Synonyms: 1,4-Benzenediamine,N,N'-bis(1,3,2-benzodioxaphosphol-2-yl)- (9CI); Phosphoramidous acid, p-phenylenedi-,cyclic P,P:P',P'-di-o-phenylene ester (8CI); Phosphoramidous acid,p-phenylenedi-, cyclic di-o-phenylene ester (7CI); 1,3,2-Benzodioxaphosphole,1,4-benzenediamine deriv.; 1,3,2-Benzodioxaphosphole,2,2'-(p-phenylenediimino)bis- (8CI); N,N'-Dipyrocatechol phosphitep-phenylenediamine; P 51; P 51 (stabilizer)