Use of tetrahydroberizoxazines 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 polyisobutene having a Mn of from 200 to 40,000,
• R2, R3, R4 and R5 are each independently hydrogen atoms, hydroxyl groups or hydrocarbyl radicals which have in each case from 1 to 3000 carbon atoms optionally having one or more heteroatoms from the group of O and S and/or one or more NR6 moieties,
• wherein the substituent R4 may also be a radical of the formula Y
• wherein 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 the substituent R4 may also be a radical of the formula Z or Z′
• (Z)
• wherein R2, R3 and R5 are each as defined above and R10, R11 and R12 are 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 also form a second tetrahydrooxazine ring, or the substituents 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 also form a second and a third tetrahydrooxazine ring,
• wherein R7 and R8 are each independently hydrocarbyl radicals which have in each case from 1 to 3000 carbon atoms and optionally have one or more heteroatoms from the group of O and S and/or one or more NR6 moieties.