Hydrolysis and aminolysis of alkyl xanthate esters and cellulose analogues

1999 ◽  
Vol 77 (5-6) ◽  
pp. 1050-1056 ◽  
Author(s):  
Eduardo Humeres ◽  
Valdir Soldi ◽  
Marilene Klug ◽  
Mauricéa Nunes ◽  
Célia MS Oliveira ◽  
...  
Keyword(s):  
Cellulose Xanthate ◽  
Covalent Bond ◽  
Hydroxide Ion ◽  
First Order ◽  
Tetrahedral Intermediate ◽  
Rate Determining Step ◽  
First Order Kinetics ◽  
Elimination Mechanism ◽  
Catalyzed Reactions ◽  
C Nmr

The hydrolysis and aminolysis of a series of S-substituted O-alkylxanthate esters was studied in 20% v/v aqueous methanol at 35°C. The pH-rate profiles of the hydrolyses showed water and hydroxide-ion-catalyzed reactions. The reaction of 2,4-dinitrophenyl cellulose xanthate (CelXDNP) and p-nitrobenzyl cellulose xanthate (CelXNB) with polyalanine and lysozyme produced a covalent bond between the polypeptide and the cellulose matrix, as shown by solid-state 13C NMR. However, the nature of the bonding could not be identified. The reaction of nucleophiles (H2O, OH-, RNH2) and xanthic esters was consistent with an addition-elimination mechanism through a tetrahedral intermediate. Brønsted plots against the pKa of the nucleophile (βnu) or the nucleofuge of the substrate (βlg) were used to characterize the rate-determining step. The pKa values of the nucleophiles ranged between -1.74 and 15.74, and for the nucleofuges, they were in the range of 10.50-0.92. For nucleophiles with pKa values up to about 10, βlg was 0.10-0.15, and βnu changed from 0.48 to 0.35 for the strongest electron-withdrawing nucleofuge. It was concluded that the water-catalyzed hydrolyses, and also aminolyses with moderately basic amines, occur with rate-determining formation of the tetrahedral intermediate. For strong bases such as hydroxide ion, the disappearance of the intermediate becomes the slowest step. The reaction of cellulose xanthic esters with external nucleophiles as hydroxide ion and amines shows simple first-order kinetics and is slower than alkyl or sugar xanthates, probably due to the diffusion effect through the tight cybotactic region of cellulose. Key words: hydrolysis, aminolysis, alkyl xanthic esters, cellulose xanthic esters, sugar xanthic esters.

Base hydrolysis of trans-Halogenoamminebis(dimethylglyoximato) (III). Complexes

1969 ◽  
Vol 22 (12) ◽  
pp. 2569 ◽  
Author(s):  
SC Chan ◽  
PY Leung
Keyword(s):  
Equilibrium Constants ◽  
Base Hydrolysis ◽  
Hydroxide Ion ◽  
First Order ◽  
Rate Determining Step ◽  
Rapid Formation ◽  
Pseudo First Order ◽  
Conjugate Bases ◽  
Hydrolysis Of ◽  
Conjugate Base

The disappearance of trans-[Co(LH)2(NH3)X] (LH = dimethylglyoximate ion, X = chloride or bromide) has been studied in aqueous solutions over a range of alkali concentrations at various temperatures. The kinetics were done with excess of hydroxide ion at a constant ionic strength so that pseudo first-order rate constants were obtained in all the runs. The results were interpreted in terms of the rapid formation of a pre- equilibrium species which then reacts in a rate-determining step to give products. The relatively large equilibrium constants support a conjugate-base pre-equilibrium, in which the proton is lost from oxygen, while the relatively low reactivities of the conjugate-bases are consistent with the absence of electropositive electromeric effects. The similarity in the reactivities of the chloro and the bromo conjugate-bases suggests the possibility of an SN2CB mechanism.

ORTHO PARTICIPATION IN THE CONVERSION OF syn-BENZALDOXIME ESTERS TO NITRILES

1965 ◽  
Vol 43 (12) ◽  
pp. 3178-3187 ◽  
Author(s):  
Robert J. Crawford ◽  
Charles Woo
Keyword(s):  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Alcoholic Solution ◽  
First Order ◽  
Rate Determining Step ◽  
First Order Kinetics ◽  
Kinetic Isotope ◽  
Marked Enhancement

Substituted syn-benzaldoxime esters are transformed, in an alcoholic solution, to the corresponding nitriles according to first-order kinetics. All ortho substituents were observed to accelerate the rate of nitrile formation relative to the corresponding para derivative. While the ko/kp ratios for the bromo, chloro, fluoro, methoxy, and methyl substituents fall within the range of 2 to 9, the iodo and methylthio substituents are 119 and 11 000 respectively. Isotopic replacement of the aldoximino hydrogen by deuterium gives rise to a kinetic isotope effect, kH/kD being 5.21 for syn-o-chlorobenzaldoxime p-toluenesulfonate, 1.22 for syn-o-iodobenzaldoxime p-toluenesulfonate, and 1.23 for syn-o-methylthiobenzaldoxime o-iodobenzoate. The marked enhancement of rate and the absence of an appreciable isotope effect are considered to be associated with sulfur and iodine participation in the rate-determining step. A mechanism which is capable of explaining the results observed is suggested.

scholarly journals KINETICS OF REACTION BETWEEN MALACHITE GREEN AND HYDROXYL ION IN THE PRESENCE OF REDUCING SUGARS

2015 ◽  
Vol 23 (23) ◽  
pp. 61-72
Author(s):  
Dayo Felix Latona ◽  
Adewumi Oluwasogo Dada
Keyword(s):  
Malachite Green ◽  
Activation Parameters ◽  
Cell Compartment ◽  
First Order ◽  
Rate Determining Step ◽  
First Order Kinetics ◽  
Hydroxyl Ion ◽  
Kinetics Of Reaction ◽  
Kinetics Of ◽  
Sphere Mechanism

The reaction was studied via pseudo-first-order kinetics using a UV-1800 Shimadzu spectrophotometer with a thermostated cell compartment and interfaced with a computer. The reaction showed first order with respect to malachite green and sugar and hydroxyl ion concentrations. However, the reaction was independent of ionic strength and showed no dependence on the salt effect, indicating an inner sphere mechanism for the reaction. There was no polymerization of the reaction mixture with acrylonitrile, indicating the absence of radicals in the course of the reaction. Michaelis-Menten plot indicated the presence of a reaction intermediate in the rate-determining step. The activation parameters of the reaction have been calculated and products were elucidated by FTIR spectroscopy. The stoichiometry of the reaction is 1:1. A mechanism consistent with the above facts has been suggested.

Aerobic oxidative N-dealkylation of secondary amines in aqueous solution catalyzed by rhodium porphyrins

2014 ◽  
Vol 18 (10n11) ◽  
pp. 937-943 ◽  
Author(s):  
Lin Yun ◽  
Ling Zhen ◽  
Zikuan Wang ◽  
Xuefeng Fu
Keyword(s):  
Aqueous Solution ◽  
Oxidation Reaction ◽  
Catalyst Deactivation ◽  
Secondary Amines ◽  
First Order ◽  
Rate Determining Step ◽  
First Order Kinetics ◽  
Biochemical Oxidation ◽  
Iminium Ion ◽  
Rhodium Porphyrins

N-dealkylation demonstrates an important biochemical oxidation reaction by cytochrome P450 and other monooxygenases. In this article, catalytic oxidative N-dealkylation of secondary amines was achieved using rhodium(III) tetra (p-sulfonato-phenyl) porphyrin (( TSPP ) Rh III ) in aqueous solution with oxygen as the sole oxidant. Addition of benzaldehyde to trap primary amine product inhibited catalyst deactivation and dramatically increased reaction turnover numbers (TONs). Substrate scope examination suggested the reaction was performed with a preference for bulkier secondary amines. Kinetic study exhibited first-order kinetics with regard of ( TSPP ) Rh III catalyst. Results from the Hammett study gave a ρ value of -1.38, suggesting formation of an iminium ion intermediate in the rate determining step.

Kinetics and mechanism of the formation of N-vinyl pyridinium cations in elimination reactions in aqueous base

1992 ◽  
Vol 70 (4) ◽  
pp. 1195-1203 ◽  
Author(s):  
John W. Bunting ◽  
Andrea Toth ◽  
James P. Kanter
Keyword(s):  
Reaction Mechanisms ◽  
Substituent Effects ◽  
Hydroxide Ion ◽  
First Order ◽  
Pyridinium Cation ◽  
Rate Determining Step ◽  
Bromide Ion ◽  
Aqueous Base ◽  
Elimination Reactions ◽  
Pyridinium Cations

The rates of the elimination reactions of N-(2-bromoethyl) pyridinium cations (1) and N,N′-ethylene bispyridinium dications (3) to give the corresponding N-vinyl pyridinium cations (2) have been measured spectrophotometrically in basic aqueous solutions (ionic strength 0.1, 25 °C) for a variety of substituents in the pyridine rings of each of these classes of pyridinium cation. The reaction kinetics are first order in 1 or 3 and first order in hydroxide ion. Brønsted-type plots of the second-order rate constants (kOH) as a function of the basicity (as pKBH) of the corresponding substituted pyridine are nonlinear for each of 1 and 3 and can be interpreted in terms of E1cb reaction mechanisms. For 1, the Brønsted-type plot displays two distinct "concave down" linear regions; rate-determining deprotonation for pKBH < 5.16 (slope = −0.30), and a change in rate-determining step to bromide ion departure for pKBH > 5.16 (slope −0.58). For 3, the Brønsted-type plot appears to be smoothly curved for symmetrically disubstituted bispyridinium dications, as a consequence of the multiple substituent effects upon each step of the E1cb reactions of these dications. However, log kOH for 3 is a smooth linear function of the previously reported log kOH for the E1cb reactions of N-(2-cyanoethyl) pyridinium cations over a range in which a change in rate-determining step has been directly demonstrated for these latter cations. Thus a change in rate-determining step as a function of pyridine basicity is also required within the E1cb mechanism for 3. The E1cb reactions of 1 are approximately 104-fold faster than the corresponding hydroxide ion catalyzed E2 eliminations from 2-phenylethyl bromides that are isoelectronic with 1.

Kinetic effects induced by cellulose on water-catalyzed reactions. Hydrolysis of 2,4-dinitrophenyl cellulose xanthate and some sugar xanthate ester analogues

1998 ◽  
Vol 76 (6) ◽  
pp. 960-965 ◽  
Author(s):  
Eduardo Humeres ◽  
Luiz Fernando Sequinel ◽  
Mauricéa Nunes ◽  
Célia MS Oliveira ◽  
Patrick J Barrie
Keyword(s):  
Cellulose Xanthate ◽  
First Order Kinetics ◽  
Acetone Water ◽  
Spontaneous Hydrolysis ◽  
Hydrolysis Of Cellulose ◽  
Entropy Of Activation ◽  
Kinetic Effects ◽  
Catalyzed Reactions ◽  
Parallel Reactions ◽  
Hydrolysis Of

The hydrolysis of 2,4-dinitrophenyl cellulose xanthate (CelXDNP) was studied in 10% v/v aqueous ethanol at 25°C and μ = 0.1 (KCl). The water-catalyzed hydrolysis showed that, as for p-nitrobenzyl cellulose xanthate, it occurs through two parallel reactions with rate constants k'H2O = 4.40 x 10-3 s-1 for the fast hydrolysis, and k''H2O = 6.90 x 10-5 s-1 for the slow hydrolysis. The entropy of activation of the fast hydrolysis was 0.7 ± 1.8 cal K-1 mol-1. External nucleophiles such as hydroxide and simple amines show simple first-order kinetics. The spontaneous hydrolysis of CelXDNP in acetone-water mixtures indicates that the fast reaction does not occur through water polymers and that for water molarity higher than 30 M there are no acetone molecules (or very few) in the highly ordered cybotactic region of cellulose. The spontaneous hydrolysis of methyl 4,6-O-benzylidene- α -D-glucopyranoside 3-(S-p-nitrobenzyl-xanthate) although is faster than the 6-isomer, it is slower than the fast hydrolysis of p-nitrobenzyl cellulose xanthate (CelXNB). Also Δ Sdouble dagger is highly negative (-41.0 cal K-1 mol-1), as it is for alkyl and sugar analogues. Only for the fast hydrolyses of CelXDNP and CelXNB is the entropy of activation almost zero. It is concluded that there is no neighbouring OH effect on the fast hydrolysis of cellulose xanthate esters. Key words: hydrolysis, water catalysis, cellulose xanthate esters, methyl glucose, xanthate esters, neighbouring OH effect.

Multiple changes in rate-determining step in the acid and base catalyzed cyclizations of ethyl N-(p-nitrophenyl)hydantoates caused by methyl substitution

1999 ◽  
Vol 77 (5-6) ◽  
pp. 849-859
Author(s):  
Iva B Blagoeva ◽  
Anthony J Kirby ◽  
Asen H Koedjikov ◽  
Ivan G Pojarlieff
Keyword(s):  
Steric Hindrance ◽  
Acid Catalysis ◽  
Isotope Effects ◽  
Base Catalysis ◽  
Ethoxy Group ◽  
First Order ◽  
Tetrahedral Intermediate ◽  
General Base ◽  
Rate Determining Step ◽  
Acid And Base

The slopes of the pH-rate profiles for the cyclization of 2-methyl- and 2,3-dimethyl hydantoates 1-NPU and 2-NPU between pH 1 and 7 change from 1 to 0 and then back to 1. A reaction first order in H+ was observed with the latter compound. The 2,2,3-trimethyl derivative 3-NPU showed only one reaction first order in OH-, but complex acid catalysis is described by slopes 0, -1, 0, and finally -1 again. The cyclizations were general base catalyzed, with Brønsted β values of 0.5-0.6. The OH- catalysis at higher pH for 1-NPU and 2-NPU showed inverse solvent kinetic isotope effects and deviated from the Brønsted relationships, while that for 3-NPU showed a normal effect and complied with the Brønsted relationship. The accelerations due to the gem-dimethyl effect were lost with the OH- and general base-catalyzed reactions of 3-NPU. This behaviour is due to a change from the rate-determining formation of the tetrahedral intermediate with 1-NPU and 2-NPU to the rate-determining breakdown with 3-NPU, due to steric hindrance to protonation of the leaving ethoxy group. The OH- reaction at higher pH involves attack of the ureide anion with 1-NPU and 2- NPU, becoming concerted with deprotonation when catalyzed by general bases and changing to acid inhibition of the anion of the tetrahedral intermediate at low pH. With 3-NPU at higher pH, T- is in equilibrium and the conjugate acids of the general bases accelerate its breakdown by protonating the ethoxy group. Acid catalysis of the cyclization of 3-NPU at higher pH is also protonation of the leaving group from T0 changing to the rate-determining formation of T at lower pH. The latter mechanism is preferred for the cyclization of 2-NPU.Key words: gem-dimethyl effect, mechanism, general base catalysis, proton transfer, steric hindrance.

Kinetics of Polymeric Substrate Removal by Activated Sludge: Hydrolysis of Polymers is the Rate-Determining Step

1992 ◽  
Vol 26 (9-11) ◽  
pp. 2457-2460 ◽  
Author(s):  
Y. Ubukata
Keyword(s):  
Amino Acids ◽  
Activated Sludge ◽  
Heterotrophic Bacteria ◽  
Removal Rate ◽  
Peptide Bond ◽  
Activated Sludge Process ◽  
First Order ◽  
Rate Determining Step ◽  
First Order Kinetics ◽  
Hydrolysis Of

A large portion of organic matter in primary effluent is polymers such as proteins and polysaccharides, and heterotrophic bacteria can directly take up only monomers such as amino acids and glucose that are produced from polymers by hydrolysis. Therefore it is assumed that the hydrolysis of polymers to monomers is the rate-determining step in activated sludge process. Activated sludges were acclimated to dextrin or peptone, and polymers (dextrin or peptone) and monomers (glucose or a mixture of free amino acids) were used as substrates for kinetics tests. Monomers were removed linearly, and the removal of polymers followed pseudo first order kinetics on the other hand. The removal rate of monomers was higher than that of polymers. The only one difference between polymer and monomer is whether glycosidic or peptide bond exists in molecule or not. It was, therefore, verified that the hydrolysis of polymer to monomer was the rate-determining step in activated sludge process. The removal of polymers followed apparently first order kinetics at higher F/M ratios, but followed nth (n&gt;l) order kinetics at lower F/M ratios.

Synthesis and Characterization of Epoxy Resin Containing Copper Acrylate

1992 ◽  
Vol 4 (2) ◽  
pp. 97-107 ◽  
Author(s):  
Manjit Anand ◽  
A. K. Srivastava
Keyword(s):  
Bisphenol A ◽  
Chemical Resistance ◽  
Spectroscopic Studies ◽  
Hydroxyl Content ◽  
First Order ◽  
H Nmr ◽  
First Order Kinetics ◽  
Sulfonium Ylide ◽  
C Nmr

Novel epoxy resins containing copper have been synthesized by reacting copper acrylate with bisphenol A and excess epicholorohydrin. Values of as epoxy equivalent weight, hydroxyl content and hydrolyzable chlorine content have been estimated. The resins have been characterized by IR, 1H-NMR and 13C-NMR analysis. The cured resins were evaluated for thermal properties. The curing of resins has been carried out with polyamide at 30 °C and with phenacyl dimethyl sulfonium ylide mercuric chloride complex by heating at 150 °C for 8 h and at 180 °C for 3 h. The cured resins have improved electrical properties and excellent thermal and chemical resistance in comparison with the control resin. The reaction follows first-order kinetics with activation energies of 47 and 34 kJ/mol in the presence and absence, respectively, of copper actrylate. The copper forms a complex with bisphenol A, as indicated by spectroscopic studies, which increases the epoxidation rate.

Studies of the variations in bond dissociation energies of aromatic compounds. I. Mono-bromo-aryles

1953 ◽  
Vol 219 (1138) ◽  
pp. 341-352 ◽  
Keyword(s):  
Hydrogen Bromide ◽  
Heat Of Formation ◽  
Activation Energies ◽  
Bond Dissociation Energies ◽  
First Order ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
Rate Determining Step ◽  
First Order Kinetics ◽  
Aromatic Radicals

Investigation of the pyrolyses of bromobenzene, β -bromonaphthalene, α -bromonaphthalene, 9-bromophenanthrene and 9-bromoanthraeene in the presence of an excess of toluene has shown that reaction (1) Ar .Br → Ar • + Br (1) is the primary and rate-determining step of the pyrolysis. The progress of reaction was measured by the rate of formation of hydrogen bromide, and it was shown that this rate obeys first-order kinetics. The following values were obtained for the activation energies and frequency factors of unimolecular decompositions represented by equation (1): compound E (kcal/mole) 10 -13 v (sec -1 ) bromobenzene 70.9 2 β -bromonaphthalene 700 1.5 α -bromonaphthalene 70.9 3.5 9-bromophenanthrene 67.7 1 9-bromoanthracene 65.6 1.5 Assuming that recombination of bromine atoms with aromatic radicals does not involve any activation energy we conclude tha t the determined activation energies correspond to the respective C—Br bond dissociation energies. The effect of molecular structure on the C—Br bond dissociation energy is discussed. The heat of formation of the phenyl radical is determined, and this result is used for calculating the various Ph — X bond dissociation energies.

Sign in / Sign up

Export Citation Format

Share Document