When ortho-nitrated benzoic acids are chlorinated in xylene and acetonitrile, the product gases, HCl and SO2, dissolve in the solvent mixture. Previously measured solubilities [Lever, S. D., Papadaki, M. (2004a). o-Chlorination of 2-nitrobenzoic acid with thionly chloride in xylene and acetonitrile. Solubility study of hydrogen chloride and sulphur dioxide in xylene and acetonitrile, IChemE transactions part B. Process Safety and Environmental Protection. 48-60.] were compared to other published data and found to be in very good agreement. The heat of solution of SO in xylene was evaluated calorimetrically and compared to the value obtained from our previous experimental work. In our previous work [Lever, S. D., Papadaki, M. (2004b). Study of condition-dependent decomposition reactions-the thermal behaviour and decomposition of 2-nitrobenzoyl chloride part_I. Journal of Hazardous Materials. 115; pp. 91-100], it was reported that the products of the decomposition are condition dependent. The current study showed that the decomposition is extensively promoted by the presence of HCl. This has important safety implications should the process operating temperature be reduced and HCl solution in the solvent mixture be increased. If a thermal runaway began in the increased availability of HCl, an undesirable escalation of the runaway could occur. (c) 2005 Elsevier Ltd. All rights reserved.