic acid in the range 16–70°C and of imidization of corresponding bis(o-carboxyamides) in acetic acid at 140°C has been studied. The reactions under study model the stages of polycondensation and intramolecular cyclization, respectively, in the high-temperature catalytic synthesis of polyimides in molten benzoic acid. It has been established that the acylation of amino groups in acetic acid proceeds as a reversible reaction and is catalyzed by the acidic medium. The kinetic and thermodynamic parameters of the above-mentioned model reactions have been determined, and the effect of the chemical structure of diamines on these parameters has been assessed. On the basis of the experimental data obtained for the model reactions, it is inferred that, in the synthesis of polyimides in benzoic acid, the overall rate of the process is determined by the rate of the intramolecular cyclization. A low sensitivity of the cyclization reaction to a change in the structure of the starting diamines explains why high-molecular-mass polyimides can be prepared at comparable rates under these conditions from both high-and low-basicity diamines.     

An iron-catalysed synthesis of amides from nitriles and amines

The cheap, commercially available iron complex, Fe(NO₃)₃·9H₂O, has been used to catalyse the formation of amides by the addition of amines to nitriles.     

Cyclization reactions of nitriles

The interaction of 2-thienylidene derivatives of malononitrile and cyanothio-acetamide with methylene active nitriles gives 2,6-diamino-3,5-dicyano-4-(2-thienyl)-4H-thiopyran which is smoothly recrystallized into 6-amino-3,5-dicyano-4-(2-thienyl)-2(1H)-pyridinethione. The latter is easily alkylated at the sulfur atom by -halocarbonyl compounds. This reaction was used in the synthesis of 3,6-diamino-4-(2-thienyl)thieno[2,3-b]pyridines.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1643–1646, July, 1991.     

Kinetics of the reactions of substituted benzoquinones with alkyl radicals

Conclusions Study has been made of the kinetics of the reactions of sec-decyl radicals with 2,6-di-tert-butyl-, and 2,6-diphenyl-p-benzoquinone, and 2,4- and 2,5-di-tert-butyl-o-benzoquinones at 50°C. Rate constants and inhibition coefficients have been determined for these reactions.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2487–2491, November, 1978.