In order to clarify the factors that affect the. hydrodechlorination (abbreviated as HDC) reactivity of aromatic chlorinated compounds, the catalytic hydrotreatment of chlorobenzene (abbreviated as CLB) and para-amino, -methoxy, -methyl, -chloro, -trifluoromethyl, -acetyl, and cyano-substituted chlorobenzenes (abbreviated as CLAN, CLAS, CLTN, DCLB, CLTF, CLAP and CLBN, respectively) was carried out over 5%-platinun-i/carbon (Pt/C) catalyst under 1 MPa of hydrogen pressure at 523 K. In the HDC of CLB and the substituted chlorobenzenes, except for CLBN and CLAP, reductive cleavage between the chlorine atom and the carbon atom took place selectively. In the case of CLBN and CLAP, in contrast, hydrogenolysis of the substituent in the para-position occurred preferentially. In the course of the reaction of CLBN, furthermore, secondary bi-molecular condensation of the hydrogenated intermediate occurred and an appreciable amount of bis(4-chlorobenzyl)amine was produced. HDC reactivity of the chlorobenzenes with electron-donating substituents decreased in the order of CLAN >> CLAS >= CLTN >= CLB. This order of the Pt/C catalyst was similar to that of a 5 %-palladium/carbon (Pd/C) catalyst, which has been reported previously. On the other hand, the reactivity of the chlorobenzenes with electron-withdrawing substituents decreased in the order of CLB >= DCLB >> CLTF. This behavior is in contrast with that observed on the Pd/C catalyst. In the molecular orbital calculation using the DFT method (B3LYP/LANL2DZ), except for CLBN, CLAP and CLTF, the most stable point was obtained when the chlorobenzenes were adsorbed through the chlorine atom on the corner platinum atom of the Pt-14 model cluster. For CLTF, adsorption on the corner platinum atom seemed to occur through the trifluoromethyl substitution in the para-position. The magnitude of the adsorption energy (absolute value) decreased in the following order: CLAN >> CLAS >= CLTN >= CLB >= DCLB >> CLTF. This order of adsorption energy was in good agreement with that of HDC reactivity. The reasons for the adsorption stability are discussed from the viewpoint of the energy level of the frontier orbital. (c) 2006 Elsevier B.V All rights reserved.