Thermodynamic properties of organic oxygen compounds XLIII. Vapour pressures of some ethers

J. Chem. Thermodynamics 1976,8,16.5-178

Thermodynamic properties oxygen compounds

Xtlll.

Vapour

pressures

of organic

of some ethers

D. AMBROSE, J. H. ELLENDER, C. H. S. SPRAKE, and R. TOWNSEND Division of Chemical Standards, National Physical Laboratory, Teddington, Middlesex TWIl OL W, U.K. (Received 22 September 1975) Vapour pressures of methyl propyl, isopropyl methyl, butyl methyl, ethyl propyl, t-butyl methyl, dipropyl, di-isopropyl, di-t-butyl, and decyl methyl ethers were measured at pressures up to 205 kPa. The measured values were fitted by Antoine and by Chebyshev equations, values already published from this laboratory for three aromatic ethers were recomputed uniformly with the present results, and published values for four additional compounds were incorporated in a scheme for correlation of the vapour pressures of ethers. Estimates were made of the vapour pressures of 10 other ethers. Between 5 and 200 kPa the vapour pressures of ethers may be represented by a single equation in which carbon number or an efective carbon number is a parameter. Chebyshev equations are given for interpolation between the upper bounds of the measurements and the critical pressures of 11 ethers for which this property has been previously determined.

1. IntroductioIl Measurements have been reported from this laboratory of the vapour pressures of diethyl ether@) and of some aromatic ethers. c3) Here we report the results of measurements of the vapour pressures up to 205 kPa of a further nine aliphatic ethers. Correlation of the measured values together with those published for dimethyl ether,(49 5, ethyl methyl ether,@) butyl ethyl ether,(‘) and dibutyl ether”) by the same method as we used for ketones (*) allowed us to check the self-consistency of the whole set, and to make estimates of the vapour pressures of some members of the series for which there are few experimental data. An equation is given with carbon number n or a non-integral efictive carbon number n* as a parameter which reproduces with fair accuracy both the observed values of the vapour pressure in the range 5 to 200 kPa and also those estimated in the way just described. The critical temperatures and critical pressures of seven of the compounds have been reported(g) and equations are presented for these compounds for interpolation in the range between 200 kPa and the critical pressure. Equations of the same form are given to represent the behaviour of dimethyl ether and ethyl methyl ether, for which the published values of vapour pressure extend to their critical points.(P6) The earlier results for three aromatic ethers c3) have been recomputed uniformly with the present work and an equation is given for methyl phenyl ether for interpolation between 133 kPa and its critical pressure.(g) 12

166

D. AMBROSE,

J. H. ELLENDER,

C. H. S. SPRAKE,

AND

R. TOWNSEND

2. Experimental The measurements were made by comparative ebulliometry with automatic recording of the resistance readings of the platinum resistance thermometers obtained with an automatic a.c. bridge.@) Some of the measurements (set a) were made with the bubblecap ebulliometers of the original design(lO) and some (set b) were made with the sample in the slightly modified ebulliometer used for diethyl ether.(2) Only 15 cm3 of di-t-butyl ether was available and for this compound the capacity of the boiler was reduced by the addition of a layer of glass balls (2 mm diameter) sufficient to raise the liquid level so that the mouths of the bubble-caps were submerged. Assessments of the impurity content of each sample are in table 1; these were obtained in the course of studies by low-temperature calorimetryol-r3) except for di-t-butyl ether. This compound had been synthesized by reaction of silver oxide with t-butyl chloride, and the initial product was shown by g.1.c. to contain about 20 mass per cent in total of diethyl ether, but-l-ene, and 2-methylpropan-2-01. Purification was by preparative g.l.c., washing with water to reduce the content of 2-methylpropan-2-01, drying with calcium chloride and molecular sieve 4A, and fractional freezing. The final material gave a negative test for peroxide, and g.1.c. analysis on a column containing diethylene glycol succinate (instrument: Perkin Elmer F 11) showed one impurity peak, identified by mass spectrometry as but-l -ene, of area 0.1 per cent of the main peak. The dry material had been sealed under vacuum in ampoules at the time of preparation and was transferred from one of these ampoules into the ebulliometer without further treatment; the purity, however, was rechecked because another part of the batch had been found to be contaminated with but-1-ene and 2-methylpropan-2-01 and it is possible that it is inadvisable for this compound to be in contact with molecular sieve. The samples of the other compounds, with the exceptions following, were dried during transfer to the ebulliometer by passing the vapour through a column containing molecular sieve 4A. For t-butyl methyl ether the column contained anhydrous calcium sulphate because it had been found that this ether decomposed on prolonged contact with molecular sieve. Di-isopropyl ether was transferred from the lowtemperature calorimeter immediately after the conclusion of the experiments in that apparatus and was not dried again. Decyl methyl ether was not dried as it was assumed that the effect of traces of water in the sample would be much less than that arising from decomposition of the sample at elevated temperatures.

3. Results The measured values are in table 2 and the coefficients of the equations fitted to them in table 3 and table 4. The equations are the Antoine equation (table 3) : logloWW and the Chebyshev equation: WK)lwloWkP4

= A -t-WWIK)

-t Cl,

= a,/2 + x21dU4.

(1)

(2)

From measurement

TABLE

G) (13) (W (W W)

89.6 68.7 20.4 8.15 12.72

Divinyl ether Ethyl vinyl ether Ally1 ethyl ether Ally1 propyl ether Ally1 isopropyl ether 3.33 2.64 0.90 0.40 0.59

0.01

0.01

0.74 0.12 0.12

17.11 6.73 2.734 2.376 3.060 0.824 1.046 1.372 0.406 0.374 0.877 0.054 0.228 0.001 0.030 0.014

kPa K-l

225.0 230.5 254.6 272.4 263.9

258.9 296.5 297.7 350.2 339.2

K-l

0.14 0.14 0.13 0.12 0.12

0.11 0.11 0.10 0.10

0.13

0.142 0.141 0.144 0.128 0.131 0.128 0.122 0.125 0.129 0.108 0.114 0.095 0.106 0.103 0.086

0.169 0.157

kPa

dpldT

p = 2 kPa

184.1 210.9 229.59 232.39 226.54 256.47 251.48 243.21 271.94 274.58 255.08 312.14 283.09 373.39 322.95 336.43 403.51

T E

301.5 308.7 340.8 363.6 352.6

346.2 394.2 395.6 460.0 446.6

248.4 280.6 307.581 311.72 303.92 343.31 336.36 328.30 363.23 365.39 341.66 413.45 380.38 489.1 426.75 442.99 531.21

T K

3.66 3.58 3.25 3.06 3.15

3.20 2.86 2.85 2.56 2.61

4.426 4.053 3.593 b 3.517 3.611 3.226 3.294 3.327 3.063 3.087 3.218 2.750 2.835 2.47 2.724 2.650 2.210

“”

,.

.,.

.,

.,

u5)

(15)

394'17' 395.6,'16' 395.5 (I') 460.65 (15) 446,'=' 445.5,'17' 446.6"" 301 (16) 308.6 (la 340.8 (16) 363.6'la' 352.6'18'

341-2,‘la’ 346 (17)

426.9 to 427.0 443.2 c's) 531.5 to 532.2

248.35 to 248.45 (lS) 280.75 (15) 307.55 to 307.75 (15' 312.05 to 312.30 (w) 305 (16) 343.4 (16) 337,'16' 334.6 (le.) 328 (l') 363.2 to 363.25 (15) 364.6 (16) 340.6 (16) 415.55 (15) 380 (17)

g (published values)

p = 101.325 kPa -- WdT kPa K-l

a The impurity content of di-t-butyl ether (see text) was assessed by g.1.c. on the assumption of equal molar area-sensitivity for all compounds, b Value in original publicationC2) is incorrect.

16.5 2.20 2.05 0.08 0.17

0.35 (W 0.007 w 0.04 C3) 0.003 (3)

0.1 a

0.14 (11)

g:3:2,

0.08 0.01 0.10 0.02 0.02

593.3 194.4 71.62 61.70 82.09 18.49 24.13 33.53 8.334 7.461 19.88 0.898 4.498 0.016 0.472 0.204 0.003

kPa

2.

WdT ___

T = 298.15 K

1. Purities (y is the mole fraction of impurity present), vapour pressures at 298.15 K, boiling temperatures at 2 kPa and 101.325 kPa, and values of dp/dT

From correlation t-Butyl ethyl ether Di-s-butyl ether Di-isobutyl ether Dipentyl ether Di-isopentyl ether

Dimethyl etherc4* 5, Ethyl methyl ether@) Diethyl ether@) Methyl propyl ether Isopropyl methyl ether Butyl methyl ether Ethyl propyl ether t-Butyl methyl ether Dipropyl ether Butyl ethyl etherc7) Di-isopropyl ether Dibutyl etherc7) Di-t-butyl ether Decyl methyl ether Methyl phenyl ether@) Ethyl phenyl etherc3) Diphenyl ether@)

F

PlkPa

7.625 9.135 10.833 12.879 15.288 17.936 21.982 26.013

(b)

9.080 10.784 12.830 15.241 17.890 25.958 31.282

265.510 269.069 272.192 275.815 279.117 282.695 286.213 289.840 293.576 301.800 305.784

(b)

3.485 4.281 5.105 6.221 7.406 8.903 10.610 12.652 15.065 21.759 25.780

Butyl methyl ether

250.183 253.215 256.504 259.812 262,953 270.618 274.664

Isopropyl methyl ether

253.500 256.731 259.868 263.198 266.492 269.702 273.855 277.570

Methyl propyl ether

T/K

1

AdPa

2 7 92 1

-1 -2 -37

I

(8)

(7)

0 0 1

(61)

::i; (25) (30) (43) (39) (54)

(13)

-1

(20)

(31) (65)

--II

5

1 83

-: -37 -2

II

293.600 297.159 301.818 305.813 310.372 314.839 319.550 324.731 329.233

278.630 282.813 287.428 291 A40 295.708 300.320 303.856

281.706 285.765 290.067 290.067 294.836 298.934 303.311 308.016

T/K

(4

(b)

@I

15.042 17.691 21.720 25.750 31.070 37.111 44.471 53.875 63.274

37.322 44.677 54.091 63.490 74.865 88.945 101.078

31.331 37.371 44.724 44.727 54.133 63.531 74.905 88.997

dkpa

AdPa

-3 -2

-1: -8 -8

::

0 1 1 3 0

:

6

11 23 3 6 -79 -61 -84 18

I

-3

-2

-1

-5 -20 -3

0 2 2 0 0

1

3

f

1

-1 12 -5 -2 -78 -50 -58 60

II

334.153 339.198 343.163 343.989 348.618 352.801 357.802 362.574 366.657

304.592 308.717 312.455 316.903 321.185 324,824

311.655 312.389 316.649 320.487 325.068 329.412 333.133

(4

(b)

(b)

74.996 88.739 100.867 103.544 119.632 135.801 157.304 180.210 201.725

103.752 119.841 136.014 157.509 180.439 201.976

101.114 103.799 119.892 136.052 157.552 180.438 201.844

plkpa

0

AdPa

1 21 -12

-: -9 -3

1 4

-11 68 3 39

-15

-31 49 -28 -60 -53 115 129

I

2 1

3 7 22 -24

-5 -6

-2

-2 19 9 82 -5 -7

30 -11 -43 45 -59

21 103

II

TABLE 2. Observed vapour pressures. Ap = (pObS - pCalc) where poaio has been obtained from: I, equation (I), and II, equation (2). Values for which the residuals are in parentheses were omitted from the sets of points fitted. The letters (a) and (b) indicate the apparatus used for the measurements

Di-isopropyl 284.779 288.403 292.095 295.639 300.265 304,237 308.776

6.442 7.621 9.130 10.829 12.873 15.283 17.938 21.981 21.992

(4

ether (a) 10.662 12.712 15.122 17.778 21.812 25.839 31.160

Dipropyl ether 292.974 296.324 300.037 303.651 307.420 311.274 314.983 319.842 319.848

ether (a) 21.805 25.843 31.156 37.194 44.576 53.942

f-Butyl methyl 287.997 291.980 296.393 300.668 305.293 310.310

(b)

3.711 4.521 5.344 6.457 7.639 9.145 10.839 12.883 15.291 17.947 21.992

ether

Ethyl propyl 261.367 264.735 267.667 271.080 274.198 277.639 280.980 284.484 288.062 291.508 296.029

-3 -5 -1 -1

-2 -3 -2 -4 -2

4

2 0

4

2 2 0

50 -48 -43 43 -15 -28

-2 -3

-2 -1

-Y -1

-1

: 4

1 0

5

0

1

34 -52 -35 59 6 -9

44

:

1 3

-1

1;’

0 2

-1 -1 -1

1

-0 -2 -3 -4 -3

4

313.230 317.928 323.103 327.604 332.390 337.573 341.547

319.856 324.020 328.777 333.446 338.378 343.811 348.533 353.554

314.675 317.985 324.332 328.178 328.976

291.507 296.026 296.027 299.896 304.322 308.671 313.250 318.302 322.697

37.199 44.561 53.961 63.367 74.743 88.818 loo.951

21.996 26.026 31.341 37.380 44.739 54.144 63.545 74.921

63.351 71.313 88.805 100.933 103.610

17.941 21.984 21.986 26.008 31.326 37.373 44.721 54.128 63.536

(4

(4

(4

(4

-3 -9

1 6 2 3 1

0 30 36 42

-9

4 7 11 16 17

1:

-4 -2

-2 -2 -3 -3 -6

-2 -5 -4

0 3

1

1 2 1 1

4 4 13 5 8

-2 -1 -0 -3 -2 -3 -4 -3 -2

342.359 347.005 351.207 356.228 361.007 365.122

358.999 363.157 364.022 368.893 373.295 378.557 383.586 387.883

333.468 337.526 342.343 347.023 350.978

327.366 332.429 336.303 337.044 341.638 345.729 350.624 355.297 359.295

103.576 119.720 135.878 157.382 180.219 201.847

89.008 101.105 103.777 119.879 136.045 157.559 180.476 202.031

119.700 135.835 157.164 180.280 201.818

74.906 88.995 101.122 103.581 119.899 136.059 157.564 180.474 202.029

(4

(4

(4

(4

1

-16 18 -12 -17 -1 16

2 3 16

-7 -8 -8 -13

41 13 -3 -37 -47

16 14 11 9 3 -5 -19 -23 -38 1 5 4 7 9 5 4

3

0

-12 27 1 -5 1 -3

1: 1 -15

-3 -2

-5 -35 -33 -16 55

-21

-2

;;; \o

methy

341.118 341.156 341.290 342.651 347.955 352.307 355.968 359.074 360.792 361.576 362.896 363.380 364.765 364.999 367.184 369.310 371.154

Decyl

289.810 292.024 294.819 298.564 301.853 305.677 309.197 313.101 316.913

Di-t-butyl

T/K

2.913 3.211 3.788 4.592 5.411 6.512 7.689 9.191 10.986

(b)

(b)

0.355 0.356 0.358 0.389 0.530 0.677 0.828 0.976 1.068 1.112 1.191 1.221 1.310 1.335 I .479 1.642 1.797

ether

ether

PIpPa

r:

-1

1: -1 -0 -1

-Y

-0

-1; -11 -11 -11

8

0 0 0

0

Ap/kPa

1:

-2

I

-0

-0

-0 -0 -1

2 -1

-3

II

0

0 0 0 0 0 9 0

0 0 0 1

0 0 2 5 I

381.310 384.008 391.913 395.910 400.514 404.789 409.475

371.476 373.865 375.055 378.169 380.905 383.345 385.580 389.651

320.913 324.990 328.901 334.060 334.046 338.483 343.555 348.517

2.88? 3.255 4.577 5.402 6.507 7.693 9.197

1.824 2.045 2.162 2.501 2.835 3.161 3.489 4.164

12.945 15.349 18.000 22.041 22.042 26.070 31.389 37.421

TABLE

(b)

@I

:

-2 -2 -2

-2 -2

7:. -3 -2

tl 1

0

2

0

1;

-14 -17 -7 -5

2-continued

7: -5 -6

-9 -4

1;

1: -1

-1

-1: -29 -34

-6

-3

0

0

2

3

414.056 418.821 423.714 428.406 434.506 439.804 445.809 451.716 457.958 464.826 470.813 476.743 483.638 489.955 496.083 501.602

353.769 359.507 364.561 369.953 375.819 380.306 381.254 386.505

10.898 12.934 15.344 17.993 22.029 26.058 31.372 37.413 44.762 54.161 63.560 74.927 89.000 103.793 119.882 136.033

44.172 54.176 63.576 74.943 89.022 101.159 103.830 119.747

PlkPa

(a)

(b)

3 1

1; -9 30

-5

-10:

-4553

II

(494) (465)

(515)

(588)

355 -34 -117

(-236)

-13 -108

:I 2 Ei :z:; (539) (g;

-0 -2 33

-85 -371

120 151

AdPa

1:: 62” 2; ‘ifi

I

phenyl

477.407 485.300 492.426 498.307 503.766 508.392

Diphenyl

ether

phenyl

390.588 398.068 404.640 410.595 415.505 420.077

Ethyl

383.030 389.411 395.203 400.014 404.429 408.242

Methyl

26.555 33.074 40.022 46.611 53.481 59.915

20.441 26.526 33.024 39.978 46.566 53.453

ether

26.547 33.024 39.966 46.587 53.424 59.950

ether

-3

-1 -3

-4

-: -2 -2

-1

-1 -1

0 1

0

1

3 0

1

-2

-1

-3

-1

-1

1 2

0 0

0 0 0 0 3

3

0 0 1

512.826 516.876 520.623 524.202 527.302 530.672

423.966 427.605 431.003 434.158 437.149 439.800

411.805 415.086 418.171 421.060 423.600 426.314

66.654 73.327 79.965 86.740 92.971 100.144

59.940 66.570 73.277 19.972 86.762 93.152

66.614 73.266 79.992 86.732 93.021 100.137

1:

-3

-4 -1

-3 -1 -2 -1

ii 4

1

2 0 0

-2

-1 -0 -3

-3 -1

-3 -1 -2

0 1 0 1 5

1

0 0 1

533.684 536.505 539.155 541.632 544.166

442.494 445.002 447.371 449.589 451.694 453.792

428.726 430.984 433.183 435.263 437.291

106.906 113.568 120.124 126.525 133.332

100.033 106.788 113.486 120.057 126.571 133.334

106.820 113.381 120.084 126.697 133.426

-3

-6 --8 -7

-2 -5 -3 -4

-3 -1

-3

2

4 5

2

3

-4 -6 -4

-3 -1 -2

-3 -2

-1

5 0

4 6 0

4

6

172

D. AMBROSE,

J. H. ELLENDER, TABLE

Dimethyl ether Ethyl methyl ether Diethyl ether Methyl propyl ether Isopropyl methyl ether Butyl methyl ether Ethyl propyl ether l-Butyl methyl ether Dipropyl ether Butyl ethyl ether a Di-isopropyl ether Dibutyl ether a Di-t-butyl ether Decyl methyl ether Methyl phenyl ether Ethyl phenyl ether Diphenyl ether

C. H. S. SPRAKE,

AND

R. TOWNSEND

3. Coefficients of equation (1) A

-B

6.0823 5.9552 6.05115 6.01737 6.02669 6.04631 6.03958 6.09379 6.03075 6.06257 5.97678 5.93018 5.94436 6.22652 6.17595 6.14658 6.13913

882.52 906.50 1062.409 1067.229 1044.324 1180.416 1151.991 1173.036 1233.748 1252.485 1143.073 1302.768 1266.583 1698.829 1489.502 1509.276 1802.984

31.90 51.11 44.967 45.674 44.203 51.166 50.787 41.366 56.708 56.685 53.810 81.481 58.778 86.683 69.577 78.502 95.013

a Coefficients for these compounds adapted from those given by Cidlinsky and Po1ak.o)

In these equations p is the pressure, A, B, C, a,, . . ., a, are adjustable coefficients, B,(x) is the Chebyshev polynomial in x of degree s, and x = (2T- (T,,,+ T,i,)}/ CT,,,- Twin), Tk, and Tmin being two temperatures respectively just above and just below the extreme measured values. Throughout, the measured International Practical Kelvin Temperatures T6s have been treated as interchangeable with thermodynamic temperatures T. Residuals Ap = (pobs-pcarc)are given in table 2, pcalc being the value obtained for the stated temperature from the appropriate equation. In some earlier papers in this series, including that reporting work on diethyl ether ,(2) two sets of Antoine coefficients have been given, one to cover the full range of the observations and the other to represent more exactly a restricted range near the normal boiling temperature. The measurements described in this paper are either of insufficient precision to warrant recommendation of a second equation or, extending over a relatively short range, are adequately represented by the equations in table 3 ; except that for ethyl propyl ether the following equation provides a closer representation in the range 54 to 202 kPa than does the equation in table 3: log,,(p/kPa)

= 6.03561-1150.141/((T/K)-50.963).

(3) It is not certain why the precision obtained for most of these compounds is lower than that obtained in our measurements on many other compounds but the most probable cause is that traces of water remaining in the samples despite the drying process through which each was passed might have resulted in incipient separation of phases in the region round the thermometer. In the case of butyl methyl ether, there is a discrepancy between the two sets of observations (a) and (b), for which no reason is apparent, and only the points of set (a) were included in the program for fitting the equations given, as these were assumed to be the more reliable; the residuals for this compound in table 2 correspond to a temperature difference of

417 248 284 285 336 326 215 221 244 261 253

Diphenyl ether &Butyl ethyl ether Di-s-butyl ether Di-isobutyl ether Dipentyl ether Di-isopentyl ether Divinyl ether Ethyl vinyl ether Ally1 ethyl ether Ally1 propyl ether Ally1 isopropyl ether 1841.835 1114.865 1276.377 1275.155 1477.244 1445.838 968.965 1001.285 1099.757 1175.571 1139.952

943.586 716.220 1481.492 1476.292

1301.141

1086.231 1139.868

1132.252

987.645 1189.879

995.841

999.016 1055.010

982.869

242.557 549.903 629.984 630.562 727.972 707.202 481.747 492.191 542.244 579.295 560.764

188.121 279.937 183.700 339.066 501.578 194.481 229.034

332.236

271.191 276.540 224.031 353.339 343.081 215.322

a AH: column (i), from equation (5); column (ii), from calorimetric real gas from AH” where appropriate.

t: 537 523 355 364 401 428 415

545 407

365 366 414 387 471 438 454

388

292

311 284 362 289 341 383 390

Butyl ethyl ether Di-isopropyl ether Dibutyl ether D-t-butyl ether Decyl methyl ether Methyl phenyl ether Ethyl phenyl ether

329 334 325 367 360 351

250 253 259 265 261 287

see table 5 see table 5

1.239 0.952 0.976 1.634 1.405 1.346

0.054 1.361 1.033 1.018 1.830

0.149 0.202 0.007 0.076 0.964 0.043 0.064

0.304

0.170 0.298 0.132 0.337 0.369 - -0.003

&

13.09 5.364 7.209 7.269 10 9.412 3.792 4.038 5.169 6.016 5.603

2 3.087 4 4.142 3.875 5.260 5.009 4.722 6 6.082 5.200 8 6.731 11.3 8.560 9.257

N,n”

65.0 32.6 40.2 43.1 54.8 51.6 26.4 27.5 32.2 36.0 33.9

36.8 32.0 44.4 37 2 6216 46.9 50 .7

18.5 23.9 27 .2 27 5 2614 32 4 31:4 29.6 35 7

(3

37 61 (x) 62:30 (26) 46.84 (z) 51 .04 cm

31.99 ul)

48.2 29.9 34.4 34.5 41.8 40.2 26.2 26.8 29.6 31.5 30.5

21.4 25.1 26 59 26 51 (=) 26:8 ’ 26.1 29.6 29.0 27.9 31.4 31.27 (la) 32.1 29 2 29 10 (lx) 3614 ’ 31.6 45.5 39.0 40.7

AH/kJ mol-l u K Tb (ii) (ii) (Q

27 .09 (as1 27 64 WA ’ 32 30 (x) 31:24 w5) 30.17 cz5) 35.55 (12) 35 ’ 66 c=)

298.15

measurements. Values from reference 25 have been readjusted for the

-1.384 -9.811 -13.298 -13.364 -16.816 -16.891 -8.224 -8.495 -9.336 - 10.768 -10.168

-1.186 -2.648 -1.248 -4.267 -9.989 -0.996 -1.507

-3.640

-2.615 -2.677 -1.681 -4.238 -4.240 -1.165

az

4. Coefficients of equation (2) applicable below 250 kPa, values of carbon number n or effective carbon number rP, and enthalpies of vaporization AH at 298.15 K and at the normal boiling temperature Tb

Dimethyl ether Ethyl methyl ether Diethyl ether Methyl propyl ether Isopropyl methyl ether Butyl methyl ether Ethyl propyl ether t-Butyl methyl ether Dipropyl ether

-

TABLE

2

174

D. AMBROSE,

J. H. ELLENDER,

C. H. S. SPRAKE,

AND

R. TOWNSEND

about 0.06 K in the region of overlap of (a) and (b), and this decreases to about 0.03 K at the lowest observations. Table 1 includes values of p and dp/dT at 298.15 K and of T and dp/dT at 2 and 101.325 kPa, all calculated from equation (2), and published values of Tat 101.325 kPa.(15-“) Results for three aromatic ethers f3) have been recomputed on IPTS-68 uniformly with the current work and entries for these compounds appear in the tables; in addition, for completeness, there are entries in several of the tables for diethyl ether.c2) 4. Correlation

and estimation

of vapour pressures

To make the survey of this series of compounds more complete and to extend the correlation which is described below, published values for some ethers not included in the present experimental programme were used in the numerical study, namely values for dimethyl ether,c4* 5, ethyl methyl ether,‘@ butyl ethyl ether,(‘) and dibutyl ether;(‘) equations for these compounds are in tables 3 and 4, and values calculated from the equations are in table 1. The precision of the observations for the first two of these compounds is relatively low but satisfactory fits were obtained. For the last two compounds the precision is similar to that of the work described here; the investigators, Cidlinsky and Polak, also reported measurements on butyl methyl ether, ethyl propyl ether, dipropyl ether, and d&isopropyl ether, and their values of pressure are 0.1 to 0.5 per cent higher than those given by the equations in table 4 (corresponding to temperature differences of 0.02 to 0.1 K). Values for dipropyl ether published by Meyer and Hotz, (I91 which are within 0.1 per cent (corresponding to 0.02 K) of those given here, are of particular interest because they were obtained with apparatus of similar type to that used in this work; such a small difference approaches the limit of agreement that can be expected between two independent investigations. Other values, reported by Bingham for methyl propyl ether, ethyl propyl ether, and dipropyl ether, (20) by Nicolini for di-isopropyl ether,(21) and by Smutny and Bondi for di-t-butyl ether@“) are not in good agreement with the present results. The vapour pressures were correlated in the manner described for ketones,“’ with the symmetrical ethers, including dimethyl and dibutyl, as the reference series. In order to extend the correlation above C,, decyl methyl ether was included as a reference compound with an effective carbon number IZ* = 11.3, a value allocated from examination of a preliminary plot of normal boiling temperature against carbon number N. When the correlated boiling temperatures of methyl propyl ether, isopropyl methyl ether, butyl methyl ether, ethyl propyl ether, di-isopropyl ether, methyl phenyl ether, and ethyl phenyl ether were compared with those calculated from the equations of table 4 agreement within 0.3 K was found in the ranges 1 to 200 kPa for the aliphatic compounds and 1 to 100 kPa for the aromatic compounds ; the agreement was slightly poorer for butyl ethyl ether, and there were discrepancies of 2 K for ethyl methyl ether. The original data for this last compound, however, are probably of low accuracy, a fact to be referred to again when pressures in the range above 200 kPa are considered. As with ketones, the branched compounds.,

VAPOUR

PRESSURES

OF

ETHERS

175

namely t-butyl methyl ether and di-t-butyl ether, showed larger discrepancies (2.5 K at 1 kPa) than the straight-chain compounds, and proved to be more volatile at low pressures than is indicated by this correlation based on the boiling temperature at 101.325 kPa. The close conformity of the two aromatic ethers with the aliphatic series is to be noted (agreement for diphenyl ether is not good, as might be expected since IZ* is greater than that for methyl decyl ether the terminating member of the reference series and the correlation involves extrapolation of polynomials). Estimates were made of the boiling temperatures of some other ethers for which there are few experimental data. For all these compounds n* was calculated from published values of the normal boiling temperature except that for dipentyl ether the true value n = 10 was used; the correlated temperatures for the nine different pressures were used as input data for fitting by equations; coefficients of these equations are in table 4, and values calculated from them are in table 1. Application of the correlation to the five compounds containing an olefinic bond is defended on the ground that satisfactory values were obtained in this way for some olefinic ketones and hydrocarbons.“) The following equation, of the same form as was used for alcohols and ketones,“) reproduces the points in the range 5 to 200 kPa for the reference compounds of the correlation just described within 0.025~ (corresponding at worst to a temperature difference of about 1 K): log,,(p/kPa) = 7.1972+0.17520n-(916.74+184.766n)(T/K)-’ -(9.6590+1.17110n)10-4T/K -(1.34082-0.152687n)10-6(T/K)2. (4) If used with the values of n* in table 4, equation (4) reproduces the values obtained in the correlation for all the other compounds, including those whose properties were estimated, nearly as well. Outside the bounds 5 and 200 kPa extrapolation in either direction quickly leads to discrepancies for some compounds of 0.1~ or more. If the vapour pressures of alkanes, alcohols, ketones, and ethers are plotted on one graph it is apparent that ketones and ethers nearly form one family different from alkanes and markedly different from alcohols, which last have much steeper curves, and it would be possible for the vapour pressures of ketones and ethers to be represented by a single equation. Such unification however would result in slightly poorer agreement than is obtained with equation (4) and its analogue for ketones. No measurements were made at pressures greater than 205 kPa, and the equations in table 5 were computed by the procedure used for ketones.c8) The equations satisfy the tests described in reference 8 but perhaps not as convincingly as do those for the ketones, and they may be less reliable. For example, the amounts by which the critical pressures exceed the values calculated from the Antoine equations vary from 4 to 11 per cent, a greater range than we have found for other families of compounds; the finding may be correct or it may arise from errors in the measured critical properties or from the fact that the lower precision of the ebulliometric measurements has resulted in poorer control of the Antoine constants and therefore less well aimed extrapolation. Table 5 also includes equations for dimethyl ether and ethyl methyl ether, for which the published values extend to the critical points. The equation for

513 501 498 531 501 646

293

261 287 292 284 383

1941.627 1976.334 2161.230 1930.159 2149.663 2091.074 2031.252 2901.313

1895.416

1474.422 2116.324

a0

aI 762.594 542.135 720.020 741.041 678.954 731.500 806.813 689.685 805.240 719.114 896.490

a This coefficient was originally printed with the wrong sign.‘2)

273 250 253 259

401 438 467 477 465

TmaxK

171

K.dK -9.679 -4.583 -6.933 -5.756 -4.992 -4.612 -7.026 -4.332 -5.636 -6.100 -5.355

a2

3.149 3.511

4.719

3.157 1.286 3.226 a 3.880 2.272 3.014 5.046 2.795

a3

0.422 0.003 -0.119 -0.063

-0.285 -0.075

-0.077

0.658

a4

400.1 437.8 466.74 476.25 464.48 512.78 500.23 497.10 530.60 500.32 645.6

T,IK

5.24 4.41 3.642 3.801 3.762 3.371 3.370 3.430 3.028 2.832 4.25

AMPa

5. Coefficients of equation (2) applicable up to the critical pressure, critical temperatures, critical pressures, and acentric factors w

Dimethyl ether Ethyl methyl ether Diethyl ether Methyl propyl ether Isopropyl methyl ether Butyl methyl ether Ethyl propyl ether &Butyl methyl ether Dipropyl ether IX-isopropyl ether Methyl phenyl ether

TABLE

0.189 0.235 0.281 0.272 0.266 0.317 0.336 0.267 0.371 0.332 0.348

w

VAPOUR

PRESSURES

OF ETHERS

177

the former compound appears to be satisfactory but that for the latter does not conform to the general pattern, and it is probable that the values on which it is based are in error. Enthalpies of evaporation AH at 298.15 K and the normal boiling temperatures Tb in table 4 were calculated according to the equation: AH = (B- V,+RT/p)T(dp/dT), (5) from the appropriate values of dp/dT. The molar volumes V, of the liquid were obtained from the known or estimated densities. For those compounds whose critical temperatures and pressures are known the second virial coefficient B was estimated by use of the equations suggested by Tsonopoulos(23) (which are based on measured values for ethyl methyl, diethyl, and d&isopropyl ethers). For comparison with those obtained by means of equation (5), values of AH at the same temperatures obtained in this laboratory by calorimetric techniques are quoted in table 4.(11, 12y24, 25) Agreement is good (within 2 per cent), and is notable particularly for decyl methyl, methyl phenyl, and ethyl phenyl ethers at 298.15 K where the values calculated in the present work depend on considerable extrapolation to low pressures of the equations in table 4; the agreement for these three compounds may be to some extent fortuitous, but it seemed to justify calculating AH at 298.15 K for the other compounds of low volatility. The calculated entropies of evaporation at the normal boiling temperature AH/T, of all the compounds except t-butyl methyl, di-isopropyl and di-t-butyl ethers are between 86 and 93 J K-l mol-I. The values for the three named branched compounds are lower, between 83 and 86 J K-l mol-I. We wish to acknowledge the contribution made to this work by Dr J. E. Connett, who prepared the sample of di-t-butyl ether. REFERENCES 1. For part Martin, 2. Ambrose, 3. Collerson, 1965,

4. 5. 6. 7. 8.

XL11 see Ambrose, D.; Connett, J. E. ; Green, J. H. S. ; Hales, J. L.; Dead, A. J. ; J. F. J. Chem. Thermodynamics 1975, 7, 1143. D.; Sprake, C. H. S. ; Townsend, R. J. Chem. Thermodynamics 1972,4, 247. R. R.; Counsell, J. F. ; Handley, R.; Martin, J. F. ; Sprake, C. H. S. J. Chem. Sot.

3697.

Cardoso, E.; Bruno, A. J. Chim. Phys. 1923,20, 347. Kennedy, R. M.; Sagenkahn, M.; Aston, J. G. J. Amer. Chem. Sot. 1941, 63, 2267. Berthoud, A.; Brum, R. J. Chim. Phys. 1924,21, 143. Cidhnsky, J.; PO&~, J. Collection Czechoslov. Chem. Comman. 1969, 34, 1317. Ambrose, D. ; Ellender, J. H.; Sprake, C. H. S.; Townsend, R. J. Chem. Thermodynamics 1975, 7, 453.

9. Ambrose, D.; Broderick, B. E.; Townsend, R. J. Appl. Chem. Biotechnol. 1974, 24, 359. IO. Ambrose, D. J. Phys. E. 1968, 1, 41. 11. Andon, R. J. L.; Counseh, J. F. ; Lee, D. A. ; Martin, J. F. J. Chem. Sot., Faraduy Z 1974, 70, 1914.

12. Andon, R. J. L.; Counsell, J. F.; Lee, D. A.; Martin,

J. F. J. Chem. Thermodynamics 1975,

7, 587. 13. Andon, R. J. 14. Ambrose, D.; 15. Timmermans, Amsterdam.

L.; Martin, J. F. J. Chem. Thermodynamics 1975, 7, 593. Counsell, J. F.; Davenport, A. J. J. Chem. Thermodynamics 1970, 2, 283. J. Physico-Chemical Constants of Pure Organic Compounds, Vols 1 and 2. Elsevier : 1950 and 1965 respectively.

178

D. AMBROSE,

J. H. ELLENDER,

C. H. S. SPRAKE,

AND

R. TOWNSEND

16. Handbook of Chemistry and Physics, 50th Ed. Chemical Rubber Company: Cleveland. 1969. 17. Goldstein, R. F.; Waddams, A. L. me Petroleum Chemicals Industry, 3rd edn. Spon: London 1967.

18. Stull, D. Ind. Eng. Chem. 1947,39, 517. 19. Meyer, E.; Hotz, R. D. J. Chem. Eng. Data 1973, 18, 359. 20. Bit-&ham, E. C. Amer. Chem. J. 191&43,287. 21. Nicolini. E. Ann. Claim. (Paris) 1951. 6. 582. 22. Smutny,. E. J.; Bondi, A: J. Phys. &em. 1961, 65, 546. 23. Tsonopoulos, C. Amer. Inst. Chem. Eng. J. 1974, 20, 263. 24. Counsell. J. F.: Lee. D. A.: Martin. J. F. J. Chem. Sot. A 1971. 313. 25. Fenwick; J. 0.; Hairop, D:; Head, A. J. J. Chem. Thermodynakx 1975, 7, 943.