Anation of cis-aquoerythro chromium(III) ion by thiocyanate ion in acidic aqueous solution
Affiliation:
1. Department of Chemical Engineering, University of Michigan, 3074 H.H. Dow, 2300 Hayward Street, Ann Arbor, MI 48109-2136, United States;2. Institute of Industrial Catalysis, School of Chemical Engineering and Technology, Xi’an Jiaotong University, Xi’an, Shaanxi 710049, China;1. VNU-HCM, Key Laboratory of Chemical Engineering and Petroleum Processing (Key CEPP Lab), Ho Chi Minh City University of Technology (HCMUT), 268 Ly Thuong Kiet Street, District 10, Ho Chi Minh City, Vietnam;2. Faculty of Chemical Engineering, Ho Chi Minh City University of Technology (HCMUT), 268 Ly Thuong Kiet Street, District 10, Ho Chi Minh City, Vietnam;3. VNU-HCM, Ho Chi Minh City University of Science, 227 Nguyen Van Cu Street, District 5, Ho Chi Minh City, Vietnam;1. Institute of Green Chemistry and Chemical Technology, School of Chemistry & Chemical Engineering, Jiangsu University, Zhenjiang 212013, PR China;2. School of Energy and Power Engineering, Jiangsu University, Zhenjiang 212013, PR China;3. Jiangsu Fluid Machinery Engineering Research Center, Jiangsu University, Zhenjiang 212013, PR China;1. Technical University of Freiberg, Institute of Energy Process Engineering and Chemical Engineering, Chair of Reaction Engineering, Fuchsmühlenweg 9, D-09596, Freiberg, Germany;2. Karlsruhe Institute of Technology, Institute of Technical Chemistry and Polymer Chemistry, D-76128 Karlsruhe, Germany
Abstract:
The rate of anation of cis-aquoerythro ion, cis-(NH3)5Cr(OH)Cr(NH3)4(OH2)5+, by thiocyanate ion has been studied in aqueous perchlorate solution. The reactions were conducted under the following experimental conditions: t = 25·0°, 32·1°, 35·6° and 40·8°, [cis-aquoerythro] = (7·0–10·0) × 10−3 M, [H+] = 0·1−0·01 M, [NaSCN] = 0·1−0·8 M and μ = 1·0 M(NaClO4). The observed rate law is first-order in cis-aquoerythro ion concentration, independent of hydrogen ion concentration, and linearly dependent in thiocyanate ion concentration. Therefore, the rate law can be expressed as: R = (ka + kb[SCN−])[cis-aquoerythro], and the values of ka and kb at 25° are 0·344 × 10−4 sec−1 and 1·01 × 10−4 M−1 sec−1. The mechanism postulated for the anation reaction involves the SN1 type and SN1 I.P. (ion pairing) mechanistic steps. The ion-pairing process is supported by the activation parameters (ΔH‡ = 19·9kcal/mole, ΔS‡ = −10·2e.u. role=presentation style=font-size: 90%; display: inline-block; position: relative;>) which is similar to the values reported for an analogous aquopentaaminechromium(III)-NCS− system. The competitive cleavage reaction of the cis-aquoerythro ion can be estimated from the cleavage rate data and its contribution accounts for 9–17 per cent of the overall reaction.
