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Streamlined Synthesis of Biomonomers for Bioresourced Materials: Bisfuran Diacids, Diols and Diamines via Common Bisfuran Dibromide Intermediates Lu Wang, Yuji Eguchi, and Eugene Y.-X. Chen Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b02920 • Publication Date (Web): 25 Sep 2017 Downloaded from http://pubs.acs.org on September 28, 2017
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Industrial & Engineering Chemistry Research
Streamlined Synthesis of Biomonomers for Bioresourced Materials: Bisfuran Diacids, Diols and Diamines via Common Bisfuran Dibromide Intermediates Lu Wang,† Yuji Eguchi,‡ and Eugene Y.-X. Chen*,† †
Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523-1872, USA
‡
Corporate R&D Center, Sekisui Chemical Co., Ltd. Tskuba, Ibaraki 300-4292, Japan
ABSTRACT: A bisfuran dibromide has been established as the versatile and common intermediate for the high-yield synthesis of the three important classes of bisfuran monomers for furan-based renewable materials, bisfuran diacids, diols and diamines. The general synthetic route involves coupling reaction of 2-methylfuran with a ketone (acetone or cyclohexanone) under acidic conditions and bromination reaction of the resulting bisfuran dimethyl compound to produce the bisfuran dibromide intermediate. This dibromide intermediate is subsequently converted to the corresponding bisfuran diacid (via oxidation reaction with KMnO4 under basic conditions), bisfuran diol (by hydrolysis reaction under mild basic conditions), and bisfuran diamine (through the Gabriel reaction). The versatility of the bisfuran dibromide intermediate and the effective transformation into the monomers with high to quantitative yield typically without the need for further purification highlight the two attractive features and potential for large-scale production.
1. INTRODUCTION In recent years, great efforts have been made to develop bio-based polymers using the monomers derived from renewable biomass, due to dwindling of petrochemical feedstocks as well as environmental concerns.1 Among the polymerizable monomers used to prepare bio-based polymers, 1,1′-geminal bisfuran compounds that possess a structure similar to that of Bisphenol A, such as bisfuran diacids, diols and diamines, have attracted increasing attention. These bisfuran compounds were typically prepared from two of the most value-added biomass building blocks or platform chemicals, furfural and 5hydroxymethyl furfural (HMF),2 which can be obtained from dehydration of biorefinery carbohydrates.
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Various bio-based polymers derived from bisfuran monomers, such as polyesters,3 polyimides,4 epoxy thermosets,5 polyazomethines,6 poly(esteramide)s,7 and polyureas8 etc., have been reported. In addition, vicinal bisfuranic diol, triol, and tetraol monomers9 were obtained via self-coupling and cross-coupling reactions of furfural and HMF, and these monomers have recently been utilized to synthesize bisfuranbased polyesters, polyurethanes, and poly(ester urethane)s10 through condensation polymerizations. As for the geminal bisfuran diol, two synthetic routes have been reported in the literature.3c,11 Lee and co-workers11 synthesized the bisfuran diol based on furan-2-carboxylic acid through three steps: (1) esterifying furan-2-carboxylic acid with methanol; (2) coupling the resulting methyl furan-2-carboxylate with acetone to give dimethyl 5,5'-(propane-2,2-diyl)bis(furan-2-carboxylate); carboxylate
intermediate
to
obtain
the
bisfuran
diol,
and (3) reducing
(5,5'-(propane-2,2-diyl)bis(furan-5,2-
diyl))dimethanol. Additionally, Sucheck and co-workers3c developed an alternative route for the bisfuran diol, based on furfural that included: (a) protecting the aldehyde group of furfural with 1,2-ethanedithiol; (b) coupling the resulting 2-(1,3-dithiolan-2-yl)furan with acetone to afford 5,5'-(propane-2,2-diyl)bis(2(1,3-dithiolan-2-yl)furan); (c) subjecting the obtained compound to dedithioacetalization to form bisfuran dialdehyde; and (d) reducing the resulting bisfuran dialdehyde to the final bisfuran diol. As for the synthesis of the bisfuran diacid, El Gharbi et al.12 reported a route that starts with the coupling reaction of ethyl furan-2-carboxylate with acetone, followed by hydrolysis reaction. Regarding the bisfuran diamine, Gandini et al.8 reported a route that begins with the preparation of bisfuran diammonium salt by coupling furan-2-ylmethanamine with acetone in the presence of HCl. The obtained compound was subsequently converted to the bisfuran diamine under basic conditions. As can be seen from the above overview, the bisfuran diacid, bisfuran diol, and bisfuran diamine monomers were synthesized through various different starting materials, intermediates and multiple steps. However, for streamlining the overall process of synthesizing various important polymerizable bisfuran compounds, it is desirable to develop a general synthetic route for such bisfuran molecules as building blocks for various biofuran-based renewable polymeric materials. In this context, we developed a common bisfuran dibromide intermediate, from commercially available 2-methylfuran (produced by the
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selective hydrogenation of furfural), which can be readily converted to the bisfuran diacid, diol and diamine compounds in high to quantitative isolated yields.
2. EXPERIMENTAL SECTION 2.1. Materials and Methods. All oxygen- and moisture-sensitive manipulations were carried out in a nitrogen-filled glovebox or under nitrogen atmosphere using standard Schlenk techniques. Cyclohexane was distilled over CaH2. HPLC-grade N,N-dimethylformamide (DMF) was dried over CaH2 overnight, followed by vacuum distillation (CaH2 was filtered before distillation). 2-Methylfuran (Aldrich), 2,2′azobisisobutyronitrile (AIBN, Aldrich), N-bromosuccinimide (NBS, Aldrich), cyclohexanone (Aldrich), KMnO4 (Aldrich), potassium phthalimide (Acros Organics), hydrazine monohydrate (Aldrich), NaHCO3 (EMD Chemicals Inc.), and K2CO3 (Fisher Scientific) were used as received. 1H and 13C NMR spectra were recorded on a Varian Inova 400 MHz spectrometer. Chemical shifts for all spectra were referenced to internal solvent resonances and were reported as ppm relative to SiMe4. High-resolution mass spectrometry (HRMS) data were collected on an Agilent 6220 Accurate time-of-flight LC/MS spectrometer. 2.2.1. Synthesis of bisfuran-Ac-dimethyl [5,5'-(Propane-2,2-diyl)bis(2-methylfuran)]. Acetone (5.36 mL, 73.0 mmol) and 2-methylfuran (10.0 g, 121.8 mmol) were mixed in a 100 mL round-bottom flask at 0 oC. An aqueous H2SO4 solution (0.325 mL (6.09 mmol) of 98% H2SO4, previously diluted in 0.325 mL of H2O) was added dropwise to the reaction mixture under stirring. Then the flask was sealed, and the reaction mixture was further stirred for 20 h at 50 °C. The reaction mixture was neutralized with saturated aqueous NaHCO3 and extracted with ethyl acetate (3 × 100 mL), and the combined organic fractions were washed with deionized water, dried with magnesium sulfate, filtered, and concentrated under reduced pressure. The titled product was obtained as an orange-yellow liquid (11.8 g, 95% yield). 1
H and 13C NMR spectra of the obtained product are shown in Figures S1 and S2, respectively. 1H NMR
(400 MHz, CDCl3): δ 1.60 (s, 6H, C(CH3)2), 2.25 (s, 6H, CH3), 5.85 (d, J = 2.8 Hz, 2H, furan ring H), 5.87 (d, J = 2.8 Hz, 2H, furan ring H).
13
C NMR (100 MHz, CDCl3): δ 13.72, 26.60, 37.33, 104.64,
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105.84, 150.63, 158.72 ppm. HRMS calculated for [C13H16O2 + H]+ [M + H]+: m/z = 205.1229, found: 205.1223. 2.2.2 Synthesis of Bisfuran-Ac-dibromide [5,5'-(propane-2,2-diyl)bis(2-(bromomethyl)furan)]. To a 100 mL round-bottom flask was added a cyclohexane (30 mL) solution of bisfuran-Ac-dimethyl (2.0 g, 9.8 mmol), NBS (4.19 g, 23.5 mmol), and AIBN (161 mg, 0.98 mmol) under nitrogen atmosphere. The mixture was stirred at 80 oC for 5 h, after which 200 mL of dichloromethane and 75 mL of deionized water were added. The mixture was stirred for about 10 min, and then phases were separated. The organic layer was further washed with deionized water three times, dried with magnesium sulfate, filtered and concentrated to dryness. Bisfuran-Ac-dibromide (3.54 g, 99.8% yield) was obtained as a black viscous liquid and was used directly without further purification. FT-IR, 1H and 13C NMR spectra of the obtained bisfuran-Ac-dibromide are shown in Figures 1(a), 1(b) and S3, respectively. 1H NMR (400 MHz, CDCl3): δ 1.65 (s, 6H, C(CH3)2), 4.49 (s, 4H, CH2Br), 5.98 (d, J = 3.2 Hz, 2H, furan ring H), 6.29 (d, J = 3.2 Hz, 2H, furan ring H). 13C NMR (100 MHz, CDCl3): δ 24.49, 26.29, 37.93, 106.09, 110.73, 148.92, 160.82 ppm. 2.2.3. Synthesis of Bisfuran-Ac-diacid [5,5'-(propane-2,2-diyl)bis(furan-2-carboxylic acid)]. To a 250 mL round-bottom flask was added NaOH (13.3 g, 332 mmol) and H2O (90 mL). Under stirring at room temperature, bisfuran-Ac-dibromide (2.0 g, 5.52 mmol, previously dissolved in 30 mL of 1,4dioxane) was added to the mixture followed by KMnO4 (5.24 g, 33.2 mmol). The reaction mixture was stirred at room temperature for 2 h. The precipitate of manganese oxide was filtered off and washed with deionized water. The filtrate was concentrated under pressure to remove the 1,4-dioxane solvent, and the pH of the aqueous filtrate was adjusted to
