An active methylene compound, malononitrile, was introduced into the structures of a series of disperse dyes previously prepared by coupling phloroglucinol, barbituric acid, and α and β-naphtho to 4-amino-3-nitrobenzaldehyde. The dyes were purified by recrystallization from ethanol. The purity of the dyes was examined by thin-layer chromatography (TLC) and the dyes were characterized by visible absorption and Fourier transform infrared spectroscopy (FTIR). The malononitrile-condensed dyes produced deeper colours and shades with better fastness to wash, light, and perspiration on application to polyester and nylon fabrics when compared to their uncondensed analogue. 1. Introduction Disperse dyes are substantially water-insoluble nonionic dyes which are applied to hydrophobic fibres (cellulose acetate, polyester, and nylon) from aqueous dispersions [1–5]. Disperse dyes are characterized by the absence of solubilizing groups and low molecular weight. From a chemical point of view, more than 50% of disperse dyes are simple azo compounds. About 25% are anthraquinones and the rest are methine, nitro, and naphthoquinone dyes [6]. The most dominant group of these dyes are the azo disperse dyes which account for approximately 60？70% of all disperse dyes manufactured [7–16]. The use of malononitrile (propanedinitrile, dicyanomethane; malonic (acid) dinitrile; propiodinitrile; methylene cyanide; cyanoacetic acid nitrile; malonitrile; malodinitrile) either as a coupling or diazo component or condensing agent with different chromophoric compounds in the synthesis of disperse dyes have been reported [1, 5, 11–16]. However, there seem to be no literatures on the condensation of disperse dyes derived from 4-amino-3-nitrobenzaldehyde coupled to phloroglucinol, barbituric acid, and α and β-naphthols with malononitrile. The present study reports the synthesis of new malononitrile-condensed disperse dyes and their application onto polyester and nylon fabrics. Malononitrile was successfully introduced into the structures of four dyes (D1–4) previously prepared by the conventional diazotization and coupling methods to give dyes (D5–8) (see Figure 2). This was achieved by the Knoevenagel condensation in which a molecule of water was eliminated by way of nucleophilic addition of an active hydrogen compound (malononitrile) to a carbonyl group (C=O) contained in 4-amino-3-nitrobenzaldehyde followed by a dehydration reaction. The base in the reaction was piperidine. The products have larger molecular weight with usually higher melting points when compared with their parent
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