Base Catalysed Racemization of Ethylenediamine-N,N,N′-triacetato-aqua-cobalt(III) |
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Authors: | C. A. Bernhard K. Bernauer |
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Abstract: | The kinetics of the base catalysed racemization of [Co(EN3A)H2O] 1 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. |
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