Abstract
The base-catalyzed decomposition of ethylaquocobaloxime has been studied by GLC, mass spectrometry, and manometric techniques at 50.0 +- 0.1/sup 0/C in aqueous solution and in D/sub 2/O. Under all conditions, a mixture of ethane and ethylene is obtained, and no photolabile organocobalt complex is formed. In D/sub 2/O the alkane product is monodeuterioethane of high isotopic purity, but little or no deuterium is incorporated into the alkene product. Unreacted starting material recovered from partial decomposition in alkane D/sub 2/O was found to have very little deuterium incorporated into its alkyl ligand. From the dependence of the product ratio on base concentration, the observed rate constant for decomposition in 1.0 M base and the spectrophotometrically determined dissociation constants for the hydroxo (and deuterioxo) species the specific second-order rate constants for the alkene-forming reaction ((1.06 +- 0.06) x 10/sup -6/M/sup -1/s/sup -1/ and (3.21 +- 0.12) x 10/sup -6/M/sup -1/s/sup -1/ for the anionic hydroxo species in H/sub 2/O and D/sub 2/O, respectively, and (5.36 +- 0.43) x 10/sup -7/M/sup -1/s/sup -1/ and (2.20 +- 0.15) x 10/sup -6/M/sup -1/s/sup -1/ for the neutral aquo species in H/sub 2/O and D/sub 2/O, respectively) and the alkane-forming reaction ((6.05 +- 0.35) x 10/supmore » -6/M/sup -1/s/sup -1/ and (5.87 +- 0.73) x 10/sup -6/M/sup -1/s/sup -1/ for the hydroxo species in H/sub 2/O and D/sub 2/O, respectively, and zero for the aquo species in both solvents) have been determined. The large inverse solvent deuterium isotope effects for the alkene-forming reaction are discussed in terms of a likely E2 mechanism. The mechanism of the alkane-forming reaction cannot be determined from the present data but is discussed in light of the recent results for methane formation from methylaquocobaloxime in aqueous base. It is concluded that the mechanism of the alkane-forming reaction may not be the same for the two organobaloximes. 3 figures, 2 tables.« less
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