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V. BALIAH AND SP. SHANYUGANATHAN
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K I and K2versus reciprocal temperature, shown in particularly in State 11. In State 111, there was
Fig. 4, yield activation energies for sorption of 10 and 16 kcal. for States I and 111,respectively. This does not imply that only one activation energy would be found in each state; more likely the activation energy increases continuously as oxygen is incorporated. Jennings and Stone found an activation energy of 7 kcal. for cuprous oxide on copper metaL9 The electrical conductance may be plotted against time or against gas uptake. Figure 5 shows typical plots of the conductance change versus the gas uptake. I n State 11, this is more or less parabolic while the data for State I11 can be fit by a more complex function. The most important point is that the conductance change is not directly proportional to the gas uptake, the shape of the curve depending strongly on the state of the film. Many measurements were made to show that the rate of oxygen sorption depends on the stoichiometry of the film as determined by the conductance. Figure 6 shows how the rate constant in State I11 varies with the conductance a t the beginning of a sorption run. Since each run followed an overnight bakeout in vacuum, the initial conductance is due to changes in the bulk stoichiometry rather than being just a surface effect. The good fit of the data as shown in Fig. 6 is typical of these results . An interesting and unexpected consequence of these measurements was the conductance change observed at the end of a run when the oxygen was pumped out of the system. The conductance change a t that point reversed direction and started to decrease. This effect is shown in Fig. 7. I n one run, the desorption was followed carefully. In six hours the conductance decrease was 75% of the original increase while only 5% of the adsorbed gas was desorbed. This behavior was noticed
little change in conductance on pumping out the oxygen. This effect can only be explained by some incorporation process in which the oxygen is presumably diffusing into the film. Adsorption-incorporation runs similar to those shown in Fig. 7 were made for varying durations of sorption. The effect was present even for very short times. This shows that adsorption and incorporation occur simultaneously even a t very low coverages. Thus the conductance change normally measured is a result of both adsorption and incorporation. IV. Conclusions The results presented here show the interesting possibilities resulting from the measurement of the electrical conductance simultaneously with the usual reaction kinetics. While these results cannot be applied rigorously to any theory, due to uncertainties in such factors as electron mobility and film porosity, they do show the role of the electronic factor in chemisorption. With further knowledge of these presently uncertain factors, the results can be used in a quantitative way. The results do show that measurements of conductance alone cannot be used for kinetic expressions based on an assumed relation of conductance change to gas uptake since different relations are obtained for even one sample under different oxidation conditions. On the other hand, measurement of gas uptake alone will not reveal the presence or extent of electronic interactions. The significant decrease in conductance without a correspondingly significant desorptioii during oxygen pump-out shows the presence of an additional, incorporation step in the gas uptake. It also shows the need for both measurements in correctly distinguishing between desorption and incorporation.
KINETICS OF BROMINE ADDITION TO SOME UNSATURATED SULFONES BY V. BALIAH AND SP. SHANMUGANATHAN Department of Chemistry, Annamalai University, Annamalainagar, Madras Stale, India Received May 16, 1960
The kinetics of bromine addition to a,@-and @, y-unsaturated sulfones in carbon tetrachloride a t 30" has been studied. It is found to be approximately second order. a,@-Unsaturated sulfones add bromine at a slightly lower rate than 6 , ~ -
unsaturated sulfones. There is no evidence of any significant conjugation between the sulfonyl and ethenyl groups in a&unsaturated sulfones in the ground state. The data obtained can be interpreted on the basis of the inductive effect of the sulfonyl group.
Introduction Sudborough and Gittins,l from a study of rates of esterification of a,p-unsaturated acids, showed that conjugation of a carboxyl group with an ethylenic linkage decreases the reactivity of the carboxyl group. Similarly the effect of conjugation with a carboxyl group on the reactivity of an ethylenic linkage was established by the deter-
mination of the rates of addition of bromine to unsaturated acids; a,&unsaturated acids add bromine a t a much lower rate than Ply- or y,bunsaturated acids.2 Furthermore, the addition of hypochlorous acid to ethylenic double bonds is also much retarded if the double bonds are conjugated with the carboxyl group.a-6
(1) J. (1909).
(3) G. F. Bloomfield, E. H. Farmer and C. G. B. Hoae. dbid., 800 (1933).
J. Sudborough and J. M. Gittina, J . Chem.
Soc., 90, 315
(2) J. J. Sudborough and J. Thomas, {bid., 97, 716, 2450 (1910).
Dec., 1959
KINETICS OF BROMINE ADDITION TO UNSATURATED SULFONES
The present investigation deals with the rates of addition of bromine to some cy,@- and P,y-unsaturated sulfones in carbon tetrachloride solution a t 30". It was thought that a comparison of these rates would reveal whether there is effective conjugation or not between the sulfonyl group and ethylenic double bonds in a,p-unsaturated sulfones.
Experimental Materials.-Methyl vinyl sulfone was prepared according to the method of Buckley, Charlish and Rosee; allyl methyl sulfone was obtained according to the method of Price and Gillis'; the procedure of Smith and Davis8 was employed for the preparation of phenyl vinyl sulfone and p-tolyl vinyl sulfone. Allyl phenyl sulfone and all 1 p tolyl sulfone were pfepared according to the method of dt;B The method of alasubramanian, Baliah and Rangarajanlo was used for the preparation of methyl styryl sulfone; phenyl styryl sulfone and styryl p-tolyl sulfone were obtained following the method of Balasubramanian and Baliah .I1 Cinnamyl phenyl sulfone, cinnamyl p-tolyl sulfone and cinnamyl methyl sulfone were obtained as already reported.l* Purification of Carbon Tetrachloride.-B .D.H. "Analar" carbon tetrachloride was shaken with 5% sodium hydroxide solution, then with 5% hydrochloric acid solution, washed several times with water and dried over fused calcium chloride for a day. It was thendistilled over hosphorus entoxide, the distillation unit being providef with a ca&um chloride guard-tube. Only the middle portion of the distillate was employed. Purification of Bromine.-About 150 ml. of analytical grade bromine was shaken thrice with an equal volume of sulfuric acid, the bromine layer separated and frozen in a bath of ice and calcium chloride. When the bromine had completely solidified, it was taken out of the bath and partly melted. The supernatant liquid was decanted off and the rest of the solid bromine was allowed to melt completely. The liquid was once again frozen and the procedure repeated several times till about 50 g. of bromine freezing at --6 to -7" was obtained. Measurement of Reaction Rate.-The general method of procedure was to prepare carbon tetrachbride solutions of the unsaturated sulfones and of bromine of the same concentration (1/8oth or 1/&h of the gram-molecular weight per liter of the solution, depending upon the solubility of the unsaturated sulfone in carbon tetrachloride). The bromine solution was standardized by means of sodium thiosulfate, potassium iodide and starch in the usual manner. One hundred ml. of each solution was placed in a ground-glass stoppered conical flask. The two soolutions were placed in a thermostat regulated to 30 f 0.1 After the attainment of thermal equilibrium, the bromine solution was run into the solution of the unsaturated gulfone and when about half the bromine solution had been run, a stop-watch was started. The mixture was swirled gently to ensure complete mixing. At suitable intervals, 10 ml. of the mixture was withdrawn and run into a conical flask containing a solution of a slight excess of potassium iodide to arrest the reaction. It then was titrated immediately against M / 3 0 or M/60 sodium thiosulfate solution using starch as indicator. The solutions of sodium thiosulfate, potassium iodide and starch were prepared in water from which carbon dioxide had been expelled. Since the sulfone and bromine are both a t the same concentration, the second-order rate constant k is given by the expression k=-1 X2
.
ta
a--2
(4) E. H.Farmer and C. G. B. Hose, J . Chem. Soc., 962 (1933). (5) G . F. Bloomfield and E. H. Farmer, ibid., 2062, 2072 (1932). ( 6 ) G. D. Buckley, J. L.Charlish and J. D . Rose, ibid., 1514 (1947). (7) C. C.Price and R. 0 . Gillis, J . Am. Chsm. Soc., 76, 4750 (1953). (8) L. I. Smith and H. R. Davis, J . Org. Chem., 16, 824 (1950). (9) R . Otto, Ann., 283,181 (1894). (10) M. Balasubramanian, V. Baliah and T. Rangarajan, J . Chem. SOC.,3296 (1955). (11) M. Balasubramanian and V. Baliah, ibid., 1844 (1954). (12) V. Baliah and Sp. Shanmuganathan, J . Indian Chem. Soc., 36, ai (1968).
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where t is the time in minutes, a is the initial titer value (for zero time) expressed in mole/l. and (a - 2 ) is the titer value after time t . The average deviation in the value of the rate constant between duplicate determinations did not exceed 2%. Trial runs with Rtyryl p-tolyl sulfone and cinnamyl ptolvl sulfone at both M/30 and Ml6O concentrations of bromine and the sulfone indicated the rate constant to be independent of concentration. In the case of other sulfones either M / 3 0 or M/60 solutions only were employed.
Results and Discussion The bimolecular rate constants and the kpJ ka,p ratios are given in Table I. TABLE I RATECONSTANTS FOR
THE
Sulfone
CHsSOzCH=CHz CHaS02CHzCH=CHz CP,H~SOZCH=CHZ CeH~0zCHzCH=CHz p-CHsCeH4SOzCHsCHz p-CHaCeHBOzCHzCH=CHz
BROMINE ADDITION k X lo'-, (mole/l.) sec.-1
'"
27.0
kp,r/ka.D
4.42
6'5 8.3
1.28
6" 8.4
1.24
~H~SO&H=CHC~HK' 14'4 2.08 cHsSOzCHzCH=CHCeH6' 42.9 C~HKS~ZCH=CHC~H~' 3'3 1.63 CeHsSozCHzCH=CHCaHs' 5.4 ~-CH~C~H~SO~CH=CHC~HK' 3'5 1.54 ~ - C H ~ C P , H ~ S O * C H ~ C H = C H ~5~. 4H ~ ~ a trans-Isomer.18
It is seen that bromine adds to a p,r-unsaturated sulfone only a t a slightly faster rate than to an a,p-unsaturated sulfone. This is in marked contrast to what is observed in the case of Ply- and cy,@-unsaturatedacids.2 Thus there is no evidence of any significant conjugation of the sulfonyl group with the ethylenic link in the ground state of +unsaturated sulfones. A similar conclusion was arrived a t by earlier workers.14J6 The slight increase in the value of ks,? over k p , can ~ be attributed to the weaker inductive influence of the sulfonyl group on the ethylenic bond in p,y-unsaturated sulfones due to the intervening methylenic group. It is significant to note that the sulfonyl group retards bromine addition more powerfully than the nitro group14Js in spite of the fact that the nitro group is a more "acidifying" substituent than the sulfonyl group." This remarkable retarding influence of the sulfonyl group toward bromine addition may be explained by the high positive charge that the sulfur atom bears if the sulfur-oxygen bond is formulated as semi-polar. 18 The electrophilic attack will be inhibited by the positive sulfur. The influence of structure on the rate of bromine addition is also interesting to note (Table I). The p-tolyl sulfones have slightly higher rates than the (13) V. Baliah and M. Seshapathirao, unpublished work. (14) I. R. C. McDonald, R. M. Milburn and P. W. Robertson, J . Chem. Soc., 2836 (1950). (15) P. B. D.de la Mare and P. W. Robertson, ibid., 2838 (1950). (16) P. B. D. de la Mare, Ann. Reports, 47, 127 (1950). (17) W. HUckel. "Theoretical Principles of Organia Chemistry," Vol. I, Elsevier, New York, N. Y.,1955,p. 337. (IS) V. Baliah and Sp. Shanmuganathan, THISJOURNAL, 62, 255 (1958).
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EDWARD J. GOON
corresponding phenyl sulfones. The tolyl group is slightly more electron-releasing than the phenyl group. Thus the positive charge on sulfur is slightly less when the sulfonyl group is attached to p-tolyl than when it is attached to phenyl. Therefore the phenylsulfonyl group exerts relatively greater inductive effect on the ethylenic link than p-toluenesulfonyl. Bromine adds to C€13S02CH=CHC6H6 at a significantly faster rate than to CH3S02CH=CH2. Thus the nature of R in CH3S02CH=CHR influences the rate considerably. This effect of R is undoubtedly polar because phenyl group, which increases the electron accessibility on the ethylenic bond, causes an increase in the rate. A careful examination of t.he rates of bromine addition to the various unsaturated sulfones listed in Table I reveals that steric effects also control the bromine addition. The rates of addition to CH3S02CH=CH2, CeH6S02CH=CH2 and p-CH&s-
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H4S02CH=CH2 do not differ much, indicating that the nature of R in RS02CH=CH2 does not have much effect on the rate. The same is not true of R in RS02CH=CHC6H6 because the rate of addition to CHaSo&H=CHCsH6 is strikingly greater than that to C~H6SOzCH==CHCeH6 and p-CH, CeH4S02CH==CHC~H6.This is presumably a steric effect. Scale models of methyl styryl sulfone and phenyl styryl sulfone reveal that the two stages of bromine addition, electrophilic and nucleophilic, involved in the bromide formation are inhibited in phenyl styryl sulfone by the shielding phenyl group. A cyclic intermediate does not seem to be involved in the addition. This is to be inferred from the fact that bromine addition to methyl styryl sulfone, methyl cinnamyl sulfone, phenyl styryl sulfone and p-tolyl styryl sulfone results in the formation of a mixture of erythro and threo isomers of the addition product in each case.13
THE NON-STOICHIOMETRY OF LANTHANUM
H Y D R I D E 1
BY EDWARD J. GOON^ Department of Chemistry, Tufts University, Medford 66, Mass. Received May 86, 1060
An interpretation of the data from a high temperature X-ray diffraction study of lanthanum hydride indicates that the hydride exists as a non-stoichiometric compound a t elevated temperatures. The non-stoichiometry may result from the movement of hydrogen out of the octahedral sites of the fluorite-type hydride lattice without the necessity of forming Schottky defects in the lanthanum lattice of the hydride. The energy which was required to create the hydrogen vacancy was calculated from thermal expansion data and found to be 0.10 e.v.
Introduction To the author's knowledge, X-ray diffraction studies which have been performed on the rare earth hydrides have been conducted at room t e m p e r a t ~ r e . ~ - The ~ dihydrides of lanthanum, cerium, praseodymium and neodymium have the fluorite-type structure with the hydrogens located in the tetrahedral interstices. Neutron diffraction evidence6 indicates that further absorption of hydrogen by the dihydride results in the filling of the octahedral interstices. Absorption of the additional hydrogen is accompanied by a contraction of the cell constant of the hydride without a change of symmetry of the metal atoms. Many metallic hydrides are normally non-stoichiometric, containing a deficiency of hydrogen. The term non-stoichiometric as applied t o lanthanum hydride, denotes a compound whose atomic ratio of hydrogen to lanthanum is between two and three. Since the lattice const,ant of lanthanum hydride, LaH, (2 7 n 7 3), is sensitive to the number (1) This research was supported by the U. 5. Atomic Energy Commission. (2) National Research Corporation, Cambridge, Mass. (3) A. Rosai, Nature, 133, 174 (1934). (4) B. Dreyfus-Alain, Compt. rend., 2S6, 540, 1295 (1952); 2S6, 1265 (1953). ( 5 ) B. Dreyfus-Alain and R. Viallard, ibid., aS7, 806 (1953). (6) F. H. Ellinger, C. E. Holley, Jr., R. N. R. Mulford, W. C. Koehler and W. H. Zachariasen, THIEJOURNAL,69, 1226 (1955). (7) W. L. Korat and J. C. Warf, Dissertation, U. of Southern California, 195G. (8) B. Stalinski, Bull. acad. polon. sci., Classe 111, 3, G13 (1955).
of hydrogen vacancies in the hydride lattice, it was believed that the information which would be obtained from a high temperature investigation, could be correlated with data from other physical chemical measurements to establish the stoichiometry of the hydride at elevated temperatures. Experimental Apparatus.-Diffraction ,patterns of metallic hydrides were obtained by the use of the high temperature assembly,g which was used in conjunction with the Straumanis type G. E. powder camera a t temperatures up to 650' and pressures up to 600 p.s.i. The accuracy of the measurement of Because the specimen temperatures was better than f3'. specimen was contained in a beryllium metal tube, films contained the diffraction pattern of beryllium metal superimposed on that of the specimen. Masking of some of the lanthanum hydride lines by beryllium diffraction bands was not a serious handicap to the method. Usually the composition of a hydride specimen a t elevated temperature is calculated from pressure-volumetemperature data. In the X-ray experiments this was not feasible because of the existence of a temperature gradient along the length of the specimen and the relatively large volume of the apparatus as compared to the small volume of hydrogen available from dissociation of the specimen. Since the temperature of that part of the specimen directly exposed to the X-ray beam and hydrogen pressure over the specimen were known, the composition of the hydride specimen was estimated whenever possible from available P- V- T data. Materials.-The lanthanum metal was of high purity and was furnished by the Ames Laboratory of Iowa State College. To prepare the metal for hydriding, the surface (9) E. J. Goon, J. T.Mason and T. R. P. Gibb, Jr., Rev. Sci. Instr., 28, 342 (1957).
