Azofärgämnen

Azofärgämnen, also known as azo dyes, are synthetic organic compounds that contain one or more azo bonds (–N=N–) linking aromatic rings. The first commercial azo dye was mauveine, discovered by William Henry Perkin in 1856 during his attempt to synthesize quinine. Since then, azo dyes have become the largest class of synthetic dyes, covering many industries such as textiles, food, cosmetics, and printing.

Chemically, azo dyes are formed by a diazo coupling reaction between a diazonium salt and a coupling component, typically an activated aromatic compound. The resulting azo bond gives the dye its chromophoric properties. The colour spectrum of azo dyes ranges from red and orange to yellow and green, depending on the substitution pattern and the electron-donating or withdrawing groups present. Variants of the basic structure are developed by incorporating different functional groups such as sulfonates, carboxylates, or ammonium ions to improve water solubility, fixation on fibres, or resistance to light and pH changes.

In textile applications, azo dyes are classified into direct, reactive, vat, and disperse dyes based on their fixation chemistry. Direct dyes quickly disperse on cotton and other cellulose fibres without auxiliary fixing agents. Reactive dyes form covalent bonds with the fibre, offering improved washfastness. Vat dyes are insoluble in water and become reduced during dyeing, forming soluble colorless intermediates that reoxidise in the fibre to lock the colour. Disperse dyes are used mainly for synthetic fibres such as polyester, where the dye is finely dispersed in the fibre matrix.

Despite their commercial importance, some azo dyes have raised environmental and health concerns. Certain dyes can release aromatic amines upon hydrolysis, which may be carcinogenic or mutagenic. Consequently, regulatory agencies have limited the use and discharge of azo dyes, and research continues to produce more biodegradable and safer variants.