Cellulose trimethylsilylation

Influence of Solvents. Etherification is also considerably affected by the solvent system used (211-217]. The preparation of cellulose trimethylsilyl ether derivative was considerably enhanced by conducting it in a DMSO-PF solution [212]. In a heterogeneous dihydroxypropylation of cellulose with glycidol, the DS cannot exceed the 1.5 level [215]. 

On the other hand, literature data show [16] that different cellulose derivatives which form liquid crystalline solutions in organic solvents may also form cholesteric thermotropic phases in the absence of a solvent—with spontaneous molecular orientation and cholesteric reflection, such as 2-acetoxypropyl cellulose, 2-hydroxypropyl cellulose, the trifluoroacetate ester of hydroxypropyl cellulose, the propanoate ester of hydroxypropyl cellulose, the benzoate ester of hydroxypropyl cellulose, 2-ethoxypropyl cellulose, acetoacetoxypropyl cellulose, trifluoroacetoxypropyl cellulose, the phenylac-etate and 3-phenylpropionate of hydroxypropyl cellulose, phenylacetoxy, 4-methoxy-phenylacetoxy, p-tolylacetoxy cellulose, trimethylsilyl cellulose, trialkyl cellulose, cellulose trialkanoate, the trialkyl ester of (tri-o-carboxymethyl) cellulose, 6-o-a-(l-methylnaphthalene)-2,3-o-pentyl cellulose, etc. Moreover, the suspensions of cellulose crystallites spontaneously form the chiral nematic phase. The formation of mesophase suspension of cellulose crystalHtes varies from one type of cellulose to another, being influenced, in the formation of the chiral nematic phase, by the mineral acid selected... 

Although this article is primarily concerned with gas-liquid chromatography of simple carbohydrates, it is worth noting that certain polysaccharides have been trimethylsilylated. Thus, chlorotrimethyl-silane in pyridine yielded fully trimethylsilylated amylose, cellulose, and pullulan, but failed with dextran and amylopectin.196 Cellulose, amylose, and polyvinyl alcohol have also been trimethylsilylated in molten N-(trimethylsilyl)acetamide.197 As examples of a new class of... 

In a study on the alkaline stability of cellulose, Clayton and Jones188 chromatographed the trimethylsilyl ether of 1-amino-1-deoxy-D-glu-citol, and the retention time of a synthetic aminodisaccharide alditol has been given.487... 

The relationship between structure and paper-chromatographic mobility of aldono-1,4-lactones has been discussed.65 Butanone, saturated with water, is suitable for the preparative separation of lactones on cellulose columns free acids and reducing sugars move very slowly in this system. Separation of aldono-1,4-lactones and of aldonic acids as their O-(trimethylsilyl) derivatives has been accomplished.66 The mass spectra of such derivatives are characteristic, so that it is possible to identify aldonic acids67 and lactones68 by means of combined gas chromatography-mass spectrometry. 

Known bicyclo[4.3.1]enone 15758 was converted into vinylsilane 158 with bis(trimethylsilyl)methyl lithium.55 Diene 158 underwent selective ozonolysis at the cis-olefin under conditions to produce differentially oxidized termini 90 alde-hydo-ester 159 was homologated with a phosphine oxide anion91 to enol 160. Subsequent hydrolysis of 161 provided substrate 162, which after tandem ozonolysis-acidification gave racemic 6,9-desmethyl analogue 155. Unfortunately, initial efforts failed to resolve 155 into its two optical isomers with cellulose triacetate.92 However, the antimalarial activity of racemate 155 is intriguing, as discussed in a later section. 

Figure 12, GLC of tar from pyrolysis of trimethylsilylated cellulose (column 2, 110-275 C at 4 °C/min). Key A, 5-hydroxumethyl 2-furaldehyde B, 14. , 6-dianhydro-a-Thglucopyranose C, 2,3-dihydr0 3, dthydroxyS-methyl- R -pyran-i-one D, unknown , 3y5-dihydroxy-2-methul-4i -pyran-4-one F, unknown G, l,5-anhydro-4-deoxy-D-glycerohex-l-en-3-ulose H and /, unknown /, levoglucosan K, Ifi-anhydro-P-Thglucofuranose L and M, fi-D-glucose N, 3 deoxy-D-erythro-hexosulose and O, O-D-glucosyllevoglw...

The influence of pyrolysis temperature on the qualitative chemical composition of the cellulose pyrolysate can be illustrated by comparing the pyrograms generated at different temperatures. This is shown in Figures 7.2.1, 7.2.2 and 7.2.3, which give the total ion chromatograms (TIC) generated by a GC/MS system for the trimethylsilylated pyrolysate of cellulose obtained at three different temperatures between 450° C and 850° C. 

The chromatographic trace shown in Figure 7.2.1 was obtained from the cellulose pyrolysate generated at 590° C followed by off-line silylation with bis(trimethylsilyl) trifluoroacetamide (BSTFA). 

Figure 7.2.1. Cellulose pyrolysate obtained at 59CP C and trimethylsilylated. The separation was done on a methyl silicone with 5% phenyl silicone type column. 1 1,2-dihydroxyethane, 2 2-hydroxypropionic (lactic) acid, 3 hydroxy acetic (glycolic) acid, 4 turanmethanol, 5 peak from silylation reagents, 6 1,3-dihydroxypropanone, 7 1,4-dioxane-2,5-diol, 8 1,3-dioxolane-4,5-diol, 9 1,3-dihydroxybenzene, 10 2-methyl-1,4-dioxane-2,5-diol, 11 1,4-dihydroxybenzene, 12 3-hydroxy-2-(hydroxymethyl)-2-cyclopenten-1-one, 13 2-hydroxy-5-(hydroxymethyl)-4(H)-pyran-4-one, 14 1,2,3-trihydroxybenzene, 15 internal standard, 16 an anhydrosugar, 17 levoglucosan (1,6-anhydro-p-D-glucopyranose), 18 a monosaccharide, 19 an anhydrosugar, 20 an anhydrosugar, 21 1.6-anhydro-P-D-glucofuranose .

Figure 7.2.2. Cellulose pyrolysate obtained at 850° C and trimethylsilylated. The separation was done on the same column as for 590° C pyrolysis. The numbers correspond to the chemical names indicated for Figure 7.2.1.

In order to identify less volatile compounds, the pyrolysis of cellulose acetate sample (at 590° C) can be followed by an off-line derivatization with bis-(trimethylsilyl)-trifluoroacetamide (BSTFA). Typically the derivatized pyrolysate is analyzed by GC/MS on a non-polar column. The results of this type of analysis (separation on a 60 m DB-5 column 0.32 mm i.d. and 0.25 p film thickness) is shown in Figure 7.3.2 and the peak identification is given in Table 7.3.3. 

Some peak identifications for Figure 7.3.6 found in trimethylsilylated hydroxypropyl methyl cellulose pyrolysate are given in Table 7.3.8. 

BIS(TRIMETHYLSILYL)AMINE (999-97-3) Forms explosive mixture with air (48°F/9°C). Violent reaction with strong oxidizers. Reacts with water, steam, alcohols. Incompatible with aldehydes, nonoxidizing mineral acids, cellulose nitrate, sulfuric acid, nitric acid, organic anhydrides, isocyanates, nitrates. Flow or agitation of substance may generate electrostatic charges due to low conductivity. 

A. Richter and D. Klemm, Regioselective suflation of trimethylsilyl cellulose using different SOs-complexes, Cellulose, 10 (2003) 133-138. 

W. Wagenknecht, I. Nehls, A. Stein, D. Klemm, and B. Philipp, Synthesis and substituent distribution of sodium cellulose sulfates via trimethylsilyl cellulose as intermediate, Acta Polym., 43 (1992) 266-269. 

S. Kohler, T. Liebert, and T. Heinze, Interaction of ionic liquids with polysaccharides. VI. pure cellulose nanoparticles from trimethylsilyl cellulose synthesized in ionic liquids, J. Polym. Set A Polym. Chem., 46 (2008) 4070 080. 

Trimethylsilyl cellulose (TMSC DS= 1.55),p-tolylacetoxy cellulose (TAC DS=0.5-1.8)/CH2Cl2 [63] (also thermotropic)... 

A new procedure described for the determination of cellulase activity is based on incubation of the enzyme with finely divided cellulose at pH 6.9 and determination of the D-glucose and cellobiose liberated as their trimethylsilyl derivatives by g.l.c. The method, although generally applicable, was specifically developed for measurement of cellulase activity in mixed enzyme preparations from sheep rumen contents the coefficient of variation of the assay was 2.4-4.5%. 

Unfortunately, both these modifications are complicated processes to carry out. There is also a negative side effect of using modified cellulose whiskers. It has been shown that modified whisker have less reinforcing effect than unmodified whiskers. Grunert and Winter [74] prepared nanocomposites with a hydrophobic thermoplastic matrix using trimethylsilylated cellulose whiskers. They found that unmodified whiskers showed a better reinforcing performance than the trimethylsilylated whiskers. Similarly, the mechanical properties of nanocomposites containing chemically modified chitin whiskers from crab shell were found to be inferior to the unmodified nanocomposites [75]. 

Very stable silyl ethers form when cellulose is treated with trimethyl chloro-silane or with bis (trimethylsilyl)-acetamide [15] ... 

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