as a secondary oxidant for use with a hindered cyclic oxammonium salt as the primary oxidant this application discusses the nitroxide oxammonium salt amine or hydroxylamine of a corresponding hindered heterocyclic amine compound the oxammonium salt is the catalytically active form but this is an intermediate compound that is formed from a nitroxide continuously used to become a hydroxylamine and then regenerated presumably back to the nitroxide the secondary oxidant will convert the amine form to the free radical nitroxide compound the term u201c nitroxide u201d is normally used for the compound in the literature the secondary oxidant will also regenerate the oxammonium salt from the hydroxylamine the method described in the application is suitable for carboxylation of chemical fibrous cellulose pulp this may be bleached sulfite kraft or pre hydrolyzed kraft hardwood or softwood pulps or mixtures of hardwood or softwood pulps the cellulose fiber in an aqueous slurry or suspension is first oxidized by addition of a primary oxidizer comprising a cyclic oxammonium salt this may conveniently be formed in situ from a corresponding amine hydroxylamine or nitroxyl compound which lacks any u03b1 hydrogen substitution on either of the carbon atoms adjacent the nitroxyl nitrogen atom substitution on these carbon atoms is preferably a one or two carbon alkyl group for sake of convenience in description it will be assumed unless otherwise noted that a nitroxide is used as the primary oxidant and that term should be understood to include all of the precursors of the corresponding nitroxide or its oxammonium salt nitroxides having both five and six membered rings have been found to be satisfactory both five and six membered.