Synthesis and characterization of picryl cellulose

Abstract

2,4,6-Trinitrophenyl cellulose (picryl cellulose) was synthesized by SNAr displacement of chloride from picryl chloride by sodium cellulosate. The cellulosate was prepared insitu from microcrystalline cellulose and sodium methoxide. Depending upon the procedure used, two products with different degrees of picrylation resulted; one contained one picryl ring per ca. 6.5 glucosyl units (PC-6), while the other had ca. one picryl ring per 12 (PC-12). These picryl ethers were characterized by several independent methods: 400-MHz 1H nuclear magnetic resonance spectroscopy of the DMSO-soluble material, temperature-dependent mass spectrometry (ion pyrograms), and differential scanning calorimetry (DSC). The nuclear magnetic resonance spectrum displays peaks in the low field region (8–9.5 ppm) assigned to the picryl rings; these resonances are well separated from those for possible alternative compounds such as unreacted picryl chloride, picric acid, or 2,4,6-trinitroanisole. It is suggested that the various picryl resonances arise primarily from different microenvironments and (or) conformational preferences of the polymer chain rather than from different substitution sites. Substitution at a primary C-6 position of the glucosyl moiety is favoured. DSC shows that while cellulose undergoes an endothermic decomposition between 320 and 350 °C, picryl cellulose exhibits an exothermic decomposition at ca. 230 °C. This exotherm is accompanied by the liberation of picric acid, as confirmed by nuclear magnetic resonance; mass spectral results indicate concurrent chain cleavage to yield smaller polysaccharides. A mechanism for initiation of pyrolytic decomposition is proposed, in which loss of picric acid is accompanied by rupture of a glycosidic bond with concomitant formation of glucosan and enolic end groups on the remaining fragments.