Carbohydrate Polymers 86 (2011) 1395–1402 Contents lists available at ScienceDirect Carbohydrate Polymers jo u rn al hom epa ge: www.elsevier.com/locate/carbpol A convenient solvent system for cellulose dissolution and derivatization: Mechanistic aspects of the acylation of the biopolymer in tetraallylammonium fluoride/dimethyl sulfoxide Romeu Casarano, Haq Nawaz, Shirley Possidonio, Valdinéia C. da Silva, Omar A. El Seoud ∗ Institute of Chemistry, University of São Paulo, P.O.B. 26077, 05513-970 São Paulo, S.P., Brazil a r t i c l e i n f o Article history: Received 8 April 2011 Received in revised form 14 June 2011 Accepted 17 June 2011 Available online 24 June 2011 Keywords: Convenient solvent for cellulose Tetraallylammonium fluoride/DMSO Mechanistic aspects of cellulose acylation Cellulose carboxylic esters Cellulose mixed carboxylic esters Acyl fluoride formation a b s t r a c t This work is concerned with the dissolution of cellulose in tetraallylammonium fluoride/DMSO; the thermal stability of electrolyte solution, and relevant mechanistic aspects of the biopolymer acylation. EMF measurements (fluoride ion-selective electrode) showed that the electrolyte is present as mono- hydrate. 1 H NMR spectroscopy showed that it does not undergo elimination via ylide intermediate, even after heating for 21 h at 70 ◦ C. A solution of TAAF in DMSO readily dissolves microcrystalline and fibrous celluloses (cotton and eucalyptus); the dissolved biopolymer can be derivatized into esters by reaction with carboxylic acid anhydrides. Cellulose ethanoate, butanoate, hexanoate, and mixed esters, ethanoate/butanoate, ethanoate/hexanoate were conveniently synthesized under homogeneous reac- tion conditions (3 h at 60, 80, and 100 ◦ C). Using longer reaction times (12, 18 h) lead to esters of low degree of substitution, due to fluoride-ion mediated ester-hydrolysis. The intermediate formation of acyl fluorides in this medium has been confirmed by FTIR spectroscopy. © 2011 Elsevier Ltd. 1. Introduction There is a growing interest in using biodegradable poly- mers from renewable raw materials instead of the (finite, almost non-biodegradable) petroleum-based counterparts, e.g., polyethylene and polypropylene. Cellulose is the most abun- dant natural raw material, it constitutes about one third of all plant material, and it is the main constituent of the plant cell walls (Imeson, 1999). The strong inter- and intra-molecular hydrogen bonding within the biopolymer mean that it cannot be processed by extrusion; presumably it decomposes before melting. The solutions of this problem include regeneration of cellulose from its solution in, e.g., N-methylmorpholine-N-oxide (the so-called Lyocell process) (Chavan & Patra, 2004; Fink, Weigel, Purz, & Ganster, 2001), or transformation into a solu- ble derivative that can be processed by extrusion into a bath, e.g., cellulose diethanoate/acetone (Rustemeyer, 2004). Cellulose derivatization under (industrial) heterogeneous reaction condi- tions is associated with a series of problems that have been discussed elsewhere (Toyoshima, 1993). In the homogeneous reac- tion scheme, the biopolymer is dissolved in a medium (physical dissolution; no covalent bond formation), then derivatized. The ∗ Corresponding author. Tel.: +55 11 3091 3874; fax: +55 11 3091 3874. E-mail address: elseoud@iq.usp.br (O.A. El Seoud). most important examples of these solvent systems are LiCl/N,N- dimethylacetamide, DMAc, and tetra(1-butyl)ammonium fluoride trihydrate/DMSO (TBAF/DMSO; hereafter, TBAF refers to the tri- hydrate). More recently, ionic liquids, especially imidazole-based ones have gained popularity, albeit their high cost, because of their structural versatility; they are composed only of ions; no additional electrolyte is required (Dawsey & McCormick, 1990; El Seoud, Koschella, Fidale, Dorn, & Heinze, 2007; El Seoud, Marson, Ciacco, & Frollini, 2000; Fidale, Possidonio, & El Seoud, 2009; Fink et al., 2001; Heinze, Lincke, Fenn, & Koschella, 2008; Le Moigne, Spinu, Heinze, & Navard, 2010; Marson & El Seoud, 1999a, 1999b; Rohleder & Heinze, 2010; Striegel, 1997). We focus here on quaternary ammonium fluorides, first reported by Heinze, Dicke, Koschella, Kull, and Koch (2000). Solu- tion of TBAF in DMSO is capable of dissolving celluloses, including those of very high degree of polymerization (DP) (Ass, Frollini, & Heinze, 2004; Ciacco, Liebert, Frollini, & Heinze, 2003). This solvent system has been successfully employed for the derivatization of celluloses by employing variable reaction times, temperatures, and derivatizing agent/cellulose molar ratios (Ass et al., 2004; Heinze et al., 2000). Depending on the experimental conditions TBAF, like the corresponding hydroxide (the F - and OH - ions are isoelec- tronic; Kluge & Weston, 2005), may be susceptible to Hofmann elimination (see Scheme 1) (Albanese, Landini, & Penso, 1998; Sharma & Fry, 1983). 0144-8617 © 2011 Elsevier Ltd. doi:10.1016/j.carbpol.2011.06.051 Open access under the Elsevier OA license. Open access under the Elsevier OA license.