Use of tetrahydrobenzoxazines as stabilisers

An antioxidant for stabilizing mineral oil products and fuels against the action of light, oxygen and heat, comprising:

• a tetrahydrobenzoxazine of formula I:
• wherein R1 is a hydrocarbyl radical having from 1 to 3000 carbon atoms which is interrupted by at least one selected from the group consisting of O, S and NR6 moieties,
• R6 is a hydrogen atom or a C1- to C4-alkyl radical, and
• R2, R3, R4 and R5 are each independently a hydrogen atom, a hydroxyl group or a hydrocarbyl radical having from 1 to 3000 carbon atoms which may optionally be interrupted by one or more selected from the group consisting of O, S and NR6 moieties,
• wherein R4 may optionally be a radical of formula Y
• wherein R1, R2, R3 and R5 are each as defined above and X is a hydrocarbon bridging element which consists of one or more isobutene units or comprises one or more isobutene units, or wherein R4 may optionally be a radical of the formula Z or Z′
• wherein R1, R2, R3 and R5 are each as defined above and R10 and R11 are each independently hydrogen or a C1- to C10-alkyl radical,
• and wherein R2 and R3 or R3 and R4 or R4 and R5, together with the part-structure —O—CH2—NR7—CH2— attached to the benzene ring, may optionally form a second tetrahydrooxazine ring, or R2 and R3 and R4 and R5, together with the part-structures —O—CH2—NR7—CH2— and —O—CH2—NR8—CH2— attached to the benzene ring, may optionally form a second and a third tetrahydrooxazine ring,
• wherein R7 and R8 are each independently a hydrocarbyl radical having from 1 to 3000 carbon atoms and are interrupted by one or more heteroatoms selected from the group consisting of O, S and NR6 moieties, with the proviso that at least one of R2, R3, R4, or R5 is a polyisobutenyl radical having a number-average molecular weight Mn of from 200 to 40,000.