2019, Kulik, Anna, Neubauer, Katja, Eckelt, Reinhard, Bartling, Stephan, Panten, Johannes, Köckritz, Angela

For the first time, the oxidative dehydrogenation of (−)-menthol to (−)-menthone and (+)-isomenthone in a marketable quality was carried out in a continuous gas phase reactor as a sustainable process using molecular oxygen as green oxidant and solid catalysts which do not contaminate the product mixture and which are easily to remove. The diastereomeric purity remained largely unchanged. Three types of catalysts were found to be very active and selective in the formation of menthone and isomenthone: AgSr/SiO2, CuO distributed on a basic support and RuMnCe/CeO2, where Ru, Mn and Ce exist in an oxidized state. The best overall yield of menthon/isomenthone obtained with an Ag-based catalyst was 58 % at 64 % selectivity, with a Cu-based catalyst 41 % at 51 % selectivity and with a Ru-based catalyst 68 % at 73 % selectivity. Reaction conditions were widely optimized. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

2019, Brunzel, Tom, Heppekausen, Johannes, Panten, Johannes, Köckritz, Angela

A selective reaction method for the efficient conversion of an isomeric mixture of 1,9-cyclohexadecadiene (1,9-CHDD) to the corresponding monounsaturated cyclohexadec-8-en-1-one (8-CHD) is described. 8-CHD was synthesized via Wacker type oxidation at room temperature using a highly electrophilic in situ formed dicationic palladium species. Isomerisation of the diene and over-oxidation of the substrate could be nearly suppressed by suitable reaction control, which has a positive effect on selectivity. The utilization of molecular oxygen as a green oxidant and environmentally benign iron(iii) salts as co-catalysts was successfully applied. This reaction strategy is promising to overcome the low overall reactivity of internal olefins in Wacker type oxidations. In addition, larger scale experiments showed further potential for industrial application. This journal is © 2019 The Royal Society of Chemistry.