Abstract
A cellulose ether that is easier to melt than benzyl cellulose was produced from the lignin degradation product veratryl alcohol. Veratryl chloride and bromide were synthesized from the alcohol, and these two chemicals were used to react with Avicel® cellulose to form the novel cellulose ether veratryl cellulose (VC). Spectroscopic characterisation techniques (1H NMR, FTIR) indicated the successful conversion of Avicel® cellulose to the cellulose ether VC, by both routes, at a degree of substitution of 1.4 to 1.6. Melting measurements of the VC samples showed a gradual softening from approximately 110 °C; the VC was melted below 200 °C. XRD analysis confirmed that the chemical treatments affect the degree of crystallinity. Size exclusion chromatography results showed that the products differ remarkably in molecular weight. The VC synthesized with veratryl chloride degraded almost twice as much as when veratryl bromide were used. The cellulose ethers were soluble in DMSO, DMAc, and CHCl3.
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Replacing Benzyl Chloride with a Lignin-degradation Product in Cellulose Etherification Decreases the Melting Point
Mohamed Yahia,a,b and Ola Sundman a,*
A cellulose ether that is easier to melt than benzyl cellulose was produced from the lignin degradation product veratryl alcohol. Veratryl chloride and bromide were synthesized from the alcohol, and these two chemicals were used to react with Avicel® cellulose to form the novel cellulose ether veratryl cellulose (VC). Spectroscopic characterisation techniques (1H NMR, FTIR) indicated the successful conversion of Avicel® cellulose to the cellulose ether VC, by both routes, at a degree of substitution of 1.4 to 1.6. Melting measurements of the VC samples showed a gradual softening from approximately 110 °C; the VC was melted below 200 °C. XRD analysis confirmed that the chemical treatments affect the degree of crystallinity. Size exclusion chromatography results showed that the products differ remarkably in molecular weight. The VC synthesized with veratryl chloride degraded almost twice as much as when veratryl bromide were used. The cellulose ethers were soluble in DMSO, DMAc, and CHCl3.
DOI: 10.15376/biores.18.1.161-174
Keywords: Veratryl cellulose; Melting measurements; Cellulose ether; Degree of substitution; Characterisation techniques; Size exclusion chromatography
Contact information: a: Department of Chemistry, Umeå University, Umeå, SE-90187, Sweden; b: Chemistry Department, Faculty of Science, Helwan University, 11795, Cairo, Egypt;
* Corresponding author: ola.sundman@umu.se
INTRODUCTION
Although cellulose is a solid and valuable polymer, it has several drawbacks; for example, it is difficult to dissolve and cannot be melted (Lindman et al. 2010; Yang et al. 2014; Acharya et al. 2021). A commonly used strategy to circumvent these problems is to modify the chemical structure of the cellulose, and the products of such chemical modifications are collectively called cellulose derivatives (Zhang et al. 2019; Oprea and Voicu 2020; Liu et al. 2021; Mali and Sherje 2022).
Cellulose derivatives are divided into two different groups: cellulose esters (e.g., cellulose acetate) and cellulose ethers (e.g., carboxymethyl cellulose) (Candido and Gonçalves 2016). Of these, cellulose ethers are dominating the market, with US$ 11.3 billion in 2021 to $ 14.62 billion in 2016 (Kukoyi 2016). Commercial cellulose ethers are used as thickening, stabilising, water-retaining, and dispersing agents in the building industry (Carraher and Charles 2003; Berglund et al. 2009).
The change towards renewable recourses is desirable. However, cellulose etherification is achieved with the use of fossil-based chemicals, e.g., chloroacetic acid and ethyl chloride from fossil sources. The historically important benzyl cellulose (BC) is produced by the etherification of cellulose with petroleum-based benzyl chloride. This cellulose ether was commercially manufactured before World War II, and it is one of few cellulose derivatives that can display a melting point (Braun and Meuret 1989; Ramos et al. 2005). BC is still relevant because it can be used in haemodialysis membranes (Sundman et al. 2015), but this polymer is not produced commercially. However, if the fossil-based benzyl chloride (Fig. 1a) could be replaced with a renewable chemical, a fossil-free polymer with similar properties can be produced. If an even more bulky substituent is used, the authors hypothesise that the formed cellulose derivative can show even more mouldable properties than BC.
A structurally related but bulkier chemical is veratryl alcohol (3,4-dimethoxybenzyl alcohol) (Fig. 1b). Veratryl alcohol is a bio-based chemical naturally synthesised from the degradation of lignin. Discovered in 1961 (Russell et al. 1961), the biological origin of this lignin-degradation product was established in 1978 (Lundquist and Kirk 1978). The present study used quite strong and toxic chemicals (SOCl2 and PBr3), but as this is only an initial laboratory study, such processes are not intended for scale-up. For industrial purposes, e.g. HCl, a catalyst, high temperature, and pressure, have potential to be used for chlorination.
Fig. 1. a) Benzyl chloride, b) Veratryl alcohol (3,4-Dimethoxybenzyl alcohol) to the left and the corresponding chloride/bromide to the right.
As shown in Fig. 1, the difference between benzyl chloride and veratryl chloride is that the latter has two electron-donating methoxy groups. These groups make the veratryl molecules less reactive but more bulky than the respective benzyl group. Thus, a lower melting point can be expected for any veratryl cellulose ether than for the respective benzyl ether.
In this paper, veratryl alcohol was converted to both veratryl chloride and bromide using chemical synthesis, and these products were tested for their reactivity towards cellulose. The produced veratryl cellulose (VC) was characterized using several chemical analyses. According to these principles, a partly bio-based cellulose ether can be synthesised via this route, but the veratryl chloride/bromide is probably less reactive than the respective benzyl. The hypothesis is that a cellulose ether that is more easily melted than benzyl cellulose should be formed. The concept presented herein will help develop and synthesise new bio-based cellulose derivatives. Based on this research, decisions can be made to apply this strategy with similar lignocellulose degradation products to further explore the production of different bio-based materials as well as develop cellulose-ether-based bioplastics, etc.
EXPERIMENTAL
Materials
Avicel®PH-101 microcrystalline cellulose (∼50 µm size, Sigma Aldrich), dimethyl sulfoxide- (DMSO, Sigma Aldrich), trimethylamine (Et3N, Sigma Aldrich), acetic acid (Sigma Aldich), chloroform (CHCl3, VWR Chemicals), dichloromethane (CH2Cl2, VWR Chemicals), phosphorus tribromide (PBr3, Sigma Aldrich), thionyl chloride (SOCl2, sigma Aldrich), veratryl alcohol (VOH, sigma Aldrich), acetone (Sigma Aldrich), benzyl chloride (Sigma Aldrich), chloroform-D (CDCl3, Armar Chemicals, 99.8 atom%D), dimethyl sulfoxide-d6 (DMSO-d6, Armar Chemicals, 99.8 atom%D), dimethylacetamide (DMAc, VWR Chemicals), 4-dimethylamino pyridine (DMAP, Reagent Plus® ≥99, Sigma Aldrich), methanol (MeOH, VWR Chemicals), propionic anhydride (Sigma Aldrich), 2-propanol (VWR Chemicals), pyridine (Sigma Aldrich), tetrabutylammonium fluoride (TBAF·3H2O, Sigma Aldrich), sodium bicarbonate (NaHCO3, VWR Chemicals), anhydrous sodium sulfate (Na2SO4, VWR Chemicals), sodium chloride (NaCl, VWR Chemicals) were all used as received. NaOH (VWR Chemicals) was pulverised and used immediately. All the mentioned chemicals were pure (≥ 98%) and used without further purification.
Synthesis of Veratryl Chloride
Following the general procedure in literature (Miyamura et al. 2013; Guan et al. 2019), 0.60 mL of SOCl2 was added to 1.157 mL of Et3N in an ice bath, and the obtained viscous yellow solution was diluted with 10 mL of dry CH2Cl2. The resulting solution was added dropwise to 1.00 mL veratryl alcohol solution in 10 mL of dry CH2Cl2. The reaction mixture was allowed to equalise overnight, after which the reaction appeared complete. The reaction mixture was quenched with 10 mL of ice water, stirred for 30 min., and then filtered. The filtrate was dried over anhydrous Na2SO4 and then concentrated by rotary evaporation yielding the final product veratryl chloride (3,4-dimethoxybenzyl chloride).
Synthesis of Veratryl Bromide
Following the general procedure in Wu and Huang (2014), veratryl alcohol (9.92 g) was dissolved in 25 mL of CH2Cl2, and the solution was cooled to 0 °C. Then, a PBr3 (1.0 M) solution in CH2Cl2 (25 mL) was added via syringe slowly to the alcohol solution. The obtained yellow mixture was stirred at room temperature for another 4 h. The reaction was carefully quenched with ice water (100 mL) and extracted with CH2Cl2 (3 x 50 mL). The combined organic layers were successively washed with saturated NaHCO3 (100 mL), distilled water (100 mL), and brine solution (NaCl solution, 100 mL) and dried over anhydrous Na2SO4. Finally, the solution was concentrated in a rotary evaporator to collect the desired veratryl bromide (3,4-dimethoxybenzyl bromide).
Synthesis of Benzyl Cellulose (BC) and Veratryl Cellulose (VC)
The synthesis method was based on the procedure reported in the literature (Ramos et al. 2005; Sundman et al. 2015). Briefly, 2.82 g (TBAF.3H2O) salt was mixed with 15 mL DMSO until fully dissolved; 0.45 g Avicel®PH-101 cellulose was added to the mixture with intense stirring at room temperature (for 30 min) then at 60 °C (for 1 h) until the solution mixture was clear. A solution of (0.37 g pulverised NaOH in 5 mL DMSO) was added to the mixture with vigorous stirring. 1 mL of benzyl chloride was added to the solution with subsequent stirring for 4 h at a constant temperature (70 °C). The produced benzyl cellulose suspension was precipitated into 1:4 H2O: MeOH solution and was then neutralised with dilute acetic acid. The benzyl cellulose polymer was obtained by filtration, washing with excess (1:4 H2O: MeOH) solution, and drying for 48 h under vacuum pressure at 50 °C. The two veratryl cellulose polymers were synthesised similarly but with veratryl chloride or veratryl bromide instead of benzyl chloride and the same molar ratio (1:3) between Avicel cellulose and halide.
Perpropionylation of Avicel® Cellulose And Cellulose Derivatives
Following the synthesis method reported by Sundman et al. (2015), a mixture of 0.3 g Avicel® cellulose, 5 mL pyridine, 5 mL propionic anhydride, and 0.2 g DMAP as a catalyst was heated and kept isothermal at 80 °C for >24 h. Then the reaction mixture was cooled to room temperature and precipitated in 200 mL 2-propanol. The obtained polymer was filtered off, washed with 2-propanol, and dried at 70 °C for one week under reduced pressure. The same procedure was used for the perpropionylation of cellulose derivatives by replacing the Avicel® cellulose with the cellulose ethers.
Solubility Measurements
The solubility of the cellulose derivatives was checked by dissolving 10 mg of dry solids in 1 mL solvent. The suspensions were placed in an ultrasonic bath for 30 min, and the samples were visibly swollen. The solubility of the samples was determined visually after resting at room temperature overnight.
Melting Measurements
A few grains of the cellulose ether were transferred to a capillary tube for measurement. The capillaries were put in a melting point apparatus (USA). The samples were heated to 80 °C. The temperature was then gently increased until the material visibly softened, and the temperature was recorded. The temperature was slowly (<10 °C/min) increased to 230 °C with a continuous inspection.
Characterisation Techniques
Nuclear Magnetic Resonances (1H-NMR) spectroscopy was performed to determine the degree of substitution (DS) of the cellulose derivatives and recorded using an Avance Bruker DPX (400 MHz). The samples were dissolved in deuterated chloroform solvent, and its 1H-NMR singlet was used as an internal reference (CDCl3, 1H 7.25 ppm).
A Bruker Vertex 80v Fourier Transformed Infrared spectrometer with Attenuated Total Reflectance mode (FTIR-ATR) was used with a detector (deuterated triglycine sulfate-DTGS) to analyse the samples with FTIR. The FTIR spectra range (from 400 to 4000 cm−1) was recorded with 128 scans per sample and a resolution of 4 cm-1.
A size exclusion chromatography (SEC) instrument coupled to a Refractive Index (RI) and a light scattering (LS) detector was used to analyse the molecular weight distribution of the perpropionylated cellulose derivatives. The samples were dissolved in chloroform for measurements at a 5 mg/mL concentration. The SEC system consisted of a high-pressure pump (Hewlett Packard-series 1100), a guard column, two serial T6000M columns, and a 0.45 µm PTFE filter in series. The auto-sampler, columns, and detector temperature were set at 35 °C, the eluent used was chloroform, and the flow rate was 1 mL min−1. The detector system was a Malvern Omnisec Reveal containing a refractive index (IR) and a multi-angle light scattering (MALS) detector. The detector response was calibrated using two polystyrene standards (one broad and one narrow). The data were evaluated with the Omnisec V11 software from Malvern using the Debye model applying a first-degree polynomial.
X-ray diffractograms (XRD) were obtained using a PANalytical Xpert3 Powder X-ray diffractometer (XRD) with operating system Cu Kα (1.54 Å) radiation at 25 mA and 40 kV. The measurements were recorded from 5o to 45o (2θ) at a scan speed of 8 s per point.
RESULTS AND DISCUSSION
Solubility Test
Table 1 summarises the solubility tests for the cellulose ethers in organic solvents at 25 °C and a concentration of 10 mg/mL. The insolubility of cellulose in common solvents is well-known. The cellulose derivatives were not soluble in hydrogen bonding solvents (MeOH and acetone) but solubilised in the less polar solvents (CHCl3, DMSO and DMAc). Compared to previous literature (Ramos et al. 2005, Sundman et al. 2015), the solubility here is seen at lower DSs. In both previous studies solubility of BCs was achieved at high DS (>2) and in CHCl3 only. The much higher solubility at more moderate DSs, are indicative of more even distribution of the substutents than in the previous studies (Ramos et al. 2005), but the solubility is the only evidence here to support this claim.
Table 1. Solubility of the Cellulose Derivatives in Different Solvents at a Concentration of 10 mg/mL
Melting Measurements
The melting of the BC and the VCs was gradual, and no exact melting point can be reported. In Table 2, the temperatures where first visible softening (FST) of the material could be seen and the temperature where a remarkable change (MST) was observed are reported. It must be stated, however, that the slow and gradual change in structure (softening/melting) can be challenging to exactly determine and that the numbers are based on observations.
Table 2. The First Visible Softening (FST) and the Major Softening Temperature (MST) of the Cellulose Ethers
The only observable change was the MST between BC and VC2. However, the softening of these cellulose ethers was gradual, and the melting also depended on impurities in the samples. Interesting, however, is that at even higher temperatures, the VC seemed to melt remarkably. At approximately 170 to 200 °C, both the VCs begun to show a whitish or light-brown melt. The BC did not show any melt; it degraded to a blackish char-like substance, as expected (Isogai et al. 1984). These authors showed that the melting of BCs depends on both DS and MW and concluded that the DS needed to be close to 3 while the degree of polymerisation (DP) needed to be < 140 if a clear melting point for BC should appear. The same conclusion cannot be drawn for the VCs studied herein. However, the presence of air bubbles in the samples complicated the interpretation of what is seen in the melting temperature measuring device. It would have been beneficial to perform both the synthesis and the melting measurements in an inert environment to avoid both bubble formation and oxygen catalysed degradation.
Fourier Transform Infrared (FTIR) Measurement
Figure 2 shows the FTIR spectra for the analysed cellulose-based polymers (Avicel® cellulose, BC, VC1, and VC2). The absorption band at (3300 to 3500 cm-1) associated with OH groups (-OH stretching) in cellulose, was diminished and shifted in the spectra for the cellulose ethers (BC, VC1 and VC2). Figure 2 also shows that the absorption band associated with the aromatic rings (CC stretching mode) appeared around (1450 to 1500 cm-1) for BC and at (1500 to 1600 cm-1) for the VCs, and this increase in wavenumber indicated an increased charge density caused by the donating methoxy groups (Young et al. 1951). In the same way, the absorption band associated with aromatic sp2 (C-H bending mode) was shifted. It appeared near 650 to 750 cm-1 for BC and around 750 to 850 cm-1 for the VCs. Lastly, an absorption band at 1300 to 1250 cm-1, related to the (C–O stretching mode) appeared solely in the VCs due to the methoxy groups in the veratryl structure. In short, the FTIR measurements indicate the successful modification and replacement of OH groups in Avicel® with veratryl groups.
Proton Nuclear Magnetic Resonance (1H NMR) Measurements
The DS values of the cellulose ethers were calculated as DSNMR of perpropionylated derivatives, in line with previous work (Ramos et al. 2005; Li et al. 2011; Sundman et al. 2015). DSNMR was estimated according to Eqs. 1 (for P-BC) and 2 (for P-VC1 and P-VC2),
where A1 represents the integral in the 1H NMR spectra for the aromatic peak (δ≈7.2 ppm for P-BC and δ≈6.7 for P-VC1,2), while A2 represents the integration for the aliphatic peaks (the integral of the area 3.0 ≤ δ ≥ 5.5) (Li et al. 2011; Ramos et al. 2005; Sundman et al. 2015). The reasoning behind equations 1 and 2 is found in the supporting information Figs. S1 and S2 (see Appendix). The resulting DSNMR values are presented in Table 3.
Table 3. The DSNMR of the Cellulose (derivatives)
Fig. 2. FTIR spectra of the cellulosic derivatives ((a) Avicel cellulose, (b) BC, (c) VC1, and (d) VC2)
Figure 3a displays (from bottom to top) the 1H NMR spectra of the benzyl chloride (B-Cl), veratryl alcohol – (V-OH), veratryl chloride (V-Cl), and veratryl bromide (V-Br), respectively. The 1H NMR spectrum (400 MHz, internal standard CDCl3) for (B-Cl) showed the two expected signals for benzyl chloride (B-Cl) that appeared at (7.50 ppm, m, 5H) and (4.46 ppm, s, 2H). The 1H NMR spectrum (400 MHz, internal standard DMSO-d6) for veratryl alcohol showed, on the one hand, the five expected peaks appeared for veratryl alcohol (V-OH) at (6.90 ppm, m, 2H), (6.80 ppm, d, 1H), (5.25 ppm, t, 1H), (4.50-4.46 ppm, s, 2H), and (3.85-3.70 ppm, s, 6H). The spectra for veratryl chloride (V-Cl) and veratryl bromide (V-Br) showed all the previously mentioned peaks for (V-OH) except the peak associated with the hydroxyl group. Thus, the 1H NMR analysis indicated the successful synthesis of veratryl chloride or veratryl bromide, respectively, from veratryl alcohol.
The 1H NMR spectra (400 MHz, internal standard CDCl3) of the per-propionylated cellulose derivatives [P-cellulose, P-benzyl cellulose (P-BC) and P-veratryl cellulose (P-VC1 and P-VC2)] are shown in Fig. 3b. The signals for the per-propionylated Avicel® between 3 and 5 ppm were associated with cellulose backbone structure: (H3) 5.10 ppm, (H2) 4.81 ppm, (H1) 4.41 ppm, (H6) 4.06 ppm, (H4) 3.71 ppm, and (H5) 3.53 ppm (Kono et al. 2016a; Li et al. 2011; Ramos et al. 2005). The signals between 0.80 and 2.5 ppm corresponded to the methyl and methylene groups of the propionic acid ester (H7 and H8). In the P-benzyl cellulose (BC) spectrum, it was apparent that additional signals appeared around 7.21 ppm (H9) and 4.65 ppm (H10), which were associated with the benzyl groups (aromatic carbon and methylene groups, respectively).
Fig. 3. (a) 1H NMR spectra for (B-Cl), (V-OH), (V-Cl), and (V-Br); (b) 1H NMR spectra for (P-Cellulose), (P-BC), (P-VC1), and (P-VC2).
In the P-veratryl cellulose derivatives (P-VC1 and P-VC2), the corresponding peaks were shifted to around 6.65 ppm (H11), 4.40 ppm (H12), respectively. The reason for the shift between BC and VC structures in the 1H NMR signals was the presence of electron-donating groups (methoxy groups (O-CH3)) within the veratryl cellulose structures (Spiesecke and Schneider 1961; Kono et al. 2016b; Miyamoto and Hada 2021). An additional peak appeared at 3.55 ppm that represents the methoxy group in the veratryl substituents (H13).
Although the 1H NMR spectra were primarily evaluated for DSNMR determination, these data also confirm the successful synthesis of the novel cellulose ether. Overlapping of the cellulose backbone 1H NMR peaks for the ethyl group in benzyl cellulose appeared and the separation of peaks also highly depended on DSNMR (Li et al. 2011; Ramos et al. 2005). In our data, this phenomenon was also evident in the veratryl cellulose samples. Additionally, as reflected in Table 3, the equal amount of reagent gave higher DSNMR if veratryl chloride (1.6) or bromide (1.4) was used than if benzyl chloride (1.2) was used. However, there is competition between etherification and hydroxide catalysed hydrolysis; hydrolysis might explain the impression of a reversed order of reactivity since it is known to be a quick reaction. However, this is hypothetical, and the molecular weight of the polymers must be considered.
X-ray Diffraction (XRD)
Figure 4 displays the X-ray diffractograms obtained for cellulosic derivatives (Avicel® cellulose, BC, VC1, and VC2).
Fig. 4. X-ray diffraction patterns for the cellulosic derivatives (Avicel® cellulose, BC, VC1, and VC2)
The WAXD patterns of Avicel® cellulose showed that there were characteristic diffraction peaks at 2θ = 34.6°, 22.5°, and 16.5°, which correspond to the planes (004), (200) and (110), in Cellulose-I crystals, respectively (Ramos et al. 2005; Ass et al. 2006; Li et al. 2011; Ju et al. 2015; Thakur et al. 2020). After derivatisation the characteristic peaks of cellulose-I disappeared, and as the degree of crystallisation of cellulosic materials is affected by chemical treatments (Wu et al. 2020), the disappearance of crystallinity during the derivatisation process was expected.
Molecular Weight Estimations (Size Exclusion Chromatography)
The SEC analysis was done in chloroform on perpropionylated samples, which all had different molecular weight than the original cellulose (ether). Thus, the molecular weight averages (MW averages: Mw and Mn) had to be calculated with this in mind. Although caution with the SEC of cellulose derivatives as an indication for cellulose molecular weight distribution is advised in the literature (Melander and Vuorinen 2001; Henniges et al. 2014; Potthast et al. 2015; Li et al. 2016; Ono and Isogai 2021), the potential loss of low-MW fractions was not critical. Because only the relative decomposition was analysed, this was not considered an issue. Table 4 displays the MW averages for the original (Avicel®) cellulose and cellulose derivatives (BC, VC1, and VC2), both as data from the SEC measurements and as corrected, calculated using Eq. 3,
where Mw,corrected represents the corrected, calculated Mw (g/mol) of the polymer in question. Mw, SEC (g/mol) represents the Mw from the SEC measurement. MAGU,non-per-propionylated (g/mol) and MAGU, per-propionylated (g/mol) represent the molecular weight of the AGU of the polymer prior and after per-propionylation, respectively. It was assumed that (DSBC or VC + DSper-propionylation) was 3, which was a simplification. However, any error brought by this simplification was small.
Table 4. Molecular Weight of the AGU (Non-propionylated), Measured and Calculated Molecular Weight Averages, and the Degree of Polymerisation (DP) for the Cellulose (Derivatives)
The M of the AGU of a cellulose derivative depends on both the DS of the AGU and the M of the substituent. The MW averages of the polymer also depend on the DP. VC1 had a higher DS for this polymer than both BC and VC2. The M of the AGU was also the highest. Nevertheless, the polymer had the lowest MW averages because of the much lower DP (cf. Table 4), which indicated a considerable degradation. VC2 showed much less degradation. The data indicated more severe degradation during the synthesis of VC1 than VC2. Also, the data indicated almost the same degradation for VC2 as for BC produced with the same amount of reagent and NaOH. The apparent degradation supported the hypothesis that the competition with alkaline hydrolysis of the cellulose polymer (which is known to happen at these temperatures (Reyes et al. 2016)) was responsible for the impression of a reversed order of reactivity towards cellulose: if hydroxide ions were consumed in the substitution reaction, fewer hydroxide ions could depolymerise the cellulose. The less reactive V-Cl consume less OH–– ions, and the opposite would be true; a low polymer DP would follow. However, also more V-Cl would remain and the reaction could continue for a long time, thus explaining the DSNMR. Consequently, the reactivity toward Na-cellulose is in the same range for veratryl bromide and benzyl chloride and lower for veratryl chloride. However, the study was brief, and these explanations are not backed by statistics. More experiments are necessary for confirmation.
CONCLUSIONS
- Veratryl cellulose was found to have excellent solubility and noticeable softening with increased temperature.
- In these experiments, both veratryl chloride and bromide reacted with cellulose and formed cellulose derivatives with slightly higher DS (1.4 to 1.6) than benzyl chloride (1.2) at 1:3 stoichiometric ratio.
- Veratryl cellulose could be produced as a proof of concept. However, the reactivity of the chemicals could only be understood with both the DS values and the MW averages in mind. The apparent reactivity of the veratryl bromide was in the same range as benzyl chloride, while the reactivity of veratryl chloride was much lower.
ACKNOWLEDGMENTS
The Kempe Foundations (Sweden) and Bio4Energy, a Strategic Research Environment appointed by the Swedish government, are both acknowledged for supporting this work.
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Article submitted: September 26, 2022; Peer review completed: October 22, 2022; Revised version received and accepted: October 27, 2022; Published: November 4, 2022.
DOI: 10.15376/biores.18.1.161-174