Kikuo Miyokawa

Influence of particle size distribution of a sample on the kinetic parameters determined by thermogravimetric curves

Abstract The influence of particle size distribution in a sample on the kinetic parameters determined by using TG and DTG curves was examined mathematically. TG and DTG curves for the reactions following the rate equations of the contracting cube (mode I), Jander (mode II), or Avrami (mode III) models were calculated by assuming that the radii of the particles in the sample were in the normal distribution with standard deviation s and by settling parameters such as activation energy E a and pre-exponential factor A arbitrarily. The rate analyses of the calculated curves were carried out by the methods of Coats—Redfern (method I) and Achar et al. (method II). The E a and A values obtained by either method were found to deviate negatively from the given values as the s values increased; the deviation was a little larger by method II than by method I. For the reactions of modes I and II, the E a and A values obtained by both methods were close to the given values and were independent of the s values. For the mode III reaction, both methods gave E a and A values which deviated substantially from the given values though good, linear Arrehnius-plots were delineated as the s values increased. It is not preferable to induce the kinetic parameters from the rate analysis of reactions such as mode III without taking the particle size distribution into consideration.

The kinetics of the thermal pyridine dissociation of pyridine[N,N′-ethylenebis(salicylideneaminato)]-alkylcobalt(III) in the solid state. Kinetic trans effect of alkyl group

Abstract The thermal behavior of RCo(salen)py (R = Me, Et, n Pr, i Pr, n -Bu, i Bu; salen = N,N′ -ethylenebis(salicylideneaminate) dianion; py = pyridine) has been investigated by means of TG, DSC, and isothermal weight-loss measurements. These complexes dissociate 1 mol of pyridine per mole of complex in the temperature range 365–445 K, which is followed by the dissociation of the alkyl group. Kinetic analysis has revealed that the pyridine dissocation reactions fit the contracting disc equation. The electronic nature of the alkyl group has been found to affect the kinetic stability of the Co(III)-alkyl bonding; the more electron-donating group labilizes the Co(III)-py bonding. A linear correlation has been observed between the inductive substitution constants of alkyl groups and the pyridine-dissociation rates at 400 K.

The kinetics and thermodynamics of the thermal pyridine dissociation of bis(pyridine)bis(N-alkyl-substituted-salicylideneaminato)nickel(II) in the solid state. Kinetic and thermodynamic bond stabilities

Abstract Thermal pyridine dissociation reactions of the bis-pyridine adducts of bis(N-alkyl-substituted-salicylideneaminato)nickel(II), abbreviated as Ni(N-R-X-salam)2py2 (R = Me; X = 5-MeO, 5-Me, H, 5-F, 5-Cl, 5-Br, 5-NO2: X = H; R = Et, n-Pr, i-Pt, n-Bu, i-Bu, n-pentyl, n-hexyl, n-heptyl, cyclohexyl), were characterized by means of TG, DSC, and isothermal weight-loss measurements. These adducts dissociated 2 moles of pyridine per mole of the adduct at one stage in the temperature range 350–470 K; the depyridination reactions for the adducts including R = i-Pr or i-Bu gave rise to pseudo-tetrahedral parent complexes and those for the remaining adducts gave square-planar parent complexes. The ΔH values, heat of depyridination, varied in the range 98–165 kJ mole−1, depending on the nature of R and X. Kinetic analyses revealed that for all the adducts the reactions followed the contracting-disc equation. The logarithmic values of the rate constants at 350 K linearly decreased with an increase in ΔH values, indicating that kinetic bond stability could be correlated with thermodynamic bond stability with respect to the Ni(II)-pyridine linkage. It was also shown that on substituting X on the aryl rings the Ni(II)-pyridine bond strength was influenced predominantly by the electronic effect of X, and on substituting R on the imine nitrogen atoms the bond strength was influenced predominantly by the steric effect of R.

Thermal characterization of nitrogen monoxide dissociation reactions of nitrosyl complexes in the solid phase. Mononitrosylcobalt(III) complexes with mixed ligand tetradentate Schiff bases

Abstract Thermal NO dissociation reactions in the solid phase of mononitrosylcobalt(III) complexes with the formula, CoL 4 NO (L 4 denotes tetradentate ligands such as bzacen, salen and its 5-NO 2 , 5-Cl, and 5-Me derivatives 2 ) have been investigated by means of TG, DSC, and pyrolysis gas chromatographic analyses. The complexes eliminated one mole of NO per mole in the 160–300°C range and reproduced CoL 4 complexes which possessed X-ray diffraction patterns similar to those of authentic CoL 4 complexes. The kinetic analyses indicated that the NO dissociation process followed a first-order equation; the activation enthalpy values were 120–124 kJ mol −1 , being invariable irrespective of the nature of L 4 . The values of heat of NO dissociation, determined by the DSC method were in the range 40–50 kJ mol −1 . From these thermochemical data and the data of heat of solution of NO, the NO dissociation energies in solution were calculated to be 52–61 kJ mol −1 . The thermal data were discussed in terms of the nature of the CoNO bond.

Pyrolysis gaschromatography of the mixed ligand complexes of molybdenum- and tungsten-dinitrosyls

Abstract The pyrolytic behavior of the cis -dinitrosyl complexes with the general formulas [M(NO) 2 Cl 2 L 2 ], [M(NO) 2 Cl 2 L′], and [M(NO) 2 L 2 ′] where M is Mo or W, L is monodentate and L′ bidentate ligands were investigated by means of the TG, DSC, and pyrolysis gaschromatography (PGC) analyses. Upon pyrolysis, these dinitrosyls have been found to yield a gaseous product composed of N 2 , N 2 P and NO; the mixed ligands L and L′ which are good π-electron acceptor and readily oxidized, favor the occurrence of the redox reaction of the nitrosyl ligands. The formation of N 2 and N 2 O are discussed by taking into account a thermally induced, intramolecular interaction between the nitrosyl and the adjacent ligand L or L′ initiating the redox reaction.

Kinetics of thermal decomposition of substituted pyridine adducts of N,N'-ethylenebis(salicylideneaminato)cobalt(II) in the solid state

Abstract Kinetic and thermodynamic aspects of the axial base dissociation of solid Co(salen) (X-py) complexes, X = H ( 1 ), 3-Me ( 2 ), 4-Me ( 3 ), 3,4-Me 2 ( 4 ), 3,5-Me 2 ( 5 ), 3-NH 2 ( 6 ), 3-Cl ( 7 ), 3-CN ( 8 ), 4-CN ( 9 ), have been investigated by means of TG-DSC and isothermal weight-loss measurements. These adducts endothermically dissociate the axial base giving rise to the oxygen-active Co(salen) complex. The axial base dissociation reactions fit the contracting disc equation and the kinetic compensation effect is observed for all the adducts excepting Adducts 4–6 . For the remaining adducts the kinetic and thermodynamic stabilities of the Co-(X-py) bond are found to increase linearly with increasing Hammetts substitution constants of X except for Adducts 3 and 9 . These results are discussed in terms of the σ and π interactions between cobalt(II) and substituted pyridine. Factors dominating the kinetic bond stability are briefly discussed.

Solid-state stability of dioxygen-{N,N′-ethylenbis(benzoylacetoneiminato)} (organic base) cobalt complexes

Abstract The thermal stability of dioxygen adducts, Co(bzacen)(B)O 2 , where B is a series of pyridine or alkylamine derivatives, has been investigated. The dissociation of O 2 proceeds accompanied by the dissociation of B, and the dissociation temperature decreases with increasing basicity of B, suggesting that a stabler adduct in solution dissociates thermally at a lower temperature in solid. On the adducts where B = pyridine derivatives, the dissociation temperature is over rather wide range 35–100°C, whereas the p K a value of B is over a narrow range 5.18–6.34. The results have been considered to evidence the existence of a predominant factor for stabilizing the solid-state of the O 2 -adduct other than those which arise from electronic, and steric molecular-structure.

Thermal intramolecular electron transfer reactions of [N,N′-ethylene-bis(salicylideneaminato)](2,4-pentanedionato)cobalt(III) complexes in the solid state

Abstract The title complexes with the formula Co(salen)L where L is a series of 2,4-pentanedionates underwent thermally induced one-electron transfer reactions from L to Co(III). The reaction left behind a stoichiometric amount of the crystalline Co II (salen) complex which took up oxygen in a molar ratio of Co:O 2 = 2:1. The kinetic analyses showed that the electron transfer reaction rate was apparently dominated by activation entropy rather than by activation enthalpy.