Chemically-derivatized nickel surfaces: Synthesis of a new class of stable electrode interfaces

The interactions of protonic acids (HClO₄ and CF₃SO₃H) and of alkylating agents (CF₃SO₃Et and Et₃O⁺BF₄^?) with cyclic ethers and 1,3-dioxacycloalkane s (DCA) in CH₂Cl₂ have been studied by dc polarography (DCP) and differential pulse polarography (DPP). All the reductions were irreversible and kinetically controlled. There is no indication that HClO₄ reacts with THF or OXP; with CF₃SO₃H the decrease of the signals due to the acid may indicate the formation of a product (sec. oxonium ion or ester) or it may be due merely to a modification of the mercury surface by the oxacyclic compound which produces a reduction in the kinetic current; no new signals appear.For the various DCAs with CF₃SO₃Et, 1,3-dioxepan (DXP) gave the clearest indication of reactions occurring and the signals have been assigned (tentatively) to EtDXP⁺ and to the hemiformal ester EtO(CH₂)₄OCH₂OSO₂CF₃. For 1,3-dioxolan (DXL) the picture was less clear, and there was no evidence that 1,3,6-trioxan (TXA) was alkylated.Our study of the DCA with acids gave no evidence that DXL interacts with HClO₄ or CF₃SO₃H, which is due to the exceptionally low basicity of DXL. The signals obtained with DXP and 1,3,6-trioxocan (TXC) are assigned to a molecular complex H₂A⁺-DCA, to the sec-oxonium ion HDCA⁺, and to the hemiformal ester HO(CH₂)₄OCH₂OA.It is concluded that the polarographic behaviour of all the species involved is so complicated that our original aim of distinguishing by this technique between sec. and tert. oxonium ions is not feasible.The sec. oxonium ions formed from cyclic ethers or DCA in conc. H₂SO₄, whose existence was indicated by the PMR spectra, could not be detected polarographically as their reduction potentials were outside the “potential window”.