The intent of this paper is to investigate the effects of leaching time and temperature on the level of desulfurization of organic sulfur by an electron-transfer process involving the transition-metal ion Ni2+ from a sub-bituminous Indian coal. The electron-transfer process was accomplished both in the presence and the absence of naphthalene with unoxidized and oxidized samples. Desulfurization has been determined to be greater in oxidized samples. The presence of naphthalene enhanced the amount of desulfurization both in unoxidized and oxidized samples, revealing that it serves as an excellent electron-transfer agent. Increases in reaction time and temperature increased the level of desulfurization. The electron-transfer process, in the presence of naphthalene, succeeded in removing a maximum of 16.3 wt % organic sulfur from unoxidized coal and 18.7 wt % from oxidized coal at 50 degreesC and 4 h. Study of a model sulfur compound indicated that the desulfurization is primarily due to aliphatic-type compounds, such as dibenzothiophene, that is unable to release sulfur under these conditions. A higher level of desulfurization in oxidized coals is consistent with the formation of oxidized sulfur compounds, as revealed by the infrared study, where it is observed that band intensities due to -S=O and -SO2 units have decreased in their respective regions in the desulfurized coals. The sulfur removal process is continuous. Application of a pseudo-first-order kinetic model produced overall rate constants for the desulfurization reaction that consistently fell in the range of 5.2 x 10(-6)-2.1 x 10(-5) s(-1), implying a slow and steady process. The frequency factor (In A) for the desulfurization reaction in different systems was in the range of 10.8-11.0 s(-1), which is in support of predicting an associated type of reaction that envisages the formation of an activated complex. The Arrhenius activation energy of the sulfur loss reaction in different systems has been observed to be in the range of 10.9-23.0 kJ/mol. A semiquantitative thermodynamic approach of transition-state theory revealed that the desulfurization reaction is nonspontaneous in nature and proceeded with the absorption of heat, accompanied by the reduction in the degree of disorder in the systems, irrespective of the leaching time and temperature.