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Substitution reactions of thiocyanate complexes. IV. Kinetic isotope effect in aquation of tetrathiocyanatobis(aniline)(chromate(III)

G. Thomas and Ľ. Treindl

Komensky-Univ., Bratislava


Abstract: The aquation of NH4[Cr(NCS)4(PhNH2)2] in D2O with the substitution of the amine ligands was studied by the polarographic method at 46-58°. The kinetic isotope effect kH2O/kD2O was detd. by comparing the rate consts. k1 and k2 with corresponding values in H2O. The activation parameters ΔH* and ΔS* were calcd. The pronounced decrease of the isotope effect with increasing temp. at the substitution of the 1st aniline mol. and the concn. dependence of the rate const. k1 indicate a preset assocn. equil., at which the monomer anion form is more reactive. The difference of the activation parameters δΔH*, δΔS* agrees with an mechanism SN1. An acid-base equil. of the present substitution of the 2nd aniline mol. was proven by pH measurements during the aquation. A more rapid increase of the reactions rate in H2O as compared with that in D2O can be explained by a different temp. coeff. of the dissocn. consts.

Full paper in Portable Document Format: 2211a809.pdf (in German)


Chemical Papers 22 (11) 809–818 (1968)

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