- Email: [email protected]
(Solid + liquid) equilibria and solid compound formation in (N-methyl-2-pyrrolidinone + benzene, or toluene, or 1,3,5-trimethylbenzene, or ethylbenzene, or chlorobenzene, or 1,2-dichlorobenzene, or 1,2,4-trichlorobenzene, or 1,1,1-trichloroethane, or dichloromethane)
J. Chem. Thermodynamics 2000, 32, 1635–1645 doi:10.1006/jcht.2000.0703 Available online at http://www.idealibrary.com on
(Solid + liquid) equilibria and solid compound formation in (N-methyl-2-pyrrolidinone + benzene, or toluene, or 1,3,5-trimethylbenzene, or ethylbenzene, or chlorobenzene, or 1,2-dichlorobenzene, or 1,2,4-trichlorobenzene, or 1,1,1-trichloroethane, or dichloromethane) a ´ Urszula Domanska
Department of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland
and Trevor M. Letcher School of Pure and Applied Chemistry, University of Natal-Durban, Private Bag X10, Dalbridge 4014, Republic of South Africa
(Solid + liquid) phase diagrams have been determined for (N -methyl-2-pyrrolidinone + benzene, or toluene, or 1,3,5-trimethylbenzene, or ethylbenzene, or chlorobenzene, or 1,2dichlorobenzene, or 1,2,4-trichlorobenzene, or 1,1,1-trichloroethane, or dichloromethane). Solid addition compounds form with the empirical formulae: {(C5 H9 NO)2 · C6 H6 }, (C5 H9 NO · 2ClC6 H5 ), (C5 H6 NO · Cl2 C6 H4 ), (2C5 H9 NO · Cl3 C6 H3 ). All are congruently melting compounds. Compound formation is attributed to a charge-transfer interaction with the benzene, or chlorobenzene, or 1,2-dichlorobenzene, or 1,2,4-trichlorobenzene acting as electron acceptors and the nitrogen, or oxygen in N -methyl-2-pyrrolidinone c 2000 Academic Press acting as electron donors. KEYWORDS: s.l.e.; NMP; benzene; toluene; 1,1,1-trichloroethane; dichloromethane; congruently melting compounds
1. Introduction N -methyl-2-pyrrolidinone (NMP) is an aprotic and a strongly dipolar substance and has the potential for use in solvent extraction processes for separating polar substances from non-polar ones.(1) (Solid + liquid) phase diagrams have been reported for (NMP + tetrachloromethane,(2) or trichloromethane,(3) or diacetylene,(4) or m-, p-, o-cresol,(5–7) a To whom correspondence should be addressed (E-mail: [email protected]).
0021–9614/00/121635 + 11 $35.00/0
c 2000 Academic Press
1636
U. Doma´nska and T. M. Letcher TABLE 1. Density ρ and refractive index n D of the pure components at T = 298.15 K ρ/kg · dm−3
Component
nD
Expt
Reference 11
Expt
C5 H9 NO
1.02800
1.02790¸
1.46862
1.4680
C6 H 6
0.87367
0.87370¸
1.49790
1.49792
CH3 C6 H5
0.86211
0.86231¸
1.49410
1.49413
(CH3 )3 C6 H3
0.86108
0.86111¸
1.49678
1.49684
C2 H 5 C6 H 5
0.86260
0.86264¸
1.49345
1.49320
ClC6 H5
1.10075
1.10090¸
1.52480
1.52481a¸
1.34250
1.3410b
1.55152
1.5509a,b
Cl3 C6 H3
1.45365
1.4540b
1.57260
1.5710a,b
C2 H3 Cl3
1.32907
1.32928¸
1.43602
1.4359
CH2 Cl2
1.31680
1.31678¸
1.42110
1.42115
Cl2 C6 H4
Reference 11
a At T = 293.15 K; b from reference 12.
275
T/K
265
255
245
235
0
0.2
0.4
0.6
0.8
1
x FIGURE 1. (Solid + liquid) phase diagram for {xC5 H9 NO + (1 − x)C6 H6 }; —, calculated values using equation (1).
or 2,5-dimethylphenol,(8) or 3,4-dimethylphenol).(9) The molecular addition compounds (m-, p-, o-cresol; 2,5-dimethylphenol) melting congruently or incongruently have been reported. The authors attributed the compound formation to a charge-transfer interac-
(Solid + liquid) equilibria for (NMP + an organic solvent)
1637
TABLE 2. (Solid + liquid) phase equilibria: T denotes the melting temperature, δT is the deviation of the experimental temperature from the temperature calculated from equation (1) and x is the mole fraction of NMP x
T /K
δT /K
x
T /K
δT /K
0 0.0214 0.0651
278.70 277.95 275.85
0.00 0.22 0.30
xC5 H9 NO + (1 − x)C6 H6 0.4307 246.95 0.02 0.4514 244.55 −0.21 0.4712 242.85a 0.02 to 0.05b
0.6682 0.6788 0.7056
246.75 246.45 246.35
0.13 −0.15 0.08
0.1133 0.1622
272.65 269.85
−0.18 0.10
0.4814 0.5097
243.15 243.95
−0.02 0.06
0.7401 0.7633
244.95 243.25
−0.06 −0.17
0.2450 0.2075 0.2826 0.3149
263.65 266.85 260.65 257.85
−0.13 0.25 −0.10 −0.15
0.5273 0.5273 0.5540 0.5825
244.45 236.45c 244.95 245.30
0.14 0.03 −0.22
0.7780 0.7851 0.8203 0.8560
242.15a 243.55 244.55 245.65
0.14 to 0.55b 0.56 0.14 −0.16
0.3507 0.3785 0.3995
254.75 252.05 250.25
−0.02 −0.10 0.15
0.6109 0.6319 0.6576
245.95 246.35 246.75
−0.10 −0.01 0.16
0.9023 0.9388 0.9671
247.53 248.65 249.55
0.03 −0.05 0.02
0.6660
246.65d
1
250.40
0.00
0.20 0.10 0.14
x
T /K
δT /K
0.03
xC5 H9 NO + (1 − x)CH3 C6 H5 0.4430 0.4959 0.5231
218.15 222.35 224.55
−0.42 0.12 0.36
0.6570 0.6870 0.7210
233.25 235.35 237.55
−0.34 −0.12 0.07
0.8664 0.9134 0.9512
244.75 246.65 248.35
0.5556
226.75
0.19
0.7606
239.45
−0.17
0.9729
249.35
0.13
0.5979
229.85
0.26
0.7883
240.75
−0.26
0.9893
249.90
−0.12
0.6303
231.75
−0.07
0.8238
242.75
0.08
1
250.40
0.00
0 0.0254 0.0676 0.0976
228.40 224.85 221.35 219.35
0.00 −0.66 −0.12 0.18
0.2958 0.3518 0.4050 0.4492
224.35 227.25 229.65 231.35
−0.14 −0.58 −0.63 −0.55
0.7425 0.7685 0.8196 0.8549
242.85 243.55 245.45 246.35
−0.12 −0.44 −0.21 −0.18
0.1395 0.1604 0.1750 0.1853 0.2056 0.2158 0.2528
217.15 215.95 215.15a 216.75 218.75 220.75 222.65
0.39 0.04 −0.30 to 0.53b −0.53 0.38 1.75 1.13
0.4959 0.5248 0.5574 0.5887 0.6186 0.6374 0.7153
233.35 234.15 235.95 237.15 238.05 238.75 241.65
−0.06 −0.18 0.53 0.60 0.34 0.27 −0.19
0.8850 0.9085 0.9405 0.9609 0.9797 1
247.15 247.55 248.75 249.15 249.65 250.40
0.02 −0.01 0.51 0.31 0.03 0.00
0.3377 0.3665 0.3970
221.70 215.15 217.15
0.00 −0.44 −0.01
0.8012 0.8418 0.8805
241.75 243.75 245.45
0.03 0.28 0.37
xC5 H9 NO + (1 − x)(CH3 )3 C6 H3
xC5 H9 NO + (1 − x)C2 H5 C6 H5 0.5428 227.45 0.68 0.6335 232.85 0.01 0.6813 235.45 −0.26
1638
U. Doma´nska and T. M. Letcher TABLE 2—continued
x
T /K
δT /K
x
T /K
δT /K
x
T /K
δT /K
0.4528
220.65
0.4943
223.55
0.07
0.7126
237.05
−0.39
0.9285
247.55
0.39
0.16
0.7396
238.35
−0.49
0.9761
249.55
0.5183
0.07
225.25
0.19
0.7618
239.65
−0.27
1
250.40
0.00
0
228.05
0.00
0.3305
208.85
0.30
0.5344
215.85
−0.23
0.0299
226.05
0.07
0.3330
209.15c
0.51
0.5802
220.65
0.32
0.0814
222.35
−0.11
0.3532
209.05
−0.15
0.6271
225.35
0.67
0.1259
219.05
−0.40
0.4018
208.55
−0.50
0.6702
229.15
0.25
0.1676
216.95
0.28
0.4324
207.95
0.41
0.7565
235.35
−2.27
0.2459
211.75
0.23
0.4480
206.15a
0.2995
208.15
0.09
0.4540
207.55
0.3100
207.15a
0.4722
209.45
0.02
0.3232
208.35
0.08
0.5020
212.15
−0.68
0
256.15
0.00
0.4214
227.15
0.0333
254.15
0.16
0.4443
224.35
0.0781
251.15
−0.11
0.4829
219.95
0.1307
248.15
0.07
0.4880
218.65a
xC5 H9 NO + (1 − x)ClC6 H5
−0.24 to 0.53b
−0.12 to 0.11b 0.46
0.8167
244.95
2.05
0.9208
247.15
−0.75
0.9586
248.95
0.20
1
250.40
0.00
0.38
0.6156
222.85
−0.05
0.00
0.6566
226.95
0.21
0.29
0.6884
229.50
−0.16 −0.22
xC5 H9 NO + (1 − x)Cl2 C6 H4
−0.3 to 0.07b
0.7247
232.65
0.26
0.7949
238.95
0.36
219.95
−0.01
0.8597
242.95
−0.19
0.5404
219.85
−0.19
0.8945
245.35
0.09
0.5559
219.75
−0.07
0.9335
247.35
−0.02
−0.22
0.5750
219.15a
0.07 to 0.05b
229.35
−0.40
0.5952
220.95
−0.04
0
289.65
0.00
0.5201
261.95
0.0452
287.35
−0.27
0.5417
0.0864
285.35
−0.45
0.5665
0.1296
283.75
−0.15
0.5720
258.15a
0.8203
249.35
0.05
0.1687
282.05
−0.11
0.5904
259.35
0.15
0.8531
246.45
0.00
0.1965
280.95
0.05
0.6194
259.95
−0.27
0.8651
245.35
−0.07
0.2126
280.55
0.39
0.6389
260.35
−0.11
0.8800
244.15a
0.04 to 0.42b
0.3043
276.15
0.47
0.6660
260.85
0.67
0.8969
245.45
0.4337
267.95
−0.24
0.6772
259.85
0.00
0.9345
247.65
0.53
0.4968
263.55
−0.28
0.6970
258.45
−0.56
0.9858
249.85
0.01
1
250.40
0.00
0.1964
243.75
−0.22
0.5200
220.15d
0.2326
241.70
0.10
0.5239
0.2677
239.25
0.04
0.3077
236.65
0.30
0.3616
231.95
0.3898
0.9697
248.95
−0.12
1
250.40
0.00
−0.13
0.7280
257.15
0.05
260.25
−0.13
0.7544
255.25
0.19
258.45
0.12
0.7765
253.05
−0.12
xC5 H9 NO + (1 − x)Cl3 C6 H3
0.29 to 0.03b
0.13
(Solid + liquid) equilibria for (NMP + an organic solvent)
1639
TABLE 2—continued x
T /K
δT /K
x
T /K
δT /K
0 0.0210 0.0388
233.85 229.95 227.25
0.00 0.02 0.03
0.5665 0.5889 0.6438
227.15 229.05 232.35
−0.02 0.20 −0.27
0.0605 0.0680 0.1002
224.55 224.05e 223.55
−0.11 0.08 to 0.18b 0.04
0.3582 0.3700 0.3895
208.45 207.65a 210.15
0.05 0.01 to 0.11b 0.30
0.7580 0.8034 0.8402
239.45 241.95 243.75
0.04 0.09 0.00
0.1367 0.1553 0.2008 0.2330
222.15 221.45 219.05 216.95
−0.04 0.10 0.18 0.08
0.4010 0.4402 0.4549 0.4749
210.65 215.75 216.95 218.95
−0.54 0.18 −0.17 −0.20
0.8741 0.9149 0.9436 0.9664
245.35 247.25 248.35 249.25
−0.04 0.02 −0.05 0.00
0.2442 0.2529
215.95 215.55
−0.18 0.00
0.4881 0.5123
220.65 222.95
0.22 0.28
0.9803 1
249.75 250.40
0.01 0.00
0.2757
213.95
−0.05
0.5418
225.05
−0.15
0.5703 0.6224
207.80 216.55
−0.11 0.23
0.9368 0.9521
246.55 247.55
0.51 0.50
0.6790
224.05
−0.07
0.8712
241.85
0.16
0.9731
248.85
0.39
0.7231 0.7797
229.25 234.40
0.01 −0.31
0.8977 0.9186
243.85 245.05
0.38 −1.77
0.9893 1
249.55 250.40
−0.03 0.00
x
T /K
δT /K
xC5 H9 NO + (1 − x)C2 H3 Cl3 0.2983 212.35 −0.10 0.3273 210.55 0.09 0.3490 208.95 −0.05
xC5 H9 NO + (1 − x)CH2 Cl2 0.8201 238.15 0.14 0.8475 239.95 −0.09
a Eutectic composition and temperature. b The two δT values are the deviations from the intersecting equations at the invariant point. The deviation from the equation for the lower x region is given first. c Metastable melting temperature. d Composition and melting temperature of congruently melting molecular addition compound. e (Solid + solid) phase transition composition and temperature.
tion. In this paper we present similar measurements for (N -methyl-2-pyrrolidinone + benzene, or toluene, or 1,3,5-trimethylbenzene, or ethylbenzene, or chlorobenzene, or 1,2dichlorobenzene, or 1,2,4-trichlorobenzene, or 1,1,1-trichloroethane, or dichloromethane). Chlorohydrocarbons include chlorine and hydrogen atoms which can interact with NMP.
2. Experimental The origin of the chemicals and their mass fraction purities were: NMP (Aldrich Chemical Co., 0.995), benzene (Aldrich Chemical Co., 0.999), toluene (Aldrich Chemical Co., 0.995), 1,3,5-trimethylbenzene (Aldrich Chemical Co., 0.98), ethylbenzene (Aldrich Chemical Co., 0.99), chlorobenzene, 1,2-dichlorobenzene and 1,2,4-trichlorobenzene (Janssen Chimica, 0.98), 1,1,1-trichloroethane (Koch-Light Laboratories Ltd., 0.98), dichloromethane (Aldrich Chemical Co., 0.998). NMP, benzene and toluene were fractionally distilled under atmospheric pressure after prolonged reflux over different drying reagents. All liquids were stored over freshly activated molecular sieves of the type
1640
U. Doma´nska and T. M. Letcher TABLE 3. Summary of invariant points x
T /K
Eutectic
0.4712
242.85
Compound (2C5 H9 NO · C6 H6 )a
0.666
246.65
Eutectic
0.778
242.15
Type of invariant point xC5 H9 NO + (1 − x)C6 H6
xC5 H9 NO + (1 − x)(CH3 )3 C6 H3 Eutectic
0.175
215.15
xC5 H9 NO + (1 − x)ClC6 H5 Eutectic
0.310
207.15
Compound (C5 H9 NO · 2ClC6 H5 )a
0.333
209.15
Eutectic
0.448
206.15
xC5 H9 NO + (1 − x)Cl2 C6 H4 Eutectic
0.488
218.65
Compound (C5 H9 NO · Cl2 C6 H4 )a
0.520
220.15
Eutectic
0.575
219.15
xC5 H9 NO + (1 − x)Cl3 C6 H3 Eutectic
0.572
258.15
Compound (2C5 H9 NO · Cl3 C6 H3 )a
0.666
260.85
Eutectic
0.880
244.15
xC5 H9 NO + (1 − x)C2 H3 Cl3 Phase transition
0.068
224.05
Eutectic
0.370
207.65
a Melting temperature of congruently melting molecular addition compound.
0.4 nm (Union Carbide) and were analysed by g.l.c. An analysis, using the Karl–Fisher technique, showed that the water mole fraction content in each of the solvents x (H2 O) was <3 · 10−3 . The densities of all the chemicals were measured, using an Anton Paar DMA 602 vibrating-tube densimeter. The densities of NMP and the other solvents are in satisfactory agreement with the literature values quoted in references 10 and 11, respectively. The characteristic properties of the pure substances are presented in table 1. NMP was stored in a dark bottle in a refrigerator to reduce decomposition. The (solid + liquid) equilibrium temperatures were determined using a dynamic method.(13) Appropriate mixtures of solute and solvent were heated very slowly (less than 1.1 · 10−3 K · s−1 near the equilibrium temperature) with continuous stirring inside a Pyrex glass cell which was placed in a glass thermostat filled with acetone and dry ice. The temperature at which the last crystals disappeared was taken as the temperature of the (solid + liquid) equilibrium. The crystal disappearance temperatures, detected visually, were
(Solid + liquid) equilibria for (NMP + an organic solvent)
1641
TABLE 4. Coefficients Ai for the fitting equation (1). Columns 1 and 2 give the range of x over which the equation applies: σ is the standard deviation of T xmin
x∗
xmax
T∗
A1
A2
A3
A4
A5
A6
σ a /K
xC5 H9 NO + (1 − x)C6 H6 0
0.4712 0
278.70 −0.15770 −0.24832
0.15
0.4712 0.778
0.666 246.65 −0.48342
1.49827
−1.16217
0.85
0.778 1
1
250.40 −0.47093
0.84767
−0.37681
0.26
0.4430 1
1
250.40 −1.35474
xC5 H9 NO + (1 − x)CH3 C6 H5 3.84435
1.34306
−3.83196
0.32
xC5 H9 NO + (1 − x)(CH3 )3 C6 H3 0
0.175 0
0.175 1
1
228.40 −0.52766 250.40 −2.48722
1.16431 15.9937
0.32 66.1171
−45.3545
−47.9814
13.7140
4.17
xC5 H9 NO + (1 − x)C2 H5 C6 H5 0.3377 1
1
250.40 −1.33658
0.310 0
228.05 −0.30447
3.87382
1.43196
−3.96752
0.72
xC5 H9 NO + (1 − x)ClC6 H5 0
0.310 0.448
0.333 209.15
0.448 1
1
0.03942
0.16
0.02297 −0.09620
250.40 −8.45208
0.51
53.5850 −143.861
196.345
−133.429
35.8113
4.52
xC5 H9 NO + (1 − x)Cl2 C6 H4 0
0.488 0
256.15 −0.26305
0.37999
−2.19546
0.488
0.575 0.488 220.15 −1.50943
5.62093
−5.23579
0.575
1
1
250.40 −1.49162
3.69636
−3.07410
0
0.572 0
289.65 −0.15782
5.10263
0.29
−5.11442
0.05 0.86903
0.13
xC5 H9 NO + (1 − x)Cl3 C6 H3 0.572 0.880
0.666 260.85
0.880
1
1
250.40 −0.22782
0
0.068 0
233.85 −0.87639
0.06307
10.2535 −82.5808
0.33
−0.21440 253.568
−374.951
268.927
0.22881
−75.3656
0.30 0.21
xC5 H9 NO + (1 − x)C2 H3 Cl3 0.068 0.370
0.068 224.05
0.370 1
1
250.40 −3.31737
0.5703 1
1
250.40 −4.08183
3.75300
0.09795 −1.37064 16.1813
0.01 1.54327 −34.1965
0.06 37.7962
−21.2678
4.80412 0.30
xC5 H9 NO + (1 − x)CH2 Cl2 14.4639
−19.7531
12.1550
−2.78414
1.65
h i1/2 2 a Given by the equation σ = Pn {(T , here n is the number of experimental points, and expt − Tcalc )i /(n − k)} i=1
k is the number of parameters.
1642
U. Doma´nska and T. M. Letcher
260
250
T/K
240
230
220
210
0
0.2
0.4
0.6
0.8
1
x
◦
FIGURE 2. (Solid + liquid) phase diagram for , {xC5 H9 NO + (1 − x)CH3 C6 H5 }; , {xC5 H9 NO + (1 − x)C2 H5 C6 H5 }; , {xC5 H9 NO + (1 − x)(CH3 )3 C6 H3 }; —, calculated values using equation (1).
250
T/K
240 230 220 210 200 0
0.2
0.4
0.6
0.8
1
x
FIGURE 3. (Solid + liquid) phase diagram for {xC5 H9 NO + (1 − x)ClC6 H5 }; —, calculated values using equation (1).
measured with a platinum resistance thermometer, Gallenkamp Autotherm II, produced by Sanyo Gallenkamp plc, Leicester, U.K. The thermometer was calibrated on ITS-90. The accuracy of the temperature measurements was judged to be ±0.001 K and the
(Solid + liquid) equilibria for (NMP + an organic solvent)
1643
255
T/ K
245
235
225
215
0
0.2
0.4
0.6
0.8
1
x FIGURE 4. (Solid + liquid) phase diagram for {xC5 H9 NO + (1 − x)Cl2 C6 H4 }; —, calculated values using equation (1).
290
280
T/K
270
260
250 240 0
0.2
0.4
0.6
0.8
1
x
FIGURE 5. (Solid + liquid) phase diagram for {xC5 H9 NO + (1 − x)Cl3 C6 H3 }; —, calculated values using equation (1).
reproducibility of the equilibrium temperatures to be ±0.1 K. Mixtures were prepared by mass and the error in the mole fraction was estimated to be less than ±5 · 10−4 .
1644
U. Doma´nska and T. M. Letcher 290
280
T/K
270
260
250
240 0
0.2
0.4
0.6
0.8
1
x
FIGURE 6. (Solid + liquid) phase diagram for , {xC5 H9 NO + (1 − x)C2 H3 Cl3 };
◦, {xC5 H9 NO + (1 − x)CH2 Cl2 }; —, calculated values using equation (1). 3. Results and discussion
Experimental results were obtained over the entire composition range for the six investigated mixtures. For toluene, ethylbenzene and dichloromethane the melting temperatures were lower than 220 K and a different experimental technique, namely d.s.c. calorimetry, was required to obtained the second liquidus curve. The (solid + liquid) equilibrium temperatures are recorded in table 2 and the invariant temperatures in table 3. The phase diagrams are shown in figures 1 to 6. The melting temperatures T were fitted using a leastsquares method to the equation:(14) ) ( n X T = T∗ 1 + a j (x − x ∗ ) j , (1) j=1
x∗
T∗
where and were taken as the stoichiometric composition and melting temperature for the congruently melting compounds and as the melting temperature Tm of pure substances (x ∗ for pure substances is the value of x at Tm ). Excellent fits were obtained for all the mixtures except for {xC5 H9 NO + (1 − x) (CH3 )3 C6 H3 } at x > 0.175 and for {xC5 H9 NO + (1 − x)CH2 Cl2 } at x > 0.5. The parameters of the fitting equation together with the standard deviations (σ ) are given in table 4. Deviations δT = {T − T (calc)} of the individual data points from the fitting equations are given in table 2. The curves in all the six figures were drawn using the fitting equations. It is evident from the phase diagrams that congruently melting solid addition compounds form in four of the mixtures with the empirical formulae: (2C5 H9 NO · C6 H6 ); (C5 H9 NO · 2ClC6 H5 ); (C5 H9 NO · Cl2 C6 H4 ); and (2C5 H9 NO · Cl3 C6 H3 ). For the mixture with 1,1,1-trichloroethane the large inflection in the liquidus curve at x = 0.068 and
(Solid + liquid) equilibria for (NMP + an organic solvent)
1645
T = 224.05 K indicates a (solid + solid) phase transition, characteristic of the pure compound. The eutectic compositions were obtained from the intersection of the melting temperature lines. It is interesting to note that addition compounds contain two, or three cyclic molecules. It is possible that two kinds of charge-transfer interactions contribute to the bonding in these mixtures: one involving the carbonyl oxygen and the other involving electron pair donation from the nitrogen group. An increase in the number of chlorine atoms on the benzene ring from one to three, results in a higher concentration of NMP in solid compound formation x ∗ = 0.333, x ∗ = 0.488 and x ∗ = 0.666 for chloro-, dichloro- and trichlorobenzene, respectively (see figures 3 to 5). On the other hand, replacing the chlorine atoms on the benzene ring by methyl, ethyl, or three methyl groups results in no solid compound formation (see figure 2). Both a congruent 1 : 1 and an incongruent melting compound have been observed by other workers in {xC5 H9 NO + (1 − x)CCl4 }(2) and in {xC5 H9 NO + (1 − x)CHCl3 }.(3) No similar solid compound occurs in the mixture of 1,1,1-trichloroethane and possibly in dichloromethane, suggesting that the chlorine atoms are weaker electron acceptors in dichloromethane than in trichloromethane and in tetrachloromethane. The authors wish to thank the University of Natal and F.R.D. (S. Africa) for financial aid. REFERENCES 1. Letcher, T. M.; Naicker, P. K. J. Chem. Eng. Data 1998, 43, 1034–1038. 2. Che, G. Q.; Ott, J. B.; Goates, J. R. J. Chem. Thermodynamics 1986, 18, 323–330. 3. Che, G. Q.; Huang, Z. Q.; Li, D.; Gu, X. L.; Luo, S. L. J. Chem. Thermodynamics 1996, 28, 159–165. 4. Szahowa, S. F.; Ksodjejewa, S. M.; Seriejewa, L. I. Zh. Phys. Khim. 1971, 45, 330–332. 5. Bugajewski, Z.; Bylicki, A. J. Chem. Thermodynamics 1988, 20, 1191–1194. 6. Bugajewski, Z.; Bylicki, A. J. Chem. Thermodynamics 1989, 21, 37–40. 7. Bugajewski, Z.; Bylicki, A. J. Chem. Thermodynamics 1989, 21, 847–850. 8. Bugajewski, Z.; Bylicki, A. J. Chem. Thermodynamics 1990, 22, 573–576. 9. Bugajewski, Z.; Bylicki, A. J. Chem. Thermodynamics 1991, 23, 901–904. 10. Letcher, T. M.; Doma´nska, U.; Mwenesongole, E. Fluid Phase Equilib. 1998, 149, 323–337. 11. Riddick, J. A.; Bunger, W. B.; Sakano, T. K. Organic Solvents: Physical Properties, Methods of Purification. Wiley Interscience: New York. 1986. 12. Aldrich Catalog, 1999–2000. 13. Doma´nska, U. Fluid Phase Equilib. 1986, 26, 201–220. 14. Ott, J. B.; Goates, J. R. J. Chem. Thermodynamics 1983, 15, 267–272. (Received 29 June 1999; in final form 13 April 2000)
WA 99/038
(Solid + liquid) equilibria and solid compound formation in (N-methyl-2-pyrrolidinone + benzene, or toluene, or 1,3,5-trimethylbenzene, or ethylbenzene, or chlorobenzene, or 1,2-dichlorobenzene, or 1,2,4-trichlorobenzene, or 1,1,1-trichloroethane, or dichloromethane) a ´ Urszula Domanska
Department of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland
and Trevor M. Letcher School of Pure and Applied Chemistry, University of Natal-Durban, Private Bag X10, Dalbridge 4014, Republic of South Africa
(Solid + liquid) phase diagrams have been determined for (N -methyl-2-pyrrolidinone + benzene, or toluene, or 1,3,5-trimethylbenzene, or ethylbenzene, or chlorobenzene, or 1,2dichlorobenzene, or 1,2,4-trichlorobenzene, or 1,1,1-trichloroethane, or dichloromethane). Solid addition compounds form with the empirical formulae: {(C5 H9 NO)2 · C6 H6 }, (C5 H9 NO · 2ClC6 H5 ), (C5 H6 NO · Cl2 C6 H4 ), (2C5 H9 NO · Cl3 C6 H3 ). All are congruently melting compounds. Compound formation is attributed to a charge-transfer interaction with the benzene, or chlorobenzene, or 1,2-dichlorobenzene, or 1,2,4-trichlorobenzene acting as electron acceptors and the nitrogen, or oxygen in N -methyl-2-pyrrolidinone c 2000 Academic Press acting as electron donors. KEYWORDS: s.l.e.; NMP; benzene; toluene; 1,1,1-trichloroethane; dichloromethane; congruently melting compounds
1. Introduction N -methyl-2-pyrrolidinone (NMP) is an aprotic and a strongly dipolar substance and has the potential for use in solvent extraction processes for separating polar substances from non-polar ones.(1) (Solid + liquid) phase diagrams have been reported for (NMP + tetrachloromethane,(2) or trichloromethane,(3) or diacetylene,(4) or m-, p-, o-cresol,(5–7) a To whom correspondence should be addressed (E-mail: [email protected]).
0021–9614/00/121635 + 11 $35.00/0
c 2000 Academic Press
1636
U. Doma´nska and T. M. Letcher TABLE 1. Density ρ and refractive index n D of the pure components at T = 298.15 K ρ/kg · dm−3
Component
nD
Expt
Reference 11
Expt
C5 H9 NO
1.02800
1.02790¸
1.46862
1.4680
C6 H 6
0.87367
0.87370¸
1.49790
1.49792
CH3 C6 H5
0.86211
0.86231¸
1.49410
1.49413
(CH3 )3 C6 H3
0.86108
0.86111¸
1.49678
1.49684
C2 H 5 C6 H 5
0.86260
0.86264¸
1.49345
1.49320
ClC6 H5
1.10075
1.10090¸
1.52480
1.52481a¸
1.34250
1.3410b
1.55152
1.5509a,b
Cl3 C6 H3
1.45365
1.4540b
1.57260
1.5710a,b
C2 H3 Cl3
1.32907
1.32928¸
1.43602
1.4359
CH2 Cl2
1.31680
1.31678¸
1.42110
1.42115
Cl2 C6 H4
Reference 11
a At T = 293.15 K; b from reference 12.
275
T/K
265
255
245
235
0
0.2
0.4
0.6
0.8
1
x FIGURE 1. (Solid + liquid) phase diagram for {xC5 H9 NO + (1 − x)C6 H6 }; —, calculated values using equation (1).
or 2,5-dimethylphenol,(8) or 3,4-dimethylphenol).(9) The molecular addition compounds (m-, p-, o-cresol; 2,5-dimethylphenol) melting congruently or incongruently have been reported. The authors attributed the compound formation to a charge-transfer interac-
(Solid + liquid) equilibria for (NMP + an organic solvent)
1637
TABLE 2. (Solid + liquid) phase equilibria: T denotes the melting temperature, δT is the deviation of the experimental temperature from the temperature calculated from equation (1) and x is the mole fraction of NMP x
T /K
δT /K
x
T /K
δT /K
0 0.0214 0.0651
278.70 277.95 275.85
0.00 0.22 0.30
xC5 H9 NO + (1 − x)C6 H6 0.4307 246.95 0.02 0.4514 244.55 −0.21 0.4712 242.85a 0.02 to 0.05b
0.6682 0.6788 0.7056
246.75 246.45 246.35
0.13 −0.15 0.08
0.1133 0.1622
272.65 269.85
−0.18 0.10
0.4814 0.5097
243.15 243.95
−0.02 0.06
0.7401 0.7633
244.95 243.25
−0.06 −0.17
0.2450 0.2075 0.2826 0.3149
263.65 266.85 260.65 257.85
−0.13 0.25 −0.10 −0.15
0.5273 0.5273 0.5540 0.5825
244.45 236.45c 244.95 245.30
0.14 0.03 −0.22
0.7780 0.7851 0.8203 0.8560
242.15a 243.55 244.55 245.65
0.14 to 0.55b 0.56 0.14 −0.16
0.3507 0.3785 0.3995
254.75 252.05 250.25
−0.02 −0.10 0.15
0.6109 0.6319 0.6576
245.95 246.35 246.75
−0.10 −0.01 0.16
0.9023 0.9388 0.9671
247.53 248.65 249.55
0.03 −0.05 0.02
0.6660
246.65d
1
250.40
0.00
0.20 0.10 0.14
x
T /K
δT /K
0.03
xC5 H9 NO + (1 − x)CH3 C6 H5 0.4430 0.4959 0.5231
218.15 222.35 224.55
−0.42 0.12 0.36
0.6570 0.6870 0.7210
233.25 235.35 237.55
−0.34 −0.12 0.07
0.8664 0.9134 0.9512
244.75 246.65 248.35
0.5556
226.75
0.19
0.7606
239.45
−0.17
0.9729
249.35
0.13
0.5979
229.85
0.26
0.7883
240.75
−0.26
0.9893
249.90
−0.12
0.6303
231.75
−0.07
0.8238
242.75
0.08
1
250.40
0.00
0 0.0254 0.0676 0.0976
228.40 224.85 221.35 219.35
0.00 −0.66 −0.12 0.18
0.2958 0.3518 0.4050 0.4492
224.35 227.25 229.65 231.35
−0.14 −0.58 −0.63 −0.55
0.7425 0.7685 0.8196 0.8549
242.85 243.55 245.45 246.35
−0.12 −0.44 −0.21 −0.18
0.1395 0.1604 0.1750 0.1853 0.2056 0.2158 0.2528
217.15 215.95 215.15a 216.75 218.75 220.75 222.65
0.39 0.04 −0.30 to 0.53b −0.53 0.38 1.75 1.13
0.4959 0.5248 0.5574 0.5887 0.6186 0.6374 0.7153
233.35 234.15 235.95 237.15 238.05 238.75 241.65
−0.06 −0.18 0.53 0.60 0.34 0.27 −0.19
0.8850 0.9085 0.9405 0.9609 0.9797 1
247.15 247.55 248.75 249.15 249.65 250.40
0.02 −0.01 0.51 0.31 0.03 0.00
0.3377 0.3665 0.3970
221.70 215.15 217.15
0.00 −0.44 −0.01
0.8012 0.8418 0.8805
241.75 243.75 245.45
0.03 0.28 0.37
xC5 H9 NO + (1 − x)(CH3 )3 C6 H3
xC5 H9 NO + (1 − x)C2 H5 C6 H5 0.5428 227.45 0.68 0.6335 232.85 0.01 0.6813 235.45 −0.26
1638
U. Doma´nska and T. M. Letcher TABLE 2—continued
x
T /K
δT /K
x
T /K
δT /K
x
T /K
δT /K
0.4528
220.65
0.4943
223.55
0.07
0.7126
237.05
−0.39
0.9285
247.55
0.39
0.16
0.7396
238.35
−0.49
0.9761
249.55
0.5183
0.07
225.25
0.19
0.7618
239.65
−0.27
1
250.40
0.00
0
228.05
0.00
0.3305
208.85
0.30
0.5344
215.85
−0.23
0.0299
226.05
0.07
0.3330
209.15c
0.51
0.5802
220.65
0.32
0.0814
222.35
−0.11
0.3532
209.05
−0.15
0.6271
225.35
0.67
0.1259
219.05
−0.40
0.4018
208.55
−0.50
0.6702
229.15
0.25
0.1676
216.95
0.28
0.4324
207.95
0.41
0.7565
235.35
−2.27
0.2459
211.75
0.23
0.4480
206.15a
0.2995
208.15
0.09
0.4540
207.55
0.3100
207.15a
0.4722
209.45
0.02
0.3232
208.35
0.08
0.5020
212.15
−0.68
0
256.15
0.00
0.4214
227.15
0.0333
254.15
0.16
0.4443
224.35
0.0781
251.15
−0.11
0.4829
219.95
0.1307
248.15
0.07
0.4880
218.65a
xC5 H9 NO + (1 − x)ClC6 H5
−0.24 to 0.53b
−0.12 to 0.11b 0.46
0.8167
244.95
2.05
0.9208
247.15
−0.75
0.9586
248.95
0.20
1
250.40
0.00
0.38
0.6156
222.85
−0.05
0.00
0.6566
226.95
0.21
0.29
0.6884
229.50
−0.16 −0.22
xC5 H9 NO + (1 − x)Cl2 C6 H4
−0.3 to 0.07b
0.7247
232.65
0.26
0.7949
238.95
0.36
219.95
−0.01
0.8597
242.95
−0.19
0.5404
219.85
−0.19
0.8945
245.35
0.09
0.5559
219.75
−0.07
0.9335
247.35
−0.02
−0.22
0.5750
219.15a
0.07 to 0.05b
229.35
−0.40
0.5952
220.95
−0.04
0
289.65
0.00
0.5201
261.95
0.0452
287.35
−0.27
0.5417
0.0864
285.35
−0.45
0.5665
0.1296
283.75
−0.15
0.5720
258.15a
0.8203
249.35
0.05
0.1687
282.05
−0.11
0.5904
259.35
0.15
0.8531
246.45
0.00
0.1965
280.95
0.05
0.6194
259.95
−0.27
0.8651
245.35
−0.07
0.2126
280.55
0.39
0.6389
260.35
−0.11
0.8800
244.15a
0.04 to 0.42b
0.3043
276.15
0.47
0.6660
260.85
0.67
0.8969
245.45
0.4337
267.95
−0.24
0.6772
259.85
0.00
0.9345
247.65
0.53
0.4968
263.55
−0.28
0.6970
258.45
−0.56
0.9858
249.85
0.01
1
250.40
0.00
0.1964
243.75
−0.22
0.5200
220.15d
0.2326
241.70
0.10
0.5239
0.2677
239.25
0.04
0.3077
236.65
0.30
0.3616
231.95
0.3898
0.9697
248.95
−0.12
1
250.40
0.00
−0.13
0.7280
257.15
0.05
260.25
−0.13
0.7544
255.25
0.19
258.45
0.12
0.7765
253.05
−0.12
xC5 H9 NO + (1 − x)Cl3 C6 H3
0.29 to 0.03b
0.13
(Solid + liquid) equilibria for (NMP + an organic solvent)
1639
TABLE 2—continued x
T /K
δT /K
x
T /K
δT /K
0 0.0210 0.0388
233.85 229.95 227.25
0.00 0.02 0.03
0.5665 0.5889 0.6438
227.15 229.05 232.35
−0.02 0.20 −0.27
0.0605 0.0680 0.1002
224.55 224.05e 223.55
−0.11 0.08 to 0.18b 0.04
0.3582 0.3700 0.3895
208.45 207.65a 210.15
0.05 0.01 to 0.11b 0.30
0.7580 0.8034 0.8402
239.45 241.95 243.75
0.04 0.09 0.00
0.1367 0.1553 0.2008 0.2330
222.15 221.45 219.05 216.95
−0.04 0.10 0.18 0.08
0.4010 0.4402 0.4549 0.4749
210.65 215.75 216.95 218.95
−0.54 0.18 −0.17 −0.20
0.8741 0.9149 0.9436 0.9664
245.35 247.25 248.35 249.25
−0.04 0.02 −0.05 0.00
0.2442 0.2529
215.95 215.55
−0.18 0.00
0.4881 0.5123
220.65 222.95
0.22 0.28
0.9803 1
249.75 250.40
0.01 0.00
0.2757
213.95
−0.05
0.5418
225.05
−0.15
0.5703 0.6224
207.80 216.55
−0.11 0.23
0.9368 0.9521
246.55 247.55
0.51 0.50
0.6790
224.05
−0.07
0.8712
241.85
0.16
0.9731
248.85
0.39
0.7231 0.7797
229.25 234.40
0.01 −0.31
0.8977 0.9186
243.85 245.05
0.38 −1.77
0.9893 1
249.55 250.40
−0.03 0.00
x
T /K
δT /K
xC5 H9 NO + (1 − x)C2 H3 Cl3 0.2983 212.35 −0.10 0.3273 210.55 0.09 0.3490 208.95 −0.05
xC5 H9 NO + (1 − x)CH2 Cl2 0.8201 238.15 0.14 0.8475 239.95 −0.09
a Eutectic composition and temperature. b The two δT values are the deviations from the intersecting equations at the invariant point. The deviation from the equation for the lower x region is given first. c Metastable melting temperature. d Composition and melting temperature of congruently melting molecular addition compound. e (Solid + solid) phase transition composition and temperature.
tion. In this paper we present similar measurements for (N -methyl-2-pyrrolidinone + benzene, or toluene, or 1,3,5-trimethylbenzene, or ethylbenzene, or chlorobenzene, or 1,2dichlorobenzene, or 1,2,4-trichlorobenzene, or 1,1,1-trichloroethane, or dichloromethane). Chlorohydrocarbons include chlorine and hydrogen atoms which can interact with NMP.
2. Experimental The origin of the chemicals and their mass fraction purities were: NMP (Aldrich Chemical Co., 0.995), benzene (Aldrich Chemical Co., 0.999), toluene (Aldrich Chemical Co., 0.995), 1,3,5-trimethylbenzene (Aldrich Chemical Co., 0.98), ethylbenzene (Aldrich Chemical Co., 0.99), chlorobenzene, 1,2-dichlorobenzene and 1,2,4-trichlorobenzene (Janssen Chimica, 0.98), 1,1,1-trichloroethane (Koch-Light Laboratories Ltd., 0.98), dichloromethane (Aldrich Chemical Co., 0.998). NMP, benzene and toluene were fractionally distilled under atmospheric pressure after prolonged reflux over different drying reagents. All liquids were stored over freshly activated molecular sieves of the type
1640
U. Doma´nska and T. M. Letcher TABLE 3. Summary of invariant points x
T /K
Eutectic
0.4712
242.85
Compound (2C5 H9 NO · C6 H6 )a
0.666
246.65
Eutectic
0.778
242.15
Type of invariant point xC5 H9 NO + (1 − x)C6 H6
xC5 H9 NO + (1 − x)(CH3 )3 C6 H3 Eutectic
0.175
215.15
xC5 H9 NO + (1 − x)ClC6 H5 Eutectic
0.310
207.15
Compound (C5 H9 NO · 2ClC6 H5 )a
0.333
209.15
Eutectic
0.448
206.15
xC5 H9 NO + (1 − x)Cl2 C6 H4 Eutectic
0.488
218.65
Compound (C5 H9 NO · Cl2 C6 H4 )a
0.520
220.15
Eutectic
0.575
219.15
xC5 H9 NO + (1 − x)Cl3 C6 H3 Eutectic
0.572
258.15
Compound (2C5 H9 NO · Cl3 C6 H3 )a
0.666
260.85
Eutectic
0.880
244.15
xC5 H9 NO + (1 − x)C2 H3 Cl3 Phase transition
0.068
224.05
Eutectic
0.370
207.65
a Melting temperature of congruently melting molecular addition compound.
0.4 nm (Union Carbide) and were analysed by g.l.c. An analysis, using the Karl–Fisher technique, showed that the water mole fraction content in each of the solvents x (H2 O) was <3 · 10−3 . The densities of all the chemicals were measured, using an Anton Paar DMA 602 vibrating-tube densimeter. The densities of NMP and the other solvents are in satisfactory agreement with the literature values quoted in references 10 and 11, respectively. The characteristic properties of the pure substances are presented in table 1. NMP was stored in a dark bottle in a refrigerator to reduce decomposition. The (solid + liquid) equilibrium temperatures were determined using a dynamic method.(13) Appropriate mixtures of solute and solvent were heated very slowly (less than 1.1 · 10−3 K · s−1 near the equilibrium temperature) with continuous stirring inside a Pyrex glass cell which was placed in a glass thermostat filled with acetone and dry ice. The temperature at which the last crystals disappeared was taken as the temperature of the (solid + liquid) equilibrium. The crystal disappearance temperatures, detected visually, were
(Solid + liquid) equilibria for (NMP + an organic solvent)
1641
TABLE 4. Coefficients Ai for the fitting equation (1). Columns 1 and 2 give the range of x over which the equation applies: σ is the standard deviation of T xmin
x∗
xmax
T∗
A1
A2
A3
A4
A5
A6
σ a /K
xC5 H9 NO + (1 − x)C6 H6 0
0.4712 0
278.70 −0.15770 −0.24832
0.15
0.4712 0.778
0.666 246.65 −0.48342
1.49827
−1.16217
0.85
0.778 1
1
250.40 −0.47093
0.84767
−0.37681
0.26
0.4430 1
1
250.40 −1.35474
xC5 H9 NO + (1 − x)CH3 C6 H5 3.84435
1.34306
−3.83196
0.32
xC5 H9 NO + (1 − x)(CH3 )3 C6 H3 0
0.175 0
0.175 1
1
228.40 −0.52766 250.40 −2.48722
1.16431 15.9937
0.32 66.1171
−45.3545
−47.9814
13.7140
4.17
xC5 H9 NO + (1 − x)C2 H5 C6 H5 0.3377 1
1
250.40 −1.33658
0.310 0
228.05 −0.30447
3.87382
1.43196
−3.96752
0.72
xC5 H9 NO + (1 − x)ClC6 H5 0
0.310 0.448
0.333 209.15
0.448 1
1
0.03942
0.16
0.02297 −0.09620
250.40 −8.45208
0.51
53.5850 −143.861
196.345
−133.429
35.8113
4.52
xC5 H9 NO + (1 − x)Cl2 C6 H4 0
0.488 0
256.15 −0.26305
0.37999
−2.19546
0.488
0.575 0.488 220.15 −1.50943
5.62093
−5.23579
0.575
1
1
250.40 −1.49162
3.69636
−3.07410
0
0.572 0
289.65 −0.15782
5.10263
0.29
−5.11442
0.05 0.86903
0.13
xC5 H9 NO + (1 − x)Cl3 C6 H3 0.572 0.880
0.666 260.85
0.880
1
1
250.40 −0.22782
0
0.068 0
233.85 −0.87639
0.06307
10.2535 −82.5808
0.33
−0.21440 253.568
−374.951
268.927
0.22881
−75.3656
0.30 0.21
xC5 H9 NO + (1 − x)C2 H3 Cl3 0.068 0.370
0.068 224.05
0.370 1
1
250.40 −3.31737
0.5703 1
1
250.40 −4.08183
3.75300
0.09795 −1.37064 16.1813
0.01 1.54327 −34.1965
0.06 37.7962
−21.2678
4.80412 0.30
xC5 H9 NO + (1 − x)CH2 Cl2 14.4639
−19.7531
12.1550
−2.78414
1.65
h i1/2 2 a Given by the equation σ = Pn {(T , here n is the number of experimental points, and expt − Tcalc )i /(n − k)} i=1
k is the number of parameters.
1642
U. Doma´nska and T. M. Letcher
260
250
T/K
240
230
220
210
0
0.2
0.4
0.6
0.8
1
x
◦
FIGURE 2. (Solid + liquid) phase diagram for , {xC5 H9 NO + (1 − x)CH3 C6 H5 }; , {xC5 H9 NO + (1 − x)C2 H5 C6 H5 }; , {xC5 H9 NO + (1 − x)(CH3 )3 C6 H3 }; —, calculated values using equation (1).
250
T/K
240 230 220 210 200 0
0.2
0.4
0.6
0.8
1
x
FIGURE 3. (Solid + liquid) phase diagram for {xC5 H9 NO + (1 − x)ClC6 H5 }; —, calculated values using equation (1).
measured with a platinum resistance thermometer, Gallenkamp Autotherm II, produced by Sanyo Gallenkamp plc, Leicester, U.K. The thermometer was calibrated on ITS-90. The accuracy of the temperature measurements was judged to be ±0.001 K and the
(Solid + liquid) equilibria for (NMP + an organic solvent)
1643
255
T/ K
245
235
225
215
0
0.2
0.4
0.6
0.8
1
x FIGURE 4. (Solid + liquid) phase diagram for {xC5 H9 NO + (1 − x)Cl2 C6 H4 }; —, calculated values using equation (1).
290
280
T/K
270
260
250 240 0
0.2
0.4
0.6
0.8
1
x
FIGURE 5. (Solid + liquid) phase diagram for {xC5 H9 NO + (1 − x)Cl3 C6 H3 }; —, calculated values using equation (1).
reproducibility of the equilibrium temperatures to be ±0.1 K. Mixtures were prepared by mass and the error in the mole fraction was estimated to be less than ±5 · 10−4 .
1644
U. Doma´nska and T. M. Letcher 290
280
T/K
270
260
250
240 0
0.2
0.4
0.6
0.8
1
x
FIGURE 6. (Solid + liquid) phase diagram for , {xC5 H9 NO + (1 − x)C2 H3 Cl3 };
◦, {xC5 H9 NO + (1 − x)CH2 Cl2 }; —, calculated values using equation (1). 3. Results and discussion
Experimental results were obtained over the entire composition range for the six investigated mixtures. For toluene, ethylbenzene and dichloromethane the melting temperatures were lower than 220 K and a different experimental technique, namely d.s.c. calorimetry, was required to obtained the second liquidus curve. The (solid + liquid) equilibrium temperatures are recorded in table 2 and the invariant temperatures in table 3. The phase diagrams are shown in figures 1 to 6. The melting temperatures T were fitted using a leastsquares method to the equation:(14) ) ( n X T = T∗ 1 + a j (x − x ∗ ) j , (1) j=1
x∗
T∗
where and were taken as the stoichiometric composition and melting temperature for the congruently melting compounds and as the melting temperature Tm of pure substances (x ∗ for pure substances is the value of x at Tm ). Excellent fits were obtained for all the mixtures except for {xC5 H9 NO + (1 − x) (CH3 )3 C6 H3 } at x > 0.175 and for {xC5 H9 NO + (1 − x)CH2 Cl2 } at x > 0.5. The parameters of the fitting equation together with the standard deviations (σ ) are given in table 4. Deviations δT = {T − T (calc)} of the individual data points from the fitting equations are given in table 2. The curves in all the six figures were drawn using the fitting equations. It is evident from the phase diagrams that congruently melting solid addition compounds form in four of the mixtures with the empirical formulae: (2C5 H9 NO · C6 H6 ); (C5 H9 NO · 2ClC6 H5 ); (C5 H9 NO · Cl2 C6 H4 ); and (2C5 H9 NO · Cl3 C6 H3 ). For the mixture with 1,1,1-trichloroethane the large inflection in the liquidus curve at x = 0.068 and
(Solid + liquid) equilibria for (NMP + an organic solvent)
1645
T = 224.05 K indicates a (solid + solid) phase transition, characteristic of the pure compound. The eutectic compositions were obtained from the intersection of the melting temperature lines. It is interesting to note that addition compounds contain two, or three cyclic molecules. It is possible that two kinds of charge-transfer interactions contribute to the bonding in these mixtures: one involving the carbonyl oxygen and the other involving electron pair donation from the nitrogen group. An increase in the number of chlorine atoms on the benzene ring from one to three, results in a higher concentration of NMP in solid compound formation x ∗ = 0.333, x ∗ = 0.488 and x ∗ = 0.666 for chloro-, dichloro- and trichlorobenzene, respectively (see figures 3 to 5). On the other hand, replacing the chlorine atoms on the benzene ring by methyl, ethyl, or three methyl groups results in no solid compound formation (see figure 2). Both a congruent 1 : 1 and an incongruent melting compound have been observed by other workers in {xC5 H9 NO + (1 − x)CCl4 }(2) and in {xC5 H9 NO + (1 − x)CHCl3 }.(3) No similar solid compound occurs in the mixture of 1,1,1-trichloroethane and possibly in dichloromethane, suggesting that the chlorine atoms are weaker electron acceptors in dichloromethane than in trichloromethane and in tetrachloromethane. The authors wish to thank the University of Natal and F.R.D. (S. Africa) for financial aid. REFERENCES 1. Letcher, T. M.; Naicker, P. K. J. Chem. Eng. Data 1998, 43, 1034–1038. 2. Che, G. Q.; Ott, J. B.; Goates, J. R. J. Chem. Thermodynamics 1986, 18, 323–330. 3. Che, G. Q.; Huang, Z. Q.; Li, D.; Gu, X. L.; Luo, S. L. J. Chem. Thermodynamics 1996, 28, 159–165. 4. Szahowa, S. F.; Ksodjejewa, S. M.; Seriejewa, L. I. Zh. Phys. Khim. 1971, 45, 330–332. 5. Bugajewski, Z.; Bylicki, A. J. Chem. Thermodynamics 1988, 20, 1191–1194. 6. Bugajewski, Z.; Bylicki, A. J. Chem. Thermodynamics 1989, 21, 37–40. 7. Bugajewski, Z.; Bylicki, A. J. Chem. Thermodynamics 1989, 21, 847–850. 8. Bugajewski, Z.; Bylicki, A. J. Chem. Thermodynamics 1990, 22, 573–576. 9. Bugajewski, Z.; Bylicki, A. J. Chem. Thermodynamics 1991, 23, 901–904. 10. Letcher, T. M.; Doma´nska, U.; Mwenesongole, E. Fluid Phase Equilib. 1998, 149, 323–337. 11. Riddick, J. A.; Bunger, W. B.; Sakano, T. K. Organic Solvents: Physical Properties, Methods of Purification. Wiley Interscience: New York. 1986. 12. Aldrich Catalog, 1999–2000. 13. Doma´nska, U. Fluid Phase Equilib. 1986, 26, 201–220. 14. Ott, J. B.; Goates, J. R. J. Chem. Thermodynamics 1983, 15, 267–272. (Received 29 June 1999; in final form 13 April 2000)
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