4-および5-ニトロサリチルアルデヒドのシッフ塩基とその金属キレート

抄録

Schiff bases of 4- and 5-nitrosalicylaldehydes (4 and 5), with amino acids and their esters were prepared, and their absorption spectra in acidic, neutral, and alkaline methanol were measured. The Schiff bases are present as anionic, I, enolimine, II, and ketoenamine, III, species according to the environment. Addition of Al(III), Cu (II), Zn (II), or Ni (II) ion to the Schiff base solution resulted in the formation of metal chelates, M, spectral properties of which are described. A transient absorption at 494 nm was observed on addition of Al (III) ion to the Schiff base of 4 and alanine methyl ester in neutral methanol and was ascribed to the formation of the Al (III) chelate of the quinoid, B, in which α-carbon of the amino acid moiety in the Schiff base is deprotonated. The loss of α-H was confirmed by nuclear magnetic resonance study. A similar species was not formed with Schiff bases derived from salicylaldehyde or 5, or those of 4 with amino acids or ester of 2-methylalanine, or with the bivalent transition metal ions.