Carbamate cellulose

Neste patented an industrial route to a cellulose carbamate pulp (90) which was stable enough to be shipped into rayon plants for dissolution as if it were xanthate. The carbamate solution could be spun into sulfuric acid or sodium carbonate solutions, to give fibers which when completely regenerated had similar properties to viscose rayon. When incompletely regenerated they were sufficientiy self-bonding for use in papermaking. The process was said to be cheaper than the viscose route and to have a lower environmental impact (91). It has not been commercialized, so no confirmation of its potential is yet available. 

In this context, the enantiomeric pair containing the eutomer of cyclothiazide can be resolved by HPLC on cellulose-derived coated CSPs. Nevertheless, the poor solubility of this compound in solvents compatible with this type of support makes this separation difficult at preparative scale. This operation was achieved with a cellulose carbamate fixed on allylsilica gel using a mixture of toluene/acetone as a mobile phase [59]. 

Carbacell [Carbamate cellulose] A process for making rayon filament and staple fibre. Cellulose is reacted with urea in an inert organic solvent at a high temperature to yield cellulose carbamate. This process avoids the environmental problems caused by carbon disulfide in the viscose process. Developed by Zimmer in the 1990s and piloted in Germany and Poland. Commercialization is expected by 1999. 

Figure 3. Structure of cellulose carbamates used as CSPs. Similar are the amylose carbamates, but with a different configuration and conformation of the basic polysaccharide (see also Figure 2).

Ekman K., Eklund V., Fors J., Huttunen J., Mandell L., Selin J.F. Turunen O.T. Regenerated cellulose fibers from cellulose carbamate solutions. Lezinger Berichte 57 38 10 (1984). 

Cellulose acid phthalate, I, 320 Cellulose acid succinate, I, 320 Cellulose benzoate, I, 320 Cellulose carbamates, N-derivatives, I, 321... 

Cellulose reacts with isocyanates in anhydrous pyridine or with urea and substituted ureas at relatively high temperature to yield carbamates. The optimum carbamation reaction of microcrystalline cellulose with urea in a dry solid mixture has been studied [51]. In addition, a preferentially C6-modified cellulose carbamate derivative has been obtained [52]. Heating of cellulose with thiourea at 180°C yielded cellulose thiocarbamate [53]. Heat treatment of cellulose isocyanate products has been utilized for the production of urethanes [54]. When ceUuIose was treated with phenylisocyanate at 100 C in DMF in the presence of dibutyltin dilaurate and triethylenediamine, celiuiose bisphenylcarbamate was formed [55]. Treatment of cellulose with urea at temperatures at or above the latter s melting point (where urea decomposes into isocyanic acid and ammonia) has been employed for the production of cellulose carbamates fibers [56]. The advantages and disadvantages of using urea as an intermediate for production of fiber have been discussed [57]. 

Cellulose carbamate and its derivatives are able to immobilize enzymes easily with the help of dialdehydes such as dialdehyde starch, glutaraldehyde, and glyoxal [62]. Since cellulose triphenylcarbamate or tricarbanilate prepared... 

The influence of the support surface chemistry on the enantioselectivity of cellulose-carbamate-coated CSPs has also been investigated 1170). It was found that stable coated phases can be produced using underivati/ed. aminopropylated and octadecylated silica... 

Enantioselective packings Polar or nonpolar Packings with enantioselective cages or enantioselective surfaces, microcrystalline cellulose triacetate, cellulose ester or cellulose, carbamate/sil-ica composites, optically active poly(acrylamide)/silica composites, chemically modified silicas (Pirkle phases), cydodextrine modified silicas Operated either with normal phase or reversed phase mobile phases... 

SMB using this revised set of conditions. They applied their results on the operation of SMB units fitted with trains of columns having slightly different porosities to the separation of the enantiomers of Troger s base on Chiralpak AD, a cellulose carbamate (see isotherm data in Figure 4.28), a case in which the competitive isotherms deviate strongly from Langmuirian behavior. Their results are discussed in Section 17.9.2. 

Mihlbachler et al. [26,59] studied the separation by SMB of the enantiomers of TrSger s base on Chiralpak AD, a cellulose carbamate CSP (see isotherm data in Figure 4.28). They compared their experimental results with the numerical solutions of an equivalent TMB process that was written within the framework of the equilibrium-dispersive model. The mass balance equation for each component i in each column k of each section j of the SMB is given by... 

To address development of chiral separations by SFC, Villeneuve and Anderegg have developed an SFC system using automated modifier and column selection valves. Columns (250 x 4.6 mm i.d., 10 pm) packed with Chiralpak AD, Chiralpak AS amylose derivative, Chiralcel OD cellulose carbamate derivative, and Chiralcel OJ cellulose ester derivative (Chiral Techologies, Exton, PA) were connected to a column-switching valve. Candidate samples were run successively on each column using fixed isocratic, isobaric, and isothermal conditions of 2 ml/min, 205 atm pressure, and 40 °C with the vari-... 

Heard and Suedee [40] reported the use of cellulose carbamates in stereoselective adsorption and membrane permeation of racemate and individual enantiomers of propranolol. In this study, three carbamates were used including cellulose tris A-(phenyl carbamate) (Ri) cellulose tris A-(3,5-dichlorophenyl carbamate) (R2) and cellulose tris A-(3,5-dimethyl-phenyl carbamate) (R3) (Fig. 4). The S-enantiomer of propranolol was found to be preferentially bound with all the three carbamates used in this study. Further, incubation at 32°C (pH 7.4) increased binding compared to room temperature. The dimethylphenyl carbamate derivative (R3) had the highest sterereoselective binding compared to the dichlorophenyl (R2) and phenyl (Ri) forms. The ratio R to S enantiomer flux values for Ri, R2, and R3 were 2.65, 2.31, and 1.35, respectively. In the control experiment with no carbamates, however, no stereoselective adsorption was observed. 

Cellulose carbamate was discovered and patented by Hill and Jacobson [77]. A polymer usually can be formed by reacting cellulose with isocyanic acid (lA) (Figure 10.47). In most reactions, the hydroxyl group present at C6 position in the repeating cellulose unit reacts with... 

The least expensive source of lA is urea. Petropavlovskii and Zimina [79] reviewed reactions of cellulose with urea and the preparation of alkali-soluble cellulose carbamates. lA and ammonia usually form when urea is heated above 135°C [3] however, as shown in Figure 10.48, lA undergoes some side reactions and various nontoxic, water-soluble byproducts can form. Because cellulose carbamate is a stable solid that is not soluble in water, the by-products can be easily separated by extraction with water. The dried polymer can be stored for a prolonged period of time. 

Sobczak [81] showed that the quality of spinning dope of cellulose carbamate depends on the following ... 

It is very important to mention that at ambient temperature carbamate groups tend to hydrolyze under alkaline conditions more easily. Therefore, solutions of cellulose carbamate must be chilled off [3]. Struszczyk [82,83] demonstrated that such solutions are stable below 0°C. All commercial processes, namely dissolution of cellulose carbamate and solution storage must be handled at low temperatures to avoid changes in viscosity. Some additives also can be used to control the solution s viscosity and to reduce gelation. The addition of 1-3% zinc oxide to a spinning dope tends to increase the viscosities of these solutions and improves the spinnability [3]. This additive also extends the solution s storage life. 

Fiber spinning of cellulose carbamate solution usually consists of three steps ... 

Researchers from the Finish company, Neste Oy, discovered their own cellulose process by activating cellulose with liquid ammonia at —35°C [87,88]. They then treated the activated cellulose with urea at 135-145°C which led to the formation of cellulose carbamate with the DS of 0.15 2.0. The polymer can be readily dissolved in diluted caustic soda solution. The main disadvantage of this technology is its relatively high cost. 

The treatment of alkali cellulose with urea in xylene, whieh leads to the formation of cellulose carbamate... 

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