Process for the production of maleamic acids

In a process for the preparation, in suspension, of a maleamic acid of the general formula:

• ##EQU4## in which:
• R represents a linear or branched alkylene radical, an arylene radical, an aralkylene radical, an alkylarylene radical, a cyclo-alkylene radical or a divalent heterocyclic radical, the two free valencies of the heterocyclic radical being carried by carbon atoms, the total number of carbon atoms in the R radical being not more than 20, the minimum number of carbon atoms in the alkylene radical being 2, from a solution of primary diamine in a solvent and a solution of maleic anhydride in a solvent, the improvement wherein
• the solution of the primary diamine is run into the solution of maleic anhydride in an amount such that there is an anhydride excess of 5 to 20 mol % relative to the theoretical amount necessary for the reaction with the amine,
• the mixture is agitated,
• and the reaction temperature is 40.degree. to 130.degree.C,
• such that the time taken to run in the amine solution is at least 67 minutes,
• and the amine solution is run in at a rate such that the slope of the curve representing the variation, as a function of time, in the rate of running in as % of the total amount of amine solution employed per minute has, at every point on this curve, a value not greater than 0.044.