Kinetics of oxidative ammonolysis of 4-bromo-<Emphasis Type="Italic">o</Emphasis>-xylene: II. Formation of by-products

Kinetic laws of formation and expenditure of by-products in the oxidative ammonolysis of 4-bromo-o-xylene in the temperature range 633–693 K were studied. It was shown that 4-bromophthalimide formation at high concentration of ammonia occurs through hydrolysis of 4-bromophthalonitrile; carbon dioxide forms by oxidation of 4-bromo-o-xylene and decarboxylation of 4-bromophthalimide; 4-bromobenzonitrile originates from 4-bromo-o-tolunitrile and 4-bromophthalimide. At low concentration of ammonia additional formation routes of 4-bromophthalimide and CO₂ from 4-bromo-o-xylene are realized.     

Kinetics of oxidative ammonolysis of 4-bromo-o-xylene: IV. Mechanism of formation of the reaction products

Generalized kinetic data were used to analyze the mechanism of formation of the oxidative oxidative ammonolysis products 4-bromo-o-xylene and 4-bromo-o-tolunitrile.     

Kinetics of oxidative ammonolysis of 4-bromo-<Emphasis Type="Italic">o</Emphasis>-xylene: I. Transformations of 4-bromo-<Emphasis Type="Italic">o</Emphasis>-xylene and 4-bromo-<Emphasis Type="Italic">o</Emphasis>-tolunitrile

Kinetic laws of 4-bromo-phthalonitrile synthesis by vapor-phase oxidative ammonolisis of 4-bromo-o-xylene in the range of 633–69 K were studied. It was shown that formation of 4-bromophthalonitrile proceeds successively through 4-bromo-o-tolunitrile. Conversion rates of 4-bromo-o-xylene and 4-bromo-o-toluinitrile were found to be described by half-order equations on the corresponding components and not to depend on the oxygen and ammonia concentrations.     

Kinetics of oxidative ammonolysis of 4-bromo-o-xylene: V. Synthesis of 4-bromophthalonitrile

Oxidative ammonolysis of 4-bromo-o-xylene on a V-Sb-Bi-Zr/γ-Al₂O₃ catalyst gives 74.82 mol % of 4-bromophthalonitrile at a high conversion of the starting xylene in a one-cycle process. The process with recirculation results in decreased number of by-products and contribution of deep oxidation and increased selectivity in 4-bromophthalonitrile up to 95.42–96.58%.     

Electronic spectra of o-, m- and p-tolunitrile—substituent effect on internal rotation of the methyl group

The S₁ ← S₀ fluorescence excitation spectra and the S₁→S₀ dispersed fluorescence spectra of o-, m-and p-tolunitrile were measured in supersonic jets. Low-frequency bands due to internal rotation of the methyl group were observed in m- and p-tolunitrile. Observed band positions and relative intensities of the internal rotational bands were reproduced by a calculation using a free rotor basis set. From the analysis, the potential curve of the internal rotation was determined in both S₁ and S₀. It was found that the barrier height increases in going from S₀ to S₁ in m-tolunitrile, while it decreases in p-tolunitrile. In contrast, no low-frequency band was found in o-tolunitrile. It is concluded that the potential curve in o-tolunitrile does not change in going from S₀ to S₁. The change of the barrier height by electronic excitation in tolunitriles differs greatly from that observed in other toluene derivatives. It is suggested that the electronic properties of a substituent are important for the methyl rotation in the excited state.     

New precursors to silafluorenes

Conversion of 2,2′-dibromo-4,4′-di-t-butylbiphenyl and o-bromo-o′chloroniphenyl to organometallic reagents suitable for reaction with Me₂SiCl₂ to produce silafluorene has been developed.     

Determination of betaines as ultraviolet-absorbing esters

A method is described for the estimation of fully N-methylated amino acids (betaines) in plant extracts. After partial purification of aqueous extracts with ion-exchange resins, a crown ether and potassium phosphate buffer are used to facilitate the esterification of betaines with α, p-dibromoacetophenone, p-nitrobenzyl bromide or α-bromo-p-tolunitrile. The esters are isolated with dilute sulphuric acid and chloroform; 10–200 nmol can be determined spectrophotometrically, and smaller amounts by high-performance liquid chromatography.     

Palladium-catalyzed oxidation of lower aliphatic alcohols with oxygen in the presence of aromatic nitriles in aqueous medium

The kinetics of oxidation of lower aliphatic alcohols (C₁–C₄) to the corresponding carbonyl compounds with oxygen in the presence of palladium(II) tetraaqua complex and aromatic nitriles (benzonitrile, phenylacetonitrile, and o-tolunitrile) in aqueous medium (c = 0.01 M) at 65°C under atmospheric pressure were studied. A probable reaction mechanism and kinetic equation were proposed. Aromatic nitriles were found to stabilize decomposition of low-valence palladium species, ensuring activation of molecular oxygen and subsequent oxidation of alcohols.     

Biochemically generated chiral intermediates for organic synthesis: The absolute stereochemistry of 4-bromo-cis-2,3-dihydroxycyclohexa-4,6-diene-1-carboxylic acid formed from 4-bromobenzoic acid by a mutant of pseudomonas putida.

The absolute stereochemistry of the 4-bromo-cis-2,3-dihydroxycyclohexa-4,6-diene-1-carboxylic acid, one of a series of diols produced by P. putida strain JT 107, was shown by X-ray crystal analysis to be (2-R, 3-R).     

Synthesis of bioactive 2-(2-(difluoromethoxy)aryl)benzo[d]thiazole derivatives via base-promoted one-pot process

A convenient synthesis of 2-(2-(difluoromethoxy)aryl)benzo[d]thiazoles from 2- (o-hydroxyaryl)benzothiazoles and commercially available ethyl difluoroiodoacetate (ICF₂CO₂Et) is described. The transformation was amenable to a one-pot, sequential three-component protocol from o-hydroxybenzaldehyde, o-aminothiophenol, and ICF₂CO₂Et promoted by KOH. Additionally, some of the prepared compounds exhibited promising activity against human ovarian cancer cells.     

Metal complexes of hybrid oxygen-arsenic ligands—VI. Stabilization of manganese(II)-arsine complexes using ligands from o-R2AsC6H4CO2Na

A reaction of MnCl₂·4H₂O with o-R₂AsC₆H₄CO₂ Na in 1:2 molar ratio in 95% EtOH yields four manganese(II)-monotertiaryarsine complexes [Mn(o-Me₂AsC₆H₄CO₂)Cl]·0.5H₂O, [Mn(o-R₂AsC₆H₄CO₂)₂(H₂O)₂]·nH₂O (n = O and R = Ph or p-tolyl; n = 1 and R = Et). The stabilization of these four complexes is significant in view of the only two already known.     

Reactivity of TpIr(C2H4)(DMAD) with carboxylic acids. A DFT study on geometrical isomers and structural characterization

The thermally unstable adduct Tp^Me2Ir(C₂H₄)(DMAD), which was generated “in situ” by the reaction of DMAD with Tp^Me2Ir(C₂H₄)₂ (1) at low temperature, reacted with different carboxylic acids to produce the following compounds: Tp^Me2Ir(E-C(CO₂Me)CH(CO₂Me))(H₂O)(OC(O)C₆H₄R), (R = H, 2a; o-OH, 2b; o-Cl, 2c; m-Cl, 2d; o-NO₂, 2e; m-NO₂, 2f;o-Me, 2g;p-Me, 2h) and Tp^Me2Ir(E-C(CO₂Me)CH(CO₂Me))(H₂O)(OC(O)Me) 3. In the reaction of derivative 2a with Lewis bases, Tp^Me2Ir(E-C(CO₂Me)CH(CO₂Me))(L)(OC(O)C₆H₅), (L = Py, 4a; m-Br-Py, 4b; m-Cl-Py, 4c; NCMe, 5) were obtained, of which 4b and 4c were isolated as a mixture of two isomers in which the substituted pyridine ring was present at different rotational orientations. All new compounds prepared were characterized by ¹H and ¹³C{¹H} NMR spectroscopy, the structure of compounds 2d, 2h and 4a being determined by X-ray diffraction analysis. DFT was used to analyze the relative stability and the structural orientation of the isomers.     

A practical synthesis of new S,N-disubstituted derivatives of 5-(4-methylpiperidino)methyl-2-thiouracil

5-(4-Methylpiperidino)methyl-2-thiouracil (1) has been obtained via the Mannich reaction between 2-thiouracil, paraformaldehyde, and a cyclic secondary amine such as 4-methylpiperidine (4-MP) in ethanol. New S,N(1)-di-o-(m- and p-)bromo-(nitro-) benzyl-substituted derivatives have been synthesized successfully in the reactions of 1 with the corresponding o-(m- and p-)bromobenzyl bromides or o-(m- and p-) nitrobenzyl chlorides in DMF solution in the presence of K₂CO₃. The opposite method of synthesis, that is, the reaction between 2-o-(m- and p-)bromobenzylthio-1-o-(m- and p-)bromobenzyluracils and 2-o-(m- and p-)nitrobenzylthio-1-o-(m- and p-) nitrobenzyluracils (8), with paraformaldehyde and 4-methylpiperidine in ethanol failed, indicating the important role of the enol form of 2-thiouracil for the Mannich reaction to be successful.     

Neighbouring group participation in reactions of sulphides with chloramine-t

Neighbouring group participation in reactions of chloramine-T with ortho-substituted aryl methyl sulphides and diaryl sulphides has been studied. The reaction is markedly hindered by the steric effect of the ortho substituent of the phenyl ring, but groups having a CO moiety show an anchimeric effect in the following order: o-CH₂CO₂Me ~ o-CH₂CO₂H < o-CH₂CO₂^- < o-CO₂Me ~ o-CO₂H < o-CO₂^- ? 2o-CO₂ in the rate-determining step may be ruled out on the basis of salt and isotope effect. Substituents with neighbouring group participation diminish the yield of sulphilimine in solvents containing water. The electrophilic chlorination of sulphides by TsNHCl may be assumed to be the rate-determining step with the positively charged sulphonium centre stabilized by the negatively polarized or charged carbonyl-oxygen in the transition state. This type of interaction hinders the nucleophilic attack of sulphonamidate ion at the sulphonium centre in the fast product-controlling steps, decreasing the yield of sulphilimine.     

Zwitterionic metal carboxylate complexes: In solid state

A flexible dicarboxylic acid having composition [(CH(o-C₅H₄N)(p-C₆H₄OCH₂CO₂H)₂] derived from corresponding bis-phenol reacts with various metal(II) acetates such as manganese(II), cobalt(II) and nickel(II) acetate leads to zwtterionic complexes with compositions [CH(o-C₅H₄N)(p-C₆H₄OCH₂CO₂){p-C₆H₄OCH₂CO₂M(H₂O)₅}].6H₂O (where M = Mn, Co, Ni). The complexes are characterised by X-ray crystallography. These complexes have chiral center due to unsymmetric structure conferred to the ligand through coordination at only one carboxylate group of the ligand. In solid state these complexes are racemic.     

Interaction of aryltrimethylstannanes with cyanogen chloride and bromide. A route to aryl cyanides

Phenyltrimethylstannane has been found to react with cyanogen chloride in methylene chloride in the presence of aluminium chloride to give benzonitrile in 60% yield; o-, m-, and p-tolyltrimethylstannane similarly give o-, m-, and p-tolunitrile, respectively. With cyanogen bromide the aryl bromides are formed.     

A new chelated C,N-benzyllithium reagent and some organometallic derivatives of selected early transition metals

The reactions of LiCH₂C₆H₄-o-NMe₂ with Cp₂MCl (M = Ti, V; Cp = η⁵-C₅H₅), CpTiCl₂, CrCl₃, and ScCl₃ have led to the isolation of thermally stable, air-sensitive organometallic complexes whose stability is attributed to chelation. The reaction of Cr(CH₂C₆H₄-o-NMe₂)₃ with CO₂ gives a paramagnetic complex in which CO₂ has inserted into only one CrC bond and with diketones to give (diketonate)Cr(CH₂C₆H₄-o-NMe₂)₂.     

Influence of the aromatic ring substituents on phase equilibria of vanillins in binary systems with CO2

Solid–liquid phase transitions of vanillin, ethylvanillin, o-vanillin and o-ethylvanillin in presence of compressed CO₂ were determined with the modified capillary method. Furthermore, the solubilities of the above mentioned vanillins in supercritical CO₂ were measured at 313.2, 333.2 and 353.2 K and in the pressure range 8–30 MPa using a static–analytic method. The experimental equilibrium solubility data have been fitted to the Peng–Robinson equation in combination with two parameter van der Waals mixing rules and binary parameters were determined from the best fit. Results showed that the phase equilibria of vanillins in dense CO₂ are influenced by the position of the hydroxyl group bound to the aromatic ring. Under the pressure of CO₂ the melting point depression and also the solubility of both o-vanillins was higher than those of p-vanillins. Oppositely, the alchoxy group (methoxy or ethoxy) showed no significant influence on the solubility of vanillins.     

Negative ion tandem mass spectrometry of leukotriene E4, and LTE4, metabolites: Identification of LTE4, in human urine

The sulfidopeptide leukotrienes, leukotriene E₄, (LTE₄,) and its N-acetyl derivative and several ω? and β-oxidized metabolites of LTE₄, have been analyzed by tandem mass spectrometry. [M?H]^? ions were produced by continuous flow fast atom bombardment, and collision-induced dissociation of these ions was studied by using a triple quadrupole instrument. The product ion spectra obtained were characteristic of the structure of LTE₄, and mechanisms of ion formation were investigated by using deuterated compounds. β-Elimination of the peptide portion of LTE₄, by loss of CO₂, and ethylene amine leaves the C-l carboxyl group ionized in the most abundant fragment ion for LTE₄, and all metabolites. Tandem mass spectrometry of fast atom bombardment-generated anions from ω? and β-oxidized metabolites of LTE₄, produced similar ions with only a minor influence of the third carboxyl group at the omega terminus evident. Tandem mass spectrometry was used to identify unequivocally the presence of unmodified LTE₄, in a high performance liquid chromatography-purified fraction of urine from a normal healthy volunteer after infusion with LTE₄.     

Kinetic study of oxidation of galactose by N-bromo phthalimide in the presence of cationic micelle in acidic medium

The kinetics of micellar catalyzed oxidation of galactose by N-bromophthalimide was studied in the presence of acidic medium at 308?K. The oxidation reaction exhibits first-order kinetics with respect to oxidant (N-bromophthalimide), fractional order with respect to substrate (galactose) and positive fractional order with respect to HClO₄ on the rate of reaction. The rate of the reaction increased with decreasing the dielectric constant of the medium. With a progressive increase in the concentration of CTAB, the rate of reaction increased and after reaching peak k _obs, decreased at higher concentrations of CTAB. There catalytic roles are best explained by Berezin??s model. The influence of salts on the reaction rate was also studied. The various activation parameters have been calculated. The rate constant and binding constant with the surfactant have also been evaluated. A suitable mechanism consistent with the experimental findings has been proposed.