Rate Of Methanolysis Research Articles

Proposed kinetic mechanism of the production of biodiesel from palm oil using lipase

Experimental determination of the separate effects of palm oil and methanol concentrations on the rate of their enzymatic transesterification was used to propose suitable mechanismic steps and to test the generated kinetic model. The reaction took place in n-hexane organic medium and the lipase used was from Mucor miehei. At a constant methanol concentration of 300 mol m −3, it was found that, initially as the palm oil concentration increased, the initial reaction rate increased. However, the initial rate dropped sharply at substrate concentrations larger than 1250 mol m −3. Similar behaviour was observed for methanol concentration effect, where at a constant substrate concentration of 1000 mol m −3, the initial rate of reaction dropped at methanol concentrations larger than 3000 mol m −3. Ping Pong Bi Bi mechanism with inhibition by both reactants was adopted as it best explains the experimental findings. A mathematical model was developed from a proposed kinetic mechanism and was used to identify the regions where the effect of inhibition by both substrates arised. The proposed model equation is essential for predicting the rate of methanolysis of palm oil in a batch or a continuous reactor and for determining the optimal conditions for biodiesel production.

Ester versus Polyketone Formation in the Palladium−Diphosphine Catalyzed Carbonylation of Ethene

The origin of the chemoselectivity of palladium catalysts containing bidentate phosphine ligands toward either methoxycarbonylation of ethene or the copolymerization of ethene and carbon monoxide was investigated using density functional theory based calculations. For a palladium catalyst containing the electron-donating bis(dimethylphosphino)ethane (dmpe) ligand, the rate determining step for chain propagation is shown to be the insertion of ethene into the metal-acyl bond. The high barrier for chain propagation is attributed to the low stability of the ethene intermediate, (dmpe)Pd(ethene)(C(O)CH3). For the competing methanolysis process, the most likely pathway involves the formation of (dmpe)Pd(CH3OH)(C(O)CH3) via dissociative ligand exchange, followed by a solvent mediated proton-transfer/reductive- elimination process. The overall barrier for this process is higher than the barrier for ethene insertion into the palladium-acetyl bond, in line with the experimentally observed preference of this type of catalyst toward the formation of polyketone. Electronic bite angle effects on the rates of ethene insertion and ethanoyl methanolysis were evaluated using four electronically and sterically related ligands (Me)2P(CH2)nP(Me)2 (n = 1-4). Steric effects were studied for larger tert-butyl substituted ligands using a QM/MM methodology. The results show that ethene coordination to the metal center and subsequent insertion into the palladium-ethanoyl bond are disfavored by the addition of steric bulk around the metal center. Key intermediates in the methanolysis mechanism, on the other hand, are stabilized because of electronic effects caused by increasing the bite angle of the diphosphine ligand. The combined effects explain successfully which ligands give polymer and which ones give methyl propionate as the major products of the reaction.

Kinetics of hydroxide‐catalyzed methanolysis of crude sunflower oil for the production of fuel‐grade methyl esters

AbstractMethyl esters from crude sunflower oil were produced via methanolysis reaction using sodium hydroxide catalyst. Methanolysis was carried out at different agitation speeds (200–600 rpm), temperatures (25–60 °C), catalyst loadings (0.25–1.00% by weight of oil), and methanol:oil mole ratios (6:1–20:1). Mass‐transfer limitation was effectively minimized at agitation speeds of 400–600 rpm with no apparent lag period. Lowering the temperature resulted in a fall in the rate of reaction prolonging the reaction time necessary to achieve maximum production of methyl ester. Using 0.50% hydroxide catalyst was found to be adequate, resulting in 97–98% conversion without compromising recovery due to soap formation. Increasing the methanol:oil mole ratio beyond the usual amount of 6:1 tended to speed up the initial rate of methanolysis and was found to lower the bonded glycerol content, especially the amount of diglyceride in the sample. Kinetic rate constants were derived from experimental results using second‐order rate expressions, and values of activation energy for glyceride methanolysis have been established. Copyright © 2007 Society of Chemical Industry

Reactivity, chemical selectivity and exhaust dyeing properties of dyes possessing a 2-chloro-4-methylthio- s-triazinyl reactive group

Several 2-chloro- s-triazinyl reactive dyes, each possessing a different substituent in the 4-position of the triazine ring, were synthesised, and their rates of hydrolysis and methanolysis were determined over a range of temperatures. The order of reactivity was 4-alkylthio > 4-methoxy > 4-dimethylamino. Unlike the 4-methylthio- and 4-dimethylamino-derivatives, in which the chlorine atom was replaced cleanly, both on hydrolysis and methanolysis, the 2-chloro-4-methoxy- s-triazine underwent concurrent displacement of both chlorine and methoxy substituents. The 2-chloro-4-methylthio-derivative displayed a high propensity to undergo methanolysis, rather than hydrolysis, in homogeneous solution and this preference for undergoing alcoholysis was mirrored in excellent fixation to cotton on exhaust dyeing.

Correlation of the Specific Rates of Solvolysis of Trimethylsilylmethyl Trifluoromethanesulfonate Using a Two-Term Grunwald–Winstein Equation

The specific rates of solvolysis of trimethylsilylmethyl trifluoromethanesulfonate have been measured at 25.0 °C in ethanol, methanol, and 2,2,2-trifluoroethanol (TFE) and their mixtures with water. Determinations were also made in aqueous acetone and in TFE–ethanol mixtures. An extended (two-term) Grunwald–Winstein equation correlation gave sensitivities towards changes in solvent nucleophilicity and solvent ionising power as expected for an SN2 pathway, consistent with a previous proposal. For four solvents specific rates were determined at three or four additional temperatures and appreciably negative entropies of activation were observed, consistent with the proposed mechanism. At −20 °C, the specific rate of methanolysis is almost identical to that for methyl trifluoromethanesulfonate, suggesting a fortuitous balance between steric hindrance effects and a favourable electronic effect upon the introduction of the trimethylsilyl group.

The effect of substrate concentrations on the production of biodiesel by lipase‐catalysed transesterification of vegetable oils

AbstractAll the kinetic studies, found in the literature, on the production of biodiesel (fatty acids methyl esters) considered the esterifications of free fatty acids rather than the transesterification of the vegetable oil itself. The main industrial interest, however, is for the production of biodiesel with the triglyceride (oil) being the substrate. A mathematical model taking into account the mechanism of the methanolysis reaction starting from the vegetable oil as substrate, rather than the free fatty acids, has been developed. From the proposed model equation, the regions where the effect of alcohol inhibition fades, at different substrate concentrations, were identified. The proposed model equation can be used to predict the rate of methanolysis of vegetable oils in a batch or a continuous reactor and to determine the optimal conditions for biodiesel production. Copyright © 2005 Society of Chemical Industry

Production of Biodiesel by Lipase‐Catalyzed Transesterification of Vegetable Oils: A Kinetics Study

Kinetics of production of biodiesel by enzymatic methanolysis of vegetable oils using lipase has been investigated. A mathematical model taking into account the mechanism of the methanolysis reaction starting from the vegetable oil as substrate, rather than the free fatty acids, has been developed. The kinetic parameters were estimated by fitting the experimental data of the enzymatic reaction of sunflower oil by two types of lipases, namely, Rhizomucor miehei lipase (RM) immobilized on ion-exchange resins and Thermomyces lanuginosa lipase (TL) immobilized on silica gel. There was a good agreement between the experimental results of the initial rate of reaction and those predicted by the proposed model equations, for both enzymes. From the proposed model equations, the regions where the effect of alcohol inhibition fades, at different substrate concentrations, were identified. The proposed model equation can be used to predict the rate of methanolysis of vegetable oils in a batch or a continuous reactor and to determine the optimal conditions for biodiesel production.

Molecular engineering of Rhizopus oryzae lipase using a combinatorial protein library constructed on the yeast cell surface

We constructed a combinatorial yeast library through cell-surface display of the pro- and mature region of lipase from Rhizopus oryzae (ProROL) and obtained clones retaining lipase activity in fluorescent plate assay. The initial reaction rates of hydrolysis and methanolysis could be measured directly as whole-cell biocatalyst without complex treatments such as concentration, purification, and immobilization. The selected clones showed wide-ranging variation of reaction specificity. The K138R mutant showed a 1.3-fold shift of reaction specificity toward methanolysis compared to the wild type, while the V-95D, I53V, P-96S/F196Y, and Q128H/Q197L mutants showed shifts toward hydrolysis of 1.6–5.9-fold. Predictions of the mutants’ three-dimensional structure suggested that the hydrogen-bond distance between threonine 83 and aspartic acid 92 may influence reaction specificity, which shifted toward hydrolysis in mutants where this distance was shorter than in the wild type, but toward methanolysis where it was longer. The positions of amino acid residues (aa) 53, 138 and 196 in ProROL are considered the sites that influence hydrogen-bond distance and change reaction specificity. Construction of a surface-displayed combinatorial library in yeast cells is thus a powerful tool in accelerating the combinatorial approach to enzyme engineering and novel whole-cell biocatalyst development.

Molecular engineering of Rhizopus oryzae lipase using a combinatorial protein library constructed on the yeast cell surface

We constructed a combinatorial yeast library through cell-surface display of the pro- and mature region of lipase from Rhizopus oryzae (ProROL) and obtained clones retaining lipase activity in fluorescent plate assay. The initial reaction rates of hydrolysis and methanolysis could be measured directly as whole-cell biocatalyst without complex treatments such as concentration, purification, and immobilization. The selected clones showed wide-ranging variation of reaction specificity. The K138R mutant showed a 1.3-fold shift of reaction specificity toward methanolysis compared to the wild type, while the V-95D, I53V, P-96S/F196Y, and Q128H/Q197L mutants showed shifts toward hydrolysis of 1.6–5.9-fold. Predictions of the mutants’ three-dimensional structure suggested that the hydrogen-bond distance between threonine 83 and aspartic acid 92 may influence reaction specificity, which shifted toward hydrolysis in mutants where this distance was shorter than in the wild type, but toward methanolysis where it was longer. The positions of amino acid residues (aa) 53, 138 and 196 in ProROL are considered the sites that influence hydrogen-bond distance and change reaction specificity. Construction of a surface-displayed combinatorial library in yeast cells is thus a powerful tool in accelerating the combinatorial approach to enzyme engineering and novel whole-cell biocatalyst development.

Methanolysis of polyethylene terephthalate (PET) in the presence of aluminium tiisopropoxide catalyst to form dimethyl terephthalate and ethylene glycol

Aluminium triisopropoxide (AIP) promoted the methanolysis of polyethylene terephthalate (PET) to form monomers, dimethyl terephthalate (DMT) and ethylene glycol (EG), in an equimolar ratio. The methanolysis at 200 °C in methanol with an AIP catalyst gave DMT and EG in 64% and 63% yields, respectively. The yields were increased by using a toluene/methanol mixed solvent containing 20–50 vol.% toluene; maximum yields, 88% for DMT and 87% for EG, were obtained at 20 vol.% toluene. These results indicate that the rate of methanolysis strongly depends on the solubility of PET. The results of GPC analysis suggest that the methanolysis of PET in the absence of the catalyst includes three steps. In the first step, the depolymerisation occurred at a tie molecule connecting PET crystals and the chain length was shortened to about 1/3. The shortened chain was depolymerized to oligomers in the second step. The GPC curve of the oligomers tailed to low molecular weight, clearly indicating that the depolymerization took place at random positions on the polymer chain. The third step, the depolymerisation from the oligomers to the monomers, was promoted only in the presence of the AIP catalyst.

Kinetic and thermodynamic study of methanolysis of poly(ethylene terephthalate) waste powder

AbstractDepolymerization of poly(ethylene terephthalate) waste (PETW) was carried out by methanolysis using zinc acetate in the presence of lead acetate as the catalyst at 120–140 °C in a closed batch reactor. The particle size ranging from 50 to 512.5 µm and the reaction time 60 to 150 min required for methanolysis of PETW were optimized. Optimal percentage conversion of PETW into dimethyl terephthalate (DMT) and ethylene glycol (EG) was 97.8% (at 120 °C) and 100% (at 130 and 140 °C) for the optimal reaction time of 120 min. Yields of DMT and EG were almost equal to PET conversion. EG and DMT were analyzed qualitatively and quantitatively. To avoid oxidation/carbonization during the reaction, methanolysis reactions were carried out below 150 °C. A kinetic model is developed and the experimental data show good agreement with the kinetic model. Rate constants, equilibrium constant, Gibbs free energy, enthalpy and entropy of reaction are also evaluated at 120, 130 and 140 °C. The methanolysis rate constant of the reaction at 140 °C (10.3 atm) was 1.4 × 10−3 g PET mol−1 min−1. The activation energy and the frequency factor for methanolysis of PETW were 95.31 kJ mol−1 and 107.1 g PET mol−1 min−1, respectively.© 2003 Society of Chemical Industry

Catalytic specificity exhibited by p-sulfonatocalix[n]arenes in the methanolysis of N-acetyl-l-amino acids.

Specific acid catalysis of p-sulfonatocalix[n]arenes (n = 4, Calix-S4; n = 6, Calix-S6; n = 8, Calix-S8) was observed in the alcoholysis of N-acetyl-l-amino acids in methanol. The methanolysis rates of basic amino acid substrates (His, Lys, and Arg) were markedly enhanced in the presence of Calix-Sn, as compared with rates observed with p-hydroxybenzenesulfonic acid (pHBS), which is a noncyclic analogue of Calix-Sn. This catalytic effect of Calix-Sn was not observed for the methanolysis of Phe, Tyr, and Trp substrates. On the other hand, (1)H NMR experiments following the effect of Calix-Sn on N-acetyl-l-amino acid substrates in CD(3)OD showed that the spectrum of a mixture of the His substrate with Calix-Sn was significantly different from the combined spectra of the respective compounds. These changes in spectra support the formation of an inclusion complex of Calix-Sn with basic amino acids. Furthermore, it was obvious that methanolysis of the His substrate catalyzed by Calix-S4 and Calix-S6 obeyed Michaelis-Menten kinetics. These results indicate that the catalytic activity of Calix-Sn originates from its forming a complex with specific substrates (basic amino acids), similar to enzymatic reactions.

Synthesis and asymmetric polymerization of a series of methyl-substituted triphenylmethyl methacrylate

Five novel ortho-, meta-, and para-methyl-substituted triphenylmethyl methacrylate monomers, such as o-tolyldiphenylmethyl methacrylate (o-MeTrMA), di-o-tolylphenylmethyl methacrylate (o-Me2TrMA), tris-o-tolylmethyl methacrylate (o-Me3TrMA), tris-m-tolylmethyl methacrylate (m-Me3TrMA), and tris-p-tolylmethyl methacrylate (p-Me3TrMA) have been synthesized. The methanolysis rates of these monomers were measured in CDCl3-CD3OD (1:1, v/v) by 1H NMR spectroscopy at 30 °C. It was found that the order of the methanolysis rates would be TrMA<o-MeTrMA<o-Me2TrMA<o-Me3TrMA<m-Me3TrMA except p-Me3TrMA, which exhibited very good stability to methanolysis. The asymmetric polymerization of these monomers was investigated by chiral anionic complexes as initiators. The results showed that the ability to form a helical chain was effected not only by the types of chiral complex initiators, but also by the position and number of methyl-substituted groups at the benzene rings of TrMA. The order of the ability of polymerization was o-MeTrMA >o-Me2TrMA>o-Me3TrMA and m-Me3TrMA> p-Me3TrMA>o-Me3TrMA. These differences would be attributed to the different sizes and “propeller” steric structures of the bulky side groups. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 430–436, 2001

Effect of Methanol and water contents on production of biodiesel fuel from plant oil catalyzed by various lipases in a solvent-free system

Methyl esters synthesized from plant oil and methanol by the methanolysis reaction are potentially important as a biodiesel fuel. The methanolysis of soybean oil by lipases from various microorganisms was investigated. Several of the lipases were found to catalyze methanolysis in a water-containing system without an organic solvent. The lipases from Candida rugosa, Pseudomonas cepacia, and Pseudomonas fluorescens displayed particularly high catalytic ability. The reaction rates of methanolysis catalyzed by the C. rugosa and P. fluorescens lipases decreased significantly when the water content was low, showing that water prevents the inactivation of these lipases by methanol. On the other hand, the methanolysis reaction rate catalyzed by the P. cepacia lipase remained high even under a low water content. In addition, the P. cepacia lipase gave high methyl ester contents in the reaction mixture up to 2 or 3 molar equivalents of methanol to oil, which is attributed to the P. cepacia lipase having substantial methanol resistance. For the same methanol content, the reaction rates of methanolysis catalyzed by the P. cepacia lipase increased with decreasing water content, and hence lipases strongly resistant to high methanol, such as that from P. cepacia, are desirable for use in methanolysis reaction processes.

Gas‐phase stability of tertiary carbenium ions and rates of solvolysis of tertiary derivatives

The stability of tertiary carbenium ions was determined in the gas phase by ion cyclotron resonance (ICR) and by dissociative proton attachment (DPA). The rate constants for solvolysis of bridgehead derivatives correlate well with the stabilities of bridgehead carbenium ions, as determined by DPA and by ICR, but the ICR data of strained ions do not correlate, indicating rearrangements under the conditions of the ICR experiment. Simple acyclic tertiary derivatives solvolyze faster than predicted on the grounds of the stability of the respective carbenium ions. The effect of nucleophilic solvent participation on the rate of methanolysis of tertiary derivatives was investigated with (R)-3-chloro-3,7-dimethyloctane (17), which reacts with 77% inversion and 23% racemization. Copyright © 2000 John Wiley & Sons, Ltd.

Gas-phase stability of tertiary carbenium ions and rates of solvolysis of tertiary derivatives

The stability of tertiary carbenium ions was determined in the gas phase by ion cyclotron resonance (ICR) and by dissociative proton attachment (DPA). The rate constants for solvolysis of bridgehead derivatives correlate well with the stabilities of bridgehead carbenium ions, as determined by DPA and by ICR, but the ICR data of strained ions do not correlate, indicating rearrangements under the conditions of the ICR experiment. Simple acyclic tertiary derivatives solvolyze faster than predicted on the grounds of the stability of the respective carbenium ions. The effect of nucleophilic solvent participation on the rate of methanolysis of tertiary derivatives was investigated with (R)-3-chloro-3,7-dimethyloctane (17), which reacts with 77% inversion and 23% racemization. Copyright © 2000 John Wiley & Sons, Ltd.

Pretreatment of immobilized Candida antarctica lipase for biodiesel fuel production from plant oil

The effects of the pretreatment of immobilized Candida antarctica lipase enzyme (Novozym 435) on methanolysis for biodiesel fuel production were investigated. Methanolysis progressed much faster when Novozym 435 was preincubated in methyl oleate for 0.5 h and subsequently in soybean oil for 12 h. The initial reaction rate of methanolysis catalyzed by both the non-treated and preincubated enzyme decreased significantly with increasing water content. The initial reaction rate increased with increasing methanol content, showed a maximum, and thereafter decreased when the methanol content was increased further. The variation of the initial reaction rate with the methanol content was therefore analyzed using a Michaelis-Menten-type equation with substrate inhibition. Based on this equation, a procedure for the stepwise addition of methanol to the reaction mixture so as to maintain the desired methanol content was determined. When preincubated Novozym 435 was used, the ME content reached over 97% within 3.5 h by stepwise addition of 0.33 molar equivalent of methanol at 0.25–0.4 h intervals.

Strong Zn2+ and Co2+ catalysis of the methanolysis of acetyl imidazole and acetyl pyrazole

The kinetics of methanolysis of acetyl imidazole (1) and acetyl pyrazole (2) have been investigated under anhydrous conditions in the presence of Zn(ClO4)2, Co(ClO4)2, and HClO4 at 25°C. In all cases, the plots of the pseudo-first-order rate constant for methanolysis (kobs) vs. [metal ion] or [HClO4] show saturation behavior indicative of equilibrium binding of the M2+ or H+ to the amide. Relative to the spontaneous methanolysis rate constant (ko), the catalytic rate constant obtained at saturation, kcat, is larger for metal-ion catalysis than for H+ catalysis. The (kcatH+/ko) ratio is 10.7 and 1.25 for 1 and 2, respectively, while the (kcatM2+/ko) for these divalent metals varies from 150-fold for 1 to between 700 and 5700-fold for 2. By contrast, in water, proton is far more effective at promoting the hydrolysis of 1 than are metals, the aqueous (kcatH+/ko) ratio being 560, while the (kcatZn2+ /ko) and (kcatNi2+/ko) ratios are 15 and 3.2, respectively.Key words: methanolysis, kinetics, metal-ion catalysis, acetyl imidazole, acetyl pyrazole.

Strong Zn&lt;sup&gt;2+&lt;/sup&gt; and Co&lt;sup&gt;2+&lt;/sup&gt; catalysis of the methanolysis of acetyl imidazole and acetyl pyrazole

The kinetics of methanolysis of acetyl imidazole (1) and acetyl pyrazole (2) have been investigated under anhydrous conditions in the presence of Zn(ClO4)2, Co(ClO4)2, and HClO4 at 25°C. In all cases, the plots of the pseudo-first-order rate constant for methanolysis (kobs) vs. [metal ion] or [HClO4] show saturation behavior indicative of equilibrium binding of the M2+ or H+ to the amide. Relative to the spontaneous methanolysis rate constant (ko), the catalytic rate constant obtained at saturation, kcat, is larger for metal-ion catalysis than for H + catalysis. The (kcat /ko) ratio is 10.7 and 1.25 for 1 and 2, respectively, while the (kcat /ko) for these divalent metals varies from 150-fold for 1 to between 700 and 5700-fold for 2. By contrast, in water, proton is far more effective at promoting the hydrolysis of 1 than are metals, the aqueous (kcat /ko) ratio being 560, while the (kcat Zn2+ /ko) and (kcat /ko) ratios are 15 and 3.2, respectively.

Bridgehead Carbocations: Solvolysis of a Series of 5-Substituted Bicycle [3.1.1]heptyl Bromides. Nucleophilic Solvent Assistance to Ionization of 1-Bromobicyclo[3.1.1]heptane

The synthesis of a range of 5-substituted bicyclo [3.1.1] heptyl bromides for solvolytic studies is described. It is found that the substituent has a profound effect on the rate of solvolysis of the system and acts principally in accordance with the magnitude of its inductive/field constant σI. The most spectacular example of the effect of the substituent is provided by the COOMe group which leads to a retardation in the rate of methanolysis by a factor of 6.5°105. While a linear relationship in the plot of log k and σI is generally obeyed, as expected for a mechanism mediated by the bicyclo [3.1.1] heptyl bridgehead cation, two of the bromides, 1-bromobicyclo[3.1.1] heptane and its 5-methoxy derivative, show deviant behaviour and react more rapidly than predicted on the basis of the Hammett plot. Evidence is presented to show that the enhanced rate of the parent is the result of nucleophilic assistance by the solvent. Anchimeric assistance in the solvolysis of 5-methoxybicyclo[3.1.1] heptyl bromide is attributed to the powerful p-donor property of the methoxy substituent which stabilizes the transition state in a unique concerted ring-opening and ionization step.