Substd. 4,4-di:amino-stilbene-2,2-di:sulphonic acid salts prodn

The prodn. of cpds. of formula (I) comprises: (a) reacting 2 mole-equivs. cyanuric chloride (CNUC) with 1 mole-equiv. of a 4,4'-di-amino-stilbene-2,2'-di-sulphonic acid salt (II) to give (III); reacting (III) with 2 equivs. sulpho-aniline (IV) to give cpd. (V); (c) reacting the dichloro cpd. (V) with 2 mole-equivs. amine of formula XH ,where M=alkali metal ion or opt. substd. ammonium ion; X=N-alkylamino or N,N-di-alkylamino; in the latter case, the two alkyl gps. (opt. contg. in-chain O, N or S) may form part of a satd. 5- or 6-membered heterocycle. Stage (b) is carried out in the presence of amine (VI) as acid-interceptor, by adding sufficient (VI) to maintain a pH of 3.0-7.0, and stage (c) is then carried out by releasing (VI) from its protonated form with the aid of a suitable base. Also claimed is a process for the prodn. of a conc. liq. prepn. of cpd. (I), in which the crude soln. of (I) is demineralised and concd. by means of a membrane process under pressure.