Process for the preparation of symmetrical diacylhydrazines

A process for the preparation of symmetrical diacylhydrazines having general formula (I):

• R1—CO—NH—NH—CO—R1 (I)
• wherein:
• R1 represents a linear or branched C1C18 alkyl group;
• a linear or branched C2-C8 alkoxyalkyl group;
• a C2-C8 cyanoalkyl group;
• a C5-C8 cycloalkyl group, said cycloalkyl group optionally containing a heteroatom selected from oxygen, nitrogen and sulfur;
• a C6-C18 aryl group;
• or a C7-C20 arylalkyl or alkylaryl group, said arylalkyl or alkylaryl groups optionally substituted with one or more hydroxyl groups, or with one or more linear or branched C1-C8 alkoxyl groups;
• comprising the following steps:
• (A) reacting an ester of a carboxylic acid having general formula (II):
• R1—CO—OR2 (II)
• wherein R1 has the same meanings defined above and R2 represents a linear or branched C1-C18 alkyl group, with hydrazine, in its pure or hydrated state, obtaining a monoacylhydrazine having general formula (III):
• R1—CO—NH—NH2 (III);
• (B) reacting the monoacylhydrazine having general formula (III) obtained in step (A), with a β-ketoester having general formula (IV):
• R3—CO—CH2—COOR4 (IV)
• wherein R3 represents a linear or branched C1-C18 alkyl group, or a C6-C18 aryl group and R4 represents a linear or branched C1-C18 alkyl group, obtaining the desired symmetrical diacylhydrazine having general formula (I);
• the monoacylhydrazine having general formula (III) and the β-ketoester having general formula (IV) being used in molar ratios ranging from 1:0.5 to 1:0.8;
• and said step (B) being carried out in the presence of a hydrocarbon solvent at the reflux temperature of the solvent ranging from 60° C. to 180° C., for a time ranging from 20 minutes to 15 hours, obtaining the desired symmetrical diacylhydrazine having general formula (I), an alkyl-pyrazolone or an aryl-pyrazolone having general formula (V), an alcohol having general formula (VI) and water as indicated in the following reaction scheme:
• wherein R1, R3 and R4 have the same meanings defined above.