HEATSOF ADSORPTION ON BORON NITRIDE
1477
The results obtained in this work support reaction 11, since it is found that the bimolecular rate constant l e z - ~ = k s m ~ . However, Adams, et a1.,l2 report a value of kll = 1.5 X lo9M-I sec-I which is a factor of 10 larger than the rate constant of 1.3 X los M-‘ sec-l derived in this work. Solutions Containing O H - Ions. The flash photolysis of aerated aqueous solutions of 5 X lov2M NaOH (“low carbonate”) leads to the formation of two transients decaying at different rates. The transient with a maximum absorption a t 240 mp is that of the 02-radical anion, and the transient with a maximum at 430 mp is identical with the one observed in the flash photolysis of aerated alkaline sulfate ions and assigned to the ozonide ion 03-. The reactions occurring are considered to be
OH- h’, OH
+ e,-
(12)
followed by reactions 3, 8, and 9. Both species decay by second-order kinetics, as shown in Figure 3e and f.
The transient species absorbing in the far-ultraviolet region is made up of two components: a relatively rapidly decaying component due to 02-absorption and a slower-decaying component. The species giving rise to the longer lived ultraviolet absorption has not been elucidated. It is considered that, at least in part, this slow-decaying absorption in the region of 2500 A is due to the ozonide 03-ion since it was foundla to have an ultraviolet absorption in this very region, in addition to the reported maximum at 4300 A. Furthermore, since ozone is also known to absorbz2with A, -2600 A and an extinction coefficient of about 3.5 X lo*, it is possible that it may be formed as a transient product in this system. Similar observations have been found in the pulse radiolysis of aerated alkaline solutions, 11,12and it is suggested that the slowdecaying transient(s) absorbing in the 2500-A region could also be due to 03- and 0 3 absorption. (22) H.Taube, Trans. Faraday SOC.,56, 656 (1957).
Heats of Adsorption on Boron Nitride
by G. Curthoys and P. A. Elkington Department of Chemistry, University of Newcastle, New South Wales, Australia
(Received October BO, 1966)
Theoretical interaction energies between an adsorbate molecule and boron nitride are calculated using the procedure proposed by Kiselev for graphite. The results obtained for simple molecules are in reasonable agreement with those obtained by other workers. Calculations for heats of adsorption of hydrocarbons are compared with those determined by gas chromatography.
The physical adsorption of gases and vapors on solids, particularly graphitized carbon black, has been the subject of intense investigations‘-a because such studies clarify the nature of the forces that cause adsorption. The surface of graphitized carbon black is sufficiently uniform to reveal both adsorbate-adsorbent and adsorbate-adsorbate interactions4and is sufficiently large for precise measurements of adsorption isotherms and
heats of adsorption to be determined and compared with theoretical predictions.6 The graphite surface (1) A. V. Kiselev, Quart. Rev. (London), 15, 99 (1961). (2) A. V. Kiselev, Rues. J . Phys. Chem., 38, 1501 (1964). (3) M.M.Dubinin, B. P. Bering, and V. V. Serpinskii, Recent Progr. Surface Sci., 2 , 1 (1964). (4) A. V. Kiselev, J. Phys. Chem., 66, 210 (1962). (5) A. V. Kiselev and D. P. Poshkus, Trane. Faraday SOC.,59, 176 (1963).
Volume 71, Number 6 April 1967
G. CURTHOYS AND P. A. ELKINGTON
1478
consists of hexagonal rings of carbon atoms in parallel planes. Each carbon ring is surrounded by three u bonds and the remaining electrons form a plane above and below the plane of the carbon atoms. The majority of theoretical approaches have assumed that interaction of adsorbed gases on such a surface is due to dispersion forces of attraction and repulsion. These theoretical calculations were first carried out by Barrer6 in 1937 using the Lennard-Jones 6-12 potential. The interaction was found by summing the interaction energy of each of the nearest 100 carbon atoms with the adsorbed atom. This method has subsequently been improved by a number of authors. Another approach by Tuck7 has completely ignored dispersion forces and extends a charge-transfer nobond concept to the adsorption on a graphite surface. An attempt has also been made to use classical polarization effects to account for the observed interaction energies. Boron nitride provides another interesting surface for such studies.' X-Ray diffraction investigations8 have shown that the hexagonal modification of boron nitride is similar to that of graphite. In boron nitride the hexagonal rings of atoms are packed directly on top of each ot>her, whereas in graphite a form of close packing exists in which half the atoms lie between the centers of the hexagonal rings of adjacent layers. Theoretical Calculation of Dispersion Energies on Graphite. The calculation of interaction energies of simple nonpolar molecules on graphite was first carried out by BarrerS6 This dispersion energy was calculated by the Lennard-Jones 6-12 potential
The calculation of theoretical interaction energies of adsorbed molecules on graphite has been extended by Kiselev, et aZ.111J2to include other forms of interaction, viz., dipole-quadrupole and quadrupole-quadrupole interactions. Interaction energy was expressed as
where CI,CZ,and C3 are constants for dipole-dipole, dipole-quadrupole, and quadrupole-quadrupole interactions. The calculation of interaction energies was improved by expressing the summations cr-", Cr-lO, and Cr-12as a function of z with the form p,rqn
c+,
cr-6 ET-8
=
plz-ql
Cr-l0
pzz-q=
cr-12
=
p32-98 p&-Q4
Kiselev" showed that the interaction energy, @i, of an adsorbed atom or group on a graphite surface can be expressed in the form -$i
=
C1plz-"
+ C ~ ~ Z Z+- C~ ~' P G - '-~ B P ~ z - " (4)
At the equilibrium distance z = zo
hence
Thus the interaction energy at z = zo is given by
C is a constant which Barrer found to be determined best by the Kirkwood-Muller equatione C = 6mc2 (adxj)
aiaj
+ (ai/xi)
(2)
where m is the mass of an electron, c is the velocity of light, at and ajare the polarizabilities of the adsorbed atom and carbon atom, and x t and xj the magnetic susceptibilities of the adsorbed atom and carbon atom. The interaction was found by summation of the individual interactions of the nearest 100 carbon atoms with the adsorbed atom. The value ro Barrer assumed to be "a little greater than the mean of the interlaminar distance in graphite and the internuclear distances of the adsorbed atom in its crystal form." Crowell and Younglo criticize this choice of ro and point out that it is actually an empirical constant.
(1
- ~)C,pGo-qa 44
(7)
This treatment is to be applied to the interaction of atoms with boron nitride. Pierotti and Petriccianila (6) R. M. Barrer, Proc. Roy. SOC.(London), A161, 476 (1937). (7) D. G. Tuck, J . Chem. Phys., 29, 724 (1958). (8) R. 8.Pease, Acta Cryst., 5,356 (1952). (9) J. Kirkwood, Physik. Z.,37, 57 (1931). (10) A. D. Crowell and D. M. Young, Trans. Faraday SOC.,49, 1080 (1953). (11) N. N. Avgul, A. A. Isirikyan, A. V. Kiselev, I. A. Lygina, and D. P. Poshkus, Izv. Akad. Nauk SSSR, Otd. Khim. Nauk, 11, 1314 (1957). (12) N. N. Avgul, A. V. Kiaelev, I. A. Lyginjna, and D. P. Poshkus, BuU. Acad. Sci. USSR,Diu. Chem. Sci., 13, 1155 (1959). (13) R. A. Pierotti and J. C. Petricoiani, J . Phys. Chem., 64, 1596 (1960).
HEATSOF ADSORPTION ON BORON NITRIDE
1479
Table I : Results of Summations and Integrations over the Four Different Sites for Both Nitrogen and Boron Atoms a t Different Distances from the Basal Plane Distance from basal plane, om X 108
2.892 3.615 4.338 5.016 5.784
2.892 3.615 4.338 5.016 5.784
Zr-6 X 106
Site A. Boron Nitrogen Boron Nitrogen Boron Nitrogen Boron Nitrogen Boron Nitrogen
ET-8
10'
X
Zr-80 X
106
Zr-12
X
106
Over a Nitrogen Atom 4301.6 321.2 27.47 4469.2 356.7 34.01 1837.8 87.56 4.902 1852.7 89 $43 5.152 914.4 29.83 1.160 918.6 29.99 1.173 513.7 12.04 0.341 513.7 12.05 0.343 299.0 5.45 0.120 308.1 5.46 0.124
2.4806 3.5526 0.2940 0.3239 0.0488 0.0499 0.0106 0.0106 0.0028 0.0028
Site B. Over a Boron Atom Boron 4469.2 356.7 34.01 Nitrogen 4301.6 321.2 27.47 Boron 1852.7 89.43 5.152 Nitrogen 1837.8 87.56 4.902 Boron 918.6 29.99 1.173 Nitrogen 914.4 29.83 1.160 Boron 513.7 12.05 0.343 Nitrogen 513.7 12.04 0.341 Boron 308.1 5.46 0.124 Nitrogen 299.0 5.45 0.120
3.5526 2.4806 0.3239 0.2940 0.0499 0.0488 0.0106 0.0106 0.0028 0.0028
Site C. Midway between the Boron and Nitrogen Atoms 2.892 Boron 4378.8 336.9 30.31 2.9418 Nitrogen 3.615 Boron 1845.6 88.40 5.98 0.3072 Nitrogen 4.338 Boron 918.4 29.93 1.17 0.0493 Nitrogen 5.016 Boron \ 514.6 12.05 0.34 0.0105 Nitrogen 5.784 Boron 307.4 5.44 0.12 0.0028 Nitrogen
with the calculation of interaction energies by Kiselev's method. The values of Cr-"were determined for the distances of the adsorbate atom from the boron atoms and from nitrogen atoms in both first and second planes of the lattice. The summation was carried out for all atoms within 10 A of the adsorbate center, the contribution of the remaining atoms being determined by integration. The following four positions over the boron nitride lattice were considered: A, over a nitrogen atom; B, over a boron atom; C , over a point midway between a boron and nitrogen atom; and D, over the center of the hexagon. The value of Cr-. for n = 6,8,10, and 12 at various distances from the basal plane are shown in Table 1. I n order to determine the repulsion constant B, the summations of Cr-. were expressed as a function of the distance of the adsorbed center from the boron nitride surface, as was done in the case of graphite. By plotting the logarithm of the summation against log z it was possible to find each value of p and q from the straight lines which were obtained. The interaction energy of the adsorbate center may now be calculated using eq 4. The value of each p and q for the four positions over the boron nitride lattice is shown in Table 11. The constants C1, C2,and C3were calculated from the formulas
} }
j
1
2.892 3.615 4.338 5.016 5.784
Site D. Over the Center of the Hexagon Boron 4300.7 321.2 27.47 Nitrogen Boron 1835.0 87.53 4.89 Nitrogen Boron 924.2 29.94 1.16 Nitrogen Boron 513.5 12.03 0.341 Nitrogen Boron 313.3 5.12 0.120 Nitrogen
} ] } } }
CI = 6mc2
a1a2
(al/xl>
c 2
=
45h2 -
1
+
+
(8) (4x2)
1
(9)
and c 3
=
105h' 2ala2 x 256m ~ c
2.481 0,2940 0.0488 0,0105 0.0028
have calculated the interaction energy of nitrogen and argon on boron nitride using the method developed by Crowell and Young.l0 These results are compared
The polarizabilities and magnetic susceptibilities of the boron and nitrogen atoms in boron nitride were the values used by Pierotti and Petri~ianni.'~The values for argon, neon, krypton, and the carbon-hydrogen groups are those given by Kiselev.12 Using eq 8, 9, and 10 the values of Cl, Cz, and C3 were calculated and are shown in Table 111. Pierotti and Petricianni'3 assumed that the equilibrium distance of argon over a boron atom in boron Volume 71,Number 6 April 1967
1480
G. CURTHOYS AND P. A. ELKINGTON
Table 11: Values for p and p over the Four Sites on Boron Nitride Log
PI
Log P2
Pl
Pl
Log PS
Pa
Log P4
P4
15 9108 14.0729
7.8969 8.1499
16.0162 12.3895
9.8677 10.3652
14.0729 15.9108
8.1499 7.8969
12.3895 16.0162
10.3652 9.8677
14.8232
8.0459
14.2945
10.1039
15.9315
7.8950
16.016
9.8677
Site A Boron Nitrogen
16.5806 16.4449
3.8541 3.8735
15.9200 14.9113
Boron Nitrogen
16.4449 16.5806
3.8735 3.8541
14.9113 15.9200
5.9147 6.0531
I
Site B 6.0531 5.9147
Site C Boron Nitrogen
}
16.6362
3.8472
15.4351
5.9812
Site D Boron Nitrogen
16.8798
3.8140
16.0168
Table 111: The Constants CI, CZ,and Ca for the Interaction of Adsorbates with Boron and Nitrogen Atoms in Boron Nitride
Adsorbate
Ne Ar Kr CHa CHz CH (aromatic)
CI X lop', Cz X 1060, cs x 10'6, koa1 mole-' cm6 koa1 mole-1 oms kcal mole-1 cmlo NitroNitroNitrcBoron gen Boron gen Boron gen
0.257 0.927 1.385 0.984 0.789 0.686
0.171 0.624 0.934 0.677 0.544 0.475
0.034 0.130 0.197 0.173 0.140 0.132
0.025 0.098 0.146 0.129 0.104 0.098
0.054 0.223 0.342 0.376 0.306 0.395
0.047 0.189 0.288 0.299 0.245 0.246
nitride is equal to the mean of the interlaminar distance in boron nitride and the internuclear separation of two argon atoms in their crystalline state. The equilibrium distance of the argon atom over a nitrogen atom was assumed to be approximately the same as the argon atom over boron. However, it is proposed that a better approximation would be to assume that the equilibrium distances over the boron and nitrogen atoms will be different and that the ratio of the boron and nitrogen contributions will be proportional t,o the ratio of the atomic radii of boron and nitrogen atoms. The selection of the correct equilibrium distance is important because it has been shown'* that an error of 0.1 A in this value causes a 10% error in the theoretical interaction energy. Since a boron atom is directly over a nitrogen atom in the lattice structure, the sum of the two van der Waals radii of boron and nitrogen will equal the interlaminar distance (3.33 A). The atomic radius of boron is 0.81 A and of nitrogen is 0.74 A.16 Hence in boron nitride the van der Waals radius of a boron atom is 1.74 A and of a nitrogen atom is 1.59 The Journal of Physical Chemistry
5.9016
A. The equilibrium distance of argon over boron in boron nitride, re, will be equal to the van der Waals radius of argon plus the van der Waals radius of boron in boron nitride. Over nitrogen, the equilibrium distance of the argon atom is equal to the van der Waals radius of argon plus the van der Waals radius of nitrogen in boron nitride. Over site C the equilibrium distance of the argon atom is equal to the square root of.re2- uz and over site D it is the square root of r 2 - (u2/4) where a is the boron nitride interatomic distance. From eq 4 and 6 it is seen that the dependence of 4 on z takes the form $(z) =
-c1p1x-q1
- C2p22-@ - c3p3z-qs +
The interaction energy of argon on boron nitride a t each position was calculated by finding the interaction of all boron atoms with argon and all nitrogen interactions with argon and summing the two interactions. The graph of the dependence of $ on z for argon on the four sites of boron nitride is shown in Figure 1. It is seen that the energetically most favorable site is over the hexagon center where the interaction energy a t the equilibrium distance is 2.45 kcal mole-'. The least favorable site is over the boron atom where the interaction energy at the equilibrium distance is 1.80 kcal mole-'. It is noted that the interaction energy of argon on boron nitride over the (14) N. N. Avgul, G. I. Berezin, A. V. Kiselev, and I. A. Lygina, Zh. Fiz. Khim., 30, 2106 (1956). (15) L. Pauling, "Nature of the Chemical Bond," Cornel1 University Press, Ithaca, N. Y., 1960,p 228.
HEATSOF ADSORPTION ON BORON NITRIDE
1481
Table IV: Interaction Energies over Boron Nitride (kcal/mole) Total interaction energy
0.0 Adsorbate
-8 I a E
-0.5
Neon Argon
-1.0
Krypton CHs CHz CH (aromatic)
a
D 8
*
Site A
Site B
Site C
0.85 2.10 1.96" 2.81 2.05 1.66 1.72
0.71 1.80 1.97" 2.41 1.76 1.42 1.48
0.78 1.93 1.96" 2.60 1.90 1.68 1.58
Site D
1.04 2.41 2.00" 3.24 2.55 1.91 2.00
0.86 2.08 2.80 2.11 1.69 1.72
.e
Results from Pierotti and Petricianni.i*
E
3
-1.5
c(
of a similar order and all are similar to results reported by Kiselev.12 I n Table IV are tabulated the interaction energies of a number of simple atoms and centers over boron nitride at the various chosen sites.
-2.0
2.8
3.2 3.6 4.0 4.4 Distance from basal plane of boron nitride, om X 108.
Figure 1. Interaction energies of argon over four sites on boron nitride.
hexagon center is higher than the value calculated by Pierotti and Petri~ianni.'~The main reason for this lies in the fact that different values for the equilibrium distances where chosen. Using eq 7 and the values in Tables I1 and I11 the interaction energies of Ar, Kr, Ne, and the CHI, CH2, and aromatic CH groups were calculated over the four boron nitride sites. Kiselev12 found the over-all interaction energy of each atom or group on graphite from the average value over the three sites that he selected. It is suggested that a more realistic approach would be to give more weight to the higher interaction energies. Thus the total interaction energies in Table IV are obtained by weighting each according to its interaction energy over the four sites. I n calculating the interaction energy of an adsorbed molecule at the surface, the contribution due to a permanent electric field near the surface of boron nitride, owing to the partially ionic character of the B-N bonds in the basal plane, has been neglected. This effect would undoubtedly be small compared to the dipole-dipole dispersion as it is even in the cage of the alkali halides. The contribution of the various dispersion forces to the total interaction energy of argon on boron nitride is shown in Table V. The relative contributions for other atoms and centers were
Table V: Argon Adsorbed on Boron Nitride. Per Cent Contributions t~ the Total Dispersion Energy
Site A Site B Site C Site D
Dipoledipole contribution
Dipolequadrupole contribution
92.6 92.6 92.7 92.8
6.6 6.7 6.6 6.5
QuadrupoleRepulaion quadrupale energy contribu(% of energy tion of attraction)
0.8 0.7 0.7 0.7
40.3 39.7 39.7 39.7
Crowell and Chang16have recently studied the interaction of some simple nonpolar molecules with boron nitride using lattice sums of a &12 potential. The constants CI and ro were obtained from combination rules suggested by Crowell and Stee1e.l' The summations were not found by direct summatoin but by integration. Their results are of the same order as ours and are shown in Table VI. The discrepancies which do occur might be attributed to the uncertainties in calculating the constants from the elastic modulus of boron nitride.I6 From the over-all interaction energies of the CHa and CHZgroups the interaction energies of a number of n-hydrocarbons were calculated using the formula '& = 2 h H 1
+ (n -
2)9CHs
(16) A. D. Crowell and C. 0. Chang, J. Chem. Phys., 43, 4364 (1965).
(17) A. D. Crowell and R. B. Steele, ibid., 34, 1347 (1861).
Volume 71, Number 6 April 1967
G.CURTHOYS AND P. A. ELKINGTON
1482
Table VI : Comparison of Theoretical Interaction Energies (kcal/mole) with Previous Work Adsorb8 t e
This work
Crowell and Chang'"
Pierotti and Petricciani'8
Ne Ar Kr
0.86 2.08 2.80
0.94 2.16 2.55
1.95
The results for n-pentane, n-hexane, and n-heptane are shown in Table VI1 together with the interaction ~ ~ energy of benzene which was found from 6 4 interaction energy. Comparison of the theoretical calculations on boron nitride with those of graphite predict interaction energies which are very similar.
Table VII: Comparison of Theoretical and Experimental Results (kcal/mole)
Sterling MTD4
Isopentane n-Pentane n-Hexane n-Heptane n-Octane Cyclohexane Benzene
Theoretical energies on graphitea
8.3 8.9 10.1 11.2 12.5 8.2 9.4
9.5 11.2 12.9 14.7 10.8
Boron nitride (heattreated)
9.4 10.5 12.4 13.7 15.6 10.2 11.3
Theoretical energies on boron nitride
9.3 11.0 12.7 14.4 10.1
a Results from Kiselev'P calculation, but the average value was found by weighting the values over the three different sites over graphite.
The method of calculating dispersion energies has been criticized by a number of authors. Samsl* has claimed that there is an uncertainty of approximately 10% in these calculations. This uncertainty arises from the following considerations. First, it is known from gas-gas studies that the Kirkwood-Muller formula yields a value that is slightly large, since it neglects electron correlations, and it would not be expected that this formula would be any more satisfactory in g a s solid calculations. Second, the selection of the value ro influences considerably the final value of the interaction energy In spite of these limitations it is to be expected that this method would still yield the correct order of interaction energies and if dispersion forces are responsible for adsorption on boron nitride, then the experimental heats of adsorption should compare favorably with these theoretical calculations. The Journal of Ph&d
Chistry
Gas Chromatographic Determination of Heats of Adsorption. Since Cremerl9 first suggested that the differential heats of adsorption could be determined gas chromatographically a number of papersz0Vz1have shown that good agreement exists between this method and heats of adsorption determined with a calorimeter at low coverages. Ross, Saelens, and OlivierZ2have shown that when log tm, where tm is the corrected retention time, is plotted against l/Tc, where T, is the column temperature, the slope of the line obtained is AH/2.303R. The adsorbents were packed in glass columns in a Pye argon gas chromatograph. The graphitized carbon black used was Sterling MTD4 and the boron nitride was obtained as a fine white powder from Hopkins and Williams Ltd. Because the peaks obtained with the boron nitride column were not very symmetrical, the particles were heat-treated at 2100" for 3 hr in a graphite crucible and nitrogen atmosphere. After this treatment the boron nitride was slightly gray which was assumed to be caused by a small amount of contamination from the graphite crucible. However, an X-ray spectrograph before and after heat treatment did not show the presence of any graphite. The surface area of boron nitride was found to decrease from 120 to 94 m2g-I after heat treatment. Table VI1 shows the gas chromatographic heats of adsorption of some hydrocarbons on boron nitride and these results are compared with the theoretical results and the results on Sterling MTD4. The gas chromatographic heats of adsorption on boron nitride are seen to be about 1 kcal mole-' higher than the theoretical interaction energies. This is attributed to the heterogeneous boron nitride surface which was shown up by the asymmetrical peaks obtained on boron nitride both before and after heat treatment. As in the case of graphite, the heats of adsorption of the alkanes increase with an increase in the number of carbon atoms. The heat of adsorption of benzene on both adsorbents is lower than that of hexane, although both molecules contain six carbon atoms. This result is predicted theoretically and indicates that there is no specific interaction of either adsorbate with the A bonds in benzene. Thus it is seen that theoretical calculations of in-
(18) J. R. Barns, Trans. Faraday SOC., 60, 149 (1964). (19) E.Cremer and F. Prior, Z.Elektrochem., 55, 66 (1951). (20) R.A. Beebe and P. H. Emmett, J. Phye. Chem., 65, 184 (1961). (21) 8.A. Greene and H. Pust,ibid., 62, 55 (1958). (22) 5. Ross, J. I(. Saelens, and J. P. Olivier, ibid., 66, 696 (1962).
INFRARED SPECTRA AND THERMODYNAMICS OF ALCOHOL-HYDROCARBON SYSTEMS
teraction energies of hydrocarbons on boron nitrides compare reasonably well with the experimental heats of adsorption and hence the adsorption of these com-
1483
pounds on both graphite and boron nitride can be attributed primarily to the existence of dispersion forces of attraction and repulsion.
Infrared Spectra and the Thermodynamics of Alcohol-Hydrocarbon Systems
by H. C. Van Ness,'* Jon Van Winkle,'* H. H. Richto1,lb and H. B. Hollingerlb Departments of Chemical Engineering and Chemistry, Rensaelaar Polytechnic Inetitute, Troy, New York (Received hTovember1 , 1966)
Infrared spectral data in the frequency range of the hydroxyl stretching mode are analyzed in conjunction with heat-of-mixing data to determine the concentrations of alcohol species in ethanol-n-heptane and ethanol-toluene solutions over the temperature range of 20-50'. The structural model which best accords with the data includes monomeric alcohol units, double-bonded dimers, and linear polymer chains. The results of analysis allow the heats of mixing to be split into the part resulting from ,hydrogen-bond rupture and a remainder. The hydrogen-bond energy is found to be about 5.2 kcal/mole of bonds, and the energy of interaction between the hydroxyl and the ir electrons of toluene amounts to about 2.0 kcal/mole of bonds. Unfortunately, spectral data do not allow a determination of the concentrations of monomeric alcohol units, snd thus do not provide suitable data for the calculation of Gibbs free energy and entropy by current theories of solution.
Introduetion Although the literature contains many references to infrared spectra of alcohols in solution with carbon tetrachloride,2 no thorough investigation of alcoholhydrocarbon solutions has been reported. A preliminary experiment showed the spectra in the frequency range associated with the hydroxyl stretching mode for methanol in n-heptane t o be quite different from that for methanol in CCL. This is shown in Figure 1. It is likely that n-heptane acts as a much more nearly inert solvent for alcohols than does CC14. We have therefore recorded the infrared spectra (3800-3100 cm-l) of ethanol-n-heptane solutions at 20, 30,40,and 50" for ethanol mole fractions between 0.01 and 0.5. Similar data were also taken for ethanol-toluene solutions. The instrument used was a Perkin-Elmer Model 421 dual-grating infrared spectrophotometer. Tem-
peratures of the samples studied were maintained to *0.5" by a thermostated air bath. Four different cell thicknesses were employed so as to confine the spectra to the region of maximum sensitivity of the instrument. The materials were of high purity as supplied and were used without further purification. The ethanol was reagent quality, 200 proof, from U. S. Industrial Chemicals, and then-heptane and toluene were Fisher Scientific Co. Certified reagents. Refractive index measurements and chromatographic analyses indicated purities of better than 99.5 mole %. Solutions were made up by weighing the components into carefully stoppered jars. Refractive index meas-
(1) (a) Department of Chemical Engineering; (b) Department of Chemistry. (2) See, for example, H. Dunken and H. Fritzsche, Spectrochim. Ada, 20, 785 (1964).
Volume 71, Number 6 April 1967
