Process for the preparation of aqueous diazonium salt solutions

A process for the preparation of aqueous solutions of diazonium salts of the formula (1)

• in which some or all of the amino groups are in protonated form,
• R1, R2, R3 and R4, independently of one another, are hydrogen, a C1-C16-alkyl, C3-C7-cycloalkyl, C2-C16-alkenyl, aryl or a 5- to 6-membered aliphatic or aromatic heterocycle, which are optionally substituted by one or more C1-C4 alkyl radicals, halogen atoms or groups of the formula ═O, —OR′, —NR′R″, —SR′, —COR′, —COOR′, —CONR′R″, —NR′CONR″R′″ or —SO2NR′R″, where R′, R″, R′″ are hydrogen or a C1-C10-alkyl, C3-C7-cycloalkyl, C2-C16-alkenyl, aryl or a 5- to 6-membered aliphatic or aromatic heterocycle, or where R′ and R″, or R″ and R′″, or R3 and R4 together with the adjacent N atom form a 5- or 6-membered aliphatic or aromatic heterocycle, and R1 and R2 may additionally be halogen or groups of the formula —OR′, —NR′R″R′″, —SR′, —COR′, —COOR′, —CONR′R″, —SO3H2, —PO4H2, —NR′CONR″R′″ or —SO2NR′R″;
• A, A′ and A″, independently of one another, are a divalent group of the formula —O—, —NR′—, —S—, —CO—, —COO—, —CONR′—, —NR′CONR″— or —SO2NR′—;
• B, B′ and B″, independently of one another, are a substituted or unsubstituted C1-C14-alkylene, C3-C7-cycloalkylene, C2-C14-alkenylene, arylene or heteroarylene radical,
• or B, B′ or B″ form, together with R3 and/or R4 and the adjacent N atom a 5- to 7-membered heterocycle;
• Y− is F−, Cl−, Br−, HSO4−, ½SO42−, H2PO4−, ½HPO42−, ⅓PO43−, an anion of a pyro-, meta- or poly-phosphoric acid, BF4−, PF6−, HCO3−, ½CO32−, NO2−, NO3−, formate, acetate, propionate, R″″SO4−, R″″SO3− or R″″COO−, where R″″ is a substituted or unsubstituted C1-C21-alkyl or aryl radical;
• k, l and m, independently of one another, are the number 0, 1, 2 or 3;
• n, o and p, independently of one another, are the numbers 0 or 1;
• x is an integer from 1 to 3;
• and
• y and z are each an integer from 1 to 4, where the sum x+y+z is 3 to 5, which comprises
• reacting an aqueous solution of a water-soluble salt of the aromatic nitro compound of the formula (2),
• with hydrogen and in the presence of a catalyst which catalyzes the reduction of aromatic nitro groups to amino groups, and diazotizing the aromatic amine formed in the process in the aqueous solution with a diazotization reagent to give the diazonium salt.