Probing the Physical Properties, Synthesis and Cellulose Dissolution Ability of Dialkyl Phosphate Ionic Liquids

Article abstract of DOI:10.1080/10426507.2014.985824

We report the synthesis, characterization and cellulose dissolution properties of a series of ionic liquids bearing alkyl and hydroxyl-functionalized imidazolium and pyrrolidinium cations, and dialkyl phosphate anions. Ionic liquids that dissolve cellulose have anions that are excellent hydrogen bond acceptors. Based on this study, it is clear that the cation also plays a role. Cellulose dissolution was achieved in the imidazolium ionic liquids but not in the pyrrolidinium ionic liquids. Thermogravimetric analysis results show that most of the ILs are thermally stable up to 240 °C and thus are more suitable solvents for high temperature applications than most organic solvents. Imidazolium ILs are less viscous and slightly more thermally stable than the pyrrolidinium ILs of the same chain length.

Full text of DOI:10.1080/10426507.2014.985824

This article was downloaded by: [Nanyang Technological University]
On: 25 April 2015, At: 13:43
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,
37-41 Mortimer Street, London W1T 3JH, UK
Phosphorus, Sulfur, and Silicon and the Related
Elements
Publication details, including instructions for authors and subscription information:
http://www.tandfonline.com/loi/gpss20
Probing the Physical Properties, Synthesis and
Cellulose Dissolution Ability of Dialkyl Phosphate Ionic
Liquids
a
b
a
a
Sharon I. Lall-Ramnarine , Marie F. Thomas , Mariyam Jalees , Firmause Payen , Samanta
a
b
a
b
b
Boursiquot , Sharon Ramati , Damian Ewko , Nicole V. Zmich & James F. Wishart
a
Department of Chemistry, Queensborough Community College of CUNY, Bayside, NY 11364
Chemistry Department, Brookhaven National Laboratory, Upton, NY 11973
b
Accepted author version posted online: 31 Dec 2014.
Click for updates
To cite this article: Sharon I. Lall-Ramnarine, Marie F. Thomas, Mariyam Jalees, Firmause Payen, Samanta Boursiquot,
Sharon Ramati, Damian Ewko, Nicole V. Zmich & James F. Wishart (2014): Probing the Physical Properties, Synthesis and
Cellulose Dissolution Ability of Dialkyl Phosphate Ionic Liquids, Phosphorus, Sulfur, and Silicon and the Related Elements, DOI:
10.1080/10426507.2014.985824
To link to this article: http://dx.doi.org/10.1080/10426507.2014.985824
Disclaimer: This is a version of an unedited manuscript that has been accepted for publication. As a service
to authors and researchers we are providing this version of the accepted manuscript (AM). Copyediting,
typesetting, and review of the resulting proof will be undertaken on this manuscript before final publication of
the Version of Record (VoR). During production and pre-press, errors may be discovered which could affect the
content, and all legal disclaimers that apply to the journal relate to this version also.
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained
in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no
representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the
Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and
are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and
should be independently verified with primary sources of information. Taylor and Francis shall not be liable for
any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever
or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of
the Content.
This article may be used for research, teaching, and private study purposes. Any substantial or systematic
reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any
form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://
www.tandfonline.com/page/terms-and-conditions

ACCEPTED MANUSCRIPT
Probing the Physical Properties, Synthesis and Cellulose Dissolution Ability of
Dialkyl Phosphate Ionic Liquids
a*
b*
a
Sharon I. LALL-RAMNARINE , Marie F. THOMAS , Mariyam JALEES , Firmause
a
a
b
a
PAYEN , Samanta BOURSIQUOT , Sharon RAMATI , Damian EWKO , Nicole V.
b
b*
ZMICH and James F. WISHART
Department of Chemistry, Queensborough Community College of CUNY, Bayside, NY
1364
Chemistry Department, Brookhaven National Laboratory, Upton, NY 11973
slallramnarine@qcc.cuny.edu; mthomas75@fordham.edu; wishart@bnl.gov
a
1
b
ABSTRACT
We report the synthesis, characterization and cellulose dissolution properties of a series
of ionic liquids bearing alkyl and hydroxyl-functionalized imidazolium and pyrrolidinium
cations, and dialkyl phosphate anions. Ionic liquids that dissolve cellulose have anions
that are excellent hydrogen bond acceptors. Based on this study, it is clear that the
cation also plays a role. Cellulose dissolution was achieved in the imidazolium ionic
liquids but not in the pyrrolidinium ionic liquids. Thermogravimetric analysis results show
that most of the ILs are thermally stable up to 240 °C and thus are more suitable
solvents for high temperature applications than most organic solvents. Imidazolium ILs
are less viscous and slightly more thermally stable than the pyrrolidinium ILs of the
same chain length.
KEYWORDS
Dialkyl phosphate, cellulose, ionic liquid
1
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
INTRODUCTION
Ionic liquids (ILs) are tunable, organic salts that melt below 100 °C. Applications
1a-c
of ILs include their use in batteries and fuel cells and as alternative reaction media.
More importantly they have been shown to dissolve cellulose and facilitate its separation
2,3
from lignin.
The current project focuses on a class of ionic liquids based on
imidazolium, and pyrrolidinium, cations and dialkyl phosphate (DAP) anions. This series
of dialkyl phosphate compounds were initially synthesized to be evaluated for the
dissolution of cellulose as a route to access biofuels. However, not all of the ILs were
suitable for dissolving cellulose. DAP ILs based on imidazolium cations have been
4a,b
4c-e
investigated by others for the dissolution of cellulosic
and lignocellulosic materials
and several were found to dissolve these polymers. The imidazolium DAPs have also
been synthesized and characterized for their physical properties by the groups of
5
4a
Wasserscheid, and Ohno. In addition, imidazolium DAPs have been successfully
6
used for enzyme-catalyzed reactions. The DAPs were shown to be non-denaturing to
proteins, so enzymes used for saccharification (breakdown of cellulose into sugars) can
8
survive in their presence. Further, 1-ethyl-3-methylimidazolium diethyl phosphate (IL 2)
7
has been reported as a potential extraction medium for the desulfurization of fuel oils.
Some imidazolium and pyrrolidinium dialkyl phosphates are now commercially
available. However, there are still structural types of dialkyl phosphates that are
unexplored. This work seeks to explore dialkyl phosphates of diverse structural types
and contribute data on their physical properties to the ionic liquid field. Presented in this
2
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
report are the synthesis and physical properties of dialkyl phosphate ILs, which includes
conductivity, viscosity, density, and thermal stability.
RESULTS AND DISCUSSION
The imidazolium and pyrrolidinium DAPs bearing alkyl and hydroxyl
functionalities were synthesized and characterized for their physical properties (Table
2). Dissolution of cellulose was accomplished only in the imidazolium ILs. IL 2 dissolved
the most cellulose, 14 wt% at 100 ˚C (see Table 1). Up to 24 wt% of microcrystalline
cellulose (MCC) can be dissolved in IL 2 at 130 °C. We were able to dissolve 7 wt% in
IL 1. Published reports indicate cellulose can dissolve in IL 1 at 2 wt% at 30 ºC and 10
1b-c
wt% at 100 ºC (Avicel cellulose used in this case). We were not able to dissolve MCC
in the pyrrolidinium ionic liquids. It is possible that the water content of the pyrrolidinium
ILs may have been too high. If an IL contains too much water, then dissolution will not
occur. The water tolerance for cellulose dissolution is IL dependent.
ILs can dissolve cellulose due to the ability of the anions to interrupt the inter-
and intra-molecular hydrogen bonds found within the polymer. It is thought that the
imidazolium cations may also play role in the dissolution process. The inability of the
pyrrolidinium ILs to dissolve MCC seems to support this idea.
The hygroscopic nature of the dialkyl phosphates lengthened their drying time
and precluded their complete characterization within the time available. The
pyrrolidinium salts were observed to be more viscous than imidazolium salts of the
3
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
same chain length. The hydroxyl-group containing IL 3 is very viscous, which may be
due to additional hydrogen bonding with the dibutyl phosphate (DBP) anion, although
the high viscosity of 1-butyl-3-methylimidazolium DBP (7) shows that the DBP anion
also contributes to higher viscosity.
CONCLUSIONS
Dialkyl phosphate ionic liquids represent a class of ILs that can be prepared
halide-free in one step (except for those bearing functionalized cations). Wasserscheid
5
previously reported the synthesis of the imidazolium DAPs. We prepared these salts
using both conventional bench top procedures as well as microwave-assisted
procedures. It was observed that imidazolium DAP ILs have much better dissolution
properties for cellulose than pyrrolidinium DAP ILs, which are generally more viscous as
8
well. We have also shown through related work that DAP ILs enhance enzyme stability
and are less toxic to fermentative bacteria than ILs such as 1-ethyl-3-methylimidazolium
acetate, which is often used to dissolve cellulose. These results suggest that the DAPs
are suitable media for the pretreatment of lignocellulose and would not impede
enzymatic saccharification into sugars and bacterial fermentation into alcohols or
biofuels
.
EXPERIMENTAL
SYNTHESIS: Functionalized ILs were prepared via 2-step reactions by first reacting the
amines N-methylpyrrolidine or 1-methylimidazole with an alkyl halide containing the
4
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
desired functional group. Next, the functionalized halide salt was reacted with dibutyl
phosphate in ethanol and sodium hydroxide at room temperature. For example, 1-(3-
hydroxypropyl)-3-methylimidazolium chloride was prepared under microwave conditions
(
settings: 40 °C/15 min, 80 °C/20 min, 90 °C/10 min). The halide anion in the resultant
salt was then exchanged for the dibutyl phosphate anion. The diethyl- and dimethyl
phosphate ILs were prepared through a halide-free route by direct reaction of the
amines with the corresponding trialkyl phosphates. For example, N-ethyl-N-
methylpyrrolidinium diethyl phosphate was prepared in the microwave at 120 °C for 20
minutes. C-13, H-1 and P-31 nuclear magnetic resonance spectroscopy was used to
verify the structures. The ILs were characterized for their physical properties including
viscosity, conductivity and thermal profile.
DISSOLUTION OF CELLULOSE: The ability of each IL to dissolve cellulose was tested
by adding 2 weight percent of microcrystalline cellulose (MCC) to the IL. The mixture
was stirred at room temperature and the temperature was gradually increased until the
cellulose dissolved. If the IL was a solid at room temperature, it was melted before
addition of MCC. If MCC dissolved, then more was added and the temperature
increased until it appeared that dissolution would not occur. Dissolution was determined
visually and the weight percent of MCC dissolved was determined based on the mass of
MCC added and the mass of the resulting solution. The cellulose was regenerated by
adding water to the IL solution. The regenerated cellulose was isolated by gravity
filtration. The IL could then be recovered by removal of water by rotary evaporation.
5
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
ACKNOWLEDGEMENTS
The authors thank Alejandra Castaño, Esi Kajno, Kijana Kerr, Tooba Imtiaz,
Bobby Layne, Barbara Mello and Dr. David Grills for assistance with this work. This
work was supported in part by PSC-CUNY Research Awards Program (SLR: PSCREG-
41-1153, TRADA-42-214), the NSF STEP program at QCC (SB and FP), the BNL Office
of Educational Programs (MJ, SR, DE, NVZ), the Louis Stokes Alliance for Minority
participation program at CUNY (SB, FP), (MFT and JFW) and the DOE Office of Basic
Energy Sciences, Division of BNL LDRD award 08-069 Chemical Sciences,
Geosciences, and Biosciences under contract # DE-AC02-98CH10886.
6
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
REFERENCES
1. (a) Wasserscheid, P.; and Welton, T., (Eds.), Ionic Liquids in Synthesis, 2003, Wiley-
VCH, Germany. (b) Armstrong, D.W., He, L., Liu, Y., Anal. Chem. 1999, 71,
3873-3876. (c) Anderson, J.L., Armstrong, D.W., Anal. Chem. 2005, 77, 6463-
6462.
2
. Swatloski, R. P., Spear, S. K., Holbrey, J. D. and Rogers, R. D. J. Am. Chem.
Soc. 2002, 124, 4974-4975.
3
. (a) Holm, J. and Lassi, U.; Ionic Liquids: Applications and Perspectives, Prof.
Alexander Kokorin (Ed.), ISBN: 978-953-307-248-7, InTech (2011), pp 545-560.
(
b) Klein-Marcuschamer, D.; Simmons, B.; and Blanch, H.W.; Biofuels,
Bioproducts and Biorefining, 2011, 5(5): p. 562-569.
4. (a) Fukaya, Y., Hayashi, K., Wada, M., Ohno, H. Green Chem. 2008, 10, 44-46;
(
b) Ohno, H., Fukaya, Y. Chemistry Lett. 2009, 38 (1):2-7; (c) Zakzeski, J.,
Jongerius, A. L., Weckhuysen, B. M. Green Chem. 2010, 12, 1225-1236; (d)
Brandt, A., Hallett, J. P., Leak, D. J., Murphy, R. J., Welton, T. Green Chem.
2010, 12, 672-679; (e) Li, Q., He, Y., Xian, M., Jun, G., Xu, X., Yang, J., Li, L.
Bioresour. Technol. 2009, 100, 3570-3575.
5. Kuhlmann, E., Himmler, S., Giebelhaus, H., Wasserscheid, P., Green Chem.
2
007, 9, 233–242.
. Moniruzzaman, M., Nakashima, K., Kamiya, N., Goto, M., Biochem. Eng. J.,
010, 48, 295-314.
6
2
7
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
7
. Nie, Y., Li, C., and Wang, Z. Ind. Eng. Chem. Res. 2007, 46, 5108-5112
. Thomas, M. F., Li, L. L., Handley-Pendleton, J. M., Van der Lelie, D., Dunn, J.
J., Wishart, J. F., Bioresour. Technol. 2011, 102(24):11200-3.
8
8
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Table 1: Cellulose dissolution properties of the ILs studied
2
H O
Ionic
Weight Temperature
IL name
Content Dissolution
Liquid
%
°C
(
ppm)
1,3-dimethylimdazolium
1
2
167
Yes
Yes
7
100
100
dimethyl phosphate
1
-ethyl-3-methylimidazoium
diethyl phosphate
1636
148
14
1
-(3-hydroxypropyl)-3-
3
4
methylimidazolium dibutyl
phosphate
Yes
9
2
105
95
N-(3-hydroxypropyl)-N-
methylpyrrolidinium dibutyl
phosphate
-
Negligible
N,N-dimethylpyrrolidinium
5
6
-
Negligible
Negligible
2
2
85
94
dimethyl phosphate
N-ethyl-N-methylpyrrolidinium
3276
diethyl phosphate
9
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Table 2. Physical properties of dialkyl phosphate ILs
Melting
point
Glass
Transition
(°C)
Viscosity Density
Water
Content
(ppm)
Ionic
(20 °C)
cP)
363
94
26 °C
5878
(23 °C)
Liquid
(
°C)
(
(g/mL)
5
1
Not Obs.
21
-64
-69
-68
-88
1.26
1.18
1.11
solid
Not Reported
3
2
3
5
6
333
133
806
@
Not Obs.
63
59
@
66 °C
737
Not Obs.
-
-73
-
1.13
1.04
511
5
7
1896
Not Reported
1
0
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
1
1
ACCEPTED MANUSCRIPT