Acylation Of Cellulose Research Articles

Rapid Homogeneous Acylation of Cellulose in a CO2 Switchable Solvent by Microwave Heating

The acylation modification of cellulose to make it processable is an important method to utilize this green, renewable material with broad prospects. However, it usually takes several hours or even more than 20 h to obtain products with a high degree of substitution (DS) through the methods reported in the existing literature, especially for cellulose acetate (CA). In this study, rapid homogeneous acylation of cellulose is achieved in a novel CO2 switchable solvent system by using microwave heating. CA products with DS ranging from 1.83 to 2.91 can be obtained within 3–15 min by using acetic anhydride as the acylation reagent. This strategy can also be applied for the synthesis of a series of cellulose esters with different side chain lengths, and it takes only 10 min to produce cellulose esters with a DS higher than 2.20 under microwave heating. This study suggests a facile and effective method for the synthesis of cellulose esters.

Super-rapid and highly-efficient esterification of cellulose to achieve an accurate chromatographic analysis of its molecular weight

Herein, a striking anion-tunnel transfer effect was demonstrated in 1-butyl-3-methylimidazolium benzoate (BmimPhCOO) ionic liquid, so a rapid, mild and efficient benzoylation of cellulose is accomplished under catalyst-free condition in BmimPhCOO. In a wide temperature range of 20–80 °C, the equilibrium of reaction is reached within only 15 min, which is much faster than the reported acylation of cellulose. Furthermore, the resultant cellulose tribenzoates have excellent solubility in conventional organic solvents, thus they can be used to accurately reflect the molecular weight and dispersity index of cellulose raw materials by gel permeation chromatography. This method is suitable for various cellulose. Therefore, we found a new principle to realize the extremely-rapid acylation of cellulose, and proposed an effective approach to accurately determine the molecular weight parameters of cellulose.

Binary mixtures of ionic liquids-DMSO as solvents for the dissolution and derivatization of cellulose: Effects of alkyl and alkoxy side chains

The efficiency of mixtures of ionic liquids (ILs) and molecular solvents in cellulose dissolution and derivatization depends on the structures of both components. We investigated the ILs 1-(1-butyl)-3-methylimidazolium acetate (C4MeImAc) and 1-(2-methoxyethyl)-3-methylimidazolium acetate (C3OMeImAc) and their solutions in dimethyl sulfoxide, DMSO, to assess the effect of presence of an ether linkage in the IL side-chain. Surprisingly, C4MeImAc-DMSO was more efficient than C3OMeImAc-DMSO for the dissolution and acylation of cellulose. We investigated both solvents using rheology, NMR spectroscopy, and solvatochromism. Mixtures of C3OMeImAc-DMSO are more viscous, less basic, and form weaker hydrogen bonds with cellobiose than C4MeImAc-DMSO. We attribute the lower efficiency of C3OMeImAc to “deactivation” of the ether oxygen and C2H of the imidazolium ring due to intramolecular hydrogen bonding. Using the corresponding ILs with C2CH3 instead of C2H, namely, 1-butyl-2,3-dimethylimidazolium acetate (C4Me2ImAc) and 1-(2-methoxyethyl)-2,3-dimethylimidazolium acetate (C3OMe2ImAc) increased the concentration of dissolved cellulose; without noticeable effect on biopolymer reactivity.

Design of Acyl Donor for Environmentally Benign Acylation of Cellulose Using an Ionic Liquid

Esterification is the most important derivatization to utilise cellulose as a sustainable resource for the materials industry. Homogeneous esterification is generally the most convenient means to achieve this aim. We found that N-methyl-N-(2-methoxyethyl)pyrrolidinium acetate [P1ME][OAc] easily dissolved cellulose. To achieve the environmental benign acylation of cellulose, we attempted to design acyl donor molecules under strong base catalyst-free conditions. It was found that a [P1ME][OAc] solution of cellulose when mixed with 2,2,2-trifluoroethyl benzoates at 80°C afforded the corresponding cellulose benzoate with a perfect (3.0) degree of substitution (DS) value in almost quantitative yield. We also succeeded in preparing 4-[(4-hydroxyphenyl)diazenyl]benzoate or 4-[(4-methoxyphenyl)diazenyl]benzoate of the cellulose with a DS value of 2.38 or 2.67 by the same protocol, respectively; the DMSO solution prepared by the resulting compounds exhibited a photochromic property, although only a slight colour change from light yellow to colourless was obtained by UV irradiation.

Effect of the Molecular Structure of Acylating Agents on the Regioselectivity of Cellulosic Hydroxyl Groups in Ionic Liquid

Homogeneous functionalization of cellulose with chloroacetyl chloride (CAC), 2-bromoisobutyryl bromide (BrBiB), and 2-chloro-2-phenylacetyl chloride (CPAC) was performed in ionic liquid to evaluate the effect of the molecular structure of the reagents on the reactivity of the cellulosic hydroxyl groups. The results showed that the reaction was very selective for the less hindered C6-OH group, but the substitution of the secondary OH group still occurred, which indicated that the acylation of cellulose was only partly regioselective. The reaction extent and regioselectivity of the cellulosic hydroxyl groups partly depended on the molecular structure of the acylating agents. The reaction rate of the CAC was much faster than the relatively bulky BrBiB and CPAC, but the bulky acylating agents showed a higher C6-OH selectivity. Moreover, the BrBiB was less reactive than the CPAC, although they showed the same regioselectivity for the three hydroxyl groups. The acylation decreased the thermal stability of the cellulose, which decreased further as the bulk of the substituted groups increased.

Cellulose fatty acid esters as sustainable film materials – effect of side chain structure on barrier and mechanical properties

Bio-based films were prepared by acylation of cellulose with saturated, unsaturated and branched fatty acids. The products showed increased thermal stability, low water vapour transmission rates and enhanced tensile and elastic properties.

Cellulose levulinate: a protecting group for cellulose that can be selectively removed in the presence of other ester groups

Levulinate is an important hydroxyl protecting group in carbohydrate chemistry but has not previously been so employed in cellulose chemistry, perhaps because of challenges involved in synthesis of cellulose levulinates. Herein we describe homogeneous acylation of cellulose in N,N-dimethylacetamide/LiCl using differently activated levulinic acid derivatives, including in situ activation with dicyclohexylcarbodiimide, p-toluenesulfonyl chloride, 1,1′-carbonyldiimidazole, or trifluoroacetic anhydride, providing and comparing several methods to access cellulose levulinates. Degree of substitution (DS) has been determined by 1H NMR spectroscopy using perpropionylated cellulose levulinates, showing that DS values as high as 2.42 are attainable. Cellulose levulinate esters were deacylated selectively by hydrazine without detectable loss of other alkanoate ester groups (acetate or propionate), indicating strong promise for levulinate as a useful protecting group for the synthesis of regioselectively substituted cellulose and other polysaccharide derivatives.

Homogeneous Acylation and Regioselectivity of Cellulose with 2-Chloro-2-Phenylacetyl Chloride in Ionic Liquid

A cellulose acylate, cellulose-CPAC, was prepared homogeneously in the ionic liquid 1-butyl-3-methyl chloride imidazole ([Bmim]Cl) from cotton dissolving pulp. The pulp was first solubilized in the solvent system [Bmim]Cl/N,N-dimethyl formamide (DMF), and then reacted with 2-chloro-2-phenylacetyl chloride (CPAC) in the presence of an acid-binding agent. The effects of functional conditions including the molar ratio of CPAC/anhydroglucose unit (AGU), reaction time, reaction temperature, kind of acid-binding agent, and cellulose concentration on the degree of substitution (DS) were studied. The reactivities of the three hydroxyl groups in the homogeneous acylation of cellulose with CPAC were also investigated. The results showed that in homogeneous reaction medium, although all the C-6, C-3, and C-2 positions within the cellulose AGU could be substituted by CPAC, the reaction was quite selective for the C-6 OH. The successful synthesis of the cellulose-CPAC was confirmed by FT-IR, 1H NMR, 13C NMR, XRD, and STA. Furthermore, the acylation of cellulose with CPAC decreased the thermal stability of cellulose.

Preparation and flocculation behavior of cellulose‐g‐PMOTAC copolymer

ABSTRACTAs a contribution to the wider use of biodegradable materials, this article reports the synthesis and testing of cationic polyelectrolyte cellulose derivatives for use as flocculation chemicals. Cellulose macroinitiator is synthesized in DMAc/LiCl solvent system by direct acylation of cellulose with 2‐bromoisobutyryl bromide. Cellulose‐graft‐poly(N,N‐dimethyl aminoethyl methacrylate) (cellulose‐g‐PDMAEMA) copolymers are prepared by copper‐mediated radical polymerization in homogeneous medium. Formation of the macroinitiator and graft copolymers is confirmed by ATR‐FTIR and 1H NMR. Quaternization of the graft chains to poly(methacryloxyethyl trimethylammonium chloride) (PMOTAC) produces cellulose‐g‐PMOTAC, which performs similarly to a commercial product in flocculation of pulp and kaolin. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40448.

Acylation of cellulose in reversible ionic liquids

1,8-Diazabicyclo[5.4.0]undec-7-ene, in conjunction with methanol after CO2 capture in DMSO created a new solvent capable of dissolving up to 8 wt% of cellulose, which could be applied as a highly efficient reaction media for the synthesis of cellulose esters under mild conditions.

Acylation of cellulose in a novel solvent system: Solution of dibenzyldimethylammonium fluoride in DMSO

A novel electrolyte, dibenzyldimethylammonium fluoride has been obtained essentially anhydrous (BMAF-0.1H2O) by a simple route. Its thermal stability, relative to tetra(1-butyl)ammonium fluoride trihydrate (TBAF3H2O) has been demonstrated by thermogravimetric analysis. DMSO solution of (BMAF-0.1H2O) dissolves microcrystalline- and fibrous celluloses; the dissolved biopolymers have been acylated by ethanoic-, butanoic-, and hexanoic anhydride. The degrees of substitution of the esters are higher than with TBAF3H2O/DMSO. The reasons are discussed in terms of differences in electrolyte structure and contents of water of hydration, whose presence leads to side reactions and decreases of the basicity of (F−). This conclusion is corroborated by molecular dynamics simulations of the interactions of glucose dodecamer/R4NF-hydrate/DMSO. These show that the interactions oligomer-F−-water is operative only for TBAF3H2O/DMSO. The efficiency of BMAF-0.1H2O/DMSO is explained based on better accessibility of the biopolymer due to efficient hydrogen-bonding between its hydroxyl groups and the essentially desolvated (F−).

Successful Application of an Ionic Liquid Carrying the Fluoride Counter‐ion in Biomacromolecular Chemistry: Microwave‐Assisted Acylation of Cellulose in the Presence of 1‐Allyl‐3‐methylimidazolium Fluoride/DMSO Mixtures

The use of ionic liquids with fluoride anion (IL-F) is challenging because of side reactions. Neat 1-allyl-3-methylimidazolium fluoride (AlMeImF) is used as a solvent in microwave-assisted acylation of cellulose. The results are disappointing due to side reactions in the IL proper, and F(-) -mediated hydrolysis of the produced ester. A dramatic improvement is observed, when AlMeImF/DMSO mixture is employed. The results are comparable to those obtained when pure 1-allyl-3-methylimidazolium chloride is employed. FTIR spectroscopy shows that dissolving a carboxylic acid anhydride in IL-F leads to the formation of acyl fluoride. Thus ILs are far from being "spectator" solvents. The new approach (use of IL-F/DMSO) is attractive because of its efficiency, low cost, and applicability to the derivatization of any polymer.

Kinetics and mechanism of imidazole-catalyzed acylation of cellulose in LiCl/N,N-dimethylacetamide

Cellulose acylation by anhydrides (ethanoic to hexanoic) plus tosyl chloride, TsCl, or imidazole in LiCl/N,N-dimethylacetamide solution has been studied. Contrary to a previous claim, TsCl does not catalyze acylation. For the diazole-catalyzed reaction, N-acylimidazole is the acylating agent. Third order rate constants (k3; 40–70°C) have been calculated from conductivity data and split, by using information from model compounds, into contributions from the primary- (k3;Prim(OH)) and secondary- (k3;Sec(OH)) hydroxyl groups of cellulose. Values of k3,Prim(OH)/k3,Sec(OH) are >1, and increase linearly as a function of increasing the number of carbon atoms of the acyl group. Rate constants and the degree of biopolymer substitution decrease on going from ethanoic- to butanoic-, then increase for pentanoic- and hexanoic anhydride, due to enthalpy/entropy compensation. Relative to the uncatalyzed reaction, the diazole-mediated one is associated with smaller enthalpy- and larger entropy of activation, due to difference of the acylating agent.

Reactive dissolution of cellulose and pulp through acylation in pyridine

The direct acylation of cellulose and different pulps with various acid chlorides was systematically screened. The syntheses were started in a heterogeneous solid–liquid reaction medium in hot pyridine with aliphatic and aromatic acid chlorides. After a few hours, depending on the reagent used, a homogenous solution was obtained. The obtained cellulose esters usually show a high degree of substitution (DS) and polymerization and are soluble in organic solvents. Esterification of softwood dissolving pulp, hardwood kraft pulp and hardwood kraft pulp-hemicellulose poor were also studied. The results show that almost identical DS were obtained for pulp derivatives compared to esters of microcrystalline cellulose. Thermogravimetric analysis and differential scanning calorimetry of the synthesized materials showed an improved thermal stability and various discrete thermal transitions compared to the original cellulose. The scanning electron microscopy images of derivatives showed a relatively flat and smooth surface with an absence of fibrous structure. The reactive dissolution of cellulose or pulp in pyridine is a straightforward and easy route to obtain long-chain aliphatic and aromatic cellulose esters.

Supercritical carbon dioxide biocatalysis as a novel and green methodology for the enzymatic acylation of fibrous cellulose in one step

Aliphatic esters of cellulose have recently raised the interest on the field of biopolymers. The objective of this work is to develop a methodology for the enzymatic acylation of cellulose with long chain fatty groups in one step. Therefore we designed a system at which fibrous cellulose was enzymatically acylated with vinyl laurate in supercritical carbon dioxide (scCO2) and as a result cellulose laurate was formed. The biocatalysts used for this reaction were immobilized lipase Candida antarctica, immobilized esterase from hog liver and the immobilized cutinase Fusarium solani. The ester content of the product varied on the specificity of the biocatalyst used, reaching a maximum of 4.1% after 9h of reaction. In our knowledge, it is the first time where fibrous cellulose is enzymatically acylated by a long chain aliphatic group in one step, without the necessity of any pretreatment.

Synthesis of cellulose-graft-poly(methyl methacrylate) via homogeneous ATRP

Cellulose-graft-poly(methylmethacrylate) (cellulose-g-PMMA) copolymers were prepared by homogeneous atom transfer radical polymerization (ATRP) under mild conditions, in an attempt to develop an efficient way to modify the surface of cellulose. A cellulose macro-initiator was successfully synthesized by direct homogeneous acylation of cellulose with 2-bromopropionyl bromide in a room temperature ionic liquid (RTIL), 1-allyl-3-methylimidazolium chloride ([AMIM]Cl). Copolymers were obtained via ATRP of methyl methacrylate (MMA) with CuBr/penta-methyldiethylenetriamine (PMDETA) as catalyst and N,N-dimethyl-formamide (DMF) as solvent without homopolymer byproduct. The grafting copolymers were characterized by 1H-NMR, 13C-NMR, and FTIR. The grafted PMMA chain was obtained by the hydrolysis of the cellulose backbone and analyzed by GPC and TGA measurements. In addition, the assemblies or aggregates formed by cellulose-g-PMMA copolymers were studied by means of TEM and AFM. The results indicated that the graft polymerization occurred from the cellulose backbone and the obtained copolymers had grafted polymer chains with well-controlled molecular weight and polydispersity; the cellulose graft copolymer in solution could aggregate and self-assemble into sphere-like structures.

Tailoring of water‐soluble cellulose‐g‐ copolymers in homogeneous medium using single‐electron‐transfer living radical polymerization

AbstractCellulose‐graft‐polyacrylamide and cellulose‐graft‐poly(N,N‐dimethylacrylamide) copolymers were prepared by single‐electron‐transfer living radical polymerization (SET‐LRP) in homogeneous medium. Cellulose macroinitiators for SET‐LRP, with different numbers of initiating sites along the cellulose backbone, were successfully synthesized by direct acylation of cellulose with 2‐bromoisobutyryl bromide in LiCl/dimethylacetamide. Dynamic light scattering revealed that cellulose macroinitiator molecules in dimethylsulfoxide (DMSO) exist primarily as individual chains with a certain amount of intermolecular aggregates. SET‐LRP of acrylamide and N,N‐dimethylacrylamide with the cellulose macroinitiators was carried out in DMSO solution. Formation of cellulose‐graft‐copolymers was confirmed using attenuated total reflectance Fourier transform infrared, 1H NMR and 13C NMR spectroscopy, and the products were water‐soluble. High content of poly(N,N‐dimethylacrylamide) in the copolymers enhanced the thermal stability relative to that of cellulose. Scanning electron microscopy studies of cellulose‐based particles formed from the copolymers using the aerosol flow reactor method revealed spherical nanoscale structures. Copyright © 2011 Society of Chemical Industry

Preparation and Properties of Internally Plasticized Bio-Based Film

This paper demonstrated acylation of cellulose with long chain fatty acid and internally plasticized cellulose films obtained by casting. The degrees of substitution (DS) and molar yields of fatty acid, Ts-Cl amounts and reaction time, and as well as the property of final products were studied. Partially derivative celluloses presented glass transition compared to starting cellulose. However, thermal behaviors of the internally plasticized esters with different DS were similar. Dynamic mechanical thermal analysis (DMTA) in tension mode revealed separate relaxations, denoted α and β, corresponding to the glass transition and side-chain melting processes, respectively. According to this, these longer chain esters (LCCEs) showed promise as internally plasticized cellulose films because the supermolecular structure of cellulose was significantly changed with the introduction of longer substituent.

Studies on regioselective acylation of cellulose with bulky acid chlorides

The regioselective esterification of cellulose by reaction with bulky acyl halides including pivaloyl chloride, adamantoyl chloride and 2,4,6-trimethylbenzoyl chloride was studied. Functionalization conditions to achieve a given degree of substitution (DS) and the resulting ester substitution pattern were described in detail. One- and two-dimensional NMR spectroscopy techniques were used to confirm the structure of the esters obtained. We compared the effects on substitution of using different esterifying reagents and solvent systems including DMAc/LiCl, DMSO/TBAF, and ionic liquids (ILs).

Direct enzymatic acylation of cellulose pretreated in BMIMCl ionic liquid

Cellulose esters are an important class of functional biopolymers with great interest in the chemical industry. In this work the enzymatic acylation of Avicel cellulose with vinyl propionate, vinyl laurate and vinyl stearate, has been performed successfully in a solvent free reaction system. At first cellulose was putted into the ionic liquid BMIMCl (1-n-butyl-3-methylimidazolium chloride) in order to facilitate the unwrap of the structure of the polysaccharide molecule and make it accessible to the enzyme. Thus, after this pretreatment the enzymatic esterification reaction was performed using various hydrolases. The enzymes capable of catalyzing the acylation of cellulose were found to be the immobilized esterase from hog liver and the immobilized cutinase from Fusarium solani, while the lipases used did not show any catalytic activity. Cellulose esters of propionate, laurate and stearate were synthesized with a degree of esterification of 1.9%, 1.3% and 1.0%, respectively. It is the first successful direct enzymatic acylation of cellulose with long chain fatty acids.