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  • Author or Editor: Katarina Anđelković x
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Experimental R M values for a series of functionalized 2-alkylidene-4-oxothiazolidines and 1,2-dithioles have been determined by reversed-phase TLC on RP-18 silica plates. Binary mixtures of methanol and water, tetrahydrofuran and water, and acetone and water were used as mobile phases. R M 0 values were determined for these mobile phase mixtures by linear extrapolation to 0% ( v/v ) organic modifier. The lipophilicity, C 0 , was calculated as the ratio of the intercept and slope values. Chromatographically obtained lipophilicity data correlated well with calculated log P values.

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Journal of Thermal Analysis and Calorimetry
Authors:
Dragica M. Minić
,
Maja T. Šumar-Ristović
,
Đenana U. Miodragović
,
Katarina K. Anđelković
, and
Dejan Poleti

Abstract

The kinetics of multi-step thermal degradation of Co(II) complex with N-benzyloxycarbonyl glycinato ligand [Co(N-Boc-gly)2(H2O)4]·2H2O, in non-isothermal conditions was studied using isoconversional and non-isoconversional methods. The degradation of complex occurs in three well-separated steps involving the loss of water molecules in first step followed by two degradation steps of dehydrated complex. The dependence of Arrhenius parameters on conversion degree showed that all observed steps of thermal degradation are very complex, involving more than one elementary step, as can be expected for most solid-state heterogeneous reactions with solid reactants and solid and gaseous products. It was shown that step 1, corresponding to the dehydration, involves a series of competitive dehydration steps of differently bound water molecules complicated by diffusion. Second step involves two parallel reactions related to the loss of two identical C6H5CH2O– ligand fragments complicated by the presence of products in gaseous state. Further degradation in step 3 corresponds to complex process with a change in the limiting stage, in this case from the kinetic to the diffusion regime, connected with the presence of gaseous products diffusing through the solid product.

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Journal of Thermal Analysis and Calorimetry
Authors:
Maja Šumar-Ristović
,
Dragica Minić
,
Dejan Poleti
,
Zoran Miodragović
,
Đenana Miodragović
, and
Katarina Anđelković

Abstract  

Thermal behavior of Co(II), Cd(II), and Zn(II) complexes with N-benzyloxycarbonylglycinato ligand was investigated using the results of TG, DSC and DTG analysis obtained at different heating rates (2.5 to 30 °C min−1), from room temperature to about 900 °C. Mechanisms of complex degradation, as well as enthalpies of the degradation processes were determined. It is shown that thermal stability of investigated complexes correlates with their crystal structures, especially with the presence of crystallization and coordinated water molecules. The values of dehydration enthalpies are discussed and correlated with composition of the complexes. Kissinger’s, Ozawa’s, and Friedman’s isoconversion methods were used for the determination of kinetic parameters: the pre-exponential factor A and the apparent activation energy E a. For all three complexes and all steps of degradation, the values of kinetics parameters obtained by Kissinger’s and Ozawa’s methods are in good agreement. The results obtained by Friedman’s method showed that some decomposition steps are simple and some others are complex ones.

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