Cuprammonium complex formation with

An alternate procedure used in a few specialty applications is the cuprammonium process. This involves stabilization of cellulose in an ammonia solution of cupric oxide. Solubilization occurs by complex formation of cupric ion with ammonia and the hydroxyl groups of cellulose. Regeneration of cellulose, after formation of the desired products, is accomplished by treatment with acid. The main application of the cuprammonium process is for the synthesis of films and hollow fibers for use in artificial kidney dialysis machines. The cuprammonium process yields products with superior permeability and biocompatibility properties compared to the xanthation process. Less than 1% of all regenerated cellulose is produced by the cuprammonium process. 

Recent studies on complexing of w c-diols with borate and with cuprammonium hydroxide have also suggested that there is little correlation between 0—0 distance and complex formation H. Kwart and G. C. Gatos, J. Am. Chem. Soc., 80, 881 (1958). 

All the glucopyranosides substituted to restrict complex formation to the 2,3 position showed marked evidence of reaction with cuprammonium. This behavior would be compatible with ring conformations Cl, B2, and 3B except that three of the substances, the 4,6-ethylidene and 4,6-benzylidene compounds, could not exist in either the B2 or 3B conformations for steric reasons because of the spatial requirements of the second ring hence, these three substances must exist in the Cl conformation. 

The cupro and lyocell processes are based on the application of direct dissolution systems. The copper ammonia complex is prepared from copper sulphate and sodium carbonate with sodium and ammonium hydroxides, as presented in the equation in Fig. 4.3. The dissolution process is carried out for cuprammonium via weakening the intra/intermolecular hydrogen bonds and complex formation. Cupro and especially lyocell processes consume lower amounts of water, but a similar magnitude of energy. 

The chemical reactions and mechanism of fixation of the am-moniacal preservatives such as ACA have not been studied extensively. The main mechanism of fixation is believed to be the formation of insoluble copper arsenate upon evaporation of the ammonia. However, the overall mechanism is undoubtedly more complex because cuprammonium ions react by ion exchange with functional groups, such as carboxyl, in wood (52). In addition, copper complexes can be formed with cellulose (52). 

Among the best-known nonderivatizing solvent systems is a combination between copper, alkali, and ammonia termed Schweizer s reagent. Solutions of cuprammonium hydroxide have been used for both analytical and industrial cellulose dissolution. Regenerated fibers with silk-like appearance and dialysis membrane have been (and partially continue to be) industrial products on the basis of cellulose dissolution in cuprammonium hydroxide. The success of this solvent is based on the ability of copper and ammonia to complex with the glycol functionality of cellulose as shown inO Fig. 11. Because of the potential side reactions (oxidation and crosslinking, Norman compound formation), alternatives to both ammonia as well as copper have been developed. Cuen and cadoxen are related formulations based on the use of ethylene diamine and cadmium, respectively. The various combinations of alkali, ammonia. 

Several known systems dissolve cellulose (126-129). These systems range from solutions in protonic acids (e.g., 78% phosphoric acid) to metallic complexes (e.g., cuprammonium). All known methods for dissolving cellulose can be fit into four main categories (128) cellulose acting as abase, cellulose acting as an acid, cellulose complexes, and cellulose derivatives. The cellulose derivatives are distinguished from those discussed previously in that dissolution occurs simultaneously with derivative formation and the derivative produced can easily be regenerated (129). 

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