Carbamates, cellulosics

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. 

Additional semipermeable membrane—forming polymers are selected from the group consisting of acetaldehyde dimethyl cellulose acetate, cellulose acetate ethyl carbamate, cellulose dimethylamino acetate, semipermeable polyamides, semipermeable polyurethanes, or semipermeable sulfonated polystyrenes. Semipermeable cross-linked selectively permeable polymers formed by coprecipitation of a polyanion and a polycation also can be used for this purpose.22 23 Other polymer materials such as lightly cross-linked polystyrene derivatives, semipermeable cross-linked poly(sodium styrene sulfonate), and semipermeable poly (vinylbenzyltrimethyl ammonium chloride) may be considered.24,25... 

Cellulose acetate, Plasticized cellulose triacetate, Cellulose acetate methyl carbamate, Cellulose acetate Ethyl- carbamate, Cellulose acetate phthalate, Cellulose acetate succinate... 

Cellulose (0.30 g) and lithium chloride (0.21 g) were dried for 3 hours and then treated with 2.0 ml of dimethylacetamide and swollen at 90°C to 100°C overnight. The mixture was next treated with 6.0 ml of pyridine and 9H-fluorenyl isocyanate (1.3 eq) and reacted for 6 hours. The carbamated cellulose was precipitated, fdtered through a glass filter, and dried, and 1.16 g of cellulose product was isolated. 

The popularity of the poly(saccharide) derivatives as chiral stationary phases is explained by the high success rate in resolving low molecular mass enantiomers. It has been estimated that more than 85% of all diversely structured enantiomers can be separated on poly(saccharide) chiral stationary phases, and of these, about 80% can be separated on just four stationary phases. These are cellulose tris(3,5-dimethylphenyl carbamate), cellulose tris(4-methylbenzoate), amylose tris(3,5-dimethylphenyl carbamate), and amylose tris(l-phenylethyl carbamate). Typically, n-hexane and propan-2-ol or ethanol mixtures are used as the mobile phase [111]. Both the type and concentration of aliphatic alcohols can affect enantioselectivity. Further mobile phase optimization is restricted to solvents compatible with the stationary phase, such as ethers and acetonitrile, as binary or ternary solvent mixtures, but generally not chloroform, dichloromethane, ethyl acetate, or tetrahydrofuran. Small volumes of acidic (e.g. tri-fluoroacetic acid) or basic (n-butylamine, diethylamine) additives may be added to the mobile phase to minimize band broadening and peak tailing [112]. These additives, however, may be difficult to remove from the column by solvent rinsing to restore it to its original condition. 

Cycio Aliphattcs AD,4S,OD AmyloKe Carbamate Cellulose Carbamate... 

The Finnish viscose producer Kemira Oy Saeteri collaborated with Neste Oy on the development of a carbamate derivative route. This system is based on work (89) that showed that the reaction between cellulose and urea gives a derivative easily dissolved in dilute sodium hydroxide ... 

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. 

The potential for use of chiral natural materials such as cellulose for separation of enantiomers has long been recognized, but development of efficient materials occurred relatively recently. Several acylated derivatives of cellulose are effective chiral stationary phases. Benzoate esters and aryl carbamates are particularly useful. These materials are commercially available on a silica support and imder the trademark Chiralcel. Figure 2.4 shows the resolution of y-phenyl-y-butyrolactone with the use of acetylated cellulose as the adsorbent material. 

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]. 

By the treatment of oat spelt xylan with phenyl or tolyl isocyanate in pyridine the fully fimctionahzed corresponding carbamates were prepared [416]. Xylan 3,5-dimethylphenylcarbamate showed higher recognition abihty for chiral drugs compared to that of the same cellulose derivative [417]. 

The first recommended soil method for oxime carbamates is the method of Honing et al. by HPLC/MS. The LOQ of the method, specifically for aldicarb, methomyl, and oxamyl, is 0.05mgkg. Soil (lOg) is Soxhlet extracted for 16h with acetone-dichloromethane (1 1) using double-thickness cellulose extraction thimbles (80 X 22-mm i.d.). Prior to extraction, the Soxhlet system and the thimbles are cleaned for 14 h by refluxing with methanol. The extracts are removed and concentrated nearly to dryness in a rotary evaporator operating at 35 °C evaporation to dryness... 

Large quantities are used as a raw material in the chemical process industry, especially for urea across C02 reaction with NH3 and later dehydration of the formed carbamate. Urea is the product most used as agricultural fertiliser. It is used in feed for ruminants, as carbon cellulose explosives stabiliser in the manufacture of resins and also for thermosetting plastic products, among others. 

Urine Extraction of sample with polydithio-carbamate resin and NaOH filtration on cellulose ester membrane neutralization with NaOH ashing dissolution and heating dilution with distilled water ICP/AES (Method P CAM 8310) 0.005 pg/mL 100 NIOSH 1984... 

In this study, Ali and Aboul-Enein [80] used cellulose tr is (3,5-d ich Ioropheny 1 carbamate) chiral stationary phase for the enantioseparation of miconazole and other clinically used drugs by high performance liquid chromatography. The mobile... 

Among optically active polymers, polysaccharide derivatives are particularly valuable. Polysaccharides such as cellulose and amylose are the most readily available optically active polymers and have stereoregular sequences. Although the chiral recognition abilities of native polysaccharides are not remarkable, they can be readily converted to the esters and carbamates with high chiral recognition abilities. The chiral recognition mechanism of these derivatives has been clarified to some extent. 

Carbamate herbicides, 13 320 Carbamates, 13 108 amine, 16 359 Carbamic acid nitrile, 3 158 Carbamide derivatives, as cellulose solvents, 11 272 Carbamodiimide, 8 158 Carbamoylated gelatin, 12 444 Carbamoyl-methylphosphoryl family, extractants of, 10 789 Carbamyl chlorides, 12 180 Carbanion coordination, 13 656—657 Carbanions, 21 101... 

Spengler and Jumar [90] used a spectrophotometric method and thin layer chromatography to determine carbamate and urea herbicide residues in sediments. The sample is extracted with acetone, the extract is evaporated in vacuo at 40°C and the residue is hydrolysed with sulphuric acid. The solution is made alkaline with 15% aqueous sodium hydroxide and the liberated aniline (or substituted aniline) is steam distilled and collected in hydrochloric acid. The amine is diazotized and coupled with thymol, the solution is cleaned up on a column of MN 2100 cellulose power and the azo-dye is determined spectrophotometrically at 440nm (465nm for the dye derived from 3-chloro- or 3.4-dichloroaniline) with correction for the extinction of a reagent blank. 

Carbamate derivatives (Table 1) of cellulose, chitin, amylose, amylopectin, and dextran were prepared using the isocyanates described in Part A of the Experimental Section. Amylose, amylopectin, dextran, and cellulose were obtained from Polysciences, Inc. and used without further purification. Chitin, obtained from Eastman Kodak, was decalcified and deproteinated by the method reported by Haye r prior to use. 

In a typical experiment the isocyanate (0.006 moles) was reacted with 1.5 g of the polysaccharide in 150 ml of a 5% LiCl/ N,N-dimethylacetamide solution at 90°C under nitrogen for two hours. The appearance of a strong infrared absorbance at 1705 cm l was an indication of carbamate formation. The derivatized polymer was isolated as a white powder by precipitation of the reaction solution into a nonsolvent such as methanol. Alternatively thin films were cast directly from solution the lithium salt could be removed by rinsing with acetone. Figure 1 illustrates the reaction of cellulose with phenyl isocyanate. 

Preweighed 1.0 mg samples of each polysaccharide carbamate derivative were submerged in aqueous solutions at three pH values 3.1 7.0 and 11.3. Three milliliter aliquots were withdrawn at periodic intervals and analyzed by ultraviolet spectroscopy. Typical results are shown in Figures 3 and 4 for pendant hydrolysis rates of carbamate derivatives of cellulose and chitin respectively as a function of pH. 

Table I lists physical data for a number of the carbamate and ester derivatives of cellulose, chitin, amylose, amylopectin, and dextran synthesized as described in the Experimental Section. The solubility of the polysaccharide starting materials as well as that of the produced derivatives allows for macromolecular characterization through techniques including UV, NMR, IR, high pressure liquid chromatography, etc.

Figures 3 and 4 illustrate typical rates of hydrolysis for carbamate derivatives of cellulose and chitin. The rates of release at a pH value 11.3 were considerably higher in both systems than at pH values of 3.1 and 7.0. After seven days in the basic medium the cellulose derivative had delivered 27.3 percent of the available aniline. In the acidic medium and neutral medium 15.6 and 10.6 percent were delivered. After seven days the chitin derivative delivered 27.7, 10.0, and 9.5 percent of the available p-methylaniline in the basic, acidic, and neutral media, respectively.

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