1150
PAOLO BELTRAME, S. C A R R AND ~ , S. MORI
boron fluoride retains the planar structure. The increase of the values of the equilibrium constant for boron isotope exchange in the weak boron fluoride complex system results from the lowering, not of the B-F force constant, but of the force constant of the BF, out-of-plane bend. As for the weakening - of the C-F bond, it is very small and the methyl carbon retains a tetrahedral geometry. Thus, the ionic carbonium
form is absent in the weak boron fluoride complex as in CH,CI.SbCI, complex.'*
Acknowledgment. The authors wish to thank Mr. Teruo Kurihara for helpful advice on the infrared analyses. (12) H. M. Nelson, J. Phys. Chem., 66,1380(1962).
Competitive-Consecutive Reactions in the Photochemical Chlorination of p-Xylene
by Paolo Beltrame, Sergio Car& and Sandro Mori Istituto d i Chimica fisica, Universe'tb di Mitano, Italy
(Received October 18, 1966)
A kinetic study of the side-chain chlorination of pxylene was carried out in CCL solution at 30 and 50" under ultraviolet irradiation. Seven products from monochloroto hexachloro-p-xylene were detected and determined by gas chromatography. On the basis of a system of kinetic equations first order with respect both to chlorine and to the organic compounds, relative rate constants, referred to the specific rate of p-xylene chlorination, were evaluated. A solution of the set of kinetic equations was obtained such as to give reagent and products concentrations as functions of the chlorination degree. Employing the values of the relative rate constants (at 50'), a good fit was obtained of calculated curves of concentrations vs. chlorination level and observed values. Taking into account statistical factors, relative rate factors, fr, for attack of chlorine atoms to single C-H bonds were derived. The fr values prove that mainly the negative inductive effect of chlorine substituents governs the rates of the reactions. A comparison is made of the relative rates constants a t 30 and 50'.
The formal kinetics of complex reaction systems has been the object of extensive mathematical research;lJ! however, the proposed calculation schemes have been applied to relatively few cases, for lack of experimental data. A suitable reaction system is the side-chain chlorination of alkylbenzenei. The simple case of toluene has been by particularly by Haring and Knol.a A xylene, for instance, the para The Journal of Phy8e'Cal C h m k t r y
isomer that we have chosen, can on principle give the pattern of competitiveconsecutive reactions shown in Scheme I. (1) J. Wei and C. D. Prater, Advan. C ' a t d y s ~ ,13, 203 (1962), and references cited therein. (2) N. M. R o d i d n and E. N. Rodiguina, "Consecutive Chemical Reactions," D. Van Nostrand Co., Inc., New York, N. Y.,1964. (3) H. G. Haring and H. W.Knol, Chem. Process E w . , 45,560,619, 690 (1964); 46,38 (1966).
PHOTOCHEMICAL CHLORINATION OF p-XYLENE
1151
Scheme I
a
CH2Cl
CHClz
CH2Cl
CH2Cl
0-0 6-+ 6' f
CHClz
+ I CH3
I
CC13
I CH,
No mention has been found in the literature about CY,a,a,a'-tetrachloro-p-xylene, and a,a,a,a',a'-pentachloro-p-xylene. The other compounds in Scheme I are known, some having been prepared by direct chlorination, others by indirect methods, but no thorough kinetic study of this system has been done so far. The present paper, following a preliminary communiati ion,^ is devoted to the kinetics of p-xylene direct side-chain chlorination in CC14 solution under ultraviolet irradiation. According to the analysis of the reacting system it has been possible to neglect two terms in Scheme I, therefore obtaining the simplified Scheme 11. Two indexes are attributed to each coma,a,a-trichloro-p-Xylene,
Scheme I1 CHClz
I
I CHC&
CHClz
I (333
pound in Scheme I1 : the letter is for general use, while the number shall be employed for the mathematical treatment from eq 6 on.
Experimental Section Materials. p-Xylene, carbon tetrachloride, and diphenylmethane (internal standard) were commercial
products of gas chromatographic purity ; p-xylene in particular was free of ortho of meta isomers and of ethylbenzene. The gc conditions follow: 0.25 in. X 5.7 m column of 10% didecyl phthalate and 10% Bentone 34 on Chromosorb W (80-100 mesh); temperature, 130"; carrier gas, hydrogen at ca. 50 cc/min; thermal conductivity detector. Chlorine was taken from a cylinder and dried over concentrated H2S04before use. a-Chloro-pay kne (M) was prepared by chlorination with C12, without ultraviolet irradiation, of a 500-ml CC14 solution of 26.5 g (0.25 mole) of p-xylene; after addition of ca. 0.5 mole of Clz at 65-70" during 1 hr, the reaction mixture was washed with a NaHCOa solution and water, then dried, and the solvent was removed by evaporation. Distillation in a Todt column at ca. 20 mm pressure yielded a fraction boiling at 90-91 ". Anal. Calcd for CsH&l: C, 68.32; H, 6.45. Found: C, 67.84; H, 6.28. ad-.Dichloro-p-xyhe (D) was isolated by crystallization from the distillation residue of the previous preparation. Recrystallized from ethanol, it had mp 100". AnaE. Calcd for CsH&lz: C, 54.88; H, 4.61. Found: C, 54.92; H, 4.45. a,a-Dichloro-p-xylene (G). Monochloro-p-xylene (11 g) was treated with 10% KOH aqueous solution (100 ml), refluxing for 5 hr. The product had mp 52" (from petroleum ether (bp 75-120"), 7 9). It was oxidized to p-tolualdehyde with lead tetraacetate in pyridine.6 The aldehyde was heated with the stoichiometric amount of PC15,6 the reaction mixture was poured into iced water, and the gem-dichloro-p-xylene was filtered off and recrystallized from ethanol: mp 47". Anal. Calcd for CsHsClz: C, 54.88; H, 4.61. Found: C, 55.20; H, 4.81. (4) P. Beltrame and 5. Cam&,Tetrahedron Letters, 3909 (1965).
(5) R. E. Partch, ibid., 3071 (1964). (6) L. Gattermann, Ann., 347, 353 (1906).
Volume YO,Number 4 April 1966
P. BELTRAME, S. CARRA,AND S. MORI
1152
a,ar,ar',cY'-Tetrachloro-p-xylene(Q) was obtained by chlorinating a 1 M p-xylene solution in CC14 with Clz under ultraviolet irradiation at 70'. After addition of about twice the stoichiometric chlorine ( 5 hr), the reaction mixture was treated as described, and a solid crystallized : mp 92-94' (from petroleum ether). Anal. Calcd for CgH6CI4: C, 39.38; H, 2.47. Found: C, 39.08; H, 2.32. ar,ar,ar,ar',ar',ar'-Hexach10r0-p-xy~ne (E). After one of the kinetic runs, the solution was exhaustively chlorinated with excess chlorine, and after the usual treatment a solid was obtained: mp 109-110" (from petroleum ether). Anal. Calcd for CgH4C16: C, 30.71; H, 1.29. Found: C. 30.49; H, 1.08. The products of the five preparations were of good gas chromatographic purity. Analytical Method. Reaction mixtures were analyzed by gc (thermal conductivity detector) on two columns. Column 1 (0.25 in. X 2 m) contained 10% Apiezon L on Chromosorb W (30-60 mesh) and was used at 135' with hydrogen (ca.400 cc/min) as carrier gas. Column 2 (0.25 in. X 1 m), filled with 2001, Apiezon L on Chromosorb W (60-80 mesh), was used in the same thermal conditions (ca.300 cc/min of Hz as carrier gas). Retention times of the pure products were approximately (in minutes) (column 1) X = 0.79, M = 2.3, G = 5.4, I1 = 10, and diphenylmethane = 16; (column 2) G = 2.1, D = 3.9, diphenylmethane = 6.1, Q = 17, and E = 43. Two other peaks, well measurable on column-2 chromatograms, emerged with retention times 8.9 and 27 min, respectively. The former was attributed to a,a,ar'-trichloro-p-xylene (T), the latter to a,a,a,a',cY'-pentachloro-p-xylene (P), as the only possible choice because of the timing of their appearance during the progress of the reaction, and taking into account Scheme I. The presence of other products, as revealed by gc, was always limited to very small amounts which were neglected. No reaction product had a retention time such as to produce overlap with the diphenylmethane peak. Diphenylmethane was introduced as an internal standard for quantitative analysis. Blanks of the pure compounds dissolved in CC14at different concentrations with addition of known amounts of the standard gave the following molar calibration factors (diphenylmethane = 1.00): X = 1.28, M = 1.66, G = 1.19, D = 1.12, Q = 1.04 and E = 1.10. As these values were affected by large statistical deviations, and for lack of the exact factors for T and P, a normalization procedure was then preferred, giving a factor 1.5 to M and factor 1.0 to all other components. A complication arose because some components The Journal of Physical C h m h t r y
(X and M) were analyzed only on column 1, other products (T, Q, P, and E) were analyzed on column 2, while G and D were analyzed on both columns. A scale factor, evaluated from the areas of the diphenylmethane peaks on the two chromatograms, was used in order to make comparable the results of the analyses of the same sample on different columns. The analytical procedure was tested on a mixture of exactly weighed amounts of X, M, G, D, and Q; the average deviation was 10%. Apparatus. The chlorination was carried out in a 358cc cylindrical semibatch Pyrex reactor. Thermostated water was circulated into its jacket, and mechanical stirring was provided at 1000 rpm. The reactor was irradiated by means of an external 3600-A ultraviolet source (Quarzelampen Hanau) kept at a fixed (20 cm) distance. Chlorine, previously saturated with CC4, was introduced through a sintered-glass disk at the bottom of the reactor. The latter was equipped with an efficient condenser and a thermometer. Apart from an initial rise owing to the starting of the reaction, the temperature was constant *0.2". A diagram of the apparatus is given in Figure 1.
U
Figure 1. Apparatus diagram: A, Clz cylinder; B, drying by concentrated H,SOa; C, empty vessels; D, variablearea flowmeter; E, CCla saturator; R, reactor; F, reflux condenser; L, ultraviolet lamp; and G, absorption in 20% NaOH solution.
Kinetic Procedure. Having introduced 150 ml of a 0.5 M CC14 solution of p-xylene into the reactor, oxygen was removed from it by flushing for 0.5 hr from a line not indicated in Figure 1. A similar washing was effected with chlorine in the equipment from B to E. Eventually the chlorine flow was diverted into the reactor (t = 0). At time t a 1-ml sample was taken from the reacting solution and added to 1 ml of a CCld solution containing a known amount of diphenylmethane; the resulting mixture was washed with 2 ml of NaHCOrsaturated aqueous solution and then with water, dried with Nad30c,and analyzed by gc.
PHOTOCHEMICAL CHLORINATION OF XYLENE
~
1153
~~
~~
Table I: Example of Kinetic Run (Temperature, 30'; Time,
~
Chlorine flow, 3000 cc/hr; CX ( t = 0) = 0.500 M )
-
Mole/].
7
min
cx
CM
CG
CD
15 30 45 60 75 90 105 120 135 150 165 180
0.232 0.141 0.014
0.244 0.281 0.281 0.063 0.009
0.009 0.019 0.031 0.034
.. ... ...
...
0.015 0.052 0.144 0.246 0.158 0.070 0.030 0.010
... ... ...
..
... ...
*..
... ... ...
0,008
... ... ...
...
... ...
A blank has shown that the washing procedure do& not affect the composition of a mixture of products (G, D, and Q). An example of kinetic run iB given in Table I. Results and Kinetic Treatment The set of kinetic equations (1, where CC is the chlorine concentration and CX) C M . .. refer to the organic compounds) derives from Scheme 11, assuming that every reaction be first order with respect both to chlorine and to the organic substrate.
dCx = -kxCcCx dt
... ... ...
...
CQ
CT
...
CP
CE
... ... ... ... ... ...
...
...
...
...
0.008 0.029 0.136 0.256 0.270 0.220 0.138 0.081 0.046 0.023 0.008
...
0.020 0.069 0.160 0.250 0.300 0.323 0.303 0.278 0.238
0.053 0.096 0.150 0.199 0.228
.,. ... ... ... ...
... ...
... . I .
0.026
+ k m - -c x at the maximum of M
~ M G
(2b)
CM
kx
CG - --_CD + I-~ Gat the maximum of T
(2e)
kQ -- _ CT _ at the maximum of Q
(2f)
kT
kD
CT
k~ CT
kT
CQ
kP
CQ at the maximum of P
- =
kQ
CP
(2g)
A seventh equation (3) is provided by the ratio of (IC) and (Id) dCG - - - kMGCM - kGCG dCD kMDCM - ~ D C D
(3)
that has an initial limit value (CG+ 0, CD-t 0) (eq 4)
dCE
- = kPCCCP dt
The concentration vs. time curve for each chlorinated compound, except E, shows a maximum. This corresponds to eq 2, each one valid at the given point of maximum.
corresponding to the limit value of the ratio (CG/CD) when CD and CG tend to zero. Therefore, for each kinetic run the ratio CG/CDwas plotted us. CDin order to extrapolate the initial value. Other plots were made reporting CM V S . CX, CG VS. CM, CD VS. CM, CT vs. CD, CQvs. CT, and Cp vs. CQfor a precise evaluation of the concentrations to be used in eq 2. The small for eq 2e was evaluated value of ( C G / C T ) ~T*needed ~ from the concentration vs. time plot. Examples of the plots are shown in Figure 2. The method just described has the advantage of ignoring the chlorine Volume 70,Number 4 April 1966
1154
P. BELTRAME, S. CARRA,AND S. MORI
first-order rate constant, ICiz, for the reaction of p xylene can be defined as 0.4
kiz = kxCc" (6) A set of relative rate constants, the same as in Table 11,can now be introduced as
0.2
0.1
0
0.2
0.3
:j:l'..
while K12 is obviously unity. Substituting relations 5 and 7 into eq 1, the latter can be written in the general form
0.1
0.1 0.2 0.3 CD Figure 2. (a) Example of CG/CD us. CD plot (run at 50'; C1, at 3000 cc/hr). (b) Example of CTus. CD plot (same run).
concentration, which is variable during the course of the runs, although it gives only relative values of the rate constants. Chlorinations have been performed mainly at 50°, covering low and high degrees of chlorination in a total of four runs. An additional run WM carried at 30". Relative rate constants, referred to kx, are reported in Table 11.
where K j t and K,, are the relative rate constants, while m is the component number; the prime on the summation signs indicates that only the terms having j # i are included. The first term in brackets refers to the formation of the ith component, and the second one to its disappearance. Eq 8 becomes m
dC, - = Z'K&'j d9 j=1
- Cr C ' K t j j-1
if one takes t
9 = kl2Sf(x)dx 0
1 0.075 0.235 0.353 0.0749 0.0277 0.00694
...
---a
60°
1 0.085 0.234 0.396 0.0793 0.0333 0.00843 0.00346
where the coefficients a,, and A, are obtained solving a set of equations of the form
r The progress of the reactions can be calculated, with the use of the relative constants, in the followingway. The variable chlorine concentration CC may be expressed as
cc
= Cc"f(t>
=
1,2) ... m
while the values of Qr are determined from initial conditions (9 = 0). Keeping T fixed, eq 12 represents a set of linear, homogeneous equations in the a,, terms; the cor-
(5)
CC"being the concentration at time zero. A pseudoThe J O U Tof ~Physical Chemistry
( 10)
Equation 9 has the typical form of the kinetic equations for the first-order competitive-consecutive reactions. The general solutions of eq 9 may be written' as
Table I1 : Relative Rate Constants -Temp, 30°
(9)
(7) A. A. Frost and R. G. Pearson, "Kinetics and Mechanism," John Wiley and Sons, Inc., New York, N. Y., 1966,p 160.
PHOTOCHEMICAL CHLORINATION OF XYLENE
1155
responding determinant of the coefficients must vanish as a condition for nontrivial solutions. For the case under consideration it is
(Kiz - A) -Klz
(K23
0 0 0 0 0 0
+
0 0 0
0
0 K24
- X)
0 (K35
-K23
- A)
- A)
-K2r
0
0 0 0 0
-K35
-K45
0 0 0
0 0 0
(K45
function of time, were expressed as a function of y by means of eq 15 and then compared with the calculated curves (Figures 4-6). 0 0 0
0
0 0 0 0
0 0 0 0
0 0 0 0
=
0 (13)
~~
Discussion
The eight solutions for X are X i = Klz = 1; Xa = Xs =
Kb6;
Xa =
K23
K67; A7
+ =
K24; A 3
K78;
=
KS;
Xq
=
KG;
Xa = 0
For the runs at 50", introducing the values of the relative rate constants from Table I1 and solving the set of equations (12), the appropriate a,, coefficients were calculated. Then the initial conditions (CX" = 0.5, CMQ = CG" = . . . = 0) were taken into account to obtain the Qr coefficients. If in eq 11 the A,, coefficients are considered as elements of a square matrix, the terms e-': as elements of a column matrix, and Ct as elements of a row matrix, the final results at 50" can be expressed as
c =
For each component of the reacting system the comparison of the calculated C,-9 curve with the experimental Ci-t curve leads to an empirical relation between 9 and t. Doing this for all the components and averaging, 29 turns out to increase more than linearly with t, in the range examined. Because of eq 10, the differential of 9 with respect to t is proportional to f(t), ie., to CC (eq 5). Therefore, the observed behavior of 9 as a function of t means that the concentration of chlorine, as expected, is increasing from the beginning of the reaction up to nearly the end of it. The 6 us. t curve for a typical run is reported in Figure 7. An approximate evaluation of dd/dt shows
0 0 0 0.5 0 0 0 0 0 0 0 -0.7342 0.7342 0 0 0 0 0 0.1033 0.8105 -0.9138 0 0 0 0.5301 0 0 0 0.1866 -0.7167 0 0 0.9977 -0.9139 0.8982 -0.0576 -0.9244 0 0 0 0.4294 - 1.2027 0.7580 0.0019 0.0991 -0.0857 0 0 0.0018 -0.0477 0.3398 -1.2858 0.9946 0 0,0000 -0.0027 0.5278 -0.9946 0.5000 0.0000 0.0000 O.oo00 0.0021 -0.0353
'exp(--b) exp( -0.3199) exp( -0.3968) X exp( -0.079321)) exp ( -0.03339) exp ( 0.008439) exp( -0.003469) 1
-
(14) I n this way it has been possible to calculate by computer the concentrations of p-xylene and of reaction products for 100 different 9 values in the range 103, practically covering the complete transformation from pure xylene to pure hexachloroxylene. At each 19 value a chlorination degree (y) has been evaluated by the formula r
m
(ncl)t being the number of chlorine atoms in the ith component. The calculated curves of Ct us. y are reported in Figure 3. Experimental values of C , obtained as a
that CC has increased by a factor around 70 between t 10 min (y = 0.68) and t 160 min (y = 5.6). Not having experimentally determined any instantaneous value of chlorine concentration in the reacting solutions, the evaluation of the second-order rate constants kx, kMG,. . . . k p was not feasible. However, the relative rate constants are by themselves sufficient, as it has been shown, to provide a complete pattern of the products distribution as a function of the chlorination level, at a given temperature. The agreement between calculated and experimental values of concentrations (Figures 4-6) is on the whole quite good, in spite of the difficulties of a gas chromatographic quantitative analysis. Such agreement proves that the evaluation Volume 70,Number 4 April 1966
P. BELTRAME, S. CARRA,AND S. MORI
1156
+ CI. Z R+.HCI R . + Clzf&SeRCl + C1.
Ci
RH
0.5
I
0.4
0.3
Accordingly, the rate-limiting step is the C1- attack on C-H bonds, and the constants of Table I1 have to be modified by statistical factors in order to discuss the reactivity of the different kinds of bonds. Taking into account the number of hydrogen atoms available for each reaction of Scheme 11, relative rate factors per C-H bond dfi) were obtained for reactions at 50". They are collected in Table I11 with regard to the group on which the attack is carried and to the substituent present in the pura position.
0.2
0.1
)
I
0
2
7
4
5
Y
6
Figure 3. Calculated distribution of products as a function of the chlorination degree, a t 50'.
"iI 0.3
I
J
Figure 5. Comparison of calculated curves and experimental data (50") for G (0)and D (a).
c 0.4
0
1
2
3
4
5
Y
.
6
Figure 4. Comparison of the calculated curves and experimental data (50') for X (a), M (0), P (A), and E (0).
of Ki,constants through equations of the type (2) and (4)is satisfactory, even from a limited number of experiments, as already pointed out for the case of a system of consecutive reactions.8 Furthermore, the knowledge of the relative rate constants is useful for the elucidation of some aspects of the reaction mechanism. The accepted scheme for photochemical chlorination is based on the following propagation reactions.9 The Journal of Physical Chemistry
0
1
2
3
4
5
Y
Figure 6. Comparison of calculated curves and experimental data (50') for T ( V ) and Q (A), (8) R. B. MacMullin, Chenz. Eng. Progr., 44, 183 (1948). Radicals in Solution," John Wiley and Sons, Inc., New York, N. Y., 1957, p 352 ff. (9) C. Walling, "Free
PHOTOCHEMICAL CHLORINATION OF p-XYLENE
1157
e lo3
on a CHzCl group is attacked at a higher rate than that on a CH3, aa for instance in the liquid phase chlorination of trimethylacetic acid." Due to the nonpolar character of solvent CC14, it is also reasonable to compare the f l factors of Table I11 with results obtained in the gas phase for the chlorine atom attack on C-H bonds. For the series methane, methyl chloride, methylene dichloride, and chloroform,12*13 the following f7 values at 50" can be derived: CH, = 1; CH3C1 = 4.3; CH&lz = 8.4; CHCh = 2.5. On the other hand, a comparison of the chlorinations of n-butane, n-butyl chloride, and other butane derivatives with electron-withdrawing substituents in the l-position14 has shown that chlorine atoms (as well as other elec-
.
102
lo//
1 .
16'
.
X - H X = c1
Table I11 : Relative b t e Factors per C-H Bond (fr) at 50" Bond belonging to the group
CHs CHzCl CHClz
--Group CHa
1 0.26
...
present in the p a m position---CHzCl CHCh CCla
0.47 0.12
...
0.79 0.10 0.025
...
... 0.021
The data in Table I11 show that both chlorine atoms in the a-position and chlorinated para substituents lower the reactivity of a side-chain C-H bond. This is in line with the electrophilic character of the chlorine atom. Obviously, the electron withdrawal by part of a C1 substituent is larger if it is adjacent to the reaction center than if it is on a para side chain. I n fact, the relative reactivities of C-H bonds belonging to CHa and CH2C1groups differ by factors in the range 4-8; between CHzCl and CHC12 the factor is 4. On the other hand, the substitution of a C1 atom for hydrogen on the para group gives a reduction of rate around 2 for the first C1, and a smaller lowering, by a factor 1.2, for subsequent substitutions, except when comparing a-chloro-p-xylene with CY,a-dichloro-p-xylene. Apart from the last case, the negative inductive effect of chlorine appears to govern the rates of the reactions. For the parallel case of the liquid phase side-chain chlorination of toluene, f l values have been found equal to 1, 0.25, and 0.087 (at 100") and 1, 0.18, and 0.042 (at 40") for C-H bonds included in CH3, CH2C1, and CHCh groups, respectively,* while values 1, 0.14,and 0.015 (at 15") are given for the same bonds by other authors.lo In different cases the C-H bond
,
X-CHz -CH2 -CH2--CH3 1 3.6 3.6 1 0.8 2.1 3.7 1
It is usually suggested that the inductive effect of electronegative atoms or groups can be opposed by a mesomeric effect due to stabilization of the incipient free radical by conjugation. The latter appears to be prevailing in the methane series above, and also for the mentioned liquid phase chlorination of trimethylacetic acid. The inductive effect prevails in the nbutane derivatives, although the rate depression when X = C1 is larger for the @- than for the a-position because of the competing mesomeric effect. The results on the p-xylene series (Table 111) confirm that the additional conjugative stabilization due to chlorine is relatively unimportant in the case of aromatic side chains. It is also interesting to observe the effect of temperature variations on the relative rate constants of the chlorinations. Data in Table I1 indicate an increase of almost all K,, constants going from 30 to 50". This does not look accidental, although the statistical error of the Km/KZ0factors is certainly considerable owing t o the narrow temperature range. Clearly, successive chlorinations after the first tend to have a higher activation energy, the increments AAE* being estimable by the formula (10) G. Benoy and J. C. Jungers, Bull. SOC.Chim. Belges, 65, 769 (1956);Chem. Abstr., 51, 9330h (1957). (11) G.Benoy, Tetrahedron, 20, 1567 (1964). (12) J. H.Knox, Truns. Faraday SOC.,58, 275 (1962). (13) G. C. Fettis and J. H. Knox, Progr. Reaction Kineties, 2 , 1 (1964). (14) P. S. Fredricks and J. M. Tedder, 1.Chem. Soc., 144 (1960); H.Singh and J. M.Tedder, ibid., 4737 (1964).
Volume 70,Number 4 April 1968
HOWARD S. SHERRY
1158
7'17'2
AAE* = R7'2
- Ti
In
K z -
Ki
where indexes 1 and 2 are related to the two temperatures. Applying eq 16 to the data on tolueneS at 40 and loo", the values of AAE* for the chlorinations turn out to be 1.2 and 2.8 kcal/mole going from toluene to benzyl chloride and benzylidene chloride, respectively. Mean values have been obtained from the data of Table 11, considering K12 and K24 for the chlorination
of CH, groups; K28, K45, and Kss for the attack on CH&l groups, and finally K n for the CHCl2 group. The results for AAE* are 1.2 (average value) and 1.9 kcal/mole going from the attack on CHBto the one on CHzCl and CHC12, respectively. These figures are quite significant with respect to the low values of the activation energies for chlorine atom attack on aliphatic C-H bonds, ranging between 0 and 4 kcal/ mole. l 3 Acknowledgment. We are indebted to the Italian Consiglio Nazionale delle Ricerche for financial aid.
The Ion-Exchange Properties of Zeolites. I. Univalent Ion Exchange in Synthetic Faujasite
by Howard S. Sherry Research Department, Socony Mobil Oil Company, Inc., Paulsboro, New Jersey
(Received October 18, 1966)
Ion-exchange isotherms describing the exchange of Li, K, Rb, Cs, Ag, and TI(1) ions into the Linde Na-X type of synthetic faujasite are presented. All the alkali metal ionexchange isotherms except the one for Li-Na exchange are sigmoidal and show selectivity reversals. The initial selectivity series is in the order Ag >> T1 > CS 2 Rb > K > Na > Li. Above approximately 40% replacement of sodium ions the selectivity series becomes Ag >> T1 > Na > K > Rb 2 Cs > Li. Evidence is also presented to demonstrate that 16 out of 85 sodium ions per unit cell are not replaceable by Rb and Cs ions in Na-X. Ion-exchange isotherms for the exchange of Li, K, Rb, Cs, Ag, Tl(I), and NH4 ions into the Linde Na-Y type of synthetic faujasite are also presented. These isotherms demonstrate that 16 out of the 50 sodium ions per unit cell cannot be replaced by Rb, Cs, TI(I), and NH4 ions. Furthermore, Rb-Na and Cs-Na ion exchange in zeolite Y gives nonsigmoidal isotherms which are compared to the sigmoidal isotherms found for these pairs of ions in zeolite X. I n addition, Na-X is much more selective for Ag than is Na-Y. From these data and the structural data for these zeolites it is concluded that there is much ion binding in Na-X and little ion binding in Na-Y.
The ion-exchange properties of zeolites are of interest for several reasons. The pore size of these materials amroaches. and in some cases is smaller than, the she Of most monatomic ions' and the patterns exhibited by these materials are quite varied. For A
example, the synthetic zeolite Linde A exhibits the selectivity pattern' Na > K > Rb > Li > Cs, and
L
The Journal of Physkd Che?nhtry
(1) R. M. Barrer, L. V. C . Reas, and D. (London), ~ 2 7 3 180 , (1963).
J. Ward, Proc.
Roy. SOC.
