3
alternative DES, but much less rapidly, affording only 67%
conversion under the same reaction conditions (time,
temperature, and concentration) employed with choline
chloride/urea. The reaction could be pushed to completion by
allowing it to run for 12 hours, to afford 90% yields of the
pyrrole product. Apparently, the weaker hydrogen-bonding
activation of glycerol compared to urea results in much weaker
catalysis of the Paal-Knorr reaction.
energy efficient methodology for condensation: an interesting
facet to the classical Perkin reaction.‖ Green Chem. 2011, 13,
2130-2134. Phadtare, S.B.; Shankarling, G.S. ―Halogenation
reactions in biodegradable solvent: Efficient bromination of
substituted 1-aminoanthra-9,10-quinone in deep eutectic solvent
(choline chloride : urea).‖ Green Chem. 2010, 12, 458-462.
Schreiner, P.R. ―Metal-free organocatalysis through explicit
hydrogen bonding interactions.‖ Chem. Soc. Rev. 2003, 32, 289-
296.
7
8
9
P-K rev
For recent reports using Lewis acids, see: Shanthi, G.; Perumal,
P.T. Tetrahedron Lett. 2009, 50, 3959-3962. Azizi, N.; Khajeh-
Amiri, A.; Ghafuri, H. Synlett 2009, 2245-2248. Rahmatpour ,
A. Appl. Organomet. Chem. 2011, 25, 585-590. Pasha, S.K.K.;
Satyanarayana, V. S. V.; Sivakumar, A. Chin. Chem. Lett. 2011,
22, 891-894. Aghapoor, K.; Ebadi-Nia, L.; Mohsenzadeh, F. J.
Organomet. Chem. 2012, 708, 25-30. Teimouri, A.; Chermahini,
A.N. Chin. J. Chem. 2012, 30, 372-376.
Scheme 3. Paal-Knorr in Choline Chloride/Glycerol.
In conclusion, the choline chloride/urea DES exhibits a
number of interesting and useful features as a solvent for organic
synthesis. It is easily prepared from inexpensive, bulk chemicals.
It is non-toxic, non-volatile, and based on potentially
biorenewable materials. In addition, the weak hydrogen-bonding
ability of urea appears to be enhanced due to the high
concentration of urea present in the DES, rendering it useful as
an organocatalytic solvent. We anticipate that it will be of value
in a number of other applications as well and efforts are currently
underway to explore this potential.
10 For recent reports using heterogeneous catalysts, see: Jafari, A.A.;
Amini, S.; Tamaddon, F. J App. Poly. Sci. 2012, 125, 1339-1345.
Rahmatpour, A. Monatshefte Chem. 2012, 143, 491-495. Devi,
A.; Sharma, S.M.L.; Singh, J. Synth. Commun 2012, 42, 1480-
1488. Rahmatpour,A. React. & Funct. Poly. 2011, 71, 80-83.
Yuan, S. Z.; Liu, J.; Xu, L. Chin. Chem. Lett. 2010, 21, 664-668.
Veisi, H. Tetrahedron Lett. 2010, 51, 2109-2114. Yuan, S.; Li,
Z.; Xu, L. J. Het. Chem. 2010, 47, 446-448. He, Y-H.; Wang, G-
Q.; Guan, Z. J. Het. Chem. 2010, 47, 486-489.
11 For a recent report using microwave conditions, see: Wilson,
M.A.; Filzen, G.; Welmaker, G.S Tetrahedron Lett. 2009, 50,
4807-4809.
12 For recent reports using non-traditional solvents, see: Wang, G.;
Guan, Z.; Tang, R. Synth. Commun. 2010, 40, 370-377. He, Y-
H.; Wang, G-Q.; Xu, K-L. Zeitschrift Natur. B. 2011, 66, 191-
196.
13 For recent reports employing these conditions, see: Nieuwland, P.
J.; Segers, R.; Koch, K. Org. Proc. Res. & Devel. 2011, 15, 783-
787. Satyanarayana, V. S. V.; Sivakumar ,A. Ultra Sono. 2011,
18, 917-922. Liguori ,L.; Bjorsvik, H-R. Org. Proc. Res. &
Devel. 2011, 15, 997-1009.
14 Representative Procedure: To a solution of dione (1 mmol) in
choline chloride/urea or choline chloride/glycerol (1 mL) was
added the amine (1 mmol). The reaction was heated to 80 C and
References and notes
1
2
Adams, D.J.; Dyson, P.J.; Tavener, S.J. ―Chemistry in Alternative
Media.‖ Wiley: New York, 2004.
For recent reviews, see: Russ, C.; Koenig, B. Green Chemistry
2012, 14, 2969-2982. Zhang, Q.; Vigier, K. D. O.; Royer, S.;
Jrome, F. Chem. Soc. Rev. 2012, 41, 7108-7146. Francisco, M.;
van den Bruinhorst, A.; Kroon, M.C. Angew. Chem. Int. Ed.
2013, 52, 3074-3085. For other representative reports, see:
Abbott, A.P.; Boothby, D.; Capper, G.; Davies, D.L.; Rasheed,
R.K. ―Deep Eutectic Solvents Formed between Choline Chloride
and Carboxylic Acids: Versatile Alternatives to Ionic Liquids.‖ J.
Am. Chem. Soc. 2004, 126, 9142-9147. Abbott, A.P.; Harris,
R.C.; Ryder, K.S.; D’Agostino, C.; Gladden, L.F.; Mantle, M.D.
―Glycerol eutectics as sustainable solvent systems.‖ Green Chem.
2011 ,13, 82-90. Lu, N.; Chang, W-H.; Tu, W-H.; Li, C-K. ―A
salt made of 4-N,N-dimethylaminopyridine (DMAP) and
saccharin as an efficient recyclable acylation catalyst: a new
bridge between heterogeneous and homogeneous catalysis.‖
Chem. Commun. 2011, 7227-7229. Baoyou, L.; Yuanyuan, W.;
Fuxiang, W. ―Characterization of novel deep eutectic ionic
liquids and their application in green synthesis.‖ Adv. Mat. Res.
2010, 113-114, 1212-1216. Gore, S.; Baskaran, S.; Koenig, B.
―Efficient synthesis of 3,4-dihydropyrimidin-2-ones in low
melting tartaric acid-urea mixtures.‖ Green Chem. 2011, 13,
1009-1013.
stirred for the designated time.
After cooling to room
temperature, the reaction was diluted with water (2 mL) and
extracted with methylene chloride (4 mL). The organic layer was
separated, dried, filtered, and concentrated in vacuo to afford the
pyrrole product in analytically pure form without need for further
purification.
15 All products aforded spectroscopic data consistent with the
assigned structure and matching the literature (where a known
compound). This information can be found in the dupplementary
material.
Supplementary Material
3
4
5
6
Abbott, A.P.; Capper, G.; Davies, D.L.; Rasheed, R.K.;
Tambyrajah, V.
― Novel solvent properties of choline
chloride/urea mixtures.‖ Chem. Commun. 2003, 70-71.
Using prices from the current Aldrich catalog (2012-2014), ACS
reagent-grade acetonitrile is $889 for 20 L, while sufficient
choline chloride an urea to make 20 L would be roughly $1,042.
Abbott, A.P.; Frisch, G.; Hartley, J.; Ryder, K.S. ―Processing of
metals and metal oxides using ionic liquids.‖ Green Chem. 2011,
13, 471-481.
Singh, B.; Lobo, H.; Shankarling, G. ―Selective N-Alkylation of
Aromatic Primary Amines Catalyzed by Bio-catalyst or Deep
Eutectic Solvent.‖ Cat. Lett. 2011, 141, 178-182. Pawar, P.M.;
Jarag, K.J.; Shankarling, G.S. ―Environmentally benign and
Supplementary material that may be helpful in the review
process should be prepared and provided as a separate electronic
file. That file can then be transformed into PDF format and
submitted along with the manuscript and graphic files to the
appropriate editorial office.
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