Kinetics of reaction between meta-substituted long chain alkyl phenols and formaldehyde

The reaction between formaldehyde and long chain alkyl phenols as cardanol and 3-pentadecylphenol is found to be of second order, when it is studied in dioxanater (1:1) system in presence of catalyst hydroxide sodium as at 28, 50 and 70°C. Individual methylols were separated and identified by thin layer chromatography. The long alkyl chain in the meta-position of the phenolic nuclei sterically hinders The reactivity of 2-position at 28°C, but at higher temperatures i. e. 50 and 70°C this position gets activated resulting in the formation of various methylols.     

Study of the reaction between resorcinol and formaldehyde

The reactions between resorcinol and formaldehyde were led in aluminium pans of a d.s.c. Perkin Elmer calorimeter. The products were separated by means of high performance liquid chromatography and identified by ¹H and ¹³C n.m.r. Depending on the catalyst concentration and molar ratio the mixtures reacted at two different temperature ranges, 317–332K and 332–366K. The heat of the reaction in the first temperature range was between 16.8 and 45.0 kJ mol^?1 for molar ratios 1:1 and 1:3 respectively. By ¹H and ¹³C n.m.r. spectroscopy five addition products were determined. The reaction heat in the second temperature range was 73.5 kJ mol^?1 and was attributed to condensation reactions. The activation energies were 95.0 and 120.0 kJ mol^?1 for addition and condensation reactions respectively. For addition, order two and for condensation, order one of reaction was established. On the basis of these foundings tentative reaction schemes were prepared.     

核桃壳木质素与甲醛反应能力的研究

为富含木质素的林果资源废弃物——核桃壳全壳制备胶粘剂提供依据。利用~1H-NMR对核桃壳磨木木质素(MWL)基本特性进行研究的基础上,着重研究了碱性条件下,核桃壳MWL与甲醛在不同反应时间和反应温度下的反应能力。研究结果表明,核桃壳木质素属含有较多愈创木基结构单元和酚羟基的愈创木基一紫丁香基型(GS型)木质素,它在碱性条件下与甲醛具有较好的反应能力,且其反应能力受反应时间和反应温度的影响较大,当反应时间为1h左右、反应温度在75～95℃之间时是比较合理、可行的。     

Study on the reaction between bisphenol A and dimethyl carbonate over organotin oxide

Organotin oxide was used to catalyze the reaction between BPA (bisphenol A) and DMC (dimethyl carbonate), and Ph₂SnO (diphenyltin oxide) displays the excellent catalytic performance in transesterification and O-methylation. However, Bu₂SnO (dibutyltin oxide), (PhCH₂)₂SnO (dibenzyltin oxide) and (C₆H₁₁)₂SnO (dicyclohexyltin oxide) exhibited weaker catalytic activity but higher selectivity for C-methylation product formation. The π–π function between Ph₂SnO and BPA provided more chances for their interaction, and π–d interaction between phenyl ring and Sn resulted in catalyst having higher activity in transesterification and O-methylation. O-methylation product formation over Ph₂SnO comes from transesterification product decomposition not from direct methylation of BPA with DMC.     

Study of the reaction between urea and formaldehyde by dsc and 13C NMR spectroscopy

The reactions of urea with formaldehyde were studied by means of ¹³C NMR spectroscopy and differential scanning calorimetry (DSC) in acid and neutral medium, the temperature range being between 290 and 390 K. At higher pH the peak of the DSC curve splits into two peaks one of which belongs to the addition of formaldehyde to urea and the second to the subsequent condensation of the latter. For both reactions, the activation energy, heat of polymerization, reaction order and temperature maximum have been determined. The usefulness of DSC to study the kinetics of more complex polycondensation reactions was established.     

Kinetics of the reaction between urea and formaldehyde in the presence of sulfuric acid

The kinetics of the reaction between urea and formaldehyde were studied in the presence of various amounts of sulfuric acid (5–45% by weight) at different temperatures (5°, 15°, and 25°C). The reaction was shown to follow first-order kinetics. The activation energy for the reaction varies from 12.51 kcal/mole to 14.59 kcal/mole in the range of sulfuric acid concentration studied.     

DSC and 13C-NMR studies of the imidazole-accelerated reaction between epoxides and phenols

The imidazole-accelerated reaction between epoxides and phenols has been studied through DSC and ¹³C-NMR of model compounds. The selectivity of the accelerator has been found to be strongly dependent on its concentration. If a low amount of accelerator is used, the reaction takes place almost exclusively through the addition of phenols to epoxides even if the latter are used in excess. However, a larger amount of accelerator will cause the secondary hydroxyls (produced by the main reaction) to react with the epoxides. In any case, the lower reactivity of the secondary hydroxyls prevents them from reacting to any significant extent as long as there are any phenols present. When polyfunctional resins are used, the effect of the selectivity of the reaction on the properties of the crosslinked network is very clear. If a low amount of accelerator is used (to promote only the epoxy–phenol reaction), the maximum glass transition temperature (T_g) occurs when the epoxides and phenols are stoichiometrically balanced, reaching 178°C. However, when an excess of epoxides over phenols is used, along with a larger amount of accelarator, the maximum T_g increases its value to 199°C.     

Theoretical kinetic study of the reaction between dimethyl disulfide and OH radicals

The potential energy profile of the reaction between dimethyl disulfide and OH^? radicals is explored by utilizing ab initio and hybrid meta density functional theory methods. Having the energies and structural data of the stationary points, statistical rate theories, such as transition state theory and variable reaction coordinate-transition state theory, are employed to compute the overall rate constants, and discuss the mechanism and product channels. On the basis of the calculations, the overall rate coefficient is predicted to be 2.49?×?10^?10?cm³?molecule^?1?s^?1 at 298?K. It is found that in the most favorable pathway, the reaction proceeds via formation of the relatively unstable intermediate CH₃S^?(OH)SCH₃ decomposing rapidly to yield CH₃S^?+CH₃SOH.     

Study of the reaction of resorcinol,formaldehyde, and ammonia

Latex dip adhesives for nylon and rayon tire cords are prepared by reacting resorcinol and formaldehyde in aqueous solution in the presence of a catalyst for a specified time and then adding a butadience–styrene–vinylpyridine latex. Ammonia improves the stability of the latex and increases the adhesion of rubber to cord. However, a white precipitate forms if ammonia is added before the resorcinol and formaldehyde have reacted sufficiently. This paper is study of the nature of this precipitate and the conditions for its formation. By measuring the heat of reaction of formaldehyde and ammonia and, subsequently, of mixtures of formaldehyde and resorcinol to which varying amounts of ammonia were added, information on the reaction mechanism has been obtained. Ammonia reacts rapidly with formaldehyde to form an unstable intermediate, presumably trimethylolamine, which then reacts further with resorcinol to form trisdihydroxybenzylamine. This compound is also very reactive and condenses withmore ammonia and formaldehyde to give a polymer of low solubility, the composition depending on the amounts of ammonia and formaldehyde available for reaction. Elemental analyses support this concept. Primary and secondary amines react in a maner similar to ammonia.     

脲醛树脂的固化研究

通过缩聚法制备出脲醛树脂,考察了制备单组分固化剂NH4C l、2%HC l、5%的H3PO4、H2O2及双组分固化剂NH4C l和2%HC l、NH4C l和5%H3PO4的使用条件,并确定了复合固化剂的配比和用量。发现双组分固化剂固化时间适宜,固化效果好。     

Anodic behaviour of silver in alkaline formaldehyde

Steady state potentiostatic polarization studies on the system Ag/HCHO, KOH reveal that the mechanism of anodic process is potential dependent. Direct oxidation of free formaldehyde (obtained as a result of the dissociation of hydrated formaldehyde) occurs at high anodic potentials range resulting in a limiting current plateau. Near the base potential region, on the other hand, the rate controlling electrochemical step appears to be the oxidation of the silver which is followed by a chemical reaction in which formaldehyde is oxidized. Results obtained from the accelerated Tafel plots on the mechanism in the base potential region are in agreement with Vielstich's earlier observations.     

Study of the oxygen electroreduction at nanostructured PtBi catalysts in alkaline medium

Nanostructured Pt_1−xBi_x/C electrocatalysts (x from 0 to 0.3) are prepared via a microemulsion method. The electroactivity of the catalysts towards oxygen reduction reaction (orr) is investigated. The following order of catalysts for electrochemical activity towards orr is obtained: Pt_0.8Bi_0.2/C > Pt_0.9Bi_0.1/C > P/C > Pt_0.7Bi_0.3/C. RDE and RRDE experiments indicate a four-electron reduction reaction mechanism in the low overpotentials region with all Pt_1−xBi_x/C electrocatalysts, whereas, at higher overpotentials a two-electron mechanism producing hydrogen peroxide co-exists with the four-electron mechanism producing water. Two Tafel slopes are obtained for all catalysts. In the low overpotentials region all Bi-containing catalysts display Tafel slopes close to −60 mV decade⁻¹, against −80 mV decade⁻¹ for pure platinum. In the high overpotentials region, the Tafel slopes are close to −120 mV decade⁻¹, except for the Pt_0.7Bi_0.3/C for which a Tafel slope close to −100 mV decade⁻¹ is observed. Results are explained in terms of protection of platinum surface from oxidation by the presence of more easily oxidizable species, leading to shift the reduction wave of 20-30 mV towards higher potentials, while the platinum surface coverage by bismuth oxides species leads to decrease the accessible platinum sites and further the orr kinetics. At last, the higher tolerance of a Pt_0.8Bi_0.2/C catalyst to the presence of ethylene glycol is demonstrate, as well as its higher performance as cathode catalyst under direct ethylene glycol solid alkaline membrane fuel cell working conditions.     

甲醇和甲醛催化合成聚甲氧基二甲醚

聚甲氧基二甲醚作为柴油添加剂,可以提高柴油的十六烷值(CN),提高燃油的利用率,作为甲醇大宗下游产品具有广阔的应用前景。在固定床管式反应器中,以改性大孔阳离子交换树脂为催化剂,在温度40～100℃、液相空速1.32～16.37 h^-1、甲醛/甲醇摩尔比1～4和反应压力0.1～3.0 MPa下,以单因素实验和正交实验相结合的方式,系统地研究了甲醛与甲醇缩醛化工艺条件,获得了较佳的工艺条件,在温度70℃、甲醛/甲醇摩尔比3:1、液相空速1.32 h^-1、反应压力2.0 MPa的条件下,甲醇的转化率为69.72%,DMM_3-8选择性为62.08%。     

Selectivity to N-mono or dialkylation in the reaction of aniline with dimethyl carbonate on faujasite,EMT and beta alkaline zeolites

Zeolite K-EMT is as active and selective to N-mono methylation as K–Y in the alkylation of aniline with dimethyl carbonate at 408 or 453 K. No C-alkylation occurs in the temperature range studied. At 503 K, K-X and Cs-X are about 75% selective for dialkylation to N,N-dimethylaniline with about 97% conversion.     

邻甲酚醛环氧树脂合成中的醚化反应研究

苄基三乙基氯化铵作为邻甲酚醛(OCN)环氧树脂合成中醚化反应的相转移催化剂(PTC),用量PTC/OCN(摩尔比)为1∶200,醚化反应最佳时间为1 h。     

Durability of carbon-supported manganese oxide nanoparticles for the oxygen reduction reaction (ORR) in alkaline medium

MnO_x/C-based electrocatalysts, prepared by the chemical deposition of manganese oxide nanoparticles on carbon, were tested towards the Oxygen Reduction Reaction (ORR) in their as-synthesized state and after ageing, either in ambient air for a year (mild ageing) or in an O₂-saturated molar KOH solution at 80 °C for three weeks (premature ageing). For each electrocatalyst, the morphology and composition were characterised using TEM, XRD and chemical analysis. ORR kinetic parameters were evaluated using the Rotating Disk Electrode (RDE) and Rotating Ring Disk Electrode (RRDE) setups. Whilst the oxygen reduction activity of the electrocatalysts barely changes after mild ageing, it decreases after premature ageing following dramatic modifications to both the chemical and crystalline structures of the carbon-supported MnO_x nanoparticles. The peroxide yield also sharply increases after premature ageing. Doping MnO_x/C with nickel or magnesium divalent cations is beneficial since it improves both the catalytic activity and selectivity towards the 4-electron ORR pathway, even after ageing.     

碳酸二甲酯甲基化反应催化剂和反应机理研究进展

碳酸二甲酯(DMC)作为一种绿色化学试剂,因其分子中含有多种活泼的官能团,可取代卤代甲烷、硫酸二甲酯等甲基化试剂被广泛应用于有机合成中。综述了近年来DMC作为甲基化试剂与相应化合物发生甲基化反应的研究进展,重点对甲基化反应的催化剂、可能的反应机理等进行了介绍和分析。基于目前的研究现状,提出了DMC作为甲基化试剂今后研究和发展的主要方向。     

DOPO与邻甲酚醛环氧树脂反应特性的研究

通过环氧值滴定和红外光谱研究反应型含磷阻燃剂(DOPO)与邻甲酚醛环氧树脂的反应特性,确定其最佳反应条件。实验结果表明:120℃下添加20%催化剂三苯基膦,反应120 min可获得最佳效果。红外谱图进一步确认DOPO与邻甲酚醛环氧树脂反应进行的程度及DOPO含磷环氧树脂的初步结构。采用DTA分析方法研究DOPO与邻甲酚醛环氧树脂的反应动力学,测得DOPO与邻甲酚醛环氧树脂反应的动力学参数lnA0为58.63,表观活化能E为298.51 kJ/mol,反应级数n为0.97。