Cobalt complex salcomine

Oxidative phenolic coupling.1 This cobalt complex and the related salcomine (2, 160, 3, 245 6, 507), both of which bind oxygen reversibly (102 2Co), catalyze the oxygenation of the phenol 1 to give carpanone 2 in 90-94% yield. Related complexes ol l c(ll) and Mn(II) are less effective. PdCl2 effects this reaction in 46% yield (4, 17(1) singlet oxygen is less efficient (29% yield). 

A cobalt complex salcomine (7.39) oxidizes substituted phenols but unsubstituted at para position, such as 2,6-di-fert-butylphenol (7.40), to give the corresponding p-quinone, 2,6-di- tert-butyl-p-benzoquinone (7.41). 

Autoxidation of 2,6-disubstituted phenols. General Electric chemists1 found that salcomine monopyridinate is superior to salcomine itself for autoxidation of 2.6-disubstituted phenols to quinones. This complex, red crystals, C2iH18CoN202, mol. wt. 404.33, has been prepared in 90% yield by the reaction of 3-ethoxy-salicylaldehyde, ethylenediamine, pyridine, and cobaltous acetate.2 Dipheno-quinones are formed to a small extent. These become more important products if the 02-bridged salcomine dimer is used in low concentration and at high temperature. 

Homogeneous catalyst systems include transition metals, e.g. the cobalt Schiff base complex salcomine." "" " However, the quite expensive Schiff base cannot be recovered and recycled, which is a drawback of this method. Copper salts, e.g. CuCl2 and CuBr2, are widely used for the oxidation of TMP with molecular oxygen at larger scales." In addition, applications of the halides of Cr, Mn, Fe, Ni and Zn as catalysts have been described. Copper halides have been combined with earth metal halides, e.g. magnesium chloride." ... 

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