Abstract

The homogeneous hydrogenation of esters, thanks to the recent advances driven by industrial and academic research groups, is becoming a technology to be reckoned with. This important transformation can provide a cost-effective, greener access to primary alcohols, important targets in pharmaceutical and flavour & fragrances chemistry. Key to the establishment of industrial applications are the capacity to commercially supply catalysts and a deeper, practical understanding of the application of the technology.

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THE CHALLENGE Over the past forty years, homogeneous catalysis has established itself as a fundamental technology in the industrial synthetic toolbox. The asymmetric reduction of carbonyl derivatives (for example ketones, aldehydes and imines) with hydrogen gas or other hydrogen transfer donors is particularly cost-effective, robust and widely accepted. On the contrary, the use of homogeneous catalysts for the reduction of carboxylic acids derivatives (esters, lactones, amides, lactams) is substantially more challenging. As a result, industrial application of homogeneous catalysis in this area lags behind by twenty to thirty years and is only now at a tipping point in terms of development and acceptance. In addition to the technical challenge, achiral hydrogenation catalysis presents a significant economic challenge: achiral targets such as primary alcohols or amines can only accept lower catalyst cost contributions than chiral targets. While chiral catalysts (homogeneous catalysts or enzymes) mostly compete with the undeniably more wasteful resolution technology, achiral hydrogenation catalysts must prove themselves to be more effective than well-established stoichiometr ...