p‐Menthadienes as Biorenewable Feedstocks for a Monoterpene‐Based Biorefinery

Abstract

the upgrading of biomass into biofuels and platform chemicals will need to be developed and integrated into new/existing chemical processes. [2] The large volumes and wide geographical distribution of lignocellulosic biomass means that it will undoubtedly play a key role as a biorenewable feedstock for bulk chemical production. [3] In this approach, fermentative processes are used to depolymerize lignocellulose biomass into sugars (e.g., glucose and fructose), with these monomers then transformed into low-value feedstocks such as bioethanol, succinic acid, glutamic acid, and 5-hydroxymethylfurfural. [4] Although highly promising, technological difficulties associated with large-scale catalytic upgrading of these highly oxygenated biopolymers cause significant problems that still need to be overcome before lignocellulose-based biorefineries become more widely established. [5] Monoterpenes (and monoterpenoids) represent an alternative biomass source for the production of biofuels, polymers, and chemicals that are available in significant volumes at low cost. Significant amounts of commercially available monoterpenes are currently produced as products and waste from the forestry and agricultural industries, all of which can be considered as potentially useful biorenewable feedstocks for fuel and chemical production. These include turpentine (≈360 000 tonnes pa), limonene-containing citrus oil (≈30 000 tonnes pa), mentholcontaining mint oil (≈20 000 tonnes pa), and 1,8-cineole from eucalyptus oil (≈7000 tonnes pa with an estimated multimillion tonne production potential per annum). [6] The structures of these energy-dense, lightly oxygenated, alkene-containing C 10 building blocks more closely resemble those of petroleum-based hydrocarbons, which means they can potentially be catalytically upgraded using existing refining technologies to produce a wide range of chemical products (including aromatics).Crude sulfate turpentine (CST) is the cheapest and most widely available source of monoterpene biomass, with around 260 000 tonnes of CST produced as a waste by-product of the paper industry annually. High pressure cooking of wood chips to produce paper pulp in the Kraft process generates around 15 kg of CST per tonne of pulp, [7] which is comprised of a mixture of monoterpenes and around 5% volatile sulfur compounds (e.g., Me 2 S). [6a] A further annual 100 000 tonnes of pinene-rich gum turpentine (GT) is also produced through sustainable tapping of the trunks of living trees. The major monoterpene components of turpentine are α-pinene, β-pinene, 3-carene, and limonene, along with small amounts of camphene and C 15 A terpene-based biorefinery is described that uses crude sulfate turpentine (CST) and gum turpentine (GT) to produce mixtures of p-menthadienes (p-MeDs) as biorenewable terpene feedstocks. An acid catalyzed ring opening reaction (6 m aq. H 2 SO 4 , 90 °C) is first used to convert the major bicyclic monoterpenes (α-pinene, β-pinene, and 3-carene) in untreated CST (or GT with 5 mol% Me 2 S) into mixtures of ...

Sustainable catalytic epoxidation of biorenewable terpene feedstocks using H2O2 as an oxidant in flow microreactors

“…5 Consequently, the development of new efficient catalytic protocols to transform abundant monoterpene feedstocks into synthetically versatile intermediates is important, since they would broaden the range of biorenewable products available from terpene biorefineries, thus helping improve their economic viability. 6,7 Epoxides are one of the most synthetically useful functional groups, 8,9 so the availability of sustainable catalytic protocols that can be used to epoxidize the alkene bonds of monoterpene feedstocks to produce monoterpenoid epoxides is highly desirable. 10 Current examples of potentially useful terpene epoxides include α-pinene oxide which is used as an intermediate to produce commercially valuable fragrance compounds, 11 and limonene 1,2-oxide which can be used as a monomer for the sustainable synthesis of biorenewable polymers.…”

Efficient Syntheses of Biobased Terephthalic Acid, p-Toluic Acid, and p-Methylacetophenone via One-Pot Catalytic Aerobic Oxidation of Monoterpene Derived Bio-p-cymene

“… 8 , 20 , 21 Therefore, a key transformation developed during this valorization study was the oxidative isomerization of p -MeD mixtures into synthetically useful bio- p -cymene in 65–75% yields ( Figure 1 ). 14 This isoaromatization process could be achieved in batch reactions using 5 mol % Me 2 S, 1 equiv of p -cymene, O 2 , and 100 °C, 8 , 14 or in flow reactions using 1 equiv of t BuOOH, 2 equiv of p -cymene, O 2 , and 138 °C. 22 p -Cymene is a useful aromatic intermediate that is produced industrially on a kilotonne scale through Friedel–Crafts alkylation of petrochemically sourced toluene, with mixtures of cymene regioisomers then separated using the energy intensive Cymex process.…”

“… 23 Major commercial uses of p -cymene include its use for the production of tonalide (synthetic musk) and other fragrances, for the synthesis of p -cresol (antioxidant precursor), and as a green solvent for cleaning applications ( Figure 2 ). 8 , 14 Therefore, the availability of facile catalytic routes from multiple terpene feedstocks to bio- p -cymene would provide convenient pathways to a series of commercially important products that are currently sourced from nonrenewable petrochemical sources.…”

“…These transformations can potentially be used as the basis of a terpene-based biorefinery, so the development of scalable processes to produce additional biorenewable products from bulk monoterpene feedstocks is highly desirable. − We have recently reported an optimal acid catalyzed ring opening process (6 M H 2 SO 4 , 90 °C, 2–4 h) to convert the major bicyclic monoterpene components (α-pinene, β-pinene, and 3-carene) present in the bulk monoterpene feedstocks CST, turpentine, and eucalyptus oil (cineole) into thermodynamic mixtures of p -menthadienes (α-terpinene, γ-terpinene, and isoterpinolene) ( p -MeDs) (Figure ). Importantly, significant quantities of other biorenewable p -MeD feedstocks are also available as byproducts of acid catalyzed hydrolysis processes used to convert turpentine into α-terpineol and camphene, while ∼30 000 t of limonene (a p -MeD) is available as a waste product from fruit peel generated by the citrus industry. − The synthetic utility of these p -MeD mixtures as biorenewable substrates in ozonolysis, Diels–Alder reactions, and hydrogenation reactions , has been demonstrated to produce biorenewable intermediates that are useful for the production of fragrance precursors, antioxidants, drug precursors, biofuels, solvents, and biopolymers (Figure ). ,− …”

“…A potential advantage of using monoterpene-based feedstocks for biorenewable chemical synthesis is the ability to convert their preexisting p -menthene ring systems into the wide range of aromatic products that are currently sourced from petroleum feedstocks. ,, Therefore, a key transformation developed during this valorization study was the oxidative isomerization of p -MeD mixtures into synthetically useful bio- p -cymene in 65–75% yields (Figure ). This isoaromatization process could be achieved in batch reactions using 5 mol % Me 2 S, 1 equiv of p -cymene, O 2 , and 100 °C, , or in flow reactions using 1 equiv of t BuOOH, 2 equiv of p -cymene, O 2 , and 138 °C .…”