Catalytic hydrogenation of aromatic rings

The field of arene hydrogenation chemistry will soon enter its second century. The initial work of Sabatier on the interaction of finely divided nickel with ethylene and hydrogen gas led to the development of the first active catalyst for the hydrogenation of benzene. Sabatier was awarded the Nobel prize for his work in 1912 

Traditionally, the area of hydrogenation eatalysis has been attracting much attention because of its technological importance in petroleum refining and reforming processes [4]. Over the past two decades, hydrogenation catalysts have also become increasingly important in the industrial production of fine chemicals. The last area will be the main focus of this chapter. 

It is not an objective of this paper to provide an elaborate literature survey on heterogeneous aromatic hydrogenation. For that, reference is made to a book by Augustine [5]. Rather it is intended to present several typical examples of arene hydrogenation with some recent literature and industrially relevant developments. 

---

Several catalytic hydrogenations of aromatic rings in compounds containing free carboxyl groups are described (cf. method 4). Low-pressure hydrogenation over platinum oxide catalyst has been used. p-Toluic acid in acetic acid at 60° gives 4-methylcyclohexanecarboxylic acid (S>5%). 

Rhodium is the most active metal for the catalytic hydrogenation of aromatic ring systems. It is also very expensive (7 Dec 1992 price ca 44,000/Kg) because of its demand in autocatalysts. In comparison, at the same time the price of palladium was only 6% that of rhodium. Hence a bimetallic catalyst which can allow thrifting of the rhodium can offer a substantial precious metal inventory cost reduction. 

---