.J. Indian Chern. Soc., ' •>I. 79, August 2002, pp. 649-654 Solvolysis of the [Cr(NCS)4(benztriazoleht ion in ethanol-water mixtures Ion Ganescua*, George Bratulescu", Ion Papaa, Anca Ganescu 0 , Liviu Chirigiuh and Alin Barbuh aFaculty of Chemistry, University of Craiova, 13 A. I. Cuza Str.. 1100 Craiova. Romania Fax : 4-051-197048 bFaculty of Pharmacy, University of Medicine and Pharmacy. Bdl. I. Antonescu. 94 Craiova. Romania Mwwscript received 5 Nm·ember 2001. revised 8 March 2002. accepTed 11 March 2002 the concentration of the free thiocyanate ion and the nontransformed [Cr(NCS)4(benztriazolc)lr ion, the rate constants of the solvolysis process have been calculated. The solvolysis includes two parallel reactions - the substitution or thiocyanate ions and of bcnztriazole molecules. The first stage of the solvolysis is the substitution of a single SCN"; this reaction is of first order with regard to the complex ion. This reaction is followed hy the very fast substitution or the second SCN". The parallel henztriazole substitution reaction seems to be a third order one, first order with regard to the complex ion and second order with regard to ethanol. The influence or the acidity been studied. The solvolysis of the complexes of the Reinecke salt type has not been thoroughly investigated. Adaml)on 1 made ex- tensive study on the hydrolysis of [Cr(NCS)iNH3hL but the analogous complex ions where NH 3 is substituted for different amines. remained almost unexplored. Only in one paper. Thomas and Hotbl mentioned an investigation 3 about the kinetics of hydrolysis in the case of the ion [Cr[NCSManiline) 2 r. These authors gave no quantitative data concerning the kinetic parameters of the reaction. They mentioned only the independence of the hydrolysis rates in the pH-range 1-4. In the present paper we report our studies on the hydrolysis of some benztriazole derivatives using ethanol- water mixtures of different compositionsas solvent. As Adamson 1 observed a constant ratio between the concentra- tion of the liberated thiocyanate ions and of the transformed complex ion. we followed the kinetics of the process measuring the concentration of the free thiocyanate ions, and the concentration versus time plots are shown in Fig. I. As seen, the curves have no exponential shape and especial- ly at lower temperatures can not reflect a unitary process. 100 ;>00 .,oo t.t,;,., Fig. 1. Variation of the free SCN- concentration with time at different temperatures: solvent : 6.7% ethanol in water; complex con- centration = 5.1 X w·' M. We can assume that this reaction is more complicated than the hydrolysis of the Reinecke salt studied by Adamson. For this reason we also measured the concentration of the nontransformed complex ions in the following runs. A plot of log yly 0 vs t (where y is the actual, Yo the initial con- centration of the ion LCr(NCS)q(benztriazole):zn showed a linear variation (Fig. 2). The slope of the straight line Table 1. Kinetic data concerning the total. reaction Solvent Rate constant. k/10"- 3 min- 1 Eo logPZ 5"298 ethanol, 32" 42" 44.4" 47" 52° kJ mol- 1 J K- 1 mol- 1 wt.o/c 67.0 2.72 5.83 12.30 136.1 18.1 91.3 13.6 3.89 8.07 16.50 130.6 17.2 76.6 27.6 1.78 7.51 15.41 29.20 123.9 16.2 56.5 425 12.62. 24.70 48.70 122.3 16.1 54.4 95.5 ,- ... 48.70 140.10 121.8 16.4 60.3 649