Base hydrolysis kinetics

Base hydrolysis kinetic data are reported for ppb solutions of carbofuran,3-OH carbofuran, methomyl and oxamyl. The results are compared with those reported previously for aldicarb, aldlcarb sulfoxide, and aldicarb sulfone. Second order reaction rate constants, k, have been calculated and range from 169 liter mln mole for oxamyl to 1.15 liter mln mole for aldicarb. The order for rate of base hydrolysis is as follows oxamyl >3-hydroxycarbofuran >aldicarb sulfone v- carbofuran >aldicarb sulfoxide > methomyl -v aldicarb. The activation energy for the base hydrolysis of carbofuran was measured to be 15.1 +0.1 kcal mole , and is similar to the value previously reported for aldicarb sulfone. Rapid detoxification of aldicarb, a representative oxime carbamate pesticide, by in situ hydrolysis on reactive ion exchange beds is reported. 

Structures have been determined for [Fe(gmi)3](BF4)2 (gmi = MeN=CHCF[=NMe), the iron(II) tris-diazabutadiene-cage complex of (79) generated from cyclohexanedione rather than from biacetyl, and [Fe(apmi)3][Fe(CN)5(N0)] 4F[20, where apmi is the Schiff base from 2-acetylpyridine and methylamine. Rate constants for mer fac isomerization of [Fe(apmi)3] " were estimated indirectly from base hydrolysis kinetics, studied for this and other Schiff base complexes in methanol-water mixtures. The attenuation by the —CH2— spacer of substituent effects on rate constants for base hydrolysis of complexes [Fe(sb)3] has been assessed for pairs of Schiff base complexes derived from substituted benzylamines and their aniline analogues. It is generally believed that iron(II) Schiff base complexes are formed by a template mechanism on the Fe " ", but isolation of a precursor in which two molecules of Schiff base and one molecule of 2-acetylpyridine are coordinated to Fe + suggests that Schiff base formation in the presence of this ion probably occurs by attack of the amine at coordinated, and thereby activated, ketone rather than by a true template reaction. ... 

T. W. Hambley, G. A. Lawrance, M. Martinez, B. W. Skelton, and A. H. White, ]. Chem. Soc., Dalton Trans., 1643 (1992). Quinquedentate Co-ordination of Amino-Substituted Tetraazacycloalkanes to Cobalt(III). Part 2. Crystal Structures of trans Isomers, Molecular Mechanics Calculations and Base-Hydrolysis Kinetics. 

In much of the early kinetic work on macrocyclic complexes the stereochemical complexities were largely ignored. Fortunately in basic solution the diastereoisomers will equilibrate (by base catalysed proton exchange) to give the most thermodynamically stable trans-lll diastereoisomer which has chair six-membered and gauche five-membered chelate rings. As a result the base hydrolysis kinetics reported for [14]aneN4 and its alkyl substituted derivatives probably relate to the trans-III diastereoisomer,(3.12)... 

An interesting kinetic study was carried out under pseudo-first-order conditions for the base hydrolysis of the three isomeric N-methyl-cyanopyridinium salts, a reaction that leads partly to CN replacement and partly to the formation of a carboxamido derivative. ... 

It is well known that the base hydrolysis of polyacrylamide is catalyzed by OH ions (first order reaction) and obeys autoretarded kinetics due to the electrostatic repulsion between the anionic reagent and the polymeric substrate(3-5). In the range of slightly acid pH (3 < pH < 5), Smets and Hesbain(6) have demonstrated a... 

The kinetic behavior of the base hydrolysis of TcCl2(acac)2 is described as an example [26], A plot of the logarithm of the concentration of the technetium complex in the organic phase against time gives a straight line. Thus, the reaction rate of the base hydrolysis of TcCl2(acac)2 is expressed as... 

Studies of the base-hydrolysis mechanism for hydrolysis of technetium complexes have further been expanded to an octahedral tris(acetylacetonato)techne-tium(III) [30], Although a large number of studies dealing with base hydrolysis of octahedral metal(III) complexes have been published [31], the mechanism of the tris(acetylacetonato)metal complex is still unclear. The second-order base hydrolysis of the cationic complex tris(acetylacetonato)silicon(IV) takes place by nucleophilic attack of hydroxide ion at carbonyl groups, followed by acetylacetone liberation, and finally silicon dioxide production [32], The kinetic runs were followed spectrophotometrically by the disappearance of the absorbance at 505 nm for Tc(acac)3. The rate law has the following equation ... 

The kinetics of base hydrolysis of several complexes of the type [Co(NH3)3L3] have been examined in order to see whether the mechanism for these uncharged complexes is the same as that operating for base hydrolysis of the standard cationic complexes (75). A comparison of kinetic parameters - a small selection is given in Table II (76,77) - suggests that all cobalt(III)-nitro-amine complexes, charged and uncharged, undergo base hydrolysis by the SnICB (Dch) mechanism. 

Kinetic Parameters for Base Hydrolysis of Selected Cobalt(III)-nitro-amine... 

A review of recent advances in chromium chemistry (82) supplements earlier comprehensive reviews of kinetics and mechanisms of substitution in chromium(III) complexes (83). This recent review tabulates kinetic parameters for base hydrolysis of some Cr(III) complexes, mentions mechanisms of formation of polynuclear Cr(III) species, and discusses current views on the question of the mechanism(s) of such reactions. It seems that both CB (conjugate base) and SVj2 mechanisms operate, depending on the situation. The important role played by ionpairing in base hydrolysis of macrocyclic complexes of chromium(III) has been stressed. This is evidenced by the observed order, greater... 

Another method for determining the absolute configurations of secondary alcohols is Horeau s method, which is based on kinetic resolution. As shown in Scheme 1-14, an optically active alcohol reacts with racemic 2-phenylbutanoic anhydride (54), and an optically active 2-phenylbutanoic acid (52) is obtained after hydrolysis of the half-reacted anhydride. 

J. R. Cashman, C. E. Berkman, G. Underiner, C. A. Kolly, A. D. Hunter, Cocaine Benzoyl Thioester Synthesis, Kinetics of Base Hydrolysis, and Application to the Assay of Cocaine Esterases , Chem. Res. Toxicol. 1998, 11, 895-901. 

The first objective has been accomplished by the development of an HPLC procedure as reported by Spalik et al. ( 5) and GC/NPD procedures developed by Lemley and Zhong ( ). The second and third objectives are being accomplished by fundamental solution studies and reactive ion exchange experiments conducted in parallel. Lemley and Zhong (7) determined recently the solution kinetics data for base hydrolysis of aldicarb and its oxidative metabolites at ppm concentrations and for acid hydrolysis of aldicarb sulfone. They have since ( ) reported similar results for ppb solutions of aldicarb and its metabolites. In addition, the effect on base hydrolysis of temperature and chlorination was studied and the effect of using actual well water as compared to distilled water was determined. Similar base hydrolysis data for carbofuran, methomyl and oxamyl will be presented in this work. 

Reaction kinetics and mechanisms for oxidation of [Fe(diimine)2(CN)2], [Fe(diimine)(CN)4] (diimine = bipy or phen) (and indeed [Fe(CN)6] ) by peroxoanions such as (S20g, HSOs", P20g ) have been reviewed. Reactivity trends have been established, and initial state— transition state analyses carried out, for peroxodisulfate oxidation of [Fe(bipy)2(CN)2], [Fe(bipy)(CN)4] , and [Fe(Me2bsb)(CN)4] in DMSO—water mixtures. Whereas in base hydrolysis of iron(II)-diimine complexes reactivity trends in binary aqueous solvent mixtures are generally determined by hydroxide solvation, in these peroxodisulfate oxidations solvation changes for both partners affect the observed pattern. ... 

The concept of preassembly as a requirement for substitution may throw light upon the vexed question of the mechanism of the base hydrolysis reaction. It has long been known that complexes of the type, [Co en2 A X]+n can react rapidly with hydroxide in aqueous solution. The kinetic form is cleanly second-order even at high hydroxide concentrations, provided that the ionic strength is held constant. Hydroxide is unique in this respect for these complexes. Two mechanisms have been suggested. The first is a bimolecular process the second is a base-catalyzed dissociative solvolysis in which the base removes a proton from the nitrogen in preequilibrium to form a dissociatively labile amido species (5, 19, 30). 

The methoxide ion has also been found to attack position 5 of 4-nitro-7-methylbenzofurazan to give adduct 168 (X = Me). By analogy with the kinetic behavior a similar reaction has been assumed for other members of the series (7-X = OMe, SMe, SPh, S02Ph).210 Further evidence for the formation of 5-adducts in this series had been provided by a preliminary, nonproductive step of the base hydrolysis of a 4-nitro-7-aryloxy-benzofurazan derived from lysozyme.2"... 

The kinetics of aquation of a number of azidochromium(III) complexes have been investigated.303,655 Compared with other acidochromium(III) complexes, the chromium-azide bonds in these species seem remarkably stable to thermal substitution. Hence in the base hydrolysis of [CrN3(NH3)s]2+ a pathway involving initial loss of NH3 concurs with the usual base hydrolysis pathway involving loss of Nj. The aquation of azidochromium(III) complexes is H+-assisted with protonation of the azido ligand accounting for the enhanced reactivity. 

KINETIC DATA FOR THE ACID AND BASE HYDROLYSIS OF SOME DIAMIDES... 

The mechanism provides (in equation 1) a pathway for proton exchange in amine complexes. (In fact, it was the observation that proton exchange in [Co(NH3)6]3+313 and the base hydrolysis of (Co(NH3)5Br]2+298 had the same kinetic form that led Garrick to propose this mechanism in 1937.314) The pathway for base catalyzed solvolysis is made up of (1) + (2) + (3) and the pathway for base catalyzed substitution is (1) + (2) + (4). It was the observation of base catalyzed ligand substitution that provided the first strong evidence for the dissociative nature of the process.315... 

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