Thermoplasticization of wood. I. Benzylation of wood

A study of converting wood into thermoplastic materials was undertaken to develop a new technique in effective utilization of wood wastes. Thermoplasticizatoin of wood carried out by means benzylation. Various reaction parameters, such as alkalinity of reaction media, reaction temperature, and time were taken into account to produce benzylated wood with different degrees of substitution (based on weight gain) FTIR, DSC, DMTA, SEM and x-ray crystallography were used to characterize the chemical and mechanical properties of benzylated wood. Experimental data showed that preswelling and reaction temperature had critical effects on benzylation reaction. Lignin in wood appeared to inhibit benzylation but extractives had little effect. Different species showed some variation in reaction rates. The thermoplasticized wood exhibited good melting properties and were readily molded into bulk materials or extruded into films and sheets. A wide range of glass transition temperatures from 66 to 280°C for the benezylatedwoods was achieved, and they were larely dependent on the weight gain. The molded and extruded products exhibited acceptable mechanical strength for structural engineering applications. The property and structure relationship for the thermoplasticized wood were discussed     

基本化学反应形式的系统分类

The old classification of basic chemical reactions was evaluated and a new systematic classification of basic reactions was proposed.In the new classification,all the chemical reactions were divided into oxidation-reduction reactions and non-oxidation-reduction reactions,and both can be divided into combination reaction,decomposition reaction and replacement reaction,respectively.In addition,a new class of basic reactions,the complicated decomposition reaction,was appended to reaction system.     

不同类型无机磷试剂辅助下苯丙氨酸自组装成肽反应的研究

该文以三氯化磷(PCl3)、三氯氧磷(POCl3)和环三聚磷酸(P3M)为辅助试剂,进行了苯丙氨酸(Phe)自组装成肽反应的研究,利用液相色谱-质谱联用以及电喷雾多级质谱技术对反应体系组分进行了分析和结构鉴定。考察了不同缩合试剂和反应时间对苯丙氨酸成肽反应的影响,并初步探讨了无机磷试剂辅助下芳香侧链氨基酸的成肽机理。反应中有Phe系列寡肽生成,同时也有少量环肽存在。该研究可为寡肽的合成工艺开发提供参考,同时对于研究生命起源中的前生命化学物质有着重要的理论意义和学术价值。     

Complexation of benzoannelated porphyrazines with magnesium(II) acetate in pyridine

The reaction of complex formation of magnesium with benzoannelated trifluoromethylphenylporphyrazines in pyridine was studied and its kinetic parameters were determined. The reaction mechanism was proposed. The successive introduction of benzene rings into a porphyrazine molecule was shown to decrease the rate of complex formation reaction.     

Theoretical and Experimental Studies on the Reaction Mechanism of Cl2 ＋ I2- 2ICl

1 INTRODUCTION The reactions between halogen and halogen are basic reactions in chemistry. Especially, in the syn- thesis of iodo-substituted aromatic hydrocarbon, the reaction Cl2 I2 = 2ICl could heighten the usage of iodine atom to 100%. So far, to the best of our know- ledge, the studies about halogen-halogen reaction mechanisms are very few. In detail, only the struc- ture and stability studies of X2Y- (X, Y = Cl, Br and I) ions by calculating reaction potential energy sur- face…     

The photokinetics of phenothiazine dyes with titanium trichloride in different solvents

The kinetic parameters of photoinduced electron transfer reaction of two phenothiazine dyes, methylene blue and methylene green with titanium trichloride, were determined in water and different aqueous-alcoholic solvents at different acidities by using a specially designed optical system. The rate of photoinduced electron transfer reaction was measured by determining the quantum yield of the reaction. The methylene green had a higher reactivity as compared to methylene blue with titanium trichloride. The graphical analysis showed that the reaction of dye with titanium trichloride follows pseudo–first-order kinetics. A reaction mechanism was proposed by considering the different excited states of dye and their possible interaction with the solvent and titanium trichloride. The different steps in the reaction mechanism were taken into consideration for deriving rate equations, which were used to determine the different rate constants in the reaction mechanism in different solvents.     

Kinetics and Mechanism of Acid-Catalyzed 2,5-Xylenol-Formaldehyde Reaction

This paper deals with kinetic studies of the 2,5-xylenol and formaldehyde reaction catalyzed by hydrochloric acid. The catalyst concentrations used were 0.008, 0.012, 0.02, and 0.04 N. The investigations were carried out at 65, 70, 75, and 80°C. It was observed that the reaction follows a second-order rate law. The rate of reaction was found to increase with an increase in acid concentration. The overall rate constant was resolved into stepwise rate constants. It is a two-step reaction, the second step of the reaction being a rapid follow-up of the first step. Activation parameters for the overall reaction have been calculated, and a mechanism conforming to the experimental observations is suggested.     

Effect of phase transfer chemistry, segmented fluid flow, and sonication on the synthesis of cinnamic esters

Wittig reaction under Phase Transfer conditions was performed in a flow reaction system. Different bases, aldehydes, phosphonium salts, and flow reaction parameters were investigated, in absence of a phase transfert catalyst. An improvement of the reaction outcome (yield and reaction time) was achieved through the immersion of the reactor into an ultrasound bath.     

Charge-transfer polycondensation of diethyl chelidonate with hexamethylenediamine

Polycondensation of diethyl chelidonate (DEC) with hexamethylenediamine (HMD) took place very rapidly under mild conditions to form a corresponding polyamide. The polycondensation reaction proceeded through the formation of a charge-transfer complex between DEC and HMD, which transformed rapidly into polyamide. Various reaction conditions to form polyamide from DEC and HMD were investigated in terms of solvents, concentration, and temperature. Model reaction of DEC with primary or tertiary amines confirmed the formation of a charge-transfer complex which transformed into chelidonamide except tertiary amine. The polycondensation of DEC with HMD was accelerated by irradiation with light.     

Exploring the lowest energy triplet potential energy surface for cyclic C4H4 isomers with the complete basis set ab initio method. Is the transformation of triafulvene into cyclobutadiene possible in their excited states?

High level computational studies were performed with the aim being to explore the possibility of converting the experimentally available triafulvene into the hard-to-detect cyclobutadiene. The method is based on the simple approach used to excite triafulvene into the triplet state, and then through various reaction channels, come to the aromatic triplet cyclobutadiene. Triplet cyclobutadiene is only a few kcal/mol higher in energy than singlet cyclobutadiene and should be easily relaxed into the latter. Several reaction pathways that include only a concerted mechanism, as well as reaction pathways that include the radical formation–recombination were also explored. Some possible approaches for experimentally obtaining the singlet or triplet cyclobutadiene were suggested.     

微波-炭还原法处理一氧化氮的研究

报道了一种不需要催化剂而直接采用微波-炭还原技术处理-氧化氮(NO)的新方法.讨论了气体流量、反应温度、微波功率和施加微波时间对活性炭与一氧化氮发生还原反应的影响.比较了连续施加微波和间歇式施加微波方式下一氧化氮与活性炭发生化学反应转化为无公害的氮气(N₂)和二氧化碳(CO₂)的效率.研究结果表明,微波功率和反应器的类型及升温速率对一氧化氮与活性炭反应效率的影响较大.在连续施加微波时,一氧化氮与活性炭反应率可达98％以上.此外,还对一氧化氮与活性炭反应后的产物进行了表征.     

A spectroscopic investigation into the reaction of sodium tetrathionate with cysteine

A spectroscopic investigation into the reaction of sodium tetrathionate with cysteine at pH 5 both at the boil and at room temperature has been carried out. The Raman and infrared spectra of the model compounds cysteine, cysteine-S-sulfonate, cysteine-S-thiosulfonate, sodium thiosulfate and sodium sulfite were also obtained and vibrations involving the sulfur atoms were analyzed in detail. These results were utilized in the interpretation of the spectra obtained from tetrathionate-cysteine reaction mixtures. The reaction supernatants were analyzed by high performance thin layer chromatography while the precipitates were analyzed gravimetrically. It was found that during the reaction, the thiol groups of cysteine are oxidised to give predominantly cysteine-S-sulfonate. Cystine was also detected but was determined gravimetrically to be a minor reaction product. No significant amounts of cysteine-S-thiosulfonate were detected. The reaction is accompanied by the formation of elemental sulfur and a small amount of sulfite. Major reaction pathways are put forth that are consistent with the experimental data.     

Effect of the reactants molar ratio on the kinetics of cycloaddition of 2,3-dimethylbuta-1,3-diene to allyl methacrylate

The cycloaddition reaction between 2,3-dimethylbuta-1,3-diene and allyl methacrylate proceeds by the second order kinetics. The rate constants increase with the increase in the excess of one of the reactants. The change in the effective rate constants is described by the Michaelis-Menten equation indicating that the reaction proceeds through the initial equilibrium stage of formation of an intermediate complex which then transforms into the product. The effective rate constants, the equilibrium constants of formation of the intermediate complex, and the rate constant of its transformation into the reaction product were determined, as well as the thermodynamic parameters of the formation of the intermediate complex and the activation parameters of the transformation of the intermediate complex into the product. The limiting stage of the reaction is established and its mechanism is suggested.     

Direct oxidative conversion of alkyl halides into nitriles with molecular iodine and 1,3-diiodo-5,5-dimethylhydantoin in aq ammonia

Various benzylic halides were smoothly and directly converted into the corresponding aromatic nitriles in high yields using molecular iodine and 1,3-diiodo-5,5-dimethylhydantoin, respectively, in aq ammonia. Similarly, primary alkyl halides were also converted into corresponding nitriles in moderate to good yields using molecular iodine and 1,3-diiodo-5,5-dimethylhydantoin in aq ammonia, although a long reaction time was required. The present reaction is a new method for the preparation of aromatic nitriles from benzylic halides and a new method for the conversion of alkyl halides into corresponding nitriles with retention of the number of carbon atoms.     

Synthesis of modified DNA by PCR with alkyne-bearing purines followed by a click reaction

Alkyne-bearing deazapurine triphosphates were prepared and successfully incorporated into DNA using the polymerase chain reaction (PCR). The obtained alkyne-labeled DNA was successfully used in a click reaction with galactose azide.     

乙醛-乙烯醇、乙烯酮-乙炔醇异构化研究

1989年,Kresge等人发现溶液中苯炔醇的酸性比苯烯醇高7pK_α,这引起理论和实验化学家的兴趣.Smith等人曾对一对典型炔醇(CHCOH)和烯醇(CH_2CHOH)的生成反应的热效应进行理论研究,本文进一步从理论上研究了这一对反应(反应(1)、(2))的反应机理。     

Zinc-mediated carbon radical addition to glyoxylic imines in aqueous media for the synthesis of alpha-amino acids

The addition of carbon radicals to glyoxylic imines was studied using zinc dust as a radical initiator. The zinc-mediated radical reaction of glyoxylic oxime ethers and hydrazones proceeded smoothly to give the alkylated products via a carbon-carbon bond-forming process in aqueous media. The reaction of the oxime ethers and hydrazones having an Oppolzer's camphorsultam group provided the corresponding alkylated products, which could be converted into enantiomerically pure alpha-amino acids. The diastereoselectivities observed in the reaction of hydrazones were better than those obtained in the reaction of oxime ethers.     

A palladium-catalyzed glycosylation reaction: the de novo synthesis of natural and unnatural glycosides

A highly stereoselective and sterospecific palladium-catalyzed glycosylation reaction of a variety of alcohols is reported. The reaction selectively converts alpha-2-substituted 6-carboxy-2H-pyran-3(6H)-ones into alpha-2-substituted 6-alkoxy-2H-pyran-3(6H)-ones with complete retention of configuration and similarly converts the pyranones with beta-carboxy groups into pyranones with beta-alkoxy groups. The reaction works equally well with both amino acid- and carbohydrate-based alcohols. To demonstrate the utility of this process for carbohydrate chemistry several of the products were selectively converted into alpha-manno-pyranosides in two additional steps. Because the 2-substituted 6-carboxy-2H-pyran-3(6H)-ones are prepared by asymmetric synthesis, this reaction can be used for the preparation of either d- or l-pyranones.     

Isomerization reaction of 1,1,2,2-tetrafluorethan on fluorinated chromia: A consideration of the adsorption behavior on the catalyst

Adsorption of HF is a crucial step in the course of heterogeneously catalyzed reaction of chlorocarbons with gaseous HF. Hence, the adsorption equilibrium of HF and haloalkanes involved in the isomerization reaction of 1,1,2,2-tetrafluoroethane into 1,1,1,2 tetrafluoroethane on the catalyst surface has been studied in detail. By evaluation of the measured reaction data using the partial differential equation of isomerization expanded for variant orders to take into account influence of the adsorption the reaction order of HF was found to be zero in all stages, that of trifluoroethylene decreases from 1 to 0.5 for the reaction to 1,1,1,2 tetrafluoroethane, all others remain essentially one. Based on experimentally determined adsorption isotherms, the cell theory of adsorption allowed the extrapolative calculation of the adsorption isotherms for both isomers of tetrafluoroethane, trifluoroethylene and HF for a wide range of temperature. The formation of a pre-adsorption layer of HF at the chromia surface is in agreement with the reaction order (0) for HF. From these results, conclusions were drawn regarding the reaction mechanism of the isomerization reaction of 1,1,2,2 tetrafluoroethane.     

Preliminary Study of a Potential Post-Column Photodegradation Reaction Scheme for the Detection of Organophosphorus Compounds

Abstract

The photodegradation of organophosphorus compounds has been studied using triethylphosphate as a model compound, A 150 W xenon lamp was used in conjunction with ammonium peroxydisulfate to achieve high yields of orthophosphate in a 100-second irradiation time. The effects of the pH of the reaction medium and the initial concentrations of a peroxydisulfate and triethylphosphate on the extent of reaction were determined. A survey of potential interferences was performed, Copper (II) ion was found to catalyze the reaction, The effect of varying the Cu (II) concentration and the pH dependence of the catalyzed reaction were determined, Organic solvents were found to interfere with the photo degradation, but the reaction shows good potential for incorporation into a post-column detection system for the liquid chromatographic determination of organophosphorus compounds where totally aqueous mobile phases can be used.