Excess volumes of (a polar liquid + an aromatic hydrocarbon) at the temperature 298.15 K

M-3166 J. Chem. Thermodynamics 1995, 27, 1349–1353

Excess volumes of (a polar liquid+an aromatic hydrocarbon) at the temperature 298.15 K III. (N,N-dimethylacetamide+an aromatic hydrocarbon) Wang Haijun, Su Zhongxing, and Zhou Xiaoxian a Department of Chemistry, Lanzhou University, Lanzhou, Gansu, 730000 , P.R. China

(Received 28 June 1995) Excess volumes have been measured by means of a continuous-dilution dilatometer for (N,N-dimethylacetamide+benzene or toluene or o-xylene or m-xylene or p-xylene or ethylbenzene or styrene) at the temperature 298.15 K. VmE values are negative over the entire range of composition for all the binary mixtures. =VmE(minimum)= and =VmE(x=0.5)= values of this series decrease in the sequence: C6 H5CH.CH2 q C6 H5CH3 q p-C6 H4(CH3 )2 q C6 H6qm-C6 H4(CH3 )21o-C6 H4(CH3 )2qC6 H5CH2CH3 . The results were compared with the results for binary mixtures containing other polar liquids, and show that there are quite strong interactions between N,N-dimethylacetamide molecules and aromatic-hydrocarbon molecules. 7 1995 Academic Press Limited

1. Introduction In continuation of our studies for binary mixtures containing (a polar liquid+an aromatic hydrocarbon),(1, 2) in this paper we report the experimental excess volumes for seven mixtures of (N,N-dimethylacetamide+an aromatic hydrocarbon). The purpose is to obtain information on the molecular interactions in (a polar component+a non-polar component) with differences in size and shape. In our laboratory, we have measured the excess volume for (N,N-dimethylacetamide+an aromatic hydrocarbon),(3) using a conventional pycnometer, but the precision and accuracy were not very satisfactory. In order to compare with the binary mixtures containing another polar liquid, in this work, which forms a part of a study of excess volumes for the binary mixtures containing a polar liquid mixed with an aromatic hydrocarbon, we have measured excess volumes at the temperature T = 298.15 K over the entire range of composition for (N,N-dimethylacetamide+benzene or toluene or o-xylene or m-xylene or p-xylene or ethylbenzene or styrene), by means of a continuous-dilution dilatometer. In this way, a

To whom correspondence should be addressed.

0021–9614/95/121349+05 $12.00/0

7 1995 Academic Press Limited

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Wang Haijun, Su Zhongxing, and Zhou Xiaoxian

it is possible to compare with the binary mixtures, in which the polar liquid is a formamide.

2. Experimental The aromatic hydrocarbons in this work were the same as those used in the previous work.(1) N,N-Dimethylacetamide was obtained from Shanghai Chemicals Factory with purity exceeding 99 moles per cent of CH3CON(CH3 )2 . The method of purification has been described elsewhere.(4) All the chemicals were kept with 0.5 nm molecular sieve to remove any trace of water, and degassed just before use. The purity of the chemicals was tested by comparing the experimental densities with the literature values. The densities of pure liquids were measured by means of an Anton Paar DMA 60/602 vibrating-tube densimeter, thermostatted at (298.1520.01) K. The experimental density for N,N-dimethylacetamide at T=298.15 K was found to be 0.9362 g·cm−3 , compared with the literature value:(4) 0.936337 g·cm−3 , at T=298.15 K. Measurements of excess volumes were carried out with a continuous-dilution dilatometer, similar to that of Kumaran and McGlashan.(5) The dilatometer had been tested by measurements of excess molar volume for {xC6 H6+(1−x)c-C6 H12 } described previously,(6) and the temperature of the water bath was controlled at T=298.15 K within 20.002 K.

3. Results The excess molar volumes VmE for the seven binary mixtures were obtained over the entire composition range. The results are summarized in table 1, and graphically presented in figure 1. The experimental results were fitted by the method of least squares with all points weighted equally to the smoothing equation: k

VmE/(cm3·mol−1 )=x(1−x) s Ai (1−2x)i. i=0

The continuous lines in figure 1 represent the values calculated from the smoothing equations. For none of the mixtures does the precision warrant the use of more than four parameters. The parameters A0 , A1 , A2 , and A3 , and the standard deviations s, along with the extreme values of excess molar volumes for each binary mixture, are shown in table 2.

4. Discussion Our results are in reasonable agreement with the earlier work,(3) in which the measurement was carried out by a conventional pycnometer. We are convinced that the new results are not only more precise, but also more accurate than the earlier results.

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V E(N,N-dimethylacetamide+an aromatic hydrocarbon) TABLE 1. Experimental excess molar volumes VmE at T=298.15 K x

VmE cm3·mol−1

x

VmE cm3·mol−1

0.0435 0.0776 0.1129 0.1368 0.1621 0.1905 0.1935 0.2149 0.2538 0.2748

−0.0308 −0.0582 −0.0814 −0.1031 −0.1177 −0.1423 −0.1405 −0.1596 −0.1824 −0.1992

xC6 H6+(1−x)CH3CON(CH3 )2 −0.2138 0.5148 −0.3118 −0.2384 0.5323 −0.3134 −0.2442 0.5571 −0.3181 −0.2614 0.5732 −0.3186 −0.2704 0.5983 −0.3215 −0.2845 0.6236 −0.3194 −0.2898 0.6554 −0.3162 −0.2991 0.6834 −0.3075 −0.3030 0.7143 −0.2959

0.7369 0.7589 0.7824 0.8201 0.8472 0.8861 0.9052 0.9366 0.9587

−0.2899 −0.2741 −0.2634 −0.2307 −0.2101 −0.1647 −0.1456 −0.1006 −0.0697

0.0473 0.0782 0.0952 0.1135 0.1410 0.1658 0.1955 0.2186 0.2371

−0.0547 −0.0917 −0.1107 −0.1301 −0.1568 −0.1847 −0.2100 −0.2260 −0.2461

xCH3C6 H5+(1−x)CH3CON(CH3 )2 0.2563 −0.2580 0.4962 −0.3860 0.2806 −0.2810 0.5119 −0.3895 0.3025 −0.2930 0.5344 −0.3877 0.3387 −0.3171 0.5763 −0.3904 0.3762 −0.3427 0.5992 −0.3896 0.4026 −0.3557 0.6132 −0.3861 0.4293 −0.3669 0.6452 −0.3795 0.4471 −0.3733 0.6790 −0.3644 0.4732 −0.3809 0.6983 −0.3569

0.7154 0.7362 0.7597 0.7787 0.8025 0.8395 0.8874 0.9155 0.9563

−0.3483 −0.3310 −0.3179 −0.3024 −0.2767 −0.2423 −0.1803 −0.1409 −0.0797

0.0443 0.0782 0.1025 0.1337 0.1692 0.1981 0.2103 0.2238 0.2557

−0.0459 −0.0781 −0.1014 −0.1303 −0.1492 −0.1716 −0.1790 −0.1873 −0.2049

xo-(CH3 )2C6 H4+(1−x)CH3CON(CH3 )2 0.2817 −0.2200 0.5124 −0.2738 0.3058 −0.2289 0.5347 −0.2776 0.3422 −0.2463 0.5549 −0.2725 0.3796 −0.2542 0.5793 −0.2740 0.4083 −0.2655 0.6015 −0.2666 0.4326 −0.2663 0.6358 −0.2632 0.4587 −0.2742 0.6702 −0.2502 0.4779 −0.2722 0.7031 −0.2380 0.4902 −0.2770 0.7343 −0.2261

0.7618 0.7815 0.8214 0.8563 0.8792 0.8973 0.9256 0.9568

−0.2118 −0.1974 −0.1752 −0.1448 −0.1295 −0.1103 −0.0819 −0.0529

0.0402 0.0735 0.1033 0.1225 0.1485 0.1795 0.2005 0.2385 0.2588

−0.0398 −0.0698 −0.0914 −0.1062 −0.1288 −0.1507 −0.1646 −0.1877 −0.1990

xm-(CH3 )2C6 H4+(1−x)CH3CON(CH3 )2 0.2736 −0.2035 0.4807 −0.2709 0.2965 −0.2181 0.4998 −0.2759 0.3254 −0.2310 0.5205 −0.2739 0.3562 −0.2430 0.5533 −0.2749 0.3862 −0.2530 0.5763 −0.2764 0.4037 −0.2599 0.5900 −0.2720 0.4305 −0.2633 0.6304 −0.2683 0.4411 −0.2647 0.6598 −0.2590 0.4685 −0.2733 0.6921 −0.2505

0.7264 0.7582 0.7813 0.8036 0.8395 0.8826 0.9216 0.9598

−0.2355 −0.2177 −0.2076 −0.1904 −0.1675 −0.1274 −0.0936 −0.0476

0.0502 0.0812 0.1182 0.1387 0.1542 0.1796 0.2059 0.2334 0.2647

−0.0593 −0.0935 −0.1307 −0.1535 −0.1681 −0.1866 −0.2079 −0.2286 −0.2501

xp-(CH3 )2C6 H4+(1−x)CH3CON(CH3 )2 0.2966 −0.2696 0.5328 −0.3367 0.3154 −0.2782 0.5539 −0.3378 0.3552 −0.2983 0.5788 −0.3332 0.3865 −0.3128 0.6043 −0.3308 0.4059 −0.3193 0.6332 −0.3215 0.4385 −0.3252 0.6771 −0.3059 0.4593 −0.3325 0.6902 −0.2983 0.4825 −0.3360 0.7362 −0.2747 0.5025 −0.3349

0.7582 0.7862 0.8112 0.8443 0.8763 0.8997 0.9363 0.9626

−0.2646 −0.2405 −0.2245 −0.1907 −0.1623 −0.1322 −0.0907 −0.0525

x

0.3025 0.3369 0.3544 0.3792 0.4058 0.4286 0.4496 0.4698 0.4922

VmE cm3·mol−1

x

VmE cm3·mol−1

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Wang Haijun, Su Zhongxing, and Zhou Xiaoxian TABLE 1—continued

x

VmE cm3·mol−1

0.0503 0.0796 0.1108 0.1396 0.1584 0.1857 0.2132 0.2364 0.2752

−0.0251 −0.0454 −0.0589 −0.0790 −0.0855 −0.1045 −0.1153 −0.1314 −0.1466

0.0382 0.0741 0.0956 0.1142 0.1386 0.1604 0.1857 0.2033 0.2258

−0.0558 −0.1042 −0.1375 −0.1605 −0.1962 −0.2237 −0.2591 −0.2817 −0.3070

x

VmE cm3·mol−1

x

VmE cm3·mol−1

xC6 H5CH2CH3+(1−x)CH3CON(CH3 )2 0.3058 −0.1648 0.5253 −0.2270 0.3363 −0.1739 0.5287 −0.2253 0.3582 −0.1866 0.5483 −0.2286 0.3874 −0.1931 0.5699 −0.2272 0.4158 −0.2062 0.5967 −0.2295 0.4363 −0.2079 0.6258 −0.2228 0.4598 −0.2176 0.6583 −0.2206 0.4726 −0.2162 0.6834 −0.2118 0.4993 −0.2218 0.7158 −0.2050 xC6 H5CH.CH2+(1−x)CH3CON(CH3 )2 0.2531 −0.3427 0.4872 −0.5302 0.2779 −0.3700 0.5134 −0.5407 0.2962 −0.3875 0.5380 −0.5440 0.3258 −0.4202 0.5739 −0.5489 0.3562 −0.4475 0.6235 −0.5417 0.3768 −0.4651 0.6529 −0.5291 0.3983 −0.4817 0.6847 −0.5121 0.4211 −0.4936 0.7036 −0.4993 0.4426 −0.5092 0.7286 −0.4791

x

VmE cm3·mol−1

0.7463 0.7782 0.7958 0.8205 0.8540 0.8773 0.8972 0.9184 0.9498

−0.1904 −0.1797 −0.1665 −0.1551 −0.1310 −0.1159 −0.1020 −0.0800 −0.0530

0.7491 0.7982 0.8146 0.8332 0.8574 0.8824 0.9125 0.9374 0.9622

−0.4584 −0.4026 −0.3840 −0.3524 −0.3170 −0.2721 −0.2083 −0.1581 −0.0956

FIGURE 1. Excess molar volumes VmE at T=298.15 K as a function of mole fraction x for {(1−x)CH3CON(CH3 )2+xB}, where B denotes: w, C6 H6 ; e +, C6 H5CH3 ; e, o-(CH3 )2C6 H4 ; × q, m-(CH3 )2C6 H4 ; ×, p-(CH3 )2C6 H4 ; +, C6 H5C2 H5 ; and q, C6 H5CH.CH2 .

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V E(N,N-dimethylacetamide+an aromatic hydrocarbon) TABLE 2. The least-squares parameters, standard deviations, and extreme values

Extreme values

(1−x)CH3CON(CH3 )2+ xC6 H6 xCH3C6 H5 xo-(CH3 )2C6 H4 xm-(CH3 )2C6 H4 xp-(CH3 )2C6 H4 xC6 H5CH2CH3 xC6 H5CH.CH2

A0

A1

A2

A3

s

x

VmE cm3·mol−1

−1.2281 −1.5436 −1.1008 −1.1002 −1.3464 −0.8912 −2.1430

0.5230 0.3629 0.0699 0.1773 0.1508 0.2796 0.6642

−0.0233 −0.0151 −0.0790 −0.0467 −0.0339 0.0760 0.0675

0.0198 −0.0169 0.0137 −0.0485 −0.0236 0.0338 −0.0316

0.0018 0.0019 0.0020 0.0017 0.0016 0.0019 0.0017

0.5966 0.5569 0.5171 0.5410 0.5284 0.5688 0.5705

−0.3201 −0.3911 −0.2755 −0.2769 −0.3377 −0.2277 −0.5477

As table 2 shows, for all the binary mixtures, A0 is negative. The sequence (in the absolute value sense) is C6 H5CH.CH2 q C6 H5CH3 q p-C6 H4(CH3 )2 q C6 H6 q m-C6 H4(CH3 )21o-C6 H4(CH3 )2qC6 H5CH2CH3 . The values of =VmE(minimum)= follow the sequence of =A0 =. Compared with the series in which the polar liquid is N,N-dimethylformamide,(1) or N,N-diethylformamide,(2) the sequence of =A0 = and =VmE(minimum)= for these three series are similar. For a given aromatic hydrocarbon, the sequence of =A0 = and =VmE(minimum)= is about N,N-diethylformamideqN,N-dimethylformamide1N,N-dimethyacetamide. In conclusion, it can be safely assumed that N,N-dimethylformamide, N,N-diethylformamide, and N,N-dimethylacetamide belong to the same conformal series. Most likely, they have similar interstitial accommodation with a given aromatic. However, for a given aromatic hydrocarbon, the interaction with N,N-dimethylacetamide is similar that with N,N-dimethylformamide, but both are weaker than N,N-diethylformamide. That is to say, the replacement of methy groups by ethyl group on a nitrogen atom has a stronger influence on the interactions between a formamide molecule and an aromatic hydrocarbon molecules than the replacement of formamide by acetamide. REFERENCES 1. 2. 3. 4. 5. 6.

Wang Haijun; Zhu Chao; Chen Mingzhi; Li Hulin J. Chem. Thermodynamics 1995, 27, 991–996. Wang Haijun; Liu Chuangui; Chen Mingzhi; Li Hulin J. Chem. Thermodynamics 1995, 27, 1205–1209. Chen Wufeng; Che Guangquan; Chen Mingzhi; Zheng Guokang J. Lanzhou Univ. 1981, 4, 58. Weast, R. C. CRC Handbook of Chemistry and Physics. 58th Edition. CRC Press Inc. 1977–1978. Kumaran, M. K.; McGlashan, M. L. J. Chem. Thermodynamics 1977, 9, 259. Wang Haijun; Zheng Guokang; Chen Mingzhi J. Chem. Thermodynamics 1993, 25, 949.