Cellulose reaction time

High temperature acetylation of cellulose above 50°C produces cellulose acetate from low purity wood pulp cellulose in shorter reaction times. In a high temperature method recently disclosed (102), cellulose reacts with 200—400% acetic anhydride in the presence of <5% acid catalyst at 68—85°C for 3—20 min. After the acid catalyst is neutralized with magnesium acetate, the cellulose acetate is hydrolyzed at 120°C for two hours (103). Several modified catalyst systems have been developed for acetylation of cellulose above 90°C (89,90). 

An 8000-member library of trisamino- and aminooxy-l,3,5-triazines has been prepared by use of highly effective, microwave-assisted nucleophilic substitution of polypropylene (PP) or cellulose membrane-bound monochlorotriazines. The key step relied on the microwave-promoted substitution of the chlorine atom in monochlorotriazines (Scheme 12.7) [35]. Whereas the conventional procedure required relatively harsh conditions such as 80 °C for 5 h or very long reaction times (4 days), all substitution reactions were found to proceed within 6 min, with both amines and solutions of cesium salts of phenols, and use of microwave irradiation in a domestic oven under atmospheric reaction conditions. The reactions were conducted by applying a SPOT-synthesis technique [36] on 18 x 26 cm cellulose membranes leading to a spatially addressed parallel assembly of the desired triazines after cleavage with TFA vapor. This concept was later also extended to other halogenated heterocycles, such as 2,4,6-trichloropyrimidine, 4,6-dichloro-5-nitropyrimidine, and 2,6,8-trichloro-7-methylpurine, and applied to the synthesis of macrocyclic peptidomimetics [37]. 

Fig. 2a-c. Morphology of an empty capsule. Capsules were produced fromo.6% HV alginate/o.6% cellulose sulfate/1.2% polymethylene-co-guanidine/r% calcium chloride. The reaction time was 30 s. The capsule size is approximately r.6o mm while the membrane thickness is 0.033 mm a the wall complex is clearly evident b progression in the membrane thickness 0.073 mm with reaction time r8o s c progression in the membrane thickness o.ro6 mm with reaction time 300 s... 

For the total hydrolysis of polysaccharides, trifluoroacetic acid (TFA) has important advantages over sulfuric acid. The reaction time is short and there is no need for conventional neutralization, as TFA is volatile and can be removed by evaporation. Several methods have been developed, depending on the substance to be hydrolyzed. Soluble saccharides (e.g., polyoses) can be hydrolyzed with diluted TFA, while cellulose, pulp, and wood need treatments with concentrated TFA in homogeneous solution. The presence of lignin impedes the hydrolysis of polysaccharides thus, especially for wood samples, an intensive treatment with TFA is necessary, and correction values have to be considered. Several application examples show that the hydrolysis with TFA enables a rapid quantitative determination of the composition of polysaccharides, pulps, and woods. 

But also a treatment with 100% TFA at high temperature results in a poor hydrolysis of cellulose. After a reaction time of 4 hr at 120°C in a closed tube, about 80% of the charge was precipitated when diluting the TFA. This residue could not be completely hydrolyzed with diluted TFA, though the average degree of polymerization was only about 30. In the electron microscope, samples of cellulose precipitated from TFA solution and treated with diluted TFA show broad crystallike platelets (Figure 5). 

To determine the velocities of the aforementioned Reactions (a), (b), and (c), products will be isolated after short reaction times and their degrees of substitution and polymerization will be determined. By selecting proper experimental conditions, we expect to be able to prepare solutions of cellulose with various desirable DS s and DP s. The preparative possibilities of these rapidly obtainable solutions of cellulose, wood, or other cellulosic substances will be investigated. 

Indeed, the oxidizing effect of a DMSO/PhNCO mixture under standard cellulose carbanilation conditions, i.e. reaction times of 2-3 d at tem-... 

Figure 3. Effect of reaction time on the yield of copolymer in the various vinyl polymer-grafted dialdehydecellulose using a quartz tube. Conditions cellulose (C = 0, 40.5 mmoi/100 g), 0.3 g monomer, 1.5 M H20, (12 — monomer) mL 50°C. Key 0, MA , MMA A, VAc V, AN O, St.

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