INDUSTRIAL AND ENGINEERING CHEMISTRY
1138
Vol. 23, No. 10
Some Fusion and Transition Data for Hydrocarbons',' G. S. Parks3 and H. M. Huffman' DEPARTMENT OF CHEMISTRY
N connection w i t h t h e
STANFORD U N I V E R S I T Y ,
CALIF.
Heats of fusion, many of which have not hitherto c a l o r i m e t e r . >lost of the work of Research Projbeen published, are tabulated for fifty-nine hydror e m a i n i n g heats of fusion ect 29 of the American carbons, including normal and branched paraffins, (i. e., those for compounds Petroleum I n s t i t u t e , occaaliphatic olefins, aromatics, hydroaromatics and naphmelting above 35" c,)have thenes. Transition values have been given for eight been measured by t h e sion h a s a r i s e n t o m a k e of these compounds. extensive use of fusion data method of m i x t u r e s or by Certain qualitative relationships are noted among means of an aneroid radiafor hydrocarbons. Accordthese fusion data. ingly t h e heats of fusion of tion calorimeter. E q u a l l y for t y - s i x compounds have important with the inherent been determined. Some of these values have already ap- accuracy of the calorimetric methods, however, is the purity peared in earlier papers (.9, 10, 11). Many, however, have of the compounds studied; and as the requirements of the never been published, and in a few instances, n-octane for present work are rather severe, difficulty has sometimes example, the earlier value is now subject to an appreciable re- been experienced in obtaining samples of sufficient purity. vision in the light of new determinations with purer samples. A material, which is satisfactory to the organic chemist for In view of this condition it now seems worth while to collect the study of reactions or of properties charwteristic of the in one place all these values for the heat of fusion of hydro- liquid state, may contain a few per cent of isomers, the carbons. For purpose of completeness, values for thirteen presence of which produces very erratic results when the compounds for which the present authors hal-e no data specific heats in the crystalline state and the heat of fusion have been taken from the literature. are measured. For this reason the authors have come to Such fusion data are of importance in practical calculations place little reliance upon the density of the sample or even of heat requirements in various processes, in thermodynamic upon the narrowness of the distillation range. From exstudies, such as the calculation of molal entropies or the pre- perience it is felt that the sharpness of the melting point is diction of solubilities, and in the estimation of intermolecular by far the best criterion of purity, as even small amounts forces within organic crystals. of impurity ordinarily cause very marked premclting and I n view of the fact that a number of these hydrocarbons render an apparently excellent material unsatisfactory for apparently exist in the solid state in two different forms fusion measurements. The normal paraffins from hexane to dodecane, inclusive, with a definite transition temperature and a very appreciable heat of transition, a table of transition data has also been were recently prepared and described by Shepard, Henne, prepared. This has seemed desirable, since in many prob- and Midgley (12); the last three in the group of normal lems such heats of transition must be considered, more or paraffins (Table I) were samples derived in the study of less, in conjunction with the heats of fusion. Thus, in com- Buchler and Graves (1). All of the branched paraffins paring the probable forces within crystalline cyclohexane except the 2-methylbutane were prepared by Edgar and his and benzene a t low temperatures, the heat of transition of co-workers (S), and were temporarily loaned to the present the former (1610 calories a t -87.3" C.) should be borne in authors for the measurements. The samples of pseudocumind in addition to its heat of fusion (620 calories a t +6.2" C.) mene, isodurene, and prehnitene were likewise loaned after in order to have it on a fairly comparable basis with ben- the completion of the work of Smith (13-15) and his students. zene (heat of fusion = 2350 calories a t +5.5" C.) which has The methylcyclopentane and 1,2-dimethylcyclopentane(trans form) were recently prepared in very pure form by Chavanne only one solid form. of the University of Brussels and will be described by him Sources of Material in the near future. The samples of n-pentane, trimethylThe collected fusion data appear in Table I. Column 1 ethylene, and diisobutylene were special materials, very kindly contains the condensed formulas of the various hydrocar- prepared for this study by Buc of the Standard Oil Developbons and column 2 their names. The melting points, meas- ment Company. Likewise the propylene, estimated to be ured in degrees Centigrade, appear in the next column of better than 99.9 per cent pure, was recently prepared by van the table, and lastly come the heats of fusion, expressed both de Griendt of the Shell Development Company. The rein calories per gram and in calories per mole. Table I1 maining eighteen hydrocarbons were mostly samples obcontains the transition data for eight of these compounds, tained from Kahlbaum and the Eastman Kodak Company arranged in exactly similar fashion. and further purified a t Stanford University. Some of these For the most part the errors in these fusion and transition have already been described by Parks (6, 9, I O ) and his covalues are u-ithin 1 or 2 per cent. Forty-three out of the workers, and the remainder will be described by Barmore fifty-nine fusion values and all eight of the transition heats and the present authors (5) in a future paper. haye heen obtained by the Nernst method with an aneroid The tabulated data for methane are those of Clusius (2). 1 Received June 1931. The fusion value for ethane is the one recently reported by results obtained in an investigation of t h e heat 9 T h i s paper cant. Wiebe, Hubbard, and Brevoort ( I @ , that for ethylene was capacities and free energ .f some typical hydrocarbon compounds, listed obtained by Eucken and Hauck (4); the value for toluene n Petroleum Institute Research. Financial a s Project 29 of the Am, is Kelley's ( 7 ) . The result for durene was obtained by Smith received from n research fund of t h e Ameriassistance in this work has 1 can Petroleum Institute dona by T h e Universal Oil Products Company. and h1acDougall (1.5) from measurements on the lowering of This fund is being administer by t h e Institute with t h e cooperation of the freezing point of solutions of isodurene in this substance of t h e National Research Council. :e the Central Petroleum Commit as solvent. The values for camphene, anthracene, phenana Director, Project 29. threne, tolane, stilbene, dibenzyl, &dihydronaphthalene, 4 American Petroleum Institute Research Associate.
I
t
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
October, 1931
and dihydrophenanthrene have been taken directlv from Landolt-Bornstein ( 8 ) . I n the cases of benzene, p-"xylene, naphthalene, isodurene, diphenyl, diphenylmethane, and triphenylmethane, the literature already contained fusion values when the present determinations were made. I n general, the newer values agree fairly well with t7ese older data in the cases, such as benzene, where the published data were quite reliable. T a b l e I-Fusion
FORMULA
D a t a for V a r i o u s H y d r o c a r b o n s MELTING POINT H E A TO F FUSION C. Cal./irnm Cal./mole
NAME
NORMAL P A R A F F I N S
CHI CzHa C4Hio CsHia CsHir C7His CsHis COHIO CIOHPZ CiiHzr CizHzs CzoHii CzsHsz C33H68
-1x2 5 -183 6 -139.0 -129.7 95.0 - 90.6 - 57.3 - 53.9 - 30.0 - 25 9 - 9.6 4- 3 6 . 4 53.3 71 1
Methane El hane n Butane n Pentane n-Heyane n-Heptane n-Oct ane n-Sonane %Decane n Undecane n Dodecane Eicosane Pentacosane Tritriacontane
-
++
14.0 22 2 18 0 27.7 36.1 33 7 43 2
224 668 1,050
2.noo
48 3 34.1 51 3 a2 0 53.6 54.0
3.110 3,370 4.930 5.280 6.870 5.330 8,730 14.680 15.890 25,080
16.9 21 2 23.6 14.0 16.0 16.9 5 3 18.9 14.9
1,220 2 120 2.260 1,400 1,600 1,690 530 2,160 1,700
25.0 16.7 25.7 16.8
700 700 1,800 1,880
30.1 17.2 29.3 25.8 38.1 20.6 25.2 36.0 57 37.4 23.0 20 0 17.2 19.5 14.9 20.1 28.8 30.4 26.4 33.7 25 0 28.7 40.0 30.7 21.1
2.350 1.580 3,110 2.740 4,040 2,180 3,030 4,610 7.600 5,020 3.080 2,680 2.310 2.620
9.6 7 4 19 5 1.5 7 16 2 22 4 17.6
790 620 1.640 1,540 1.590 2.920 3.160
41 2
BRANCHED PARAFFINS
CsHii CiHia CiHis CiHie C7Hl8 CiHis CiHl8 CsHis CaHis
2-Met hvlbutane 2 - b l e t h ) lhexane 3 - E t h i IiJeritane 2.2- Dimrt h \ lpentane 2 4.Dimeth~lpentane 3.3-Dimethy lpentane 2.2.3-Trimeth~llrutane 2,2,4-Trimethylpentane Hexamethylethane
C2H4 CaHs CsHis CsHis
Ethylene Propylene Trimethylethylene Diisotiutylene
C6He CiHs CsHio CiHio CsHio CsHio CvHiz CioHs CloHii CioHir ClOHl4 CiaHi4 CioHia ClOHI4 CioHii CiiHia CIZHLO CizHis CizHiz Ci4Hio CirHio CirHio Cl4H12 Cl4Hl4 Ci~Hi6
Benzene T oI u e n e o-Xr Iene m-X, lene +Xylene Ethvluenzene PseGdocumene Naphthalene Camphene Durene Isodiirene Prehnitene $-Cymene n-Biitylbenzene l e y [ - Biityli,enzene p-Meth!lnaphtbalene Diphenyl Hcxamethylbenzene Diphenylmethane Anthracene Phenanthrene
-160.5 -119.1 -118.5 -125.0 -1110.6 -134.9 25.4 -107.8 104
-
+
ALIPHATIC OLEFINS
-169.5 -184.9 -134.2 101
-
+- 9 55 . 51
AROMATICS
-
25 3 53 5 13 2
+-- 9.5
1
5 ++- 4480.0 51
+- 79 3 24.0 -
7.7 68.9 88.5 - 58.1 34.1 68.6 +165 5 25.2 4-216.5 96.3 60 124 51.4 92.1
++ + ++ ++ +
Tolane
Stilsene Dibenzil Triphenylmethane
2.ono
2.8.50 4,440 4.930 4,440 6,890 4.450 5.1 10 7.200 5.600 5,150
HYDROAROMATICS AND NAPHTHENES
+
CeHio Cyclohexene -104.1 6 2 CaHiz C? clohexarie ChHu hleth, Icyclopentane -143 0 l . ~ - ~ i m e t h ~ l c y c l o p e n t a n e-119 0 C7H14 C~HM Me! hylcyclohexane -126.9 23.9 CioHi~ 11-Dihydronaphthalene C14Hln Dihydrophenanthrene 94 (CsHa. CHz)z
++
T a b l e 11-Transition FORXUL.4
CH4 CIHIO CaHio C~HII C~HM CsHis CIIH24 CizHis CizHis
Data for S o m e Crystalline Hydrocarbons TRANSITION NAME POINT H E A TOF TRANSITION C. Cal./gram Cnl./mole Methane -252.7 1.1 18.1 n-Biitane - 165 8.7 500 Cyclohexene -134.4 11.9 980 Cvcl:,he\ane - 87.2 19 1 1610 2,2.4-Trimethylbutane 152. 1 5 7 570 Hexamelh\lethane -125.0 4 2 480 n-Undecane - 37.0 9.7 1510 Hexameth\ lbenzene - 165 1.5 240 Hexamethylbenzene 4-110.6 2.6 420
-
In the special case of wnonane there seems to be a sharp transition between two crystalline forms only 2.4 O C. below the melting point. Under the circumstances it was found practically impossible t,o measure this transition heat with reasonable accuracy and therefore it has been lumped in with the heat of fusion. For most practical purposes this procedure will cause no difficulty.
1139
Conclusions
In a recent paper by Parks and Todd (11) the equation AS!
=
4
- 1.43
was suggested, in which the molal entropy of fusion (i. e. the molal heat of fusion divided by the absolute temperature of the melting point) is related to n, the number of carbon atoms in a normal paraffin. According to this equation, the heats of fusion of n-pentane and n-decane, for example, should be, respectively, 27.4 and 44.1 calories per gram. The values which have now been found experimentally are 27.7 and 48.3 calories per gram. Thus in some cases the predicted heats of fusion of Parks and Todd come very close to the actual values, wliile in other cases they involve rather considerable errors. As a result of the present additional data, it is now believed that it is practically impossible for any such simple relationship, connecting up the heat of fusion and the chemical constitution, to be more than a rough first approximation. In spite of the fact that quantitative relationships seem t o be lacking, it is possible to indicate the following qualitative tendencies among these fusion data: I n proceeding upward in the series of normal paraffins, the molal heats of fusion increase, a t first very rapidly and later more slowly. IncreaFed branching in a paraffin hydrocarbon (the total number of carbon atoms remaining constant) leads to a marked decrease in the heat of fusion. Cyclic hydrocarbons, like branched paraffins, have much lower heats of fusioa than the corresponding normal paraffins. Withdranal of hydrogen from a paraffin or a naphthene t o produce an olefin or a benzenoid hydrocarbon results in no regular or marked effect on the heat of fusion. Thus, the molal values are 668 calories for ethane and 700 calories for ethylene, and 1590 calories for methylcyclohexane and 1580 calories for toluene. I n general, when there are two crystalline forms of a given hydrocarbon at low temperatures, the sum of the heat of transition and the heat of fusion is comparable in magnitude to the heat of fusion of a compound existing in only one crystalline form. Thus for cyclohexane this sum is 2230 calories per mole as against 2350 calories for the heat of fusion of benzene. Acknowledgment
The writers wish to take this opportunity to thank their collaborators, S. Benson Thomas, Mark Barmore, Albert C. Daniels, Monroe E. Spaght, and Samuel S. Todd, for some of the data used in the present paper. They also desire to acknowledge their indebtedness to the Ethyl Gasoline Corporation, the Standard Oil Development Company, the Shell Development Company, the Standard Oil Company of Indiana, Lee Irwin Smith of the University of Minnesota, George8 Chavanne of the University of Brussels, and Albert L. Henne a t Ohio State University for the valuable hydrocarbon samples which made this investigation possible. L i t e r a t u r e Cited (1) Buchler and Graves, ISD. END. CHEX., 19, 718 (1927). (2) Clusius, Z. physzk. Chem., Abt. B3, 41 (1929). (3) Edgar, Calingaert, and Marker, IND. EKG. CHEW, 19, 146 (1927); J. A m . Chrm. Soc., 61, 1483 (1929). (4) Eucken and Hauck, Z . p h y s i k . Chem., 134, 161 (1928). ( 5 ) Huffman, Parks, and Barmore, J . A m . Chem. SOL., 63 (Oct., 1931). (6) Huffman. Parks, and Daniels, I b i d . , 62, 1547 (1930). (7) Kelley. I b i d . , 61, 2738 (1929). (8) Landolt-Bornstein, " Physikalisch-Chemische Tabellen," Vol. 11. p p , 1471-73, Springer, 1923. (9) Parks and Huffman, J . A m . Chem. Soc., 62, 4 3 P (1930). (10) Parks, Huffman, and Thomas, I b i d . , 62, 10 2, 3241 (1930). (11) Parks and Todd, IND. EKG.CHEX.,21, 1236 ,.1929). (12) Shepard. Henne, and Midgley, J . A m . Chenh. SOL, 63, 1948 (1931). (13) Smith and Li nd, Ibid., 62, 4144 (1930). (14) Smith and Lux, I b i d . , 61, 2994 (1929). (15) Smith and MacDougall, I b i d . . 61, 3001 (1929). (16) Wiebe, Hubbard, and Brevoort, I b i d . , 62, 611 (1930).
