Rhodium-Catalyzed Tandem Isomerization/Hydroformylation of the Bio-Sourced 10-Undecenenitrile: Selective and Productive Catalysts for Production of Polyamide-12 Precursor

The hydroformylation of 10‐undecenenitrile (1) – a substrate readily prepared from renewable castor oil – in the presence of rhodium‐phosphane catalysts systems is reported. The corresponding linear aldehyde (2) can be prepared in high yields and regioselectivities with a (dicarbonyl)rhodium acetoacetonate‐biphephos [Rh(acac)(CO)2‐biphephos] catalyst. The hydroformylation process is accompanied by isomerization of 1 into internal isomers of undecenenitrile (1‐int); yet, it is shown that the Rh‐biphephos catalyst effectively isomerizes back 1‐int into 1, eventually allowing high conversions of 1/1‐int into 2. Recycling of the catalyst by vacuum distillation under a controlled atmosphere was demonstrated over 4–5 runs, leading to high productivities up to 230,000 mol (2)⋅mol (Rh)−1 and 5,750 mol (2)⋅mol (biphephos)−1. Attempted recycling of the catalyst using a thermomorphic multicomponent solvent (TMS) phase‐separation procedure proved ineffective because the final product 2 and the Rh‐biphephos catalyst were always found in the same polar phase. Auto‐oxidation of the linear aldehyde 2 into the fatty 10‐cyano‐2‐methyldecanoic acid (5) proceeds readily upon exposure to air at room temperature, opening a new effective entry toward polyamide‐12.