Abstract
Upgrading C1 chemicals (for example, CO, CO/H2, MeOH and CO2) with C–C bond formation is essential for the synthesis of bulk chemicals. In general, these industrially important processes (for example, Fischer Tropsch) proceed at drastic reaction conditions (>250 °C; high pressure) and suffer from low selectivity, which makes high capital investment necessary and requires additional purifications. Here, a different strategy for the preparation of ethylene glycol (EG) via initial oxidative coupling and subsequent reduction is presented. Separating coupling and reduction steps allows for a completely selective formation of EG (99%) from CO. This two-step catalytic procedure makes use of a Pd-catalysed oxycarbonylation of amines to oxamides at room temperature (RT) and subsequent Ru- or Fe-catalysed hydrogenation to EG. Notably, in the first step the required amines can be efficiently reused. The presented stepwise oxamide-mediated coupling provides the basis for a new strategy for selective upgrading of C1 chemicals.
Highlights
Upgrading C1 chemicals with C–C bond formation is essential for the synthesis of bulk chemicals
ethylene glycol (EG) preparation from methanol, formaldehyde and methyl formate are notable, but low selectivity limits their application too[10,11,12,13]. Contrary to all these reductive coupling strategies, oxidative dimerization of CO to oxalates might allow for improved efficiency and two main approaches were developed since the 1990s as follows: (1) carbonylation of MeOH with oxygen in the presence of a Pd/V/Ti system[14] and 2) nitric oxidemediated carbonylation of alcohols to dialkyl oxalates using palladium complexes
Reactions with CO constitute powerful tools for the introduction of carbonyl groups into all kinds of organic molecules[19,20,21], oxidative carbonylations including the synthesis of heterocycles, carbonates, carbomates, ureas and oxamides are still challenging regarding catalyst productivity and selectivity[22,23]
Summary
Upgrading C1 chemicals (for example, CO, CO/H2, MeOH and CO2) with C–C bond formation is essential for the synthesis of bulk chemicals. Here we disclose that EG can be selectively produced (up to 99% for CO) by sequential Pd-catalysed oxidative carbonylation of piperidine to the corresponding oxamide and subsequent Ru- or Fe-catalysed hydrogenation to EG. Reactions with CO constitute powerful tools for the introduction of carbonyl groups into all kinds of organic molecules[19,20,21], oxidative carbonylations including the synthesis of heterocycles, carbonates, carbomates, ureas and oxamides are still challenging regarding catalyst productivity and selectivity[22,23].
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