Partial silylation of cellulose with predictible degree of silylation – stoichiometric silylation with hexamethyldisilazane in ammonia

Abstract

SUMMARY: The silylation of cellulose with hexamethyldisilazane (HMDS) in liquid ammonia at elevated temperature has been extended to the synthesis of partly silylated trimethylsilylcellulose. Predictable degrees of silylation (DS) were obtained either with excess ammonia or in a nearly 1 : 1 ratio of NH 3 /AGU (anhydroglucose unit) or with toluene as co-solvent. Complete reaction of the silylating agent allows to adjust the DS directly by simple variation of the ratio of OH groups to trimethylsilyl groups of the silylating agent. With chlorotrimethylsilane more than the stoichiometric amount of silylating agent is required to obtain a desired DS and the work up is more tedious. A simple method to determine the DS of trimethylsilylcellulose based on infrared spectroscopy is proposed. It is applicable to cellulose with a DS greater than 1.3.

Structure analysis of 1,4-glucan derivatives

“…One of them, TMSC1, was prepared by direct silylation to a DS of 1.65 in a heterogeneous reaction with hexamethyldisilazane in liquid ammonia, [79] while TMSC2 was produced via homogeneous desilylation of a persilylated cellulose (DS 1.86). [80] The monomer composition showed significant differences with preferred 2-and 2,6-di-O-trimethylsilylation for the direct modified sample, while the indirect method mainly yielded 2,3,6-, 2,3-and 2-O-substitution, similar to directly and indirectly prepared acetates. The oligomer analysis showed a slight heterogeneity for both samples with no significant differences (Fig.…”

Silylation of hyaluronan to improve hydrophobicity and reactivity for improved processing and derivatization

“…In the paper and textile industry, cellulose was silylated to improve its solubility in organic solvents [16,18], or to produce a melt-processable derivative [19,20]. Various combinations of silylation reagents and solvents, such as trimethylchlorosilane (TMCS) in pyridine [21], N,Obis(trimethylsilyl)acetamide (BSA) in dimethylsulfoxide (DMSO) [22] and hexamethyldisilazane (HMDS) in liquid ammonia [18], have been successfully used to obtain trimethylsilylcelluloses. Compared with cellulose, chitin is more difficult to silylate [16], but b-chitin was completely silylated with a mixture of HMDS and TMCS in pyridine at 70 8C [23].…”

“…However, the DS values calculated from FT-IR are below that obtained with the weight gain method, due to the conflicting presence of the amide -NH vibration at 3500 cm K1 . The DS values from FT-IR need to be calibrated with those from weight gain [18]. A linear correlation between the two DS values is obtained (Fig.…”

Functionalisation of bamboo and sisal fibres cellulose in ionic liquids

“…9,15,16 The silylation of bamboo flour (Fig. 10b) is also confirmed by the characteristic absorption peaks of trimethylsilyl (TMSi-) cellulose at 1250, 840 and 750 cm 21 corresponding to the bending vibrations of OSi-CH 3 , stretching vibrations of Si-OC and OSi-CH 3 respectively.…”

“…2,3 Synthesis of trimethyl silyl cellulose and cellulose acetates in ionic liquids by hexamethyl disilazane and acetic acid were briefly studied and reviewed. [14][15][16][17] Several studies have been done on cellulose functionalisation in different media and reagents. [9][10][11][12] The lack of solubility, need for the activation before reaction and non-polar character of the cellulose, the acetic anhydride and hexamethyldisilazane require special reaction media for the functionalisation.…”