Reactive azo dyes

The invention comprises water-soluble reactive azo dyes which contain at least one group of the formula -O-arylene-(CH2-NH-CO-R-Hal)n wherein R represents a divalent saturated or unsaturated aliphatic hydrocarbon radical, which may be substituted by halogen and has 1 to 3 carbon atoms, n represents one of the integers 1 or 2, Hal represents chlorine or bromine and arylene represents an arylene radical of the benzene or naphthalene series which may contain one or more substituents chosen from alkyl groups with 1 to 5 carbon atoms, alkoxy groups with 1 to 5 carbon atoms and cyclo-alkyl groups and if desired in addition at least one halogen atom. The dyes are prepared by reacting with an appropriate mono- or diazo dye or an appropriate organic compound capable of azo dye formation a reaction product of formaldehyde or a compound which splits off formaldehyde and an amide of an aliphatic saturated or unsaturated halogen carboxylic acid with 2 to 4 carbon atoms and converting the product obtained from an organic compound capable of azo dye formation by suitable reaction to an azo dye. In examples: the dye 1-aminobenzene-2,5-disulphonic acid --> 1-[41-(411-methyl)-phenoxyl]-phenyl-3 -methyl-5-pyrazolone is dissolved in sulphuric acid and reacted with chloracetic acid-N-hydroxymethylamide (1); and 3-amino-41-methyl-1, 11-diphenyl-ether-4-sulphonic acid is dissolved in sulphuric acid and reacted with chloroacetamide and symmetrical dichlorodimethyl ether, the product is diazotized and coupled with 1 - (21,51 - dichloro) - phenyl - 3 - methyl-5-pyrazolone-41-sulphonic acid to obtain a yellow dye (2). Additional examples are furnished. The dyes are suitable for colouring wool, silk, synthetic polyamide fibres, leather and natural and regenerated cellulose.