Kinetics and Mechanism of Unimolecular Heterolysis of Framework Compounds: XVII. Solvation Effects in Dehydrobromination of <Emphasis Type="Italic">tert</Emphasis>-Butyl Bromide, 1-Bromo-1-Methylcyclohexane,and 2-Bromo-2-methyladamantane in Dipolar Aprotic Solvents

Dehydrobromination rate of tert-butyl bromide, 1-bromo-1-methylcyclohexane, and 2-bromo-2-methyladamantane grows with increasing polarity and dipole moment of solvents. No correlation was found between rate constants of the process and electrophilicity or ionizing power of the solvents. The observed solvation effects are due mainly to dispersion interactions.     

Kinetics and mechanism of the thermal decomposition of 1-bromo-4-nitroxymethylcubane

The thermal decomposition kinetics of 1-bromo-4-nitroxymethylcubane in the liquid phase is typical of C-ONO₂ bond heterolysis, which occurs if the nitro ester has a strong donor substituent. A comparison between 1-bromo-4-nitroxymethylcubane and tert-butyl nitrate shows that bromocubyl is close to the tert-butyl group in induction properties and cubyl itself is a stronger donor than this group.     

Kinetics and Mechanism of Monomolecular Heterolysis of Commercial Organohalogen Compounds: XXXIV. Solvent Effect on the Heterolysis Rate of 1-Chloro-1-methylcyclohexane. Correlation Analysis of Solvation Effects in Heterolysis of 1-Chloro-1-methylcyclohexane and 1-Chloro-1-methylcyclopentane

The kinetics of heterolysis of 1-chloro-1-methylcyclohexane in 9 protic and 25 aprotic solvents at 25°C were studied by the verdazyl method. The kinetic equation is v = k[RCl] (E1 mechanism). The heterolysis rate of 1-chloro-1-methylcyclohexane in protic solvents is two orders of magnitude lower than that of 1-chloro-1-methylcyclopentane, whereas in low-polarity and nonpolar aprotic solvents the rates are close. A correlation analysis was made to reveal the solvation effects in heterolysis of both chlorides in a set of 9 protic and 25 aprotic solvents, and separately in protic and aprotic solvents.     

Kinetics and Mechanism of Monomolecular Heterolysis of Commercial Organohalogen Compounds: XXXIII.1 Correlation Analysis of Solvation Effects in Monomolecular Heterolysis of 1-Bromo-1-methylcyclopentane, 1-Bromo-1-methylcyclohexane, and 2-Bromo-2-methyladamantane

The rate of heterolysis of 1-bromo-1-methylcyclopentane and 1-bromo-1-methylcyclohexane is determined by the equation v = k[RBr], mechanism E1. Comparative correlation analysis of solvation effects in heterolysis of these substrates and 2-brom-2-methyladamantane was performed.     

Kinetics and Mechanism of Monomolecular Heterolysis of Commercial Organohalogen Compounds: XXXVII.1 Effect of Nucleofuge and Solvent of the Relative Rates of Heterolysis of 1-Halo-1-methylcyclopentanes and 1-Halo-1-methylcyclohexanes. Correlation Analysis of Solvation Effects

The effect of solvent ionizing ability on heterolysis rate enhances in the series 1-chloro-1-methylcyclohexane < 1-bromo-1-methylcyclohexane 1-chloro-1-methylcyclopentane < 1-bromo-1-methyl- cyclopentane. The lower sensitivity of cyclohexyl substrates compared with cyclopentyl is determined by conformational effects. Bromides are more sensitive to solvent effects than chlorides because of the stronger polarizability of the C-Br bond.     

Effect of the medium on the reaction of <Emphasis Type="Italic">tert</Emphasis>-butyl hypochlorite with hydrocarbons

The selectivity in the reaction of tert-butyl hypochlorite with 2,3-dimethylbutane in various solvents may be described by a three-parameter correlation equation taking into account the ability of solvents to nonspecific solvation and their cohesion energy density.     

Kinetics and mechanism of monomolecular heterolysis of commercial organohalogen compounds: XLIII. Solvent effect on activation parameters of dehydrochlorination of 3-chloro-3-methylbut-1-ene. Correlation analysis of solvation effects

The influence of temperature on the rate of dehydrochlorination of 3-chloro-3-methylbut-1-ene in 17 aprotic and 13 protic solvents, ν = k[C₅H₉Cl], was studied by the verdazyl method. In aprotic solvents, the electrophilicity, ionizing power, and cohesion of solvents decrease ΔG ^≠ by increasing ΔS ^≠. The nucleophilicity and polarizability increase both ΔH ^≠ and ΔS ^≠ to equal extent and therefore do not affect ΔG ^≠. In protic solvents, the solvent nucleophilicity increases ΔH ^≠ to a greater extent than ΔS ^≠, and the overall effect of the nucleophilic solvation is small and negative.     

Chemoselective acylation of monosubstituted thiacalix[4]arene with di-<Emphasis Type="Italic">tert</Emphasis>-butyl dicarbonate

Mono-, di-, and tetrasubstituted derivatives of p-tert-butylthiacalix[4]arene containing tert-butylcarbamate, tert-butylcarbonate, and tert-butyl fragments have been prepared for the first time. Depending on the reaction conditions (reagents ratio, temperature, and the presence of a base), the interaction of the monoamine derivative of p-tert-butylthiacalix[4]arene with di-tert-butyl dicarbonate can lead to the formation of mono-, di-, and tetrasubstituted products.     

Solvation and Conformational Effects in Heterolysis of 1-Methylcycloalkyl Halides

In the series of substrates 1-bromo-1-methylcyclopentane, 1-bromo-1-methylcyclohexane, 1-methyl-1-chlorocyclopentane, 1-methyl-1-chlorocyclohexane, the heterolysis rate in acetone at 25 °C is reduced by four orders of magnitude; v = k[RX], E1 mechanism. The decrease in reaction rate as we go from a cyclopentyl compound to a cyclohexyl compound is due to the decrease in entropy of activation as a result of rapid solvation of the transition state as the conformational barrier is overcome.     

Synthesis of urethane—acrylic multi-block copolymers via electrochemically mediated ATRP

The electrochemically mediated atom transfer radical polymerisation (eATRP) of n-butyl acrylate was investigated under a variety of catalyst concentrations. Poly(n-butyl acrylate)-block-polyurethane-block-poly(n-butyl acrylate) copolymers were prepared via electrochemically mediated atom transfer radical polymerisation (eATRP) using only 7 × 10^?6 mole % of Cu^II complex. The successful chain extension and formation of penta-block copolymers confirmed the living nature of the poly(alkyl acrylates) prepared by eATRP. In this work, the tri-block and penta-block urethane-acrylate copolymers were synthesised for the first time by using tertiary bromine-terminated polyurethane macro-initiators as transitional products reacting with n-butyl acrylate, and subsequently with tert-butyl acrylate in the presence of the Cu^IIBr₂/TPMA catalyst complex. The results of ¹H NMR spectral studies support the formation of tri-block poly(n-butyl acrylate)-block-polyurethane-block-poly(n-butyl acrylate) copolymers, and penta-block poly(tert-butyl acrylate)-block-poly(n-butyl acrylate)-block-polyurethane-block-poly(n-butyl acrylate)-block-poly(tert-butyl acrylate) copolymers.     

(Liquid + liquid) equilibria of methanol + ethylbenzene + isooctane + methy <Emphasis Type="Italic">tert</Emphasis>-butyl ether quaternary system at <Emphasis Type="Italic">T</Emphasis> = 303.15 K

Tie line data of {methanol + methyl tert-butyl ether + isooctane} ternary systems were obtained at T = 303.15 K, while data for {methanol + ethylbenzene + isooctane} were taken from literature. The ternary system {methanol + methyl tert-butyl ether + ethylbenzene} and {methyl tert-butyl ether + ethylbenzene + isooctane} were completely miscible. A quaternary system {methanol + ethylbenzene + isooctane + methyl tert-butyl ether} was also studied at the same temperature. In order to obtain equilibium data of the quaternary system, four quaternary sectional planes with several methyl tert-butyl ether/methanol ratios were studied. The effect of the addition of methyl tert-butyl ether on the liquid-liquid equilibrium data of {methanol + ethylbenzene + isooctane} ternary system has been investigate at the same temperature. The distribution curves for ternary and quaternary system was analysed. For the quaternary system {methanol + ethylbenzene + isooctane + methyl tert-butyl ether}, experimental data demonstrated that the distribution coefficient of ethylbenzene between the hydrocarbon and methanol phase on a methyl tert-butyl ether–free basis slightly increases with the increase of methyl tert-butyl ether/methanol ratio. Ternary experimental results were correlated with the UNIQUAC and NRTL equation. The NRTL equation is more accurate than the UNIQUAC equation for the ternary systems studied here. The equilibrium data of three ternary systems were used for determining interactions parameters for the UNIQUAC equation. The UNIQUAC equation fitted to the experimental data appeared to be more accurate than the UNIFAC method for the same quaternary system.     

Basicity of isomeric ditetrazolylbenzenes and their <Emphasis Type="Italic">N-tert</Emphasis>-butyl derivatives

The basicity constants \((pK_{BH^ + } ,pK_{BH^{2 + } } )\) of 1,2-, 1,3-, and 1,4-bis(tetrazol-5-yl)benzenes and their N-tert-butyl derivatives in aqueous sulfuric acid and the dissociation constants (pK _HB) of the corresponding H-complexes with p-fluorophenol in carbon tetrachloride were determined by UV and IR spectroscopy. Mono-and diprotonation of isomeric ditetrazolylbenzenes is observed in the acidity range (H ₀) from ?1 to ?5 (\(pK_{BH^ + } \) ?2.5 to ?3.0; \(pK_{BH^{2 + } } \) ?3.8 to ?4.9). Introduction of a tert-butyl group into the 2-position of the heteroring almost does not affect the basicity of ditetrazolyl benzenes. Among the examined compounds, 1,2-bis(2-tert-butyltetrazol-5-yl)benzene is the strongest proton acceptor with respect to p-fluorophenol as standard proton donor, presumably due to formation of a complex with bifurcated (three-center) hydrogen bond.     

Reactions of Arylenedioxytrihalophosphoranes with Acetylenes: XV.<Superscript>1</Superscript> Reaction of 2,2,2-Tribromo-4,6-di-<Emphasis Type="Italic">tert</Emphasis>-butylbenzo-1,3,2λ<Superscript>5</Superscript>-dioxaphospholedioxaphosphole with Pent-1-yne

2,2,2-Tribromo-4,6-di-tert-butylbenzo-1,3,2λ⁵-dioxaphospholedioxaphosphole reacted with a terminal alkyne, pent-1-yne, to give a mixture of two isomeric 1,2-benzoxaphosphinine derivatives, 6,8- and 5,7-di-tert-butyl-2-bromo-4-propylbenzo-1,2λ⁵-oxaphosphinin-2-oxides, at a ratio of 5.9: 1. The regioselectivity of substitution of oxygen in the dioxaphosphole fragment by carbon differs from that observed previously in the reaction with 4,6-di-tert-butyl-2,2,2-trichlorobenzo-1,3,2λ⁵-dioxaphosphole: the minor isomer was formed as a result of substitution of the oxygen atom in the ortho position with respect to one tert-butyl group of the initial phosphole.     

Synthesis,Crystal Structure,and Catalytic Property of a Dioxomolybdenum(VI) Complex Derived from <Emphasis Type="Italic">N</Emphasis>'-(3-Bromo-5-Chloro-2-Hydroxybenzylidene)-4-Nitrobenzohydrazide

New dioxomolybdenum(VI) complex [MoO₂(L)(CH₃OH)], where L is the dianionic form of N'- (3-bromo-5-chloro-2-hydroxybenzylidene)-4-nitrobenzohydrazide (H₂L), was prepared and characterized by IR and UV-Vis spectra, as well as single crystal X-ray diffraction (CIF file ССDС no. 1567063). The complex crystallizes as the monoclinic space group P2₁/c with unit cell dimensions a = 13.8471(10), b = 7.5618(6), c = 17.9445(12) Å, β = 90.107(2)°, V = 1878.9(2) ų, Z = 4, R¹ = 0.0821, wR₂ = 0.0907, GOOF = 1.024. X-ray analysis indicates that the complex is a dioxomolybdenum(VI) species with the Mo atom in octahedral coordination. The catalytic oxidation property of the complex with tert-butylhydroperoxide in CH₂Cl₂ was studied.     

Titanium tetra-<Emphasis Type="Italic">tert</Emphasis>-butoxide-<Emphasis Type="Italic">tert</Emphasis>-butyl hydroperoxide oxidizing system: Physicochemical and chemical aspects

The reaction of titanium tetra-tert-butoxide with tert-butyl hydroperoxide (1: 2) (C₆H₆, 20 C) involves the steps of formation of the titanium-containing peroxide (t-BuO)₃TiOOBu-t and peroxytrioxide (t-BuO)₃TiOOOBu-t. The latter decomposes with the release of oxygen, often in the singlet form, and also homolytically with cleavage of both peroxy bonds. The corresponding alkoxy and peroxy radicals were identified by ESR using spin traps. The title system oxidizes organic substrates under mild conditions. Depending on the substrate structure, the active oxidant species can be titanium-containing peroxide, peroxytrioxide, and oxygen generated by the system.     

One-Pot Assembly of Alkyl [(5-Amino-1<Emphasis Type="Italic">H</Emphasis>-pyrrol-2-yl)sulfanyl]-acetates from Propargylamines,Isothiocyanates, and Alkyl Bromoacetates

Methyl and tert-butyl 2-{[5-(diethylamino)-1-methyl-1H-pyrrol-2-yl]sulfanyl|acetates have been synthesized in one preparative stage from accessible N,N-diethylprop-2-yn-1-amine, methyl isothiocyanate, and methyl 2-bromoacetate.     

Design,synthesis and anti-mycobacterial evaluation of some new <Emphasis Type="Italic">N</Emphasis>-phenylpyrazine-2-carboxamides

N-Phenylpyrazine-2-carboxamides (anilides of pyrazinoic acids with simple substituents in various positions) were previously shown to possess significant biological activities in vitro, markedly anti-mycobacterial and photosynthesis-inhibiting activity. Based on structure-activity relationships (SAR) extracted from previously published series, 25 new anilides of non-substituted pyrazinoic acid (POA), 5-CH₃-POA, 6-Cl-POA, 5-tert-butyl-POA and 5-tert-butyl-6-Cl-POA were designed and synthesised. The phenyl part was substituted with simple hydrophobic substituents chosen from methyl and halogens. 5-tert-Butyl-N-(5-fluoro-2-methylphenyl)pyrazine-2-carboxamide (9), N-(3-chloro-4-methylphenyl)-5-methylpyrazine-2-carboxamide (12), 6-chloro-N-(3-chloro-4-methylphenyl)pyrazine-2-carboxamide (13) and 6-chloro-N-(5-iodo-2-methylphenyl)pyrazine-2-carboxamide (18) possessed whole cell anti-mycobacterial activity in vitro against Mycobacterium tuberculosis H37Rv with minimum inhibitory concentration (MIC) of around 10 μM. Importantly, no cytotoxicity in the HepG2 model was detected in vitro at the concentrations tested and the estimated IC50 values were in hundreds of μM, indicating promising selectivity. N-(3-Chloro-4-methylphenyl)pyrazine-2-carboxamide (11) and N-(4-chloro-2-iodophenyl)pyrazine-2-carboxamide (21) exerted significant activity against Mycobacterium kansasii with MIC 12.6 μM and 8.7 μM, respectively. No activity was detected against Mycobacterium avium. SAR were in accordance with those observed for the derivatives previously published.     

Effect of solvent nature on the photoreduction kinetics of substituted benzoquinones

Effect of the solvent nature on the kinetics of photoreduction of substituted benzoquinones in the presence of hydrogen donors has been studied. It has been found that the effective photoreduction rate constant (k_H) for quinones decreases with an increase in solvent polarity. For the 3,6-di-tert-butylbenzoquinone–1,2-N,N-dimethylaniline pair, the dependence of ln k_H on the difference of the reciprocals of optical and static solvent permitivities (1/ε _∞–1/ε₀) is stepwise with a break point corresponding to CH₂Cl₂. A similar relationship lnk_H = f(1/ε _∞–1/ε₀) is observed for the p-chloranil–mesitylene pair. In the study of the photoreduction kinetics for a series of seven o-benzoquinones in the presence of p-derivatives of N,N-dimethylaniline in CH₂Cl₂, it has been found that the dependence of k_H on the free energy of electron transfer (ΔG_e) has a maximum for the 3,6-di-tert-butylquinone-1,2–N,N-dimethylaniline pair at ΔG_e = 0.11 eV.     

6,6'-[piperazine-1,4-diylbis(methylene)]bis[3,5-di(<Emphasis Type="Italic">tert</Emphasis>-butyl)-1,2- benzoquinone]: Synthesis and properties

Preparation method is developed for a new 6,6'-[piperazine-1,4-diylbis(methylene)]bis[3,5-di(tert-butyl)- 1,2-benzoquinone], including the stage of 3,5-di(tert-butyl)pyrocatechol aminoalkylation by Mannich reaction followed by oxidation. The molecular structure of one of its hydrolysis products, 4,6-di(tert-butyl)-2,3-dihydroxybenzaldehyde, is established by X-ray diffraction (XRD) analysis.     

Synthesis and characterization of half-sandwich ruthenium(II) complexes with N-alkyl pyridyl-imine ligands and their application in transfer hydrogenation of ketones

A series of new arene ruthenium(II) complexes were prepared by reaction of ruthenium(II) precursors of the general formula [(η⁶-arene)Ru(μ-Cl)Cl]₂ with N,N′-bidentate pyridyl-imine ligands to form complexes of the type [(η⁶-arene)RuCl(C₅H₄N-2-CH=N-R)]PF₆, with arene = C₆H₆, R = iso-propyl (1a), tert-butyl (1b), cyclohexyl (1c), cyclopentyl (1d) and n-butyl (1e); arene = p-cymene, R = iso-propyl (2a), tert-butyl (2b). The complexes were fully characterized by ¹H NMR and ¹³C NMR, UV–Vis and IR spectroscopies, elemental analyses, and the single-crystal X-ray structures of 2a and 2b have been determined. The single-crystal molecular structure revealed both compounds with a pseudo-octahedral geometry around the Ru(II) center, normally referred to as a piano stool conformation, with the pyridyl-imine as a bidentate N,N ligand. The activity of all complexes in the transfer hydrogenation of cyclohexanone in the presence of NaOH and iso-propanol is reported, the compounds showing turnover numbers of close to 1990 and high conversions. Complex 2b was also shown to be very effective for a range of aliphatic and cyclic ketones, giving conversions of up to 100 %.