Polarographic behaviour of ω-diazoacetophenones in aqueous buffer solutions

Abstract

The polarographic behaviour of ω-diazoacetophenone and 12 meta- and para-substituted ω-diazoacetophenones has been studied in aqueous buffer solutions. The polarograms generally show three waves corresponding to successive reduction of the diazo-ketone to the corresponding ω-aminoacetophenone, acetophenone, and either 2-phenylethanol or 2,3-diphenylbutane-2,3-diol. The reduction scheme may be represented: first wave, XC₆H₄·CO·CHN₂+ 7H⁺+ 6e → XC₆H₄·CO·CH₂·NH₂+ NH₄⁺, second wave, XC₆H₄·CO·CH₂·NH₂+ 3H⁺+ 2e → XC₆H₄·CO·CH₃+ NH₄⁺, third wave, XC₆H₄·CO·CH₃+ 2H⁺+ 2e → XC₆H₄·CH(OH)·CH₃, or 2XC₆H₄·CO·CH₃+ 2H⁺+ 2e →[graphic omitted] where X is the meta- or para-substituent (including H). For the p-nitro-substituted compound an additional wave is observed, preceding that for the diazo-ketone reduction, and corresponding to reduction of the nitro-group.

The polarographic behaviour of p-bromo-ω-diazoacetophenone and preparative controlled potential electrolysis experiments indicate that the six-electron reduction follows the scheme: XC₆H₄CO·CHN₂+ 2H⁺+ 2e → XC₆H₄CO·CH:N·NH₂, XC₆H₄CO·CH:N·NH₂+ 2H⁺+ 2e → XC₆H₄CO·CH₂·NH·NH₂, XC₆H₄CO·CH₂·NH·NH₂+ 3H⁺+ 2e → XC₆H₄CO·CH₂·NH₂+ NH₄⁺