Verfahren zur Herstellung einer Dispersion eines Silberfaellungsmittels

The invention comprises dyes which contain as a silver halide developing group an o or p-dihydroxyphenyl group, or an alkyl or halogen derivative thereof, and which also contain at least one oxalyl ester of an aromatic or aliphatic hydroxyl group. The invention includes dyes which contain an alkoxalyl or aryloxalyl ester of at least one of the hydroxy groups of the developing group. The dyes are made by conventional acylation processes. Azo and anthraquinone dyes are mentioned. For the first group of dyes the preferred oxalyl group is of formula where R is alkylene, R1 is alkylene of 2-4 C atoms, n is O or 1-3 and R2 is alkyl or aryl. Preferably R is lower alkylene, e.g. ethylene, trimethylene and propylene. Specified for R1 are the listed values for R. R2 is specified as ethyl, butyl, hexyl, lauryl, phenyl and tolyl and, when alkyl, is preferably of 1-12 C atoms when n is O, and 1-4 C atoms when n is 1-3. The o- and p-dihydroxyphenyl groups may be linked to the chromophore component of the dye molecule by a divalent radical or a covalent bond. Typical of specified divalent radicals are ethylene, phenylene, -COCH2-, thio oxy, sulphonyl, -S-CH2-CH2-, , and -SO2-CH2-CH2-. Preferred dyes are of formula where Me is alkylene, p is 1 or 2, R1, n and R2 are as above and ??? is an azo or anthraquinone dye radical, preferably of a mono- or dis-azo dye. Representative of specified first group products are 4 - [p - (21, 51 - dihydroxyphenethyl) - phenylazo] - 3 - [N - (b - hexoxalyloxyethyl) - carboxamido] - 1 - phenyl - 5 - pyrazolone, 2-[p-(21, 51 - dihydroxy - phenethyl) - phenyl azo] - 4 - [N - (b - ethoxalyloxyethoxy) - 1 naphthol and 4 - [b - (21, 51 - dihydroxy - phenyl) - a - methylethylamino] - 1 - ethoxalyl-oxyethylamino - anthraquinone. Dyes of the second group preferably have the formula where R2 is an alkyl group and Z is the residue of a dye molecule, preferred being azo and anthraquinone dyes which are free from aliphatic alcohol groups. Any free aliphatic alcohol groups in the dyes used in this modification of the invention should also be esterified during the process used for the obtention of the oxalyl esters. Representative of specified second group products are 2-[p-(21-51-bis-ethoxalyloxyphenethyl)-phenylazo] - 4 - methoxy - 1 - naphthol, 1 - phenyl - 3 - amino - 4 - [p-(21, 51 - bis-ethoxalyloxyphenethyl) - phenylazo] - 5 - pyrazolone and 1 - phenyl -