Solvent‐Promoted Oxidation of Aromatic Alcohols/Aldehydes to Carboxylic Acids by a Laccase‐TEMPO System: Efficient Access to 2,5‐Furandicarboxylic Acid and 5‐Methyl‐2‐Pyrazinecarboxylic Acid

Abstract

challenging, because most of the aerobic alcohol oxidations stop at the aldehyde stage even with noble metals. [4] In addition, many methods suffer from such drawbacks as use of environmentally unfriendly catalysts (e.g., metals) and/ or solvents (e.g., aqueous alkaline solutions and chloroalkanes), harsh reaction conditions, and unsatisfactory selectivities. According to Tojo and Fernández, [1a] approximately 40% of the processes toward carboxylic acids were still performed through a two-step oxidation, with the isolation of the aldehyde intermediates; therefore, this technique for direct access to carboxylic acids is still immature.Nitroxyl radicals are versatile organocatalysts for catalytic oxidations, where they, alone or in combination with other catalysts (e.g., transition metals, NO x and laccase), are used in the presence of oxidants. [5] 2,2,6,6-Tetramethylpiperidinyl-1-oxy (TEMPO) and its derivatives, a type of stable nitroxyl radicals, have been widely used for the production of pharmaceuticals, fragrances and flavors, agrochemicals, and specialty chemicals. [6] To date, few studies on catalytic oxidation of primary alcohols to carboxylic acids by nitroxyl radicals have been reported, [7] although the routes to aldehydes have been well established. [8] In Anelli's oxidation, primary alcohols were oxidized to carboxylic acids by TEMPO and KBr in a biphasic CH 2 Cl 2 /water mixture in the presence of a phasetransfer catalyst (Scheme 1a), with chlorine bleach (NaOCl) as an oxidant. [9] Then a series of modified Anelli's protocols were developed by using alternative oxidants (e.g., NaClO 2 , and bis(acetoxy)iodobenzene (BAIB)). [10] Yakura et al. reported a TEMPO-iodobenzene hybrid catalyst for the synthesis of carboxylic acids in acetic acid in the presence of peracetic acid (Scheme 1b). [11] Stahl and co-workers presented a clean direct electrochemical method to oxidize primary alcohols and aldehydes to carboxylic acids in the presence of 4-acetamido-TEMPO (Scheme 1c). [12] Ma and co-workers found that a threecomponent catalyst (TEMPO, Fe(NO 3 ) 3 •9H 2 O and KCl) enabled room-temperature aerobic oxidation of primary alcohols to carboxylic acids in 1,2-dichloroethane (Scheme 1d), [13] in which Fe(NO 3 ) 3 •9H 2 O catalyzed further oxidation of aldehydes to carboxylic acids. [14] From the perspective of green and sustainable Laccase coupled with 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO) is a wellknown catalytic system for the oxidation of alcohols to the carbonyl compounds. In this work, a simple yet effective solvent engineering strategy is developed to enable aromatic alcohols/aldehydes to be efficiently oxidized to carboxylic acids by a laccase-TEMPO system. Citrate buffer (100-300 mm, pH 6) rather than the widely used acetate buffer (pH 4-5) proves to be optimal for this purpose. The roles of citrate are discussed in laccase-TEMPOcatalyzed synthesis of carboxylic acids. 5-Hydroxymethylfurfural (HMF) of 200 mm is oxidized to 2,5-furandicarboxylic acid (FDCA), a top-value biobased chemical in the...

Current Advances in the Sustainable Conversion of 5‐Hydroxymethylfurfural into 2,5‐Furandicarboxylic Acid

“…Laccase is a blue multi‐copper oxidase able to oxidize alcohols in the presence of mediators (e. g., TEMPO), under mild conditions. This catalytic system was used to produce FDCA from HMF in 28 h with a yield up to 97 %, using air as the oxidant and producing water as the sole by‐product, but with a very low substrate concentration (HMF up to 100 m m ) [137] . A tandem reaction was developed by Chang et al., used laccase (CotA‐TJ102@UIO‐66‐NH2) and lipase Novozym 435.…”

“…This catalytic system was used to produce FDCA from HMF in 28 h with a yield up to 97 %, using air as the oxidant and producing water as the sole by-product, but with a very low substrate concentration (HMF up to 100 mm). [137] A tandem reaction was developed by Chang et al, used laccase (CotA-TJ102@UIO-66-NH2) and lipase Novozym 435. Laccase oxidized HMF to FFCA, then the lipase was added to complete the oxidation to FDCA.…”

(Chemo)biocatalytic Upgrading of Biobased Furanic Platforms to Chemicals, Fuels, and Materials: A Comprehensive Review

“…The combination of laccase and TEMPO represents the prevailing catalytic system in the chemoenzymatic production of FDCA. In some cases, good FDCA productivities (e.g., up to 2.6 g/L h) were achieved. ,− In addition to the oxidation of HMF, the enzymatic carboxylation of FCA also may provide access to FDCA, , which will be discussed in the section Catalytic Formation of the C–C Bond.…”

“…FFCA was obtained from 30 mM HMF in 96 h with 82% yield, along with 4% DFF and 10% FDCA (Table , entry 1). Actually, the complete conversion of HMF to FDCA could be implemented by this chemoenzymatic route upon fine process optimization, , which will be discussed in detail in the section FDCA Synthesis. A highly selective chemoenzymatic route consisting of the integration of laccase (spore coat protein A, CotA-TJ102) from Bacillus subtilis TJ-102 with TEMPO was developed for the HMF conversion to FFCA .…”

“…Recently, a simple yet effective solvent-engineering strategy was developed by our group to enable HMF to be efficiently oxidized to FDCA by the laccase− TEMPO system (Scheme 13). 43 On the basis of the pathway proposed by de Vires and co-workers, 162 TEMPO is first converted to the oxoammonium cation via single-electron oxidation in the presence of laccase and O 2 ; the resulting oxoammonium serves as the actual oxidant to oxidize HMF/ DFF hydrate/FFCA hydrate to the corresponding carbonyl compounds via hydride transfer, along with the coproduct hydroxylamine; TEMPO is regenerated through the noncatalytic comproportionation of oxoammonium with hydroxylamine. In citrate buffer (0.1−0.3 M, pH 6) rather than the commonly used acetate buffer (pH 4−5), HMF of up to 200 mM was oxidized to FDCA within 28 h in the presence of 20 mol % TEMPO, with 97% yield (Table 4, entry 19).…”