Dehydrogenation to Aromatic or Heteroaromatic Compounds

The use of renewable feedstocks from natural sources is probably a field where heterogeneous catalysis can bring considerable improvements. The dehydrogenation of cheaply available mono-terpenes from citrus production or the pulp and paper industry to furnish the more commercially valuable p-cymene is a good example (Table 1, Seheme 1). This reaction has been studied in detail over metallic 

The role of acidity is emphasized when an OH group is present in the limonene structure (reaction lb) [23]. The acidity of the carrier must then be strongly reduced to avoid dehydration. Carriers such as carbon, silica, and alumina are appropriate, although other forms than y-Al203 are usually used. The introduction of a base such as triethylamine directly into the reaction mixture is also imperative. Considering these restrictions, the temperature of the reaction must not exceed 150°C. Thus, it is essential to reduce the pressure ( 0.01 bar) to increase the yield. 

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