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Energy & Fuels 2000, 14, 734-735
Communications Reaction of N-Methyl-2-pyrrolidinone with Carbon Disulfide Zhimin Zong, Yaoli Peng, Zhihong Qin, Jianzhou Liu, Lin Wu, Xiaohua Wang, Zhigang Liu, Shilu Zhou, and Xianyong Wei* Department of Energy Utilization and Chemical Engineering, China University of Mining and Technology, Xuzhou 221008, Jiangsu, China Received December 17, 1999. Revised Manuscript Received February 11, 2000 Since a carbon disulfide-N-methyl-2-pyrrolidinone (CS2-NMP, 1: 1 v/v) mixture was found by Iino et al. to be an excellent mixed solvent for extraction of some bituminous coals at room temperature,1 it has attracted great attention of many coal chemists.2-5 On the basis of consideration that the mixed solvent may extract some coals more effectively at higher temperatures, we attempted to investigate coal dissolution behavior in the mixed solvent at elevated temperatures. The reaction between CS2 and NMP is undesirable during coal extraction. So, we first investigated thermal interaction between CS2 and NMP. We found unexpectedly that a significant amount of NMP was converted by reacting with CS2 at elevated temperatures. In this communication, we present our preliminary results regarding the reaction of NMP with CS2. CS2 and NMP were commercial reagents and were used without further purification. A prescribed amount of CS2 and 5 mL of NMP were put into a 100 mL stainless steel, magnetically stirred autoclave. After being pressurized with nitrogen to 5 MPa at room temperature, the autoclave was heated to an indicated temperature within 10 min and kept at the temperature for a prescribed period of time. Then the autoclave was immediately cooled to room temperature in an ice-water bath. The reaction mixture was taken out from the autoclave and analyzed by GC (HP 6890), GC/MS (HP 6890/5973), and GC/FTIR (HP 6890/Nicolet IR-560). Only one product from the liquid phase was detected. Figure 1 shows the mass spectrum of the product. The molecular ion M+ at m/z 115 undergoes the CH3-N bond cleavage to afford a fragmental ion at m/z 100 and undergoes ring cleavage to afford fragmental ions at m/z 73 and 42. Similar ring cleavage in the resulting fragmental ion at m/z 100 leads to the formation of the fragmental ions at m/z 58 and 42. The fragmental ion at m/z 87 is afforded by losing -CH2CH2- from M+, whereas the fragmental ion at m/z 82 results from the cleavage of * Author to whom correspondence should be addressed. (1) Iino, M.; Kumagai, J.; Ito, O. J. Fuel Soc. Jpn. 1985, 64, 210-212. (2) Cai, M. F.; Smart, R. B. Energy Fuels 1993, 7, 52-56. (3) Mochida, I.; Kinya, S. Advances in Catalysis; Eley, D. D., Pines, H., Haag, W. O., Eds.; 1994, Academic Press: New York, 1994; Vol. 40, pp 39-80. (4) Chervenick, S. W.; Smart, R. B. Fuel 1995, 74, 241-245. (5) Gao, H.; Nomura, M.; Murata, S.; Artok, L. Energy Fuels 1999, 13, 518-528.
Figure 1. Mass spectrum of the product derived from the reaction of NMP with CS2.
Figure 2. FTIR spectrum of the product derived from the reaction of NMP with CS2.
the CdS and its adjacent C-H bonds in M+. The fragmental ions at m/z 85 and 30 are produced by ring cleavage in M+ followed by hydrogen shift. The product was further identified by its infrared spectrum shown in Figure 2. No absorption bands in the 1775-1685 cm-1 range were observed, indicating no carbonyl group exists in the product. The existence of -CH3 and -CH2- can be seen from their absorption bands at 2970, 2931, 2877, and 1462 cm-1. The absorption band at 1508 cm-1 is attributed to >N-CdS moiety. The absorption bands at 1404, 1223, 1142, and 1088 cm-1 testify to the presence of CH3-NCdS stretching vibrations. Therefore, the product was identified to be N-methylpyrrolidine-2-thione (NMPT), suggesting the oxygen atom in carbonyl of NMP was substituted by a sulfur atom in CS 2 during thermal reaction shown in Scheme 1.
10.1021/ef9902597 CCC: $19.00 © 2000 American Chemical Society Published on Web 04/05/2000
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Energy & Fuels, Vol. 14, No. 3, 2000 735
Scheme 1. Mechanism for NMPT Formation from Thermal Reaction of NMP with CS2
Table 1. Effects of Reaction Temperature, Time, and Volume Ratio of CS2 to NMP on NMPT Formation temperature, °C
time, h
VRa
NMPT yield, %b
180 185 195 210 225 250 220 220 220 225 225 225
3.0 3.0 2.0 2.0 2.0 2.0 1.0 2.0 4.0 2.0 2.0 2.0
2:1 2:1 2:1 2:1 2:1 2:1 2:1 2:1 2:1 1:1 4:1 8:1
0 1.8 29.5 74.3 84.5 86.5 60.4 70.3 88.8 67.7 81.7 14.2
a
Volume ratio of CS2 to NMP. b Based on NMP.
Table 1 shows NMPT yields under different conditions. First, fixing the volume ratio of CS2 to NMP to 2:1, we examined the effects of reaction temperature and time on NMPT yield. NMPT was not detected from the thermal treated mixture heated to 180 °C. In 3 h reaction at 185 °C, only 1.8% of NMP was converted to NMPT. NMPT yield increased with raising reaction temperature, but the increase is not remarkable above 225 °C. In 1 h reaction at 220 °C, more than 60% of NMP was converted to NMPT. NMPT yield steadily increased with reaction time until 4 h reaction. The volume ratio of CS2 to NMP also affected the reaction significantly. NMPT yield increased from 67.7 to 84.5% by increasing the ratio from 1:1 to 2:1, but subsequent increase in the ratio led to the decrease in NMPT yield. The reason for the decrease is not clear.
Under the conditions shown in Table 1, no peaks were found by GC analysis for products other than NMPT and the reaction mixture was observed to be a solution. However, at temperatures higher than 250 °C a significant amount of black solid was observed from the reaction mixture. The solid is not dissolved either in CS2-NMP mixed solvent or in many other solvents and not melted or volatile even at 300 °C in vacuo. It may result from NMPT polymerization, but its detailed structure remains to be investigated. Although the synergic effect of CS2-NMP mixed solvent on coal extraction was found more than 10 years ago,1 its mechanism is still not well understood. According to the above results, we consider that the synergic effect may be related to the π-π interaction between CS2 and NMP, by which NMP reacts with CS2 at high temperatures. Our results also suggest that CS2-NMP mixed solvent is not appropriate for coal extraction at high temperatures because of the reaction between the two compounds. Acknowledgment. This research was financially supported in part by Natural Science Foundation of China (Project No. 29676045), the Fund for Scientific Research (Project No. 97006K) from Open Laboratory of Comprehensive Utilization for Carbon Resources, Dalian University of Technology and Special Fund for National Key Fundamental Research (Project No. G199902210101). EF9902597
