Raney® nickel-catalyzed hydrodeoxygenation and dearomatization under transfer hydrogenation conditions—Reaction pathways of non-phenolic compounds

Catalytic reduction of oxygen-containing aromatic compounds has been studied under transfer hydrogenation (TH) conditions at 150 degrees C in 2-PrOH as a hydrogen donor. Raney (R) nickel is used as a heterogeneous catalyst. The reaction of aromatic non-phenolic carbonyl compounds is most likely to proceed through the pathway "aromatic ketone (aldehyde)-> aromatic alcohol -> alkylaromatics -> saturated alkylcyclohexane". One of the main reactions under the TH conditions is a hydrodeoxygenation (HDO) process. Unexpectedly, the hydrodeoxygenation of aromatic ketones to alkylaromatics (C=O -> CH2) occurs faster than of corresponding aromatic alcohols (HC-OH -> CH2) that means either additional reaction pathway of its hydrodeoxygenation missing for the corresponding aromatic alcohols or specific interaction of OH functionality with Raney (R) nickel surface obstructing (hindering) the further reduction. Benzaldehyde is shown to be less reactive than the aromatic ketones under the same reaction conditions. The main reason is proposed to be carbon monoxide release resulted from the decarbonylation of the aldehyde. Carbon monoxide demonstrates a poisoning effect on Raney (R) nickel surface that is evidenced in the catalyzed TH reaction of acetophenone. The HDO reaction of anisole under the same reaction conditions was a little slowly than of oxygen-containing non-phenolic aromatics.