Other kinetic studies

The decomposition of Ir02C0Cl(PPh3)2 in nitrogen at 379—397 K [1142] yields 02 by a nucleation and growth reaction which obeys the Avrami—Erofe ev equation [eqn. (6), n = 2] and E = 232 kJ mole-1. At higher temperatures (405-425 K), a phase boundary mechanism is rate controlling, the contracting area equation [eqn. (7), n = 2] is obeyed, and E = 180 kJ mole-1. 

Ball and Pope [1143] have made a detailed study of the reversible reaction 

The rate of the addition reaction is determined by a phase boundary process, the contracting area expression [eqn. (7), n = 2] is obeyed and E = 37 kJ mole-1. The value of E for decomposition of the frarcs-chloro isomer (right-hand side of above equation) is 51 kJ mole-1, which is less than that (130 kJ mole-1) for HC1 elimination from the cis-chloro isomer. 

The rate of isotopic exchange in the solid state, between cobalt in the cation and in the anion of [60Co(H2O)6] [Co(edta)]2 4 H20, was increased [1144] by irradiation (100 Mrad) of the reactant. It was concluded that exchange occurred via vacancies, rather than through motion of a ring of cobalt atoms, one from a cationic site and the other from a neighbouring anionic site. 

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References to a number of other kinetic studies of the decomposition of Ni(HC02)2 have been given [375]. Erofe evet al. [1026] observed that doping altered the rate of reaction of this solid and, from conductivity data, concluded that the initial step involves electron transfer (HCOO- - HCOO +e-). Fox et al. [118], using particles of homogeneous size, showed that both the reaction rate and the shape of a time curves were sensitive to the mean particle diameter. However, since the reported measurements refer to reactions at different temperatures, it is at least possible that some part of the effects described could be temperature effects. Decomposition of nickel formate in oxygen [60] yielded NiO and C02 only the shapes of the a—time curves were comparable in some respects with those for reaction in vacuum and E = 160 15 kJ mole-1. Criado et al. [1031] used the Prout—Tompkins equation [eqn. (9)] in a non-isothermal kinetic analysis of nickel formate decomposition and obtained E = 100 4 kJ mole-1. 

The TEAF system can be used to reduce ketones, certain alkenes and imines. With regard to the latter substrate, during our studies it was realized that 5 2 TEAF in some solvents was sufficiently acidic to protonate the imine (p K, ca. 6 in water). Iminium salts are much more reactive than imines due to inductive effects (cf. the Stacker reaction), and it was thus considered likely that an iminium salt was being reduced to an ammonium salt [54]. This explains why imines are not reduced in the IPA system which is neutral, and not acidic. When an iminium salt was pre-prepared by mixing equal amounts of an imine and acid, and used in the IPA system, the iminium was reduced, albeit with lower rate and moderate enantioselectivity. Quaternary iminium salts were also reduced to tertiary amines. Nevertheless, as other kinetic studies have indicated a pre-equilibrium with imine, it is possible that the proton formally sits on the catalyst and the iminium is formed during the catalytic cycle. It is, of course, possible that the mechanism of imine transfer hydrogenation is different to that of ketone reduction, and a metal-coordinated imine may be involved [55]. 

The investigation of electrode kinetics has one paramount advantage over other kinetic studies the rate of the electron transfer reaction... 

Kinetics of the transformations of the N-F class of fluorinating agents in water, acetonitrile, alcohols, and aqueous solutions of alkali metal hydroxides have been studied.159 Other kinetic studies include die reactions of triphenylphosphine with 3-methoxy- or 3-acctoxy-4,4,5,5-tetrasubstitutcd-1,2-dioxolanes,160 the reactions of 2-amino-5-chlorobenzophenone witii HC1 in MeOH-H20 (die aspect of nucleophilic aliphatic substitution lies in certain products arising from attack of AH2 on CH3OH there are six products in all, and rate constants are evaluated for die formation of each of them),161 and the hydrolysis of derivatives of diazidophenyhnethane.162... 

The rule of Price and Hammett has been found to hold in several other kinetic studies. However, it has been shown to fail in oxime formation under conditions identical with those of the semicarbazone study (Fitzpatrick and Gettler, 1956). This is perhaps not surprising in view of the known complexity of semicarbazone and oxime formation, but it should serve as a warning that the effect of structure on entropy is by no means well understood. 

Among other kinetic studies in aqueous solutions are those of the reaction of chlorate with vanadium(II) and with chromium (II) °. The reactions of bromate with hydrazoic acid" and with hypophosphite" have been examined. 

Among other kinetic studies of picryl chloride and I-chloro-2,4 dinitro-benzene with bases the works should be mentioned of Parker and Read [112) and Zollinger and co-workers [113] which have shown a much higher reactivity of picryl chloride. The reactions are greatly influenced by solvent and in some instances l-chloro-2,4-dlnitrobenzeneisinore reactive than picryl cliloride [114). 

Only limited data are available for the kinetics of oxo synthesis with the water-soluble catalyst HRh(CO)(TPPTS)3. The hydroformylation of 1-octene was studied in a two-phase system in presence of ethanol as a co-solvent to enhance the solubility of the olefin in the aqueous phase [115]. A rate expression was developed which was nearly identical to that of the homogeneous system, the exception being a slight correction for low hydrogen partial pressures. The lack of data is obvious and surprising at this time, when the Ruhrchemie/ Rhone-Pou-lenc process has been in operation for more than ten years [116]. Other kinetic studies on rhodium-catalyzed hydroformylation have been published, too. They involve rhodium catalysts such as [Rh(nbd)Cl]2 (nbd = norbomadiene) [117] or [Rh(SBu )(CO)P(OMe)3]2 [118], or phosphites as ligands [119, 120]. 

Other kinetic studies of complexation using relaxation techniques can be found in Bridger et al. (1983) [hydroxo and chloro complexes of Fe(III)], Bridger et al. (1982) [complexation of Fe(III) by picolinic and dipicolinic acids], Strahm et al. (1979) (complexation of aqueous iron chloride), and Patel and Taylor (1973) (complexation of magnesium pyrophosphates). 

The resulting hydroperoxo-ferriheme complex is nonetheless unstable, as the peroxide ligand weakly ligates the heme iron , and the dissociation rate constant for the peroxide anion as the sixth ligand in Fe-microperoxidase-8 (Fe-MP8) and Mn-MP8 is in the neighborhood of 10-20 s (ref [60]). Similar estimates can be made from other kinetic studies" which measured the and values for the formation of Compound I in reaction of HRP with hydrogen peroxide. The reported millimolar values and the observed cat order of 10 M s suggest that... 

The a- and p-L-fucosyl esters of UMP and dTMP have been prepared as anomeric mixtures by treating the nucleotides with orthoester (15) in DMF. In the absence of methylenetetrahydrofolate cofactor, thymidylate synthetase has been observed to catalyse nucleophilic addition reactions at the ethynyl moiety of 5-ethynyl-2 -deoxyuridylate. On the basis of isotope effects and other kinetic studies, it has been suggested that addition of a thiol group of the enzyme at C-6 of the nucleotides results in formation of the allenic intermediate (16), followed by addition of 2-mercaptoethanol, morpholine, or other nucleophiles at the jp-hybridized carbon of the allene, and subsequent elimination of the enzyme. 

Measurements of rate coefficients and activation parameters were carried in some cases and the results are given in Table 16. Other kinetic studies were made at one temperature, for purpose of evaluation of medium and/or structural effects some of the relevant rate coefficients are gathered in Table 17. For the reaction between FiC CCU and butadiene derivatives, partial rate coefficients attributable to every double bond were also calculated, taking into account the product analyses , and are given in parentheses. All reactions were found to be first-order with respect to both reactants. 

When the war was over most of the chemists returned to their pre-war interests, but some embarked on new ventures - Linnett in problems of molecular structure (although retaining his war-time interest in flames and combustion). Woodward in Raman spectroscopy, and Staveley in thermodynamics that he had studied before the War with Klaus Clusius in Munich but had not yet been able to follow up. Hinshelwood published some of the previously classified papers and continued work on the reactions on charcoal surfaces and other kinetic studies, but his heart was not in it as it had been earlier all that he was now really interested in was the kinetics of bacterial growth and adaptation. 

These results indicate that two mechanisms may occur simultaneously for the reaction of benzoxazine with phenols. Other kinetic studies, performed in CCl solution, confirmed these results. 

There are of course many other kinetic studies of electrophilic aromatic substitution, particularly of the halogenation of activated aromatic species such as phenols and anilines. These are frequently complicated by the effect of pH and halide ion concentration upon equilibria between different halogenating species and between different forms of the aromatic substance. The role of bases in removing a proton has been rarely investigated directly, and much of the mechanistic information comes from a study of isotope effects, which will be considered in Chapter 12. 

Interaction of cyclohexa-amylose with optically active benzene derivatives shows a small but distinct chiral discrimination. Other kinetic studies with cydoamyloses have been reported as have details of various of their formation constants. ... 

In this chapter, the above way of thinking is used in two novel kinetic analyses of single-pulse initiation experiments. It is shown that the kinetic scheme of such experiments can be presented so that the termination rate coefficient can be determined as a function of chain length in a (virtually) model free fashion. In other words, no a priori choice is made for (or restriction set to) the functional dependence of kt upon chain length, but rather, this functional form can be determined. Hence, the exact dependence of L upon chain length can be determined with these methods. In this respect, the kinetic analyses presented here are distinctly different from any other kinetic study employing laser initiation reported so far in literature. 

Other kinetic studies of [Cr(NH3)5X] ions reported recently include a computer-based spectrophotometric investigation of the halide complexes/ and a study of the effect of alcohol (ROH R = Me, Et, Pr, or Bu)-water mixtures... 

Though this order is unexpected, it should be remarked that there is at least one other kinetic study which has reported just this order of effectiveness, viz. depolymerization of diacetone. The role of solvent structure and consequences for initial state and transition state hydration have also been discussed in relation to the replacement of histamine and related ligands from their pen-tacyanoferrate(II) complexes by pyridine.Again the discussion centers on the interaction between the solvent and the leaving group. 

Other kinetic studies concerned with square-planar nickel(ii) complexes include those of [Ni(trigly)] with Qfanide, redistribution reactions involving pairs of bis-bidentate nickel(n) complexes, and square-planar tetrahedral interconversions of [Ni(tertiary phosphine)2X2] compounds. ... 

Aquation of /ra 5-[Co(dmgH)2(urea)X] results in the loss of urea rather than of halide. The reported kinetic parameters, 12.7 < Aff< 15.6 kcal mol" and — 34 < AS" " < — 25 cal deg mol, are thus not strictly comparable with the results in Table 5. The effects of varying X on the reactivities of these complexes mirror the expected /m/w-effect order in this type of complex. There has been one other kinetic study of substitution at dioximato-cobalt(m), and that was of the reaction of rra j-[Co(dmgH)2L(OHa)] +, where L = OHa, py, or NO, with pyridine. Though these are formation reactions, their close similarity to the other systems in this and the preceding paragraph suggested that they be mentioned here. 

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