Water-insoluble monoazo-pyrazolone dyestuffs

The invention comprises monoazo dyes free from acid groups imparting stability in water of the formula in which A represents an aryl residue, B an arylene residue, X an unsubstituted or substituted alkyl or aryl group, R an alkyl group with at most 6 carbon atoms, m=1, 2 or 3, z=1 or 2, wherein m must have at least the same value as z and "alk" represents an alkylene residue with at most 6 carbon atoms. The dyes are prepared by conventional diazotization, coupling and/or esterification procedures. In examples, 4-aminobenzoic acid benzyl ester is diazotized and coupled with 1-(b -ethanoyl-oxyethyl) - 3 - methyl - pyrazolone - 5 to obtain a yellow dye (1) and the same dye is obtained by reacting the acid chloride prepared from the dye obtained by coupling diazotized 4-amino-benzoic acid with 1-phenyl-3-methyl-pyrazolone-5, with benzyl alcohol (4). Many additional starting materials are listed. The dyes are suitable for dyeing and printing cellulose esters and ethers, polyamides, polyurethanes, polyvinyl chloride and fibres of polyesters, e.g. polyethylene terephthalates.