Über zweistufige Redoxsysteme, XXVI. Einfluß von N-Substituenten in 4,4′-Bipyridylen auf das Redoxverhalten, die Radikalstabilität und die Elektronenspektren

Electrochemical study of the mushroom toxin orellanine and of related pyridine-1-oxides—I. Reduction

Publisher Summary The chapter discusses the electrochemistry of pyridines with regard to industrially significant processes. Over 90% of the reported studies on pyridine electrochemistry deal with cathodic transformations. One reason for this is that the experimental techniques for studying cathodic reactions are more numerous and tractable. One-third of all pyridine electrochemical reports cite reduction of pyridinium quaternary salts. Such transformations have biochemical significance and the products are industrially important. Reductions of pyridine itself are next most frequent, although catalytic hydrogenation has largely replaced electrolytic reduction. The process of reducing pyridine electrolytically represents the largest scale commercial electrolysis of a pyridine compound. There are other processes besides the production of piperidine that occur during cathodic transformations of pyridine. Depending on conditions, dimers, crossed hydrocoupling products, or polymers can be formed; these other products can also have a partially or fully reduced ring. Reduction of pyridine by electrolytic methods is the oldest reported industrial process involving pyridine compounds. Reduction of pyridine under many conditions leads to dimeric reduced products (bipyridyls and bipiperidyls), partial reduction products (3-piperideine), condensation products, polymeric products. The chapter discusses alkylpyridines, vinylpyridines, and hydroxyalkylpyridine under cathodic reaction. It also includes anodic reactions that have low reported yields but are nevertheless of industrial interest. These methods are sometimes an excellent way to obtain functionalized pyridines in a single step, which would otherwise require a multistep conventional process.

Synthesis of Pyridines by Electrochemical Methods

Polarographische untersuchung von substituierten 2,2′-bipyridyl-n-oxiden

The polarographic behavior of 4-methoxy-2,2′-bipyridyl 1-oxide has been investigated in 20% dioxane-water solution. Two well defined reduction waves appear in the pH range 0.76–8.8, a third wave in pH 9.3–10.4, but only one wave in more alkaline solutions. The variation of E1⁄2 with pH followed the relations (E1⁄2)1=−0.37–0.10 pH and (E1⁄2)2=0.84−0.065 pH for waves 1 and 2, respectively. The diffusion current constant for the second wave decrease with increasing pH whereas for the first wave it remains constant upto pH 7.0 and decreases afterwards. Variation of diffusion current with temperature and reservoir height indicates the diffusion controlled nature. Wave 1 is produced by the 2 electron reduction of protonated N-oxide to 4-methoxy-2, 2′-bipyridyl. This intermediate is further reduced, at more negative potentials, to 1,4′-dihydro-4-methoxy-2,2′-bipyridyl by consuming two more electrons and two hydrogen ions simultaneously. The third wave is presumably due to catalytic hydrogen evolution.

M. Lalithambika

Papers

Polarographic Studies on Substituted 2,2′-Bipyridyl N-Oxides

Polarographische untersuchung von substituierten 2,2′-bipyridyl-n-oxiden