Cellulose reaction mechanism

Cation (Section 1 2) Positively charged ion Cellobiose (Section 25 14) A disacchande in which two glu cose units are joined by a 3(1 4) linkage Cellobiose is oh tamed by the hydrolysis of cellulose Cellulose (Section 25 15) A polysaccharide in which thou sands of glucose units are joined by 3(1 4) linkages Center of symmetry (Section 7 3) A point in the center of a structure located so that a line drawn from it to any element of the structure when extended an equal distance in the op posite direction encounters an identical element Benzene for example has a center of symmetry Cham reaction (Section 4 17) Reaction mechanism m which a sequence of individual steps repeats itself many times usu ally because a reactive intermediate consumed m one step is regenerated m a subsequent step The halogenation of alkanes is a chain reaction proceeding via free radical intermediates... 

The xanthate method [62] is considered as one of the most promising methods for industrial chemical modification. The principal involved in the xanthate method of grafting is that cellulosic xanthate either ferrated or in acidic conditions reacts with hydrogen peroxide to produce macroradicals. The following reaction mechanism has been proposed ... 

Cellulose pyrolysis kinetics, as measured by isothermal TGA mass loss, were statistically best fit using 1st- or 2nd-order for the untreated (control) samples and 2nd-order for the cellulose samples treated with three additives. Activation parameters obtained from the TGA data of the untreated samples suggest that the reaction mechanism proceeded through an ordered transition state. Sample crystallinity affected the rate constants, activation parameters, and char yields of the untreated cellulose samples. Various additives had different effects on the mass loss. For example, phosphoric acid and aluminum chloride probably increased the rate of dehydration, while boric acid may have inhibited levoglucosan... 

Moreover the presence of chelate bonds makes it possible to explain both certain properties of nitrocellulose and phenomena connected with the esterification reaction mechanism of cellulose, all of which will be discussed later. 

An alternative picture of this may be the possibility that the intermediate volatile fragments do not form as such and the cellulose is catalytically dehydrated by the same reaction mechanism as that generally accepted for dehydration of alcohols. 

The so-called copper number is still the method of choice in the pulp and paper industry in process control, but sometimes also in the research lab. The reducing power of cellulose is measured by reaction with an alkaline Cun-salt under defined conditions, the formed Cu1 ions can be titrated after re-oxidation [82]. The underlying reaction mechanisms are still not entirely understood, neither are the types of oxidized structures recorded. However, even though the copper number is only a sum-parameter, the data of which cannot be directly linked to the quantity of a specific oxidized function, it remains a valuable parameter for control in a number of industrially relevant processes. 

Keywords Cellulose Trapping Reactive intermediates Reaction mechanism... 

Rosenau, T., Potthast, A. and Kosma, R Trapping of Reactive Intermediates to Study Reaction Mechanisms in Cellulose Chemistry. Vol. 205, pp. 105-149. 

In the fourth chapter, Thomas Rosenau, Antje Potthast, and Paul Kosma describe current investigations on reactive intermediates and reaction mechanisms in cellulose chemistry. The chemical modification and regeneration of cellulose requires its activation and/or dissolution in media like sodium lye, N-mclhybnorpholine-N-oxide (NMMO), N, N-dimethylacetamide (DMAc), or in carbanilation mixtures containing dimethylsulfoxide (DMSO). In these media - very important for research and large-scale processes - the trapping and characterization of the intermediates has been carried out. 

Trapping of Reactive Intermediates to Study Reaction Mechanisms in Cellulose Chemistry... 

Considering that both grafting efficiency as well as conversion in this study shows optimal values for pH 4 - 7, we have used pH 5 which favors the attachment of ferrous ion on partial cellulose xanthate and other ion exchange groups present. (The term "partial cellulose xanthates" stands for xanthates bound statistically to any component of the pulp (cellulose, hemicellulose, lignin). The importance of the presence of ferrous ions on grafting is shown in Diagrams I-II-III, which show reaction mechanism sug-... 

Entwistle et al. (21) orginally adapted a general free radical mechanism to the autoxidation of alkali cellulose. The reaction mechanism presented below for the interaction of cellulose with oxygen was proposed by Shafizadeh and Bradbury (22) ... 

The basic reaction mechanism for the autoxidation process just presented provides a useful frame of reference for a discussion of this reaction system. However, much needs to be learned about the interaction of cellulose with a composite system that includes oxygen, water, and metallic contaminants. A better understanding of this reaction system is essential for the development of practical measures for the inhibition of the autoxidative degradation of paper. 

In this paper, cellulose was reacted in hot-compressed water at different reaction temperatures and time using a reduced nickel catalyst. The aim of the study is to elucidate the overall reaction mechanism on the low temperature catalytic gasification and to get an insight into the hydrogen production. 

Molecules of low molecular weight (e.g., drugs) are likely to adsorb to polymers present in the formulation. Adsorption occurs by the formation of weak (localized) interactions, hydrogen bonds, or ionic bonds between molecules and polymers. Microcrystalline cellulose, which is an important pharmaceutical excipient, has been demonstrated to influence chemical and photochemical reaction mechanisms of adsorbed compounds (Wilkinson et al., 1991). Interactions between drugs and polymeric compounds and the subsequent influence on photoreactivity are further discussed in Chapter 15. 

Figure 9.14 Proposed reaction mechanisms of cellulase catalysis (A) hydrolysis of cellulose and (B) polymerization of 3-CF into synthetic cellulose. (Reproduced with permission from [250]. Copyright (2005) John Wiley Sons, Inc.).

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