KOTES
Nov., 1962 The silver-silver chloride electrodes were thermal type prepared by heating to about 550’ a, 1:s weight mixture of silver oxide and silver chlorate. The procedure outlined by Greeley, Smith, Stoughton, and Lietzke? was followed closely. The glass electrodes were Beckman commercial glass electrodes. Both the Amber Glass #43509 and the General Purpose #41203 were tried with no detectable difference in results. In most of the runs the Amber Glass electrode was used. The empirical constant B’ was calculated from the slope of a plot of
E: - 21c log m
%kAm”z + -___ 1 + Bm1I2
against m. Values of the necessary constants at 65’ were taken from the tabulation of Manov, Bates, Hamer, and Acree.8 The Debye-Hiickel A is 0.5480 kg.’/z mole-’/z and k was converted to absolute volts and is 67.093 mv. The constant B was treated as an empirical constant. Guggenheim and Prue8 suggest B = 1.0, Scatchardlo suggests B = 1.5 satitifactorily fits most data for 1-1 electrolytes. The data were plotted using B = 1.0, 1.5, 2.0, and 3.0. All four plots were linear; the least squares slopes, the standard error of fit, and the B’ values are in Table I. The minimum standard error of fit was found with B = 1.0. The calculated activity coefficients are compared with the values determined by Greeley, Smith, Lietzke, and Stoughton” in Table 11. The calculated activity coefficients agree well with both B = 1.0 and B = 1.5, with the B = 1.5 values giving a slightly closer check.
2269
would be equally successful at that temperature with the advantage that the asymmetry potential seemed to become linear in a shorter time at the higher temperature.
Acknowledgment.-We wish to thank Dr. M. H. Lietzke and Dr. R. ITr. Stoughton of the Oak Ridge National Laboratory for an introduction to this problem. T H E EFFECT OF SUBSTITUTION ON T H E IONIZATION POTENTIALS OF FREE RADICALS AND MOLECULES. IV. 83 VALUES FOR ALCOHOLS, ETHER?, THIOLS, AND SULFIDESla BY JOYCE J. K A U F M A N ~ ~ M A S , Baltimore 18,Maryland Received April 86, 1968
It has been shown p r e v i o u ~ l ythat ~ ~ ~the effects of substituent groups on ionization potentials of alkylamines (K&) and alkyl free radicals (Y3C) were almost identical. From measured photoionization potentials of amines a new set of constants, 8~ values, which quantitatively reflect changes in ionization potential with substituent groups, were derived and using these, ionization TABLE I potentials of alkyl free radicals could be estimated VAISJES OF B‘ AS A FUNCTION OF B FROM THE LEASTSQUARES to within the experimental error of their measure2kA.m1/2 ments. There is a “saturation” effect and these SLOPE of E - 2k log m + AQAINST m values are not linearly additive but can be combined 1 $. Bm‘12 following certain set precepts. 8 3 values obtained B Slope Bj d i t , mv, from linear and branched alkyl substituents proved 1.0 30.4 0.227 0,350 to be extendable to cyclic substituents in which 1.5 13.6 ,102 ,392 the carbon from whence the unpaired electron was 2 0 0.844 ,0063 .394 being withdrawn was itself part of the ring.3 3.0 -17.3 - .I29 .398 However, effects of substitution on ionization TABLE I1 potentials are not the same for the series of alcohols and ethers as for the amines. 8 3 values for these MEAN I O N I C ACTIVITY C O E F F I C I E N T S O F HYDROCHLORIC oxygen-containing compounds now will be treated Am1t2 ACIDAT 65’ CALCULATED FROM log y = + B’m here. This problem has assumed importance 1 + Bm‘’a recently because of the use of 8~ values as a measure Accepted of the magnitude of penetration integrals of neutral activity Mean ionic activity coefficients calcd. with B substituent groups in quantum chemical calculacoequal Molality effioients“ 1.0 1.5 2.0 3.0 tions. Although these penetration integrals custo0.005 0.923 0.922 0.924 0.925 0.928 marily are neglected, they have been shown in .01 .898 .896 .Si98 .900 .910 several cases to be comparable in magnitude to .02 .867 .864 .867 .870 .877 other terms being ~ a l c u l a t e d . ~ .05 .817 .815 .819 .824 .832 Since 8~ values derived from nitrogen compounds .10 .774 .778 ,781 .784 .791 do not carry over into the oxygen series, a specific .20 .743 .752 .748 .745 .741 set of 8~ values for use with oxygen compounds is Reference 11. presented in Table I. These values are based on A series of runs at 50” before the experimental technique photoionization measurements of the molecules.5 The purpose of these values is twofold: first, to was refined to rigorously exclude oxygen from the Ag-AgC1 7--
7
electrode and to prevent all evaporation losses gave almost equally good values of activity coefficient but the uncertainty due to the scatter of e.m.f. values was unacceptable. An incomplete set of data a t 85” indicated the technique
-
(7) R. J. Greeley, W. T. Smith, Jr., R. W. Stoughton, and &/I. H. Lietzke, J . Phys. Chem., 6 5 , 652 (1960). (8) G. G. Manov, R. G. Bates, W. J. Hamer, and 9. F. Acree, J . A m . Chem. SOC., 6 5 , 1765 (1943). (9) E. A. Guggenheim and J. E. Prue, Trans. Furaduu Soc., BO, 231 (1954). (10) See footnote 9 of M. H. Lietzke and R. W. Stoughton, J . A m . Chem. SOC.,78,4520 (1956). (11) R. S. Greeley, W. T. Smith, Jr., M. H. Lietzke, and R. W. Stoughton, J . Phys. Chem., 64, 1445 (1960).
(1) (a) This work was supported in part by the Office of Naval Research; (b) 1962 Visiting Staff Member, Centre de MPcanique Ondulatoire AppIiqu6e, 23 Rue du Maroc, Paris IsE, France. (2) (a) J. J. Kaufman and W. S. Koski, J . A m Chem. Soc., 89, 3262 (1960): (b) J. J. Kaufman and W. S. Koski, presented before the Section on Physical Chemistry-Structure and Reactivity of Small -Molecular Species, 18th International Congress of Pure and Applied Chemistry, Montreal, August, 1961. (3) S. J. Kaufman, Part I11 of this series, ONR-TR3. NONR3471(00), March, 1962; (accepted for publication in J . A m . Chem. SOC.).
(4) S. Bratoi and S. Besnainou, J . Chem. Phus., 34, 1142 (1961). ( 5 ) K. Watanabe, T. Nakayama, and J. Mottl, “Final Report on
Ionization Potential of Molecules by a Photoionization Method.” Deut. of the Armv kSB 99-01-004. December. 1959.
2270
NOTES 6~
Vol. 66
TABLE I VALUESDERIVEDFOR 0 AND S MOLECULES (IN E.v.) HzO and H2Sparent molecules
Oxygen
Substituent
6K,O(1)
CH3-
1.74
CnHr
2.11
6K,O('-')
6K,O(')
1.74
3.32 2.39 3.39 2.43
2.55
Sulfur Substituent
6K,S(''
CHa-
1.02
CzHfi-
1.17
0.73
0.69
0.80
0.81
6K,8(1--0)
8K,S(')
6K-31e.S'"
6K,P1)
6I-Me,S(2)
1.77 0.75 2.03 1.17
0.15
0.26
0.24
0.39
0.86
1.26
2.16 1.26
n-C4Hg-
0.65 0.96
1.02
n-CaHr
0.47
0.93
2.43
n-C4Hg-
0.37 0.95
2.39
GC3H7-
~K--M~,o(')
0.85 3.06
2.11
n-CaH7-
6~-?d~,o(l)
8~,0(~-l)
2.59
0.90
1.32
0.30 1 32
enable one to estimate ionization potentials of other oxygen-containing molecules, and second, to permit one to differentiate effects of penetration
I I
integrals on different cores, -C.
*.
and -N:
I I
(a) I(MeSEt)
I(H2S) - B K , s ( ~ ) (Et) 8~,~(2-')
on
one hand and -0-.. on the other hand. The symbolism and sign convention for 8~ values ) are the same as those of ref. 2a: 8~ (or 8 ~ ( l ) and 8 ~ ' are ~ ) the changes in ionization potential caused by substituting one or two identical groups, respectively, for H atoms (on the same central 0 atom from which the electron is being withdrawn upon ionization). To differentiate these 8~ values from those derived from nitrogen compounds, an extra subscript 0 will be used : ~ K , O and ~ K , o ( ~ ) 8K-Me,0(1)and ~ K - M ~ , O (are ~ ) the changes in ionization potential caused by substituting one or two groups for methyl groups (under the same conditions as above). Since there is a saturation effect, another type of 8K value is the difference in ionization potential found by adding a second identical substituent group when a first substituent group already is present. aK,o(1-0) (or 8K,o or 8K,O(')) and 8 K , 0 ( ~ - l ) are the differences in ionization potential between monoand unsubstituted and between di- and monosubstituted molecules. The symbols for values from sulfur compounds are exactly the same with the exception of a subscript S instead of 0. With the 8~ values in Table I, it is possible to: (1) calculate the ionization potentials of mixed ethers or sulfides: As an example one can reproduce by calculation the experimentally measured ionization potential of CH3SCzHs.
=
(Me)
=
10.46 e.\'. - 1.17e.v. - 0.75 e.v.
=
8.54 e.v. (calcd.)
=
I(H2S) -
or (b) I(3leSEt)
~ K , s ( ~(Me) )
-
8 K ,9 ( 2 -1)
(Et)
=
10.46 e.v. - 1.02 e.v. - 0.86 e.v.
=
8.58 e.v. (calcd.)
Each of these calculated values is extremely close to the experimentally measured value of 8.55 f. 0.01 e.v. The convention to be adopted for calculation of ionization potentials for S and 0 comand 8K,S(or 0)(2-1) (Rz) where if pounds is 811,S(oro)(l)(R1) R1 # R2,then R1> Rz. ( 2 ) calculate the ionization potential of a cyclic ether or sulfide: In a previous paper3 it has been demonstrated that it is possible to calculate ionization potentials of cyclic entities by extension of the 8K values for the corresponding linear groups. (a) Estimation of the ionization potential of tetrahydrofuran (THF) confirms this conclusion. I(THF)
=
I(HzO) -
I(THF)
~ K , o ( (Et) ~ ) =
12.59 e.v. 3.06 e.v.
=
9.53 e.v. (calcd.)
=
9.54 e.v. (expt.)
(b) Estimation of the ionization potential of tetrahydropyran (THP) serves as a conclusive
XOTES
Nov., 1962 check on the validity of calculation of ionization potentials of cyclic ethers by the b~ method.
I(THP)
=.=
I(HzO) - k,o(I)(Pr) - k,o(Z-l)(Et)
== 12.59 e.v.
.T(THP)
- 2.39 e.v. - 0.95 e.v.
:=
9.25 e.v. (calcd.)
:.=
9.26
&
0.03 e.v. (expt.)
For cyclic compounds if possible use R1 = Rz; if not, then R1 >. Ra. The much larger effect of the Me group on I(Mesa) radical relative to I(MS.) radicala (2.44 e.v. as compared to 1.02 e.v. for MeSH relative to HzS) indicates an enhanced resonance contribution (due possible to a planarity of the MeSf ion). This observation carries with it, the subtle implication that one should perhaps use different evaluations of penetration integrals depending upon whether one or two electrons from 0 or S are contributed t o a delocalized system. Ionization potentials of ethers and sulfides have become of great interest recently in connection with charge-transfer complexes. Formation of various types of complexes is dependent on basicities and therefore on ionization potentials of the donors, and positions of new ultraviolet or visible charge-trrznsfer absorption bands are directly related to ionization potentials of the donors. Acknovv1edgment.-The author wishes to thank Dr. 2'. 1'. Lossing for graciously sending information on experimentally measured ionization potentials in advance of publication. (6) F. P. l,ossing, private communication.
COSFCRMATIOX O F T H E NATURE OF CATION DEPOPULATION IN SYKTHETIC CRYSTALLINE ZEOLITES BY GEORGET. KERR Socony iMobil Oil Companv, Inc., Research Dspt., Paulsboro,
New Jersey Recezrsd May 16, 1863
Freeman and Stamiresl studied the electrical conductivity of zeolites A, X, and Y. The two latter zeolites, isostructural with faujasite, differ in composition. These workers defined zeolite X as having molar ratios of silica to alumina between 2.1 and 3.0 and zeolite Y as having ratios between 3.0 and 5.2. Consequently, zeolites of the X group have a higher cation density (number of cations per unit cell) than zeolites of the Y group since zeolites clontain one equivalent of cation for each gram-atom of aluminum in the zeolitic framework. The differences in the energies of activation for conduction between zeolites X: and Y supported the postulation of Breck and Flanigenz that t,here is (1) D. C . Freeman and D. N. Stamires, J . Chem. Plays., 86, 799 (1961). (2) D. W. Breck and E. M. Flanigen, Abstract 134 of the 134th National Meeting of the American Chemical Society, September, 1958, Chicago, Illinois.
2271
more than one type of cation site in zeolites. Freeman and Stamires found that the highest energysite type (in which the cations are relatively loosely bound to the lattice) is eliminated or depopulated as the cation density decreases; the low energy-site type (tightly bound cations) is retained. They proposed that the loosely bound cations are located in the large cavities or in the eight- or twelve-membered oxygen rings of the zeolite lattices; the tightly bound cations are located in the vicinity of the six-membered rings. In summary, this proposal states that for a given zeolite crystal structure, as the silica to alumina ratio is increased, the cation sites located in the large cavities or rings are depopulated in preference to those located in the smaller cavities or rings. The information to follow supports this proposal. Sodium zeolite A3 (2.0 molar ratio of silica to alumina) will not sorb straight chain hydrocarbons. However, replacement of 30 to 40% of the sodium ions by calciurn ions renders zeolite A capable of sorbing straight chaimab At this level of exchange the unit cell of zeolite A contains an average of 9.6 to 10.2 cations. Reed and Breck3C interpreted this as indicating that sodium ions located in the eight-membered oxygen rings (through which hydrocarbon sorption occurs) are preferentially replaced over the sodium ions located in the sixmembered oxygen rings. On the basis of these findings it would be expected that upon increasing the silica to alumina molar ratio of a zeolite A structure, the cation sites located in the eight-membered oxygen rings would be depopulated in preference to those in the sixmembered rings. 'If the molar ratio of silica to alumina were a t least 2.7, the number of sodium ions still located in the eight-membered rings should not be sufficient to preclude the sorption of straight chain hydrocarbons. Sodium zeolite ZK-4,* with a silica to alumina molar ratio of 3.4, fulfills this requirement. This zeolite, containing nine sodium ions per unit cell, has essentially the same sorptive capacity for straight chain hydrocarbons as calcium zeolite A (for example, 12.5 and 12.6 wt. %, respectively, for n-hexane on samples purged a t 350' with nitrogen), If the nine sodium ions per unit cell in zeolite ZK-4 were distributed among six- and eight-membered oxygen rings in the same proportion as in sodium zeolite A, then each eight-membered oxygen ring would contain one sodium ion thus blocking free passage of a straight chain hydrocarbon through the main crystal cavity, as shown by Reed and B r e ~ k . ~ ~ Hence, the findings of Freeman and Stamires explain our observations. Additional confirmation might he obtained by comparing the energies of activation for conduction of zeolites A and ZK-4 as was done with zeolites X and Y by Freeman and Stamires. (3) (a) D. W. Breck, W. G. Eversole, and R. &I. Milton, J . A m . Chem. SOC.,7 8 , 2338 (1956): (b) D. W. Breok, W. G . Eversole, R. M. Milton, T. B. Reed, and T. L. Thomas, ibzd., 78, 6963 (1956); ( e ) T. B. Reed and D. W.Breck, zbzd., 78, 5972 (1956). (4) G . E ' . Kerr and G. T. Kokotailo, zbzd., 88, 4675 (1961).
