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     

Thermoplasticization of wood. II. Cyanoethylation

Cyanoethylation was attempted to convert wood into thermoplastic material as a means to utilize low quality wood species as well as wood waste materials. Cyanoethylation reaction was conducted with control of the alkalinity of the reaction media, reaction temperature and time, and wood-to-acrylonitrile ratio. Cyanoethylated wood was purified and its nitrogen content and weight gain were determined. Fourier transform infrared (FTIR) spectroscopy was used to monitor the absorption peak of cyano group. Thermoproperties of cyanoethylated wood were analyzed by means of a differential scanning calorimeter (DSC) and a dynamic mechanical thermal analyzer (DMTA). Reaction mechanisms and chemistry influencing the thermoproperties of cyanoethylated wood were discussed.     

Kinetics of heterogeneous cellulose reactions. I. Cyanoethylation of cotton cellulose

Sakurada's equation and fundamental kinetic laws were applied to the heterogeneous cyanoethylation of cellulose, performed by reacting fiber with liquid acrylonitrile, with sodium hydroxide as the catalyst. The data fit Sakurada's equation better at higher temperatures; deviation occurs at the initial stage, and the rate of reaction falls abruptly at a later stage. The degree of substitution at which the abrupt rate change occurred decreased as the temperature increased from 31 to 60°C. and also as the crystallinity of the fiber decreased. Diluting the reagent with different solvents decreased the rate of reaction and changed its transition points, but did not change the essential nature of the reaction, each segment of which fits Sakurada's equation very well. A uniform distribution of the catalyst (sodium hydroxide) throughout the fiber was attempted, and then the reaction was studied at 50°C. Diffractograms of the samples provided further evidence that the position of the rate change is associated with the change of cellulose (I) crystalline structure. Approximate energy of activation has been calculated, from the specific rate constants, between 31 and 40°C. as 10.6 kcal. and between 45 and 50°C. as 16.7 kcal. At other temperatures the determination was handicapped, due to temperature dependence of the order of reaction. An empirical relation between the constants of Sakurada's equation and the reaction temperature has been sought and correlated with the Arrhenius equation. Energies of activation, determined from this relationship, have been found to be very close to the above values. The change of order of reaction with temperature suggests that the reaction is affected by diffusion and the mechanism is interpreted as a diffusion-controlled reaction where hydrogen bonds play a significant role in diffusion.     

Cover Picture: Angew. Chem. Int. Ed. 13/2002

The cover picture shows benzoborirene, the product of the crossed‐molecular‐beam reaction between benzene molecules and boron atoms, displayed above the three‐dimensional plot of the angular‐ and translational‐energy‐dependent flux of the benzoborirene molecules in the center‐of‐mass system. As the reaction conditions preclude secondary collisions, the intermediate initially formed from the reactive collision decays by ejection of a hydrogen atom. The structure of the benzoborirene depicted is based on a DFT computation, which, combined with results of highly accurate coupled‐cluster calculations has been used to assign the reaction product by comparing experimental and theoretical reaction energies. Details are described by R. I. Kaiser and H. F. Bettinger on p. 2350 ff.     

Alkoxylation of hydridophosphorane. II. Reaction of hydridophosphorane with benzenesulphenic esters

The spirophosphorane 4 underwent reaction with a series of benzene-sulphenic esters 3 to give the corresponding isolable alkoxyphosphoranes. The reactivities of benzenesulphenic esters 3 in this reaction were seen to be dependent on steric hindrance of the R groups. The yields of alkoxyphosphoranes were influenced by the reaction temperature. The probable mechanism was suggested in terms of experimental observations.     

Bromothiophene reactions. I. Friedel-crafts acylation

Friedel-Crafts acylation of 2,5-dibromo- and 2,3,5-tribromothiophenes with different acyl chlorides and anhydrous aluminium trichloride has been studied. The reaction afforded a mixture of acyl derivatives and tetrabromothiophene. The results obtained suggest a mechanism which involves the formation of bromine cations in the reaction medium. Several products obtained in this reaction are described.     

Diazepines. V. The reaction of homophthalic anhydride with hydrazines

The reaction of homophthalic anhydride with hydrazine and a number of substituted hydrazines has been investigated. Only in the case of the reaction of homophthalic anhydride and 1,2-dimethylhydrazine has a diazepine been isolated. The previously reported (2) diazepine from homophthalic anhydride and hydrazine appears to be a product resulting from the reaction of twomolec of homophthalic anhydride with one mole of hydrazine.     

Polymer reactions. IV. Thermal decomposition of polypropylene hydroperoxides

The thermal decomposition of polypropylene hydroperoxide (PPH) consists of two consecutive reactions. The initial, faster reaction has rates up to 60 times that of the slower process. The former is largely suppressed by the addition of an excess of 2,6-di-tert-butyl-p-cresol. The course of reaction is the same in either solid state or in solution. The results are consistent with an intramolecular radical-induced mechanism for the initial reaction. This faster reaction consumes about 70–95% of the total hydroperoxides. The decomposition of PPH yields a maximum of about 1.8 radicals. Samples prepared from crystalline and amorphous polypropylenes have identical decomposition kinetics.     

Acylation and related reactions under microwaves. 4. Sulfonylation reactions of aromatics.

Solvent-free sulfonylation of benzene and its activated or deactivated derivatives were carried out under microwave (MW) irradiation and a catalytic amount of iron(III) chloride, which, under these conditions, is more active than other metallic salts. With more reactive and/or nonvolatile reagents (anisole, xylenes, mesitylene) expeditious conditions (short reaction time at constant MW power without control of the temperature) were used. With less reactive and/or low-boiling reagents (benzene, toluene, halobenzenes), the rise in temperature and the increase of reaction time were controlled either by sequential MW irradiation or by a temperature order. It was shown that MWs cause preferential interactions with polar species present in the reaction, especially the aryl sulfone and its FeCl3-complexed form. A MW nonthermal effect was not observed when identical temperature gradients were produced by classical heating and MW irradiation, and if reaction temperature was strictly controlled.     

Addition reactions of heterocycles. VII. Pyrrole and C-Acetyl-N-phenylnitrilimine

The addition reaction of C-acetyl-N-phenylnitrilimine to pyrrole has been investigated. The products obtained show that the reaction proceeds via two distinct pathways. The 1,3-addition reaction leads to the non-cyclic-adduct III, whereas the 1,3-cycloaddition reaction gives a mixture of regioisomeric Δ₂-pyrroline IV and V, and Δ₁ -pyrroline VI and VII mono-cycloadducts. These latter compounds cannot be isolated because they undergo a further 1,3-cycloaddition reaction leading to the N-substituted bis-adducts X and XI, and to the bis-adduets XII and XIII. The stereochemical assignment for X, XI, XII and XIII is provided by nmr data which suggest also that in X and XI the rotation around the exocyclic N-C bond is relatively slow on the instrument time scale.     

Solvent effects on methyl transfer reactions. 2. The reaction of amines with trimethylsulfonium salts.

The reaction of ammonia and pyridine with trimethylsulfonium ion has been studied in gas phase and solution. Density functional theory at the B3LYP/6-31+G level was used to describe the energy changes along the reaction coordinate in the gas phase, and the self-consistent isodensity polarizable continuum model (SCI-PCM) was used to calculate the effect of cyclohexane and dimethyl sulfoxide as the solvent on the energy changes. The effect of water as the solvent was studied using the Monte Carlo free energy perturbation method. The reaction with both ammonia and pyridine follows a similar rather convoluted path in gas phase, with the formation of several reaction complexes before and after the formation of the transition state. All the species found in gas phase persist in cyclohexane, yielding a reaction path very similar to that in gas phase but with significant differences in the relative energy of the critical points. In DMSO, the energy profile is greatly simplified by the disappearance of several of the species found in gas phase and in cyclohexane. The activation free energy increases with the polarity of the solvent in both reactions. Increasing the polarity of the solvent also increases the exothermicity of the reaction of trimethylsulfonium ion with ammonia and reduces it in the reaction with pyridine. In water, the free energy profile follows the same trend as found for DMSO, and free energy of activation is calculated to be larger by about 2-3 kcal/mol. This is in good agreement with an experimental measurement of the effect of solvent on the rate of reaction.     

Diffusion-controlled reaction. VI. Radiation graft polymerization of styrene to polyethylene

The radiation graft polymerization of styrene to polyethylene was studied under diffusion-controlled conditions of radiation intensity I, monomer concentration M₁, and polymer sample thickness L. The results of the present study together with previous work under diffusion-free conditions verify our theoretical model for the diffusion-controlled reaction. The grafting rate is inverse first order in L for diffusion-controlled reaction and independent of L for diffusion-free reaction. The order of dependence of grafting rate on radiation intensity for diffusion-controlled reaction is one-half that for diffusion-free reaction. Diffusion control leads to a decrease in the order of dependence of grafting rate on monomer concentration. The decrease is greater than theoretically predicted; possible reasons for this effect are described.     

Bioactive Polymers. XXVI. Immobilization of Pepsin on Biozan R

Pepsin was immobilized on BIOZAN R (Hercules) with dicyclohexylcarbodiimide as activator. The reaction product obtained has a protein content of 35–110 mg/g of polymer and a proteolytic activity between 20.85–28.75 μmol tyrosine/L·min·g of polymer). The coupling reaction rate is maximum under the following conditions: pepsin/BIOZAN R ratio = 0.52 g/g, DCCI/BIOZAN R ratio = 0.2 g/g, pH = 3.4, reaction time = 4 h.     

Heterocyclic compounds. X. A new synthesis of thiadiazasteroids

The reaction of ν-ketoacids or ν-aldehydo acids with o-amino amides results in the formation of 4-quinazolones. Using this reaction a number of polyheterosteroid analogs were synthesized. Thus, when 2-amino-3-carboxamido-4,5,6,7-tetrahydrobenzothiophene (9) was refluxed with levulinic acid (10) in a high boiling solvent, thiadiazasteroid analog (11) was obtained in 78% yield. It was found that this facile one-step reaction could be used to synthesize a variety of tetra and pentacyclic compounds. Nmr spectroscopy was used to assign stereochemistry to the 17-methyl “steroids” (31) and (32).     

Reaction of inorganic cyanates with halides. II. Reactions of chlorohydrins

The reaction of ethylene and trimethylene chlorohydrins with cyanate ion in anhydrous dimethylformamide (DMF) forms 2-oxazolidinone and tetrahydro-2H-1, 3-oxazin-2-one, respectively. These are the major products over a wide concentration range, and at initial chlorohydrin concentration of 1 M and lower, the yields are high enough to make the reaction useful for synthesis of oxazine and oxazolidine derivatives. The corresponding reaction with tetramethylene chlorohydrin gave tetrahydrofuran as the major product with the by-products being polymeric. Pentamethylene and hexamethylene chlorohydrins yield linear polyurethanes when allowed to react with cyanate in DMF. Examination of the relative rates of reaction of these chlorohydrins indicate that the mechanism by which urethanes are formed (both cyclic and polymeric) is an S_N2 displacement of chloride by cyanate ion to give an isocyanate intermediate which then reacts with an alcohol group to form urethane.     

Analysis of lipid peroxidation kinetics. 1. Role of recombination of alkyl and peroxyl radicals

The kinetics of the lipid peroxidation reaction is only partly understood. Although the set of reactions constituting the overall reaction are believed to be known, it has not been possible to predict how the reaction will respond to a change of one or more of the parameters, e.g., initial concentrations of reactants or different ways of initiating the reaction, nor has it been possible to predict the time dependence of the products. The reason for these problems is the complicated structure of the kinetic scheme, which includes a chain reaction. In this work we perform an in-depth analysis of the importance of the individual reaction steps, and we introduce a new quasi-stationary concentration method based on the assumption that one or more concentrations vary much slower than the others. We show that it is justified to use a quasi-stationary concentration approximation for the alkyl radical L (*), but not for the peroxyl radicals LO 2 (*) as assumed in previous works. The method allows us to derive manageable analytical expressions. On the basis of literature values of the rate constants, we are able to introduce specific simplifications that allow us to obtain simple analytical expressions for the time dependence of all concentrations involved in the process.     

Thermal decompositions of formates. Part VII. Thermal decomposition of yttrium formate dihydrate

The thermal dehydration of yttrium formate dihydrate and decomposition of yttrium formate anhydride were studied in flowing nitrogen and carbon dioxide atmospheres by means of TG and DTA.The dehydration reaction was not affected by the atmospheric condition and took place successively without any intermediate hydrate. The mechanism of the dehydration reaction was found to be a phase boundary controlled interface reaction.The decomposition of yttrium formate occurred in three stages, and yttrium oxyformate and yttrium oxycarbonate were formed as the intermediate products.In a carbon dioxide atmosphere, the decomposition took place at a higher temperature than in a nitrogen atmosphere.The anhydrous salt melted during the main stage of the decomposition and the kinetic behaviour of this stage was characteristic of a homogeneous first order reaction.     

Chemistry of novolac resins. II. Reaction of model phenols with hexamethylenetetramine

It is proposed that the reactions of hexamethylenetetramine (HMTA) with 2,4-xylenol and with 2,6-xylenol occur by different pathways. The rate of reaction and the final product distribution depend on the initial xylenol : HMTA ratio and are different in the two systems. Measured by HMTA consumption, with 2,4-xylenol the reaction rate increased with increasing xylenol : HMTA ratios, whereas with 2,6-xylenol the rate of reaction decreased with increasing 2,6-xylenol : HMTA ratio. In systems which contain both 2,4- and 2,6-xylenol, a strong preference for reaction of the HMTA with the ortho site of 2,4-xylenol was noted. This preference was apparent even in mixtures in which 2,6-xylenol was present in greater amounts than 2,4-xylenol. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1389–1398, 1997     

Kinetics of polyesterification. II. Foreign acid-catalyzed dibasic acid and glycol systems

Polyesterification of diacid and diol in the presence of the foreign acid p-toluene sulfonic acid as catalyst was carried out under constant reaction temperatures of 140–166°C (rather than at the usual constant oil-bath temperature) and at molar ratios r of diol to diacid of 1.2–3.5. The experimental data obtained do not fit conventional rate equations as they appear in the literature. On the basis of ion pair formation, consideration of proton transfer from acid to alcohol, variation in dielectric constant of the reaction mixture as conversion increases, and inclusion of reverse reaction due to presence of unremoved water, we proposed a reaction mechanism and rate equations. The rate equation fitted our experimental data quite well. In addition the self-catalysis (absence of foreign acid) also showed promise, as confirmed by the experimental data measured under constant reaction temperatures, which appear in Part I.     

Pseudomonas cytochrome c peroxidase. XII. Product inhibition studies.

Kinetic studies of the reaction mechanism of Pseudomonas cytochrome c peroxidase (PaCCP) were made by the method of product inhibition using oxidized cytochrome C (551 P.aeruginosa) and oxidized Pseudomonas azurin as products. Inhibition by the two oxidized substrates was linearly non-competitive towards the respective reduced electron donor and towards hydrogen peroxide. Although a full kinetic analysis is experimentally impossible in a peroxidase-type reaction, the results do provide some evidence in favour of an ordered reaction mechanism in which hydrogen peroxide is the first to add to PaCCP and electron donor the second.