Kinetics of bulk polymerization of trimeric phosphonitrilic chloride

The kinetics of the pure bulk polymerization of trimeric phosphonitrilic chloride were investigated in the temperature range 240–255°C. The reaction was found to be secondorder with an activation energy of 57 kcal./mole. Polymerization catalyzed by benzoic acid was first-order, and the reactivities of benzoic acid and sodium benzoate at 235°C. were found to be about similar. The volatile decomposition products for the benzoic acid reaction were identified. Mechanisms are postulated for the catalyzed and uncatalyzed reactions.     

Bismuth-catalyzed benzylic oxidations with tert-butyl hydroperoxide

[reaction: see text] Oxidation of alkyl and cycloalkyl arenes with tert-butyl hydroperoxide catalyzed by bismuth and picolinic acid in pyridine and acetic acid gave the corresponding benzylic ketones (48-99%). Alternatively, oxidation of methyl arenes gave the corresponding substituted benzoic acids (50-95%). Preliminary mechanistic studies were consistent with a radical mechanism rather than a bismuth(III)-bismuth(V) cycle.     

Activation of nitrous oxide and selective epoxidation of alkenes catalyzed by the manganese-substituted polyoxometalate, [Mn(III)2ZnW(Zn2W9O34)2]10-

A manganese(III)-substituted polyoxometalate of the "sandwich" structure, [MnIII2ZnW(ZnW9O34)2]10-, catalyzed the highly selective (>99.9%) epoxidation of alkenes, such as 1-octene, 2-octene, and cyclohexene with nitrous oxide. Reactions occurred in homogeneous media at 150 degrees C under 1 atm N2O. The epoxidation had a linear reaction profile; turnover frequencies of 0.5-1.4 h-1 were measured. The reactions were also stereoselective; for example, cis-stilbene gave cis-stilbene oxide. From ESR spectroscopy, it was shown that a Mn(II) octahedral species is reversibly formed by reaction between the original Mn(III) polyoxometalate and N2O. Therefore, it would appear that a Mn(V)-oxo active species is not formed; it is possible that the activation of nitrous oxide was by its oxidation by the Mn(III) polyoxometalate.     

Thermal and Photofragmentation of N-Benzoylhydrazone Derivatives

Two selected benzoylhydrazones I and II were subjected to thermolysis by reflux at 200 °C. Benzil, benzoic acid, biphenyl, benzanilide together with the corresponding ketones, nitriles and imines were isolated. Similar treatment of the third hydrazone III at 250 °C afforded, in addition to the previous products, bibenzyl, stilbene, and 2-phenylindole. Photolysis of the same hydrazones I-III in acetonitrile gave the previously reported products but in different ratios along with azine derivatives and substituted methanes. A free radical mechanism involving homolysis of the N-N and C-N bonds is suggested, substantiated by trapping of phenyl radical with isoquinoline, to account for the formation of the identified products.     

Study on the condensation and crosslinking reactions of furfuryl alcohol and tris(2-hy-droxyethyl)isocyanurate by thermal methods

Condensation and crosslinking reactions of furfuryl alcohol (FA) and FA with tris (2-hydroxyethyl )isocyanurate (THEIC) are studied by means of DSC, TG, TBA, NMR and elemental analysis. Four exothermic peaks are observed on the DSC curves of thermal condensation of FA and FA with THEIC in the presence of sulfuric acid. The peaks I, II (50–80°C), III (110–130°C) and IV (150–190°C) correspond to linear polycondensation of FA through head-to-tail condensation, head-to-head etherification, crosslinking dehydration reaction between methylene group and terminal hydroxy group of FA polymeric chain and to further crosslinking reaction at higher temperature, respectively. The reactivity of FA and THEIC increases sharply at 130–150°C and THEIC is reacted completely at 150°C. Addition of THEIC raises the initial decomposition temperature of FA polymer by 60°C.     

Aromatic amino-claisen rearrangement in the synthesis of ellipticine

A convenient route is described for the preparation of 1,4-dimethylcarbazole — the key compound in the synthesis of the antitumoral alkaloid ellipticine. The interaction of 2,5-xylidine with 3-chlorocyclohexene led to N-(cyclohex-2-enyl)-2,5-xylidine (I), the two-hour heating of which at 140–150°C gave the product of an amino-Claisen rearrangement, 6-(cyclohex-2-enyl)-2,5-xylidine (II) with a yield of 82%. The intramolecular cyclization of compound (II) in polyphosphoric acid (130–140°C, 5 h) led to 5,6,7,8,12,13-hexahydro-1,4-dimethylcarbazole (III) in a yield of 75%. The dehydrogenation of substance (III) by boiling in trimethylbenzene in the presence of Pd/C gave 1,4-dimethylcarbazole (IV) with a yield of 87%. The conditions for performing the reactions and the physicochemical constants of the compounds obtained are given.     

Ru(III)‐catalyzed oxidation of cysteine hydrochloride by methylene blue in acidic medium; synergetic effect of Cu(II): A kinetic study

Cysteine hydrochloride and methylene blue (MB) interact in a molar ratio of 2:1 in acidic medium forming cystine and dihydromethylene blue, and the reaction is catalyzed by Ru(III). At low concentrations (ca. 2.0 × 10^?8 M), Cu(II) does not catalyze the reaction significantly but at this concentration level the catalytic activity of Ru(III) is found to be augmented by the addition of Cu(II) and the kinetics of Ru(III)‐catalyzed reaction has been studied in the absence and in the presence of externally added Cu(II). The reaction follows a half‐order kinetics in MB that increases to ¾ on increasing [MB] beyond 1.5 × 10^?5 M in the Ru‐catalyzed reaction. In the Ru–Cu catalyzed reaction; the order in MB is ¾ even at lower concentrations of MB. The order in cysteine is unity. The rate decreases on increasing [MB] in both cases but attains a limiting value at higher concentrations of MB (ca. >2.0 × 10^?5 M) in the presence of Ru(III) alone. The rate increases on increasing [H⁺] and in Ru‐catalyzed reaction, an optimum is noticed. The rate increases linearly with increasing [Ru(III)], but equilibration of the catalyst with other ingredients of the reaction system decreases the rate. The FTIR spectra of the reaction system exhibit time‐dependent changes in the stretching as well as bending modes of –SH group. The synergetic effect of Cu(II) has been attributed to its ligation with cysteine and its subsequent interaction with Ru(II) produced in situ in the system. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 145–150, 2008     

Synthesis and catalytic application of Pd complex catalysts: Atom‐efficient cross‐coupling of triarylbismuthines with haloarenes and acid chlorides under mild conditions

Palladium‐catalysed cross‐coupling reactions are some of the most frequently used synthetic tools for the construction of new carbon–carbon bonds in organic synthesis. In the work presented, Pd(II) complex catalysts were synthesized from palladium chloride and nitrogen donor ligands as the precursors. Infrared and ¹H NMR spectroscopic analyses showed that the palladium complexes were formed in the bidentate mode to the palladium centre. The resultant Pd(II) complexes were tested as catalysts for the coupling of organobismuth(III) compounds with aryl and acid halides leading to excellent yields with high turnover frequency values. The catalysts were stable under the reaction conditions and no degradation was noticed even at 150°C for one of the catalysts. The reaction proceeds via an aryl palladium complex formed by transmetallation reaction between catalyst and Ar₃Bi. The whole synthetic transformation has high atom economy as all three aryl groups attached to bismuth are efficiently transferred to the electrophilic partner.     

膦、胂叶立德的化学与应用 XII. 对硝基苯基亚甲基三苯基膦、胂与2-全氟炔酸甲酯的反应以及(Z)3-全氟烷基 4-对硝基苯基-3-丁烯酸甲酯的立体专一性合成

溴化对硝基苄基三苯基 (1a)、 (1b)在碳酸钾存在下与2-全氟炔酸甲酯(2)在常温下反应, 生成加合物3(当M=As时)或3和4的混合物(当M=P时), 其中3的含量随反应温度升高而增加, 当反应温度为90℃时, 产物全部为3。4c加热时转化为3c。膦加合物3或4在甲醇-水中于封管内150℃加热, 发生P-C键断裂。两者都立体专一性地生成(Z)3-全氟烷基-4-对硝基苯基-3-丁烯酸甲酯(5)。胂加合物3在甲醇-水中回流, 发生As-C键断裂, 生成(Z)-5。对水解机理进行了研究。     

Ligand Substitution Reaction of Bis(ethylenediamine)glycinatocobalt(III) Complex with Ethylenediamine Catalyzed by the Photo-excited Tris(2,2′-bipyridine)ruthenium(II) Complex

Substitution reaction with ethylenediamine of coordinated glycinate ligand in bis(ethylenediamine)-glycinatocobalt(III) complex has been studied in the presence of photo-excited tris(2,2′-bipyridine)ruthenium(II) complex in alkaline aqueous solution (buffered around pH 12) containing 1.0M chloride ion at 25°C. VIS absorption and CD spectra were used for the racemate and the optically active isomers of the Co(III) complexes, respectively. The reaction was catalyzed by the excited Ru(II) complex to give tris(ethylenediamine)cobalt(III) complex. Mechanism of the ligand-substitution reaction and role of the excited Ru(II) complex were discussed.     

Synthesis and reactions of 3-carbethoxy and 3-aroyl-3,4-dihydro-1h-2,3-benzoxazin-1-ones

A series of 3-substituted 3,4-dihydro-1H-2,3-benzoxazin-1-ones (IV) (Scheme I) was prepared by reaction of 2-bromomethylbenzoyl chlorides (II) with N-hydroxyethylcarbamate (III) or with benzohydroxamic acids. Acid hydrolysis of 3-carbethoxy (IVa) and 3-benzoyl derivatives (IVb) afforded a mixture of 2-(hydroxyaminomethyl)benzoic acid (V) and 2,3-dihydro-2-hydroxy-1H-1-isoindolinone (VII). Compound IVa reacted with ethanol, amines or hydrazine to yield the ethyl ester X, amides XIV (Scheme II) and the hydrazide XII of 2-(N-carbethoxy-N-hydroxy-aminomethyl)benzoic acid. Diazotization of the hydrazide XII afforded the unstable azide XIII which did not undergo the Curtius reaction but gave the benzoxazinone IVa by loss of hydrazoic acid.     

Dioxouranium (II) Chelates with Nitrogen Donor Ligands

The chelates formed by the reaction of dioxouranium (II) with (α-benzoylmethyl-benzylideneimino)benzene sulphonic acid (H₂BB), (α-benzoylmethyl-benzylideneimino) ethane sulphonic acid (H₂BE), 3-(α-benzomethyl-benzylideneimino) propanoic acid (H₂BPA) & 0-(α-benzoylmethyl-benzylideneimino) benzoic acid (H₂BBA) have been prepared and studied potentiometrically using Calvin's extension of Bjerrum's method in aqueous medium at different ionic strengths (0.01, 0.05 and 0.1 M NaClO₄) at 25°, 35° and 45°. The thermodynamic parameters for all the chelates have been evaluated. These compounds have also been isolated as crystalline solids and are characterised by analytical data, electrical conductance, magnetic moment and IR studies.     

Decomposition of di-tert-butyl nitroxide in aqueous solutions

Di-tert-butyl nitroxide (DTBN) decomposes in aqueous solutions producing 2-methyl-2-nitroso propane (MNP) and tert-butanol. The process is acid catalyzed, it is of second order in DTBN, and takes place with a rate constant of (1.0 ± 0.1) M^?2 s^?1. The reaction is also catalyzed by the anionic surfactant sodium dodecyl sulfate and by Fe(II) and Fe(III) ions. The catalysis by Fe(III) involves a very fast reduction of Fe(III) ions with concomitant formation of 2-methyl-2-nitroso propane. The reaction catalyzed by Fe(II) also produces 2-methyl-2-nitroso propane with a formation rate given by: d[MNP]/dt = (0.25 ± 0.10) [Fe(II)] [DTBN]. This reaction rate is nearly pH independent.     

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.     

The role of benzoic acid in proline‐catalyzed asymmetric michael addition: A density functional theory study

In asymmetric Michael addition between ketones and nitroolefins catalyzed by L ‐proline, we observed that it was benzoic acid or its derivatives rather than other proton acid that could accelerate the reaction greatly, and different benzoic acid derivatives brought different yields. To explain the experimental phenomena, a density functional theory study was performed to elucidate the mechanism of proline‐catalyzed asymmetric Michael addition with benzoic acid. The results of the theoretical calculation at the level of B3LYP/6‐311+G(2df,p)//B3LYP/6‐31G(d) demonstrated that benzoic acid played two major roles in the formation of nitroalkane: assisting proton transfer and activating the nitro group. In the stage of enamine formation from imine, the energy profiles of benzoic acid derivatives were also calculated to investigate the reasons why different benzoic acid derivatives caused different yields. The results demonstrated that the pK_a value was the major factor for p‐substituted benzoic acid derivatives to improve the yields, whereas for m/o‐substituted benzoic acid derivatives, both pK_a value and electronic and steric effects could significantly increase the yields. The calculated results would be very helpful for understanding the reaction mechanism of Michael addition and provide some insights into the selection of efficient additives for similar experiments. © 2012 Wiley Periodicals, Inc.     

Model studies on the kinetics and mechanism of polyarylate synthesis by acidolysis

Model reactions were carried out to simulate the acidolysis process for polyarylate synthesis by using p-tert-butylphenyl acetate (ptBuPhOAc) and benzoic acid in diphenyl ether. p-tert-Butylphenol was formed in the reaction mixture and its concentration stayed constant throughout the reaction. Acetic benzoic anhydride and benzoic anhydride were detected by NMR. Based on this experimental evidence, a mechanism for the acidolysis was proposed involving the mixed anhydride. The kinetics of the acidolysis reaction was studied for this model reaction. The overall reaction order is two and the reaction order with respect to each reactant is one. Second-order reaction rate constants were measured at different reaction conditions (200–250°C). The activation energy (E_a), activation enthalpy (ΔH^≠), and activation entropy (ΔS^≠) were calculated from these data. The thermodynamic parameters of the acidolysis reaction were also measured for the analogous reaction of p-tert-butylphenyl pivalate (ptBuPhOPiv) and benzoic acid. The kinetics of two other elementary reactions involved in the acidolysis reaction were also studied: p-tert-butylphenol with acetic anhydride or benzoic anhydride, and p-tert-butylphenyl pivalate with benzoic acid.     

The roles of benzoic acid and water on the Michael reactions of pentanal and nitrostyrene catalyzed by diarylprolinol silyl ether

The roles of benzoic acid and water on the Michael reaction of pentanal and nitrostyrene catalyzed by diarylprolinol silyl ether are revealed by density functional theory calculations. The calculations demonstrate that the benzoic acid is ready to attack the catalysts and form a hydrogen bond between the hydrogen atom of the COOH of benzoic acid and one of the N atoms of the catalyst. The complex formed from pentanal, catalyst and benzoic acid attacks nitroalkene and forms transition states. Finally, the transition states hydrolyze and the products are formed. The calculations demonstrate that the stereoselectivity is dominated by the steric hindrance of the 2-substituent groups, and the benzoic acid can increase the reaction rate evidently by decreasing the activation energies; however, H(3)O(+) or strong acid may prevent the formation of the transition states between enamines and nitroalkenes. The employed solvent can decrease the activation energies and promote the proton transfer from benzoic acid onto the catalyst 2. The calculated enantiomeric excess values are in good agreement with the experimental results. These calculations also reveal that the role of benzoic acid is dependent on the sophisticated structures of the catalysts and provide a valuable index for the structural design of new catalysts and selection of additives or co-catalysts.     

Kinetics of anhydride formation in poly(acrylic acid) and its effect on the properties of a PAA-alumina composite

The kinetics of anhydride formation of poly(acrylic acid) (PAA) in porous PAA–alumina composites have been investigated by using a thermogravimetric technique (TGA). Three distinct reaction peaks at 200°C (I), 250°C (II), and 390°C (III) were identified in the dynamic TGA thermogram. These peaks were attributed to bound water removal (I), anhydride formation (II), and polymer degradation (III). The kinetics of the anhydride reaction were studied in a temperature range of 220–240°C and found to follow a second-order mechanism with an activation energy of approximately 38 kcal/mole. In addition, the bound water was found to inhibit the onset of anhydride formation. The degree of conversion to anhydride was correlated with the equilibrium swelling level attained by the composite in water.     

Synthesis and characterization of poly[4-(4-hydroxyphenoxy) benzoic acid]

Poly[4-(4-hydroxyphenoxy) benzoic acid] was prepared by the bulk polycondensation of 4-(4-acetoxyphenoxy) benzoic acid. Polycondensation was conducted at 350°C for 3 h under a reduced pressure of 0.1 mmHg and gave a polymer with X?n of 255. The polymer was characterized by elemental analysis, IR spectroscopy, differential scanning calorimetry, and wide-angle X-ray measurement. The crystal/nematic and nematic/isotropic phase transition temperatures of polymer, which depend on the molecular weight, were observed at about 300°C and 410°C, respectively. The polymers with low molecular weights showed nematic textures above 300°C. This nematic/isotropic phase transition temperature is lower than that of poly (4-hydroxybenzoic acid). This thermal behavior of polymer comes from ether units, which increase the flexibility (the rotation or torsion of skeletal bonds) of the polymer chain. © 1994 John Wiley & Sons, Inc.     

The Reaction of Indole Magnesium Bromide with Ketones I. The Reaction of Indole Magnesium Bromide with Cyclohexanone

Indole magnesium bromide, produced by reacting indole with n-butyl magnesium bromide in ether, was reacted with cyclohexanone at ice or room temperature to yield 1-(indol-I-yl)-cyclohexanol (I), which is unstable and may be decomposed easily into indole and cyclohexanone in acidic condition. Indole magnesium bromide reacted with cyclohexanone in refluxing benzene or in anisole at 80°C, to form two products, 1-(indol-3-yl)-cyclohexanol (II) and 1-(indol-3-yl)-cyclohexene (III). (II) could be converted to (III) by heating (II) in phosphoric acid. Reaction of III with maleic anhydride gave a Diels-Alder adduct (IV). Reaction of indole magnesium bromide with cyclohexanone in anisole at 130°C yielded (III) and a trimolecular condensation product of cyclohexanone (V).