Experimental Enthalpies of Formation and Strain of the Methylated 1-Amino-2-phenylethanes

The standard molar enthalpies of formation H _f ^00B0; (liq) at the temperature t = 298.15 K were determined using combustion calorimetry for N-methyl-3-methyl-3-phenyl-2-butaneamine 1a, N,N-dimethyl-3-methyl-3-phenyl-2-butaneamine 1b N-methyl-2,3-dimethyl-3-phenyl-2-butaneamine 2a, and N,N-dimethyl-2,3-dimethyl-3-phenyl-2-butaneamine 2b. The standard molar enthalpies of vaporization H _vap ^00B0; of these compounds were obtained from the temperature variation of the vapor pressure measured in a flow system. The following standard molar enthalpies of formation in gaseous phase H _f ^00B0; (g) are obtained from these data: for 1a – 10.9 ± 1.9; 1b – 3.6 ± 1.8; 1c – 26.6 ± 1.4, and 1d – 23.0 ± 1.8 kJ mol^–1. From the standard molar enthalpies of formation for gaseous compounds which are available in the literature, improved values for the increments of the Benson group addivitiy scheme of amines were calculated. They are used to determine the strain enthalpies of the amines 1 and 2 from this investigation.     

NMR study of the sigmatropic [1,3]-B shift in 7,8-dipropyl-7-borabicyclo[4.2.2]deca-2,4,9-triene

Activation parameters of the interconversion of geometric isomers6a and6b were determined by a complete lineshape analysis of the temperature-dependent¹³C NMR spectra of 7,8-dipropyl-7-borabicyclo[4.2.2]deca-2,4,9-triene (6). For the reaction6a 6b, G ₂₉₈ = 52.2±0.1 kJ mol^–1, H = 27.9±0.5 kJ mol^–1, S = –82±8 J mol^–1 K^–1; For the reaction6b 6a, G ₂₉₈ = 52.6±0.1 kJ mol^–1, H = 24.7±0.5 kJ mol^–1, S = –93±10 J mol^–1 K^–1. The interconversion of deuteropyridine complexes9a and9b proceedsvia their dissociation, which indicates that the rearrangement of borane6 occurs according to the [1,3]-B shift mechanism.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2243–2250, September, 1996.     

Molecular structure,conformational mobility,vibrational spectra,and thermochemistry of peroxyacetic acid: an ab initio and density functional study

The structure of the peroxyacetic acid (PAA) molecule and its conformational mobility under rotation about the peroxide bond was studied by ab initio and density functional methods. The free rotation is hindered by the trans-barrier of height 22.3 kJ mol^–1. The equilibrium molecular structure of AcOOH (C _s symmetry) is a result of intramolecular hydrogen bond. The high energy of hydrogen bonding (46 kJ mol^–1 according to natural bonding orbital analysis) hampers formation of intermolecular associates of AcOOH in the gas and liquid phases. The standard enthalpies of formation for AcOOH (–353.2 kJ mol^–1) and products of radical decomposition of the peroxide — AcO^· (–190.2 kJ mol^–1) and AcOO^· (–153.4 kJ mol^–1) — were determined by the G2 and G2(MP2) composite methods. The O—H and O—O bonds in the PAA molecule (bond energies are 417.8 and 202.3 kJ mol^–1, respectively) are much stronger than in alkyl hydroperoxide molecules. This provides an explanation for substantial contribution of non-radical channels of the decomposition of peroxyacetic acid. The electron density distribution and gas-phase acidity of PAA were determined. The transition states of the ethylene and cyclohexene epoxidation reactions were located (E _a = 71.7 and 50.9 kJ mol^–1 respectively).     

The mean enthalpy of the lanthanide-oxygen bond in 2,2,6,6-tetramethyl-3,5-heptanedione chelates of praseodimium and holmium

The general thermochemical reaction LnCl₃·6H₂O(c)+3Hthd(1)+73.92H₂O(1) = Ln(thd)₃(c) +3HCl·26.64H₂O(aq); rHm (Ln = Pr, Ho and thd = 2,2,6,6-tetramethyl-3,5-heptanedionate) was employed to determine through solution-reaction calorimetry at 298.15 K the standard molar enthalpies of formation of crystalline chelates, –2434.3±11.5 (Pr) and –2384.8±11.5 (Ho) kJ mol^–1. These values and the corresponding molar enthalpies of sublimation enabled the determination of the standard molar enthalpies of chelates in the gaseous phase. From these values the mean enthalpies of the lanthanide-oxygen bond, 265±10 (Pr) and 253±10 (Ho) kJ mol^–1 were calculated.     

Single crystals of regio-selectively substituted cellulose hetero-esters

Lamellar single crystals of some regio-selectively substituted cellulose hetero-esters: cellulose propionate diacetate (CPDA, 2,3-di-O-acetyl-6-O-propionyl cellulose), cellulose acetate dipropionate (CADP, 6-O-acetyl-2,3-di-O-propionyl cellulose), cellulose butyrate diacetate (CBDA, 2,3-di-O-acetyl-6-O-butyryl cellulose) and cellulose acetate dibutyrate (CADB, 6-O-acetyl-2,3-di-O-butyryl cellulose), have been prepared at high temperature in a mixture of dibenzyl ether andn-tetradecane. The CPDA crystals were lozenge-shaped whereas those of CADP, CBDA and CADB had a ribbon morphology. CPDA crystals gave well-resolved electron diffractograms from which the reciprocal lattice parameters a^*=0.807 nm^–1,b ^*=0.400 nm^–1 and ^*=90° could be determined. Systematic absences occurred at every odd reflection along the two orthogonal axesa ^*andb ^*. Thus, the CPDA diffraction pattern is consistent with a p_gg symmetry. For CADP, the electron diffraction pattern is consistent with a p_mg two-dimensional space group withb the unique axis along the ribbon direction. The diagram yields the reciprocal lattice parameters a^* = 0.902 nm^–1,b ^*=0.651 nm^–1 and ^*=90°. The CBDA electron diffractogram yields the following cell parameters and two-dimensional space group:a ^*=0.482 nm^–1,b ^*=0.659 nm^–1 and ^*=90°, and a p_gg symmetry; and that of CADB:a ^*=0.834 nm^–1,b ^*=0.645 nm^–1 and ^*=90°, and a p_mg symmetry.     

Kinetic exchange studies of metal ion substitution in EDTA chelates Fe(III)- UO2 EDTA exchange

A kinetic study of the exchange reaction between UO₂EDTA complex and Fe(III), at a constant ionic strength of 0.1, over the concentration range of 5×10^–3–1×10^–2 M of each reactant and pH 4.5–5.5 has been carried out radiometrically. The rate of the exchange process can be expressed by the equation: R=k₁[UO₂EDTA][Fe]+k₂[EDTA][H⁺]^–1. The activation parameters calculated were H^*=25.95 kJ mol^–1 and S^*=0.67 kJ mol^–1 K^–1.     

A study of naphthyridines

4,4-Diaryl-1,4-dihydro-2,3-benzo-1,8-naphthyridines have been synthesized by the cyclization of diaryl 2-arylaminopyridin-3-yl carbinols. The latter were obtained by the reaction of methyl 2-arylaminonicotinates with arylmagnesium halides. With acid chlorides, the 4,4-diaryl-1, 4-dihydro-2,3-benzo-1,8-naphthyridines form 1-acyl derivatives. The pK_a values of the 4,4-diaryl-1,4-dihydro-2,3-benzo-1,8-naphthyridines in nitrobenzene have been determined, and a correlation has been found of the pK _a values with the ^* constants of the substituents (r=0.955, ^*= –1.53, pK _a ^° calc=2.51, s=0.01).For Communication II, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 119–121, January, 1974.     

High levelab initio stabilization energies of benzene

Summary G2 theory is shown to be reliable for calculating isodesmic and homodesmotic stabilization energies (ISE and HSE, respectively) of benzene. G2 calculations give HSE and ISE values of 92.5 and 269.1 kJ mol^–1 (298 K), respectively. These agree well with the experimental HSE and ISE values of 90.5±7.2 and 268.7±6.3 kJ mol^–1, respectively. We conclude that basis set superposition error corrections to the enthalpies of the homodesmotic or isodesmic reactions are not necessary in calculations of the stabilization energies of benzene using G2 theory. The calculated values of the enthalpies of formation of such molecules containing multiple bonds such as benzene ands-trans 1,3-butadiene, which are found from the enthalpies of isodesmic and homodesmotic reactions rather than of atomization reactions, demonstrate good performance of G2 theory. Estimates of theH _f ^o value for benzene from the G2 calculated enthalpies of homodesmotic reaction (2) and isodesmic reaction (3) are 80.9 and 82.5 kJ mol^–1 (298 K), respectively. These are very close to the experimentalH _f ^o value of 82.9±0.3 kJ mol^–1. TheH _f ^o value ofs-trans 1,3-butadiene calculated using the G2 enthalpy of isodesmic reaction (4) is 110.5 kJ mol^–1 and is in excellent agreement with the experimentalH _f ^o value of 110.0±1.1 kJ mol^–1.     

Synthesis,complexing properties and molecular modelling of open chain receptors of barbiturates derived from 2,6-diamino pyridine

Three new derivatives of 2,6-diacyldiaminopyridine are reported. NMR shift titrations were performed in CDCl₃ with barbiturates. The diamide1 affords a greater complexation energy (–13.00 kJ mol^–1) with bemegride than the dithioamide2 (–9.15 kJ mol^–1). This result, unexpected on the basis of the proton acidities, is explained by the great torsion energy induced in2 by the bulky sulfur atom. Compounds3 and4 present unusual four and five H-bond features with barbital and relatively weak complexation energies (–9.53 and –16.34 kJ mol^–1, respectively). Molecular mechanics indicates that ligand4 displays a helical secondary structure which is disrupted by complexation. Calculations of the H-bond energies (E _calc.) of the intermolecular assemblies with barbital or phenobarbital and other host-guest complexes given in the literature give a good correlation (r=0.98) with experimental values: E _calc.=1.07 G _a–42.0. Limitations of this relation are discussed.     

Thermogravimetric and differential scanning calorimetric investigations of manganese–glycine interactions

Thermogravimetric (t.g.) and differential scanning calorimetric (d.s.c.) data have been used to study metal–amino acid interactions in adducts of general formula MnCl₂ · ngly (gly = glycine, n = 0.7, 2.0, 4.0 and 5.0). All the prepared adducts exhibit only a one step mass loss associated with the release of glycine molecules, except for the 0.7gly adduct, which exhibits two glycine mass loss steps. From d.s.c. data, the enthalpy values associated with the glycine mass loss can be calculated: MnCl₂ · 0.7gly = 409 and 399 kJ mol^–1, MnCl₂ · 2.0gly = 216 kJ mol^–1, MnCl₂ · 4.0gly = 326 kJ mol^–1 and MnCl₂ · 5.0gly = 423 kJ mol^–1, respectively. The enthalpy associated with the ligand loss, plotted as function of the number of ligands for the n = 2.0, 4.0 and 5.0 adducts, gave a linear correlation, fitting the equation: H (ligand loss)/kJ mol^–1 = 67 × (number of ligands, n) + 76. A similar result was achieved when the enthalpy associated with the ligand loss was plotted as a function of the _a(COO^–) bands associated with the coordination through the carboxylate group, 1571, 1575 and 1577 cm^–1, respectively, for the n = 2.0, 4.0 and 5.0 adducts, giving the equation H (ligand loss) /kJ mol^–1 = 33.5 × _a(COO^–) /cm^–1 – 52418.5. This simple equation provides evidence for the enthalpy associated with the ligand loss being very closely related to the electronic density associated with the metal–amino acid bonds.     

The structure and thermochemistry of 3:4,5:6-dibenzo-2-hydroxymethylene-cyclohepta-3,5-dienenone (1) and some related compounds

Condensed and gas phase enthalpies of formation of 3:4,5:6-dibenzo-2-hydroxymethylene-cyclohepta-3,5-dienenone (1, (−199.1 ± 16.4), (−70.5 ± 20.5) kJ mol⁻¹, respectively) and 3,4,6,7-dibenzobicyclo[3.2.1]nona-3,6-dien-2-one (2, (−79.7 ± 22.9), (20.1 ± 23.1) kJ mol⁻¹) are reported. Sublimation enthalpies at T=298.15 K for these compounds were evaluated by combining the fusion enthalpies at T = 298.15 K (1, (12.5 ± 1.8); 2, (5.3 ± 1.7) kJ mol⁻¹) adjusted from DSC measurements at the melting temperature (1, (T _fus, 357.7 K, 16.9 ± 1.3 kJ mol⁻¹)); 2, (T _fus, 383.3 K, 10.9 ± 0.1) kJ mol⁻¹) with the vaporization enthalpies at T = 298.15 K (1, (116.1 ± 12.1); 2, (94.5 ± 2.2) kJ mol⁻¹) measured by correlation-gas chromatography. The vaporization enthalpies of benzoin ((98.5 ± 12.5) kJ mol⁻¹) and 7-heptadecanone ((94.5 ± 1.8) kJ mol⁻¹) at T = 298.15 K and the fusion enthalpy of phenyl salicylate (T _fus, 312.7 K, 18.4 ± 0.5) kJ mol⁻¹) were also determined for the correlations. The crystal structure of 1 was determined by X-ray crystallography. Compound 1 exists entirely in the enol form and resembles the crystal structure found for benzoylacetone.     

Relative Stability ofcis andtrans conformers of 2- and 3-fluorostyrene: An ab initio SCF-MO study

Ab initio SCF-MO calculations, mainly at the 6-31G F^* level with 3-21G F^* fully optimized geometries, were performed for 2- and 3-fluorostyrene in different comformations.Structures and conformational preferences of these molecules are compared with available data and discussed. It was found that the 2-fluorostyrene molecule has acis-trans energy difference of ca. 2.4 kJ mol^–1, showing a small barrier to planarity of 0.26 kJ mol^–1 in thetrans form. While the reduced stability of thecis form is mainly ascribed to a repulsive F ... vinyl group interaction, the partial loss of resonance stabilization between the ring and the vinyl group in the trans form and the H₆ ... H_c repulsive interaction in this form are taken to explain the local maximum at=180. In the 3-fluorostyrene molecule, thecis form is favored over thetrans by ca. 0.5 kJ mol^–1. An appreciable asymmetry of charge distribution found for thetrans form is assumed to slightly overweigh the difference in nuclear repulsion energy favorable to this conformation, thus explaining the observed relative stability.     

Molecular structure and decomposition mechanism of peracetic acid esters AcOOR (R = Me,Bu<Superscript>t</Superscript>)

The molecular structure and conformational mobility of methyl and tert-butyl esters of peracetic acid AcOOR (R = Me (1), Bu^t (2)) were studied by the ab initio MP4(SDQ)//MP2(FC)/6-31G(d,p) method and density functional B3LYP/6-31G(d,p) approach. The B3LYP calculated equilibrium conformations of the molecules are characterized by the C-O-O-C torsion angles of 93.6° (1) and 117.0° (2). Structural features of the molecules under study and a distortion of tetrahedral bond configuration at the C_α atom were explained using the natural bonding orbital approach. The standard enthalpies of formation of AcOOMe (−328.5 kJ mol⁻¹) and AcOOBu^t (−440.4 kJ mol⁻¹) were determined using the G2 and G2(MP2) computational schemes and the isodesmic reaction approach. The transition state of AcOOMe decomposition into AcOOH and formaldehyde was calculated (E _a = 122.8 kJ mol⁻¹). The thermal effects of homolytic decomposition of the peroxy esters following a concerted mechanism (Me^· + CO₂ + ^·OR) and simple homolysis of the peroxide bond (AcO^· + ^·OR) were found to be 97.5±0.3 and 155.1±0.3 kJ mol⁻¹, respectively. At temperatures below 400 K, the most probable decomposition mechanism of peroxy esters 1 and 2 involves simple homolysis of the O-O bond.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2021–2027, October, 2004.     

Formation Enthalpy and Entropy of Exciplexes with Variable Extent of Charge Transfer in Solvents of Different Polarity

Temperature dependence was studied for relative quantum yields of emission from some exciplexes of pyrene, 1,12-benzoperylene, and 9-cyanoanthracene with methoxybenzenes or methylnaphthalenes in solvents of different polarity (ranging from toluene to acetonitrile). The enthalpy H _Ex ^*, the entropy S _Ex ^*, and the Gibbs free energy G _Ex ^*of formation of the exciplexes were determined. Depending of the Gibbs free energy of excited-state electron transfer (G _et ^*) and solvent polarity, the values of H _Ex ^*, S _Ex ^*, and G _Ex ^*vary over the ranges from –5 to –40 kJ mol^–1, from +3 to –90 J mol^–1K^–1, and from +3 to –21 kJ mol^–1, respectively. The possibility is discussed that the effect of solvent polarity G _et ^*on the exciplex formation enthalpies can be rationalized in terms of the model of correlated polarization of an exciplex and the medium.     

Kinetics and mechanism of oxidation of tellurium(IV) by cobalt(III) in perchloric acid

Summary The kinetics of oxidation of Te^IV by Co^III have been studied in aqueous HClO₄. A mechanism presuming [Co(OH₂)₅(OH)]²⁺ to be the reactive species has been proposed, which leads to the rate-equation shown. Rate=–d[Co^III]/dt=2kKK _h ² [Co^III] _t ² [Te^IV]/[H⁺]² K_b is the hydrolysis constant of Co^III, K is the formation constant of the complex between Co^III and Te^IV and k is the rate of decomposition of that complex. E_a and S are 95.0±2.1 kJ mol^–1 and 28.3±7.1 JK^–1 mol^–1, respectively.     

Static and dynamic stereochemistry of 1,1′-bi(9,10-dihydro-9,10-ethano-anthryl)

Summary The title compound2 was prepared either by highpressure reaction of 1,1-bianthryl with ethylene or by coupling of 1-bromo-9,10-dihydro-9,10-ethanoanthracene (4). Both syntheses afforded a mixture of diastereoisomers (meso2a and racemate2b) in a ratio of 1.5:1 and 2.3:1, respectively. Configurational assignment was possible both from the¹H- and¹³C-NMR spectra and by coupling of laevorotatory4 (accessibly by enantioselective chromatography on triacetyl cellulose in ethanol) to laevorotatory2b. (+)-4 was tranformed into the dextrorotatory carboxylic acid (+)-5 of known configuration (9R) thus establishing the configuration of (+)-4 as (9R) too and hence the centrochirality in (–)-2b as (9S)(9S). The racemic form2b is a conformational (appr. 1.8:1) mixture of two rotamers.The rotational barrier was established as G ^#=92–95 kJ mol^–1 (depending on the temperature) both by¹H-NMR and CD kinetics (based on equilibration of the separated optically active rotamers ofracem.2). For the latter preferred conformations were assumed allowing the assignment of the axial chirality: e.g. (–)-(9S)(R)_a(9S) for the main rotamer of (–)-2 b [and (–)(9S)(S)_a(9S) for the underpopulated one].All assumptions were confirmed by X-ray crystal structure analyses of2 a and the main rotamer of2b with torsional angles around the 1,1-bonds of –111.1 and –121.2°, respectively.Dedicated to Prof. K. L. Komarek (Vienna) with cordial wishes on the occasion of the 65th anniversary of his birthday     

Thermochemistry of Alcohols: Experimental Standard Molar Enthalpies of Formation and Strain of Some Alkyl and Phenyl Congested Alcohols

The standard molar enthalpies of formation _f H _m ^° (cr) at the temperature T = 298.15 K were determined using combustion calorimetry for di-tert-butyl-methanol (A), di-tert-butyl-iso-propyl-methanol (B), and di-phenyl-methyl-methanol (C). The standard molar enthalpies of sublimation _cr ⁸ H _m ^° of these compounds and of di-phenyl-methanol (D) were obtained from the temperature variation of the vapor pressure measured in a flow system. Molar enthalpies of fusion _cr ¹ H _m ^° of the compounds A–D and of tri-phenyl-methanol (E) were measured by differential scanning calorimeter (DSC). From these data and data available from the literature, the following standard molar enthalpies of formation in gaseous phase _f H _m ^° (g) for A, (–397.0 ± 1.2); B, (–418.1 ± 2.3); C, (–34.2 ± 1.3); and D, (0.9 ± 2.1) kJ · mol^–1 were derived, which correspond to strain enthalpies (H _S) of 46.1, 114.7, 8.1, and 5.0 kJ · mol^–1, respectively.     

Kinetics and mechanism of the reactions ofcis-tetraaminediaqua-cobalt(III) with nitrite,azide and salicylate ions in aqueous acidic media

Summary Kinetic studies of the anation of the title complex by NO ₂ ^– show that it occurs in a stepwise manner leading to thecis-dinitro-complex both steps having a common rate equation:-d[complex]/dt = a[NO ₂ ^– ]/{[NO ₂ ^– ] + b}. The variation ofpseudo-first-order rate constant (k_obs) with [NO ₂ ^– ] indicates that the reaction proceeds through ion-pair interchange path. Activation parameters calculated by the Eyring equation are: H ₁ = (65±7) kJ mol^–1 and S ₁ = (–82±11) JK^–1 mol^–1 for the formation of [Co(NH₃)₄(NO₂)(H₂O)]²⁺, and H ₂ = (97±1) kJ mol^–1 and S ₂ = (6±2) JK^–1 mol^–1 for the formation of [Co(NH₃)₄(NO₂)₂]⁺. Anation of the title complex by N ₃ ^– at pH 4.1 also occurs in a stepwise manner ultimately producing thecis-diazido species. At a fixed pH the reaction shows a first-order dependence on [N ₃ ^– ] for each step. pH-variation studies at a fixed [N ₃ ^– ] show that the hydroxoaqua-form of the complex reactsca. 16 times faster than the diaqua form. Evidence is presented for an ion-pair preequilibrium at high ionic strength (I = 2.0 mol dm^–3). Activation parameters obtained from temperature variation studies are: H ₁ = (121±1) kJ mol^–1 and S ₁ = (104±3) JK^–1 mol^–1 (for the first step anation), and H ₂ = (111±2) kJ mol^–1 and S ₂ = (74±9) JK^–1 mol^–1 (for the second step anation). The reaction ofcis-tetraaminediaquacobalt(III) ion with salicylate (HSal^–) has been studied in aqueous acidic medium in the temperature range 39.8–58.2°C. The reaction is biphasic corresponding to the anation of two salicylate ions. The kinetic results for the first phase reaction are compatible with the equation: k_obs = k_IPQ[HSal^–]/(1 + Q[HSal^–]) where Q denotes ion-pair formation constant and k_IP is the first-order rate constant for the interchange reaction. The activation parameters obtained from the temperature dependence of rate are: H = (138±3) kJ mol^–1 and S = (135±4) JK^–1 mol^–1. The reaction seems to take place by a dissociative interchange mechanism.     

Thermal decomposition and kinetic data of Cd(BF4)2·6H2O

The thermal dehydration and decomposition of Cd(BF₄)₂·6H₂O were studied by means of DTA, TG, DSC and X-ray diffraction methods and the end products of the thermal decomposition were identified. The results of thermal analysis show that the compound is fused first, then it is dehydrated until Cd(BF₄)₂·3H₂O is obtained, which has not been described in the literature so far. The enthalpy of phase transition is H _ph.tr.=115.6 kJ mol^–1 Separation of the compound is difficult since it is highly hygroscopic. Then, dehydration and decomposition take place simultaneously until CdF₂ is obtained which is proved by X-ray diffraction. On further increasing the temperature, CdF₂ is oxidized to CdO and the characteristic curve assumes a linear character.Based on TG data, kinetic analyses were carried out separately for both parts of the curve: first until formation of the trihydrate and then — until formation of CdF₂. The formal kinetic parameters are as follows:for the first phase:E ^*=45.3 kJ mol^–1; rate equationF=^2/3; correlation coefficient 0.9858 for the second phase:E ^*=230.1 kJ mol^–1; rate equationF=(1–)^2/3[1-(1–)^1/3]^–1; correlation coefficient 0.9982.     

Kinetics and mechanism of the oxidation of [N-(2-hydroxy-ethyl)ethylenediamine-N,N′,N′-triacetatocobalt(II)] by vanadate ion

The kinetics of oxidation of Co^IIHEDTA {HEDTA = N-(2-hydroxyethyl)ethylenediamine-N,N,N-triacetic acid} by vanadate ion have been studied in aqueous acid in the pH range 0.75–5.4 at 43–57 °C. The reaction exhibits second-order kinetics; first-order in each of the reactants. The reaction rate is a maximum at pH = 2.1. A mechanism is proposed in which the species [Co^IIHEDTA(H₂O)]^– and VO₂ ⁺ react to form an intermediate which decompose slowly to give pentadentate Co^IIIHEDTA(H₂O) and V^IV as final products. The rate law was derived and the activation parameters calculated: H* = 26.96 kJ mol^–1 and S* = –311.08 JK^–1 mol^–1.