T H E SOLUBILITY OF NAPHTHALENE I K SOME DERIVATIVES OF FURFURAL*
ARTHUR A. SCNIER
Of late years several investigators’ have expressed the view that polarity and internal pressure effects were largely responsible for deviations from Raoult’s law; and quite recently Sidgwick* has emphasized that solubility data often throw considerable light on the nature of the bond in chemical compounds; in particular, such data assist in distinguishing between polar and non-polar bonds. Naphthalene is believed to be a non-polar compound; it can be readily prepared in a high state of purity; its melting point is rather low, and its latent heat of fusion is known with a fair degree of certainty. Considerations such as these have led several investigators to determine the solubility of naphthalene in a rather large number of solvents. Thus far, however, no determinations have been recorded for derivatives of furfural, no doubt because such compounds have only lately become commercially available. Since furfural is a ring compound containing double bonds and oxygen in the ring it was felt that solubility studies of some of its derivatives might prove of general interest in connection with the general subject of valence mentioned above, as well as of interest to anyone working more directly with these compounds. I n the present paper the solvents used were furfuryl alcohol, furfuryl acetate and methyl, ethyl, n-propyl, n-butyl furoates.
Experimental The synthetic method of AlexejenJ was employed in making the solubility determinations recorded in the paper. The method consists in heating a sealed tube containing weighed quantities of solvent and solute and noting the highest temperature a t which but few small crystals of solute remain in equilibrium with the solution. Ward4 has described precautions which must be taken to assure the attainment of equilibrium conditions a t the solubility temperature. The whole matter has been studied rather thoroughly in this laboratory; the results of this study are to be found el~ewhere.~The apparatus and procedure were essentially those of Sunier and Rosenblum6
* Contribution
from the Chemical Laboratory of the University of Rochester. ‘Hildebrand: “Solubility” (1924); Proc. Kat. Acad. Sei., 13, 267 (1927); J. Am. Chern. SOC., 51, 66 (1929); Ward: J. Phys. Chem., 30, 1316 (1926). Sidgwick: “The Electronic Theory of Valency” (1928). Alexejew: W e d . Ann., 28, 305 (1886). Ward: J. Phys. Chem., 30, 1316 (1926). Sunier: J. Phys. Chem., 34, 2582 (1930). 6Sunier and Rosenblum: J. Phys. Chem., 32, 1049 (1928).
SOLUBILITY O F NAPTHALENE I N FCRFURAL DERIVATIVES
1757
which in turn are only slight modifications of the apparatus and procedure used by Ward. I n the present research four units were built in close proximity to one another and all stirred and shaken from one motor; it was therefore possible to makc four determinations a t once. I n two of the units were placed bi-metallic thermo-regulators, capable of keeping the two four liter baths to 0.01’;these regulators could be easily adjusted a t the end of an hour or half hour period to the next tenth degree (the procedure adopted by Sunier and Rosenblum) ; this facilitated matters considerably. A two-unit outfit possessing certain advantages is described and discussed in another paper.l The tubes were made up in much the same way as described earlier. With the solvent furfurylalcohol a slight momentary flash was noted on sealing tubes containing considerable quantities of liquid; this did not, however, cause a loss in weight of more than two milligrams The thermometers used were compared, before and after most of the runs were completed, with thermometers recently standardized by the Bureau of Standards. Materials All materials were obtained from the Eastman Kodak Company and were their best grades. The naphthalene was recrystallized from methyl alcohol and care was taken2 to remove adsorbed solvent from the crystals. The melting point of the recrystallized material was 80.12’ when determined carefully in the manner recommended by the Bureau of Standards3. Kone of the solvents was purified further. It would seem desirable to give the physical constants supplied by the manufacturers at the time the materials were purchased : Furfuryl Alcholol B. P. 75- 76’ / 1 7 mm. ” Acetate ” 84- 85’ / z j mm. Methyl Furoate ” 83- 84’ / zj mm. Ethyl ” M.P. 30- 33’ n-Propyl ” B. P. 105--107’ / 2 5 mm. n-Butyl ” ” 118-120°/ 2 5 mm. Results The experimental results are given in Table I. The weight of solute is given first, then the weight of solvent, then the calculated mol fraction and finally the solubility temperature in degrees centigrade. 1 2
3
Sunier: J. Phys. Chem., 34, z j 8 z (1930). Sunier: J Phys. Chem., 34, 2582 (1930). Bureau of Standards, Sci. Paper No. 340.
ARTHUR A. SUNIER
I758
TABLE r Solvent: Furfuryl Alcohol Weight CIoH,
I . 486 1.639 1.309 1.011
0.862 0.712
0.826 0.643 0.4667
Mol Fraction
Solub. Temp.
0,4045 0.344 0.617 0.606
0.738 0.785 0.619 0.561
71.4 72.6 68.3 67.2
0.792 1.649
0,455 0.249 0,332 0.186 0.1094
64.3 53.0 58.7 46.3 32.4
Weight Solvent
1.273 I59 2.910 2 .
Solvent: Furfuryl Acetate ,638 I . 261 I
0.941 0.712 I ,076 0.541 0.746 0.660 0.798 0.4226
0,404 0,703 0.732 0.870 0.438 0.922 0.935 0.925 I ,688 I . 902
0.816 0.662 0.584 0.472 0.729 0.378 0.466 0,438 0.341 0.196
70.0
61.4 56.2 48.3 65.2 40.9 48.3 46.2 37.4 19.4
Solvent: Methyl Furoate 1.462
0.992
1.854 I . 119 0.887
0.515
0.765 0.647
56.8
1.035
0.592 0.780 0.516
51.8
1,355 I ,652 1.927
0.392 0.3'3 0.2484
42.3 35.0 27.7
67.9
Solvent: Ethyl Furoate 1,340 1 . '77 1.150
0.423 0.495 0.825
0.776 0.723 0.604
1,039
I . 280 1.624 I . 223
0.470 0.353 0.288
0.812
0.452
66.8 63.5 55.5 44.9 33.8 25.6
SOLUBILITY O F NAPTHALENE I N FURFURAL DERIVATIVES
I759
TABLE I (Continued) Solvent: n-Propyl Furoate Weight CloH,
Mol Fraction
Solub. Temp.
0.698
0.791 0.674
67.9 60. I
1.035 1.376
0.544 0.481
1.772
0,393 0.303
Weight Solvent
1.656
0.525
1.201 I .027
1.059 0.953 0.684
1.895
50.2
45.3 36.4 25.6
Solvent: n-Butyl Furoate 0.530 0,934
0,754 0.615
1.514 1.873
0,523 0,434
I . 241
0.383 0.232
I
,810
64.9 54.9 47.7 39.2 33.9 21.3
FIG. I
The results have been plotted in Fig. I in the customary W3y-k~g IrT vs I/T. Large plots were constructed and the mol fractions a t rounded temperatures were read off; these values are found in Table 11.
I 760
ARTHUR A. SUNIER
TABLE I1 Solubility of Naphthalene in Derivatives of Furfural at Rounded Temperatures, expressed in Mol Fractions of Naphthalene Temp.
75
70 65 60
55 50 45 40 35 30 25 20
Furiuryl Alcohol
0.857 0.684 0.474 0.352 0.275 0.219 0.1758 0.1446 0.1194 0.1048 0.0849 0.0728
Furfuryl Acetate 0,900
Methyl Furoate
Ethyl Furoate
n-Propyl Furoate
n-Butyl Furoate
0.908 0.824
0.272
0 . goo 0.811 0.726 0.644 0 .j 6 j 0.491 0.425 0.366 0,313 0.267
0.233 0 . I99
0.913 0.830 0.753 0.684 0.618 0.555 0.498 0.445 0,379 0,351 0.309
0.192
0.910 0.826 0.750 0.678 0.607 0.543 0.483 0.430 0.379 0.338 0.297 0.260
0.811 0.726 0.644
0.565 0,491 0.42j
0.367 0.316
0.227
0.747 0.668 0.597 0. j31 0.471 0.415 0,36; 0.321 0.281 0.246
0.272
FIG.z
Discussion of Results As has been mentioned earlier no recorded data could be found in the literature bearing on these systems; comparison with previous results is thus impossible. In an earlier paper' it was shown that errors in the solubility temperature as large as 0.1' were not likely t o occur if only fine crystals were ~
Sunier: J. Phys. Chem., 34,
Zj82
(1930).
SOLCBILITY O F NAPTHALENE IN FGRFURhL DERIVATIVES
1761
present in the tube and if the rate of heating was 0.01' per minute or less; since these two precautions were taken it i s thought the recorded temperatures are accurate to i0.1'. However it is realized that various impurities might have been present in the solvent, but it would seem quite likely that the shapes of the curves relatiye to one another would not be greatly changed by the presence of some common impurity. Furfuryl alcohol is the poorest and n-butyl furoate the best solvent for naphthalene of any of the materials under consideration. The curve for the former solvent approximates that of n-but'yl alcohol' as can be seen from an inspection of Fig. z which compares data on various aliphatic alcohols. The curve for the latter solvent is very near, if not equal to, that shown by an ideal system such as naphthalene and chlorobenzene' or naphthalene and ethylidene bromide.3 The solubilities of furfuryl acetate and methyl furoate appear to be identical from So down to 40'; below this the latter substance dissolves a little less naphthalene. The influence of methyl, ethyl, n-propyl and n-butyl groups is clearly seen in Fig. I ; a very regular increase in the solubility is noted for these substances. It would be of interest to study the longer chained derivatives to see if a solubility greater than the ideal would he obtained; if such were the case it is quite likely that solvation effects inus? he operative as Hildebrand' has pointed out. I t seems rather remarkable tha.t furfuryl alcohol, cont~ainingfive carbon atoms, has a solubility one might expect for normal pentnnol; the former compound has a ring structure containing two double bonds and oxygen, the latber is of course a straight chain compound. It would appear that n-butyl furoate is a non-polar compound. In an earller pape? the subject of polarity and solubility is discussed briefly and reference is there made t(J tlie work of Debye," Smyth7 and Stewart.8 Further diecussion docs not wern necessary at this tinie.
Summary The solubility of naphthalene in six deribatives of furfural has been determined a t a variety of temperatures. Certain regularities have been pointed out. Sunier: J . Phys. Chem., 34, 2 5 8 2 11930); Ward: 30, 1316 1 1 9 2 6 1 \\-ard: J. P h x Chem.. 30, 1316 (1926). Sunier and Hosenblum: J . Phys. Chern.. 32. 1049 1 9 z b ) . ' Hildebranc!: "Solubility" i192.i'. Sunirr: J. Phys. Chem., 34. 25k2 (1930). fi Debye: "Polar ~ I o l e c u l e s " 11929). Smyth: Chem. Reviews, 6, j49 :19291. Stewart: Chem. Reviews, 6, 483 !1929'1. 1
