Selective alkylation method for producing p, p′-di-alkylated diphenylamine antioxidants

1. A process for preparing a liquid alkylated diphenylamine composition comprising from 80 to 100 wt % of one or more di-alkylated diphenylamines wherein more than 50 wt % of the di-alkylated diphenylamines are 4,4′-di-alkylated diphenylamines, 15 wt % or less of mono-alkylated diphenylamines, from 0 to 5 wt % tri-alkylated and tetra-alkylated diphenylamines,

and less than 1 wt % unsubstituted diphenylamine, wherein each alkyl group is selected from C 4-24 alkyl and wherein at least one alkyl group of at least one di-alkylated diphenylamine contains from 8 to 24 carbon atoms, wherein in said process, to a reaction mixture comprising:

a di-alkylated diphenylamine,

less than 25% by weight of mono-alkylated diphenylamine,

less than 6% by weight of non-alkylated diphenylamine,

Lewis acid catalyst comprising a metal halide, metal alkyl, alkylated metal halide, or acid clay, and

a first olefinic agent to suppress dealkylation, which first olefinic agent is capable of producing the mono-alkylated diphenylamine and di-alkylated diphenylamine of the reaction mixture when reacted with diphenylamine in the presence of an acidic catalyst, wherein each wt % is based on the total weight of all substituted and unsubstituted diphenylamine compounds in the reaction mixture, and a majority of any other diphenylamine compounds are comprised of di-alkylated diphenylamine compounds, is added a second olefinic agent, which is chemically different from the first olefinic agent, comprising one or more compounds of formula (IV)

wherein

R 1 is C 1-21 straight chain alkyl or C 3-21 branched alkyl, R 2 is C 1-10 straight chain alkyl or C 3-10 branched alkyl, and R 3 and R 4 are each independently selected from the group consisting of H, C 1-10 straight chain alkyl and C 3-10 branched alkyl,

in sufficient quantity to reduce, upon reaction with the reaction mixture, the amount of mono-alkylated diphenylamine to 15 wt % or less of the total weight of substituted and unsubstituted diphenylamine compounds in the reaction mixture, wherein the alkyl groups of the mono-alkylated diphenylamine and di-alkylated diphenylamine in the mixture to which the second olefinic agent is added are selected from C 8-24 alkyl, and wherein neither of the first nor second olefinic agent as added comprises isobutylene, styrene or alpha-methyl styrene.

2. The process according to claim 1 for preparing a liquid alkylated diphenylamine composition wherein 80 wt % or more of the di-alkylated diphenylamines in the liquid alkylated diphenylamine composition are 4,4′-di-alkylated diphenylamines.

3. The process according to claim 1 wherein the Lewis acid catalyst comprises a metal halide.

4. The process according to claim 1 wherein the first olefinic agent and/or the second olefinic agent comprises more than one olefin.

5. The process according to claim 1 wherein the second olefinic agent comprises tetramethylethylene or diisobutylene.

6. The process according to claim 1 wherein the first olefinic agent comprises propylene trimer or propylene tetramer.

7. The process according to claim 1 comprising:

a) alkylating diphenylamine and/or mono-alkylated diphenylamine with a first olefinic agent in the presence of a Lewis acid catalyst comprising a metal halide, metal alkyl, alkylated metal halide, or acid clay, until less than 25% mono-alkylated diphenylamine and less than 6% non-alkylated diphenylamine remains, and a majority of any other diphenylamine compounds is comprised of di-alkylated diphenylamine compounds,

b) adding additional first olefinic agent in an amount sufficient to suppress dealkylation, and

c) adding the second olefinic agent, either after step b) or together with step b), in sufficient quantity to reduce the amount of mono-alkylated diphenylamine to 15% or less of the total weight of substituted and unsubstituted diphenylamine compounds in the reaction mixture.

8. The process according to claim 7 wherein the first olefinic agent comprises propylene trimer or propylene tetramer.

9. The process according to claim 7 wherein the second olefinic agent comprises tetramethylethylene or diisobutylene.

10. The process according to claim 7 wherein the Lewis acid catalyst comprises a metal halide.

11. The process according to claim 7 wherein the first olefinic agent and/or the second olefinic agent comprises more than one olefin.