Preparation of Cellouronic Acids and Partially Acetylated Cellouronic

Sierakowski, M. R.; Milas, M.; Desbrières, J.; Rinaudo, M. Carbohydr. .... Da Silva Perez, D.; Montanari, S.; Vignon, M. R. Biomacromolecules 2003, 4...
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Biomacromolecules 2004, 5, 565-571

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Preparation of Cellouronic Acids and Partially Acetylated Cellouronic Acids by TEMPO/NaClO Oxidation of Water-Soluble Cellulose Acetate Silvia Gomez-Bujedo,† Etienne Fleury,‡ and Michel R. Vignon*,† Centre de Recherches sur les Macromole´ cules Ve´ ge´ tales, C.N.R.S., and Universite´ Joseph Fourier, BP 53, 38041 Grenoble Cedex 9, France, and Rhodia, Centre de Recherches de Lyon, 85 Avenue des Fre` res Perret, BP 62, 69192 Saint-Fons Cedex, France Received October 14, 2003; Revised Manuscript Received November 25, 2003

Water-soluble cellulose acetates with a degree of substitution (DS) of 0.5, prepared by partial deacetylation of cellulose acetate of DS ) 2.5, were oxidized with catalytic amount of 2,2,6,6,-tetramethyl-1-piperidinyloxy radical (TEMPO), sodium hypochlorite, and sodium bromide to provide useful cellouronic acids. The oxidation was conducted at a constant pH of 10 and at 2 °C to avoid the occurrence of side products. Whereas only the primary hydroxyl groups of cellulose acetate were oxidized, a variable degree of oxidation (DO) resulted in a range of 0.33 to 1.0, depending on the concentration in sodium hypochlorite. Thus, polyglucuronic acid as well as partially acetylated cellouronic acid, having a range of DO were obtained. Introduction Water-soluble cellulose derivatives are important products that find a large number of applications in various formulations. Besides their main characteristic, which is to provide specific rheological properties, these products are also important as film forming, water-binding, lubricating, thickening, and gelling agents. They find their end uses in many fields, ranging from those of agriculture, food, comestics, coating, oil industry, paper, textile, pharmaceutical, etc. Most water soluble cellulose derivatives correspond to cellulose ethers, among which sodium carboxymethyl cellulose, hydroxyethyl cellulose, and hydroxypropylmethyl cellulose are produced in the highest volume.1 Besides these products and other cellulose ethers, some water soluble cellulose esters produced in smaller quantity, e.g., cellulose sulfate, phosphate, etc. are also commercially available for high added value applications in the field of medical, membrane chromatography, etc.2 Despite these few niches, most commercial cellulose esters such as cellulose acetate are water insoluble3 and cannot therefore apply for or supplant the water soluble cellulose derivative market. Water soluble cellulose acetate, i.e., cellulose acetate having a degree of substitution (DS) from 0.5 to 1, has been described and prepared at laboratory scale.4,5 This product is potentially important as its water solubility coupled with hydrophobic groups enable it to be used in a number of aqueous processes. In this context, one can quote a recent application where polyamide or cotton fibers could be modified by the use of water soluble cellulose acetate in the alkaline conditions of a washing machine. In that case, the * To whom correspondence should be addressed. Telephone: 33-476 037614.Fax: 33-476547203.E-mailaddress: [email protected]. † C.E.R.M.A.V.-C.N.R.S. ‡ Rodia, Centre de Recherches de Lyon.

acetate moieties were released during the washing cycle to yield a fine precipitate of cellulose at the surface of the fibers.6 Many other applications can be envisaged for water soluble cellulose acetate. In particular, its partial hydrophobic character, coupled with enhanced hydrophilic properties, could be of a great benefit to obtain new versatile products. A selective oxidation would be one way to achieve this goal. Oxidation has been reported in a number of paper and patents, which describe the use of various oxidizing agents to produce oxidized polysaccharides with various degrees of oxidation (DO), degree of polymerization (DP), and different sites of oxidation. Preferential oxidation of primary hydroxyl groups with nitrogen oxides, yielding polyuronic acids with preserved ring structures were reported by Yackel and Kenyon7 and Maurer and Reiff.8 The selectivity of this reaction was further improved, in particular by Painter,9,10 by dissolving the substrates in concentrated phosphoric acid and oxidizing them with sodium nitrite. Despite this progress, a substantial degradation of the oxidized products could not be avoided. A new method was developed by Davis and Flitsch,11 to oxidize primary hydroxyl groups into carboxyl groups by using a mixture of sodium hypochlorite, sodium bromide, and 2,2,6,6-tetramethyl-1-piperidinyloxy radical (TEMPO). In polyols, it appeared that this method was very selective, primary hydroxyl groups being exclusively oxidized, whereas secondary hydroxyl groups remained unaffected. Following the Davis and Flitsch paper, the TEMPO-NaBr-NaClO system was applied to a wealth of products including many polysaccharides. De Nooy et al.12-14 used this reaction to selectively oxidize the primary hydroxyl groups of watersoluble polysaccharides, namely inulin, amylodextrin, starch, amylodextrin, and pullulan. Heinz and Vieira prepared new ionic polymers by oxidation of cellulose derivatives.15 Rinaudo et al. studied the TEMPO oxidation of galactoman-

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Figure 1. Scheme of reaction.

nans16 and hyaluronan.17 Chang and Robyt18 described the oxidation of 10 polysaccharides including R-cellulose. Isogai and Kato19 and Tahiri and Vignon20 described the oxidation of several native, mercerized, and regenerated celluloses with the TEMPO system, starting from heterogeneous oxidation conditions to obtain water soluble or insoluble polyglucuronic acids. Recently, Vignon et al.21 showed that the conversion of cellulose I into the IIII allomorph increased substantially the reactivity of cellulose toward the TEMPO-mediated oxidation reaction. Despite these progresses, the initial insolubility of cellulose in the water-based oxidation medium was always a disadvantage for the homogeneity of the oxidized product. The present study overcomes the problem of partial oxidation of crystalline cellulose by TEMPO-mediated oxidation. Following a recent report,22 we have applied the TEMPO-mediated oxidation technique to water soluble cellulose acetate of a low degree of substitution (DS ∼ 0.5). Using this derivative as a starting material and varying the reaction parameters, we report here the production of a series of products (Figure 1), ranging from partially acetylated and oxidized cellulose (1) to pure polyglucuronic acids (2). Experimental Section Materials. All reagents were of analytical grade and used as received. Partially acetylated cellulose (DS ) 2.5) was obtained from Fluka. A NaClO fresh solution from Fluka containing ∼13% active chlorine was used. It had a pH of ∼13, which was lowered to 10 by addition of 4M HCl under the monitoring of a pH meter. Preparation of Water-Soluble Cellulose Acetate Samples (DS ) 0.5). Cellulose acetate (200 g) with an acetyl content of 40 wt % (DS ) 2.5) was dissolved in a mixture of 26 mL of methanol and 74 mL of acetic acid at room temperature for 16 h. Then, 0.25 mol of sulfuric acid was added, and the medium was heated to 72 °C. The mixture was kept at this temperature for 200 min, during which deacetylation and concomitant depolymerization resulted. After cooling, 0.5 mol of sodium acetate were added in order to neutralize the acid, and the solution was poured in methyl acetate. Depolymerized cellulose mono-acetate (DS ) 0.5) was recovered after filtration, washed with methyl acetate in order to remove any byproduct, and dried at 45 °C. The

sample prepared under this protocol contained 20 wt % of Na2SO4, which could be desalted by dialysis or ultrafiltration. Preparation of Partially Acetylated and Oxidized Cellulose Samples (1). Cellulose acetate (DS ) 0.5; 560 mg, 2.44 eq of anhydroglucose, 20 wt % Na2SO4) was dissolved at room temperature in distilled water (50 mL). The solution was cooled to 0-4 °C with an ice bath, and this temperature was maintained throughout the experiments. The pH was brought to 10 by addition of 0.5 M aq NaOH. TEMPO (4.85 mg, 0.031 mmol) and NaBr (107.6 mg, 1.605 mmol) were added. Specific quantities of a 1.668 M NaClO solution adjusted to pH 10 were added dropwise, while the pH of the reacting solution was monitored to 10 by dropwise addition of 0.5 M aq NaOH. The quantities of NaClO were of 1.1, 1.7, 2.3, and 2.9 mL repectively in runs A-D. The oxidation progress was monitored by the consumption of NaOH, which represents the formation of uronic acids. After 1 h, the reaction was quenched by adding 3 mL of MeOH. The reaction mixture was neutralized with 1 M aq HCl and concentrated (1/3 volume), and then it was precipitated with 2-propanol (10 volumes), followed by centrifugationwashing. The precipitate was concentrated in a vacuum to eliminate the 2-propanol, dialyzed, and freeze-dried to obtain the partially oxidized and acetylated cellulose sample. Oxidation of All of the Primary Alcohols: Preparation of Polyglucuronic Acids (2). This preparation involved a preliminary partial deacetylation of the water soluble cellulose acetate before applying the oxidation treatment, which was achieved under an excess of NaClO. Cellulose acetate (DS)0.5) (2.44 eq of anhydroglucose, 446 mg if desalted or 560 mg if not) was dissolved at room temperature in distilled water (50 mL). The pH was brought to 11 by dropwise addition of 0.5 M aqueous NaOH and the solution kept at room temperature during approximately 90 min during which substantial deacetylation occurred. A NMR control of an aliquot of this solution indicated a cellulose acetate sample with a DS ) 0.3. The solution was cooled to 0-4 °C in an ice bath and the pH was brought to 10 by addition of 1 M aq HCl. TEMPO (4.85 mg, 0.031 mmol) and NaBr (107.6 mg, 1.605 mmol) were added. Variable quantities of a 1.668 M NaClO solution, previously adjusted to pH 10 were added dropwise adjusting the pH at 10 by simultaneous addition of 0.5 M aq NaOH (4 mL). Throughout the experiment, the solution was stirred at 0-4 °C and

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the pH was kept at 10 by dropwise addition of 0.5 M aq NaOH. The oxidation was monitored by the consumption of NaOH, which represents the formation of uronic acids. The reaction was quenched after 3 h by adding 3 mL of MeOH and neutralized with 1 M aq HCl. A small amount of NaBH4 was added, and the solution was stirred for 16 h. The reaction mixture was neutralized with 1 M aq HCl and concentrated (1/3 volume), and then it was precipitated with 2-propanol (10 volumes), followed by centrifugationwashing. The precipitate was concentrated under reduced pressure to eliminate the 2-propanol, dissolved in water, dialyzed, and freeze-dried to obtain 388 mg (80%) of pure polyglucuronic acid (2). NMR Spectroscopy. 13C NMR experiments were recorded with a BRUKER AC 300 spectrometer operated at frequency of 75.468 MHz. Samples were studied as solutions in D2O (30 mg in 0.5 mL of solvent) at 333 K and pH 7 in 5 mm o.d. tubes (internal acetone standard 13C (CH3): 31.5 ppm relative to Me4Si). The degrees of oxidation were determined by 13C spectra acquired under quantitative conditions, using both the integration of peak areas and excision of the chart paper followed by weighing. The absence of any residual CH2OH at 60.3 ppm or CH2OAc at 63.5 ppm showed that the degree of oxidation was 100%. Quantitative 13C spectra were recorded using the INVGATE Bruker sequence, with 90° pulse length (6.5µs), 15 000 Hz spectral width, 16K data points, 0.54 s acq. time, a relaxation delay of 2 s, and 60 000 scans were accumulated. Under these conditions, it appeared that the quaternary carbons were not entirely relaxed with a delay of 2 s. This observation accounted for the insufficient area of the peak of COONa carbons. IR Analysis. Dried samples (1 mg) were dispersed in 100 mg of KBr and pressed. The IR spectra were recorded with a Perkin-Elmer FT-IR 1720X instrument. Gel Permeation Chromatography (GPC). The molecular weights were determined by GPC. The samples were dissolved in distilled water at a concentration of 1 g/L. A Waters apparatus was used with two columns (Shodex OHpack B-804 and Shodex OHpack B-805) in series, eluted at 1 mL/min flow rate with 0.1 M aqueous NaCl and NaN3 (2/10 000, w/w) solution and at 25 °C. The column effluent was monitored using a refractive index detector (RI Waters 410). The apparatus was equipped with a multiangle laser light scattering detection system from Wyatt Technology, USA, which permitted the determination of the absolute molecular weights of the samples. Results and Discussion Preparation of Water-Soluble Cellulose Acetate Samples (DS ) 0.5). In the cellulose acetate series, the solubility in a given solvent depends on its degree of substitution (DS). Cellulose triacetate (DS ) 3) is soluble in chloroform, whereas “cellulose diacetate” (DS ) 2.5) is soluble in acetone. On the other hand, it was shown by Crane23 and Malm et al.24 that water-soluble cellulose acetate could be obtained at a DS comprised between 1 and 0.5, where neither chloroform nor acetone act as solvents. Cellulose partially

Table 1. Preparation of Partially Acetylated and Oxidized Cellulose Samples by the TEMPO-NaBr-NaClO System with Different Amounts of NaClO at 0-4 °C run

eq. NaClOa

% COONab

% CH2OH

% CH2OAc

A B C D

0.6 0.95 1.3 1.6

33 47 65 68

36 25 8 0

31 28 27 32

a Mol NaClO/mol glucosyl unit. b The DO at C6 is 0.33, 0.47, 0.65, and 0.68 for runs A, B, C, and D, respectively.

acetylated can be prepared either by direct acetylation of cellulose from solution25 or by deacetylation from industrial cellulose di- or triacetate. Different procedures were described for deacetylation. First, Malm et al.24 have described the preparation of water-soluble cellulose acetate by the hydrolysis of cellulose triacetate (CTA) in the presence of an aqueous mineral acid such as sulfuric, chlorhydric, or perchloric acids. More recently, other deacetylation methods have relied on the use of Lewis acids, namely ZnI226 or BuSnO, Zn(OAc)2, Mg(OAc)2 and MoO3,27 or that of strong mineral acid in the presence of acyl anhydride, combined with trifluoroacetic acid.28 Deacetylation by hydrolysis in alkaline medium has also been described. Since this method does not induce any depolymerization, it has been used extensively in the past for the molecular weight determination by intrinsic viscosity measurement.29 Recently, Philipp et al.30 have described the deacetylation in complex medium consisting of a mixture of amine, dimethyl sulfoxide, and water. In this case, water solubility was obtained only for products with DS between 0.8 and 1.0. In this work, which requires the use of water-soluble cellulose acetate, we have partially deacetylated a commercial “cellulose diacetate” sample with a DS of 2.5. This product was dissolved in a methanol/acetic acid mixture, and the deacetylation procedure was carried out under the catalytic sulfuric acid conditions of Malm et al.24 Under these conditions, deacetylation occurred, but simultaneous depolymerization was observed, due to the hydrolysis of glycosidic linkages in the catalytic acid media. The resulting cellulose acetate sample was water soluble and had a DS of 0.5 and a molecular weight Mw ∼ 7300 measured by gel permeation chromatography (GPC). Synthesis of Partially Acetylated and Oxidized Cellulose Samples (1). To obtain partially acetylated cellulosic compounds with different degrees of oxidation in the primary position (1), the oxidation has to be performed at low temperature to avoid the formation of side products. The influence of the relative amount of the oxidizing agent NaClO on the DO was evaluated. Four different runs, corresponding to increasing amounts of NaClO in the range of 0.6-1.6 mol NaClO/ mol glucosyl unit were performed, and the characteristics of the resulting products were analyzed (Table 1), by recording quantitative 13C NMR spectra (Figure 2). Despite the fact that the four samples were oxidized to different levels, each of them was nevertheless water-soluble. Thus, these products were different from the partially soluble products resulting from the heterogeneous oxidation conditions of native cellulose, which always showed some waterinsolubility.20,21

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Figure 2. 13C NMR spectra in D2O at 333 K of the starting material and partially oxidized and acetylated cellulose samples. DO depends on the mol NaClO/ mol glucosyl unit: (A) 0.6; (B) 0.95; (C) 1.3; (D) 1.6, mol NaClO/ mol glucosyl unit, respectively. Table 2. 13C Chemical Shift Dataa of Partially Acetylated and Oxidized Cellulose (Sodium Salts of the Uronic Acids) glucosyl unitb

C1

C2

C3

C4

C5

C6

COO Na 103.0 73.5 75.0 81.6 76.1 175.3 CH2OAc 103.0 73.5 75.0 79.6 76.1 63.5 CH2OH 103.0 73.5 75.0 79.3 76.1 60.6

CH3CO CH3CO 20.9

174.6

a In ppm relative to the signal of internal acetone in deuterium oxide at 31.5 ppm relative to Me4 Si. b With position C6 oxidized (COO Na), acetylated (CH2OAc), or free (CH2OH).

The 13C spectrum of the starting partially acetylated sample (DS ) 0.5) is characterized by (i) a signal at 103.0 ppm (C1); (ii) two signals at 79.7 and 79.3 ppm corresponding respectively to C4 with CH2OAc or CH2OH at position C6; (iii) two signals at 63.5 and 60.6 ppm, corresponding respectively to C6 of CH2OAc and CH2OH. The quantitative 13C NMR spectra of products resulting from the four oxidation experiments are reported in Figure 2. In these, the amount of C6 oxidized or acetylated units together with that of remaining free CH2OH could be deduced from the analysis of the chemical shifts of the products (Table 2) and the relative intensities of the characteristic signals. In Figure 2, the signal at 60.6 ppm, corresponding to free CH2OH, decreased continuously with the increase of NaClO, to be completely absent in the spectrum 2D. Conversely, a signal at 175.3 ppm corresponding to the COONa group increased accordingly, and there was a downfield shift of

the C4 signal by about 2 ppm. As for the signal at 63.5 ppm, indicating the presence of CH2OAc, it remained unaffected in each experiment. From these observations, we can conclude that whenever free hydroxymethyl groups were present in the starting products they could be oxidized. On the other hand, when the hydroxymethyl groups were acetylated in the starting product, they could not be oxidized, at least in the temperature range of 0-4 °C and the relatively low concentrations in NaClO, which were used in this section. Thus, under these conditions, both the initial and oxidized product kept the same degree of acetylation. An alternate explanation to these observations could be that some acetate had migrated from C2 or C3 to C6. As shown in Figure 3, the oxidation of a hydroxymethyl group to a carboxyl via an aldehyde requires two moles of NaClO per mole of hydroxyl, in good relation with the data reported in Table 1. Indeed in the four runs, the amount of carboxylate was close to one-half of the amount of the oxidizing agent. Thus, the degree of oxidation (DO) of the product could be monitored by the addition of controlled quantities of NaClO, as shown in Table 1 (DO ) 0.330.68). As the starting material had an initial DS of 0.3 in acetyl content at C6, i.e., 70% primary hydroxyl group were free, a good correlation could be noticed between the relative ratio of CH2OH and COONa. The samples were further characterized by infrared spectroscopy. Their FTIR spectra (Figure 4) showed the

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Figure 3. Simplified oxidation scheme.

Figure 4. IR spectra (a) partially acetylated polyglucuronic acid under sodium salt (1); (b) polyglucuronic acid under sodium salt (2).

characteristic absorptions of the hydroxyl groups at ∼3380 cm-1. Typical bands were found at 1730 cm-1 (νCO) for the acetate moiety and at 1640 cm-1 (νCO) for the sodium carboxylate group (Figure 4a). As these two carbonyl bands were overlapping, they did not allow us to do any quantitative analysis. The molecular weights of the four oxidized samples were measured by GPC and varied between 3500 and 4500. Synthesis of Polyglucuronic Acids (2). Because the acetylated hydroxymethyl groups in the starting product could not be oxidized with the TEMPO mediated oxidation process following the protocol of the preceding section, the preparation of fully oxidized polyglucuronic acid samples (2) required a specific procedure designed for the C6 deacetylation of the cellulose acetate. Unfortunately, extensive deacetylation induces detrimental precipitation of the starting product. Thus, a compromise had to be found between deacetylation and water solubility. Our strategy was first to induce a partial C6 deacetylation and then to pursue with a protocol based on concomitant deacetylation and oxidation. As explained in the Experimental Section, a solution of water-soluble cellulose acetate (DS ) 0.5) was partially deacetylated until it started to be turbid agent. A NMR control of this solution indicated a cellulose acetate sample with a DS of ∼ 0.3 (among the acetyl groups, 66% were located at C6 position, i.e., DS ∼ 0.2 at this position). Because during the reaction the pH had a tendency to drop, due to the formation of carboxylic acid, the evolution of the reaction could be followed easily by measuring the amount of NaOH required to neutralize the carboxylic acids generated in C6 and thus maintaining the pH at 10. After

completion of the reaction (i.e., when the pH became stabilized), the reaction was quenched by addition of methanol. A small amount of NaBH4 could then be added to reduce the partially oxidized carbonyl groups that eventually could be present (Figure 3). However 13C NMR experiments never showed any resonance signal, corresponding either to aldehydic groups due to the partially oxidized C6 position or to the carbonyl carbons that could be formed at C2 or C3 during the oxidation. These results confirmed that under these oxidation conditions, due in particular to the fact that the reaction was conducted in water-medium, whenever the aldehyde groups were obtained, they became immediately oxidized into carboxyl moieties, and therefore, the addition of NaBH4 is not necessary. Among the numerous runs that we undertook, varying the amount of NaClO and the time of reaction, the best conditions to produce fully deacetylated and fully oxidized cellouronic acid sample were obtained when the sample was partially deacetylated for 90 min at room temperature and then oxidized with 3.2 mol of NaClO per mole of glucosyl residue for 3 h at 2 °C. Under these conditions, a reaction yield of about 85% was obtained, and the resulting polyglucuronic acid was not contaminated by degradation products. Its 13C NMR spectrum (Figure 5a) indicates that this product is fully oxidized as it displays only the 6 characteristic signals at 175.3, 103.0, 81.6, 76.1, 75.0, and 73.5 ppm. The absence of the C6 carbon resonance in the range 60-63 ppm and the presence of a carboxylic carbon near 175 ppm indicate that the primary hydroxyl groups were completely oxidized. According to the literature,20,31 a

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Figure 5. 13C NMR spectra in D2O at 333° K: (a) polyglucuronic acid (2); (b) degraded polyglucuronic acid of experiment carried out at room temperature.

spectrum such as the one shown in Figure 5a refers to the sodium salt of the β-(1f4)-polyglucuronic acid. The same results were obtained either on desalted samples or on those containing up to 20% sodium sulfate. However, in the last case, we observed a decrease in the rate of oxidation. Molecular weights of the polyglucuronic acids obtained were ∼4300 measured by GPC. The IR spectrum of the fully oxidized sample was recorded in their sodium glucuronate forms. The FTIR spectrum of polysaccharide (2) shown in Figure 4b presented the characteristic absorptions of the hydroxyl groups at ∼3380 cm-1. The typical peak for the carboxylic group is found at 1640 cm-1(νCO). To examine the different factors influencing the TEMPO mediated oxidation process, several oxidation experiments were studied using different conditions. When the reaction was performed by using directly commercial NaClO solution, the pH was maintained at 10 by adding dropwise the hypochlorite, without adding any NaOH solution, as the pH of the sodium hypochlorite commercial solution was ∼13. In this case, the oxidation reaction was faster than the deacetylation and the acetyl groups did not have enough time to be removed. The final product was not fully oxidized because 15% of the C6 hydroxymethyl groups were still acetylated. We also observed that reaction times, starting material concentrations, and temperature had an important influence in the oxidation reaction. Indeed when the oxidation was achieved at room temperature, or with longer reaction times, or higher starting material concentrations, more extensive degradation of the cellulose was found. For instance, when the reaction was performed at room temperature, a number of degradation products resulted. Their presence is denoted in the 13C spectrum of the corresponding product, which, in addition to the six glucuronic unit signals, showed also the presence of significant signals at 94.8, 92.5, 79.7, 72.2, 70.9, and 68.8 ppm distinguished by an asterisk in Figure 5b. Indeed, it was reported by de Nooy et al.14 that depolymerization of polyuronic acids occurred primarily by the β-elimination mechanism at room temperature in alkaline

solutions. Such a side reaction is likely responsible for the degradation products that are observed in Figure 5b. Isogai and Shibata32 suggested that the hydroxyl radicals formed from NaBrO and TEMPO at pH 10-11 were responsible for the depolymerization during the oxidation. Conclusion The TEMPO-mediated oxidation of water-soluble cellulose acetate having a DS between 0.5 and 0.3 induced a rapid selective oxidation of the hydroxymethyl groups of this cellulose derivative. All products were water soluble, but their chemical composition depended on (i) the amount of NaClO used in the reaction and (ii) the DS of the starting cellulose acetate. A small amount of oxidizing agent together with a high acetyl content in the starting product led to partially acetylated and oxidized cellulose, whereas an excess of NaClO together with low acetyl content led to pure polyglucuronic acid. Degradation products, resulting from β-elimination in the alkaline medium of the reaction, could be controlled by using reaction temperatures in the range of 2-4 °C and reaction times not exceeding 3 h. The synthesis of cellouronic acids or that of partially acetylated cellouronic acids described in this paper open the way to a number of cellulose-based polyelectrolytes having hydrophobic and hydrophilic characters. In addition, these products can serve as a base for a number of further chemical modifications, based either on ester or amide linkages. Acknowledgment. The authors acknowledge the ADEME (Agence de l′Environnement et de la Maitrise de l′Energie) for financial support (AGRICE: Agriculture for Chemicals and Energy; Grant No. 9 901 048). References and Notes (1) Majewicz, T. G.; Podlas, T. J. Kirk-Othmer Encyclopedia of Chemical Technology; Wiley-Interscience: New York, 1993; p 541. (2) Shelton, M. C. Kirk-Othmer Encyclopedia of Chemical Technology; Wiley-Interscience: New York, 2003, in press.

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TEMPO-Mediated Oxidation of Cellulose Acetate (3) Gedon, S.; Fengi, R. Kirk-Othmer Encyclopedia of Chemical Technology; Wiley-Interscience: New York, 1993; p 496. (4) Malm, C. J. Brit. Patent 356,012, October 22, 1929. (5) Bellas, M.; Buchanan, C. M.; Edgar, K. J.; Germoth, T. C.; Wilson, A. K. WO 91/16,359, October 31, 1991. (6) Chanzy, H.; Deroo, S.; Fleury, E.; Lacelon-Pin, C.; Rochat, S. WO 00/22,224, April 14, 2000. (7) Yackel, E. A.; Kenyon, W. O. J. Am. Chem. Soc. 1942, 64, 121. (8) Maurer, K.; Reiff, G. J. Makromol. Chem., 1943, 1, 27. (9) Painter, T. J. Carbohydr. Res., 1977, 55, 95. (10) Painter, T. J.; Cesaro, A.; Delben, F.; Paoletti, S. Carbohydr. Res. 1985, 140, 61. (11) Davis, N. J.; Flitsch, S. L. Tetrahedron Lett. 1993, 34, 1181. (12) de Nooy, A. E.; Besemer, A. C.; Bekkum, H. Recl. TraV. Chim. PaysBas. 1994, 113, 165. (13) de Nooy, A. E.; Besemer, A. C.; Bekkum, H. Carbohydr. Res. 1995, 269, 89. (14) de Nooy, A. E.; Besemer, A. C.; Bekkum, H.; van Dijk, J. A. P. P.; Smit., J. A. M. Macromolecules 1996, 29, 6541. (15) Heinze, T.; Vieira, M. Polym. News 2001, 26, 274. (16) Sierakowski, M. R.; Milas, M.; Desbrie`res, J.; Rinaudo, M. Carbohydr. Polym. 2000, 42, 51. (17) Jiang, B.; Drouet, E.; Milas, M.; Rinaudo, M. Carbohydr. Res. 2000, 327, 455.

(18) (19) (20) (21) (22) (23) (24) (25) (26) (27) (28) (29) (30) (31) (32)

Chang, P. S.; Robyt. J. F. J. Carbohydr. Chem. 1996, 15 (7), 819. Isogai, A.; Kato, Y. Cellulose 1998, 5, 153. Tahiri, C.; Vignon, M. R. Cellulose 2000, 7, 177. Da Silva Perez, D.; Montanari, S.; Vignon, M. R. Biomacromolecules 2003, 4 (5), 1417. Fleury, E.; Gomez, S.; Vignon, M. R. French Patent 2,831,171, April 25, 2003. Crane, C. L. U.S. Patent 2,327,770, August 24, 1943. Malm, C. J.; Barkey, K. T.; Salo, M.; May, D. C. J. Ind. Eng. Chem. 1957, 49, 79. Meyer, G.; Brandner, A.; Diamantoglou, M. U.S. Patent 4,543,409, September 24, 1985. Staud, C. J.; Murray, T. F., Jr. U.S. Patent 2,005,383, June 18, 1935. Edgar, K. J.; Wilson, A. K.; Bellas, M.; Germroth, T. C.; Buchanan, C. M. U.S. Patent 5,142,034, August 25, 1992. Buchanan, C. M.; Parker, S. W. WO 91/16,356, October 31, 1991. Cox, L. A.; Battista, O. A. J. Ind. Eng. Chem. 1952, 44, 893. Philipp, B.; Klemm, D.; Wagenknecht, W. Papier 1995, 49, 58. Heyraud, A.; Courtois, J.; Dantas, L.; Colin-Morel, Ph.; Courtois, B. Carbohydr. Res. 1993, 240, 71. Shibata, I.; Isogai, A. Cellulose 2003, 10, 151.

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