Aminodiphenylamine 4-ADPA

The reaction of aniline and aniline derivatives with p-chloronitrobenzene is the critical coupling reaction practiced by Bayer and Monsanto for the manufacture of 4-nitrodiphenylamine, 2. Hydrogenation of 2 produces 4-aminodiphenylamine (4-ADPA), 3, which is a key intermediate in the p-phenylenediamine class of antioxidant used in rubber products (Figure 8). 

The research began as an exploration of new routes to a variety of aromatic amines that would not rely on the use of halogenated intermediates or reagents. Of particular interest was the identification of novel synthetic strategies to 4-aminodiphenylamine (4-ADPA), a key intermediate in the Rubber Chemicals family of antidegradants. The total world volume of antidegradants based on 4-ADPA and related materials is approximately 300 million pounds per year, of which Flexsys is the world s largest producer. 

Reductive alkylation is an efficient method to synthesize secondary amines from primary amines. The aim of this study is to optimize sulfur-promoted platinum catalysts for the reductive alkylation of p-aminodiphenylamine (ADPA) with methyl isobutyl ketone (MIBK) to improve the productivity of N-(l,3-dimethylbutyl)-N-phenyl-p-phenylenediamine (6-PPD). In this study, we focus on Pt loading, the amount of sulfur, and the pH as the variables. The reaction was conducted in the liquid phase under kinetically limited conditions in a continuously stirred tank reactor at a constant hydrogen pressure. Use of the two-factorial design minimized the number of experiments needed to arrive at the optimal solution. The activity and selectivity of the reaction was followed using the hydrogen-uptake and chromatographic analysis of products. The most optimal catalyst was identified to be l%Pt-0.1%S/C prepared at a pH of 6. 

Recently, this difficulty was overcome when the starting diazonium was the aniline dimer (4-aminodiphenylamine or ADPA) [157]. In that case the grafted layer is electro-active and aniline oxidation remains possible in aqueous sulfuric acid and leads to a strongly adherent PANI film on the modified surface. The first experiments were performed on carbon and extension to an oxidizable metal has not yet been reported. However, as it has been proven that the covalent grafting of diazonium salts was also successful with iron and other oxidizable metals [178-182], we think that the same procedure might be applied in the case of iron. A strong increase of the adhesion should be expected, and therefore an improvement of the protection properties. 

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