Methanol 7

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Methanol: Heat Capacity, Enthalpies of Transition and Melting, andThermodynamic Properties from 5300KH. G. Carlson and Edgar F. WestrumCitation: J. Chem. Phys. 54, 1464 (1971); doi: 10.1063/1.1675039View online: http://dx.doi.org/10.1063/1.1675039View Table of Contents: http://jcp.aip.org/resource/1/JCPSA6/v54/i4Published by theAmerican Institute of Physics.Additional information on J. Chem. Phys.Journal Homepage: http://jcp.aip.org/Journal Information: http://jcp.aip.org/about/about_the_journalTop downloads: http://jcp.aip.org/features/most_downloaded

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T H E J O U R N A L OF C H E M I C A L P H Y S I C S V O L U M E 5 4 , N U M B E R 4 15 F E B R U A R Y 1971

Methanol: Heat Capacity, Enthalpies of Transition and Melting, and ThermodynamicProperties from 5-300 oKH. G. CARLSON AND EDGAR F. WESTRUM, JR.

Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48104(Received 22 June 1970)

Thermal properties of methanol were studied by adiabatic calorimetry. The first-order nature of thephase transition at 157.4K with an entropy increment of 0.97 cal mole-I. K-l was confirmed. The heatcapacity of the crystalline phase stable just below the triple point was defined and shown to be extremelysensitive to impurity. No evidence for a second previously-reported phase transition could be detected.The standard entropy (SO) and Gibbs energy function (-[Go-HooJ/T) for the liquid at 298.15K are30.40 and 15.18 cal mole-I. oK-I, respectively. The proposed classification of methanol as a plastic crystalon the basis of its small entropy of melting (4.38 cal mole-l.oK-I) is considered with respect to hydrogenbonding in the liquid phase.INTRODUCTION results in a depression of the freezing point of the alcohol

by about 10 K. Davidson9 also found a second transi-The numerous studies of the physicochemical proper- tion in methanol-d of 0.04 cc mol-J at 158K in addities of methanol include an early heat capacity study tion to the "known" calorimetric transition, which heover a limited range by Parks ,! who in 1925 reported found to have a volume change of 0.43 cc mol-J

the existence of a transition at 161K. In a later However, if the additional transi tion is energeticallycalorimetric study, extending from 14OK in o the liquid small (as expected), the precision of the previousphase, Kelley2 interpreted the transformation with a calorimetric work may have been too low for dismaximum at 157.4K as lambda-type. More recently crimination.a semimicrocalorimetric study was made by Staveley In addition to the aforementioned studies, severaland Gupta3 from lOOoK through the melting point. measurements have been made of the variation in diHowever, their use of a very small sample gave low electric constant in the solid state. Smyth and Mcprecision. Lower-temperature heat capacity measure- NeightiO demonstrated the presence of a hysteresisments were made by Ahlberg, Blanchard, and Lund- loop in the dielectric constant vs temperature similarberg4 over the range 3-28K. in appearance to that for phenol containing a traceAn x-ray structural determination on methanol at of water.!! The dielectric constant associated with113K (Crystal II ) and 163K (Crystal I) by Tauer Crystal I was observed as low as 133K in this study.and Lipscomb5 established the crystals as monoclinic A more recent investigation of the dielectric constantand orthorhombic, respectively. More compact packing of crystalline methanol by Davidson!2 involved a therin Crystal II was attributed to a slight displacement mal conditioning process (cooling to 120oK, heatingof members of the infinite, hydrogen-bonded methanol to 153K, and equilibrating the sample there for severalchains in planes normal to the direction of the chains. hours to remove any undercooled Crystal I) prior toPreparation of singly crystalline Crystal II was found making measurements on Crystal II . Dielectric conto be difficult, and faint superlattice lines were noted stant measurements made without this thermal conin Crystal II as studied. Dreyfus-Alain and Viallard6 ditioning showed a decrease near 150oK, presumablyused an x-ray powder diffraction technique and found associated with conversion from the under cooled Crysa hexagonal structure for Crystal 1. A monoclinic tal I to the stable Crystal II form. Several staticstructure for Crystal II at 93K has also been reported measurements made of the dielectric constant at variousin a recent study by Murti.7 In none of the Crystal II temperatures after equilibration periods of at least 3 hstructure studies is any mention made of a thermal revealed a gradual rise in the dielectric constant atconditioning process to ensure complete phase trans- 155K. This was associated by Davidson with theformation on cooling to low temperatures. Because of gradual rise in molal volume reported by Staveley andthe finding by Staveley and Gupta that methanol Hogg at 156K. At 159.6K a sharp rise in dielectrictends to shatter glass bulbs on warming through the constant occurred which was taken to represent thetransi tion region, a dilatometric investigation was made calorimetric transition. Above this temperature theby Staveley and Hogg.8 With isopentane as the dil- dielectric constant was continuous through the Crystal Iatometric fluid an abrupt volume increment of 0.49 phase. Davidson further noted an electrical conductivi tycc mol-1 at 159K and a smaller gradual change of maximum near 130oK, which he assumed to be oconly 0.14 cc mol-! at 156K were found (rather than casioned by the formation of a small amount of liquidthe single increment, t::.Ht, found in the calorimetric phase at the temperature of the water-methanolinvestigations l- 3) in addition to the 2.75 cc mol-l eutectic. 13 A similar phenomenon at 123K in samplesvolume change attendant on melting. However, the which had not been thermally conditioned was takeninteraction between isopentane and methanol (solu- to represent a eutectic in the under cooled Crystal 1-bility of isopentane is 1.3 mol% in the liquid at 175K) wate r system.

1464


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THERMODYNAMICS OF METHANOL 1465Since recent experimentsl2 indicated the necessity for

adequate thermal conditioning to ensure a pure CrystalII phase, and dilatometric as well as dielectric constantstudies showed the presence of two solid phase transformations where only one had been found by heatcapacity measurements, a new calorimetric investigation waS initiated in this laboratory to clarify the phasebehavior of methanol and to provide a complete, accurate table of the thermodynamic functions. In addition, because of the present interest in globularmolecules,14 a re-evaluation of the plastically crystallinenature of methanol provided a further incentive.

EXPERIMENTALSamples

A sample of Belle refined methanol produced by thePolychemicals Department of E. 1. du Pont de Nemoursand Company was generously provided to this laboratory by Perkins. The alcohol was an extremely purebatch having the reported analysis (in ppm): 0.3acetone, 10 ethanol, 0.3 water, 99.92%-100% methanol,boiling range=0.035C (ASTM). Sample I was distilled into Calorimeter W-14 and weighed 53.551 gin vacuum. Sample II , removed from the bottle twoyears later and transferred to Calorimeter W-24,weighed 61.428 g in vacuum. Final purity of the sampleswas evaluated from the fractional melting data below.

CalorimetersCalorimeter W-14, fabricated from fine silver rod,had a wall thickness of 0.50 mm and was gold plated

on all surfaces. It s geometry resembled that of anotherpreviously describedl5 except that eight 0.40-mm-thickradial (circular) vanes and the bottom were machinedintegrally with the thermometer-heater well, and thata demountable valve designed for sealing fluids withinthe calorimeter was added. The length of the cylindricalportion containing the sample was 7.6 cm and thediameter was 3.9 cm.Since experience indicated that transitions in condensed phases with significant volume increments tendto fracture a soldered joint of the type with which thecylindrical portion of Calorimeter W-14 was solderedto the bottom, a new calorimeter, W-24, was constructed to eliminate this source of failure. The cylindrical shell and the bottom of this calorimeter wereturned from a single rod of OFRC copper and weregold plated. A well with 10 equispaced, 0.25-mm-thick,integral circular vanes was inserted as a press fit fromthe inside of the calorimeter into a machined aperturein the bottom. With the soldered seam made on theoutside of the press fit, expansion of the calorimeter'scontents put the seam under compression rather thantension. Both calorimeters had internal volumes ofabout 80 cc. A pressure of 10 cm Hg of helium gas wasused for conduction within the calorimeters.

CryostatsSample I was measured in the Mark I cryostat,16with manual shield control to maintain adiabatic conditions about the calorimeter. The heat capacity ofSample II was determined in the Mark III Cryostatl7which is designed to utilize automatic adiabatic shieldcontrol during normal heat capacity measurement andthroughout the long periods frequently required forthermal equilibration during phase transitions. De

partures of adiabaticity were in general not greaterthan 0.03K at the time of a thermal upset in thesystem, lasted not more than a minute, and were compensated for by damped sinusoidal regulation in boththe manual and automatic shield control systems. Allmeasurements of temperature, time, potential, resistance, and mass were referred to devices calibratedby the National Bureau of Standards.

CalculationsThe defined thermochemical calorie equal to 4.184abs J, an ice point of 273.15K, and one mole= 32.043 gare assumed in the calculations. Temperatures meas

ured with the platinum resistance themometer (laboratory designation A-3) are considered to correspondwithin 0.04 to the international temperature scalefrom 90-3500 K and within O.03K from 1O-90K,From 4-lOoK a provisional scale was constructed froman equation given by Roge and Brickwedde18 fit tothe resistance, the slope of the resistance vs temperature, and the measured value of the resistance at theboiling point of helium. The heat capacity was adjusted for the slightly different amounts of Apiezon-Tconduction grease and helium gas present with theempty and filled calorimeters. Correction (amountingto 0.1 % of the heat capacity at 325K) in the liquid_'egion of the sample was made for the vaporizationof methanol into the space above the sample. Appropriate adjustment was also applied to the data for curvature (i.e., the difference of the measured t.H/ .T fromdH/dT= Cp ). All calculations including curve fittingand integration were developed by an IBM-704 computer programl9 which first fit a least-squares polynomial in temperature to the heat capacity data andthen performed the necessary operations upon thispolynomial to obtain the final values of the functions.

Heat Capacity MeasurementsMolal heat capacity data on both samples are presented in chronological sequence in Table I. Determinations of enthalpy increments and heat capacities intransition regions are summarized in Table II and may

be integrated into the thermal history by referenceto Table I. Comparison of directly measured enthalpyincrements with those obtained by numerical quadrature beneath the smoothed Cp vs T curve is givenin Table III and provides a test both of the data andof the integration procedure. Table IV summarizes


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1466 H. G. CARLSON A N D E . F . WESTRUM , JR .TABLE I. Heat capacity of methanol. Units are degrees Kelvin and calories per mole-degree Kelvin.

T Cp T Cp T Cp T CpSample I, Mark I Cryostat

Series 1 6.32 0.031 153.84 14.43 Series 147.12 0.047 154.66 14.09i lHt Detns A 7.93 0.069 155.19 14.13 153.68 14.148.48 0.098 155.63 14.23 155.10 14.29Series 2 8.98 0.118 156.06 14.53 156.22 14.269.40 0.135 156.48 14.37 157.40 14.4056.08 6.440 10.45 0.199 156.91 14.2859.42 6.832 11.83 0.284 i lHt Detn F65.32 7.482 12.88 0.374 Series 1571.26 8.067 13.94 0.471 Series 1077.01 8.607 15.15 0.600 153.81 14.0083.09 9.161 16.70 0.776 154.76 11.06 155.02 14.2089.69 9.731 18.48 1.009 156.17 11.14 156.25 14.2297.04 10.26 20.52 1.299 157.02 11.12 1.57.45 14.26105.4 10.84 22.76 1. 631 157.36 11.36113.18 11.49 25.19 2.010 157.78 11.18121.32 12.01 27.86 2.444 158.26 12.31 Series 1630.66 2.881 158.69 11.42Series 3 33.85 3.392 159.19 11.18 129.81 12.4837.51 3.995 160.52 11.24 135.43 12.88

Enthalpy Detn B 41.61 4.504 165.77 11.66 142.30 13.3646.15 5.204 Melting Detns G 149.01 13.83Series 4 50.64 5.780 152.59 13.8855.20 6.362 Series 11 153.82 14.18128.09 12.42 155.02 14.23136.69 13.03 Melting Detns H 156.21 14.26Series 7145.54 13.20 Series 12 157.39 14.255.09 0.014

i lHt Detn C 5.98 0.025 180.38 16.94 Series 176.95 0.043 188.28 16.93Series 5 7.84 0.068 196.86 16.95 156.82 14.128.52 0.090 205.86 16.99 157.95 14.29161. 65 11.32 9.33 0.136 215.17 17.08162.44 11.37 10.43 0.199 224.59 17.2011. 71 0.279 233.92 17.34 Series 18163.00 11.36163.44 11.45 13.08 0.392 243.12 17.53163.96 11.47 14.48 0.528 252.17 17.75 Trans. Detns K164.64 11.48 15.97 0.697 261. 05 17.97165.40 11.53 269.87 18.26 Series 19166.25 11. 61 Series 8 278.78 18.59167.56 11. 72 287.97 18.95 158.33 12.87169.49 12.02 297.41 19.37Enthalpy Detn D

306.81 19.83Enthalpy Detn E 316.10 20.33 Series 20Series 6 325.17 20.83Series 9 159.32 11.054.86 0.014 Series 13 160.19 11. 275.68 0.022 152.81 13.16 Melting Detns J Melting Detns L

Sample II , Mark II I CryostatSeries 21 Series 22 Series 23 Series 24

68.45 7.788Trans. Detns M Melting Detns N 76.04 8.503 Enthalpy Detns P82.86 9.128


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THERMODYNAM ICS O F METHANOL 1467the evaluation of fractional melting data. In thesetables, Ti and Tf refer to the initial and final temperatures of the determination, T to the mean temperature, and AT to the temperature increment involved.Since thermal conditioning is a prerequisite to formation of pure Crystal II,12 a procedure was adopted inwhich the methanol was cooled slowly (i.e., severaldegrees per hour) through the transition region toabout l()()OK, then heated to 150-155K, and thesample kept in this region for 8 h or more after completion of the energy liberation before measurementsTABLE II . Transition region of methanol." Units are degreesKelvin and calories per mole.

T;

151.25

150.04

157.12

151. 25

t:>.Hor'Lt:>.H

Sample I, Mark I CryostatSeries 1, Detns A (6 detns)167.94 358.36

Series 2, Detn C167.10 364.20

Series 9, Detn F167.16 266.47

Sample II , Mark III CryostatSeries 21, Detns M (6 detns only)

157.91 202.27

T t:>.TSample I, Mark I Cryostat

Series 18, Detns K (3 detns)157.42 0.02 43.72157.44 0.01 90.351 ~ . ~ 0.00 ro.M

Sample II , Mark III CryostatSeries 21, Detns M

129.44 8.041 12.45148.40 2.383 13.74150.76 2.358 13.89153.10 2.328 14.09155.34 2.180 15.33156.86 0.887 44.42157.32 0.021 1330157.34 0.014 1900157.38 0.076 679157.64 0.437 549159.12 2.574 12.20161.71 2.635 11. 77

t:>.Ht

152.5

151.5

151.9

152.3

a T i an d Tf ar e the initial an d final temperatures; T, th e mean tem-perature; an d AT the temperature increment involved. AH or l ; i lH refersto directly determined enthalpy increments over th e range TrTi . ; fl.Htis the enthalpy increment associated with the transition after deletion ofthe normal background vibrational or lattice enthalpy.

TABLE III. Comparison of directly measured enthalpy increments of methanol with the integral under the smoothed Cpcurve." Units are degrees Kelvin and calories per mole. Sample I,Mark I cryostat.T; T, t:>.H t:>.Hca1c

Series 3, Detn B53.49 126.59 698.7 698.4

Series 8, Detn D4.21 52.58 127.7 127.7

Series 8, Detn E52.58 153.03 1052.7 1050.5

a T an d T f ar e the initial an d final temperatures of the determinations;t:>.H=HT,-HT;; t:>.Hcalc=digital computer evaluated enthalpy withreference to th e smoothed Cp curve.

were made on Crystal II . The rate of energy liberation,and hence of phase conversion, was increased by reheating the sample to temperatures nearer the transition. The heat capacities of undercooled Crystal I andof superheated Crystal II were also measured in Series10 and are shown in Fig. 1. Sample I invariably superheated 1 or 2 above the heat capacity maximum beforeit would finally begin to transit and absorb energy.I t was not convenient to follow this absorption ofenergy quantitatively with manual shield control; however, three enthalpy-type determinations were madeover the entire transition region to determine theenthalpy of the transition and the completeness of theconversion of the sample to Crystal II . As a furthercheck of the data on Crystal II , enthalpy-type runsB, D, and F were made and compared with the integral under a smooth polynomial curve constructedwith the IBM-704 computer (results shown in TableIII). While the data presented do not permit a detailed picture of the minutiae of the thermal historyof the samples, they do indicate that it is possibleunder suitable precautions to make reliable measurements of the heat capacity of pure methanol exceptin the transition region.

The fractional melting technique was applied to bothsamples to permit calculation of their purities and oftheir melting points. Since Sample I showed (d . Fig. 1)comparatively little premelting, the Crystal I heatcapacity of Sample I was extended smoothly throughthe melting point and used to represent the backgroundheat capacity contribution (i.e., lattice Cp ) to measurements for both samples in this region. The magnitude of this contribution may be seen from the dataassembled in Table IV. From this treatment the excessenthalpy was calculated and used in the calculation ofreciprocal fraction melted vs temperature. A plot ofthese data was fit well by a straight line and extrapolated to the melting point of the calorimetric samplesand that of pure methanol. I t was also used to deter-


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1468 H . G. CARLSON AND E . F . WE STRUM , JR .

I-.J0::EI

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THERMODYNAMICS OF METHANOL 1469studies of Tauer and Lipscomb.5 The entropy of theliquid at 298.15K found in this present investigationagrees within 0.01 cal mol-I. K-I with that calculatedby Pitzer and Weltner.21 Failure to correct for dimersand tetramers in the gaseous state accounts for theearlier apparent discrepancy22.23 between the third lawand spectroscopic determinations of the entropy.Sugisaki, Suga, and Seki24 .25 have studied the thermalproperties of an amorphous "glassy" state of methanolobtained by slow condensation from the vapor phaseat about 70K. Their adjustment of data from 2Q-104Kfor the presence of some crystalline phase, inclusionof a glass-type transition at 105K, and extrapolationof the liquid-phase data from 175-105K correspondsto an apparent zero-point entropy for the "glass" of6.6 cal/ (mol OK). Their crystalline heat capacity datafrom 21-112K accord with the present data withinthe relatively low precision (1.4%-0.5%) of theirmeasuremen ts.

Mechanism of Transition and MeltingFrom the heat capacity data presented in this paper

it is seen that no evidence was found for the existence ofthe reported second transition slightly below the observed transition. However, the finding of other investigators12 that reliable measurements can be made of theproperties of Crystal II only after an adequate thermalconditioning procedure is confirmed. The marked effectof small traces of impurity on the thermal behavior inthe transition region of Crystal I is also notable.

In view of the ease of both superheating and undercooling the transition in pure Sample I and the sharpness of the transition revealed both by the enthalpytype measurements with Sample I and the equilibriummeasurements with Sample II , the transition shouldbe regarded as of first order, rather than of lambdatype. Although numerous reports have been made ofsuch phenomena associated with first-order transformations, none are known for second-order phase transformations. Treatment of the methanol transition asfirst order has also been suggested by authors ofdilatometric and dielectric constant studies,l2The temperatures deduced from dilatometric data8for the maximum rate of volume increase (156 and

159K) differ significantly from that of the calorimetricheat capacity peak (157.4K). The dielectric constantstudies were more suggestive than conclusive in establishing the existence of a "second transition." Sincethermal and phase equilibria in the transition regionwere not attained for several hours in this calorimetricstudy, it is suggested that some of the other reportedphysical measurements in this region may be representative of transitive, rather than pertinent properties of thesolid phase.Nature of the Fusion Transition

Dielectric constant12 and proton magnetic resonance26 ,27 studies have indicated that a more marked

TABLE V. Thermodynamic properties of methanol. Units arecalories, moles, and degrees Kelvin.

T

510152025303540455060708090100110120130140150

160165170175

180190200210220230240250260270280290300310320273.15298.15

0.0150.1680.5841.2191. 9832.7763.5664.3305.0505.7196.9057.9218.8259.66810.47

11.2411.9312.5413.1013.73

11.2511.5111.9312.43

16.9116.9216.9617.0317.1417.2917.4717.7017.9618.2718.6319.0319.4819.9820.5418.3819.39

so

Crystal II0.0050.0470.1860.4360.7891.2211. 7082.2352.7873.3544.5055.6476.7657.8538.9149.94910.95711. 93712.88613.811

0.020.372.146.5714.5426.4642.3262.0885.54112.5

175.8250.0333.8426.3527.1635.7751.6874.01002.31136.2

Crystal I

15.63515.98516.33416.687Liquid

21.52322.43823.30724.13624.93125.69626.43527.15327.85028.53629.20729.86730.52031.16731.81028.7530.40

1421.11477.91536.41597.3

2447.42616.62786.02955.93126.83298.93472.73648.53826.84007.94192.44380.64573.24770.44973.040664537

0.0010.0110.0430.1080.2070.3390.4990.6830.8861.1041.5752.0752.5923.1163.6434.1704.6945.2135.7286.236

6.7537.0287.2967.539

7.9268.6669.37710.06010.71811.35311. 96612.55913.13413.69214.23414.76215.27615.77816.26913.8615.18


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1470 H. G. CARLSON AND E. F . WESTRUM, JR .TABLE VI. Comparison of thermal measurements on methanol." Units are degrees Kelvin, calories, and moles.

Investigator T, t.Ht t.StO T,p t.Hmo t.Smo S0298.16Parks 161.1 140 0.87 175.3 759 4.33 32.6Kelley 157.4 154.3 0.98 175.22 757.0 4.32 30.30.2Staveley and Gupta 157.8 1702 1.08 175.37 755.13 4.31This research 157.34 152.00.5 0.966 175.59 768.51 4.377 30.4O0.03

a Tt. transition temperature; Ttp. triple point; S0298.15 values are for the liquid phase.

change in properties occurs at the transition than atfusion. Furthermore, in this study the effect of a smallamount of impurity on Crystal I of Sample II wasnoted, whereas no such effect was found for Crystal II .Extensive hydrogen bonding exists in the liquid20 aswell as in the solid; however, in the former bonding islimited to chains of fewer members than in the solidstate. The transition mechanism of Tauer and Lipscomb postulates that the methanol molecules arehydrogen bonded into relatively stable, discrete chains.Premelting phenomena and the melting process itselfcould involve rupture of the chains into smaller units,or at least a more rapid interchange of members amongthe chains. However, Luck28 has deduced the percentage of non-H-bonded CH30H in liquid methanolfrom infrared spectral data and concludes that lessthan 1 % is dissociated below 250oK. They haveevaluated the trend of the heat capacity of the liquidfrom 250-400oK on the basis of their model. Wertzand Kruh29 have further established that the hydrogenbonded oxygen-oxygen contacts occur in methanol atabout the same distance in both crystalline and liquidstates.

Plastic Nature of Crystal ITimmermans'14 empirical definition of a plastic crys

ta l as a substance which has an entropy of melting lessthan 5 cal mol-l.oK-1 would occasion classification ofmethanol as a plastic crystal. Other characteristicmacroscopic properties of typical plastic crystals(plasticity, high vapor pressure, relatively entropictransition into the plastically crystalline state, andmore marked change in physical properties on t r a n s i ~ tion than on melting) occur as a consequence ofglobularity of the molecule. However (as noted previously), persistence of hydrogen bonding in the liquidand gaseous phases21 causes methanol to have unusualproperties for a molecule of its small mass, e.g., arelatively low vapor pressure and an extended liquidrange (163K). In this respect it resembles succinonitrile30 more than a characteristic plastic crystal.

The considerable similarity between the Crystal Iand liquid states is noted in the section on melting anddiscussed subsequently in connection with proton magnetic resonance experiments. (Timmermans'14 error inasserting that there is a continuity in the heat capacityacross the melting transition apparently arises from a

plotting error.) However, the abnormally small entropy of the liquid phase-a consequence of the ordering resulting from hydrogen bonding-is the primecause for the small entropy of melting rather than thesupposed plastically crystalline nature of Crystal I.This is confirmed by examination of the data in TableVI I comparing the behavior of methanol with that ofother small molecules. Hence, the small entropy ofmelting (ASm=4.377 cal mol- I. OK-I) is a consequenceof intermolecular structures (ordering in the liquid)rather than of independent molecular behavior (reorientational-rotation) in the Crystal I phase.

The small entropy of transition (ASI=0.966 calmol- I. OK-I) and the decrease in heat capacity acrossthe Crystal I I ~ C r y s t a l I transition (similar to thatin dimethyl acetylene31 ) is atypical for plastic crystals.

This argument against the plastically crystallinenature of phase I finds support in the proton magneticresonance (PMR) measurements of Cooke and Drain,26which showed that the spin-lattice relaxation timechanges discontinuously across the transition but continuously through the melting point. This had beentaken as an indication that the molecular reorientationis of the same order in the Crystal I phase as in theliquid. Das32 concluded that the spin-lattice relaxationtimes in the Crystal I phase are less likely a consequenceof rolling motion of the entire molecule or a correlatedmotion of the methyl and hydroxyl groups than ofuncorrelated motion of the methyl group above thetransition. On the other hand, Krynicki and Powles,21who also used the PM R technique, found a gradualincrease in relative intensity of the narrow line together with the simultaneous persistence of the broadline to the melting point. However, they asserted thatonly 3% of the molecules are rotating even at 163Kin the Crystal I phase and also confirmed that the bulkof the Crystal I phase should not be considered to bea "rotator" phase. A further linewidth narrowingthrough two orders of magnitude was found on melting.

In conclusion, we note that although the thermophysics of the methyl alcohol system have now beenwell defined under saturation pressure, the striking3-cal mol-I. K-I drop in heat capacity at the transitionhas not proven accountable in terms of molecular freedom. Hence, data on the isothermal compressibilityand the thermal expansion for conversion of the heatcapacity to constant volume are clearly desiderata.


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THERMODYNAM ICS O F METHANOL 1471TABLE VII. Thermodynamic properties of selected monosubstituted methanes. Units are degrees Kelvin, grams, calories per mole,

and calories per mole degree Kelvin.

MoleCompound wt. T, AStMethylamineb 31.06 101.5 0.230Methanol 32.04 157.3 0.966Methanethiolc 48.10 137.6 0.350Chloromethaned 50.49Nitromethanee 61.01Bromomethane f 94.95 173.8 0.653

" J. Timmermans, Physico-Chemical Constants of Pure Organic Compounds (Elsevier, New York, 1950).

b J. G. Aston, C. W. Siller, an d G. H. Messerly, J. Am. Chern. Soc. 59 ,1743 (1937).

C H. Russell, Jr . D. W. Osborne, an d D. M. Yost, J. Am. Chern. Soc.64 , 165 (1942).

ACKNOWLEDGMENTSWe thank the Division of Research of the U. S.Atomic Energy Commission for partial financial support, Dr. Lowell R. Perkins, Supervisor of the GeneralResearch Section of the Polychemicals Department ofE. I. Du Pont de Nemours and Company, for provisionof a high-purity sample, and our colleagues for assistance and suggestions.1 G. S. Parks, J. Am. Chern. Soc. 47, 338 (1925).2 K. K. Kelley, J. Am. Chern. Soc. 51, 180 (1929).3 L. A. K. Staveley and A. K. Gupta, Trans. Faraday Soc. 45,50 (1959).4 J. E. Ahlberg, E. R. Blanchard, and W. O. Lundberg, J. Chern.Phys. 5, 539 (1937).6 K. J. Tauer and W. N. Lipscomb, Acta Cryst. 5,606 (1952).6 B. Dreyfus-Alain and R. Viallard, Compt. Rend. 234, 536(1952) .7 G. S. R. K. Murti, Indian J. Phys. 33, 458 (1959).8 L. A. K. Staveley and M. A. P. Hogg, J. Chern. Soc. 1954,1013.9 D. W. Davidson, Can. J. Chern. 34,1243 (1956).10 C. P. Smyth and S. A. McNeight, J. Am. Chern. Soc. 58,1597(1936) .11 C. P. Smyth and C. S. Hitchcock, J. Am. Chern. Soc. 54, 4631(1932) .12 D. W. Davidson, Can. J. Chern. 35, 458 (1957).13 G. Baume and W. Borowski, J. Chim. Phys. 12, 276 (1914).14 J. Timmermans, J. Phys. Chern. Solids 18, 1 (1961).16D. W. Osborne and E. F. Westrum, Jr., J. Chern. Phys. 21,1884 (1953).16 E. F. Westrum, Jr., G. T. Furukawa, and J. P. McCullough,"Adiabatic Low-Temperature Calorimetry," in Experimental

S0298.160K

T", ASm (liq.) (ideal gas) T b"179.70 8.157 35.90 57.73 266.5175.59 4.377 30.40 57.24 337.65150.16 9.399 60.86 280.6175.44 8.760 36.74 55.94 248.78244.73 9.476 41.05 65.73 374179.44 7.964 58.61 276.56

d G. H. Messerly an d J. G. Aston, J. Am. Chern. Soc. 62 , 886 (1940).e W. M. Jones an d W. F. Giauque, J. Am. Chern. Soc. 69, 983 (1947).f C. J. Egan and J. D. Kemp, J. Am. Chern. Soc. 60 , 2097 (1938).g Reference 21.h References 22 and 23.

Thermodynamics, edited by J. P. McCullough and D. W. Scott(Butterworths, London, 1968), p. 133.17 H. G. Carlson, "Thermodynamic Properties of MethylAlcohol, 2-Methyl- and 2, 5-Dimethylthiophene, and 2-Methylfuran," Ph.D. dissertation, University of Michigan, 1962.18 H. J. Hoge and F. G. Brickwedde, J. Res. Nat!. Bur. Std. 22,351 (1939).19 B. H. Justice, "Calculation of Heat Capacities and DerivedThermodynamic Functions from Thermal Data with a DigitalComputer," Appendix I to Ph.D. dissertation, University ofMichigan, 1961; also see TID-12722, Office of Technical Services,Oak Ridge, Tenn., 1961.20 D. D. Tunnicliff and H. Stone, Anal. Chern. 27, 73 (1955).J. H. Badley, J. Phys. Chern. 63, 1991 (1959). S. V. R.Mastrangelo and R. W. Dornte, J. Am. Chern. Soc. 77, 6200(1955); S. S. Todd, G. D. Oliver, and H. M. Huffman, ibid. 69,1519 (1947).21 K. S. Pitzer and W. Weltner, Jr., J. Am. Chern. Soc. 71, 2842(1949) .22 J. O. Halford, J. Chern. Phys. 18, 361 (1950).23 J. O. Halford and G. A. Miller, J. Chern. Phys. 61, 1536(1957) .24 M. Sugisaki, H. Suga, and S. Seki, Bull. Chern. Soc. Japan40,2984 (1967).26 M. Sugisaki, H. Suga, and S. Seki, Bull. Chern. Soc. Japan41, 2586 (1968).26 A. H. Cooke and L. E. Drain, Proc. Phys. Soc. (London) 65,894 (1952).27 K. Krynicki and J. G. Powles, Proc. Phys. Soc. (London)1964,983.28 W. A. P. Luck, Discussions Faraday Soc. 43, 115 (1967).29 D. L. Wertz and R. K. Kruh, J. Chern. Phys. 47, 388 (1969).30 C. A. Wulff and E. F. Westrum, Jr., J. Phys. Chern. 67, 2376(1963) .31 D. M. Yost, D. W. Osborne, and C. S. Garner, J. Am. Chern.

Soc. 63, 3492 (1941).32 T. P. Das, J. Chern. Phys. 27, 763 (1957).

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