Abstract
Currently, investigations of polymer-building blocks made from biorenewable feedstocks such as, for example, fatty acids, are of high interest for the chemical industry. An alternative synthesis of nitrile-substituted aliphatic carboxylic acids as precursors for ω-amino acids, which are useful to produce polymers, was investigated starting from biorenewable fatty acids. By hydroformylation of unsaturated fatty acids or unsaturated acids being accessible from unsaturated fatty acids by cross-metathesis reactions, aldehydes are formed. In this work, the hydroformylation of such unsaturated acids led to the formation of the corresponding aldehydes, which were afterwards converted with hydroxylamine to aldoximes. Subsequent dehydration by an aldoxime dehydratase as a biocatalyst or by CuII acetate led to the desired nitriles. Within this work, C7-, C9- and C11-carboxylic acids with a terminal nitrile functionality as well as a branched nitrile-functionalized stearate derivative were synthesized by means of this approach. As these nitriles serve as precursors for amino acids being suitable for polymerization, this work represents an alternative synthetic access to polyamide precursors, which starts directly from unsaturated fatty acids as biorenewable resources and avoids harsh reaction conditions as well as and by-product formation.
Highlights
Polyamides (PAs) are important polymers that are used in industry and in our everyday life
As the first step of this research project, we investigated the hydroformylation of these unsaturated acids to the corresponding aldehydes, followed by the condensation of these aldehydes to the corresponding aldoximes and their dehydration to the desired nitrile products in the presence of an aldoxime dehydratase (Oxds) or CuII acetate as catalysts (Scheme 3)
Access to a fatty acid-derived amino acid as polymer building block exemplified for the synthesis of 11-aminoundecanoic acid (20)
Summary
Polyamides (PAs) are important polymers that are used in industry and in our everyday life. Castor oil consists of 90% of triglycerides of ricinoleic acid, which is converted within five steps to 11-aminoundecanoic acid [4]. A disadvantage of this process is the pyrolysis step, which proceeds under very harsh reaction conditions with temperatures of up to 600 ◦C and at high pressures. This route requires the use of hydrobromic acid for the synthesis of 11-bromoundecanoic acid, which undergoes a substitution with ammonia to give the final product. The synthetic route towards 11-aminoundecanoic acid starts from castor oil as biorenewable feedstock, alternatives to produce nylon-11 are required to overcome these drawbacks
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