Ananda Amarasekara, PhD, Prairie View A&M University
(1). Hydrolysis of D-cellobiose using aqueous 1-(1-propylsulfonic)-3-methylimidazolium chloride and sulfuric acid solutions at 90, 105, and 120 °C
Catalytic activities of 1-(1-propylsulfonic)-3-methylimidazolium chloride was compared with the activities of sulfuric acid of the same molar H+ ion concentration, and according to Oscarson and Izatt’s expression on temperature dependence of the first and second dissociation constants of sulfuric acid in water, it is assumed that H2SO4 completely dissociates to give two H+ ions in the temperature range of the study [1, 2]. These experiments clearly showed that Brönsted acidic ionic liquid PSMIMCl has a higher catalytic activity than sulfuric acid of the same acid strength. Furthermore, catalytic activity enhancement is more significant at higher temperatures, for instance at 120 °C PSMIMCl produced 64.5% glucose yield after 40 min. reaction, whereas H2SO4 produced only 42.2% during the same period, and this is a 52.8% enhancement of catalytic activity due to the alkylimidazolium group attached to the sulfonic acid group. This catalytic activity enhancement may be due to an interaction of alkyl imidazolium group with hydroxyl groups of D-cellobiose. In fact Xiang has observed  similar interactions of 1-ethyl-3-methylimidazolium acetate with D-cellobiose in DMSO using 13C NMR spectroscopy. Additionally, the glucose yield showed slight decrease with longer reaction times, especially at higher temperatures, and this could be due to well known decomposition of glucose to various products like 5-hydroxymethulfurfural, 1,6-anhydroglucose, levulinic acid, and formic acid in the acid medium [4,5].
(2). 1H NMR Studies of D-cellobiose hydrolysis in D2O using1-(1-propylsulfonic)-3-methylimidazolium chloride and sulfuric acid-d2 as catalysts
A series of 1H NMR spectra were recorded during the hydrolysis of D-cellobiose in 0.0321 mol H+/L 1-(1-propylsulfonic)-3-methylimidazolium chloride in D2O medium. D-Cellobiose sample heated in sulfuric acid-d2 medium also used to produce a similar series of spectra. The spectrum recorded at t = 0 h. showed a mixture of a and b anomers of D-cellobiose and only a trace amount of D-glucose. The anomeric composition of D-cellobiose in this mixture was calculated as a : b = 1.00 : 1.60 using the peak area ratio of two doublets at 4.97 and 4.40 ppm spectrum, and this value is compatible with the reported anomeric ratio  of D-cellobiose in water. A gradual increase in D-glucose and the disappearance of D-cellobiose is seen in the series of spectra recorded during the course of the reaction.
h. PSMIMCl H2SO4
a : b a : b
2 1:1.56 1:1.62
6 1:1.65 1:1.58
12 1:1.60 1:1.59
24 1:1.63 1:1.65
Calculated anomeric ratios of D-glucose produced remains approximately constant during the course of the reactions as seen in table1, and this may be due to a rapid equilibration of D-glucose formed. 1H NMR study of ionic liquid failed to reveal any reaction intermediates, and similarly NMR spectra of H2SO4 catalyzed reaction also showed no reaction intermediates. This can be explained by a mechanism involving a slow protonation of glycosidic oxygen in D-cellobiose and fast attack of water on the anomeric carbon, resulting fast hydrolysis D-cellobiose to D-glucose. In conclusion, we have shown that Brönsted acidic ionic liquid1-(1-propylsulfonic)-3-methylimidazolium chloride (PSMIMCl) has a higher catalytic activity than sulfuric acid in the hydrolysis of D-cellobiose to D-glucose in water at 90-120 °C. This catalytic activity enhancement is more significant at higher temperatures, and may be due to an interaction of alkylimidazolium group with D-cellobiose. 1H NMR monitoring of the PSMIMCl as well as sulfuric acid catalyzed D-cellobiose hydrolysis reactions at 90 °C failed to show any intermediates in the reaction, and this is possibly due to fast conversion of any intermediate(s) to product.
 L. Kupiainen, J. Ahola, J. Tanskanen, Comparison of Formic and Sulfuric Acids as
a Glucose Decomposition Catalyst, Ind. Eng. Chem. Res. Vol. 49, pp. 8444-8449,
 J. L. Oscarson, R. M. Izatt, P. R. Brown, Z. Pawlak, S. E. Gillespie, J. J. Christensen,
Thermodynamic quantities for the interaction of SO42- with H+ and Na+ in aqueous solution
from 150 to 320 °C, J. Solution Chem. Vol. 17, pp. 841-863, 1988.
 J. Zhang, H. Zhang, J. Wu, J. Zhang, J. He, J. Xiang, NMR spectroscopic studies of
cellobiose solvation in EmimAc aimed to understand the dissolution mechanism of cellulose
in ionic liquid, Phys. Chem. Chem. Phys. Vol. 12, pp.1941-1947, 2010.
 Q. Xiang, Y. Y. Lee, R. W. Torget, Kinetics of Glucose Decomposition During
Dilute-Acid Hydrolysis of Lignocellulosic Biomass, Appl. Biochem. Biotech. Vol.
115, pp. 1127-1138, 2004.
 X. Huang, H. Duan, S. A. Barringer, Effects of buffer and temperature on formation
of furan, acetic acid and formic acid from carbohydrate model systems, Food Sci.
Technol. Vol. 44, pp.1761-1765, 2011.
 M. U. Roslund, P. Tähtinen, M. Niemitzc, R. Sjöholma, Complete assignments of
the 1H and 13C chemical shifts and JH,H coupling constants in NMR spectra of d-
glucopyranose and all d-glucopyranosyl-d-glucopyranosides, Carbohyd. Res. Vol.
343, pp. 101-112, 2008.