Described are compounds, compositions, and methods that include oxygenated aromatic amines, such as an aminophenol-, phenyl-p-phenylenediamine-, and diaminobenzene-based compound useful as antioxidants. The oxygenated aromatic amine includes a secondary and/or tertiary amine group having a nitrogen that is attached to one or two carbon-containing group(s), the carbon-containing group(s) having a hydroxyl and/or ether group separated from the nitrogen by one or more carbon atoms.

High temperature antioxidant additives and methods that improve a liquid fuel composition's thermal oxidative stability are disclosed. A liquid fuel composition may comprise a liquid fuel and a high temperature antioxidant additive. The high temperature antioxidant additive may comprise an indoline compound with a bicyclic ring structure, wherein the indoline compound comprises a six-membered aromatic ring and a five-membered aliphatic ring that share a carbon-carbon aromatic bond. The five-membered aliphatic ring may be heterocyclic and may comprise a nitrogen positioned in an alpha position to the six-membered aromatic ring.

High temperature antioxidant additives and methods that improve a liquid fuel composition's thermal oxidative stability are disclosed. A liquid fuel composition may comprise a liquid fuel and a high temperature antioxidant additive. The high temperature antioxidant additive may comprise an indoline compound with a bicyclic ring structure, wherein the indoline compound comprises a six-membered aromatic ring and a five-membered aliphatic ring that share a carbon-carbon aromatic bond. The five-membered aliphatic ring may be heterocyclic and may comprise a nitrogen positioned in an alpha position to the six-membered aromatic ring.

A fuel additive for fuel formulations comprising calcium sulfonates in an amount effective to limit or eliminate valve seat recession in engines utilizing such fuel formulations. The fuel additive may also include a detergent, particularly in an amount to enhance the VSR limiting effect of the calcium sulfonates. Also included are fuel formulations containing calcium sulfonates in a concentration effective to limit vale seat recession in engines utilizing the fuel formulations. Methods for treating VSR in piston engines are also provided.

Methods of making antidegradant compounds are disclosed in which a p-phenylenediamine is reacted with a dicarbonyl to thereby obtain a diimine, which is reduced to obtain mixtures comprising the antidegradant compound.

High temperature antioxidant additives and methods that improve a liquid fuel composition's thermal oxidative stability are disclosed. A liquid fuel composition may comprise a liquid fuel; and a high temperature antioxidant additive comprising a nitroxide radical having a formula: ##STR00001##
wherein R.sub.1, R.sub.2, R.sub.3, and R.sub.4 are individually selected from an alkyl group or a hetero atom substituted alkyl group, and wherein R.sub.5 and R.sub.6 are any atom or group except hydrogen which can bond covalently to carbon.

High temperature antioxidant additives and methods that improve a liquid fuel composition's thermal oxidative stability are disclosed. A liquid fuel composition may comprise a liquid fuel; and a high temperature antioxidant additive comprising a nitroxide radical having a formula:

##STR00001##

wherein R.sub.1, R.sub.2, R.sub.3, and R.sub.4 are individually selected from an alkyl group or a hetero atom substituted alkyl group, and wherein R.sub.5 and R.sub.6 are any atom or group except hydrogen which can bond covalently to carbon.

Methods of making antidegradant compounds are disclosed in which a p-phenylenediamine is reacted with a dicarbonyl to thereby obtain a diimine, which is reduced to obtain mixtures comprising the antidegradant compound.

Methods of making antidegradant compounds are disclosed in which a p-phenylenediamine is reacted with a dicarbonyl to thereby obtain a diimine, which is reduced to obtain mixtures comprising the antidegradant compound.

A compound represented by the formula: ##STR00001## wherein R is selected from the group consisting of (i) substituted or unsubstituted alkyl with C=0 to 12 inclusive; (ii) substituted or unsubstituted aryl; and (iii) substituted and unsubstituted alkylaryl; wherein X.sup.1, X.sup.2, X.sup.3 and X.sup.4 are each selected from the group consisting of alkyl, aryl, alkylaryl groups and hydrogen; wherein R.sup.1, R.sup.2, R.sup.3, and R.sup.4 are each selected from the group consisting of alkyl, aryl, alkylaryl groups and hydrogen and R.sup.2 and R.sup.3 may optionally be bridged by a polymethylene group; wherein when C=0 in R, the combined group R.sup.1 R.sup.2 is the same as the combined group R.sup.3 R.sup.4; and wherein when C=1 in R, each of R.sup.1, R.sup.2, R.sup.3, and R.sup.4 are hydrogen.