Kinetics of alkali-catalyzed m-cresol-formaldehyde reaction

The alkali-catalyzed reaction of m-cresol with formaldehyde carried out at 65°, 70°, 75° and 80°C and at pH 7, 8, 9, 9.4, and 10 follows second-order kinetics. The rate is found to increase with increase of pH. The overall rate constant (k) has been resolved into stepwise rate constants (k₁, k₂, and k₃) for the formation of monomethylol, dimethylol, and trimethylol cresol, respectively. For this purpose, the rate equations for the various possible steps have been given and the concentrations of the various methylol cresols formed determined. The experimental and calculated values of k at pH 10 and temperatures of 65°, 70°, and 80°C have been found to agree well within the experimental errors. Entropy of activation and the Arrhenius parameters for the overall reaction have also been calculated.     

Comparative sorption equilibrium studies of toxic phenols on flyash and impregnated flyash

In the present study, the sorption of toxic phenols, which include phenol, o-cresol, m-cresol, p-cresol, o-nitrophenol, m-nitrophenol and p-nitrophenol, has been investigated. The influences of various factors, such as particle size, impregnation of flyash (IFA), pH and temperature on the sorption capacity have been studied. Equilibrium modelling has been carried out using Langmuir and Freundlich isotherm equations and constants have been calculated under different conditions. Thermodynamic studies have also been carried out and values of standard free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) calculated.     

Kinetics of the acid-catalyzed phenol–formaldehyde reaction

A kinetic study of the reaction of phenol with formaldehyde has been carried out at temperatures of 65° ± 0.05°C, 70° ± 0.05°C, 75° ± 0.05°C, and 80° ± 0.05°C using hydrochloric acid as catalyst. The pH maintained was 1.14, 1.32, 2.20, and 3.00. The reaction follows a second-order rate law. The rate is found to increase with decrease in pH. The overall rate constants are resolved into step rate constants. The values of the Arrhenius parameters and the entropy of activation for the overall reaction as well as for the step reactions have been calculated. A mechanism conforming to the energies and entropies of activation of the reaction has also been suggested.     

Processable heat-resistant polymers. VII. Synthesis and characterization of polyamideimide from N-(p-carboxyphenyl) trimellitimide and p,p′-di(aminocyclohexyl) methane

Polyamideimides were prepared either directly from N-(p-carboxyphenyl)trimellitimide and p,p′-di(aminocyclohexy)methane (PACM-20) by low temperature (<5°C) polycondensation in presence of thionyl chloride or by reacting the diacid chloride of N-(p-carboxyphenyl)trimellitimide and PACM-20 at 30–70°C. The polymers were characterized by nitrogen analysis and IR spectra. The polymers are soluble in highly polar solvents such as DMF, DMAC, NMP, and m-cresol. The solubility parameter was calculated from the Small's group contribution, which agrees well with the experimental value. The solution viscosity of the polymer is fairly stable against ageing. The T_g of the polymer calculated from the DTA curve is 270°C or even higher. Thermal analyses indicated that the polymer is fairly stable and only 5–6% weight loss occurs up to 350°C or 380°C. Dielectric constant, dielectric loss, and electrical conductivity of the polymer were also studied.     

Advanced oxidation with ozone of 1,3,6‐naphthalenetrisulfonic acid in aqueous solution

The kinetics of oxidation with ozone of 1,3,6‐naphthalenetrisulfonic acid was analysed by studying the influence of different experimental parameters such as the concentration of tert‐butyl alcohol (2‐methyl‐2‐propanol), initial concentration of the acid, pH, and temperature. The rate constant of the direct reaction at 25 °C was calculated (k_D = 6.72 M ^?1s^?1). The constant of the free radical reaction was determined with the competitive kinetics method, using sodium 4‐chlorobenzoate as reference compound, obtaining a value of k_OH = 3.7 × 10⁹ M ^?1s^?1. It was demonstrated that even at very acid pH values, 80% of the 1,3,6‐naphthalenetrisulfonic acid was degraded by free radical reactions, so that the ozonation of this acid may be considered an advanced oxidation process. © 2002 Society of Chemical Industry     

Mechanistic and kinetic studies on the polymerization of styrene initiated by dimethyl sulfonium 2-pyridyl carbonyl methylide

Dimethyl sulfonium 2-pyridyl carbonyl methylide (Y_py-s) initiated radical polymerization of styrene in dimethyl sulfoxide at 85±0.1°C for 6 h under a nitrogen blanket using dilatometric techniques has been studied. The initiator and monomer exponent values were calculated to be 0.5 and 1.2, respectively. The system follows ideal radical kinetics with bimolecular termination. The higher monomer exponent value is ascribed to significant solvent effects on the initiation rate. The overall activation energy and average value of k²_p/k_t are 52.0 kJ mol^?1 and 1.0 × 10^?3 litre mol^?1 s^?1, respectively. The polymerization was retarded in the presence of hydroquinone or benzene; dimethylformamide, however, enhanced the rate of polymerization. Kinetic data and ESR studies indicate that the overall polymerization takes place via triplet carbene formation which acts as a source of free radicals.     

A comprehensive study on the kinetics of aqueous free-radical homo- and copolymerization of acrylamide and diallyldimethylammonium chloride by online 1H-NMR spectroscopy

Free-radical homo- and copolymerization of acrylamide (AAm) and diallyldimethylammonium chloride (DADMAC) initiated with potassium persulfate (KPS) were performed in the presence of 0.1 M NaCl solution in D₂O at 50 °C. Online ¹H-NMR kinetic experiments were used to study polymerization kinetics via determination of the individual and overall conversion of the comonomers and compositions of the comonomer mixture and produced copolymer as a function of the reaction time. Reactivity ratios of the AAm and DADMAC were calculated by Mao-Huglin (MH) and extended Kelen-Tudos (KT) methods to be 7.0855?±?1.3963, 0.1216?±?0.0301 and 6.9458?±?2.0113, 0.1201?±?0.0437 respectively. “Lumped” kinetic parameter (k _p k _t ^??0.5 ) was estimated from experimental data. Results showed that k _p k _t ^??0.5 value increases by increasing mole fraction of the AAm in the initial reaction mixture. Drift in the comonomer mixture and copolymer compositions with reaction progress was evaluated experimentally and theoretically. Theoretical values were calculated from Meyer-Lowry equation by using reactivity ratios obtained from MH method. A good fitting between the experimental and theoretical values was observed, indicating accuracy of the reactivity ratios estimated in the present work. It was found from following changes in the copolymer composition with the comonomer conversion that produced copolymer has a statistical structure.     

Catalysis by Dihydrofolate Reductase from the Psychropiezophile Moritella profunda

The influence of temperature and pH on the stability and catalytic activity of dihydrofolate reductase (MpDHFR) from the cold‐adapted deep‐sea bacterium Moritella profunda was studied. The thermal melting temperature was found to be ～38 °C and was not affected by pH, while activity measurements demonstrated that its stability was maximal at pH 7 and was reduced dramatically below pH 6 or above pH 8. The steady‐state rate constant (k_cat) was maximal at neutral pH and higher temperatures, while the Michaelis constants (K_M) for both substrate and cofactor were optimal at lower temperatures and at elevated or reduced pH. For both temperature and pH, any change in k_cat was therefore offset by a similar change in K_M. Both the activation enthalpy and entropy of the MpDHFR‐catalysed reaction were lower than those of DHFR from E. coli leading overall to a very small difference in activation free energy and therefore similar steady‐state rate constants at the same temperature. The chemical step of the reaction is not rate limiting at pH 7, but becomes progressively more rate limiting as the pH increases. These results demonstrate adaptation of MpDHFR to its environment and show compromises between enthalpic and entropic contributions to the reaction, and between k_cat and K_M.     

p‐Acetylbenzylidene triphenylarsonium ylide initiated radical polymerization of methyl acrylate

Polymerization of methyl acrylate (MA), initiated by p‐acetyl benzylidene triphenylarsonium ylide (p‐ABTAY) in dioxan at (60 ± 1)°C for 1 h, follows nonideal kinetics (R_p ∝ [I]^0.21[M]^1.40) due to primary radical termination as well as degradative chain transfer reaction. The polymerization proceeded upto 20.49% conversion without gelation and results in the polymer of high molecular weight 98,000. The overall activation energy and the value of k_p²/k_t are 14 kJ mol^–1 and 18.75 × 10^–6 L mol^–1 s^–1, respectively. The ylide dissociates to form phenyl radical, which initiates the polymerization of MA. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis of end-group functionalized poly(octadecyl vinyl ether)

The cationic polymerization of octadecyl vinyl ether (ODVE) initiated by trimethylsilyl iodide and 1,1-diethoxyethane in the presence of ZnI₂ in toluene at 0°C and 10°C has been investigated. For molecular weights lower than 6000, a linearity of M̄_n with conversion was observed, but for higher molecular weights a strong deviation from calculated values, assuming a living mechanism, was found. Kinetic analysis of the polymerization and the variation of molecular weight as a function of conversion was in agreement with a transfer to monomer with k_tr/k_p ≌ 0.006 at 10°C. Analysis of the polymers obtained by termination with methanol provided evidence that the alkenyl ether end-groups formed by the transfer reaction lead to the same acetal end-groups as the active species. As a consequence, it is possible to prepare functionalized polyODVE polymers by end-capping with alcohols. This was confirmed by the synthesis of polyODVE macromonomers by end-capping with 2-hydroxyethyl methacrylate.     

Radical polymerization behavior of dimethyl vinylphosphonate: Homopolymerization and copolymerization with trimethoxyvinylsilane

Dialkyl vinylphosphonates such as dimethyl vinylphosphonate (DMVP) and diethyl vinylphosphonate were quantitatively polymerized with dicumyl peroxide (DCPO) at 130°C in bulk. The polymerization of DMVP with DCPO was kinetically studied in bulk by fourier transform near‐infrared spectroscopy (FTNIR) and electron spin resonance (ESR) spectroscopy. The initial polymerization rate (R_p) was given by R_p = k[DCPO]^0.5[DMVP]^1.0 at 110°C, being the same as that of the conventional radical polymerization involving bimolecular termination. The overall activation energy of the polymerization was estimated to be 26.2 kcal/mol. The polymerization system involved ESR‐observable propagating polymer radicals under the practical polymerization conditions. ESR‐determined rate constants of propagation (k_p) and termination (k_t) were k_p = 19 L/mol s and k_t = 5.8 × 10³ L/mol s at 110°C, respectively. The molecular weight of the resultant poly(DMVP)s was low (M_n = 3.4 ? 3.5 × 10³), because of the high chain transfer constant (C_m = 3.9 × 10^?2 at 110°C) to the monomer. DMVP (M₁) showed a considerably high reactivity in the radical copolymerization with trimethoxyvinylsilane (TMVS) (M₂) at 110°C in bulk, giving an inorganic component‐containing functional copolymer with potential flame‐retardant properties; r₁ = 1.6 and r₂ = 0. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Kinetics and mechanism of radical polymerization of methylmethacrylate using p-acetylbenzylidene triphenylarsonium ylide (p-ABTAY) as an initiator

Solution polymerization of methylmethacrylate (MMA) initiated by p-acetylbenzylidene triphenylarsonium ylide in dioxane was carried out at 60±0.2 °C up to 10 hrs. in a polymerization tube under a nitrogen atmosphere. The values of the initiator and the monomer exponent were computed as 0.46 and 1.03, respectively. The overall activation energy and kp²/k_t were calculated as 53 KJ/mole and 1.19 × 10⁻² L/mol·s, respectively for the polymerization.     

Cryo-kinetics Reveal Dynamic Effects on the Chemistry of Human Dihydrofolate Reductase

Effects of isotopic substitution on the rate constants of human dihydrofolate reductase (HsDHFR), an important target for anti-cancer drugs, have not previously been characterized due to its complex fast kinetics. Here, we report the results of cryo-measurements of the kinetics of the HsDHFR catalyzed reaction and the effects of protein motion on catalysis. Isotopic enzyme labeling revealed an enzyme KIE (k_H^LE/k_H^HE) close to unity above 0 °C; however, the enzyme KIE was increased to 1.72±0.15 at −20 °C, indicating that the coupling of protein motions to the chemical step is minimized under optimal conditions but enhanced at non-physiological temperatures. The presented cryogenic approach provides an opportunity to probe the kinetics of mammalian DHFRs, thereby laying the foundation for characterizing their transition state structure.     

Using 1H‐NMR spectroscopy for the kinetic study of the in situ solution free‐radical copolymerization of styrene and ethyl acrylate

The free‐radical copolymerization of styrene and ethyl acrylate in benzene‐d₆ as the solvent in the presence of benzoyl peroxide as an initiator at 70°C was studied by online ¹H‐NMR spectroscopy. The chemical composition of the copolymer at different reaction times was calculated from the conversion of the monomers to the copolymer, and then the reactivity ratios of styrene and ethyl acrylate were determined at both low and high conversions. Data for the overall monomer conversion versus the time were used to estimate the ratio k_pk_t^?0.5 for different compositions of the initial feed (k_p is the propagation rate constant, and k_t is the termination rate constant). k_pk increased with an increasing molar fraction of ethyl acrylate in the initial feed. The monomer mixture and copolymer compositions versus the overall monomer conversion were calculated with the data of ¹H‐NMR spectra. The incorporation of the styrene monomer into the copolymer structure was more favored than that of the ethyl acrylate monomer. Reducing the molar fraction of styrene in the initial feed intensified this. Drawing the molar fraction of styrene (or ethyl acrylate) in the copolymer chains versus that in the initial feed showed a tendency of the system toward random copolymerization. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Kinetics of copolycondensation of bis(4-hydroxybutyl) terephthalate and bis(2-hydroxyethyl) terephthalate by ester-interchange reaction

The kinetics of polycondensation and copolycondensation reactions were investigated using bis(4-hydroxybutyl) terephthalate (BHBT) and bis (2-hydroxyethyl) terephthalate (BHET) as monomers. BHBT was prepared by ester interchange reaction of dimethyl terephthalate and 1,4-butanediol. BHBT and BHET were polymerized at 270°C in the presence of titanium tetrabutoxide (TBT) as a catalyst. Applying second-order kinetics for polycondensation, the rate constants of polycondensation of BHBT and BHET, k₁₁ and k₂₂, were calculated as 3.872 min⁻¹ and 2.238 min⁻¹, respectively. BHBT and BHET were also copolymerized at 270°C using TBT. The rate constants of crossreactions in the copolycondensation of BHBT and BHET, k₁₂ and k₂₁, were obtained by using the results obtained from a proton nuclear magnetic resonance (¹H-NMR) spectroscopy and a high-performance liquid chromatography (HPLC). It was found that the rate constants during the copolycondensation of BHBT and BHET at 270°C decreased in the order k₂₁ > k₁₁> k₂₂ > k₁₂ and the monomer reactivity ratio of BHBT was four or five times larger than that of BHET. In calculating the crossreactions, the method by the ¹H-NMR spectroscopy gave more accurate results than that by the HPLC. © 1996 John Wiley & Sons, Inc.     

Design of polymers for migration imaging application II: Synthesis and polymerisation of p-isobutyl styrene

A copolymer series was synthesized for migration imaging applications from isobutyl methacrylate and isobutyl styrene such that each homopolymer and all copolymers had glass transition temperature (T_g) near 55°C. The T_g of poly (p-isobutylstyrene) was predicted from literature values of similar polymers to be near 55°C. Poly (p-isobutylstyrene) was synthesised by acetylation of isobutyl benzene, reduction of p-isobutylacetoph-enone to the carbinol, dehydration to p-isobutylstyrene and free radical polymerisation to the polymer. The T_g of the homopolymer was 55°C, in excellent agreement with the predicted value. Copolymers of isobutyl methacrylate and p-isobutyl styrene were synthesised and their T_g's measured across the series by DSC (57°C ± 5°C). refractive index temperature coefficient (42°C ± 5°C). The copolymer series was also characterised by melt viscosity measurements.     

Thermal decomposition of potassium persulfate in aqueous solution at 50°C in the presence of ethyl acrylate

Potassium persulfate modes of thermal decomposition and reactions with ethyl acrylate in aqueous solution at 50°C in nitrogen atmosphere have been investigated. It has been found that the rate of persulfate decomposition may be expressed as ?d(S₂O)/dt ∝ (S₂O)^{1.00 ± 0.06} × (M)^0.92±0.05 while the steady state rate of polymerization (R_p) is given by R_p ∝ (S₂O)^{0.50 ± 0.50} × (M)^{1.00 ± 0.06} in the concentration ranges of the persulfate, 10^?3?10^?2 (m/L), and monomer (M), 4.62?23.10 × 10^?2 (m/L), i.e., within its solubility range. In the absence of monomer, the rate of persulfate decomposition was slow and first order in persulfate at the early stages of the reaction when the pH of the solution was above 3.0. The separating polymer phase was a stable colloid at low electrolyte concentrations even in the absence of micelle generators. It has been shown that the oxidation of water soluble monomeric and oligomeric radicals by the S₂O ions in the aqueous phase, viz., \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm M}_j^ \cdot + {\rm S}_2 {\rm O}_8^{2 - } \to {\rm M}_j - {\rm O} - {\rm SO}_3^ - + {\rm SO}_4^{ \cdot - } $\end{document} is not kinetically significant in this system. It has been found that the reaction \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm M} + {\rm S}_2 {\rm O}_8^{2 - } \rightarrow{k}{\rm M} - {\rm O} - {\rm SO}_3^ - + {\rm SO}_4^{ \cdot - } $\end{document} would also lead to chain initiation at the outset of the polymerization reaction. k has been estimated as 5.41 × 10^?5 (L/m/s) at 50°C. Taking k_p as 10³ (L/m/s), k_t has been estimated as 0.168 × 10⁶ (L/m/s). The partition confficient (β) of the monomer between the polymer phase and the aqueous phase was found to be 16 ± 2, at 50°C. The rate constant for persulfate ion dissociation has been found as 1.40 × 10^?6 s^?1 at 50°C.     

Deterioration Kinetics of Crude Palm Oil,Canola Oil and Blend During Repeated Deep-Fat Frying

The oxidation of vegetable oils is generally treated as an apparent first order kinetic reaction. This study investigated the deterioration of crude palm oil (CPO), refined canola oil (RCO) and their blend (CPO:RCO 1:1 w/w) during 20 h of successive deep‐fat frying at 170, 180 and 190 °C. Kinetics of changes in oil quality indices, namely, free fatty acid (FFA), peroxide value (PV), anisidine value (p‐AV), total polar compounds (TPC) and color index (CI) were monitored. The results showed that FFA and PV accumulation followed the kinetic first order model, while p‐AV, TPC and CI followed the kinetic zero order model. The concentration and deterioration rate constants k, increased with increasing temperatures. This effect of temperature was modeled by the Arrhenius equation. The results showed that PV had the least activation energies E_a (kJ/mol) values of 5.4 ± 1 (RCO), 6.6 ± 0.7 (CPO) and 11.4 ± 1 (blend). The highest E_a requirement was exhibited by FFA with a range of 31.7 ± 3–76.5 ± 7 kJ/mol for the three oils. The overall E_a values showed that the stability of the blend was superior and not just intermediate of CPO and RCO. The correlation of the other oil quality indices with TPC indicated a positive linear correlation. The p‐AV displayed the strongest correlation, with mean correlation coefficient r_s of 0.998 ± 0.00, 0.994 ± 0.00 and 0.999 ± 0.00 for CPO, RCO and blend, respectively.     

Kinetics and mechanism of the vapour phase oxidation of 3-picoline by nitric oxide over nickel oxide–aluminium oxide catalyst

The kinetics of the catalytic transformation of 3-picoline to 3-cyanopyridine by nitric oxide (NO) have been investigated over nickel oxide-aluminium oxide catalyst (2NiO·Al₂O₃) in a differential flow reactor between 300 and 360°C. A maximum yield of 98% was achieved with a catalyst having a Ni: Al atomic ratio of 1:1 and preheated in the presence of air at 600°C for 24 h. The rate equation R_n = k_pk_nP_pP_n/(k_pP_p + k_nP_n) deduced, assuming a steady state involving a two-stage irreversible oxidation-reduction process, represented the data most satisfactorily for conversion of 3-picoline to nicotinonitrile. A tentative mechanism for the reaction is proposed.     

Intrinsic viscosity–molecular weight relationship for low molecular weight nylon 6

Samples of nylon 6 have been prepared by the hexamethylene diamine-initiated polymerization of ?-caprolactam at 220°C. Fractionation of these with m-cresol–diethyl ether at 26°C yielded 15 amino-terminated fractions of M?_n of 337–10,940 determined conductometrically. Below M?_n = 4,306 the Mark-Houwink parameters in m-cresol at 30°C are K = 3.0 × 10^?3 dl/g and v = 0.53 ± 0.02. Thereafter v exhibits a pronounced increase. The value of K is similar to the values of Kθ derived from Stockmayer-Fixman plots of published data in good solvents. The findings thus corroborate a current hypothesis that fractionated, low molecular weight polymers in good solvents tend to behave viscometrically, as if they were under θ conditions (i.e., K = K_θ and v = 0.50).