Cadoxene complex

The precipitation data for cellulose from diluted solutions of cadoxen have shown that the precipitation process has a positive temperature coefficient. The kinetics observed fitted a unidimensional nucleation rate law. The low crystallinity of the product suggests that dissociation of the cellulose-cadoxen complex rather than phase separation occurs. 

Several solvents, such as cupriethylenediamine (cuen) hydroxide [111274-71 -6] depend on the formation of metal—ion complexes with ceUulose. Although not as widespread in use as the viscose process, cuen and its relatives with different metals and ammonium hydroxide find substantial industrial use (87). The cadmium complex Cadoxen is the solvent of choice in laboratory work (91). 

Dialysis studies122 of ofellulose and dextran in aqueous solutions of barium hydroxide, sodium hydroxide, and cadoxene (cadmium hydroxide in ethylenediamine) showed no difference in complexing ability between the two polysaccharides. Furthermore, in solutions having equal base normality, Ba2 , Na ,, nd Cd (ethylenediamine) had loughly equal complexing abilities. 

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. 

D-glucosc residues. Comparable values have been obtained for cellulose acetate in acetone Am = 114 A.), and for cellulose in the complex solvent Cadoxen Am = 107 A.). 

Cadoxen, a solution of CdO in aqueous ethylenediamine, is a clear, colorless (which allows detection by RI), and stable solvent for cellulose with DP up to about 10,000. Cellulose can reportedly be dissolved in this solvent for long periods with little to no degradation (135,136). Cadoxen is thought to dissolve cellulose by formation of a complex. The literature contains several reports describing the use of cadoxen for the SEC analysis of cellulose (11,12,17,18,27,85,109). 

A solution of Cd(OH)2 in aqueous ethylenediamine (cadoxen) [68] is a good cellulose solvent, giving stable colourless solutions. Probably the complex formed is similar to that obtained with Schweitzer s reagent, but the bonding here is much weaker, and only a small proportion of the base units forms the complex [69,70]. We found a negative plain ORD curve between 550 and 220 nm [67]. 

Amylose is also soluble in cadoxene. The ORD clearly shows the superposition of a positive basic rotation of the amylose (Curve A in Figure 19) and a negative contribution from the complexed part. Therefore the difference of both curves was calculated. (Curve AM in Figure 19). 

This curve as well as the ORD of pure amylose can be described by a single term Drude equation, given Xo=228 and 169 nm respectively. Cyclodextrin in cadoxene yields a quite similar ORD with a X for the Cd-complex of 229 nm. Inulin in H2 O has a negative plain rotatory dispersion curve in cadoxene the optical rotation is shifted toward positive values and the difference gives a positive ORD for the Cd-complex. Again we find for the Cd complex a Xo= 230 nm. 

Analogs of copper-ethylenediamine solvents have been developed in which metal ions of cobalt, zinc, nickel or cadmium are used to replace copper. The cadmium analog, known as cadoxen, is colorless. Evidently, cadmium also complexes with cellulose to bring about its dissolution. ... 

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