Cellulose 6-tosylates

The most prominent cellulose ester produced on the industrial scale is cellulose acetate. The reaction is usually performed with acetic anhydride and with sulfuric acid as a catalyst. To minimize heterogeneities, acetylation is allowed to run nearly to completion, and subsequently partial ester hydrolysis is initiated by the addition of water until a desirable solubility is achieved that corresponds to a DS of about 2.5. Such higher acyl homologues as propanoyl or butanoyl exhibit more thermoplastic properties. Many specialized esters such as chiral (-)-menthyloxyacetates, furan-2-carboxylates, or crown-ether-containing acylates have been prepared on the laboratory scale and characterized by NMR spectroscopy. Various procedures have been applied, using anhydrides and acyl chlorides as acylating agents in combination with such bases as pyridine, 4-dimethylaminopyridine (DMAP), or iV,iV -carbonyldi-imidazole. The substitution pattern of cellulose acetates has also been modified by postchemical enzymatic deacetylation. Cellulose 6-tosylates have been used as activated intermediates for nucleophihc substitution to afford 6-amino-6-deoxy, 6-deoxy, or 6-deoxy-6-halo-celluloses. ... 

As shown, an asymmetric carboxylic-sulfonic acid anhydride is formed, but the cellulose attack occurs on the C = O group, since a nucleophilic attack on sulfur is slow, and the tosylate moiety is a much better leaving group than the carboxylate group [193]. Similar to other acylation reactions, there is a large preference for tosylation at the 5 position, and cellulose tosylates... 

Since iodide ion is a strong nucleophile, the action of iodides on cellulose tosylate, mesylate, and nitrate in ketones, and chlorodeoxycellulose in DMF or 2,5-hexanedione can generate iododeoxycellulose. In use of chlorodeoxycellulose, the chlorine substituents were almost completely replaced by iodide in 2,5-hexanedione. The iododeoxycellulose thus prepared was 6-dexoy-6-iodocellulose. lododeoxycelluloses having iodo substituents at C2 and C3 were also prepared by treating various sulfonates having a DS higher than 1.0 or 6-0-trityl-2(3)-p-nitrobenzenesulfonate of cellulose with sodium iodide in DMF. Ishii [134,135] succeeded in the almost quantitative preparation of 5,6-cellulosene acetate by the treatment of acetylated 6-deoxy-6-iodocellulose (DS 0.8) with 1,8-diazobicyclo [5,4,0]undec-7-ene in DMF. 

Another type of cellulose anhydro derivative, a mixed polysaccharide containing glucose and 3,6-anhydroglucose units, has been synthesized by the alkaline saponification of cellulose tosylate (V) tl,12) and 6-0-tosyl-2,3-di-0-acetylcellulose (VI) 13) ... 

The monosaccharide composition of the products of the alkalii saponification of cellulose tosylates containing tosyloxy groups at Cg has been established on the basis of data obtained from a study of the composition of the products of acetylation, nitration, and periodate oxidation, and from quantitative paper chromatography of the products of complete hydrolysis of the mixed polysaccharides synthesized. The content of 3,6-anhydroglucose units in the 3,6-anhydro derivatives of cellulose was found to be 50-70 mol.-% (10-13). 

Interesting data have been obtained from the determination of the content of methoxyl groups in the products of the saponification of cellulose tosylate with a methanol solution of KOH (Table 3). 

The replacement of the tosyloxy groups in cellulose tosylate and its derivatives upon interaction with amines leads to the formation of mixed polysaccharides containing units of N-alkyl(aryl)-substituted amino-deoxy sugars. 

A study of the effect of the structure and size of the amine radical (butylamine, dibutylamine, hexylamine, piperidine, aniline) on its reactivity in the nucleophilic replacement of tosyloxy groups in cellulose tosylate has shown (29) that this reactivity depends primarily on the basicity of the amine. TTiis assumption was confirmed by a study of the interaction of cellulose toxylates of different degrees of substitution (DS from 0.3-1.7) wit iminodiacetic and anthranilic acids 30, 31). TTie degree of substitution of the reaction products with respect to the N-carboxyalkyl(aryl)amino groups was found to be lower than that of the corresponding N-alkyl(aryl)araino derivatives. 

The low nucleophilicity of the amino (imino) groups in iminodiacetic and anthranilic adds meant that the DS of the products of their interaction with cellulose tosylate did not exceed 0.7-0.8. Hence, the appearance of a product with a DS of about 2 through the interaction of anthranilic acid with cellulose nitrate was unexpected (32). The reaction rates for cellulose toxyiate and nitrate are shown in Fig. 3. 

Fig. 3. Time dependence of Hk d ee of substkution of products of the interaction of cellulose tosylate and nitrate with anthranilk acid in aqueous solutioa Reaction time (in hours) is dotted along the abscissa, degree of substitution with respect to amino groiqps along the ordinate 1 cellulose nitrate 2 cellulose tc date...

The reaction of butyllithium with cellulose iodotosylate prepared by iodination of cellulose tosylate of high DS (1.65) has bwn studied. General considerations concerning the direction of the reactions proceeding in the system RX + R Li suggest that the interaction between iododeoxycellulose and organolithium compounds may involve the normal Wurtz reaction (7), the reaction of metallization (8), and the... 

A comparison d data on the monosaccharide composition of mixed polysaccharides formed tte action of a KOH solution on cellulose tosylate (see above) or 6-iododeoxycellulose indicates that the direction of the reactions taking place in the repeating units of the macromr aile under the action of nucleo diilic resents is strongly dependent on the... 

Ethynyl- and phenylethynyldeoxycellulose have also been synthesized (60) through the interactirm of cellulose tosylate with sodium acetylide and phenylacetylide in liquid ammonia according to tte scheme ... 

Moreover, a number of aminodeoxycellulose were accessible. Water soluble 6-trialkylammonium-6-deoxycellulose could be prepared [56]. Conversion of cellulose tosylate with diamines like 1,4-phenylenediamine yields polymers that can be applied for the immobilization of enzymes by diazo coupling, for example [57]. 

Cellulose Sulfonates. Cellulose sulfonates are inorganic esters of cellulose and sulfonic acids in which there is a sulfur-oxygen bond formed to link the cellulose and sulfonic acid moieties. Figure 4 depicts the three most common cellulose sulfonates described in the literature, cellulose methanesulfonate (mesylate) (4), cellulose toluenesulfonate (tosylate) (5), and cellulose dansylate (6) (22-25). Cellulose tosylate is the most commonly described cellulose sulfonate in the literature. Cellulose sulfonates are typically prepared in a homogeneous process by dissolving cellulose in a dimethylacetamide/lithium chloride (DMAc/LiCl) mixture and reacting the cellulose with sulfonylchloride in the presence of triethylamine (Fig. 5) (25). Cellulose sulfonates can also be prepared in situ for use as reactive intermediates (26,27). The use of cellulose tosylate as a reactive intermediate is be discussed in more detail later in this report. 

SynthGtiC IntGrnriGdiatGS. Cellulose sulfonates have been evaluated as S5mthetic intermediates (27,46-49). Cellulose tosylate activates the C6 hydroxyl for substitution with various nucleophiles (eq. 2 where Nu = Cl , Ns", NH2—(CH2)m NH2, or other nucleophiles). 

Additionally, cellulose sulfonates can also function as a protecting group to prevent reaction of the C6 hydroxyl during esterification reactions (Fig. 8). Cellulose tosylates with degrees of substitution from 0.38 to 2.30 have been reported. Although an effective synthetic tool, the expense of organic solvents utilized and the cost and corrosive nature of tosyl chloride have limited the use of this methodology on a commercial scale. 

Figure 1.28 Structure of dipropylenetriamine (DPTA) cellulose tosylate. Note that some tosylate residues are present at the C-2 and C-6 positions during the synthesis, as indicated by N NMR spectroscopy. Reproduced with permission from Ref [74] 2007, Wiley-VCH Verlag GmbH Co. KGaA.

Mesylated and Tosylated Celluloses. It has been estabUshed that the flame resistance of ceUulose (qv) is improved by oxidation of —CH2OH groups to —COOH (58—60). To correct some of the shortcomings of this treatment, mesyl or tosyl ceUulose was prepared and then the mesyl (CH2SO2) or tosyl (CH2CgH4S02) group was replaced with bromine or iodine (58—60) ... 

Fig. 3 Suggested mechanisms for the reaction of cellulose with tosyl chloride in the presence of pyridine (Py) and/or triethylamine (EtsN) base catalyst. Redrawn from [147]...

Fig. 7 Use of tosyl chloride as an acid activator for the synthesis of cellulose esters, from [23]...

Two of the hydroxyl groups present in each glucose unit of the cellulose are secondary, one is primary. Studies on the relative rates of etherification of the three hydroxyls are not conclusive. Mahoney and Purves,18 using a method which takes advantage of the rapid reaction between tosyl chloride and a primary hydroxyl, combined with a determination of unsubstituted glycol groups, have studied the relative num-... 

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