July, 1960
THERYODYNdMIC
PROPERTIES O F Cis A N D
t?'anS I S O h l E R S
OF HEXdHYDROINDAN
927
HEATS OF COXBUSTIOS, FORMATION AND ISOMERIZATIOX OF THE cis ,4ND trans ISO-VIERS OF HEXAHYDROIXDASI BY CL.4RENCE
c. B R O W K AEN~D FREDERICK D. ROSSINI
Cheriaical and Petroleum Research Laboratory, Carnegie Institute of Technology, Pittsburgh 13, Pennsylvania Received X a r c h 9 1980
A new thermochemical laboratory for making precise calorinictric measurements of heats of reaction was assembled. Measurements were made of the heats of combustion of the cis and trans isomers of hexahydroindan (hydrindan) in the liquid state. Values were calculated for the heats of combustion, formation and isomerization of the two isomers for both the liquid and gaseous states. eter,b and a lanip and scalc. assembly. The thermometric I. Introduction sPnsitivit,y is such that 1 mm. on the scale corresponds t o A new therniochemical laboratory for making about 0.0003' when the riirrent through the platinum reprecise calorimetric measurements of heats of sistance thermometer is 5 milliamperes. reaction was assembled. Measurements were made 111. Chemical Apparatus of the heats of combustion of the cis and trans The oxygen combustion bomb: is a commercially availisomers of hexahydroindaii (hydrindan), with the energy equivalent of the calorimeter system being able modification of the bomb previously described by Proand Rossini,S and had an internal volume of 380 ml. determined with st8andard benzoic acid. These sen Important features of the present, bomb a,re the Teflon d a h , along with values for the heats of vaporiza- head gasket and valve packing, the inlet tube and elertrodes tion, permit calculation of the heats of formation made of 10% iridium-platinum, and the provision of a'nd isomerizat'ioii of the two isomers for both the snap-on fittings a t the inlet valve and of standard taper fittings a t the outlet valve. A short section of platinum liquid and gaseous states. The relation of energy wire was attached t'o earh electrode. The twelve headless mit,h the molecular structure of the t,mo isomers steel set screws in the cap mere tightened with a calibrated is discussed. t,orque wrench. The chemical train for purifying the oxygen :md filling The thermochemical method employed is the bomb is quite similar to the one previously substit'ution method in which a standa,rd calorim- the and includes the following: -4,oxygen cylinder; 13, pressure eter is used as the absorber and comparator of gage, needle valve, and safety valve assembly; C, hightwo kinds of ciiergy. one of which is the heat, pressure steel tube, electrically heated and filled n.ith copper el-olved in the combustmionof a measured amount oxide t o oxidize combiist.ible impurit,ies in the oxygen; of the reart,ioii of comhustion of the "unknown" D, high-pressure steel cooling coil, immersed in water; E, high-pressure steel purifying t.ube, filled with -isclarite t o xnd the other of which is the heat, evolved in the remove all carbon dioxide from the oxygen; F, l3ourdon(aomt)ust8ionof a ineasuwd amount of the reaction type pressure gage; G, the combustion bomb; H, a flow meter. The temperature of the heated osidizing tiibc was of cwmhustioii of standard benzoic acid. measured with a chromel-alumel thermocouple. The chemical train for analysis of the products of combus11. Calorimetric Apparatus
The valorimeter is one available commercially.3 The general design was made a t the Xational Bureau of Standards hy Prosen and Rossini and is a modification of the original Dickinson design,* the important difference being that the vontainer for the calorimeter can is sealed and immersed in the jac,ket water during the csperiment . The wat#erjacket. containing approximately 38 liters of wat'er, is maintained near 30.1" a t a constant temperature within a few thousandths of a tkgrec by means of an :tutomatic regulator systpni. The calorimeter can, supported on three pointed Lucitc pins, contains in each experiment a standard amount of water (4450.00 It 0.02 g . ) , the stirrer, platinum resistance thermometer, heater and the bomb with its contents. The stirrer is operated a t approximately 300 r.p.m. with a flexible shaft drive from a synchronous motor. The calorimet,er heater, which fits snugly on the bomb, is similar to the one described by Prosen and Rossinij and was made of a cylinder of 26 gage copper, 7 . 8 cm. in diamet,er and 6.4 cm. in height. The thermometric system included a platinum resistance thermometer of the regular flat calorimetric t'ype,6 a Type G-2 Mueller resistance bridge,$ a high sensitivity galvanoni.-___
(1) T h i s investigation w a s supported in part by a grant from the Xational Science Foundation. Submitted in partial fulfillment of the requirements for t h e degree of n o r t o r of Philosophy in Chemistry at, the Carnegie Institute of Technology. (2) Du P o n t Fellow in Chemistry for 1952-1953. (3) Catalog No. 3028. Precision Scientific Company. Chicago. I I linois. (4) H. C. Dickinaon B d I . B v r . Stnndardg, 11, 189 (1915). ( 5 ) E . J. Prosen and F. D. Rossini, .I. Research .Val/. B u r . Sinnrlnrds, a i , 289 (1941). (6) Catalog Numbers 8160A. 8069, and 2 2 6 4 4 , respectively, Lecdx a n d Northrup Company, Philadelphia. Pennsylvania.
tion is similar to that previouslv desrribedj and includes the folloning: A, cylinder of oxygen used for flushing the train; 13, a two-stage pressure regulator; C, a Pyres-glass pressure safety trap, containing mercury; D , an e1wtric:dly hc,at,ed furnace, with quartz tuhe cwntaining c o p p ~ roxide to osidiae combustible, iinpiiritiee in the oxygen; 1,:. ii Pyrexglass purifying tub? containing -4scarite, to wniove carbon dioside; F, thr coml)iistion bomb; G, a f l ( ~ i h 1 0gIa,ss (,nil, t o f:trilitate tmnsfer of thc. bomb into or oiit, of thc tr:i,in; Irpt ion tubc, to r r m o wr.trr, ~ ~ (sotit ,inic,siiim perchlitrate barktd \\-ith phosphorus pentoxidr; I, it Pyrcs-glass n-eighctl :i,t,sorpt,ion tube, to remove carhon dioxide, v-hich contailis .\scnritc, backed, in ordw, with anhydrous magnesiiini perchlorate and phosphorus pentoside; ,J, a duplicate of D; Ti. a. duplicate of H; L, a dup!icat)e of I ; 31, a Pyres-glass giiitrd tube containing, in order, phosphorus pentoside, xtihytlrous magnesium perchlorate and r\srarite, to pwvent hack iliffusion of water vapor or carhon dioxide; S , a flow mcter. The safety-trap. C, prevents excessive build u p of pressnrc in the train while oxygen from the cy1indt.r is flowing ant1 facilitates adjustinciit of the needlc valve to thv wtting r(*quired for the propcr rate of flow of oxygen (liii,iiig ing period. Thc temperatiire of each fmtracc is with uhroniel-alumel thermoconplcs, with thithe furnace being controlled wit11 :t miiithle t r:iiisforincr. The absorption tube ii; tltrl same as th:tt prr\-ioiisl>. c b scribed,* n-ith a cylindrical body in plare of t h v former 1.tube. The absorption tubes were fluslied oiit : m i tilled with helium free of water vapor and carbon dioxide beforp each weighing, in a train designed to Rmid contn.mina.tionnf the a,bsorption t,iiheand its contents. i i ) Catalog
So.1002, l'air Instruiixiit Company, IRIoline. 1ui11016. ( 8 ) E. J. Prosen and F. I). Rossini, J . Research Nail. B u r . Standards, 33, 255 (19-44).
CLARENCE C. BROWNE AKD FREDERICK D. ROSSINI
928
IV. Calorimetric Procedure Ignition was accomplished by the use of standard iron fuse wire, 5 cm. in length, weighing approximately 8 mg. The total ignition energy was about 0.02% of the heat evolved in a calorimetric combustion experiment. The procedure followed in the calorimetric combustion experiments was substantially the same as previously described.6v8 A standard mass of water, 4450.00 =k 0.02 g.. was used in each experiment. 1.00 ml. of water was placed in the bottom of the bomb before each combustion rxperiment. The calorimetric observations were divided into the ugiial thrre parts: a “fore” period of 20 minutes, with observations of the steadv state being made every 2 minutes; a “reartion” period of 16 minutes, in which the rombustion occurred, followed by re-establishment of the steady state; and an “after” period of 20 minutes, with observations of the steady state being made every 2 minutes. I n the first five minutes of the “reaction” period, observations were recorded of the time, to the nearest hundredth of a minute, at, which the resistance of the thermometer attained certain preqelected values. The value of ARC,the corrected increase in temperature of the calorimetric svstem, expressed as the increase in resistance in ohms of the given platinum thermometer a t the mean temperature of 29”, as measured on the given resistance bridge, was determined substantially as previously desrribed w Although the nature of the substitution method employed makes i t unnecessary, formal calculation was made of the contribution t o the rise of temperature from stirring, etc., and the heat flow from the jacket t o the ralorimeter. The contribution from stirring, etc., was taken as p ohms/min., the total contribution for an entire experiment, for the reaction period of 16 minutes, being
U = 16fiohms (1) The heat leak constant was taken as k ohms/min-ohm, or klmin., the total contribution for an entire experiment, for the reaction period of 16 minutes, being K = k A ohms
(2) where il is the area, in ohm-minutes, between the curves of the ralorimeter resistance and the jacket resistance, from the 20th to the 36th minute. The corrected temperature rise is then given by ARC = (RT6- Rzo)- I< U ohms (3) The value of Ai-”, the rise in temperature prodiiced by the heat evolvrrl in the formation of a small amount of nitric acid, according to the reaction 51 Ndg) 1 HzO(liq) 5 O4g) = HKOdaq) (4)
-
+
+
was calruhted from the amount of nitric arid formed, using the valiie .is kj./mole for the heat evolved in the formation of dilute aqueous nitric acid in the bomb process.698
V.
Chemical Procedure
The compounds measured in the present investigation were API Research hydrocarbons made available through the API Resrarch Projert 44 a t the Carnegie Institute of Technology. These samples had the purities in mole per cent : cis-hexahgdroindsn, 93.95 rt 0.02; trans-hexahydroindan, 99.71 It 0.11. The purification and determination of puritv of these samples alrezdv has heen describrd 1” The rmponles in which the hydrocarbon materid was sealgd prior to combustion were similar in dimensions to thow previouelv tiescribed,E but were made with one onen ing instead of two Dctails of these ampoulrs and the fillin: of th-m a r l drscrihrd elsewhere.” The average mws of the ampoules used in the present invrstijintinn was 0 23 8 . For romhustion in the bomb, the filled and sealed g11,ss ampoule was laid on one of its two flat sides in the criiriblr. The iron fiise wire, 5 em. in length, was placed with its central roil 1 to 2 mm. distance from the iipper flat side of the ampoule. An alternating rurrcnt a t 21 volts from an ignition unit1* supplied the energy for ignition of the fuse __-
(9) F. D. Rossini, J. Res. Natl. BUT Stds., 6 , 1 (1931). (10) A . J. Streiff, A, R. Hulme, F. A. Cowie, X. C. Krouskop and F. D. Roesini. A n d . Chsm. 87, 411 (1955). (11) H. F. Bartolo and F. D. Rossini, T H I S JOURNAL.in preas. (12) Catalog No. 2901, Parr Instrument Company, Moline, Illinois.
Vol. 64
wire. Alter a combustion, the glass of the ampoule was found in the bottom of the crucible in the form of one or more globules, varying from clear t o dark in appearance. As discussed previously,S the heat effect associated with the darkening was believed to be not significant. The oxygen used for the combustion was ordinary commercial oxygen, freed of combustible impurities as previouslv reported6 with the apparntus desrribrd in Section I11 of this paper The initial pressure of oxygen for ezch experiment, corrected to E o , was 30 atmospheres. Th(2 products of each hydrocarbon combustion experiment were exnmined to determine the amount of rarbon dioxide formed in the main reaction of combustion in the bomb, the amount of aqueous nitric acid formed by oxidation of some of the nitrogrn in the ovvgen used for combustion, and the amount of carbon dioxide formed by subsequent oxidation of any products of incomplete combustion. The products of each benzoic acid combustion experiment were examined only to determine the amount of aqueous nitric arid formed. In each case, the detailed proredures were substantially as previously described.5 The mass of carbon dioxide collected in each hydrocarbon combustion experiment was near 2.8 g., on the average. It has been shown previouslv~J3that no significant amount of nitric acid is lost from the bomb during the removal of the carbon dioxide. The absorption tubes wercs handled as described previoiisly,Qand were weighed on a keyboard tvpe analytiral balance14 using as a counterpoise a substantially identical ahsorption tub(,, rlowd, containing some glass beads and a fived Inass of air. The counterpoise tube had a total mass of about 135 g , approximately the same a2 that of the working absorption tube before absorption of carbon diovide. The weights used on the balanw pan were brass, while those added from the lrevboard were gold with some smaller ones in aluminum. Thr following expression was used to obtain the true mass (in VCLMLO) of the carbon dioxide absorbed’s
+
-
0.00007Am(total) - 0.00014Am(brass) 0.00007Am(gold) - 0.00044Am(a~uminum) (5)
m(COz)= 1
In this equation, Am(tota1) is the total mass of the brass and keyboard weights (after absorption) minus the total mass of the brass and keyboard weights used in the first weighing (before absorption). The factor 0.00007 by which Am(tota1) is multiplied corrects for the decreased amount of helium present in the tube a t the second weighing because of expansion of the ilscarite in the amount of 0.45 cmS3 per g. of carbon dioxide absorbed.16 The last term in the foregoing equation is negligible because the largest aluminum-piece was 0.03 g. The amount of reaction in a given calorimetric hydrorarbon combustion rxperiment Gas determined from the mass of rarbon dioxide collected in the given experiment, as determined above. For conversion to moles of hydrovarbon, the molecular weight of carbon dioxide was taken as 44.010 g./mole. The small amount of nitric acid f o r m d during the coinbustion cvperiment was determined, after the removal of the gasrous products of rombnstion from the bomb, hv rarefully washing the inside of the bomb with water anti titrnting the aqueous solution with standard 0.01 N aqueous 80dium hydroxide using phenolphthalein as the indicator. ~
VI. Data of the Present Investigation ‘The cnergy equivaleiit of the calorimeter, for the temperature interval 38 t o :XI”,was determined hy burning XI33 Standard Sample benzoic acid, KO. 39g, in the bomb, using the value 26433.8 joules per grani mass for the heat of combustion of this sample under the coiiditions of the standard bomb process at 2.3’ with appropriate corrections for the differences hetweeii the actual and standard bomb processes. The results of the calibration experiments are shown in Table I, The symbols (13) R. S. Jessiip. J . Research Nail. Bur. Standards, 18, 115 (19371. (14) Type TC, N o . 25877, Wm. Ainsaorth and Sona, Denver, Colorado. (15) F. D.Rossini, 3. Research Natl. Bur. Standards, 6, 37 (1931).
THERMODYNAMIC PROPERTIES OF cis AND trans ISQMERS
July, 19GO
RESULTS OF Expt.
Mass of benzoic acid, g.
k, min. -1
1 2 3 4 5 6
1.54125 1.53741 1.54049 1.54020 1.54273 1 ,54051
0.001611 ,001592 ,001588 ,001578 .001601 .001589
Expt.
1 2 3 4
5
u,
ARc, ohm
ohm
ohm
0.000836 ,000839
0.000186 .000037 .000046 ,000136 .000067 .000056
.000857 .000846 .000861 ,000838
K,
U, ohm
ARo,
ohin
ohm
ohm
2.763873 2.876832 2.892734 2.911151 2.718551
0.001581 ,001602 .001602 .001581 .001595
0.001024 .000772 ,000793 ,000813 ,001066
0.000082 .000120 ,000187 ,000208 .000123
0.191717 .199481 .200562 ,201751 ,188577
0.000431 .000432 .000430 ,000419 .000438
+ +
E , - D(1.21m.
87.5 88.9 89.3 90.1 88.1 88.4
- 0.711nig)
Ari,
Deviation from mean, ]./ohm
206041 206001 206005 206023 205990 205991 206009 &8
B,
1rn,
ohm/g. COa
ohm
0.00000!1 .000010 .000012 .000010 ,000011 Mean Standard deviation of the mean
a t the heads of the columns are defined as follows: ARo = the corrected increase in temperature of the calorimeter system, expressed as the increase in resistance in ohms of the given platinum resistance thermometer a t a mean temperature of 2S0, as measured with the given resistance bridge; qi = the heat evolved, in absolute joules, by the ignition process of heating and burning the iron wire; q n = the heat evolved, in absolute joules, by the formation of the small amount of nitric acid in the combustion; E i = the energy equivalent, over the temperature interval 28 to 30°, of the initial calorimeter system used in the calibration experiments, obtained as the ratio ( - A E ql Q n ) / A R a , where -AE is the heat evolved by combustion of the given mass cf benzoic acid under the conditions of the experiment. The mean value of the energy equivalent E i is for an initial system containing a benzoic acid pellet having a mass equal to the mean of the masses of the pellets used in the experiments. However, the desired energy equivalent for the hydrocarbon experiments is that for a system containing no pellet, but coiitaining instead a mass of soft glass equal to the mean mass of the glass ampoules used in the hydrocarbon experiments. The following expressions were used in calculatiiig the desired energy equivalent, E s i =
jJohm
q n , j.
+32 - 8 - 4
+14 - 19 - 18
..
..
TABLE I1 COMBUSTION EXPERIMENTS O N CZ'S-HEXAHYDROINDAX ( cZ'S-HYDRINDAN)
min. - 1
E.,
Ei, pi. j.
17.7 2.2 1.5 9.1 10.6 9.0 Mean Standard deviation of the mean 0.198207 ,197685 .198075 ,198061 .198415 .198123
g.
k.
HYXAHYDROINDAN 929
TABLEI CALIBRATION EXPERIMENTS WITH BENZOIC ACID
K,
RESULTS O F THE hlass of coz formed,
THE
OF
(6)
ITcre. D = number of degrees Celsius (centigrade) equivalent to one unit of the temperature scale used (9.93 degrees per ohm for the thermometric system used in our experiments); ma = the mean mass, in grams, of the pellets of benzoic acid ured in the calibration experiments (1.54 g.); ? n g = the mean mass of the soft glass ampoules uied in the hexahydroindan experiments (0.233 g). In the above rquationq, Ei and Esi are expressed in joules per ohm. With the value of E i equal to
0.0692107 .0691920 .0691853 ,0691607 ,0692064 0,0691910
&0.0000089
Dev. from mean, ohm/g. COX
f0.0000196 .0000010 - .0000057 - ,0000304 ,0000153
+ +
.. . . .. ... . . . . .. . . .
206009 f 8 joules per ohm, the value of 205992 & 8 joules per ohm was obtained for EBi. The results of the combustion experiments on cis-hexahydroindan and trans-hexahydroindan are shown in Tables I1 and 111. The symbols at the heads of the columns are defined thusly: Ar, = the increase in temperature of the calorimeter system, expressed as the increase in resistance in ohms of the platinum thermometer, produced by the ignition process cf heating and burning the iron wire: Ar, = the increase in temperature of the calorimeter system, expressed as the increase in resistance of the platinum thermometer, produced by the formation of the small aniount of nitric acid in the combustion; B = [(ARC AT, - A r n ) / ~ ~ c o , ] [ 1 (C f 6 ) / E s i I ; ~ Z C O , = the mass of carbon dioxide farmed in the combustion of the hydrocarbon; C = the heat capacity of the amount of hydrocarbon placed in the bomb, expressed as joules per ohm increase in resistance of the giren platinum resistance thermometer: 6 = a correction term, too small to be significant in this series of experiments, expressed as joules per ohm increase in resistance of the given platiiium resistance thermometer, to take acvount of in) the variations in mass of the glass ampoule from the "standard" value of 0.233 g., and (bl variations in the mean temperature of ai1 experiment from the standard value of 29". VII. Heats of Combustion, Formation and Isomerization of the cis and trans Isomers of Hexahydroindan In Table IT' are presented the resulting values ( J f the standard heats of combustion of the cis and trans iioniers of hexahydroindan from this investigation. There are given the values of the constant B for 30", in ohms per gram of carbon dioxide formed, -@B, the heat evolved in the bomb process at 30" in kilojoules per inole of
+
CLARENCE C. BROWNE AND FREDERICK D. ROSSINI
930
Vol. 64
TABLE I11 RESULTS OF Expt.
1 2
3 4 5
Mass of CO? formed,
THE
COMBUSTION EXPERIMENTS ox ~~U~S-HEXAHYDROISDAX ( trans-I-I~u~1~11.4~ j
g.
k, min. -1
ohm
ohm
u,
4Ro, ohm
2.816673 2 .go4192 2.8544-1'3 2.713013 2.813633
0.001727 .0015M ,001684 ,001597 ,001612
0.001061 , OOOi86 ,000913 ,000954 ,000912
0.000086 ,00006i ,000054
0.195195 ,201336 ,197772 ,190191 ,194959
K,
,000195 .000154
Ari,
ohm/g. Cot
ohm
0.000431
0.000026 ,000026 ,000024 ,000024 .000024 Mean uf the mean
.000399 ,00042i ,000428 .000430
St.andard ckviatioii
Dev. from mean, ohm/g. COz
B,
AT%
ohm
-0.0000101
0.0691424 ,0691775 ,0691326 ,0691757 ,0691344 0,0691525 10.0000100
C .0000250 - .0000199
+
,0000232
- ,0000181
. .... . . , , . . . . . . . ,
TABLE I\VALl-E:Sa OF THE s 1 . 4 s D A R D
7 -
Name
H m w O F COSlIB ['S'TIOX
CompoundFormula
B
7
State
C~S-HEXAHYDROINDAS (C;&-HYl>RIXI>AX)A S D ~~,~~-HEX.~HYUROIN.I~AN ( ~XWZS-HYDRIXDAN) - AEn, - AI,"3 - AH3 -AH:
FOR
a t 30'. kj./rnole
a t 30' ohm/g. CO?
a t 30", kj./mole
cis-Hesahydroindxn CpHlti I i q . 0,0691910 5645.39 5643.30 (cis-hydrindan) f0.0000178 i 1.52 i 1.32 Irans-Hesah~droindaii C,HI,i Liq. 0.0691525 5642.25 5640.16 ( tmns-hydrindan) +0.0000200 i 1.69 i 1.ti9 a All the uncertaint,ies in this talde are equal to twice the standard deviation.
hydrocarbon : - ABo the decrease in interiial energy for the ideal reaction at 30", with all reactants and products in their standard states; -AHo the decrease in heat content (or heat evolved 111 the ideal combustion at constant pressure) for the ideal reaction at 30'; and - A H o for the ideal reaction at 25'. The recorded values of - aEo and - A H o apply to the reaction, with each CJMliq)
+ 13Odg) = 9COdg) + 8HZOUiq)
ti)
a t 30°, kj./mole
5653.38 i 1.52 3650. 24 i
1.GD
kj.'niole
a t 25 , kcal./mole
,5655.10 1.52 5651.99 i 1.69
i
1351.60 f 0.36 1350.86 i 0.40
therrnocheniical calorir itsiiig t lie re1:ition : I calorie = 4.184 (exactly) joules. Table T' gives the values for the standard heats of formation of the two isomers for both the liquid and gaseous states. For the latter values, use is made of the values of heats of vaporization at 25", calculated from vapor pressure data, with wme For the heats of vaporization a t 25", the values are 11.00 i= 0.30 and 10.70 i 0 30, kcal. 'mole, respectively. for the cis and
TABLE V The correction which was applied to -AEs iii obtaining - AEo was calculated by the method of v 9 L I h b OF I H E hlA\L).4RD HEATS IIF l!ORM\lIOA ANI) \ N Ah]) ~ ? C I I ~ ~ - H E X ~ \Vashburn,16using, where possible, values for 50'~ 15OMERIZSTION OF CLS-HEXAHYDROI\II and taking advantage of more recent espressioiih I-IYDROINDAS l i e a t of for the solubility of oxygen and carbon dioxide isomern. in nitric acid s01utions.l~ The ralue for this cor(referred t,o the rection .i\.as -0.037% or 2.09 kj. per mole for Heat of transformation. isomer) both isomers. Coiiversion from - AE0 to - AHo, AHOzsa.!o. a t 30°, involved 10.08 kj. per mole for -A(PJ7)". kcal.; mole Coniwsioii to - A H o at 25" involved 1.72 hj. 0.i-1 per mole for czs-hexahydroindan and f1.75 kj. rto.52 per mole for trans-hexahydroindan. The over-all uncertainty assigned to each final value of the heat 1 .05 of combustion of a compound was taken as the f O . 53 square root of twice the resulting standard deviation t,ans-HexahSdroiiidan CgHIti Iiq. -12,lj 0 00 of the mew, including both the combustion exi 0.40 periments and the calibratioii experiments.I8 frnns-Hexahydroiridnn (.'SHI6 (:a. -31 , 4 5 0.00 Values for the standard heat capacities (at 25') 1 0.50 of O,(g), C02(g) and H20(liq), as well as values for the standard heats of formation (at 25") of ir(i1i.s isomers. The differewe in the heats oi ('02(g) and H20(liq), were obtained froni the \-aporiaatjion is taken as 0.30 i 0.10 kczal., 'niolc. tables of the API Rebearch I'rojevt 11.'9 The VIII. Results of Previous Investigation T-alues in joules were converted to the defined Only one report of the heat,s of combustion of (16) E. W. Washburn, zbzd., 10, 525 (1933). (17) W. N. Hubbard. D . W. S c o t t a n d G . Waddington, THISJOUR- cis- and trans-hexahydroindan has appeared in the NAL, 68, 152 (1954). literature, and t,hat as an incidental part, of an(18) F. D . Roasini a n d W. E Deming J . Wash Acad. Sci.. 29, 416 other investigation,21 with Becker and Roth?' (1939).
+
+
+
(19) F. D . Rossini, K. S. Pitaer, R. L. Arnett, R. >I. Braun and C . Pimentel. "Selected Values of Physical a n d ThermodynarniL Propert1e.n of Hydrocarbons and Related Compounds," Cariirgic Press, Pittshurgti, Pennqvlt anla. 19iJ. (7.
(20) D. L. Camin, Chemical a n d Petroleum Research Laboratory, Carnegie Institiite of Technology. unpubliahed d a t a . (21) TT. Huckel, E . Kamens, A . Gross a n d W. Talxpe, . 4 i i r i . , 633, 1 (lR3i).
NOTES
July, 1960
931
reported marking three combustion experiments from the cis isomer to the trans isomer, should give with each of the compounds. From their meager a difference of energy nearly twice that observed. data, one calculates a value of AH = +1.5 i As previously pointed O U ~ , the ~ ~explanation , ~ ~ lies 0.9 kcal./mole for the heat of isomerization, in in the fact that the six-membered ring requires the liquid state, of the trans isomer to the cis some distortion in order to bring together the isomer. Because of a number of uncertainties, it is desired bonds for the fusion of the two rings. difficult to recover an absolute value for the heat of This distortion is not much for the cis isomer but rombustion of the isomers from the little informa- is appreciable for the trans isomer. This introtion supplied. Within the limits of uncertainty, duces additional strain which keeps the energy the heat of isomerization derived from Becker of the trans isomer from becoming as low a$ I t and RothZ1is in accord with the value from the might otherwise become, and hence makes the present investigation. difference in energy of the two f o r m less than originally expected. Similar considerations may IX. Discussion be inquired into in the case of (a) the cis and trans The data of the present information yield isomers of decahydronaphthalene, formed by t~ AHo = 1.04 & 0.53 for the heat of isomerization like fusion of two six-membered cycloparaffiii of the i r a m isomer to the cis isomer in the gaseous rings, and (b) the cis and trans isomers of bicyclostate at 2 5 O , making the trans isomer more stable. [3.3.0]octane, formed by a like fusion of two fiw:is discussed by a number of i i i v e s t i g a t o r ~ , ~ membered ~,~~ cycloparaffin rings. a five-membered cycloparaffin ring and a sixMcCullough and co-workersz4 have nieawred mernbered cycloparaffin ring may be fused to- calorimetrically the entropies of the cis and trans gether through two adjacent carbon atoms com- isomers of hexahydroindaii and find the entropy mon to both rings either through (a) one equatorial of the cis form to be greater than that of the trans and one axial hoiid or (b) two equatorial bonds. form by 1.68 0.10 cal. deg. mole, for the liquid T i l the former case, the cis isomer of hydrindan is state at 25". From this value. and the heat formed and in the latter case the trans isomer. It of isomerization determined in the present investii p expected that. on the basis of the conformation, gation, the standard free energy of isomerimtioii the trans isomer would be more stable energeti- of the trans form t o the cis form is calculated to he (*ally,that ib, have a lower energy content, as shown by the experimental data. However, .i?-ithout AF02ss = 0.24 rt 0.52 kcal. 'mole (8) othtbr complicating factors, a simple substitution This rewlt indicates that, within the limits of 1111( i f one equatorial bond for one axial bond, in going certainty, the two isomerL: hare sub+taniidly tho (12) IT. G . Dauben a n d I
