Benzothiophene Heat Capacity, Heat of Transition, Heat of Fusion and Entropy. An Order Disorder Transition1,2

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1、H.L.FINKE,M.E.GROSS,J.F.MESSERLYANDGUYWADDINGTONVOl.76[CONTRIBUTIONNO.43FROMTHETHERMODYNAMICSLABORATORY,PETROLEUMEXPERIMENTSTATION,BUREAUOFMINES]Benzothiophene:HeatCapacity,HeatofTransition,HeatofFusionandEntropy.AnOrder-DisorderTransition1S2BYH.L.FINKE,AI.E.GROSS,J.F.MESSERLYANDGUYWADDINGTONRE

2、CEIVEDSEPTEMBER24,1953Theheatcapacityofbenzothiophenewasstudiedbetween12and335’K.ThesolidexhibitedalargeA-typetransitionbetween250and261.6OK.ThehightemperaturecrystalsI1werereadilysupercooled,andheatcapacitymeasurementsweremadebelowthetransitiontemperaturebothonthestablelowtemperaturecrystalsIa

3、ndonthesupercooledcrystalsI1Thetriplepoint(304.50”K.)andtheheatoffusion(2826.8cal.mole-’)weredetermined.Theentropyofthesolidat298.16’K.andthatoftheliquidatthetriplepointwerefoundtobe42.33and53.31cal.deg.-lmole-’,respectively.SupercooledcrystalsI1werefoundtohavearesidualentropyofapproximatelyRIn

4、2cal.deg.-lmole-‘,andthetransition,1-11,wasfoundtoinvolveanentropychangeofapproximatelyRIn4cal.deg.-’mole-’.Itissuggestedthatsometypeoforder-disorderphenomenonmaycausetheseentropydifferencesbetweencrystalsIand11.Astudyofthelowtemperaturethermalproper-TheApparatus.-Themeasurementsweremadewithant

5、iesofbenzothiophenehasbeenmadeasapartofadiabaticvacuum-typecalorimetricapparatussimilartothatdescribedbyRuehrweinandHuffman.*ThesampletheprogramofthisLaboratorytodeterminetheofbenzothiophene(ca.0.4mole),freedofairandwater,wasthermodynamicpropertiesofselectedsulfurcom-sealedinaplatinumcalorimete

6、rthatcontainedperforatedpoundsthatoccurinorarederivedfrompetroleum.horizontalgolddiskstofacilitateattainmentofthermalBenzothiophenehasbeenfoundinseveralshaleequilibriumandpreventsettlingofthesolidphaseduringfusionexperiments.Tominimizeheatinterchangebe-Ctweenthecalorimeteranditselectricallyheat

7、edadiabatic/shieldsystem,thetemperatureofthelatterwasmaintainedcc-Cascloseaspossibletothatofthecalorimetersurface.Thetemperaturedifferencebetweentheenvironmentandthecalorimeterwasdeterminedbymeansofasystemofinter-connectedthermoc