Preparation of Cellouronic Acids and Partially AcetylatedCellouronic Acids by TEMPO/NaClO Oxidation of Water-Soluble

Cellulose Acetate

Silvia Gomez-Bujedo,† Etienne Fleury,‡ and Michel R. Vignon*,†

Centre de Recherches sur les Macromolecules Vegetales, 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 Freres 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 deacetylationof cellulose acetate of DS) 2.5, were oxidized with catalytic amount of 2,2,6,6,-tetramethyl-1-piperidinyloxyradical (TEMPO), sodium hypochlorite, and sodium bromide to provide useful cellouronic acids. The oxidationwas conducted at a constant pH of 10 and at 2°C to avoid the occurrence of side products. Whereas onlythe primary hydroxyl groups of cellulose acetate were oxidized, a variable degree of oxidation (DO) resultedin a range of 0.33 to 1.0, depending on the concentration in sodium hypochlorite. Thus, polyglucuronic acidas well as partially acetylated cellouronic acid, having a range of DO were obtained.

Introduction

Water-soluble cellulose derivatives are important productsthat find a large number of applications in various formula-tions. Besides their main characteristic, which is to providespecific rheological properties, these products are alsoimportant as film forming, water-binding, lubricating, thick-ening, and gelling agents. They find their end uses in manyfields, ranging from those of agriculture, food, comestics,coating, oil industry, paper, textile, pharmaceutical, etc.

Most water soluble cellulose derivatives correspond tocellulose ethers, among which sodium carboxymethyl cel-lulose, hydroxyethyl cellulose, and hydroxypropylmethylcellulose are produced in the highest volume.1 Besides theseproducts and other cellulose ethers, some water solublecellulose esters produced in smaller quantity, e.g., cellulosesulfate, phosphate, etc. are also commercially available forhigh added value applications in the field of medical,membrane chromatography, etc.2 Despite these few niches,most commercial cellulose esters such as cellulose acetateare water insoluble3 and cannot therefore apply for orsupplant the water soluble cellulose derivative market.

Water soluble cellulose acetate, i.e., cellulose acetatehaving a degree of substitution (DS) from 0.5 to 1, has beendescribed and prepared at laboratory scale.4,5 This productis potentially important as its water solubility coupled withhydrophobic groups enable it to be used in a number ofaqueous processes. In this context, one can quote a recentapplication where polyamide or cotton fibers could bemodified by the use of water soluble cellulose acetate in thealkaline conditions of a washing machine. In that case, the

acetate moieties were released during the washing cycle toyield a fine precipitate of cellulose at the surface of thefibers.6 Many other applications can be envisaged for watersoluble cellulose acetate. In particular, its partial hydrophobiccharacter, 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 andpatents, which describe the use of various oxidizing agentsto produce oxidized polysaccharides with various degreesof oxidation (DO), degree of polymerization (DP), anddifferent sites of oxidation. Preferential oxidation of primaryhydroxyl groups with nitrogen oxides, yielding polyuronicacids with preserved ring structures were reported by Yackeland Kenyon7 and Maurer and Reiff.8 The selectivity of thisreaction was further improved, in particular by Painter,9,10

by dissolving the substrates in concentrated phosphoric acidand oxidizing them with sodium nitrite. Despite this progress,a substantial degradation of the oxidized products could notbe avoided.

A new method was developed by Davis and Flitsch,11 tooxidize primary hydroxyl groups into carboxyl groups byusing 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, whereassecondary hydroxyl groups remained unaffected. Followingthe Davis and Flitsch paper, the TEMPO-NaBr-NaClOsystem was applied to a wealth of products including manypolysaccharides. De Nooy et al.12-14 used this reaction toselectively oxidize the primary hydroxyl groups of water-soluble polysaccharides, namely inulin, amylodextrin, starch,amylodextrin, and pullulan. Heinz and Vieira prepared newionic polymers by oxidation of cellulose derivatives.15

Rinaudo et al. studied the TEMPO oxidation of galactoman-

* To whom correspondence should be addressed. Telephone: 33-476037614.Fax: 33-476547203.E-mailaddress: michel.vignon@cermav.cnrs.fr.

† C.E.R.M.A.V.-C.N.R.S.‡ Rodia, Centre de Recherches de Lyon.

565Biomacromolecules 2004,5, 565-571

10.1021/bm034405y CCC: $27.50 © 2004 American Chemical SocietyPublished on Web 12/25/2003

nans16 and hyaluronan.17 Chang and Robyt18 described theoxidation of 10 polysaccharides includingR-cellulose. Isogaiand Kato19 and Tahiri and Vignon20 described the oxidationof several native, mercerized, and regenerated celluloses withthe TEMPO system, starting from heterogeneous oxidationconditions to obtain water soluble or insoluble polyglucuronicacids. Recently, Vignon et al.21 showed that the conversionof cellulose I into the IIII allomorph increased substantiallythe reactivity of cellulose toward the TEMPO-mediatedoxidation reaction. Despite these progresses, the initialinsolubility of cellulose in the water-based oxidation mediumwas always a disadvantage for the homogeneity of theoxidized product.

The present study overcomes the problem of partialoxidation of crystalline cellulose by TEMPO-mediatedoxidation. Following a recent report,22 we have applied theTEMPO-mediated oxidation technique to water solublecellulose acetate of a low degree of substitution (DS∼ 0.5).Using this derivative as a starting material and varying thereaction parameters, we report here the production of a seriesof products (Figure 1), ranging from partially acetylated andoxidized cellulose (1) to pure polyglucuronic acids (2).

Experimental Section

Materials. All reagents were of analytical grade and usedas received. Partially acetylated cellulose (DS) 2.5) wasobtained from Fluka. A NaClO fresh solution from Flukacontaining∼13% active chlorine was used. It had a pH of∼13, which was lowered to 10 by addition of 4M HCl underthe monitoring of a pH meter.

Preparation of Water-Soluble Cellulose Acetate Samples(DS ) 0.5).Cellulose acetate (200 g) with an acetyl contentof 40 wt % (DS) 2.5) was dissolved in a mixture of 26mL of methanol and 74 mL of acetic acid at roomtemperature for 16 h. Then, 0.25 mol of sulfuric acid wasadded, and the medium was heated to 72°C. The mixturewas kept at this temperature for 200 min, during whichdeacetylation and concomitant depolymerization resulted.After cooling, 0.5 mol of sodium acetate were added in orderto neutralize the acid, and the solution was poured in methylacetate. Depolymerized cellulose mono-acetate (DS) 0.5)was recovered after filtration, washed with methyl acetatein order to remove any byproduct, and dried at 45°C. The

sample prepared under this protocol contained 20 wt % ofNa2SO4, which could be desalted by dialysis or ultrafiltration.

Preparation of Partially Acetylated and Oxidized Cel-lulose Samples (1).Cellulose acetate (DS) 0.5; 560 mg,2.44 eq of anhydroglucose, 20 wt % Na2SO4) was dissolvedat room temperature in distilled water (50 mL). The solutionwas cooled to 0-4 °C with an ice bath, and this temperaturewas maintained throughout the experiments. The pH wasbrought to 10 by addition of 0.5 M aq NaOH. TEMPO (4.85mg, 0.031 mmol) and NaBr (107.6 mg, 1.605 mmol) wereadded. Specific quantities of a 1.668 M NaClO solutionadjusted to pH 10 were added dropwise, while the pH ofthe reacting solution was monitored to 10 by dropwiseaddition of 0.5 M aq NaOH. The quantities of NaClO wereof 1.1, 1.7, 2.3, and 2.9 mL repectively in runs A-D. Theoxidation progress was monitored by the consumption ofNaOH, which represents the formation of uronic acids. After1 h, the reaction was quenched by adding 3 mL of MeOH.The reaction mixture was neutralized with 1 M aq HCl andconcentrated (1/3 volume), and then it was precipitated with2-propanol (10 volumes), followed by centrifugation-washing. The precipitate was concentrated in a vacuum toeliminate the 2-propanol, dialyzed, and freeze-dried to obtainthe partially oxidized and acetylated cellulose sample.

Oxidation of All of the Primary Alcohols: Preparationof Polyglucuronic Acids (2). This preparation involved apreliminary partial deacetylation of the water soluble cel-lulose acetate before applying the oxidation treatment, whichwas 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 roomtemperature in distilled water (50 mL). The pH was broughtto 11 by dropwise addition of 0.5 M aqueous NaOH and thesolution kept at room temperature during approximately 90min during which substantial deacetylation occurred. A NMRcontrol of an aliquot of this solution indicated a celluloseacetate sample with a DS) 0.3. The solution was cooled to0-4 °C in an ice bath and the pH was brought to 10 byaddition of 1 M aq HCl. TEMPO (4.85 mg, 0.031 mmol)and NaBr (107.6 mg, 1.605 mmol) were added. Variablequantities of a 1.668 M NaClO solution, previously adjustedto pH 10 were added dropwise adjusting the pH at 10 bysimultaneous addition of 0.5 M aq NaOH (4 mL). Through-out the experiment, the solution was stirred at 0-4 °C and

Figure 1. Scheme of reaction.

566 Biomacromolecules, Vol. 5, No. 2, 2004 Gomez-Bujedo et al.

the pH was kept at 10 by dropwise addition of 0.5 M aqNaOH. The oxidation was monitored by the consumptionof NaOH, which represents the formation of uronic acids.The reaction was quenched after 3 h by adding 3 mL ofMeOH and neutralized with 1 M aqHCl. A small amountof NaBH4 was added, and the solution was stirred for 16 h.The reaction mixture was neutralized with 1 M aq HCl andconcentrated (1/3 volume), and then it was precipitated with2-propanol (10 volumes), followed by centrifugation-washing. The precipitate was concentrated under reducedpressure to eliminate the 2-propanol, dissolved in water,dialyzed, and freeze-dried to obtain 388 mg (80%) of purepolyglucuronic acid (2).

NMR Spectroscopy.13C NMR experiments were recordedwith a BRUKER AC 300 spectrometer operated at frequencyof 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 mmo.d. tubes (internal acetone standard13C (CH3): 31.5 ppmrelative to Me4Si). The degrees of oxidation were determinedby 13C spectra acquired under quantitative conditions, usingboth the integration of peak areas and excision of the chartpaper followed by weighing. The absence of any residualCH2OH at 60.3 ppm or CH2OAc at 63.5 ppm showed thatthe degree of oxidation was 100%.

Quantitative13C spectra were recorded using the INV-GATE 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 quaternarycarbons were not entirely relaxed with a delay of 2 s. Thisobservation accounted for the insufficient area of the peakof COONa carbons.

IR Analysis. Dried samples (1 mg) were dispersed in 100mg of KBr and pressed. The IR spectra were recorded witha Perkin-Elmer FT-IR 1720X instrument.

Gel Permeation Chromatography (GPC).The molecularweights were determined by GPC. The samples weredissolved in distilled water at a concentration of 1 g/L. AWaters apparatus was used with two columns (ShodexOHpack B-804 and Shodex OHpack B-805) in series, elutedat 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 effluentwas monitored using a refractive index detector (RI Waters410). The apparatus was equipped with a multiangle laserlight scattering detection system from Wyatt Technology,USA, which permitted the determination of the absolutemolecular weights of the samples.

Results and Discussion

Preparation of Water-Soluble Cellulose Acetate Samples(DS ) 0.5). In the cellulose acetate series, the solubility ina 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 inacetone. On the other hand, it was shown by Crane23 andMalm et al.24 that water-soluble cellulose acetate could beobtained at a DS comprised between 1 and 0.5, where neitherchloroform nor acetone act as solvents. Cellulose partially

acetylated can be prepared either by direct acetylation ofcellulose from solution25 or by deacetylation from industrialcellulose di- or triacetate. Different procedures were de-scribed for deacetylation. First, Malm et al.24 have describedthe preparation of water-soluble cellulose acetate by thehydrolysis of cellulose triacetate (CTA) in the presence ofan aqueous mineral acid such as sulfuric, chlorhydric, orperchloric acids. More recently, other deacetylation methodshave relied on the use of Lewis acids, namely ZnI2

26 orBuSnO, Zn(OAc)2, Mg(OAc)2 and MoO3,27 or that of strongmineral acid in the presence of acyl anhydride, combinedwith trifluoroacetic acid.28 Deacetylation by hydrolysis inalkaline medium has also been described. Since this methoddoes not induce any depolymerization, it has been usedextensively in the past for the molecular weight determinationby intrinsic viscosity measurement.29 Recently, Philipp et al.30

have described the deacetylation in complex medium con-sisting of a mixture of amine, dimethyl sulfoxide, and water.In this case, water solubility was obtained only for productswith DS between 0.8 and 1.0.

In this work, which requires the use of water-solublecellulose acetate, we have partially deacetylated a commercial“cellulose diacetate” sample with a DS of 2.5. This productwas dissolved in a methanol/acetic acid mixture, and thedeacetylation procedure was carried out under the catalyticsulfuric acid conditions of Malm et al.24 Under theseconditions, deacetylation occurred, but simultaneous depo-lymerization was observed, due to the hydrolysis of glyco-sidic linkages in the catalytic acid media. The resultingcellulose acetate sample was water soluble and had a DS of0.5 and a molecular weightMw ∼ 7300 measured by gelpermeation chromatography (GPC).

Synthesis of Partially Acetylated and Oxidized Cel-lulose Samples (1).To obtain partially acetylated cellulosiccompounds with different degrees of oxidation in the primaryposition (1), the oxidation has to be performed at lowtemperature to avoid the formation of side products. Theinfluence of the relative amount of the oxidizing agent NaClOon the DO was evaluated. Four different runs, correspondingto increasing amounts of NaClO in the range of 0.6-1.6mol NaClO/ mol glucosyl unit were performed, and thecharacteristics of the resulting products were analyzed (Table1), by recording quantitative13C NMR spectra (Figure 2).Despite the fact that the four samples were oxidized todifferent levels, each of them was nevertheless water-soluble.Thus, these products were different from the partially solubleproducts resulting from the heterogeneous oxidation condi-tions of native cellulose, which always showed some water-insolubility.20,21

Table 1. Preparation of Partially Acetylated and OxidizedCellulose Samples by the TEMPO-NaBr-NaClO System withDifferent Amounts of NaClO at 0-4 °C

run eq. NaClOa % COONab % CH2OH % CH2OAc

A 0.6 33 36 31B 0.95 47 25 28C 1.3 65 8 27D 1.6 68 0 32

a Mol NaClO/mol glucosyl unit. b The DO at C6 is 0.33, 0.47, 0.65, and0.68 for runs A, B, C, and D, respectively.

TEMPO-Mediated Oxidation of Cellulose Acetate Biomacromolecules, Vol. 5, No. 2, 2004 567

The13C 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 correspondingrespectively to C4 with CH2OAc or CH2OH at position C6;(iii) two signals at 63.5 and 60.6 ppm, correspondingrespectively to C6 of CH2OAc and CH2OH. The quantitative13C NMR spectra of products resulting from the fouroxidation experiments are reported in Figure 2. In these, theamount of C6 oxidized or acetylated units together with thatof remaining free CH2OH could be deduced from the analysisof the chemical shifts of the products (Table 2) and therelative intensities of the characteristic signals.

In Figure 2, the signal at 60.6 ppm, corresponding to freeCH2OH, decreased continuously with the increase of NaClO,to be completely absent in the spectrum 2D. Conversely, asignal at 175.3 ppm corresponding to the COONa groupincreased 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 unaffectedin each experiment. From these observations, we canconclude that whenever free hydroxymethyl groups werepresent in the starting products they could be oxidized. Onthe other hand, when the hydroxymethyl groups wereacetylated in the starting product, they could not be oxidized,at least in the temperature range of 0-4 °C and the relativelylow concentrations in NaClO, which were used in thissection. Thus, under these conditions, both the initial andoxidized product kept the same degree of acetylation. Analternate explanation to these observations could be that someacetate had migrated from C2 or C3 to C6.

As shown in Figure 3, the oxidation of a hydroxymethylgroup to a carboxyl via an aldehyde requires two moles ofNaClO per mole of hydroxyl, in good relation with the datareported in Table 1. Indeed in the four runs, the amount ofcarboxylate was close to one-half of the amount of theoxidizing agent. Thus, the degree of oxidation (DO) of theproduct could be monitored by the addition of controlledquantities of NaClO, as shown in Table 1 (DO) 0.33-0.68). As the starting material had an initial DS of 0.3 inacetyl content at C6, i.e., 70% primary hydroxyl group werefree, a good correlation could be noticed between the relativeratio of CH2OH and COONa.

The samples were further characterized by infraredspectroscopy. Their FTIR spectra (Figure 4) showed the

Figure 2. 13C NMR spectra in D2O at 333 K of the starting material and partially oxidized and acetylated cellulose samples. DO depends onthe 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 andOxidized Cellulose (Sodium Salts of the Uronic Acids)

glucosylunitb C1 C2 C3 C4 C5 C6 CH3CO CH3CO

COO Na 103.0 73.5 75.0 81.6 76.1 175.3CH2OAc 103.0 73.5 75.0 79.6 76.1 63.5 20.9 174.6CH2OH 103.0 73.5 75.0 79.3 76.1 60.6

a In ppm relative to the signal of internal acetone in deuterium oxide at31.5 ppm relative to Me4 Si. b With position C6 oxidized (COO Na),acetylated (CH2OAc), or free (CH2OH).

568 Biomacromolecules, Vol. 5, No. 2, 2004 Gomez-Bujedo et al.

characteristic absorptions of the hydroxyl groups at∼3380cm-1. Typical bands were found at 1730 cm-1 (νCO) forthe acetate moiety and at 1640 cm-1 (νCO) for the sodiumcarboxylate group (Figure 4a). As these two carbonyl bandswere overlapping, they did not allow us to do any quantitativeanalysis. The molecular weights of the four oxidized sampleswere measured by GPC and varied between 3500 and 4500.

Synthesis of Polyglucuronic Acids (2).Because theacetylated hydroxymethyl groups in the starting productcould not be oxidized with the TEMPO mediated oxidationprocess following the protocol of the preceding section, thepreparation of fully oxidized polyglucuronic acid samples(2) required a specific procedure designed for the C6deacetylation of the cellulose acetate. Unfortunately, exten-sive deacetylation induces detrimental precipitation of thestarting product. Thus, a compromise had to be foundbetween deacetylation and water solubility. Our strategy wasfirst to induce a partial C6 deacetylation and then to pursuewith a protocol based on concomitant deacetylation andoxidation. As explained in the Experimental Section, asolution of water-soluble cellulose acetate (DS) 0.5) waspartially deacetylated until it started to be turbid agent. ANMR control of this solution indicated a cellulose acetatesample 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 thereaction could be followed easily by measuring the amountof NaOH required to neutralize the carboxylic acids gener-ated in C6 and thus maintaining the pH at 10. After

completion of the reaction (i.e., when the pH becamestabilized), the reaction was quenched by addition ofmethanol. A small amount of NaBH4 could then be addedto reduce the partially oxidized carbonyl groups that eventu-ally could be present (Figure 3). However13C NMRexperiments never showed any resonance signal, correspond-ing either to aldehydic groups due to the partially oxidizedC6 position or to the carbonyl carbons that could be formedat C2 or C3 during the oxidation. These results confirmedthat under these oxidation conditions, due in particular tothe fact that the reaction was conducted in water-medium,whenever the aldehyde groups were obtained, they becameimmediately oxidized into carboxyl moieties, and therefore,the addition of NaBH4 is not necessary.

Among the numerous runs that we undertook, varying theamount of NaClO and the time of reaction, the bestconditions to produce fully deacetylated and fully oxidizedcellouronic acid sample were obtained when the sample waspartially deacetylated for 90 min at room temperature andthen oxidized with 3.2 mol of NaClO per mole of glucosylresidue for 3 h at 2°C. Under these conditions, a reactionyield of about 85% was obtained, and the resulting poly-glucuronic acid was not contaminated by degradationproducts. Its13C NMR spectrum (Figure 5a) indicates thatthis product is fully oxidized as it displays only the 6characteristic signals at 175.3, 103.0, 81.6, 76.1, 75.0, and73.5 ppm. The absence of the C6 carbon resonance in therange 60-63 ppm and the presence of a carboxylic carbonnear 175 ppm indicate that the primary hydroxyl groups werecompletely oxidized. According to the literature,20,31 a

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).

TEMPO-Mediated Oxidation of Cellulose Acetate Biomacromolecules, Vol. 5, No. 2, 2004 569

spectrum such as the one shown in Figure 5a refers to thesodium salt of theâ-(1f4)-polyglucuronic acid. The sameresults were obtained either on desalted samples or on thosecontaining up to 20% sodium sulfate. However, in the lastcase, 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 recordedin their sodium glucuronate forms. The FTIR spectrum ofpolysaccharide (2) shown in Figure 4b presented thecharacteristic absorptions of the hydroxyl groups at∼3380cm-1. The typical peak for the carboxylic group is found at1640 cm-1(νCO).

To examine the different factors influencing the TEMPOmediated oxidation process, several oxidation experimentswere studied using different conditions. When the reactionwas performed by using directly commercial NaClO solution,the pH was maintained at 10 by adding dropwise thehypochlorite, without adding any NaOH solution, as the pHof the sodium hypochlorite commercial solution was∼13.In this case, the oxidation reaction was faster than thedeacetylation and the acetyl groups did not have enough timeto be removed. The final product was not fully oxidizedbecause 15% of the C6 hydroxymethyl groups were stillacetylated.

We also observed that reaction times, starting materialconcentrations, and temperature had an important influencein the oxidation reaction. Indeed when the oxidation wasachieved at room temperature, or with longer reaction times,or higher starting material concentrations, more extensivedegradation of the cellulose was found. For instance, whenthe reaction was performed at room temperature, a numberof degradation products resulted. Their presence is denotedin the13C spectrum of the corresponding product, which, inaddition to the six glucuronic unit signals, showed also thepresence 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 depolymer-ization of polyuronic acids occurred primarily by theâ-elimination mechanism at room temperature in alkaline

solutions. Such a side reaction is likely responsible for thedegradation products that are observed in Figure 5b. Isogaiand Shibata32 suggested that the hydroxyl radicals formedfrom NaBrO and TEMPO at pH 10-11 were responsiblefor the depolymerization during the oxidation.

Conclusion

The TEMPO-mediated oxidation of water-soluble celluloseacetate having a DS between 0.5 and 0.3 induced a rapidselective oxidation of the hydroxymethyl groups of thiscellulose derivative. All products were water soluble, buttheir chemical composition depended on (i) the amount ofNaClO used in the reaction and (ii) the DS of the startingcellulose acetate. A small amount of oxidizing agent togetherwith a high acetyl content in the starting product led topartially acetylated and oxidized cellulose, whereas an excessof NaClO together with low acetyl content led to purepolyglucuronic acid.

Degradation products, resulting fromâ-elimination in thealkaline medium of the reaction, could be controlled by usingreaction temperatures in the range of 2-4 °C and reactiontimes not exceeding 3 h.

The synthesis of cellouronic acids or that of partiallyacetylated cellouronic acids described in this paper open theway to a number of cellulose-based polyelectrolytes havinghydrophobic and hydrophilic characters. In addition, theseproducts can serve as a base for a number of further chemicalmodifications, 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 Chemicalsand Energy; Grant No. 9 901 048).

References and Notes

(1) Majewicz, T. G.; Podlas, T. J.Kirk-Othmer Encyclopedia of ChemicalTechnology; Wiley-Interscience: New York, 1993; p 541.

(2) Shelton, M. C.Kirk-Othmer Encyclopedia of Chemical Technology;Wiley-Interscience: New York, 2003, in press.

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

570 Biomacromolecules, Vol. 5, No. 2, 2004 Gomez-Bujedo et al.

(3) Gedon, S.; Fengi, R.Kirk-Othmer Encyclopedia of ChemicalTechnology; 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. Pays-

Bas. 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.Macromolecules1996, 29, 6541.(15) Heinze, T.; Vieira, M.Polym. News2001, 26, 274.(16) Sierakowski, M. R.; Milas, M.; Desbrie`res, J.; Rinaudo, M.Carbo-

hydr. Polym.2000, 42, 51.(17) Jiang, B.; Drouet, E.; Milas, M.; Rinaudo, M.Carbohydr. Res.2000,

327, 455.

(18) Chang, P. S.; Robyt. J. F.J. Carbohydr. Chem.1996, 15 (7), 819.(19) Isogai, A.; Kato, Y.Cellulose1998, 5, 153.(20) Tahiri, C.; Vignon, M. R.Cellulose2000, 7, 177.(21) Da Silva Perez, D.; Montanari, S.; Vignon, M. R.Biomacromolecules

2003, 4 (5), 1417.(22) Fleury, E.; Gomez, S.; Vignon, M. R. French Patent 2,831,171, April

25, 2003.(23) Crane, C. L. U.S. Patent 2,327,770, August 24, 1943.(24) Malm, C. J.; Barkey, K. T.; Salo, M.; May, D. C.J. Ind. Eng. Chem.

1957, 49, 79.(25) Meyer, G.; Brandner, A.; Diamantoglou, M. U.S. Patent 4,543,409,

September 24, 1985.(26) Staud, C. J.; Murray, T. F., Jr. U.S. Patent 2,005,383, June 18, 1935.(27) Edgar, K. J.; Wilson, A. K.; Bellas, M.; Germroth, T. C.; Buchanan,

C. M. U.S. Patent 5,142,034, August 25, 1992.(28) Buchanan, C. M.; Parker, S. W. WO 91/16,356, October 31, 1991.(29) Cox, L. A.; Battista, O. A.J. Ind. Eng. Chem. 1952, 44, 893.(30) Philipp, B.; Klemm, D.; Wagenknecht, W.Papier 1995, 49, 58.(31) Heyraud, A.; Courtois, J.; Dantas, L.; Colin-Morel, Ph.; Courtois,

B. Carbohydr. Res.1993, 240, 71.(32) Shibata, I.; Isogai, A.Cellulose2003, 10, 151.

BM034405Y

TEMPO-Mediated Oxidation of Cellulose Acetate Biomacromolecules, Vol. 5, No. 2, 2004 571