Salts of pyromellitic acid, a process for their preparation and their use

A process for preparing a salt of pyromellitic acid which consists essentially in reacting pyromellitic acid with an amine of the formula (A) in the ratio of 1 mol of pyromellitic acid with 0.5 to 2 mol of the amine, wherein formula (A) is:

• ##STR31## wherein in (A) R.sub.1, R.sub.2 and R.sub.3, identical or different, are C.sub.1-20 aliphatic, C.sub.3-20 cycloaliphatic, C.sub.5-20 araliphatic or C.sub.5-20 aromatic hydrocarbon radicals or mixtures thereof;
• wherein one or more CH.sub.2 groups in the carbon chain can be replaced by O atoms or by NR.sub.4 wherein R.sub.4 is C.sub.1-6 -alkyl,
• and wherein one or more terminal methyl groups can be replaced by dialkyl-substituted amino groups having 1 to 6 carbon atoms;
• or wherein R.sub.1 and R.sub.2 may form a joint ring in which a CH.sub.2 group may be replaced by an O atom or by an NR.sub.4 group,
• or wherein R.sub.1, R.sub.2 and R.sub.3 are each --CH.sub.2 --CH.sub.2 -- and are attached by way of the valance bond not joined to the N atom of formula (A) to a common N atom;
• in a solvent which is H.sub.2 O or ethanol, or a mixture thereof at 50.degree. C. to 100.degree. C;
• and
• after reaction has finished, isolating said salt of pyromellitic acid from said solvent.