Thermal decomposition kinetics of diethyl dithiocarbamate complexes of copper(II) and nickel(II)

Abstract

Thermogravimetric (TG), derivative thermogravimetric (DTG) and differential thermal analysis (DTA) curves of CuL~ and NiL2 (L-= diethyl dithiocarbamate anion) in air are studied. The main decomposition temperature ranges are: For CuL2, DTG 250--350 ~ DTA 300--320 ~ and for NIL2, DTG 290--390 ~ DTA 360--400 ~ Mass loss considerations at the main decomposition stages indicate conversion of the complex to sulphides. Mathematical analysis of TG data shows that first order kinetics are applicable in both cases. Kinetic parameters (energy and entropy of activation and preexponential factor) are reported.Transition metal dithiocarbamates have important technical applications, for example, as vulcanization accelerators, as fungicides, etc. As part of an investigation on the thermal decomposition of transition metal complexes [1 ], we have now studied the dithiocarbamate complexes. Thermoanalytical data (TG, DTG and DTA) of two typical complexes, i.e., diethyl dithiocarbamato complexes of copper(ll) and nickel(II) are presented in this communication. Interpretation and mathematical analysis of these data and evaluation of order of reaction and the energy and entropy of activation, based on the differential method employing the Freeman-Carroll equation [2], the integral method using the Coats-Redfern equation [3] and the approximation method using the Horowitz-Metzger equation [4] are also given. Experimental Preparation of samplesSamples of diethyl dithiocarbamato copper(II) and diethyl dithiocarbamato nickel(II) [hereafter abbreviated as CuL2 and NiL2 respectively, where L = = (C2Hs)2NCS2] were prepared by adding, at room temperature (30~ 0.l M aqueous solutions of copper(H) sulphate and nickel(II) sulphate respectively to 0.1 M solutions of sodium diethyl dithiocarbamate. An excess of the ligand was employed (molar ratio, ligand/metal = 4). The precipitates were filtered, washed thoroughly with water, then with alcohol and dried in a vacuum desiccator.

Kinetic analysis of thermogravimetric data on some nickel(II) N-alkyldithiocarbamates

“…Kinetic parameters calculated by employing the above equations are given in Table 3. reported value of 261.6 kJ mol-1 [17] for the decomposition of [Ni(S2CNEt2)2]. If we assume that the activation energy calculated with the Coats and Redfern method is nearly correct, then the activation energy calculated with the Horowitz and Metzger method has a 12% error.…”

“…where w, = total mass loss in the first stage and # = rate of heating (deg min -1 ~-=--"~ -6.4 obtained from the equation [17]:…”

“…It is therefore advisable to use more than one method to treat the data when trying to ascertain the correct activation energy. For this reason, it was considered worthwhile to try one more method mentioned in the literature [15,17], and for this the Horowitz-Metzger equation [11] was chosen: where 0 is the difference between the given temperature T and the temperature T i corresponding to the maximal decomposition rate.…”

Synthesis and thermal studies of mixed ligand complexes of Cu(II), Co(II), Ni(II) and Cd(II) with mercaptotriazoles and dehydroacetic acid

“…5) The entropy values for all degradation steps of all degradation steps of all complexes were found to be negative, which indicates a more ordered activated state that may be possible through the chemisorption of some decomposition products [51][52][53].…”

Thermal studies on tris-chelate complexes of nickel

“…In spite of the large number of studies reported on the thermal analysis of coordination compounds, there are relatively few reports [1][2][3][4] on the calculation of the kinetic parameters and their relationship with the nature of the bonding. This may be due primarily to the uncertainties involved in the experimental measurements.…”