Leif Johnen

Myrcene as a Natural Base Chemical in Sustainable Chemistry: A Critical Review

Currently, a shift towards chemical products derived from renewable, biological feedstocks is observed more and more. However, substantial differences with traditional feedstocks, such as their hyperfunctionalization, ethical problems caused by competition with foods, and problems with a constant qualitative/quantitative availability of the natural products, occasionally complicate the large-scale market entry of renewable resources. In this context the vast family of terpenes is often not taken into consideration, although the terpenes have been known for hundreds of years as components of essential oils obtained from leaves, flowers, and fruits of many plants. The simple acyclic monoterpenes, particularly the industrially available myrcene, provide a classical chemistry similar to unsaturated hydrocarbons already known from oil and gas. Hence, this Review is aimed at reviving myrcene as a renewable compound suitable for sustainable chemistry in the area of fine chemicals. The versatility of the unsaturated C(10)-hydrocarbon myrcene, leading to products with several different areas of application, is pointed out.

Telomerization: Advances and Applications of a Versatile Reaction

The transition-metal catalyzed telomerization of 1,3-dienes with different nucleophiles leads to the synthesis of numerous products, such as sugar ethers, substituted lactones, or terpene derivatives, which can be applied in the cosmetic and pharmaceutical industry as well as in polymers and flavors. The reaction can be controlled by the choice of the catalytic system, the feedstock, and the reaction conditions. Since telomerization was developed in 1967, there have been many efforts to utilize this reaction. Herein we give an overview of the versatility of telomerization based on examples from research and industry, particular emphasis is placed on catalyst and process development as well as mechanistic aspects.

Telomerization of Myrcene and Catalyst Separation by Thermomorphic Solvent Systems

Telomerization of common petrochemical 1,3‐dienes such as butadiene and isoprene have long been successful with different nucleophiles; however, the telomerization of the C10 hydrocarbon myrcene was not known until now. Herein, the first telomerization of the monoterpene myrcene with diethylamine is discussed, which provides an atom‐economical way of generating C20 amines in a single step. Variation of the palladium precursors and phosphorous ligands and optimization of solvent and additives led to the optimum catalyst system [Pd(MeCN)4](BF4)2/PPh3. By using a thermomorphic solvent system, the Pd complex can be easily separated with low leaching values.

A sustainable route from the renewable myrcene to methyl ethersvia direct hydroalkoxylation

A direct route to odoriferous methyl ethers from the monoterpene myrcene is presented. Investigating the activity of different catalytically active Lewis acids, the non-toxic and low-cost AlCl3 appeared to be very suitable. Thus, the common route to ethersvia the corresponding alcohols was reduced from four steps to one.

A liquid immobilisation concept for enzymes by thermomorphic solvent systems

Biotechnology is playing an ever increasing role in industrial supply chains, however, only a few processes exist in which the expensive native enzyme can be economically separated and re-used with little or no loss of activity. In this report, a new and innovative recycling method for free enzymes is presented which is based solely on the temperature-dependent miscibility gap of the selected solvent mixture. The reaction is carried out under monophasic conditions with no mass transfer limitations. Cooling down leads to a biphasic system in which the catalyst phase containing the enzyme can be simply separated from the product phase and used again. The performance of this new recycling method was proven by the lipase-catalysed hydrolysis of p-nitrophenyl palmitate. Only a 2% loss in maximum yield was observed over five sequential recycling runs.

First methoxycarbonylation of the renewable β-myrcene: high selectivity through reduced isomerisation

A direct route from a renewable material to odoriferous methyl esters is presented with the first methoxycarbonylation of the monoterpene β-myrcene. A simple homogeneous catalyst system of Pd(OAc)2 and the bidentate ligand 1,4-bis(diphenylphosphino)butane (DPPB) in combination with low amounts of inexpensive acetic acid as an activator leads to a mixture of four isomers with a yield of 61%. The challenge of myrcene isomerisation induced through the necessary reaction conditions was overcome by systematic reaction optimisation. As an important parameter for the success of this reaction, the ester/isomer ratio was defined and improved during the research process. The atom economic reaction which uses the inexpensive bulk chemicals carbon monoxide and methanol could be upscaled to a multigram scale without the loss of activation.

Ruthenium-Catalyzed Cross Metathesis of β-Myrcene and its Derivatives with Methyl Acrylate

The reaction of β‐myrcene with methyl acrylate produces 3‐methylenecyclopent‐1‐ene in the presence of the Ru catalyst Neolyst M2 by ring‐closing metathesis in the first step. In the second step, the generated methylidene unit reacts with methyl acrylate to give the corresponding unsaturated cyclic ester by cross metathesis. Under the optimized reaction conditions (80u2009°C, Neolyst M2, 16u2005equivalents of methyl acrylate), derivatives of β‐myrcene, myrcenol, myrcenyl acetate, and β‐ocimene, react to yield functionalized acyclic esters.