Oxidation of cellulose

Paper exists in air that contains about 20% of oxygen. Cellulose is capable of reacting slowly with oxygen in ambient conditions (autoxidation). Such oxidation reactions involve intermediates called free radicals. In a simple compound A-B, the single bond between A and B contains two shared electrons, if both go to B then two ions are produced A+ and B. If the electrons are shared between A and B, two free radicals A and B are produced because each has an unpaired electron. Such free radicals can participate in chain reactions in which the reaction of a free radical with a neutral molecule creates a product and another free radical (propagation). The process of 

Metal ions that are capable of changing their valency, in particular, ions of copper and iron, are powerful oxidation catalysts as they can initiate oxidation reactions. During a valency change, negatively-charged electrons (e ) are donated or accepted. 

Loss of strength of the paper is caused during oxidation as chain scission is produced. During oxidation, carbonyl ( C=0) groups can be formed on some of the carbon atoms in the cellulose molecule. 

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Though a negative value for AGe is a necessary condition for a reaction to take place at all under a given set of conditions, further information is still needed as the — AGe value tells us nothing about how fast the starting materials are converted into products. Thus for the oxidation of cellulose,... 

Scheme 12 Hydrolytic degradation preceding free radical oxidation of cellulose macromolecules.

It is difficult to find any definitive information that indicates ozone damage as extensive as that suggested in the mri report. The latter identified cotton, nylon, and rayon as particularly susceptible to ozone. The oxidation of cellulose fibers by ozone was the subject of a study in 1952 that showed that dry cotton was not seriously degraded by ambient ozone. In more recent studies, these conclusions were confirmed. The only information available on fibers other than cotton addressed the effect of ozone on modacrylic, acrylic. Nylon 66, and polyester fabrics.The results indicated minimal effects on these fibers. 

D-fructose,509,510 D-arafoino-hexosulose511 and the oxidation of cellulose by chlorine.382... 

The selective oxidation of cellulose to dialdehyde by sodium periodate is well known. It has been postulated by Criegee (74) and by Waters (73) that this reaction proceeds by a free radical mechanism. Toda (76) and Morimoto, Okada, Okada, and Nakagawa (77) have concluded that sodium periodate oxidation should initiate graft polymerization. They succeeded in grafting methyl methacrylate and acrylonitrile onto cellulose substrates, such as rayon and paper. A similar procedure is recommended in a patent of Chemische Werke Huels (78) to graft vinyl monomers onto cotton, polyethylene oxide, copolymers of vinyl chloride-vinyl acetate, and others. 

Cellulose may also serve as the starting material for the preparation of D-glucurono-6,3-lactone. However, the methanolysis of cellulose to methyl a,/3-D-glucopyranoside (66) has thus far been reported to proceed in only low yield. Whereas the oxidation of cellulose to cell-uronic acid (65) proceeds in high yield,344 the hydrolysis of this material to 63 has not yet been efficiently achieved. The preparation of 63 has been reviewed in detail,345-349 as have its subsequent reactions.350... 

Kenyon and coworkers17 much information concerning the preparation and properties of the product of oxidation of cellulose with nitrogen dioxide has been elaborated. This oxidation has been shown to occur with the initial rapid incorporation of nitrogen by the cellulose followed by a slower loss.174 This is interpreted as an initial nitration followed... 

Further studies verified the intermediate formation of free radicals, as demonstrated by the electron-spin resonance spectra obtained during autooxidation of cellulose,75 and hydrogen peroxide was identified as a byproduct in the autooxidation of D-glucitol. Similar oxidations of cellulose in the presence of alkenic monomers afforded graft copolymers. The autooxidation of cellulose and of the cello-oligosaccharides was shown to be more extensive in the presence of transition-metal cations. 

M. Lewin, Bleaching and oxidation of cellulose by hypobromite and hypochlorite-bromine solutions, Tappi, 48 (1965) 333-343. 

Fig. 8-14. Example of the oxidation of cellulose by chlorine radicals. After oxidation at C-1, the glycosidic bond is cleaved with formation of a gluconic acid end group. R denotes cellulose chain.

Transition metals such as cobalt, copper, iron, and manganese catalyze free-radical oxidation of cellulose pulps when present in low concentratipns. Nickel is harmless. 

Tahiri, C. and Vignon, M. R., TEMPO-oxidation of cellulose Synthesis and characterisation of polyglucuro-nans. Cellulose 2000,1 (2), 177-188. 

The theoretical factor for total oxidation of glucose is 7.5 mg of glucose per meq of dichromate. For total oxidation of cellulose, the factor is 6.75 mg cellulose per meq of cellulose. As indicated in TAPPI T 235, the actual oxidation is not quite theoretical and is given as 6.85 mg cellulose per meq of dichromate. Pentosans and paper sizing materials give different oxidation factors. 

Thus, Heuser took up the alcoholates of cellulose, its esters, its ethers, and the oxidations of cellulose which led to carbonyl groups and to carboxyl groups. But he also had an important chapter on the hydrolysis and the acetolysis of cellulose, on its decomposition by heat, and its degradation by bacteria. His final chapter, on the constitution of cellulose, was largely historical in nature, and, viewed from present-day knowledge, it was, perhaps, less successful than were some of the others. But the entire little volume was conceived from a logical viewpoint—one that was very welcome to those of us who had tried to cope with some of the older literature. The book was relatively brief and very clearly written. 

In this book, he emphasized the importance of the microscopic and the submicroscopic structure of fibrous high polymers. The reactions of cellulose with water, aqueous alkalis, organic bases, ammonia, and strong salt solutions were all stressed. Special attention was given to various types of cellulose esters, to cellulose xanthate, and to the cellulose ethers. The oxidation of cellulose under a variety of conditions was described, as were the hydrolysis reactions. The latter included discussions on reversion and on the kinetics of acid hydrolysis. It is interesting to note that Heuser, who earlier had criticized the terms hydrocellulose and oxycellulose, and had... 

The oxidation of cellulose, besides endgroups, may be discussed in three major types as illustrated in Fig. 11. The first type (A) is a glycol cleavage oxidation of a,(3-diol units with periodate giving the dialdehyde derivative... 

Glycol cleavage. The initial periodate oxidation of cellulose, like other chemical reactions, was largely limited to the readily accessible component and has also been used to indicate the accessibility of cellulose substrates [151] (Table 1). Rowland and Cousins [232], based on the influence of periodate oxidation in the crystallinity of cotton, observed about 40% of the component being noncrystalline. Since the m-diol unit is generally more reactive than the /ran.9-diol, the cleavage of the mannose residues would proceed faster than that of the glucose or xylose residues. 

Oxidation and acid hydrolysis are the two principal deterioration mechanisms for paper, and recently chemiluminescence (CL) has been used to follow the oxidation of cellulosic materials at temperatures of 40 °C and below (I). CL is thought to be produced by the termination... 

The initiation efficiency depends on the relationship between the rate of macroradical formation and that of initiation. In Table 1 are compiled results on certain redox systems employed for the initiation of cellulose grafting either by direct oxidation of cellulose (or its derivative) or chain transfer from active low molecular weight radicals. Table 1 indicates that in systems where the matrix acts as a reducing agent (1st group), the initiation efficiency does not exceed 15%, i.e. only a minor portion of macroradicals formed at the first stage of oxidation initiates graft polymerization while the rest is oxidized to stable... 

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