Rate of formation of N-(hydroxymethyl)benzamide derivatives in water as a function of pH and their equilibrium constants

The third-order rate constants for the pH-dependent formation of the carbinolamides generated from the reaction of formaldehyde and benzamide, 4-chloro, 4-nitro, 4-methyl and 4-methoxybenzamide, are reported. The acid-catalyzed reaction was found to occur via rate-limiting proton transfer, whereas the hydroxide-dependent reaction occurred via a specific-base process. Coupling the rate constants for carbinolamide formation reported herein with the previously established rates for carbinolamide breakdown yielded equilibrium constants for the carbinolamides studied in water.     

Kinetic study on disproportionations of C1 aldehydes in supercritical water: methanol from formaldehyde and formic acid

The reaction pathways and kinetics of C1 aldehydes, formaldehyde (HCHO) and formic acid (HCOOH=HOCHO), are studied at 400 degrees C in neat condition and in supercritical water over a wide range of water density, 0.1-0.6 g/cm3. Formaldehyde exhibits four reactions: (i) the self-disproportionation of formaldehyde generating methanol and formic acid, (ii) the cross-disproportionation between formaldehyde and formic acid generating methanol and carbon dioxide, (iii) the water-independent self-disproportionation of formaldehyde generating methanol and carbon monoxide, and (iv) the decarbonylation of formaldehyde generating hydrogen and carbon monoxide. The self- and cross-disproportionations overwhelm the water-independent self-disproportionation and the formaldehyde decarbonylation. The rate constants of the self- and cross-disproportionations are determined in the water density range of 0.1-0.6 g/cm3. The rate constant of the cross-disproportionation is 2-3 orders of magnitude larger than that of the self-disproportionation, which indicates that formic acid is a stronger reductant than formaldehyde. Combining the kinetic results with our former computational study on the equilibrium constants of the self- and cross-disproportionations, the reaction mechanisms of these disproportionations are discussed within the framework of transition-state theory. The reaction path for methanol production can be controlled by tuning the water density and reactant concentrations. The methanol yield of approximately 80% is achieved by mixing formaldehyde with formic acid in the ratio of 1:2 at the water density of 0.4 g/cm3.     

A study on the kinetics of condensation reaction of phenol‐modified cardanol–formaldehyde resin

Phenol‐modified cardanol–formaldehyde novolac resins have been synthesized using equal proportions of phenol and cardanol. To this mixture of phenol and cardanol, 0.6 and 0.8 mol of formaldehyde were added separately, under acidic conditions, at five different temperatures ranging between 80 and 120°C with an interval of 10°C. This was carried out for a maximum period of 6 h. The free formaldehyde and free phenol contents were determined at regular time intervals to check the completion of the reaction. The synthesized novolacs have been studied by infrared spectroscopic analysis (FT‐IR). The reaction between cardanol, phenol, and formaldehyde was found to follow a second‐order rate kinetics. The overall rate constant (k) increased with the increase of temperature. Based on the value of rate constants, various other parameters such as activation energy (E_a), change in enthalpy (Δ H) and entropy (Δ S), and free energy change (Δ G) of the reaction were also evaluated. It was found that the condensation reaction of phenol and cardanol with formaldehyde was nonspontaneous and irreversible. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 380–389, 2010     

Some Aspects of the Reaction of Polyacrylamide with Formaldehyde

The reaction of polyacrylamide with formaldehyde was studied in a neutral aqueous medium at equal initial molar concentrations of amide groups and of formaldehyde (0.05 mol/L) and in a range of temperatures from 45 to 75°C. The process was investigated by measuring the loss of free formaldehyde in the reaction mixture and the changes of the sum of free formaldehyde and methylol groups versus time. The addition of HCHO to an amide function of the polymer leads to its N-methylol derivative which may transform into the product of condensation between the latter and another amide group. Because of high dilution of polyacrylamide macromolecules in the reaction mixtures studied, cross-linking of the polymer chains with formaldehyde is rather unlikely. Therefore the disappearance of the N-methylols formed is probably due to some intramolecular reactions. It is believed that they involve the condensation of N-hydroxymethyls with neighboring amide groups which results in cyclic structures containing methylenediamide sequences. The occurrence of intramolecular reactions was confirmed by applying Flory's theory of gelation. The addition of HCHO to amide functions is a rate-determining stage in the case of polyacrylamide. For this reaction the rate constants were estimated and the corresponding activation energy was found to be 62 kJ/mol.     

On the representation of force fields for chemically reacting systems

“Relaxed” force constants are uniquely defined for systems involving redundant coordinates, in contradistinction to the usual “rigid” force constants, and thus their use allows meaningful correlations to be made between force fields calculated for reactants, transition state, and product of a chemical reaction, for example formaldehyde hydration.     

The Initial Stage of the Reaction of Melamine with Formaldehyde

The concentration-time relationships of the individual active species in the oligocondensation stage of the reaction of melamine with formaldehyde have been investigated, mainly by electrochemical methods. Based on the reaction equations, a kinetic model of the overall reaction was established and the rate constants were calculated by numerical methods. The results suggest the hydroxy-methylamines are converted to methylene and dimethylene ether bridged compounds by acid- and base-catalyzed reactions, respectively. At pH 7-10 the formation of methylene bridges by base-catalyzed scission of dimethylene ether bridges may occur.     

Solvent effect on the rate of the Mannich reaction of butyraldehyde with formaldehyde

The Mannich reaction of formaldehyde with butyraldehyde and diethylamine in hydrophilic solvents ensuring homogeneity of the medium follows the kinetic relations typical of an irreversible second-order reaction. The rate constants are determined by the ability of solvents to undergo self-association and their electrophilic solvation power; additional inclusion of the solvent polarity via multiparameter Koppel’-Pal’m equation is necessary to obtain a satisfactory quantitative correlation.     

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.     

Kinetics of the metal-catalyzed condensations of phenols and polyflavonoid tannins with formaldehyde

The rate constants and free energies of activation of Zn²⁺ -accelerated and Cr³⁺ -retarded condensations of resorcinolic A rings of polyflavonoid wattle tannins, as well as of the model compounds resorcinol and catechol with formaldehyde, were determined. A quantitative indication of the effect of strong metallic ion catalysts on phenol/aldehyde reactions was obtained. Second-order kinetics have been found to fit these metallic ion-catalyzed reactions. The dependence of the tannin/formaldehyde reaction on the concentration of Zn²⁺ and Cr³⁺ under acid and alkaline reaction conditions has been investigated and the respective catalytic coefficients determined. In the presence of the metallic ions used the reaction proved to be considerably less sensitive to variations of OH-concentration, hence of pH.     

1-三氯锡烷基-2,3-丁二烯和2-三氯锡烷基-1,3-丁二烯与甲醛反应的B3LYP研究

用密度泛函方法在B3LYP/6-31G^**水平上研究了1-三氯锡烷基-2,3-丁二烯和2-三氯锡烷基-1,3-丁二烯与甲醛的反应.优化得到各驻点的几何构型,通过振动分析和内禀反应坐标对过渡态进行了确认,解析了反应路径.并用SCRF(PCM)方法在同一水平上对在CH₂Cl₂溶液中的两反应进行了研究.计算了两反应在气相和CH₂Cl₂溶液中的活化能垒、自由能和平衡常数.结果表明,反应具有很强的选择性,主要得到1-三氯锡烷基-2,3-丁二烯与甲醛反应的产物.该结果与实验事实一致.     

The reaction of trans-2-aminocyclohexanol with formaldehyde

From a study of the geminal coupling constants for -O-CH₂-N- protons structure II has been assigned to the product of the reaction between trans-2-aminocyclohexanol and formaldehyde. The previously proposed structure I is shown to be incorrect.     

On the importance of prereactive complexes in molecule-radical reactions: hydrogen abstraction from aldehydes by OH.

In this work, the OH + formaldehyde and OH + acetaldehyde reactions have been characterized using accurate ab initio methods with large basis sets. The results clearly indicate that the reaction occurs by hydrogen abstraction, and that the OH addition channel is unfavorable. Close to zero (for formaldehyde) and negative (for acetaldehyde) activation energy values are obtained, which are in excellent agreement with the experimentally observed values. The reaction rate constants, calculated using the classical transition-state theory as applied to a complex mechanism involving the formation of a prereactive complex, reproduce very well the reported experimental results. Consideration of the prereactive complex is shown to be essential for the determination of the height of the energy barrier and thus for the correct calculation of the tunneling factor.     

Effect of formaldehyde on the cationic polymerization of styrene

Polymerization of styrene has been carried out in the presence of formaldehyde at 30°C in benzene solution by using boron trifluoride etherate as a catalyst. The rate of polymerization in the initial stage was accelerated with addition of formaldehyde, while the steady-state rate of polymerization was retarded in the presence of formaldehyde. The acceleration for the rate of polymerization was found only in a short time from the beginning. The steady-state rate of polymerization followed the equation: where [C]₀ and [F]₀ are initial concentrations of catalyst and formaldehyde, [M] is the monomer concentration, and k₁, k₂, and k₃ are constants. It has been assumed that the chain-transfer reaction does not involve formaldehyde itself but rather the reaction products of formaldehyde, such as polystyrene having ethoxy or hydroxymethyl ends. The apparent chain-transfer constant for the added formaldehyde has been determined to be 1.63.     

三聚氰胺-甲醛加成反应的研究

The addition reaction between melamine and formaldehyde involves the conversion of melamine into nine different methylol melamines.The reaction mechanism of the complex system can be summarized in a simple reaction model as below:(这里有图片19890824-878-1.gif)The rate equations of above reactions are evaluated by using Runge-Kutta method, and the rate constants are determined by means of fitting them to reaction species concentrations at various times.The molecular distribution formula of methylol derivatives of polyamine, which we developed previously, is used to form simultaneous equations with reaction rate equations and the contents of various meth-ylol-melamine are calculated.The results are good in agreement with the experiment data.     

化学动力学中隧道效应的研究 Ⅰ.甲醛单分子热反应中隧道效应的研究

本文用不对称Eckart势垒研究了甲醛单分子热解体系.改进了Forst的工作并计算了不同热效应条件下的一系列反应速率常数及相应的活化能,在考虑隧道效应的条件下详细讨论了势垒不对称性对计算结果的影响.计算结果与实验结果一致.     

Energetics of the Acid-Catalyzed o-Cresol-Formaldehyde Reaction

The acid-catalyzed reaction of o-cresol with formaldehyde follows second-order kinetics. The reaction was carried out at 65, 70, 75, and 80°C and at pH values of 1.30, 1.80, 2.00, 2.50, and 3.00, using hydrochloric acid as a catalyst. The rate was found to increase with decreasing pH. The overall rate constant (k) has been resolved into stepwise rate constants (k₁ and k₂) for the formation of monomethylol and methylene derivatives. Values of Arrhenius parameters and of the entropy of activation for the overall reaction were also calculated. A mechanism consistent with our kinetic data is given.     

Hydrothermal carbon-carbon bond formation and disproportionations of C1 aldehydes: formaldehyde and formic acid

Hydrothermal reaction pathways and kinetics of C1 (carbon-one) aldehydes, formaldehyde (HCHO) and formic acid (HCOOH = HOCHO), are studied at 225 degrees C without and with hydrochloric acid (HCl) up to 0.6 M (mol dm(-3)). Reactions unveiled are the following: (i) the self-disproportionation forming methanol and formic acid, a redox reaction between two formaldehydes, (ii) the cross-disproportionation forming methanol and carbonic acid, a redox reaction between formaldehyde and formic acid, and (iii) the acid-catalyzed C-C bond formation producing glycolic acid (HOCH2COOH) as a precursor of the simplest amino acid, glycine. Reaction iii is a hydrothermally induced chemical evolution step from C1 aldehydes, formaldehyde and formic acid. Disproportionations i and ii are found to proceed even without base catalysts unlike the classical Cannizzaro reaction. Acid catalyzes the self-disproportionation (i) and the C-C bond formation (iii), but retards the cross-disproportionation (ii). The rate constants of noncatalyzed and acid/base-catalyzed paths for reactions i, ii, and iii are given additively as 2 x 10(-4) + (2 x 10(-3))[H+], 10(-4) + 10(3)[OH-], and (2 x 10(-3))[H+] M(-1) s(-1), respectively; the concentrations of proton [H+] and hydroxide ion [OH-] are expressed in M. The rate constant of the noncatalytic (neutral) cross-disproportionation is 1 order of magnitude larger than that of the self-disproportionation. The reaction pathways are controlled on the basis of the kinetic analysis to make the glycolic acid and methanol productions dominant by tuning the concentrations of formaldehyde, formic acid, and HCl. The conversion to glycolic acid reaches approximately 90% when formaldehyde, HCl, and formic acid are mixed in the ratio of 1:2:17. The conversion of formaldehyde to methanol reaches approximately 80% when formic acid is added in excess to formaldehyde.     

Rate constant dependence on the size of aldehydes in the NO(3) + aldehydes reaction. An explanation via quantum chemical calculations and CTST

The reactions of NO(3) with formaldehyde, acetaldehyde, propanal, n-butanal, and isobutanal have been modeled using accurate ab initio and hybrid DFT methods with large basis sets. The results clearly indicate that the reaction is a simple aldehydic H atom abstraction; no adduct was found to support the idea of a complex mechanism. Alternative hydrogen abstractions were modeled for the alpha carbon hydrogen atoms and for the Cbeta of n-butanal; the differences in activation energies ruled out the possibility that competitive abstraction could be responsible for the anomalous increase of the rate constants with the size of aldehydes. The anomalous behavior was found to be a consequence of the preexponential factor increase, due to the enlargement of the internal rotation partition functions with the size of the aldehydes. The reaction rate constants, calculated using the conventional transition-state theory as applied to a proposed simple mechanism, reproduce remarkably well the reported experimental results. Consideration of the internal rotation partition functions is shown to be essential for the determination of the preexponential parameters and thus for the correct calculation of the rate constants. The tunneling correction was found negligible due to the features of the transition vector.     

Kinetics of Alkali-Catalyzed 2,5-Dimethylphenol-Forrnaldehyde Reaction

A kinetic study of the reaction between 2,5-dimethylphenol (2,5-DMP) and formaldehyde has been carried out at 65, 70, 75, and 80 ± 0.05° C by using sodium hydroxide as the catalyst. The solvent mixture used in the kinetic experiments was 50% (v/v) methanol-water. The various alkali concentrations used were 0.003, 0.006, 0.010, 0.018 and 0.025 N. The reaction was found to obey second-order rate law. The rate of reaction was observed to increase with an increase in the alkali concentration. The effect of changing the reactant concentrations and the nature of the solvent was also studied. The overall rate constant has been resolved into stepwise rate constants. The entropy of activation and Arrhenius parameters for the overall reaction have also been calculated.     

The role of charge transfer in the stripping of a hydrogen atom by peroxide radicals

Transition states of the reactions of hydrogen atom stripping by a formylperoxide radical from propylene and formaldehyde molecules were calculated in the MINDO/3 (UHF) approximation. A parameter characterizing the reactivity of reagents, which is a linear function both of the electronic properties of the reacting particles and of the reaction rate constants, is proposed.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 29, No. 1, pp. 37–40, January–February, 1993.