Electrochemical reduction of quarternized 2-pyridinio-1,3-indandiones at a mercury electrode—I. Electroreduction in aprotic medium

✍ Scribed by J. Stradins; J. Benders; V. Kadysh

• Publisher: Elsevier Science
• Year: 1986
• Tongue: English
• Weight: 717 KB
• Volume: 31
• Category: Article
• ISSN: 0013-4686
• DOI: 10.1016/0013-4686(86)87030-x

✦ Synopsis

The electrochemical reduction of 2-pyridinio-1,3-indandiones (quarternized pyrophthalones and quinophthalones as well as N-ylides) was studied at a dropping mercury electrode in aprotic medium (DMF). The first one-electron stage ranging from -1.1 to -1.9 V leads to free-radical species in which the density of the unpaired electron is located predominantly at the indandione moiety (radicals of the semidione type) although the pyridinium moiety is also involved. Dimerization of the resultant species gives dimers that can be identified by characteristic anodic oxidation peaks over the -0.6 to -0.9 V potential range. The dimerization rate constant determined for the primary radicals (in case of y-N-methylpyrophthalone) by the Nicholson method was found to be 5 x lo"1 mole-'s-l. In the case of 2-methyl-2-pyridinio-1,3indandiones, two types of free radical species identified by ESR are formed which correspond to one-and three-electron reduction. A product of two-electron reduction was obtained by electrochemical reductive acetylation and assigned with the aid of mass spectrometry. Electroreduction pathways for all types of compounds under investigation were proposed revealing that the indandione moiety is reduced at less negative potentials than the pyridinium one. Quantum chemical interpretation of such reduction sequence is provided.