[CONTRIBUTION FROM THE DABNEY CHEMICAL LABORATORY OF THE UNIVERSITY OF TENNESSEE]

PARACHOR STUDIES AT VARIOUS TEMPERATURES

C. A. BUEHLER, THOMAS S. GARDNER, AND MILTON L. CLEMENS, JR.

Received March $8, 1037

The parachor, P, as derived by Sugden, has been stated in the form

p = - M r t D - d ’

where M is the molecular weight, y the surface tension, and D and d are the densities of the liquid and vapor respectively at the same tempera- ture.

The CH, group.*-By applying the above formula to hundreds of organic compounds and fixing, as a standard for comparison, the covalent bond at zero, Sugden’ arrived at an average value of 39.0 for the CH2 group. This value has been the subject of much discussion ever since. Mumford and Phillips2, from a study of high-molecular-weight compounds, con- cluded that the CH2 group should be given a value of 40.0, VogeP, from parachor determinations on the methyl and ethyl esters of n-dibasic acids, obtained 40.3, and Desreux4, from the higher members of the paraffin and normal alkyl fluoride and chloride series, found values which varied but slightly from 39.9. More recently Sugdens has been inclined to accept the value of 39.6 for the CH, group.

These variations at once detract from the usefulness of the parachor in any quantitative approach to the determination of structure. Although the differences were at first thought to be due to impurities or inaccurate measurements, it now appears that they are of a more fundamental nature. As Desreux point,ed out, they doubtless indicate that the atomic parachors are not strictly additive. In fact the CH2 values of Desreux for the paraffins and alkyl fluorides and chlorides are unique in their constancy.

*Shortly after the submission of this manuscript Baylise, J . Am. Chem. Soc., 69, 444 (1937), by the method of least squares, found the C& value to be 39.92.

* SUQDEN, “The Parachor and Valency,” George Routledge t Sons, Ltd., London,

9 MUMFORD AND PHILLIPS, J . Chem. soc., 1%8, 2112. a VOGEL, J . SOC. Chem. Ind., 63,8b (1934). 4 DESREUX, Bull. 8oc. chim. Belg., 44,249-287 (1935). 6 SUQDEN, J . Chem. SOC., 1936, 15M).

1950, p. 35.

167

168 BUEHLER, GARDNER AND CLEMENS

D

0 8744 0 8615

0 8638 0 8529 0 8414

0 8579 0 8480 0 8379

0 8541 0 8342 0 8250 0 7943

Of the numerous determinations made in this laboratory on purified compounds, those for the acetates in Table I and benzene and its homo- logues in Table I1 will illustrate the variation shown in the CH2 group values even in the same homologous series. To make certain that there was no temperature effect, the determinations were carried out a t several temperatures, and from these the mean parachors, to be used in finding the CH2 values, were obtained. In the acetate series, if the first member be excluded, it is to be noted that the values agree very well

TABLE I PARACEOR6 OF TEE ACETATE6

d Y Obs. Litr. __--__-

0 0009 21 16 216 2 216 7 0 0013 20 10 216 8

Mean 216 5

0 0005 22 39 257 2 267 1 0 0007 21 20 257 0 0 OOO9 19 97 256 7

Mean 257 0

23 18 296 9 21 96 296 3

0 ooo6 20 92 296 5 Mean 296 6

23 65 335 9 21 68 336 6 20 69 336 0

0 0010 17 70 336 4 Mean 336 2

Ethyl acetate

Propyl acetate

Mc'd'

216.0

266.0

294.0

333 0

n-Butyl acetate

CHI --

40.5

39.6

39.6

n-Amyl acetate

TEMP.. "C.

Obs.

40.0 50.0

40.0 60 .O 60.0

400 50.0 60.0

40.0 60.0 70.0 00.0

- Corr.

40.0 50.1

40.0 50.1 60.2

40.0 50.1 60.2

40.0 60.2 70.3 .XI. 9

I I 1 PABACEOm

In all calculated parachors, unless otherwise noted, the original atomic and

Brit. Assoc. Advancement Sci. Rep., 265-83 (1932). structural parachors of SUGDEN, ref. 1, p. 38, have been used.

c SUQDEN, J. Chem. SOC., 125,1183 (1924).

with the more recent parachors for the CH2 group. However, the ben- zene series not only shows a fluctuation from member to member, but the CH2 parachors are lower than is to be expected on the basis of the newer determinations. It is apparent from these results, which are typi- cal, that, in using the parachor, it is necessary either to employ a mean value, as Sugden did, or to regard the constant value of Desreux as be- ing normal.

The temperature efect and the coordinate link.-In the original studies of

PARACHOR STUDIES AT VARIOUS TEMPERATURES 169

Obs. Corr.

40.0 40.0 50.0 50.1

---

Sugden6 on the influence of temperature on the parachor, a small but steady rise, to which no significance was attached, was recorded for the coordinate compounds, dimethyl sulfate, diethyl sulfate and triethyl phosphate. Later similar differences were observed in this laboratory with phenol-amines under conditions which appeared to exclude dissocia-

D

0.8530 0.8421

COMPOUNDS d

0.0007 0,0010

0.0005 0.0006 0.0008

Benzene

Toluene

Y Obs. ----

26.41 207.6 205.7 24.97 207.4

Mean 207.5

2494 246.2 245.C 24.01 246.6 22.76 246.7

Ethylbenzene

50.0 60.0 70 0

Butylbeneene

50.1 0.8361 60.2 0.8271 70.3 0.8158

Amylbenzene

40.0 60.0

100.0

TABLE I1 PARACRORS OF BENZENE HYDROCARBONS

T'E?dP., OC. I I I I PARACHOBB

40.0 0.8489 27.20 285.4 284.C 60.2 0.8302 24.80 285.1

100.9 0.7935 0.0010 20.71 285.6

40.0 60.0 70.0

100 0

40.0 0.8551 28.10 361.0 361.: 60.2 0.8390 25.81 360.3 70.3 0.8306 24.83 360.4

100.9 0.8036 0.0005 21.84 361.0

60 0 70 0

100 0

60 2 0.8405 70 3 0 8328

100 9 0 8084

iMean I 2 8 5 . 4 1

Mean 360 7

1 28 471 399 5 402 ( 40 0 i l l 40 0 0 8564 40.01 40 01 0.85641 I 28 471 399 51 402 (

a Brit. Assoc. Advancement Sci. Rep., 265-83 (1932).

Calc'd

207.1

246.1

285.1

363.1

402.1

CHrb

39.0

38.9

(2 X)37.7

39.2

b With no details, DESREUX, ref. 4, states that the CHz group varies from 38.58 to 40.32 in this homologous series.

tion.' More recently Rays has reported a like effect with azoxy com- pounds, which are now represented with the oxygen attached by a co- ordinate bond.

6 SUGDEN, ibid. , 127, 1539 (1925). 7 BUEHLER AND SPREEN, J . Am. Chem. SOC., 66,2061 (1934). 8 RAY, J . Indian Chem. SOC., 18,194 (1936).

170 BUEHLER, GARDNER AND CLEMENS

Y

-- 26.52 25.30 24.57 23.15

27.15 24.56 21.55 18.51

31.28 28.66 26.13 23.29

40.66 37.48 34.67 31.38

41.10 38.63 35.56 33.11

33.26 30.64 28.88 26.61

32.53 31.08 29.75

TABLE I11 PARACHORS OF CO~RDINATE COMPOUNDS

ka

1.72

2.07

1.K

2.1$

2.0t

2.0t

1.9!

COMPOUNDS

30.0 40.0 50.0 60.0

40.0 70.0 100 .O 130.0

40.0 70.0 100.0 130.0

40.0 70.0

130.0

40.0 70.0

100.0

150.0

30.0 40.0 50.0

Ethyl nitrate ----

30.0 1.09280.000E 40.01.07840,OOOi 50.1 1.06420.000( 60.21.04790.001:

40.01.0605 70.3 1.0262

100.9 0.9890 0 .000t 130.40.9521 0.001t

40.01.1563 70.3 1.1239

100.9 1.0883 130.4 1.0661 0.000f

40.01.3556 70.3 1.3242

L00.0100.9 1.2905 130.41.2583

40.0 1.2087 70.3 1.1823

100.0100.91.1552 130.0130.41.1282

100.9 1.2336 130.0130.41.2051

150.4 1.1837 175.0174.81.1526

30.0 1.64430.001: 40.01.62180.0011 50.1 1.58990.002!

Ethyl sulfite

189.2 189.5 190.6 190.8

297.3 299.7 301.2 301.5

315.3 317.3 320.2 320.8

328.9 329.9 332.0 332.1

389.9 392.5 393.5 395.8

371.0 372.0 373.2 375,5

196.2 196.7 198.6

Ethyl sulfate

--- 189.6c 190.8

299, 7d 298,4

313.8d 318.4

332.6

393.3

367.P 371.C

193.3d 196.E

Bensenesulfonyl chloride

Methyl p-toluene- sulfonate

p-Toluenesulfonyl chloride

Sulfuryl chloride

D d 4Bl I PARACEOBZI

- P

P :m. )

-1.6 -1.3 -0.2 0 0

-1.1 1.3 2.8 3 . 1

IS&)-

-

-3.1 -1.1

1.8 2 .4

-3.6 -2.6 -0.5 -0.4

-3 .4 -0 .8

0 .2 2.5

-0 .5 0.5 1.7 4.0

-0.6 -0.1

1.8

a Ramsay-Shields-Eijtvos constant. 6 Sugden's original value of -1.6 for the ccijrdinate bond has not been included. c SUGDEN, J . Chem. SOC., 126,1186 (1924). d SUGIDEN, REED, AND WILKINS, ibid., 127,1526 (1925). 0 FREIMAN AND SUGDEN, ibid., 1928,264.

Because of these irregularities it seemed of interest to study the effect of temperature more fully. Coordinate compounds were chosen as one type since some uncertainty has existed over the parachor value for the

PARACHOR STUDIES AT VARIOUS TEMPERATURES 171

coordinate bond in these compounds. Sugdene originally obtained a mean of -1.6 from a series of widely varying values for this bond. In more recent years the same investigator5 has advanced a value of 0 in agree- ment with that of the normal covalent bond.

The parachors as found for the purified coordinate compounds are given in Table 111. I t is apparent that the values are not constant over any considerable range of temperature. At the lower temperatures, as com- pared to Sugden’s calculated parachors, there is a negative anomaly which usually becomes positive a t higher temperatures. Under the circum- stances it appears that we can only arrive at an approximate value for the coordinate bond in these compounds. Since zero values have been ob- tained in all the compounds investigated, save one, this value may be accepted as an approximation. It is of interest to point out that this variation with temperature, a t least for the compounds studied, will permit a distinction to be made between the coordinate and the normal covalent bond.

Although the parachor is constant for many liquids regardless of the temperature, it does exhibit, as a rule, a steady increase with tempera- ture for associated liquids. Because of this there has been a tendency to attribute such temperature variations to association. In the present in- stance such an explanation will not suffice. The compounds studied do not possess the characteristics of associated liquids; in addition, although the validity of the Ramsay-Shields-Eotvos constant, IC, in Table I11 is open to question, it is interesting to note that most of these compounds give values near 2.12 in agreement with the great majority of non-associ- ated liquids.

The temperature e$ect and the hydrogen bridge.-Sidgwick and Bayliss’O have determined the parachors of certain chelate compounds and their isomers. Assuming the parachor to be uninfluenced by temperature, these investigators found the value for the link of the hydrogen bridge used in closing the chelate ring to be - 14.4 units.

In Table IV we have recorded the parachor results obtained at various temperatures on a series of compounds very similar to those investigated by Sidgwick and Bayliss. The ortho compounds are singular in giving values much lower than their meta and para isomers. If we assume that the former contain a chelate bond, its value varies from - 10.8 to - 14.2. Thus, whatever the nature of this bond may be, it differs from the co- ordinate bond in the compounds previously described in having no tem- perature coefficient and, if we accept Sugden’s original parachor values, in being decidedly negative. Of interest, too, is the fact that the chelate, ortho compounds may, as a rule, be distinguished from their meta and

SUGDEN, ref. 1, p. 116. l o SIDGWICK AND BAYLISS, J. Chem. Soc., 2027-34 (1930).

T H E JOURNAL OF ORQANIC CHBMIBTRY, VOL. 2. NO. 2

172 BUEHLER, GARDNER AND CLEMENS

Y

40 46 35.34 31.66 30.06 Mean

40.96 39.25 38.16 36.66

45.36 43.15 41.31 40.33

38.82 34.95 29.94 27.13 Mean

37.77 34 93 33.52 30 96 29.50

34.61 32.47 30.42

41.71 37.83 32.81 29 23 Uean

40.43 38.11 36.23 35.10

TABLE I V PARACHORS OF CHELATE COMPOUNDS AND THEIR ISOMERS

i g __-

274.5 274.9 275.0 275.0 274.9

280.5 282.2 283.1 286.3

285.6 286.0 288.9 289.9

323.3 323.3 323.4 323.3 323.3

327.0 328.0 330.3 330.6 330.9

332.4 333.2 334.0

270.1 270.5 270 5 270 6 270.4

275.3 275.4 278.0 278.3

COMPOUNDS

60.0 100.0 130.0

130.0 150.0 175.0

130.0 150.0 175.0 190.0

30.0 60.0 100 .o

130.0 150.0 175.0 190.0

150.0 175.0 190.0

30.0 60.0 100.0

130.0 150.0

o-Nitrophenol --___-

60.2 1.2776 100.9 1.2333 130.4 1.2OOOO.000!

150.0150.41.18460.000;

130.4 1.2539 150.4 1.2334 174.8 1.2209

190.0191.61.1950

130.4 1.2640 150.4 1.2462 174.8 1.2201 191.6 1.2088

30.0 1.1739 60.21.1436

100.9 1,1000 130.0130.4 1.0735

100.0100.41.1528 130.4 1.1271 150.4 1.1077 174.8 1.0850 191.61.0711

150.4 1.1097 174.8 1.0893 191.61.0691

30.01.1483 60.21.1190

100.9 1.0799 1 3 0 . 0 1 3 0 . 4 1 . 0 4 9 5 0 . ~

130.4 1.1179 150.4 1,1011

175.0174.81.07800.000: L90.0191.61.0683/0.000!

m-Nitrophenol

p-Kitrophenol

Methyl salicylate

m-Methyl hydroxy- benzoate

p-Methyl hydroxy- benzoate

o-Hydroxybenzal- dehyde

m-Hydroxybenzal- dehyde

I PARACEOR8

e i ;ri

274.7 -

283.2

283.2

322.1

331.8

268. C

274. E

- a 3 __

289.1*

283 0

283 0

337.0b

330.9

330,9

281.2b

275.1

~

P OBB.) -

P CALC'D)

-14 2

-1 5 -0 8

0 1 3 3

2 5 3 0 5 9 6 9

-13 7

-3 9 -2 9 -0 6 -0 3

0 0

1 5 2 3 3 1

-10 8

0 2 0 3 2 9 3 2

PARACHOR 8'l'VDrEB AT VARIOUS TEMPERATURES

TABLE IV-Concluded

p-Hydroxybeneal- dehyde

o-Hydroxyaceto- phenone

173

--- 130.0 130.4 1.1171 150 .O 150.4 1.1119 175.0 174.8 1.0914 190.0191.61.0860

30.0 30.0 1.1191 60.0 60.2 1.0914 100.0 100.9 1.0644 130.0130.41.0269

I I I

-- 42.71 41.59 39.11 38,38

40.87 37.15 32.45 29.15 Mean

p-Hydroxyaceto- phenone

130.0 130.4 1.0920 40.06 313.5 150.0 150.4 1.0765 38.28 314.4 175.0 174.8 1.0567 36.71 315.1 190.0191.61.0428 34.78 316.9

8 279, 3c 278,8 279.7 279.7

307.4 307.8 308.0 308.2 307.9

278.2 275.1

320.26

314.1

P

P CALC'D)

4.2 3.7 4.6 4.6

OB0.)-

-

-12.3

-0.6 0.3 1 .o 2.8

0 SIDQWICK AND BAYLISS, ref. 10, p. 2031. b In this value, 6.1 has been included for the six-membered ring. c A noticeable coloration during the heating process may account for the abnor-

mality shown by p-hydroxybenzaldehyde.

para isomers not only by their lower parachor values, but by the fact that they show no variations with the temperature. Such results might be anticipated on the basis of association alone, for it is well known that the chelate compounds present a striking contrastll to their meta and para isomers in possessing little or no association.

EXPERIMENTAL

The liquids, which were mostly Eastman Kodak Company's best products, were fractionated two or three times through a "cold point" column packed with Lessing contact rings. The solids also largely Eastman products, were purified either by fractionation or recrystallization from various solvents. The boiling and melting points, both corrected, follow:

Ethyl acetate, b. p. 76.1-76.4" (740 mm.) Propyl acetate, b. p. 100.7-101.2" (740 mm.) n-Butyl acetate, b.p. 124.3-125.2" (740 mm.) n-Amyl acetate, b.p. 146.5-148.5" (743 mm.) Benzene, b. p. 79.6' (742 mm.) Toluene, b. p. 109.3-109.6" (742 mm.) Ethylbenzene, b. p. 135.1-135.3" (740 mm.) Butylbenzene, b. p. 182.6-185.6' (743 mm.)

11 SIDQWICK, "The Electronic Theory of Valency," Oxford University Press, London, 1999, p. 146.

174 BUEHLER, GARDNER AND CLEMENS

Amylbenzene, b. p. 201.7-203.7" (743mm.) Ethyl nitrate, b. p. 86.9-87.1" (744 mm.) Ethyl sulfite, b. p. 157.0-157.2' (746 mm.) Ethyl sulfate, b. p. 77.8-78.0" (6 mm.) Benzenesulfonyl chloride, b. p. 143.0-143.4" (25 mm.) Methyl p-toluenesulfonate, b. p. 144.6-145.2' (5 mm.) p-Toluenesulfonyl chloride, m.p. 68.0-68.2" Sulfuryl chloride, b. p. 68.4-68.5" (742 mm.) o-Nitrophenol, m. p. 45.345.7" m-Nitrophenol, m. p. 97.2-98.0' p-Nitrophenol, m. p. 114.9-115.6" Methyl salicylate, b. p. 221.2-221.5" (744 mm.) m-Methyl hydroxybenzoate, m. p. 72.2-72.4" p-Methyl hydroxybenzoate, m. p. 127.7-128.3' o-Hydroxybenzaldehyde, b. p. 194.0-194.6 (744 mm.) m-Hydroxybenzaldehyde, m. p. 104.9-106.3' p-Hydroxybenzaldehyde, m. p. 115.8-116.1" o-Hydroxyacetophenone, b. p. 219.0-219.5' (744 mm.) p-Hydroxyacetophenone, m. p. 110.2-110.4"

Physical measurements.-Surface tension determinations were made by the maximum bubble pressure method of Sugden12 in which a glass bubbler was em- ployed. A cathetometer was used to find the manometer levels, and highly purified benzene was the standardizing liquid for determining the apparatus constant from the diameter of the smaller bubbler tube as measured by a filar micrometer. Densi- ties of the compounds were found with a 10-cc. pycnometer; the densities of the vapor, d, were calculated from the relation13:

loglo d/db 5 5 (T/Tb - 1)

where T is the absolute temperature, Tb, the boiling point at 760 mm. in degrees absolute, and db, 0.0122 M/Tb, in which M is the molecular weight. Vapor density values less than 0.0005 were disregarded.

SUMMARY

The parachor of the CHs group is usually not constant even in the same homologous series.

An increase in the parachor with a temperature rise does not always indicate association.

The coordinate bond in the compounds studied has a value of approxi- mately zero; however, this value increases with the temperature.

The bond of the hydrogen bridge employed in forming the chelate ring differs from the above coordinate bond in having a pronounced negative value which is unaffected by the temperature. These chelate compounds differ from their meta and para isomers in that the latter possess higher parachors and, like other associated compounds, show a parachor varia- tion with the temperature.

l2 SUGDEN, ref. 1, p. 208. 13 SUGDEN, {b id . , p. 205.