1530
sfl. 11.('IONSTANCE
~ E F F L E R-4ND FREDERICK D. ROSSINI
The spectral changes observed on drying alumina can be accounted for logically. After calcination a t 600" and exposure to moist air, the alumina surface at room temperature holds both molecular water and surface hydroxyl groups. As it is heated during drying, water molecules not desorbed and removed from the system react to form hydroxyl groups. At higher temperatures, the rcverse reaction causes surface hydrinyl groups to form water molecule-.. n-hich are desorbed and removed. Ultimately. three types of hydroxyl groups remain, which represent isolated groups 011 different types of surface sites. Figure 8 shons detailed changes in the spectrum of a fairly thick plate of "deuterated" aluminri as it is dried above 500". The spectra recorded after drying at 300 and 600" have more than three absorption maxima. Several bands disappear betwelen 500 and 700". Some of these bands are probably caused by hydrogen-bonding between closely spaced hydroxyl groups. The broad tail at frequencies helow those of the isolated hydroxyl bands is also believed to be caused by vibrations of hydrogc?n-bondedhydroxyl groups. (16) 31 -5toii and D E. Willinins, J Cham i'hijs, 31, 32q ilq59)
Vol. 64
Conclusion The high frequencies of the bands remaining after drying at high temperatures suggest-but do not prove-that the attachment of hydroxyl groups to the surface is largely ionic in character. The observed frequencies lie above those normally found for metallic hydroxides which are not hydrogen honded.16probably as a result of the location of the hydroxyl groups on the surface. The largely ionic character of alumina" appears to support this interpretation. The groups correspoiiding to the band at 3698 rm.-l are apparently the most "acidic" of the three types of hydroxyl groups, as shown by the greater ease with which they exchange hydrogen. This behavior appears consistent with t heir lower vibrational frequency. The different types of hydroxyl groups may well play different roles in catalytic reactions on alumina. Variations in the relative abundance of these types may be more important than the total amount of chemically bound water. Further work is in progress to elucidate the nature of t h e v groups and the sites to which they are bound. (17) R. Bersolin, zbid., 29, 326 (19%).
HEATS OF COMBUSTIOS ,4ND FORI\IATIOi\; OF THE HIGHER SORMAL ALKJ'I, C'\7CI,0PESTANES, CYCLOHEXANES, BENZENES ASD 1-SLKEYES I N THE LIQUID STATE AT %501 BY SISTERM. COSSTASCELOEFFLER, R.S.M., AND FREDERICK D. ROSSIXI? Chemicol and Petroleum Resmrch Laboratory, Carneyie Institute of Txhnology, Pittsburgh 13, Pennsylvania Rrceiiud 4 p 1 z l $9, 1960
Measurements were made of the heats of combustion, relative to that of n-hexadecane, of n-decylcyclopentane, n-decylcyclohexane, I-hexadecene and n-decylbenzene, in the liquid state a t 25'. The data confirm the work of Fraser and Prosen that, within the limits of present-day measurements, the increment per CH, group, in the heat of combustion or formation, ij, constant for the higher members of these normal alkyl series of hydrocarbons in the liquid state a t 25". Recommended values are given for the heats of combustion and formation, for the liquid state a t 2 5 O , for the members of theee normal alkyl series of hydrocarbons having more than three carbon atoms in t h e normal alkyl chain. Values for the corresponding heats of vaporization x t 25' are also given.
the same value as for the series of normal parafI. Introduction It has been shown by Prosen and R o ~ s i n i , ~fins. from measurements on 8 liquid normal paraffins in the rsnge C5to CM,t)hat the increment per CH, group in the h.eat of formation of the higher normal paraffin hydrocarbons in the liquid state at 25" is a constanr, within the limits of present-day measurements. Lat'er, Fraser and Prosen" reported data on one higher member of each of four other normal alkyl series of hydrocarbons and concluded that the increment per CH, group in the heat of formation of the higher members of t'hese other normal alkyl series of hydrocarbons in t8he liquid stat'e at 26" is also a constant of subst,aiitially (1) This investigation was supported in part b y a grant from the Sational Science Foundation. Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemistry a t the Carnegie Institute of Technology. ( 2 ) University o t Notre Dame, Notre Dame, Indiana. (3) E. J. Prosen .and F. D. Rossini, J . Research N a f 7 . Bur. Standards, 3 4 , 263 (1945). (4) F. AI. Fraser and E. J. Prosen, ibid., 56, 329 (1955).
In the assembly of the extensive set of precise and internally consistent tables of thermodynamic properties of hydrocarbons and related compounds, prepared by the American Petroleum Institute Research Project 44, the values for the normal paraffins assume a great importance in providing a base-line framework from which values for many compounds of other classes are calculated without experimental mea~urement.~Where possible, it is desirable to use the increments per CH2 group derived from extensive measurements on the paraffin hydrocarbons in calculating values of appropriate thermodynamic properties for the members of other series of normal alkyl hydrocarbons. ;iccordingly, because of the great importance of ( 6 ) E'. D. Roszini. IC. R. Pitzer, R . L. Arnett, R. AI. Braiin and G. C. Pimentel, "Selected values of physical and thermodynamic properties of hydrocarbons and related compounds," A P I Research Project 44. Carnegie Press, Pittsburgh, Pennsylvania, 1953.
Oct., 1960
HEATSOF CONBUSTION OF HIGHER NORMAL ALKYLATED HYDROCARBONS
establishing the fact that the increment per CH2 group in the heat of formation of the higher members of other normal alkyl series may be taken the same as for the normal paraffins, an investigation was carried out in this Laboratory to provide independent experimental evidence on this point. The present investigation reports experimental data on the heats of combustion, relative to that of n-hexadecane, of n-decylcyclopentane, n-decylcyclohexane, I-hexadecene and n-decylbenaene, with present ntion of the conclusions resulting therefrom.
11. Apparatus and Experimental Procedures The experimental values of this investigation are based on the absolute joule as the unit of energy. Conversion to the defined thermochemical calorie is made using the relation 1 calorie = 4.184 (exactly) joules In order to be consistent in the comparison of these values with those previously reported from this Laboratory, the molecular weight of carbon dioxide was taken as 44.010 g./mole. In this investigation, the chemical and calorimetric apparatus and procedures were the same as desrribed by Browne and Rossini.6 The compounds measured in the present investigation were API Research hydrocarbons, made available through the API Research Project 44 from materials purified by the API Research Project 6. The samples had the following values of purity, in mole per cent.: n-hexadecane, 99.96 f 0.04; n-decylcyclopentane, 99.80 f 0.18; n-decylclohexant., 99.88 rt 0.11; 1-hexadecene, 99.93 rt 0.06; n-decylbenzene, 99.88 + 0.10. Description of the purification and determination of the purity of these samples already has been given.' The impurities in these samples would most likely be isomeric and would have an insignificant effect on the measurements. The ampoules employed to contain the liquid hydrocarbon material were made of soft glass, and had a single capillary opening of such length as to permit the, tip of a S o . 27 hypodermic needle t o extend a short distance into the body of the bulb. The hydrocarbon was first drawn into a 2ml. glass syringe fitted with the hypodermic needle and then transferred directly to the weighed ampoule of the proper size. To minimize expansion of the liquid, the ampoule was handled as little as possible x i t h the fingers during the filhng process. The ampoule, filled t o the tip of the capillary, was cooled with ice to draw the liquid far enough down into the neck to permit sealing of the tip with a hot flame. The rise of temperature in each calorimetric experiment was near 2", with the final temperature being near 30°, tht, temperature of the jacket of the calorimeter. The pressure of oxygen in the bomb before combustion was 30 atm., calculated for 25". One ml. of water was placed in the bomb prior to each combustion experiment. The internal volume of the bomb was 380 ml. The amount of reaction in each experiment was based on thii mass of carbon dioxide formed in the combustion reaciion in the bomb. One mole of carbon dioxide, 44.010 g., was taken as l / n mole of hydrocarbon, where n is the number of carbon atoms per mole of the given hydrocarbon. The true mas3 of carbon dioxide was obtained as previously described.6 The energy supplied t o the calorimeter system by the melting and burning of the iron fuse wire was determined in a series of blank experiments in which the starting temperature was close to the jacket temperature. The bomb contained the fuse ( 5 em. wire, No. 36 BWG, Parr KO. 45C10), purified oxygen, etc., as in a regular experiment, but without the hydrocarbon. The increase in the resistance of the platinum resistance thermometer was determined after the fuse was fired. Any unburned wire was weighed. The heat of combustion of the iron wire in oxygen in the bomb was taken as 6.63 kj./g. The electrical energy added t o the calorimeter system in the firing of the fuse was thus JOURWAL,64,927 (1960). ( 6 ) C. C Rrowne and F. D. Rossini, THIB ~ iA.) J. Streiff, 1. R. Hulme, P. -4. Cowir, K. C. Kroiiskop and F. D. Rossini, Anal. Chem., 27, 411 (1955).
1531
determined to be 35.70 f 0.46 j. (This portion of the work was performed in collaboration with D. M. Speros.)
111. Data of the Present Investigation The results of the calorimetric combustion experiments are given in Table I for n-hexadecane, n-decylcyclopentane, n-decylcyclohexane, l-hexadecene and n-decylbenaene, respectively. The symbols are its defined previously.6 The quantity B, expressed in ohms per gram of carbon dioxide, represents the corrected increase in temperature of the standard calorimeter system caused by the formation of one gram of carbon dioxide formed in the combustion of the given hydrocarbon. From the values of B given in Table I, values may be calculated for the standard heat of combustion, AHcO at 25", according to the reaction
aCOr(g) f
b
3 HnO(liq\
(1)
Because for n-hexagecane the value of the heat of combustion in the liquid state has been previously measured accurately,s and because it is similar to the other four compounds measured, n-hexadecane was used as the reference substance for the present measurements. For n-hexadecane, the standard heat of combustion at 2 5 O , AH@, was taken as -2557.M f 0.48 kral.,/m~le,~.* for the reaction C18Hdliq)
+ 24 21 O d d = 16C02(g)
+ lTHzO(liq)
(2)
From the value of AHcO at 2 5 O , with appropriate values of heat capacities, the value of AHcO at 30" was calculated. Subtraction of 4(PV)O at 30" yields the value of AEcO at 30°, in accordance A(PV)o. Appliwith the relation AHo = AEo cation of the Washburng correction in the reverse direction, for the conditions of the bomb process in the present measurements, yields the ralue of AEg at 30" for n-hesadecane in the preqent investigation. With the value of AEB for n-hexadecane, and the appropriate values of B, one may calculate values of AEg for the other four compounds in acrordance with the equation
+
( -A E ~ ) , /A~E ~ ) ,= , BJB,
(3)
To reduce the heat evolved in the bomb process, -AEB, to the change in internal energy, --E@, for all the reactants and products in their standard states, the complete Washburii correctiong was applied. The improyed values of some constantsio to be used in making the Washburn correction to 30" were incorporated in these calculations. The percentage correction to the bomb process at 30" was calculated to be -0.030 for n-hexadecane, -0.033 for n-decylcyclopentane, n-decylcyclohexane and 1-hexadecene, and -0.040 for ndecglbenzene. The heat evolved in the combustion a t constant pressure at 30°, --Heo, was obtained from ( 8 ) E. J. Prosen and F. D. Rossini, J . Research N n t l . Bur. Ptandards, 8 8 , 25.5 (1944). (9) E. W. Tashburn. zbod., 10, 525 (1933).
(IO) W. N. Hubbard, D. IT.Scott and G. Waddington, THISJOUR68, 152 (1954).
NAL,
SR. M. CONSTANCE LOEFFLER AND FREDERICK D. ROSSINI
1532
Vol. 64
TABLE I RESULTSOF THE COMBUSTION EXPERIMENTS Range of ma- of
No. of expt.
Cot
formed,
Range of
k,
K,
Range of
Range of
U.
Range of
AR.3,
Range of Am,
Ari,
ohm
ohm
2.64642 0.001505 to to 2.73772 0.001615
0.000717 to 0.000968
-0.000026
2.51289
0.001573
0.000778
0.000069
to
to
to
to
to
2.78635
0.001599
0.001268
0.000234
0.201242
2.70543
0.001577
0.000694
0.000056
to
to 0.001501
to
to
0.000995
0.000181
0.
min. - 8
Range of
ohm
ohm
Mean value and stand. dev. of the mean. ohm/g. COS
Range of
B,
ohm
ohm/g. COn
0.000009
0.0735714
n-Hexadecane
9
0,195655 0.000395
to
to
to
0.000266
0.0736056
to
0.201870 0.000433
*0.0000080
0.000027
0,0736523
0.000021
0.0720653
to
to
n-Decylcyclopentane
6
0.181516 0.000401 to
0.000440 0.000027
0.0720854 rt0.0000065
0.0721109
n-Decylcyclohexane
6
2.84374
0.194859 0.000372 to
to
0.204857 0.000435
0.000014 0.0718737 to to 0.000024 0.0719296
0.0718928 ~0.0000085
I-Hexadecene
5
2.73697 to 2.77923
0.001580 0.000737 to to 0.001598 0.000825
to
to
0.000165
0.202064
2.76565
0.001582
O.OOO069
0.186875
0.000388
0.000012
0.0673834
to
to
to
to
tro
to
3.01009
0.001612
to 0,000238
0.000022
0,198980 0.000382
0.000024 0.0728250 to
to
0.0725483 -1O.OOOOo73
to
0.000435 0.000027 0.0725656
n-Decylbenzene
6
0.000787 to 0.001287
0,203242 0.000413
0.0674143 rt0.0000107
0.000023 0,0674440
TABLEI1 VALUES" OF THE: STANDARD HEATSOF COMBUSTION OF n-DECYLCYCLOPENTANE, n-DECYLCYCLOIIEXANE, 1-ITEXADECENE AND WDECYLBESZENE
-
-
B AEB, -A@ AH0 CompoLnd at 30°, at 30°, ?t 30", at 30O. AHO, Name Formula State ohmjg. COY kj./mole kl./mole kj./mole kj./mole liq 0.0720854 9805.41 i:2 . 7 4 9802.18 i: 2 . 7 4 982r.08 2 . 7 4 9824.08 f 2 . 7 4 n-DecylcyaloCraHso =!z0.0000130 pentane liq 0.0718928 10431.17 f 3 . 3 3 10427.72 f 3 . 3 3 10117.89 f 3 . 3 3 10451.10 f 3 . 3 3 n-DeoylaytloClsHsz =t0.0000170 hexane 0.0725483 10526.27 3 . 0 5 10522.SO f 3 . 0 5 10542.9G f 3 05 105413.01 =t3 . 0 ; I-Hexadecim CIOHII liq 10.0000146 n-Decylberizene C~sHza liq 0.0674143 9781.37 3 . 7 0 9777.45 3 . 7 0 9793.84 3 . 7 0 9796.29 3.iO =t0.0000214
-
*
*
a
*
*
nt
23O.
kcal./mole 2348.01 f0.06 2497.87
* 0.80
2320.56 f 0 . 7 3
2341.37 =ttO.88
The uncertainties in this table are twice t,he standard deviation.
AEcO. The term, A(PV)O was determined to be partially cancelled and insignificant for the liquid substances, and becomes equal to RT times the increase in moles of gaseous products over reactants. The values of the heat capacities at constant pressure of COZ(g),Os(g) and liquid water, which were employed in the evaluation of the temperature coefficient of the heat content, in order to calciilate -AH@ at 25", have been r e p ~ r t e d . ~The heat capacities of the hydrocarbons were obtained from unpublished data." The uncertainties assigned to the various quantities dealt with in this investigation were derived by the method previously described.6 The final values for the standard heats of combustion a t 25" For n-decylcyclopentane, n-decylcyclohexane, 1-hexadecene and n-decylbenzene, in the liquid state, are given in Table 11. IV. :Data of Other Investigations The ciiily previous measurements on the heats of combustion of these compounds so far reported (11) J. € . McCullough, ef al., C'. S. Bureau of Mines, Bartlesvillev Oklahoma.
in the literature appear to be those of Fraser and Yrosen.4 The most direct way of comparing their results with those of the present investigation is to compare the ratio of the heat of combustion of each of the compounds to that of n-hexadecane, measured in the same investigation in the same apparatus with the same procedure. This comparison is shown in Table 11. It is seen that the two sets of measurements are, within the respective limits of uncertainty, in excellent agreement, with the values from the National Bureau of Standards having smaller uncertainties.
V. Increment Per CH2 Group for Normal Alkyl Series of Hydrocarbons in the Liquid State at 25' Using the values given in the tables of the API Research Project 4 4 for the n-butylcyclopentane, n-butylcyclohexane, n-butylbenzene and 1-hexene, with the latter value adjusted slightly on the basis of measurements made on 1-heptene and 1-octene in this Laboratory, l2 in conjunction with the values re(12) J. D. Rockenfeller and F. D. Rossini, Chemical and Petroleum Research Laboratory, Carnegie Institute of Technology. Unpublished data.
Oct., 1960
HEATSOF COMBUSTION OF HIGHER NORMAL ALKYLATED HYDROCARBONS 1533
ported in this investigation for the one higher member of these four series, one obtains the following values of the increments per CH2 group in the heat of combustion, - AHc", for the liquid a t 25" in kcal./ mole: normal alkyl cyclopentanes, 156.32 f 0.12; normal alkyl cyclohexanes, 156.18 f 0.14; normal alkyl monoolefins, 1-alkenes, 156.35 f 0.10; normal alkylbenzenes, 156.32 f 0.15. The mean of these values is 156.29 i 0.07 kcal./mole. From the data of Fraser and P r o ~ e n the , ~ corresponding values, for the same series, respectively, are, in kcal./mole: 156.26 f 0.07; 156.19 f 0.08; 156.36 f 0.09; 156.19 f 0.07. The mean of these values is 156.25 f 0.04 kcal./mole. Utilizing all the available experimental data from the National Bureau of Standards, Fraser and Prosens reported a mean value of 156.24 kcal./mole. The value found by Prosen and Rossini3 for the series of normal paraflins was 156.26 f 0.05 kcal./mole. TABLEI11 COMPARISON OF PREVIOUS RESULTS WITH THOSE OF
PRESENT INVESTIGATION Compound
THE
-
Ratio of the standard heat of combustion. AHGO' for the liq. state at 25', of the given compd. to that of n-hexadecanea From the present
From Fraser and Prosen4
investigation
n-Decylcyclopentane 0 91803 f 0 00024 0.91804f0.00031 n-Decylcyclo97683 =k .00023 .97663 f .00036 hexane 98515 f .00024 .9S550 f 00034 1-Hexadecene ,91831 f ,00022 ,91544 f .00038 n-Decylbenzene The uncertainties given in this table are equivalent t o twice the standard deviation of the mean.
On the basis of all the foregoing data, it appears that, within the limits of present-day measurements, the increment per CEI2group in the heat of formation of the higher (more than three carbon atoms in the normal alkyl chain) members of any normal alkyl series of hydrocarbons in the liquid state at 25" is constant. Since the values of the increment per CH2 group from Fraser and Prosen4and from the present investigation are in good over-all accord with the value from the work of Prosen and Rossini on their extensive investigation of the normal paraffins, and because extensive tables of thermodynamic properties based upon the values for the normal paraffins have been created, it appears desirable to use for the higher members of other normal alkyl series of compounds the values of the increment per CH2group as for the series of normal paraffills. VI. Values of the Standard Heats of Combustion and Formation for the Liquid State at 25' On the foregoing basis, the values of the standard heats of combustion and formation for the members
of the normal alkyl series of hydrocarbons, Y(CH2),-H, for values of m greater than 3, will be as follows for the liquid state at 25" Normal alkyl cyclopentanes
(nr
+ 5 ) C (c, graphite) + ( m + 5) H P(g) =
C s H d CHz ),-H(liq 1 (4) -AH@ = 785.05 156.263m kcal./mole. ( m > 3) (5) AHfo = -26.50 - 6.106 m kcal./mole. ( m > 3) ( 6 )
+
Normal alkyl cyclohexanes
(m
+ 6) C (c, graphite) + ( m + 6) H? (g) = C&-(
-AHco = 935.73 AHfo = -38.48
CH&-H(liq
+ 156.263 m kcal./mole. -
G.106 m kcal./mole.
1 (7
( m > 3) (8)
(m
> 3)
(9)
Normal alkyl monoolefins, 1-alkenes
+
-AHCO = 331.87 156.263mkcal./mole: ( m> 3j ( i i j AHfo = 7.12 6 . 1 0 6 ~kcal./mole. ( m > 3) (12) Normal alkvl benzenes
-
+
-AHco = 778.41 156.263m kcal./mole. ( m > 3) (14) AHfo = 9.14 - 6.106m kcal./mole. ( m > 3) (15)
In equations 4, 7, 10 and 13, the end group Y is cyclopentyl, cyclohexyl, vinyl and phenyl, respectively, with m being the number of carbon atoms in the normal alkyl radical. The values of the standard heats of formation AHfO, for liquid water and for gaseous carbon dioxide, at 25", appropriate to the foregoing calculations are as follows, in kcal./mole, respectively5 - 68.3174 and -94.0518.
VII. Values of Standard Heats of Vaporization Utilizing the foregoing values for the standard heat of formation and the corresponding values for the standard heat of formation for the gaseous state, as given in the tables of the API Research Project 44,5 one obtains the following equations giving the values for the standard heat of vaporization of the higher members of these normal alkyl series a t 25" Normal alkyl cyclopentanes: AHvO = 6.28 1.1Sm kcal./mole.
( m > 3)
(16)
Normal alkyl cyclohexanes: AHvO = 7.24 1.18m kcal./mole.
(7%
> 3)
(17)
( m > 3)
(18)
( m > 3)
(19)
+ + Normal monoolefins (1-alkenes): AHvo = 2.62 + 1.18m kcal./mole. Xormal alkyl benzenes: AHvO = 7.26 + 1.18m kcal./mole.
In the foregoing equations 4 to 15, inclusive, nt is the number of carbon atoms in the normal alkyl radical.
