Base Catalysed Racemization of Ethylenediamine‐N,N,N′‐triacetato‐aqua‐cobalt(III)
Claus Bernhard, Klaus Bernauer · Helvetica Chimica Acta · 1977
Abstract The kinetics of the base catalysed racemization of [Co(EN3A)H2O] Abbreviations: EN3A3−=(−OOCCH2)2N(CH2)2NHCH2COO−; ME3A3−=(−OOCCH2)2N(CH2)2 N(CH3)CH2COO−; EDDA2−=−OOCCH2NH(CH2)2NHCH2COO−; EDTA4−=(−OOCCH2)2N(CH2)2N(CH2COO−)2;TNTA4−=(−OOCCH2)2N(CH2)3N(CH3COO−)2; HETA3−=(−OOCCH2)2N(CH2)2N(CH2COO−)CH2CH2OH; en=H2N(CH2)2NH2; Meen=H2N(CH2)2NHCH3; sar−=−OOCCH2NHCH3. were studied polarimetrically in aqueous buffer solution. The reaction rate is first order in OH− and in complex, in weakly acidic medium. Activation parameters are ΔH≠=22 kcal · mol−1, ΔS≠=26 cal · K−1. The results are discussed in terms of an SN1CB mechanism involving exchange of the ligand water molecule. The N‐methylated analogue [Co(ME3A)H2O] does not racemize in the pH‐range investigated. Loss of optical activity occurs at a rate which is about 1,000 times slower than the racemization of [Co(EN3A)H2O](60°) and coincides with the decomposition of the complex.