Preparation of diketones

#Reference is made to applicants' copending application Ser. No. 641,958, filed on even date herewith and assigned to the same assignee.

#The present invention relates to a method for producing diketones of a type which are themselves useful in the production of certain tetraketones which may be used for the manufacture of thermally stable quinoxaline polymers.

#Polyquinoxaline resins have become widely sought after in recent years due to their unique thermal properties. Because of their desirable properties, the polymers are useful for high temperatures adhesives, coatings and films in a number of critical industries. As stated in Stille, U.S. Pat. No., 3,661,850, polyquinoxaline polymers are "suitable for high temperature electrical insulators, battery separators, foams, ablative materials for re-entry bodies and rocket nozzles." Other patents which discuss these unique resins, their properties and uses are: Augl, U.S. Pat. Nos. 3,766,141 and 3,642,700; and Hergenrother, U.S. Pat. No. 3,778,412.

#The reaction of the present invention to produce diketones of formula I can be carried out with or without a solvent, but for ease of operation, i.e., separation of unreacted base from the product, etc., it is generally carried out in an inert solvent. The active-hydrogen compound of formula II and the base are mixed in an inert, anhydrous, liquid solvent at a temperature of from about -100.degree. C. to about 200.degree. C., and then the dicarboxylic acid derivative is added. The reaction time can vary considerably, as, for example, from 10 minutes to 10 hours. The relative amount of the base employed to the active-hydrogen compound used can vary from an equal molar amount to a very large excess, but generally a three molar excess of base is used. Any anhydrous liquid solvent that is inert under the reaction conditions can be used. Examples are: liquid ammonia; aliphatic, cycloaliphatic, or aromatic hydrocarbons; chlorinated hydrocarbons; ethers; etc. The selection of the solvent and the temperature used will depend upon the base being used, the active-hydrogen compound used, etc.

#A reaction intermediate of formula III is formed. It can be isolated by evaporating the solvent if one has been used, and converted to the corresponding diketone by heating with water or an acid, such as sulfuric acid, hydrochloric acid, phosphoric acid, acetic acid, etc., or mixtures of these acids. The conversion, which involves hydrolysis and decarboxylation, is carried out at a temperature of from about 50.degree. to about 250.degree. C. for a time sufficient to effect substantial reaction. The reaction time can vary from 1 hour to 48 hours. Alternately, the intermediate can be converted without isolation to the corresponding diketone in situ by adding the acid or mixture of acids to the reaction mixture and heating at a temperature of from about 50.degree. to about 200.degree. C. for a period of from about 1 hour to about 48 hours.

#The reaction intermediate of formula III can also be converted to a di(beta-ketocarboxylate) salt in situ or after isolation by reaction with a base, such as sodium hydroxide, barium hydroxide, etc., or mixture of these hydroxides, under mild conditions. The hydrolysis is run in dilute base at a temperature of from about 0.degree. to about 50.degree. C. for a period of from about one hour to forty-eight hours. The salt is then decarboxylated by heating with water or an acid, such as, sulfuric acid, hydrochloric acid, etc., at a temperature of from about 25.degree. to about 200.degree. C. for a period of from about 1 hour to 48 hours.