Metallsalze aus 5,5′-methinbisbarbitursäurederivaten, ihre verwendung als pigmente

Abstract

A few methinebisbarbituric acid derivatives have already been reported in the literature. Their description is, however, limited to the symmetric compounds, as free ligand or as sodium and potassium salts. In order to evaluate the pigment properties of such derivatives we prepared the known symmetric as well as new symmetric, asymmetric, mono- and divalent metal salts of such methines. Two known routes have been used for their preparation. The condensation reaction of the ketomethylene compound and its corresponding aldehyde (as free ligand or as sodium salt) in a hot organic solvent or mixture thereof, like ethanol and acetic acid, led to the free monomethineoxonol or its corresponding sodium salt in good yield and purity. The subsequent metallisation step starting from the ligand has been carried out preferably with the metal acetates in boiling ethanol. The same products were obtained in good yield and purity by the condensation of two molecules of ketomethylene compound with esters of orthoformic acid at high temperature followed by metallisation. During the synthesis of asymmetric methineoxonol derivatives we observed a surprising side reaction whose course can be influenced by the reaction conditions. For the formation of these by-products we propose a Michael type nucleophilic attack of a ketomethylene compound at the β-position of the methine double bond of the methineoxonol. The chemical structure of this class of compounds was investigated by spectrometric methods such as 1H- and 13C-NMR, mass-spectroscopy and visible and infrared spectroscopy. All these spectroscopic data agree with a keto configuration of these derivatives. Finally the pigment properties of these compounds such as shade, light and migration fastness in soft PVC are discussed in detail.