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An activation energy of Ea = 213.73 kJ tool d has been determined for the thermal decomposition of SmC204C1 to SmOCI, CO and CO2. The result is predictable on the basis of the Kahwa-Mulokozi expression + for the activation energy and its extended interpretation.The basis for our mechanistic interpretation of the thermal decomposition kinetics of oxalate is the Kahwa-Mulokozi expression for the activation energy

A mechanism for the thermal decomposition of ionic oxalates has been proposed on the basis of three quantitative relationships linking the quantities re/rt (the ratio of the Pauling covalent radius and the cation radius of the metal atom in hexacoordination) and 2JIt (the sum of the ionization potentials of the metal atom in kJ tool -1)~ with the onset oxalate decomposition temperature (Td) (Eq. 1) the average C--C bond distance (d) (Eq. 2), and the activation energy of oxalate decomposition (E~) (Eq. 3):( 1) ri d= 1.527 + 5.553 x 10-6 (122 -r~c (Zli)~) zrl (2) Ea = 127 -t-1.4853 X 10 .6 --9800On the basis of these results it is proposed that the thermal decomposition of ionic oxalates follows a mechanism in which the C--O bond ruptures first. From Eq. 3 it is further proposed that strong mutual electronic interactions between the oxalate and the cations restrict the essential electronic reorganization leading to the products, thereby increasing E~.

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Pharmaceutical intended for use in the tropics are required to maintain their stability under the most severe storage conditions. Chloroquine phosphate, a common antimalarial formulation, was exposed to the sun of the roof topunder the extreme heat of the Saharan climate during the hot and dry season (February to June) at an average day temperature of 43 ~ The heat of melting A H determined by differential scanning calorimetry decreased from 60.1 J/g to 33.2 J/g after exposure for 73 days, corresponding to 49% decomposition. Differential scanning calorimetry is shown by this work to be a rapid and reliable technique for the routine quality control of chloroquine phosphate powders and tablet formulations.Since pharmaceuticals are often organic compounds with well-defined melting points, differnential scanning calorimetry can be used for their easy, rapid and reliable quality control.This technique has been found to be quite appropriate for determination of the deterioration of chloroquine phosphate on exposure to the sun under the severe Saharan climatic conditions obtaining in Sokoto during the dry season (January to May). This study is particularly relevant, because antimalarial formulations including chloroquine phosphate (dominant on the market) are sold locally by traders who in the majority of cases are ignorant of the ideal storage requirements. It is therefore possible that millions of users in the tropics receive the antimalarials after they have been subjected to considerable exposure to the sun.Pure chloroquine phosphate shows a main endothermic peak at 196.5 ~ followed by a small one at 210.3 ~ These peaks are associated with the melting of its two crystalline forms. The heats of melting derived from the integrated peak areas on a DSC scan were used to determine the content of chloroquine phosphate in the sunexposed samples.