Cellulose oxidized groups

Oxidation with periodate under acidic conditions, the Malaprade reaction, is mainly used to introduce a large number of aldehydes into cellulose [45]. Whether a similar reaction proceeds also under conditions of natural or accelerated aging conditions has not been clarified, but corresponding processes have been postulated to occur [46]. The oxidized groups introduced are either used to further functionalize the cellulose, e.g., by reaction with... 

Celluloses oxidized to an aldehyde at C6 are found for instance as intermediates of the TEMPO oxidation [50]. Depending on the reaction conditions a large number of such groups may survive in the final products, the poly-glucuronic acids, and also in partially TEMPO-oxidized pulps materials it is highly likely that a large number of carbonyl groups are present as C6-aldehyde. 

The analysis of oxidized groups in celluloses will remain a hot topic in cellulose chemistry and analytics, as we are only beginning to understand the enormous importance of these groups in governing chemical behavior and macroscopic properties of cellulosic material. 

While some of the above can occur with cellulose treated with the alkaline earth hydroxides or carbonates, their tendency to insolubilize compounds with carboxyl groups will work against swelling and the increase in accessibility. For example, cellulose oxidized with N204 swells and dissolves in sodium hydroxide but is not soluble in lime solution. 

However, once introduced on the cellulose molecule, the hydroxyethyl group is highly reactive and capable of further reaction with another molecule of ethylene oxide. This type of reaction, called graft etherification, can build up relatively long-chain substituents on the cellulose molecule without involvement of many additional cellulosic OH groups ... 

When cellulose is exposed to the unlimited supply of oxygen present as 21% of the air, unstable peroxide radicals form. In the autocatalytic reaction of cellulose oxidation, decomposition of peroxide forms cellulose radicals that react with oxygen to form R02- radicals. These radicals attack other cellulose molecules to form oxycelluloses (carbonyl, aldehyde, and carboxyl acid groups) along with more cellulose free radicals (34). 

Heat catalyzes free radical formation in cellulose. Aldehydes form from C2 and C3 hydroxyls. Aldehydes oxidize to carboxyls, and with dehydration, carbon monoxide (CO) and carbon dioxide (C02) form as well as conjugated carbonyl-ethylenic chromophoric groups that selectively absorb blue light and impart yellowness (35). During the induction stage of cellulose oxidation, yellowness may increase steadily with selective carbonyl and ethylene group formation. By artificially aging... 

Figure 8. Incorporation of oxidized groups in cellulose at 190 °C. The numbers of lactone and carboxyl groups formed in nitrogen at 190 °C are represented by -V-.

Cellulose, oxidized with nitric acid, yields isosaccharinates and dihy-droxybutanoates when the product is treated with lime-water. Cellulose which has been oxidized with acidic potassium permanganate solution contains some uronic acid groups, and, when placed in dilute alkaline solutions, forms chains with a degree of polymerization (D. P.) of about 90. In more concentrated alkaline solutions, the chains are shortened more, and have a D. P. of about 35. 

The SOM in Table 4.1 is richer in carbon than is plant matter. SOM tends to contain more aromatic (cyclic and resonating carbon-carbon bond) compounds, and contains less oxygen, than the plant matter from which it is derived. Alternatively, because cellulose oxidizes faster than lignin, the aromatic groups may represent an accumulation of aromatic carbon from unreacted lignin. All of these materials eventually oxidize in soils, but each succeeding oxidative step is much slower. The half-... 

In Sirvib s work [39], a water-soluble cationic cellulose derivative was synthesized by cationizing dialdehyde cellulose (DAC) produced by periodate oxidation of birch cellulose pulp by means of a reaction between aldehyde groups and cationic Girard s reagent T ((2-hydrazinyl-2-oxoethyl)-trimethylazanium chloride, GT) to produce cationic dialdehyde cellulose (CDAC). A schematic illustration of this cellulose oxidation and DAC cationization processes is shown in Fig. 3.3. 

McGee, P.A., Fowler, W.F. Jr. and Kenyon, W.O. (1947a) Investigation ofthe properties of cellulose oxidized by niuogen dioxide. III. The reaction of die carboxyl groups of polymronides with calcium acetate. fAm. Chem, Soc., 69, 347-49. 

Saito T, Isogai A. Ion-exchange behavior of carboxylate groups in fibrous cellulose oxidized by the TEMPO-mediated system. Carbohydr Polym 2005 61 183-190. 

It should also be noted that some nonradical ionic and condensation reactions of monomers with cellulose are used to modify the properties of cellulosic products. In one type of anionic-initiated reaction of monomers, cellulose is reacted with concentrated aqueous solutions of alkali metal hydroxides to yield cellulose copolymer. Free alkali metal in liquid ammonia or alkali metal alkoxides in nonaqueous systems may also be used as initiators of cellulose alkoxide derivatives. In cationic-initiated formation of copolymers, cellulose is reacted with an acid, such as boron trifluoride, to yield a cellulosic carbonium ion which initiates reactions with vinyl monomers. Condensation reactions of cyclic monomers with cellulose also form copolymers. Cellulose is usually slightly oxidized and also has reactive hydroxyl groups on carbons C-2, C-3 and C-6 of the anhydroglucose unit. The reactions of cyclic monomers are initiated at these carbonyl groups. A heating step may increase cellulosic oxidation and thereby increase the yield of these condensation products of cellulose and cyclic monomers." ... 

Antimony Oxide as a Primary Flame Retardant. Antimony oxide behaves as a condensed-phase flame retardant in cellulosic materials (2). It can be appHed by impregnating a fabric with a soluble antimony salt followed by a second treatment that precipitates antimony oxide in the fibers. When the treated fabric is exposed to a flame, the oxide reacts with the hydroxyl groups of the cellulose (qv) causing them to decompose endothermically. The decomposition products, water and char, cool the flame reactions while slowing the production and volatilization of flammable decomposition products (see Flaa retardants for textiles). 

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) ... 

Natural Products. Many natural products, eg, sugars, starches, and cellulose, contain hydroxyl groups that react with propylene oxide. Base-cataly2ed reactions yield propylene glycol monoethers and poly(propylene glycol) ethers (61—64). Reaction with fatty acids results ia a mixture of mono- and diesters (65). Cellulose fibers, eg, cotton (qv), have been treated with propylene oxide (66—68). 

Emulsion polymerizations of vinyl acetate in the presence of ethylene oxide- or propylene oxide-based surfactants and protective coUoids also are characterized by the formation of graft copolymers of vinyl acetate on these materials. This was also observed in mixed systems of hydroxyethyl cellulose and nonylphenol ethoxylates. The oxyethylene chain groups supply the specific site of transfer (111). The concentration of insoluble (grafted) polymer decreases with increase in surfactant ratio, and (max) is observed at an ethoxylation degree of 8 (112). 

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