Sustainable economic in the production of industrial products has attracted much attention in the past decades. For a better comparison respectively to green processes, a standard set of 12 principles has emerged that can be used to assess any process. It is not possible to implement all 12 principles but the principles help to improve existing industrial applications. The formation of adipic acid is based on a hydrogenation of benzene to cyclohexane, followed by an air oxidation of cyclohexane to a mixture of cyclohexanone and cyclohexanol at low conversions of 4 to 8 %. Disadvantages of this route are the by-products such as alcohols, aldehydes or ketones because the treatment of these during the oxidation step is very expensive. In addition, an oxidation via peroxides is realized which is essentially associated with explosion risk. Alternative to these routes, a selective hydrogenation of benzene to cyclohexene and a hydration over H-ZSM5 zeolites to cyclohexanol is possible. With respect to the 12 principles, this route is much attracted because of its simplicity and atomic economy. A key step in the technical development is the formation of cyclohexene based on benzene because the formation of cyclohexene is thermodynamically not preferred (formation of cyclohexene: −23 kJ/mol, formation of cyclohexane: −98 kJ/mol). Therefore, a formation of cyclohexene in high yields requires a complex four-phase system (g/l/l/s) consisting of hydrogen (g), an organic (l) and aqueous phase (l) and a solid Ru-catalyst (s).