Kinetics of the reaction of arylethanediylidene‐bis‐dithiocarbazonoate Ni complexes with morpholine in benzene: Substituent and temperature effects

[1‐Arylethanediylidene‐bis(methyl dithiocarbazonoate) NN′SS′ (−2)]Ni(II) complexes were prepared by condensation of arylglyoxals with methyl dithiocarbazoate to give the corresponding hydrazonoates. The chelation of nickel(II) with these hydrazonoates gave square planar Ni complexes. The k 3 values for the substitution of SCH 3 close to the aryl group with morpholine (Mo) in benzene were found to increase steadily (20–35°C) followed by a sudden drop after 35°C. A continuous decrease in k 3 values was observed by further elevation in the temperature. The Arrhenius plot showed a convex curve at the whole temperatures 20–55°C, and negative Δ H # values for the reactions were obtained at 40–55°C. The Hammett plots at the temperature ranges 20–35° and 40–55°C exhibited good straight lines with ρ values of 1.44–0.73 and 1.18–1.25, respectively. The proposed mechanism is a nucleophilic aromatic substitution‐like, in which the rate‐determining step is the proton transfer process in the temperature range 20–35°C whereas the mechanism in the range 40–55°C passes through the attack of Mo on the carbon carrying the SCH 3 group followed by the addition of the second Mo molecule on Ni to form an intermediate, which undergoes elimination of Mo and CH 3 SH to give a monosubstitution complex. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 44: 27–40, 2012