Products and mechanisms of photochemical transformations of <Emphasis Type="Italic">o</Emphasis>-quinones

The photochemical transformations of quinones by the action of light at λ > 500 nm, namely, the photodecarbonylation and photoreduction reactions were studied with the use of a series of o-benzoquinones and 9,10-phenanthrenequinone as examples. The two-stage mechanism of the decarbonylation reaction of o-benzoquinones was established. At the first stage, rearrangement of a photoexcited quinone molecule into a bicyclic compound that spontaneously decomposes in the dark reaction into cyclopentadienone and CO takes place. It has been found that the formation of the photoreduction products of both o-benzoquinones and 9,10-phenanthrenequinone in the presence of various H donors (N,N-dimethylanilines and polymethylbenzenes) follows the same mechanism. In the first step, a phenol ether is produced, which subsequently undergoes quantitative transformation into pyrocatechol or ketol via the heterolytic mechanism. The stability of phenol ethers is determined by the structure and redox properties of the reactants.     

Synthesis of <Emphasis Type="Italic">o</Emphasis>(<Emphasis Type="Italic">m</Emphasis>)-carborane-containing azomethines

A method of preparative synthesis of o(m)-carborane-containing azomethines via the condensation of o(m)-carboranyl-C-methylene-4-formylbenzoates with aliphatic, cycloaliphatic, and aromatic amines was developed.     

Molecular structure of <Emphasis Type="Italic">N</Emphasis>-(<Emphasis Type="Italic">o</Emphasis>-and <Emphasis Type="Italic">p</Emphasis>-hydroxybenzyl)cytisine

The molecular structures of N-(o-and p-hydroxybenzyl)cytisine were investigated by NMR spectroscopy, x-ray structure analysis, and molecular modeling. It was found that NMR resonances of the OH and aromatic protons in N-(o-hydroxybenzyl)cytisine were doubled because of the presence of two conformers in solution. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 165–168, March–April, 2008.     

New tin(<Emphasis Type="SmallCaps">iv</Emphasis>) <Emphasis Type="Italic">o</Emphasis>-iminosemiquinone complexes

New tin(iv) mono- and bis-o-iminosemiquinone complexes were obtained by the exchange reaction of radical anion lithium salt of 4,6-di-tert-butyl-N-(2,6-diisopropylphenyl)-o-imino-benzoquinone with tin(iv) organochlorides. The compounds synthesized were characterized by EPR spectroscopy and X-ray diffraction analysis. Substituents on the tin atom were found to affect stability of paramagnetic metal derivatives formed.     

Chemiluminescence determination of <Emphasis Type="Italic">o</Emphasis>-chlorobenzylidenemalonic acid dinitrile in extracts

A chemiluminescence method was developed for determining o-chlorobenzylidenemalonic acid dinitrile (o-CBMA DN) in extracts. The method is based on chemiluminescence developed in a strong alkaline solution upon the interaction between 3-aminophthalic hydrazide (luminol) with the superoxide radical formed in the reaction of atmospheric oxygen activated by hemin with the products of the alkaline hydrolysis of o-chlorobenzylidenemalonic acid dinitrile and with the products of their condensation with p-nitrobenzaldehyde. The luminescence intensity of luminol was proportional to the concentration of o-CBMA DN in the range 1 × 10⁻⁶−1 × 10⁻¹ mg/mL. The determination limit for o-CBMA DN was (1 ± 0.3) × 10⁻⁶ mg/mL (p = 95%, n = 5, RSD = 29%) at 293 K.     

Reactions of 6,7-dimethoxy- 3,4-dihydroisoquinoline with <Emphasis Type="Italic">o</Emphasis>-quinone methides

Products of heterocyclization, 9,10-dimethoxy-12,13-dihydro-7aH,15H-naphtho[1',2':5,6][1,3]oxazino-[2,3-a]isoquinolines, were isolated on condensing 6,7-dimethoxy-3,4-dihydroisoquinoline with 1-dimethylaminomethyl-2-naphthols. In the case of o-hydroxybenzyl alcohols products of a Michael aza reaction, 2-[(6,7-dimethoxy-3,4-dihydroisoquinolin-2(1H)-yl)methyl]phenols were obtained.     

Investigation of photochemical transformations of tetrathiafulvalene-bridged di-<Emphasis Type="Italic">o</Emphasis>-quinone

It has been found that irradiation of tetrathiafulvalene-bridged di-o-quinone with visible light leads to the successive decarbonylation of the o-benzoquinone fragments. The molecular structure of the final product dicyclopentadienone has been established by X-ray diffraction measurements. The features of the photoconversion kinetics of the substrate di-o-quinone and the intermediate product of its photolysis in benzene solutions by the action of 546-nm monochromatic radiation have been revealed.     

Photolysis of <Emphasis Type="Italic">p</Emphasis>-benzoquinone and <Emphasis Type="Italic">p</Emphasis>-chloranil in aqueous sodium sulfite solution

Photosubstitution of the sulfo group for hydrogen (chlorine in chloranil) is observed under irradiation of sulfonated derivatives of hydroquinone formed upon dissolving of p-benzoquinone and p-chloranil in aqueous solutions of sodium sulfite. The quantum yield of the photochemical reaction is 0.18 ± 0.02 for p-benzoquinone. The rate constant of the thermal reaction of substitution is 5.5 × 10⁻⁴ l mol⁻¹ s⁻¹. The substitution reaction is sensitized by eosin upon irradiation with visible light. During the course of irradiation of sulfohydroquinones, the formation of a product with an absorption maximum at 235 nm was found. The product decays with a rate constant of 0.005 s⁻¹.     

Quantum-chemical study of color reactions of the nitrite ion with <Emphasis Type="Italic">o</Emphasis>-arylenediamines

For the prediction of promising directions of the modification of o-arylenediamines as reagents for the nitrite ion, quantum-chemical studies of the corresponding color reactions were performed. It was found that the introduction of C-substituents into aromatic rings insignificantly affects the analytical characteristics of the reactions. An increase in the number of condensed aromatic rings and N-substitution are of interest in searching for a new analytical reagent. The spectrophotometric characteristics of the reaction products of reagents based on 2,3-and 1,8-naphthylenediamines are close to each other, which, possibly, will allow the replacement of 2,3-naphthylenediamine, whose synthesis is extremely complicated, with substantially more available 1,8-naphthylenediamine or its substituted derivatives. The obtained results allowed for the selection of a group of o-arylenediamines interesting as analytical reagents for the nitrite ion, which should be examined practically.     

Synthesis of new hydrazones based on <Emphasis Type="Italic">o</Emphasis>- and <Emphasis Type="Italic">p</Emphasis>-hydroxybenzohydrazides

o- and p-Hydroxybenzohydrazides reacted with various unsaturated aromatic aldehydes to give the corresponding N′-(hydroxybenzoyl)hydrazones. Inhibitory activity of the obtained hydrazones against cathepsin E was evaluated.     

Electrochemical transformations of catecholate and <Emphasis Type="Italic">o</Emphasis>-amidophenolate complexes with triphenylantimony(V)

The electrochemical properties of catecholate and o-amidophenolate complexes with triphenylantimony(V) with various substituents in the aromatic ring were examined. Introduction of electron-donating groups into the catecholate ligand or replacement of an O atom (in catecholate) by a N atom (o-amidophenolate) stabilizes the monocationic forms of the complexes obtained by one-electron oxidation. Complexes with electron-withdrawing substituents undergo irreversible two-electron oxidation resulting in the elimination of o-quinone. Complexes containing electron-withdrawing ligands do not form o-semiquinones and are inert to atmospheric oxygen. According to electrochemical data, oxygen can be bound reversibly by catecholate complexes containing the electron-donating methoxy groups in the 3,6-di-tert-butylcatecholate ligand and o-amidophenolate derivatives with half-wave oxidation potentials lower than or equal to 0.70 V (vs. Ag/AgCl), which form relatively stable cationic complexes upon the oxidation.     

Study of the mechanism of redox transformations of sterically hindered <Emphasis Type="Italic">N</Emphasis>-aryl-<Emphasis Type="Italic">o</Emphasis>-iminoquinones

The mechanisms of redox transformations of sterically hindered [¹IBQ]-[³IBQ], 9,10-iminophenanthraquinone [⁴IFQ], and o-aminophenol [⁵AP] have been studied by cyclic voltammetry. It has been shown that the reduction process in tetrahydrofuran consists of two consecutive reversible steps leading to the formation of a radical anion and a dianion. In the case of acetonitrile, only the first redox process is detected, which involves the steps of protonation and electron addition resulting in the formation of a monoanion. Quantum-chemical calculations indicate a lower degree of participation of the six-membered nonaromatic carbon ring in the spin density delocalization in the o-iminosemiquinonate radical anions as compared to o-benzosemiquinonate radical anions. The oxidation of iminoquinones results in the formation of an unstable radical cation, which undergoes further chemical transformations. An increase in the acidity of a medium leads to the formation of protonated forms with the reduction potential being shifted anodically. The introduction of screening groups makes it possible to suppress side reactions of hydrolysis and cyclization of oxidized o-aminophenol [⁵AP] forms. Therefore, the major product of complete electrolysis is o-iminobenzoquinone [²IBQ].     

Activation and reaction volumes of the reactions of <Emphasis Type="Italic">o</Emphasis>-and <Emphasis Type="Italic">p</Emphasis>-nitrophenylsulfenyl chlorides with styrene and cyclohexene in some solvents

The effect of hydrostatic pressure below 1000 kg cm⁻² on the rate of reactions of o-and p-nitrophenylsulfenyl chlorides with styrene and cyclohexene was studied. The activation and reaction volumes (cm³ mol⁻¹) for the reactions of o-nitrophenylsulfenyl chloride with styrene in acetonitrile (−23.1 and −23.6), 1,2-dichloroethane (−29.2 and −24.7), chlorobenzene (no, −20.2), and anisole (−25.1 and −21.2) and for the reaction of p-nitrophenylsulfenyl chloride with styrene in carbon tetrachloride (−39.5±1.5 and −22.0) were determined. In carbon tetrachloride the activation volumes for the reactions of cyclohexene with o-and p-nitrophenylsulfenyl chlorides (−37.7±2.0 and −40.9±1.2 cm³ mol⁻¹, respectively) are almost the same and coincide with the data for the reactions with styrene. The considerable decrease in the volume of the transition state in the nonpolar solvent is considered as a consequence of the enhanced electrostriction of carbon tetrachloride in the solvate sphere of the transition state of the reaction, which excludes the nonpolar transition state of the sulfuran type. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 477–480, March, 2007.     

Curing reaction of <Emphasis Type="Italic">o</Emphasis>-cresol-formaldehyde epoxy/LC epoxy(<Emphasis Type="Italic">p</Emphasis>-PEPB)/anhydride(MeTHPA)

The curing kinetics of a bi-component system about o-cresol-formaldehyde epoxy resin (o-CFER) modified by liquid crystalline p-phenylene di[4-(2,3-epoxypropyl) benzoate] (p-PEPB), with 3-methyl-tetrahydrophthalic anhydride (MeTHPA) as a curing agent, were studied by non-isothermal differential scanning calorimetry (DSC) method. The relationship between apparent activation energy E _a and the conversion α was obtained by the isoconversional method of Ozawa. The reaction molecular mechanism was proposed. The results show that the values of E _a in the initial stage are higher than other time, and E _a tend to decrease slightly with the reaction processing. There is a phase separation in the cure process with LC phase formation. These curing reactions can be described by the Šesták–Berggren (S–B) equation, the kinetic equation of cure reaction as follows: \frac\textda\textdt = Aexp( - \fracE_\texta RT )a^m ( 1 - a )ⁿ {\frac{{{\text{d}}\alpha }}{{{\text{d}}t}}} = A\exp \left( { - {\frac{{E_{\text{a}} }}{RT}}} \right)\alpha^{m} \left( {1 - a} \right)^{n} .     

Synthesis and structure of tri(<Emphasis Type="Italic">o</Emphasis>-tolyl) antimony dioximates

Tri(o-tolyl) antimony dioximates were synthesized by the reaction of tri(o-tolyl) antimony with 5-nitrofurfural and thiophen-2-carbaldehyde oximes in ether in the presence of hydrogen peroxide or tert-butylhydroperoxide (1: 2: 1 mol). Antimony atoms in the reaction products have distorted trigonal-bipyramidal coordination with the intramolecular distances Sb···N shorter than the sum of the van der Waals radii of Sb and N by ~1 Å.     

<Emphasis Type="Italic">N</Emphasis>-aryl-<Emphasis Type="Italic">o</Emphasis>-iminobenzoquinones as novel regulators of radical polymerization

The effect of a number of quinoid compounds on methyl methacrylate polymerization initiated by azo-bis(isobutyronitrile) has been studied. It has been revealed that N-aryl-o-iminobenzoquinones, in contrast to o-benzoquinones, can provide radical polymerization of methyl methacrylate in controllable mode. The efficiency of the compounds as chain growth regulators has been found to depend on their composition and reaction conditions. It has been established that 4,6-di-tert-butyl-N-(2,6-diethylphenyl)-o-iminobenzoquinone and 4,6-di-tert-butyl-N-(2,6-diisopropylphenyl)-o-iminobenzoquinone under radical initiation conditions provide the synthesis of poly(methyl methacrylate) with wide-range molecular weight, retaining polydispersity indices about ~1.4–1.8 up to deep conversions.     

Synthesis and study of the structure of the reaction products formed from cyclopenta[<Emphasis Type="Italic">c</Emphasis>]quinolinium quarternary salts and <Emphasis Type="Italic">p</Emphasis>-dimethylaminobenzaldehyde

The presence of active methylene group in the molecules of cyclopenta[c]quinolinium quarternary salts permitted to obtain products of their reaction with p-dimethylaminobenzaldehyde. Structures of the reaction products were established from ¹H and ¹³C NMR spectral data using the correlation spectra. The effect of substituents at nitrogen on the visible absorption spectra was studied. The investigation of formation of the frontier orbitals in the reaction products by quantum chemical calculations revealed the reason of the coloration of the dyes synthesized.     

Kinetics of photolytic transformations of 4,4′-Bi(3-methyl-6-<Emphasis Type="Italic">tert</Emphasis>-butyl-<Emphasis Type="Italic">o</Emphasis>-benzoquinone)

The quantum yields and apparant rate constants of the photolysis of 4,4′-bi(3-methyl-6-tert-butyl-o-benzoquinone) and of accumulation of its transformation products in hydrocarbon solutions under the action of light with λ 313 and 405 nm were determined. The probable scheme of photochemical reactions was suggested. Original Russian Text O.G. Mishchenko, S.V. Maslennikov, I.V. Spirina, N.O. Druzhkov, Yu.A. Kurskii, V.P. Maslennikov, 2007, published in Zhurnal Obshchei Khimii, 2007, Vol. 77, No. 12, pp. 1997–2001.     

Photolysis of <Emphasis Type="Italic">ortho</Emphasis>-azidophenol in various solvents

The photolysis of ortho-azidophenol in water, ethanol, acetonitrile, chloroform, and benzene was studied by IR and electronic spectroscopy and thin-layer chromatography. It was found that an equilibrium between ortho-azidophenol and its quinonoid form occurred in benzene. In the photolysis of ortho-azidophenol in benzene, intramolecular hydrogen bonding facilitates the degradation of the azido group through the mechanism of formation of intermediate triazene structures. In the other solvents, which exclude intramolecular hydrogen bonding, the nitrene mechanism of photolysis yielding ortho-aminophenol, ortho-iminoquinone, and an azo compound is operative. The rate of formation of photolysis products depends on the nature of the solvent.     

Excess enthalpies of binary mixtures of <Emphasis Type="Italic">ortho</Emphasis>-, <Emphasis Type="Italic">meta</Emphasis>-, <Emphasis Type="Italic">para</Emphasis>-structural isomers containing aliphatic group

To obtain further systematic information for the isomer systems, the excess molar enthalpies for binary (o + m), (o + p), (m + p)-isomers of methoxymethylbenzene, ethylmethylbenzene, diethylbenzene, chloromethylbenzene, tolunitrile and fluorobenzonitrile, tolylacetonitrile were measured at 298.15 K. In this article, the results are discussed and compared with those of previous works. The excess enthalpies of binary systems in different solid and liquid states were measured when the pure component of o-/m-tolunitrile, fluorobenzonitrile was titrated into the prior (o + p) or (m + p) mixtures. A series calculation for the interaction energies (IE) between the isomers was carried out for the pair molecules by ab initio MO of Gaussian 09. Correlations between the excess enthalpies at a molar fraction of x = 0.5 and the intermolecular energy are discussed.