Diphenylamine, 4-nitroso, hydrogenation

Studies of the hydrogenation of aromatic nitroso compounds have rarely been published. One of the earliest studies is the Pd/C catalyzed hydrogenation of p-nitrosothymol to its corresponding amine (100%) in ethanol at 1 atm hydrogen.289 Useful antioxidants and gasoline stabilizers are made from diamines, which can be produced by hydrogenating their relatively easily formed nitroso derivatives.290 As a result, the hydrogenation of 4-nitroso-diphenylamine has been studied more heavily than others.291-293... 

The Fischer-Hepp rearrangement generally gives only the 4-isomer and, apart from examples in the naphthyl series, the 2-isomer has rarely been identified. Now the 2-isomer has been characterized96 as the minor product from the reaction of the diphenylamine derivative 96. The 2-nitroso product gives the cyclized product 97 on treatment with hydrogen peroxide (Scheme 17). 

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