Patent ID: 7982052

Claim:
A process for the preparation of stable nitroxyl radicals having the general formula (I), wherein R 1 , R 2 , R 3 and R 4 , the same or different, represent alkyl or isoalkyl groups containing from 1 to 8 carbon atoms, which comprises: a. preparing a first intermediate N-benzylphthalimide starting from phthalic anhydride and benzylamine by reaction in an aromatic solvent, and removing the reaction water by means of azeotropic distillation; b. transforming the N-benzylphthalimide, in the same aromatic solvent, into N-benzyl-1,1,3,3-tetra-alkylisoindoline by treatment with a Grignard reagent prepared in methyl-tert-butyl ether starting from magnesium and a C 1 -C 4 alkyl halide; c. continuously distilling the methyl-tert-butyl ether solvent during the reaction; d. purifying the reaction mixture, by oxidation with air, stirring the same for times ranging from 3 to 5 hours and filtering the raw reaction product thus obtained; e. subjecting the purified intermediate N-benzyl-1,1,3,3-tetra-alkylisoindoline obtained from step (d) to a hydrogenolysis reaction in methanol, in the presence of hydrogen and a supported palladium catalyst, at room temperature and atmospheric pressure; and f. subjecting the hydrogenolysis product of step (e) to an oxidation reaction in a polar solvent compatible with methanol, with hydrogen peroxide in the presence of a catalyst selected from polymolybdic and polytungstic acids or salts, optionally incorporating an element selected from phosphorous or silicon.