Studien zum Vorgang der Wasserstoffübertragung, XXXIV¹⁾ Elektrochemische Hydrodimerisierung von Schiffbasen

Abstract

An N-Benzyliden-p-toluidin als Modellsubstanz wurden durch systematische Variation der Elektrolyseparameter die optimalen Bedingungen fur die elektrolytische Hydrodimerisierung zu I ,2-Diphenyl-N,N'-di(p-tolyl)~thylendiamin ermittelt. Die Produktzusammmsetzung hangt ab: 1) von der Protonenverfugbarkeit in der elektrischen Doppelschicht (verstarkte Bildung des Hydrodimeren in wasserfreien Grundelektrolytsystemen unter Verwendung hydrophober Leitsalzkationen und -anionen); 2) vom Kathodenmaterial (an Quecksilber ist die Bildung des Hydrodimeren, an Kupfer, Blei und ,,Glassy Carbon" die Bildung des sekundaren Amins begunstigt) ; 3) von der durchgeleiteten Elektrizitatsmenge (die Stromausbeute in bezug auf Hydrodimeres ist bis ca. 60 % des theoretischen Umsatzes konstant, sinkt aber bei weiterem Umsatz ab); 4) von der Depolarisatorkonzentration und der Katholyttemperatur (vgl.Tabellen 7 und 8). Das ~~/rneso-VerhaItnis wird in den meisten Ansatzen zu ca. 0.9-1.1 gefunden; bei tieferen Temperaturen verschiebt es sich zu ca. 1.2. -Unter den fur N-Benzyliden-p-toluidin ermittelten optimalen Bedingungen wurden 12 weitere N-substituierte Benzylidenamine hydrodimerisiert und die DL/rneso-Verhaltnisse der Hydrodirneren bestimmt. Die bei Verwendung optisch aktiver Leitsalze entstehenden Hydrodimeren sind racemisch. (Die aus prochiralen rx-Methylbenzylidenaminen gleichzeitig gebildeten sekundaren Amine sind optisch aktiv.) Bei der Coelektrolyse von Schiffbasen mit Carbonylverbindungen ahnlichen Reduktionspotentials entstehen vicinale Aminoalkohole, wie am Beispiel der gemischten Hydrodimerisierung von Benzaldehyd und N-Methylbenzylidenamin zu o~-eryrhro-2-(Methylamino)-1.2-diphenylathanol gezeigt wird. Studies on the Occurrence of Hydrogen Transfer, XXXIV1). -Electrochemical Hydrodimerization of SchiffbasesThe optimal conditions for the hydrodimerization of N-benzylidene-p-toluidine to I ,2-diphenyl-N,N'-di(p-tolyl)athylenediamine have been investigated by systematic variation of the electrolysis parameters. The product composition depends upon : I ) the proton availability in the electrical double layer (increased yield of hydrodimer in non aqueous. base electrolyte systems and hydrophobic supporting electrolyte anions and cations); 2) the electrode material (on mercury, the hydrodimer is the main product while on copper, lead and glassy carbon, reduction t o the secondary amine is favoured); 3 ) the number of coulombs passed (the current yield in relation to the hydrodimer is constant until about 60% of the theoretical conversion; this yield falls however on further passage of current); 4) the depolarizer concentration and *) Korrespondenz bitte a n diesen Autor richten. 1975Studien zum Vorgang der Wasserstoffubertragung, XXXIV 121 1 the catholyte temperature (compare Tables 7 and 8). The DL/meso ratio was found in most cases to be 0.9-1.1; this was shifted at lower temperature to about 1.2. -12 further Nsubstituted benzylideneamines were dimerized under the optimal conditions obtained for N-benzylidene-p-toluidine and the D...

Oxidative Deamination of Benzylamine by Electrogenerated Quinonoid Systems as Mimics of Amine Oxidoreductases Cofactors

“…They indicated that the main product of benzylamine oxidation was PhCHNCH 2 Ph, whereas PhCHO was present as a minor product. As earlier reported, dibenzylamine 5 resulted from a two-electron reduction process, while dimers 6 and 7 , isolated as meso and ( D , L ) forms, arose from a one-electron reduction mechanism. The formation of imidazolidine 8 could be reasonably regarded as proceeding through a tandem two-electron oxidation−cyclization reaction of a dimer form, during isolation or upon column chromatography (Scheme ).…”

“…Interesting enough, the isolation of mixed dimer 9 constituted a proof of the presence, in the exhaustively oxidized solution, of benzaldehyde as the minor product. Mixed dimer 9 resulted obviously from the condensation reaction of radicals formed consecutively to the one-electron reduction of both PhCHO and PhCHNCH 2 Ph 2 1 Yields of Catalytic Deamination of Benzylamine Mediated by Electrogenerated Model Quinonoid Cofactors in Deaerated CH 3 OH a yield (%)substrate(a)(b) 1 red 2600 53 2 red 800 16 3 red 3200 64 4 red 3200 64 a Electrochemical oxidation of the substrate was performed at a mercury pool ( E = +100 mV vs SCE), [substrate] = 2 mM, [PhCH 2 NH 2 ] = 100 mM, under N 2 , in CH 3 OH.…”

Simple electrochemical reduction of nitrones to amines

“…We envisioned that we could carry out the direct reduction of nitrones to amines using electrochemistry. The cleavage of N–O bonds with electricity has been described and it is known for some organic moieties, such as nitrile N -oxides or oximes,12 whereas there are some electrochemical examples of reductive processes with imines, although guided to the synthesis of diamines 13,14…”

A one-pot chemoselective synthesis of secondary amines by using a biomimetic electrocatalytic system

“…In some cases (entries 2, 8 and 9, Table 1), diamines B arising from a one-electron reduction mechanism were also observed as dimeric by-products (Scheme 3). The formation of related diamines has been previously reported from the one-electron reduction of aldimines [43][44][45][46]. In some cases, the electrochemical method enabled to perform the synthesis of vicinal diamines with a high degree of selectivity [44,46].…”