Mangat Singhab,
Nishant Pandeyab and
Bhuwan B. Mishra*a
aCenter of Innovative and Applied Bioprocessing (CIAB), Sector 81 (Knowledge City), S.A.S. Nagar, Mohali-140306, Punjab, India. E-mail: bhuwan@ciab.res.in; Tel: +91-172-5221541
bDepartment of Chemistry, Faculty of Science, Panjab University, Chandigarh-160014, India
First published on 21st December 2020
Extraction of commercial essential oil from several aromatic species belonging to the genus Cymbopogon results in the accumulation of huge spent aromatic waste which does not have high value application; instead, the majority is burned or disposed of to vacate fields. Open burning of spent aromatic biomass causes deterioration of the surrounding air quality. Therefore, a new protocol has been developed for chemical processing of spent biomass to obtain 5-(chloromethyl)furfural (CMF) with high selectivity (∼80%) and yields (∼26 wt% or ∼76 mol% with respect to pre-treated biomass) via refluxing in aqueous HCl in the presence of NaCl as a cheap catalyst. No black tar formation and gasification were observed in the processing of the spent aromatic biomass. Spent aromatic waste-derived CMF was further converted to 5-(hydroxymethyl)furfural (HMF) in good yields by a novel one pot method using iodosylbenzene (PhIO) as a reagent under mild reaction conditions.
Spent aromatic biomass contains varying composition of hemicellulose, cellulose, and lignin depending on the source, species, and region of the cultivation. Besides having a high calorific value, the high cellulose (35–40%) and hemicellulose (25–30%) content makes it a suitable biomass for bioenergy production. Terpenoids obtained from the aromatic crops have been found economic and fungible with the existing liquid fuels due to low temperature operable properties.3 Ethanol production from spent aromatic biomass has also been prospected, however, residual volatiles e.g. citral, geraniol, limonoids, etc., in the spent waste may inhibit the growth of Saccharomyces cerevisiae during microbial fermentation in biorefineries.4 The biomass has been also investigated for supply of nutrients to the other crops, nutrient recycling for fertilizer economy,5 and for the production of high value chemicals, e.g., xylose, levulinic acid, lignin, etc., by the chemical processing.6
Synthesis of 5-(hydroxymethyl)furfural (HMF) and its derivatives have recently been advanced as a highly promising platform compounds for easy access to a range of renewable chemicals and materials.7 However, the HMF has only been produced from fructose at pilot scales, and to date no scalable approach for its production from raw biomass has been reported.8 Frequent water solubility, high boiling point, and sensitivity to the acidic conditions impose difficulties in large scale production of HMF from carbohydrates. Therefore, a potentially disruptive innovation in the arena of renewable chemicals has recently been introduced in the form of the HMF analog, 5-(chloromethyl)furfural (CMF) which unlike HMF, can be obtained in high yield and purity from glucose or even directly from the cellulosic biomass (Table 1). CMF being hydrophobic in nature, can readily be isolated from reaction media, and converted further into different compounds, e.g., 2,5-dimethylfuran (DMF), 5-ethoxymethylfurfural (EMF), HMF, etc., due to the interesting reactive chemistry.9–12 Conventionally, CMF is prepared by the treatment of HMF or cellulose with dry hydrogen halide, wherein, the hydroxyl group in HMF undergoes substitution by a halogen atom.13–15 Other methods involve, treatment of carbohydrate with HCl–LiCl,11,16 deep eutectic solvents (such as choline chloride),17,18 HCl–H3PO4 in presence of CHCl3 under biphasic condition,19 and metal chlorides (such as CrCl3, AlCl3 and ZnCl2) or mixed metal chlorides (CrCl3–ZnCl2).20 Notwithstanding the numerous efforts depicted above, each of them suffers from at least one of the following limitations: low product selectivity, formation of by-products, low conversion efficacy and product yield, harsh reaction conditions, requirement of costly reagents, prolonged reaction times and tedious operations with complex setups (facility for continuous extraction). These drawbacks seriously hamper their potential applications in industries and warrant searching for more general and efficacious route for CMF synthesis from lignocelluloses.
Entry | Substrate | Catalyst | Temperature (°C) | Time (h) | Solvents | CMF yield (mol%) | Ref. |
---|---|---|---|---|---|---|---|
a DCE, dichloroethane; MIBK, methyl isobutyl ketone. | |||||||
1 | Corn stover | HCl | 100 | 3 | DCE | 70.0 | 10 |
2 | Cellulose | HCl + LiCl | 65 | >18 | DCE | 71.0 | 11 |
3 | Chitin | HCl | 150 | 1 | DCE | 44.5 | 12 |
4 | Fructose | ChCl + AlCl3 | 120 | 5 | MIBK | 50.3 | 18 |
5 | Inulin | ChCl + AlCl3 | 120 | 5 | MIBK | 22.6 | 18 |
6 | Sucrose | ChCl + AlCl3 | 120 | 5 | MIBK | 17.8 | 18 |
7 | Eucalyptus kraft pulp | HCl + H3PO4 | 45 | 20 | CHCl3 | 21.3 | 19 |
8 | Norway spruce soft wood TMP | HCl + H3PO4 | 45 | 20 | CHCl3 | 33.7 | 19 |
9 | Eucalyptus hard wood | HCl + H3PO4 | 45 | 20 | CHCl3 | 47.4 | 19 |
10 | Bamboo pulp | HCl + ZnCl2 + CrCl3 | 40 | 10 | CHCl3 | 32.7 | 20 |
11 | Eucalyptus pulp | HCl + ZnCl2 + CrCl3 | 40 | 10 | CHCl3 | 36.2 | 20 |
12 | Bagasse pulp | HCl + ZnCl2 + CrCl3 | 40 | 5 | CHCl3 | 50.1 | 20 |
13 | Palmarosa | HCl + NaCl | 100 | 1 | CHCl3 | 76.5 | This work |
14 | Lemon grass | HCl + NaCl | 100 | 1 | CHCl3 | 72.4 | This work |
15 | Citronella grass | HCl + NaCl | 100 | 1 | CHCl3 | 65.8 | This work |
In recent years, hypervalent iodine(III) compounds, such as [bis(trifluoroacetoxy)iodo]benzene (PIFA) and iodosylbenzene (PhIO), and iodine(V) compounds, such as iodylbenzene (PhIO2), have been extensively used in organic synthesis owing to their low toxicity, ready availability and easy handling.21 In organic chemistry, they are frequently used for the development of green methodologies for various oxidative transformations.22–27 Hypervalent iodine reagents have been prospected for selective oxidation of benzylic halides to corresponding carbonyl compounds in good yields. However, oxidative transformation of CMF to corresponding alcohol (HMF) in good yields is not realized so far under mild one pot reaction condition using hypervalent iodine reagents. Therefore, we envisioned exploring the feasibility of utilizing the oxidation potential of iodosylbenzene (PhIO) in oxidation of biomass derived CMF to afford HMF in good yields.
This manuscript describes an efficacious protocol for production of CMF directly from spent aromatic biomass via chemical processing in a biphasic reaction media consisting of concentrated HCl and chloroform in the presence of NaCl using a sealed pressure glass reactor. No such attempt has been made earlier for waste to wealth recovery of value added products from spent aromatic biomass, and the methodology appears to be economically attractive due to high selectivity in product formation with minimal by products, short reaction time, and use of NaCl as a cheap catalyst under mild reaction condition. The manuscript also describes a novel one pot synthesis of HMF from biomass derived CMF by the application of PhIO as a reagent under mild oxidative reaction conditions.
Thin layer chromatography (TLC) was performed on 60 F254 silica gel pre-coated aluminium plates and revealed with either a UV lamp (λmax = 254 nm) or a specific colour reagent (Dragendorff reagent or iodine vapours) or by spraying with methanolic-H2SO4 solution and subsequent charring by heating at 100 °C. Infrared spectra recorded as Nujol mulls in KBr pallets. Monosaccharides, carboxylic acids, HMF, CMF, and ethyl levulinate were detected and quantified by HPLC (Agilent, Model 1260) using Hi-Plex H (Agilent) analytical column (300 mm length, 8 mm porosity). Gas chromatographic analysis was performed on Thermo Scientific GC-MS (Model-Trace 1300 gas chromatograph) with auto sampler and ISQ LT mass spectrometer with columns: HP-5MS (0.25 × 30 m), film thickness 1.0 μm. 1H and 13C NMR were recorded at 500 and 125 MHz, respectively. Chemical shifts given in ppm downfield from internal TMS; J values in Hz.
Concentration of organic phase under reduced pressure resulted in a dense yellow liquid which was further purified by column chromatography to afford a light yellow oil in good yield (∼26% with respect to pre-treated biomass) and purity (∼98%). 1H NMR (500 MHz, CDCl3): δ 9.64 (s, 1H), 7.22 (d, J = 3.6, 1H), 6.60 (d, J = 3.6, 1H), 4.62 (s, 2H). 13C NMR (125 MHz, CDCl3): δ 177.76, 156.07, 152.86, 121.80, 111.96, 36.52.
In order to access the yield further, we optimize the reaction condition with respect to temperature, reaction time, effect of solvents, amount of conc. HCl, and loadings of NaCl. Without NaCl, the liquid products of pre-treated biomass under thermal processing in presence of HCl alone were many, with low yield and selectivity. GC-MS analysis of the organic phase displayed the presence of CMF and ethyl levulinate in low yields, meanwhile the HPLC analysis of aqueous phase (see ESI Fig. S1†) displayed the formation of monosaccharides and cellulose degradation products e.g. glucose, levulinic acid, 5-HMF, formic acid, ethyl-α,β-glucosides etc. A rise in HCl loading did not cause a substantial change in the selectivity and yield of products. Upon addition of NaCl, a significant enhancement in the concentration of CMF was observed in the organic phase after 1 h reaction time (Table 2). This indicated that the NaCl promotes both the yield of, and selectivity to CMF under heating condition. In HPLC analysis of aqueous phase, a decreasing glucose concentration at increasing NaCl loadings was attributed to its efficient conversion to CMF which being insoluble to aqueous phase readily diffuses to organic phase and detected therefrom by GC analysis (see ESI Fig. S2†). Thus, the yield of CMF increased with increasing the amount of NaCl at fixed HCl loading in the reactions. Highest CMF concentration in organic phase was detected at 0.05 equivalent of NaCl (5 wt% with respect to pre-treated biomass). A further increase in the amount of NaCl did not cause an enhancement of CMF yield due to near complete degradation of cellulose occurring in the pre-treated biomass.
Entrya,b | NaCl (wt%) | Cellulose degradation productsc (wt%) | |||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Organic phase | Aqueous phase | ||||||||||
Furfural | EL | HMF | CMF | Glucose | EADG | EBDG | LA | FA | HMF | ||
a Reaction condition: biomass, 1.0 g; concentrate (35%) HCl, 5 mL; chloroform, 15 mL; temperature, 100 °C; reaction time, 1 h.b Solid–liquid ratio, 1![]() ![]() |
|||||||||||
1 | BLK | 0.01 | 0.35 | 0.19 | 14.52 | 6.77 | 0.44 | 0.81 | 0.23 | 0.10 | 0.34 |
2 | 2.5 | 0.06 | 0.68 | 0.22 | 18.18 | 5.21 | 0.17 | 0.12 | 0.57 | 0.18 | 0.16 |
3 | 5.0 | 0.06 | 1.40 | 0.14 | 25.87 | 2.15 | 0.23 | 0.05 | 1.34 | 0.64 | 0.22 |
4 | 10 | 0.07 | 1.41 | 0.13 | 25.37 | 2.68 | 0.21 | 0.06 | 1.00 | 0.48 | 0.23 |
5 | 20 | 0.09 | 0.66 | 0.13 | 24.23 | 3.07 | 0.31 | 0.05 | 1.81 | 0.76 | 0.19 |
6 | 40 | 0.04 | 0.92 | 0.06 | 21.08 | 2.17 | 0.19 | 0.08 | 1.43 | 0.47 | 0.20 |
Mascal group10–12 has earlier established the crucial role of chlorinated solvents in the synthesis of CMF from carbohydrates under thermal condition. Therefore, the effect of organic solvents on the yield of CMF from biomass was investigated by carrying out reactions in presence of CHCl3, DCM, and DCE as the solvent system. The results suggested that the ability of organic solvents to extract out CMF from aqueous phase is highly desired. CMF was detected in low yields when DCM was used as reaction solvent. Similarly, DCE displayed moderate efficacy in CMF extraction from aqueous phase. The solvent CHCl3 performed well due the high ability of CMF extraction from aqueous phase, hence, established as the solvent of choice for the reaction.
The effect of temperature on the yield of CMF was also studied at constant loading of NaCl and HCl. Lowering of the temperature below 100 °C caused a rapid decrease in the CMF yield. Maximum yield of CMF from the biomass could be obtained at 100 °C. An increase in reaction temperature beyond 100 °C lowered the CMF yield due to the formation of unidentified soluble products (Fig. 1). Similarly, the reaction time was also found to have a profound impact on cellulose degradation and transformation of resulting monosaccharide to CMF. Lowering of the reaction time from 1 h at constant temperature (100 °C) resulted in a lot of glucose remained unreacted in reaction liquid. Processing of biomass under prolonged reaction time beyond 1 h at 100 °C resulted into an increased concentration of LA and polymeric materials in the hydrolysate (Fig. 2). Since, the designed methodology shows high selectivity towards CMF (Table 3), the reaction predominantly produces CMF which being insoluble in aqueous phase, simply diffuses to organic phase and recovered therefrom in good yields via concentration under the reduced pressure. Pure CMF (∼98%) was produced by column chromatography followed by validation through GC analysis (see ESI Fig. S3†) and characterization by spectroscopic techniques such as NMR (see ESI Fig. S4 and S5†) and MS (see ESI Fig. S6†).
SN | Biomass | Products selectivity | Glucose (wt%) | Conversionc (wt%) | ||||||
---|---|---|---|---|---|---|---|---|---|---|
Furfural | EL | HMFa | CMF | LA | FA | Othersb | ||||
a Both in aqueous and organic phases.b Others such as ethyl-α,β-glucopyranosides and unreacted glucose.c Based on glucan content in spent biomass. | ||||||||||
1 | Palmarosa | 0.18 | 4.36 | 1.10 | 80.56 | 4.20 | 1.98 | 7.60 | 2.15 | 71.08 |
2 | Lemon grass | 0.22 | 4.84 | 1.62 | 80.27 | 5.23 | 2.62 | 5.21 | 1.30 | 69.43 |
3 | Citronella grass | 0.19 | 3.88 | 1.78 | 79.55 | 6.11 | 3.21 | 5.28 | 1.16 | 66.38 |
The cellulose degradation products, e.g., glucose, LA, FA, and ethyl glucosides etc. were all together detected in a very small quantity (∼2–3%) in aqueous phase. Further, dissolving the residue (solid left after the reaction) in methanol established no black tar formation. Hence, neither black tar formation nor gasification could be observed in processing of biomass with NaCl and HCl under the optimized reaction conditions. As evident from Table 2, the highest concentration of CMF from pre-treated aromatic biomass (1.0 g) was obtained with a condition of 100 °C temperature, 1 h reaction time, 0.05 equivalent NaCl, 1:
5 w/v loading of conc. HCl and 1
:
15 w/v loading of CHCl3.
Once the production of CMF from pre-treated palmarosa biomass was established using NaCl and HCl under solvo-thermal condition, the methodology was successfully extended over the other pre-treated biomass such as lemongrass and citronella grass, wherein, the results demonstrated a near complete conversion of cellulose to CMF (Fig. 3). A plausible mechanism involves the acid hydrolysis of polymeric cellulose into glucose by the activity of mineral acid in presence of NaCl. A subsequent isomerization of glucose generates fructose which on dehydration results into the formation of 5-hydroxymethylfurfural (HMF) as intermediate that undergoes chlorination to form CMF in good yields.10
![]() | ||
Fig. 3 Comparative yield of cellulose degradation products from spent aromatic waste under the optimized reaction condition. |
The FT-IR spectrum of the isolated lignin exhibited absorption bands indicative to the presence of phenolic and alcoholic groups (3500 cm−1), –CH2–H and C–H stretching (2800–2900 cm−1), carbonyl function (1600–1780 cm−1) and aromatic ring (∼1400 cm−1). Absorption bands corresponding to syringyl and guaiacyl residues were observed between 1300–1100 cm−1 (see ESI Fig. S7†). X-ray diffraction pattern of lignin showed many sharp diffraction peaks in which the peaks centred at 19.19° and 32.31° were typical to pure lignin (see ESI Fig. S8†). Other sharp peaks indicated a certain level of crystallinity due to the impurities and/or small crystalline fragments. Elemental composition of the isolated lignin was determined by energy-dispersive X-ray spectroscopy (EDS) analysis which established the elemental composition: C, 71.33%; O, 21.94% as presented in (see ESI Fig. S9†). Other elements such as Na (3.19%), Cl (1.79%), and S (1.03%) were also detected as impurities due to the use of dilute NaOH and H2SO4 in the process of lignin isolation.
The mass balance and the carbon balance of product distribution from spent aromatic biomass was calculated based on the experiments performed in this paper, results are summarized in Table 4. The main products were xylose, CMF, and lignin. In the designed process, most of lignin present in the spent biomass was degraded (∼10–15%). About ∼10–20% weight loss was attributed to the presence of solvent extractives and residual volatiles. It is noticeable that the mass balance closures were not close to 100% because some degradation products from the hemicelluloses and cellulose were not detected in HPLC analysis. Additionally, some solids were adsorbed on to the filter paper and wall of funnel during the filtration process, therefore, could not be collected. Moreover, the designed methodology produces CMF in high selectivity which being highly soluble in chloroform, is isolated easily from the reaction mixture. We carried out a weight based analysis to check the formation of gases during the processing of spent aromatic biomass for production of CMF under the optimized reaction condition. Results of screening test carried out at different temperatures such as 80, 100, and 120 °C as summarized in Table 5, established that no significant loss in the weight of reaction mixture before and after the reaction was observed, hence, ruled out the formation of gases e.g. CO2, CO, CH4 etc.
SN | Type of biomass | Qty. of biomassa (g) | Liquefied products (wt%) | Residueb (wt%) | Lignin (wt%) | Biomass conversion (wt%) | Carbon balancec (wt%) | |
---|---|---|---|---|---|---|---|---|
Organic phase | Aqueous phase | |||||||
a Biomass loading at conc. HCl (5 mL), chloroform (15 mL), 100 °C temperature, reaction time 1 h.b Unreacted biomass recovered in reaction.c Carbon balance after degradation of cellulose. | ||||||||
1 | Palmarosa | 1.0 | 27.47 | 4.42 | 29.0 | 14.21 | 58.35 | 91.08 |
2 | Lemon grass | 1.0 | 25.12 | 4.04 | 27.5 | 13.47 | 59.64 | 83.14 |
3 | Citronella | 1.0 | 22.29 | 4.03 | 27.0 | 13.23 | 57.61 | 79.31 |
Entrya | Reaction temperature (°C) | Reaction mixture weightb (g) | Weight lose (wt%) | Gaseous products (CO, CO2, CH4) | |
---|---|---|---|---|---|
Before reaction | After reaction | ||||
a Reaction condition: biomass, 1.0 g; concentrate (35%) HCl, 5 mL; chloroform, 15 mL; reaction time, 1 h.b Weight of reaction mixture including the sealed glass reactor. | |||||
1 | 80 | 269.0 | 268.87 | 0.05 | ND |
2 | 100 | 270.7 | 270.65 | 0.02 | ND |
3 | 120 | 266.9 | 266.53 | 0.14 | ND |
The reaction was investigated with respect to effect of temperature, effect of reaction time, and the ratio of DMSO and water as solvent system. The reaction carried out in DMSO as a solvent alone under the anhydrous condition did not cause the formation of HMF even at the prolonged reaction time (24 h) that established the essentiality of water for a successful reaction. The reaction performed in presence of H2O as solvent alone could result in the low yield of HMF probably due to the substrate insolubility in the water. Hence, the use of two-phase solvent system comprising of water and organic solvent was anticipated, wherein, the mixtures of H2O and water immiscible solvents, i.e., dichloromethane, chloroform, ethyl acetate, etc., did not work due to the high affinity of CMF to remain in the organic phase. Similarly, the reaction could not be successful with water miscible solvents, e.g., methanol, ethanol, acetonitrile, etc. Considering the DMSO as a high-polarity water miscible solvent, we performed the oxidation of CMF with PhIO in a mixture of DMSO–water under mild heating condition, wherein, the peak corresponding to HMF was significantly detected in GC-MS analysis. Increasing the reaction temperature beyond 60 °C resulted into the formation of levulinic acid as a side product. Moreover, the concentration of water decisively influenced the efficacy of oxidation as no reaction was observed with excess of water when used along with DMSO as solvent. Thus, different gradients of DMSO/H2O were screened for an efficient oxidation of CMF to HMF by using PhIO, where a mixture of DMSO/water in a ratio of 4:
1 (v/v) demonstrated the best results. Also, high loadings of PhIO was required for completion of reaction. Thus, under the optimized reaction condition, the CMF (1.0 equiv.) was reacted with PhIO (3.0 equiv.) in presence of DMSO and water in a ratio of 4
:
1 (v/v) as solvent system under mild heating for 3 h to afford HMF as a light yellow liquid in good yields (∼90%) and purity (see ESI Fig. S10 and S11†).
Although, a detailed understanding of the mechanism for such an oxidative transformation of CMF to HMF will require additional studies, however, it is assumed that the initial reaction of CMF with DMSO may lead to the formation of an addition product I which reacts with PhIO and generates intermediate II that decomposes to a more stable intermediate III. Action of water molecule cause an easy release of product HMF via the decomposition of intermediate IV (Fig. 5).
To date no scalable method is available for production of HMF from raw biomass. High sensitivity of HMF to the acidic conditions results in the formation of numerous side products which impose difficulties in its production from biomass. Therefore, a new method for synthesis of HMF from the biomass derived CMF under oxidative condition using hypervalent iodine reagent PhIO has also been investigated in this manuscript. Use of PhIO as an oxidant provides easy access to HMF from CMF in high yields and selectivity under the mild reaction condition. Thus, this approach would be promising and commercially more acceptable method for the production of CMF, HMF and their derivatives from spent aromatic residues.
Footnote |
† Electronic supplementary information (ESI) available: FT-IR, EDS and XRD spectra of isolated lignin, HPLC chromatograms of biomass hydrolysate, GC-MS chromatograms of CMF and HMF, and NMR spectrum of CMF. See DOI: 10.1039/d0ra09310f |
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