Patent ID: 7501386

Claim:
A composition comprising a lubricating oil and a synergistic mixture of antioxidants, said mixture comprising a) from 0.1 to 10 weight percent of a first antioxidant according to formula I: wherein R 1 and R 2 are each independently selected from the group consisting of hydrogen, alkyl from 1 to 20 carbon atoms, —OR, —SR and —NRR′, where R and R′ are independently hydrogen or alkyl from 1 to 6 carbon atoms, or R 1 and R 2 when adjacent to each other together form a 5 to 6 membered alicyclic or aromatic ring which may be optionally substituted with 1 or 2 alkyl groups each having from 1 to 20 carbon atoms; each R 3 is hydrogen or alkyl from 1 to 6 carbon atoms, X and X′ are independently selected from —CHR 4 —, oxygen, sulfur or NR 5 , wherein R 4 and R 5 are independently hydrogen or alkyl from 1 to 6 carbon atoms, with the proviso that at least one of X or X′ is a heteroatom positioned ortho or para to the bridging nitrogen atom, and when X or X′ are nitrogen then R 1 or R 2 is not hydroxyl; and further provided that when one of X or X′ is —CHR 4 — then the other may not be oxygen; and n is an integer from 1 to 2; and b) from 0.01 to 10 weight percent of a second antioxidant selected from the formula wherein R a and R b are each independently aryl from 6 to 10 carbon atoms which may be unsubstituted or substituted with one or two alkyl groups each having from 1 to 20 carbon atoms.