Synthesis of Dimer Fatty Acid Methyl Esters by Catalytic Oxidation and Reductive Amination: An Efficient Route to Branched Polyamides

Abstract

A novel and versatile route toward dimer fatty acid methyl esters (dimer FAMEs) via catalytic oxidation and reductive amination is described. The oxyfunctionalization of mono-unsaturated FAMEs bearing different chain lengths (C11, C18, C22) is accomplished by a co-catalyst-free Wacker Oxidation process in a high pressure reactor. The applied catalytic system of palladium(II) chloride in a dimethylacetamide/water mixture enabled the formation of ketoFAMEs in the presence of molecular oxygen as sole re-oxidant. In a first attempt, partially renewable dimer FAMEs are synthesized by reductive amination of keto-FAME (C18) in the presence of various aliphatic and aromatic diamines and sodium triacetoxyborohydride as selective reducing agent. In another approach, the keto-FAMEs directly underwent reductive amination using Raney-Nickel in order to obtain the corresponding aminoFAMEs. Subsequently, the keto-and amino-FAMEs are used for the synthesis of fully renewable dimer FAMEs via reductive amination with sodium triacetoxyborohydride as reducing agent. In order to demonstrate a possible application for these new dimer FAMEs, three out of the thirteen synthesized dimer FAMEs are selected and studied in a polycondensation with renewable 1,10-diaminodecane using TBD as catalyst. The polyamides are obtained in molecular weights (M n ) of up to 33 kDa and are carefully characterized by 1 H-NMR spectroscopy, FTIR, SEC, and DSC analysis. Practical Applications: The described catalytic route to defined dimer fatty acids has potential applications in lubricants, detergents, polymeric materials, and others. Compared to commercially available dimer fatty acids, a molecularly highly defined mixture of regioisomers is obtained, without contamination of monofunctional or trifunctional fatty acid derivatives, which is advantegous for most of the mentioned applications. Especially for polycondensations, the known stoichiometry of exactly two is a considerable benefit.

Fatty Acids and their Derivatives as Renewable Platform Molecules for the Chemical Industry

“…A large variety of structurally defined dimer acids, some fully renewable (i.e. 50 , Scheme 24), were prepared via catalytic Wacker‐type oxidation of 2 b , 6 b , or 17 b , leading to the respective keto fatty acid derivatives, which were subsequently dimerized via reductive amination [159] . When these compounds were copolymerized with 1,10‐diaminodecane, high‐molecular‐weight polyamides with low glass transition and melting temperatures were obtained.…”

Polymers Based on Cyclic Carbonates as Trait d'Union Between Polymer Chemistry and Sustainable CO2 Utilization

“…Synthesis of 4n-q and 4q' reported by to Cramail andco-workers. [155] 4v was obtained by Averous and co-workers from the reaction of the bisacyl halide of aD FA (Radiacid 0970) with two equivalents of GC. They contain cycloalkane rings formed during the syntheticp rocess.…”

“…Polymeric compounds are also generally present (the structures in Figure 4a re representativeso ft he dimericc ompounds). [155] 4v was obtained by Averous and co-workers from the reaction of the bisacyl halide of aD FA (Radiacid 0970) with two equivalents of GC. [156] 4v was reacted with renewable diamines for the synthesis of PHU networks with high renewable content.…”

Plant‐Oil‐Based Polyamides and Polyurethanes: Toward Sustainable Nitrogen‐Containing Thermoplastic Materials

“…Another selective approach toward dimer fatty acid derivatives is based on a sequence of catalytic oxidation to yield keto‐fatty acid derivatives followed by reductive amination. In this way, partially as well as fully renewable dimer fatty acids were obtained (Scheme , right) . For instance, the symmetric dimer obtained from oleic acid was copolymerized with 1,10‐diaminodecane to yield a fully renewable branched polyamide in high molecular weight ( M n = 33.5 kDa) and a melting point of 161 °C.…”