Studies about Thermal Decarboxylation of Hydroxyl Acids used in Thermal Imaging Benzoic

Six isomers of drhydroxyl benzoic acid and three isomers of trihydroxyl benzoic acid were analysed systematically with thermogravimetric analysis. They, the starting temperatures (TS), the peak temperatures (Ti) and the end temperatures (Te) in the decarboxylation reactions,were worked out based on the integral curves (TG) and the differential curves (DTG) in thermogravimetric analysis of these compounds. The carbon atoms of benzene rings connected with carboxyl groups of these compounds are numbered as C1, and the carbon atoms of carboxyl groups are numbered as C,. The chemical shift values of C1 ( S ,) and C, ( l ,) are from the NMR spectra of these compounds, and it is found that there is a linear relation between TP and S 1 or (s , 61). The net charge values of C1 (q1) and C, (q,) are from the calculations of quantum chemistry. After compared 81 and( S 7 S 1) with q1 and(q,q1) respectively, it is also found that there are linear relations between them. These prove that there is a close relation among S i, q1 and the reactivity of i-position on the benzene ring of a phenolic compound.