Thermal decomposition of benzofuroxan compounds

A study has been made of thermal decomposition of some benzofuroxan compounds by using DTA technique. The samples studied benzofuroxan are 5,7-diamino-4,6-dinitrobenzofuroxan (DADNBF) ,5-methylamino-4, 6-dinitrobenzofuroxan (MADNBF), 5-acetylamino-6-nitrobenzofuroxan (ACNBF), 5-methylamino-4-nitrofurxan-[4, 3-h] benzofuroxan (MANFBF), 7-acetylaminobenzofuroxan (ACBDF), 6-nitrobenzofuroxan (NBDF), benzotrifuroxan (BTF), bi(5-benzofuroxan)-sulfone (DBFS). The formal kinetic parameters of thermal decomposition have been calculated by methods of Kissinger and Ozawa. Analyzing calculated results, we find out that the chemical structure of above-mentioned compounds greatly influence on the formal value of activation energy of thermolysis (E) and of exponential factor (A). The formal value of E changes in the range of 160-240 kJ·mol^-1. At the same time the shape of DTA curve, e.g. the property of acceleration period, changes in various way. Increasing the number of furoxan introduced to benzonic nucleus makes the value of E of benzofuroxan compounds lower. For example, the maximum value of E demonstrates one substitution compound DADNBF (E = 420.31 kJ·mol^-1), meanwhile the minimum E demonstrates BTF (three substitution compound). Another substitution groups, for example, amino-, nitro-, methylamino- and carbonyl group do the similar effect on the value of E of these compounds, because chemical structure of compounds determines some physical property of compounds, for example, melt point. As well known, the state of sample influences on the thermal decomposition rate and acceleration trend of samples under the DTA conditions, therefore, it is difficult to judge the complicated effect of chemical structure of above-mentioned benzofuroxan compounds. The results of investigation show that the decomposition rate of BTF is similar to that of RDX.