Acetylation of cellulose in LiCl-N,N-dimethylacetamide: first report on the correlation between the reaction efficiency and the aggregation number of dissolved cellulose

Abstract

The acylation of three cellulose samples by acetic anhydride, Ac 2 O, in the solvent system LiCl/ N,N-dimethylacetamide, DMAc (4 h, 110°C), has been revisited in order to investigate the dependence of the reaction efficiency on the structural characteristics of cellulose, and its aggregation in solution. The cellulose samples employed included microcrystalline, MCC; mercerized cotton linters, M-cotton, and mercerized sisal, M-sisal. The reaction efficiency expresses the relationship between the degree of substitution, DS, of the ester obtained, and the molar ratio Ac 2 O/AGU (anhydroglucose unit of the biopolymer); 100% efficiency means obtaining DS = 3 at Ac 2 O/AGU = 3. For all celluloses, the dependence of DS on Ac 2 O/AGU is described by an exponential decay equation: DS = DS o -Ae -[(Ac2O/AGU)/B] ; (A) and (B) are regression coefficients, and DS o is the calculated maximum degree of substitution, achieved under the conditions of each experiment. Values of (B) are clearly dependent on the cellulose employed: B (M-cotton) [ B (M -sisal) [ B (MCC) ; they correlate qualitatively with the degree of polymerization of cellulose, and linearly with the aggregation number, N agg , of the dissolved biopolymer, as calculated from static light scattering measurements: (B) = 1.709 ? 0.034 N agg . To our knowledge, this is the first report on the latter correlation; it shows the importance of the physical state of dissolved cellulose, and serves to explain, in part, the need to use distinct reaction conditions for MCC and fibrous celluloses, in particular Ac 2 O/AGU, time, temperature.

First report on the kinetics of the uncatalyzed esterification of cellulose under homogeneous reaction conditions: a rationale for the effect of carboxylic acid anhydride chain-length on the degree of biopolymer substitution

“…A possible reason for the smaller ratios is that the acylation of CHM and CHD has been carried out under homogenous conditions, where the hydroxyl groups are readily accessible; this is not the case for the OH groups of cellulose under heterogeneous conditions. Additionally, cellulose solutions in LiCl/DMAc-in the Cellulose (2012) 19:199-207 203 concentration employed in the present study-are not molecularly dispersed, but present as aggregates (Ramos et al 2011), whose hydroxyl groups are less accessible than those of the model compounds. This difference in accessibility should result in larger k 2,Prim(OH),MCC /k 2,Sec(OH),MCC , as compared with k 2,Prim(OH),CHM /k 2,Sec(OH),CHD .…”

Effect of the Molecular Structure of Acylating Agents on the Regioselectivity of Cellulosic Hydroxyl Groups in Ionic Liquid

“…In recent decades, with the clear understanding of the structure-property relationships, researchers have applied great effort toward the synthesis of regioselectively acylated cellulose derivatives Xu et al 2012). Their physical, chemical, and biochemical properties are influenced not only by the degree of substitution (DS), but also by the position of the substitution and the distribution of the functional substituent groups in the anhydroglucose units (AGU) (Martin et al 1999;Heinze et al 2003;Xu et al 2011;Ramos et al 2011;Chen et al 2014). However, the control of regiochemistry in the synthesis of cellulose-based materials is one of the most significant scientific challenges.…”

Ésteres de celulose: síntese e posterior preparação de filmes com incorporação de nanopartículas de magnetita

“…O sistema de solvente não derivatizante composto por LiCl e dimetilacetamida (DMAc/LiCl), investigado inicialmente por McCormick et al (1985), mostra um enorme potencial para a dissolução da celulose e para a preparação de uma ampla variedade de derivados, sendo utilizado em larga escala até os dias de hoje (DUPONT, 2003;ASS;FROLLINI, 2006;CIACCO et al, 2008CIACCO et al, , 2010CHADLIA;FAROUK, 2011;RAMOS et al, 2005RAMOS et al, , 2011aRAMOS et al, , 2011bRATANAKAMNUANA et al, 2012;MAHADEVA;NAYAK;KIM et al, 2013;ZHOU et al, 2014). A popularidade do solvente DMAc/LiCl está relacionada a clara vantagem que um método de dissolução direta tem sobre a derivatização por ser mais rápida, fácil e reprodutível (DUPONT, 2003).…”

“…(RAMOS et al, 2005;RAMOS et al, 2011a;RAMOS et al, 2001b;ALMEIDA et al, 2013;MORGADO et al, 2013), onde o presente estudo foi desenvolvido.…”

“…Pode-se observar uma dependência exponencial entre a razão mol anidrido /mol UAG e o GS obtido experimentalmente para os acetatos de celulose de sisal em DMAc/LiCl. Ramos et al (2011a) também mostrou uma dependência exponencial do GS com a razão mol anidrido /mol UAG para as celuloses de sisal, linter e microcristalina, sob as mesmas condições de reação de acetilação (4 h a 110 °C) em DMAc/LiCl.…”