Dec., 1945
2075 HEATCAPACITY, HEATOF FUSION AND ENTROPY OF I~-?$-DECYLHENEICOSANE
the invariance of the classical keto-enol and acid dissociation constants over the entire neutralization range. Thus, within the 2.7 and 2.0% differences noted above for acetylacetone and benzoylacetone, a satisfactory correlation has been demonstrated between the enol plus enolate ion fraction determined by the Kurt Meyer procedure and that calculated from the acid enol properties. Taking the latter as a basis, it may be concluded that the Kurt Meyer bromine addition procedure described above for partially neutralized solutions furnishes results that are reliable to within the 2.7 and 2.0% deviations observed. Summary 1. At 25', the fraction of acetylacetone prese n t b the enol form in dilute aqueous solution (3.3 X lo-* M ) is 0.170. The corresponding
[CONTRIBUTION FROM
THE
value for benzoylacetone in 1.7 X M aqueous solution containing 7.5% ethyl alcohol by weight is 0.341. The classical acid dissociation constants of the enol forms of the above compounds at and 5.89 * 25.0 * 0.1' are 6.88 * 0.15 X 0.11 X respectively. 2. The fraction of the above compounds present in the enol plus enolate ion form a t 25' has been measured as a function of the fraction neutralized in dilute aqueous solution by the Kurt Meyer bromine addition reaction. An equation expressing this relationship has been derived that is based on the dissociation constant and the keto-enol equilibrium. Values predicted by this equation are larger than the measured values for acetylacetone and benzoylacetoneby 2.7 and 2.00J0, respectively. FLUSHING, NEWYORK
RECEIVED AUGUST28,1945
SCHOOL OF CHEMISTRY AND PHYSICS OF THEPENNSYLVANIA STATE COLLEGE AND
THE
DEPARTMENT OF CHEMISTRY OF STANFORD UNIVERSITY ]
The Heat Capacity, Heat of Fusion and Entropy of 11-n-Decylheneicosane BY F. B. FISCHL,~ B. F. NAY LOR,^ C. W. ZIEMER,' G. S. PARKS~ AND J. G. ASTON' This is the beginning of a series of investigations a t The Pennsylvania State College, dealing with hydrocarbons of high molecular weight. A similar series of investigations has been in progress a t Stanford University since 1937. The object of both series is the establishment of a relationship between structure and various thermodynamic functions. Thus it should be possible to estimate the entropy of a high-molecular weight hydrocarbon from previous systematic calorimetric data on other compounds. This paper furnishes a comparison of data on the same compound obtained independently in the laboratories of Stanford University and The Pennsylvania State College. Preparation and Purification of Sample.-The sample was one of the first compounds prepared by API Project 42. It was synthesized by treating decylmagnesium bromide with ethyl carbonate. The alcohol, after careful fractionation, was dehydrated to the olefin which was catalytically hydrogenated. The saturated hydrocarbon was fractionated through a 10-platelow pressure fractionation column (0.1 mm.) and passed several times through silica gel. The Heat Capacity Measurements.-In the measurements a t The Pennsylvania State College the sample was accurately weighed into calorimeter D, which was designed for the measurement of thermal data of solids and liquids. After freeing the sample from the last traces of air by repeated freezings and evacuations to lo-' mm. of mercury, the calorimeter space above the (1) At The Pennsylvania State College. (3) At Stanford Univu#ity.
compound was filled with approximately one-half atmosphere of helium. The detailed description of this adiabatic solids calorimeter will be published shortly along with a discussion of the accuracy.' It is estimated that all thermal data obtained with it, above 40°K., have an accuracy of 0.2oJo. It is possible to reproduce the heat capacity data on the solid with a precision of better than 0.1% above 80'K. The measurements a t Stanford University were carried out as described previously.' In view of the accuracy of the various factors involved, the absolute error in the experimental values of the heat capacities and heat of fusion is probably less than 0.7%, except insofar as impurities in the sample of this hydrocarbon may cause premelting or otherwise influence the results. The fortuitous errors were ordinarily under 0.25%. The defined calorie, taken equal to 4.1833 international joules, has been used throughout the studies in both laboratories. Temperature measurements have been on the basis: 0°C. = 273.16' K. The value 436.822 has been adopted as the molecular weight of 11-n-decylheneicosane. The sample of this material used in the calorimeter at The Pennsylvania State College was 0.15216 mole: that used a t Stanford was 0.06905 mole. The heat capacities measured at The Pennsylvania State College on the solid compound, uncorrected for premelting, are listed in Table IA. Here the temperature rise can be estimated from the intervals between points of a series. The results of the heat capacity measurements ob(8) Aston and Ziemer, to be published. (4) Parka, THISJovami, 47, a88 (1916),
2076
F. B. FISCHL, B. F. NAYLOR, C.W. ZIEMER,G.S. PARKSAND J. G.ASTON
0
40
80
120
160
200
Vol. 67
240
Fig. 1.-The heat capacity of solid 11-n-decylheneicosaneat The Pennsylvania State College, without premelting CWrection 0; with premelting correction 8 ; at Stanford University 0 .
tained at Stanford University in both the solid and liquid range are listed in Table IB. The two sets of heat capacity results for the solid phase are also represented in Fig. 1, where all the Pennsylvania State College data have been plotted to-
TABLEIB TABH~~~ cApAcIm OF 1 l - n - D ~ c n ~ ~ ~ ~ r m m ~ (At Stanford University) Con
T$gR,cWt;../
CP Temp., cal./d;g./
OK.
mole
CP Temp., cal./d;g./ OK. mole
250.2 162.5 Crystals 185.0 118.2 TABLE IA 255.8 168.3 195.5 124.1 80.3 66.62 THE HEATCAPACITY OF SOLID ~ ~ - ~ - D E C Y L H E N E I C ~ S A82.5 N E 67.93 259.7 173.5 201.7 127.2 (At The Pennsylvania State College) 264.9 182.9 83.9 69.85 206.0 130.4 CP, CS CP Temp., cai./deg./ T:p, cal./d;g./ Temp., cal./d;g./ 89*5 72.29 213'' 134' Liquid OK. mole mole OK. mole 94.6 74.70 218.2 137.3 Series I 209.22 131.66 27.53 17.679 108.1 81.82 223.7 140.8 282.0 224.0 30.89 21.175 124.0 89.55 228.2 143.8 285.0 224.6 58.73 46.54 215.34 135.18 34.78 25.16 137.6 95.66 232.8 147.6 289.8 226.0 60.94 50.21 222.02 139.49 39.18 29.76 149.6 101.7 237.7 150.4 293.9 227.6 66.27 54.69 228.49 143.86 44.17 35.20 166.6 108.9 239.7 152.3 297.4 229 4 71.66 58.92 235.92 149.66 49.61 40.30 175.4 113.3 243.4 155.9 77.33 62.94 243.46 155.80 55.20 45.28 88-68 70.56 248.07 160.39 60.75 60.07 gether with the Stanford values which have been 95.70 74.80 256.91 167.93 05.92 54.37 deduced for rounded temperatwe. 103.28 79.03 262.63 178 25 The heat capacity measurements on the liquid 111.22 82.91 268.43 223 62 Series111 (misc.) a t The Pennsylvania State College are listed in 119.50 86.87 SeriesII 92 88.14 Table I1 and shown graphically in Fig. 2. There 129.88 91.67 138.71 95.81 12.37 4. 140 206.85 130.06 was definite evidence of lack of reproducibility of 147.67 99.97 13.14 4.535 213.67 134.00 these liquid heat capacities* The Of the 166.74 104.03 15.31 5.724 155.52 sample prior toeachdeterminationisshown below: 166.33 176.00 185.96 196.07 206.86
108.43 113.32 118.40 123.65 129.40
16.60 17.79 19.21 21.36 24.29
6.848 249.99 7.814 9.385 11.540 14.590
161.72
Series A.-The sample was cooled to 55'K., heated slowly, and melted; the heat capacity measurements were started immediately after the fusion which was in all cases within ten minutes.
2077 HEATCAPACITY, HEATOF FUSION AND EwrKorY OF ~~-~-DECYLHENEICOSANE
De.,1945
277.6
282.6
287.5
292.5
297.5
T, O K . Fig. 2.-The
heat capacity of liquid ll-n-decylheneicosane at The Pennsylvania State College 0; at Stanford University 0 .
urements on the liquid were begun one hour after the fusion. Series E and F.-In both cases, tlie sample was treated exactly alike. The compound was supercooled in one-half hour from 297 to 274'K. Series G.-The compound was heated to 315'K. and allowed to remain a t this temperature for twenty hours. It was then supercooled in fifty minutes to 275'K. TABLE11 Series H.-After heating the sample to 303'K. TEE HEATCAPACITY OF LIQUID ~~-~-DECYLHENEICOSANE and allowing it to remain at this temperature (At The Pennsylvania State College) for ten hours, it was supercooled to 276'K. Temp., CP, Temp., CP, over a period of twenty-four hours. The liquid OK. cal./deg./mole OK. cal./deg./mole sample was then kept between 275-276'K. for Series A another twenty-f our hours. 288.36 222.78 292.41 226.30 I11 contains a comparison of heat capacTable 293.36 224.47 296.52 226.70. ity values at rounded temperatures as derived 297.76 226.13 Series F independently in our two laboratories. In this Series B 276.32 219.68 connection an attempt has been made to correct 284.84 222.08 285.63 222.71 for remelting in the values €or the solid from 250 B upward. The estimates for such premelting 280.16 223.63 290.38 224.18 295.74 225.54 295.11 225.78 corrections have differed considerably in magnitude in the two laboratories, although the comSeries C seiies G parative heat capacities as actually measured in 288.65 223.41 277.32 220.26 the neighborhood of 260' were within 0.5%. 293.81 225.39 281.78 221.68 The Melting Point and Heat of Fusion.Series D 286.60 223.21 The procedure at The Pennsylvania State Col291.20 224.68 290.72 224.16 lege was the same as that described previously.' 296.15 226.39 226.29 296.36 ~. The melting point data thus obtained indicated series H 3.52 mole per cent. impurity (liquid soluble, solid Series E 277.78 220.24 insoluble) with 282.34 * 0.05'K. as the resulting 276.16 220.39 221.69 282.33 melting point, corrected to the pure state. Four 279.61 221.51 223.00 287.16 determinations of the heat of fusion are summa283.82 222.75 224.58 291.95 rized in Table IV. These results were corrected
Series €3.-The
sample was supercooled over a period of 20 hours from 287 to 277'K. Series C.-The sample was cooled to ll'K., heated slowly, and measurements on the liquid were taken immediately thereafter. Series >The sample was cooled slowly to 180°K.,heated rapidly, and melted; the meas-
288.26
224.03
287.01
226,
a
(6) Aston and Mouerb. Taxi
Jomwu,68,2864 (1986).
2078
F. R. FISCHL, B. F.NAYLOR, C. W.ZIEMER, G. S. P w s
AND
J. G. ASTON
Vol. 67
~ ' A B L B 111 TABLEI V THEMOLALHEATCAPACITY OF 11-DECYLHENEICOSANE AT MOLALHEAT OF FUSION OF ~~-~-DECYLHENEICOSANE ROUNDED TEMPERATURES (At The Pennsylvania State College) C, in cal./deg./mole Cor. Re.
Temp., O K .
(At The Pennsylvania State College)
(At Stanford University)
Dev..
Yo
6 , 25
8.66 10.13 15.23 20.27 30.78 40.65 42.43 57.60 64.89 71.40 77.21 82.35 87.10 91.71 96.35 100.92 105.58 110.36 115.38 120.46 125.90 131.93 138.18 145.00 152.60 160.13 167.50 171. 18
280 290 300
220.92 223.98 227.00
...
....
....
....
.... ....
.... .... ....
....
....
....
.... .... ....
..". .... ....
66.40 72.56 77.97 82.95 87.76 92.52 97.11 101.82 106.24 110.69 115.63 121.13 126.59 132.62 138.69 145.46 152.67 161.19 170.36 ....
+2.32 $1.63 +0.98 +O. 73 $0.76
Liquid 223.2 225.8 230.2
OK.
heat in ut, cal.ymole
271.121-285.996 257.058-286.065 254.751-287.432 255.241-289.153°
19479.34 22208.29 22891.37 23207.96
S C dT, effect cal.$mole cal./moie
rn
fusion cal./moie
2808.85 349.89 17020.4 5207.83 22.88 17023.3 5890.10 14.79 17016.7 6212.80 16.05 17011.2 Av. 17017.7 * 6.0 This heat of fusion was found by summarizing the energy inputs required for the determination of the melting point.
Solid
12 15 20 25 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 265
meiting
Temp. interval,
The Entropy from Thermal Data.-Tables VA and VB summarize the calculation of the entropy at.25'C. from calorimetric data. The difference between the two laboratories in molal entrop change from 80-298.16'K. is 1.48 e. u. ( 0 . 7 1 4 which is within the experimental error of both laboratories. The molal entropy of the liquid a t 298.16'K., based entirely on the data a t The Pennsylvania State College and including an extrapolation from 0-15'R. using the Debye theory with six degrees of freedom, is 259.60 ( t 0 . 5 ) e. u. 44sthe heat 'capacity measurements at Stanford University did not go below SO'K., the entropy increment from 0-80'K. has also been estimated by the application of the extrapolation method of Kelley, Parks and HufTman6 to $e Stanford data a t 80 and 110'. Thereby the increment has been computed as 52.1 ( 1.5) e. u. Combination
$0.88
f0.80 +0.89 +0.63 $0.30 +0.22 +O. 56 +o. 55 +0.52 +0.37 +0.32 $0.05 +0.66 +1.71
f
.... f1.03 $0.81 +1.41
for premelting on the basis of 3.52 mole per cent. impurity.
TABLE VA MOLAL ENTROPYOF 11-1Z-DECYLHENEICOSANE FROM THERMAL DATAAT 80°K. (The Pennsylvania State College Measurements) 0-15.00°K., Debye extrapolation (6 degrees of freedom, 0 = 64.303) 2.710 1540°K. graphical, XC, d In T 48.004 * 0 . 1 Mdal entropy at 80'K.
50.714
=t
0.1 e. u.
TABLE VB MOLALENTROPY CHANGE OF 1l-n-DECYCHENEICOSANEFROM THERMAL DATAFROM 80 TO 298.16'K. (At Stanford University) (At The Pennsylvania State College) 137.78 * 0.7 80-282.34"K. graphical, J C p d In T 136.390 0.3 80-282.2'K. graphical, JC, d In T Fusion, 16980/282.2 60.17 =t 0 . 3 Fusion, 17018/282.34 60.27 * 0 . 1 282.2-298.16OK. graphical, s C p d In T 12.45 * 0 . 1 282.34-298.16"K.graphical,$CPdIn T 12.220 * 0.02 (liquid) (liquid) 210.40 * 1.1e. u. Total (80"K.-298.16"K.) 208.884 * 0 . 4 e. u. Total (8OoK.-298.16 OK.) f
-
CorresDondindv. o , , the measurements at Stanford @ & ,.ejd 282.2 0.10K. as the corrected melting point, with an estimate of 3.4 mole per cent. Of impurity. Two determinations for the heat of
( 0 ) Kelley, Parks and Huffman, J . Phys. Chcm., 88, 1802 (1929). The constants for Class I ( i . e., aliphatic) compounds have been used in obtaining the present estimate. Recent tests have shown that the extrapolation method with these constants is valid to within 2 or 3% for aliphatic compounds that are straiaht-chained or involve no
follows: run 1, 16,984 cal./m
