Mechanism of phthalic anhydride formation in the oxidation of n-pentane on a vanadium-phosphorus oxide catalyst

The reaction paths of product formation in the partial oxidation of n-pentane on vanadium-phosphorus oxide (VPO) and VPO-Bi catalysts are considered. The condensed products of n-pentane oxidation were analyzed by chromatography-mass spectrometry, and the presence of C₄ rather than C₅ unsaturated hydrocarbons was detected. It was found that the concentration of phthalic anhydride in the products increased upon the addition of C₄ olefins and butadiene to the n-pentane-air reaction mixture. With the use of a system with two in-series reactors, it was found that the addition of butadiene to a flow of n-butane oxidation products (maleic anhydride, CO, and CO₂) resulted in the formation of phthalic anhydride. The oxidation of 1-butanol was studied, and butene and butadiene were found to be the primary products of reaction; at a higher temperature, maleic anhydride and then phthalic anhydride were formed. The experimental results supported the reaction scheme according to which the activation of n-pentane occurred with the elimination of a methyl group and the formation of C₄ unsaturated hydrocarbons. The oxidation of these latter led to the formation of maleic anhydride. The Diels-Alder reaction between maleic anhydride and C₄ unsaturated hydrocarbons is the main path of phthalic anhydride formation.     

Methylthiofurane: Herstellung und Reaktionen

Preparation and Reactions of Methylthiofurans By lithiation of 3,4-dimethoxyfuran, 2-methylfuran and furan, followed by reaction with dimethyldisulfide, the methylthiofurans 2, 8 , and 10 have been prepared. Reaction of 8 with maleic anhydride has yielded 6-methyl-3-(methylthio)phthalic anhydride ( 9 ), a yellow substance with a strong greenish fluorescence, obviously formed by elimination of H₂O from an unstable cycloadduct. An analgous reaction of 2 resulted in an unexpected mixture from which the following yellow compounds were isolated: 3-hydroxy-4,5-dimethoxy-6-(methylthio)phthalic anhydride ( 3 ), 4-hydroxy-5-methoxy-3,6-bis(methylthio)phthalic anhydride ( 4 ), and bis(S-methyl) (2Z,4E,6Z)-2,3,6,7-tetramethoxy-4,5-bis(methylthio)-2,4,6-octatrienethioate ( 5 ). Compound 5 is also formed on standing of 2 at RT. Mild acid hydrolysis of 2 results in ring-opening accompanied by an intramolecular oxido-reduction to yield S-methyl(3Z)-3-methoxy-4-(methylthio)-2-oxo-3-butenethioate ( 6a ). The structures of compounds 5 and 6a have been determined by X-ray analysis.     

Thermal stability and structure of a new co-crystal of theophylline formed with phthalic acid

A new co-crystal of theophylline and phthalic acid with 1:1 molar ratio has been prepared. It crystallises in the monoclinic crystal system, space group P2₁/c, a=11.5258(9), b=10.1405(6), c=13.9066(12) Å, β=106.827(4)°. The structure of the co-crystal has been revealed by single crystal X-ray diffraction. An infinite helical polymeric chain is formed by intermolecular hydrogen bonds of the two neutral constituents. The hydroxyl group and carbonyl oxygen atom in one of the carboxyl groups of phthalic acid form hydrogen bonds to O6 and to N(7)H atoms of theophylline, respectively, while the other carboxyl OH group of phthalic acid is in hydrogen bond to N9 atom of theophylline by very strong intermolecular interactions proven by 1883 cm^?1 centred peak in FTIR spectrum.Thermal degradation of this new supramolecular compound is a two-step process in air. At first phthalic acid (47.4%) released up to 230°C, meanwhile it loses water and transforms into phthalic anhydride. In EGA-MS spectra, the characteristic fragments of water (m/z=17, 18) appear from about 180°C, while absorption bands of phthalic anhydride are shown in EGA-FTIR spectrum at about 210°C. In the second step theophylline begins to sublime, melts at 276°C, and then evaporates up to 315°C with minute residues.     

Lithium-promoted V2O5?TiO2 catalysts for o-xylene oxidation to phthalic anhydride

A V₂O₅–Li₂O–TiO₂ (a) based catalyst for o-xylene oxidation to phthalic anhydride has been synthesized. The activity and selectivity of the specimen obtained are comparable with those of industrial catalysts.     

Analysis of Anisodine and Identification of Twenty of Its Metabolites in Rat Urine by Liquid Chromatography–Tandem Mass Spectrometry

A simple and rapid high-performance liquid chromatographic-electrospray ionization (ESI) tandem mass spectrometric method has been developed for elucidation of the structures of the metabolites of anisodine in rat urine after administration of a single dose (20 mg). Different extraction techniques (free fraction, acid hydrolysis, and enzyme hydrolysis) were compared for investigation of the metabolism of anisodine. After extraction the pretreated samples were injected into a reversed-phase C₁₈ column with 60:40 (v/v) methanol–0.01% triethylamine solution (2 mM, adjusted to pH 3.5 with formic acid) as mobile phase. Detection was by on-line MS-MS. Identification of the metabolites and elucidation of their structure were performed by comparing changes in molecular masses (ΔM), retention-times, and spectral patterns of product ions with those of the parent drug. At least twenty metabolites (norscopine, scopine, α-hydroxytropic acid, aponoranisodine, apoanisodine, noranisodine, anisodine N-oxide, hydroxyanisodine, hydroxyanisodine N-oxide, methoxyanisodine, hydroxymethoxyanisodine, trihydroxyanisodine, dihydroxymethoxyanisodine, hydroxydimethoxyanisodine, glucuronide conjugates, and sulfate conjugates of noranisodine, hydroxyanisodine and the parent drug) and the parent drug were found in the urine after ingestion of 20 mg anisodine by healthy rats. Anisodine N-oxide, hydroxyanisodine, and the parent drug were detected in rat urine for up 120 h after ingestion of the drug.     

Kinetic studies of polyamide-imide synthesis

To understand the kinetic of synthesis of polyamide-imide (PAI) via p-chlorophenol-(PCP) blocked 4,4′-diphenyl methane diisocyanate (MDI) with trimellitic anhydride (TMA), a series of reactions of blocked MDI with excess phthalic anhydride (PA) and benzoic acid are designed. PCP-blocked phenyl isocyanate (BPI) which also released isocyanate at higher temperatures was used as a model compound for BMDI. The dissociation constants of BPI and BMDI in the presence of excess PA or BA was measured by collecting the evolved CO₂. The effect of the catalyst concentration and temperatures were combined by a Hostettler equation. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 1703–1710, 1997     

Selective vapor‐phase oxidation of o‐xylene to phthalic anhydride over Co‐Mn/H3PW12O40@TiO2 using molecular oxygen as a green oxidant

The oxidation of o‐xylene to phthalic anhydride over Co‐Mn/H₃PW₁₂O₄₀@TiO₂ was investigated. The experimental results demonstrated that the prepared catalyst effectively catalyzed the oxidation of o‐xylene to phthalic anhydride. Also, the synergistic effect between three metals plays vital roles in this reaction. From a green chemistry point of view, this method is environmentally friendly due to carrying out the oxidation in a fixed‐bed reactor under solvent‐free condition and using molecular oxygen as a green and cheap oxidizing agent. The resulting solid catalysts were characterized by FT‐IR, XRD, XPS, ICP‐OES, FESEM, TEM, EDX, DR‐UV spectroscopy, BET and thermogravimetric analysis. The oxidation of o‐xylene yields four products: o‐tolualdehyde, phthaldialdehyde, phthalide and finally phthalic anhydride as the main product. The reaction conditions for oxidation of o‐xylene were optimized by varying the temperature, weight hourly space velocity and oxygen flow rate (contact time). The optimum weight percentage of phosphotungstic acid (HPW) and Co/Mn for phthalic anhydride production were 15 wt % and 2 wt%, respectively. The best Co/Mn ratio was found to be 10/1. Oxygen flow rate was very important on the phthalic anhydride formation. The optimum conditions for oxidation of o‐xylene were T = 370 °C, WHSV = 0.5 h^?1 and oxygen flow rate = 10 mL min^?1. Under optimized conditions, a maximum of 88.2% conversion and 75.5% selectivity to phthalic anhydride was achieved with the fresh catalyst. Moreover, reusability of the catalyst was studied and catalytic activity remained unchanged after at least five cycles.     

Effects of mixed aqueous‐organic solvents on the rate of intramolecular carboxylic group‐catalyzed cleavage of N‐(4′‐methoxyphenyl)phthalamic acid

Kinetic study on the cleavage of N‐(4′‐methoxyphenyl)phthalamic acid (NMPPAH) in mixed H₂O‐CH₃CN and H₂O‐1,4‐dioxan solvents containing 0.05 M HCl reveals the formation of phthalic anhydride (PAn)/phthalic acid (PA) as the sole or major product. Pseudo first‐order rate constants (k₁) for the conversion of NMPPAH to PAn decrease nonlinearly from 60.4 × 10^?5 to 2.64 × 10^?5 s^?1 with the increase in the contents of 1,4‐dioxan from 10 to 80% v/v in mixed aqueous solvents. The rate of cleavage of NMPPAH in mixed H₂O‐CH₃CN solvents at ≥50% v/v CH₃CN follows an irreversible consecutive reaction path: NMPPAH PA. The values of k₁ are larger in H₂O‐CH₃CN than in H₂O‐1,4‐dioxan solvents. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 316–325, 2004     

One-pot,four-component synthesis of 2H-indazolo[2,1-b]phthalazine-triones catalyzed by cellulose-SO3H as a reusable heterogeneous and efficient catalyst

A practical and green method for the synthesis of 2H-indazolo[2,1-b]phthalazine-1,6,11(13H)-trione derivatives using cellulose-SO₃H as a solid acidic catalyst for the four-component condensation reaction of hydrazinium hydroxide, phthalic anhydride, dimedone, and aromatic aldehydes under thermal solvent-free conditions is described. Cellulose-SO₃H as a recyclable green chemical compound has been demonstrated as a new catalyst for the synthesis of this class of compounds.     

Validated, Stability-Indicating LC Method for Analysis of Pipenzolate Bromide and Its Hydrolysis Products

A liquid chromatographic method has been developed and validated for quantitative analysis of pipenzolate bromide (PP), its hydrolysis products, and phenobarbitone, sodium benzoate, and sodium saccharine. A 5-μm particle ODS column was used with acetonitrile–KH₂PO₄ (10 mm, pH 3.5) 40:60 (v/v), containing 5 mm heptanesulfonic acid sodium salt, as mobile phase. Quantitation was achieved by UV detection at 210 nm, on the basis of peak area. Forced degradation studies were performed on a bulk sample of PP using 0.1 M hydrochloric acid, 0.01 M sodium hydroxide, 0.33% hydrogen peroxide, heat (70 °C), and photolytic degradation. The proposed LC method was used to study the kinetics of acidic hydrolysis and pH-rate profiles of hydrolysis of PP in Britton–Robinson buffer solutions.     

Amine/anhydride reaction versus amide/anhydride reaction in polyamide/anhydride carriers

Polyamide 6 (PA6) and poly(metaxylene adipamide) (PAmXD6) were blended in a batch mixer with anhydrides such as phthalic anhydride, n-octadecyl succinic anhydride, and anhydride-grafted ethylene propylene rubber. The melt viscosity, the solution viscosity, and chain end concentration were studied during the mixing. PA was first mixed 5 min to get an homogeneous melt prior to the anhydride addition. The introduction of the anhydride to the molten polyamide resulted in large decreases of melt and solution viscosities and of amine chain end concentrations. The anhydride units react with amine chain ends to form imide groups. The resulting low amine chain end concentration causes hydrolysis reaction to maintain the condensation equilibrium. As a consequence an increased carboxylic chain end concentration is observed. The imide concentration was studied by IR. It was shown that when most of the amine chain ends are consumed, the remaining anhydride reacts with amino groups formed by polyamide hydrolysis. © 1995 John Wiley & Sons, Inc.     

Stability-Indicating RP-HPLC Method for Simultaneous Determination of Metformin Hydrochloride and Sitagliptin Phosphate in Dosage Forms

A new stability-indicating high-performance liquid chromatographic method has been developed for simultaneous analysis of metformin hydrochloride (MET) and sitagliptin phosphate (SIT) in pharmaceutical dosage forms. Chromatographic separation was achieved on a C₈ column. The mobile phase was methanol–water 45:55 % (v/v) containing 0.2 % (w/v) n-heptanesulfonic acid and 0.2 % (v/v) triethylamine; the pH was adjusted to 3.0 with orthophosphoric acid. The flow rate was 1 mL min^?1 and the photodiode-array detection wavelength was 267 nm. The linear regression coefficients for metformin and sitagliptin were 0.9998 and 0.9996 in the concentration ranges 50–450, and 10–150 μg mL^?1, respectively. The relative standard deviations for intra and inter-day precision were below 1.5 %. The drugs were subjected to a variety of stress conditions—acidic and basic hydrolysis, and oxidative, photolytic, neutral, and thermal degradation. The products obtained from photolytic degradation were similar to those from neutral hydrolytic degradation and different from produced by acidic and basic hydrolysis. The method resulted in detection of 15 degradation products (D1–D15); among these, the structures of D1, D3, D9, and D13 were identified. The respective mass balance for MET and SIT was found to be close to 97.60 and 99.12 %. The specificity of the method is suitable for a stability-indicating assay.     

Enhanced Xylose Recovery from Oil Palm Empty Fruit Bunch by Efficient Acid Hydrolysis

Oil palm empty fruit bunch (EFB) is abundantly available in Malaysia and it is a potential source of xylose for the production of high-value added products. This study aimed to optimize the hydrolysis of EFB using dilute sulfuric acid (H₂SO₄) and phosphoric acid (H₃PO₄) via response surface methodology for maximum xylose recovery. Hydrolysis was carried out in an autoclave. An optimum xylose yield of 91.2 % was obtained at 116 °C using 2.0 % (v/v) H₂SO₄, a solid/liquid ratio of 1:5 and a hydrolysis time of 20 min. A lower optimum xylose yield of 24.0 % was observed for dilute H₃PO₄ hydrolysis at 116 °C using 2.4 % (v/v) H₃PO₄, a solid/liquid ratio of 1:5 and a hydrolysis time of 20 min. The optimized hydrolysis conditions suggested that EFB hydrolysis by H₂SO₄ resulted in a higher xylose yield at a lower acid concentration as compared to H₃PO₄.     

The vibrational spectrum of (maleic anhydride)iron tetracarbonyl

On the basis of solid-phase IR and Raman spectra, with some solution data for the IR, a reasonably complete vibrational assignment has been made for the modes of maleic anhydride in (maleic anhydride)iron tetracarbonyl. Shifts in v(C=C) and δ(CH) are consistent with a strong interaction with the metal, but relatively little coupling between the modes. More restricted assignments were made for modes associated with the (maleic anhydride)iron and Fe(CO)₄ fragments.     

化学修饰木瓜蛋白酶的酶学性质研究

采用邻苯二甲酸酐(PA)对木瓜蛋白酶进行了化学修饰,通过三硝基苯磺酸法、紫外光谱、荧光光谱及FT-IR光谱对修饰效果进行了初步表征,采用动力学方法考察了pH和温度对修饰酶水解活性和稳定性的影响,并计算了一系列动力学和热力学参数.实验结果表明:PA对木瓜蛋白酶的平均氨基修饰度为43%,未对酶的活性基团-SH发生修饰,修饰酶较原酶的紫外吸收峰和最大荧光发射峰均发生蓝移,紫外吸收强度降低、荧光强度增大;PA修饰未改变木瓜蛋白酶的最适反应温度,但将其最适反应pH由7.0提高到8.5,且酶活力也提高了约20%;PA修饰有效提高了酶的催化水解效率和酶与底物的亲和力,如40℃、最适pH条件下修饰酶的转化数kcat(3.03 s-1)和亲和力kcat/Km(1.70 s.L.g-1)均较原酶的(2.28 s-1、1.15 s.L.g-1)高,修饰酶催化水解反应的活化能Ea(25.4 kJ.mol-1)较原酶的(29.3 kJ.mol-1)低;PA修饰还明显提高了酶的pH稳定性和热稳定性,半衰期t1/2延长,酶分子的热变性活化能Ea,d由77.0 kJ.mol-1提高到94.5 kJ.mol-1.可见PA化学修饰法是一种有效改善木瓜蛋白酶的催化性质和稳定性的方法.     

Transfer reaction of the polystyrene radical with electron-acceptor molecules of tetrachlorophthalanhydride

The transfer constants (C_s) of the polystyrene radical with some derivatives of phthalic acid have been determined. Among the agents used, tetrachlorophthalanhydride (TCPA) differs distinctly from other compounds by its value of C_s 3·1 × 10^?3 for thermal and 3·4 × 10^?3 for initiated polymerization of styrene. The values of C_s for phthalanhydride, dimethyl phthalate, and tetrachlorodimethyl phthalate are lower by two decimal orders. The considerable decrease in the degree of polymerization of styrene prepared in the presence of TCPA is mainly attributed to the increased reactivity of chlorine atoms in TCPA induced by the acceptor effect of anhydride ring. Participation of a TCPA-styrene complex in transfer reaction has been assumed but not proved.     

The use of HPLC for the analytical determination of diisocyanates and acid anhydrides in the air of working environments

Abstract

Measurements of airborne concentrations of (monomeric) 2,4- and 2,6-toluene diisocyanate (2,4- and 2,6- TDI), 4,4′ - diisocyanato diphenylmethane (MDI) and phthalic anhydride have been performed at 17 Danish manufactories using these compounds in the production of polyurethane foams, insulating materials, elastomers, coatings, lacquers and glues.

Diisocyanate vapours at workplaces were collected in impingers, containing a solution of 9-(N-methylaminomethyl)-anthracene (1 × 10^?4 M) in toluene. By reaction with this amine compound the diisocyanates are converted to stable urea derivatives. Phthalic anhydride particles were collected on glass fiber filters.

For separation and detection of the diisocyanate derivatives and the phthalic acid formed upon hydrolysis of its anhydride, reversed phase high performance liquid chromatography on a bonded octadecylsilyl phase using isocratic elution with acetonitrile/water and UV-monitoring at Λ = 254 nm were used. The results obtained for each manufactory are presented.     

Fluorescent-tagged block copolymer as an effective and green inhibitor for calcium sulfate scales

Allyloxy polyethoxy ether (APEG) and succinic anhydride were used to prepare allyloxy polyethoxy carboxylate (APEL). 8-Hydroxy-1,3,6-pyrene trisulfonic acid trisodium salt (PY) was reacted with allyl chloride to produce fluorescent monomer 8-allyloxy-1,3,6-pyrene trisulfonic acid trisodium salt (PA). APEL and PA were copolymerized with maleic anhydride (MA) to synthesize PA tagged no phosphate and nitrogen free CaSO₄ inhibitor MA–APEL–PA. Structures of PA, APEG, APEL, and MA–APEL–PA were identified by ¹H NMR. The observation shows that the dosage of MA–APEL–PA plays an important role on CaSO₄ inhibition. The effect on formation of CaSO₄ was investigated with scanning electron microscope (SEM) analysis. Relationship between MA–APEL–PA’s fluorescent intensity and its dosage was studied. Correlation coefficient R ² of MA–APEL–PA fluorescent intensity and MA–APEL–PA dosage is 0.9991.     

o-Nitrobenzoyl group as a new amino protecting group for peptide synthesis and the synthesis of some anthranilyl peptides

N (o-nitrobenzoyl)amino acids can be coupled with other amino acids using DCC and the resulting product on hydrogenation gives peptides, containing the anthranilyl group as —NH₂ end group. N (anthranilyl)amino acids or peptides can also be obtained by reaction of isatoic anhydride on amino acids or peptides. The anthranilyl end group is easily cleaved by metal (Cu⁺²) catalysed hydrolysis to give α-amino acid peptides and the insoluble copper(II) anthranilate.     

Distorted-wave calculations for the three dimensional chemical reaction H + H2(v ⩽ 2, j = 0) → H2(v′ ⩽ 2, j′, mj) + H

Calculations of the vibrational—rotational product state population distributions and differential cross sections for the chemical reaction H + H₂(v ? 2, j = 0) → H₂(v′ ? 2, j′, m_j) + H have been carried out on the Porter—Karplus potential energy surface. The vibrationally-adiabatic-distorted-wave (VADW) method has been used. The relative rotational product distributions, differential cross sections and the helicity m_j, dependences of these quantities for the v = 0 reaction agree well with accurate close-coupling results. The absolute integral cross sections are considerably smaller than the accurate quantum values, however. The calculations for the v = 1 reaction agree with the findings of previous sudden quantum, limited close-coupling and quasiclassical theoretical studies and experiments that product H₂(v′ = 1) is more likely to be produced than H₂(v′ = 0). For the reaction with v = 2, it is found that at high translational energies product H₂(v′ = 2) is favoured over H₂(v′ = 1) or H₂(v′ = 0). The VADW differential cross sections for the v = 1 and v = 2 reactions have a similar shape to those of the v = 0 reaction, with backward peaking when summed over all m_j states. The relative rotational distributions for the v = 2, j = 0 → v′ = 2, j and v = 1, j = 0 → v′ = 1, j reactions are also similar to those obtained for the v = 0, j = 0 → v′ = 0, j reaction, with low rotational excitation.