1318
NOTES
systems a t room temperatures higher than about 25'. In order to obtain relatively high water vapor pressures the entire vacuum system was enclosed. A "room temperature" of 52 f 0.1' was attained. It was noted that after starting a run the pressure would drop about 15% from the original pressure (on opening the stopcock to the evacuated adsorbent chamber at t = 0), quickly become constant, then would increase for several minutes by as much as 1 cm. DBP, and then decrease, continuing to do so in normal fashion. A series of experiments established that whenever a sudden pressure change occurred, a slow and decelerating pressure change followed, suggesting extensive ad- and desorption of water by the glass tubing of the system. Similar effects were noted with methanol and ethanol vapors. The effect was not noticed at room temperatures of 20-25', and consequently several experiments were made with 10.0 g . of ZnO at 100 or 250'. At the end of a run a pressure of 10-6 mm. could be obtained by pumping for 4 hours at 410' and consequently a standard pumping-off period of 8 hours was established between runs. A rapid, voluminous, but quickly decelerating adsorption occurred at 100'. For example, in run 40 a t PO= 9.1 cm. DBP, amounts adsorbed after 1, 10 and 100 minutes were 3, 10 and 25 ml., respectively. The adsorption was diminished in magnitude and rate at 250': in run 14 at PO = 8.0 cm. DBP, amounts adsorbed after 1 , l O and 100 minutes being 1.8, 4.25 and 4.4 ml., respectively. The Elovich equation expressed adsorption rates over major parts of the course of adsorption. The rates and extents of water adsorption by ZnO yere greatly decreased by pre-adsorbed hydrogen. At 100 , in run 38 at Po = 20.3 cm. DBP, for instance, 8, 12.5, 18, 21 and 25 ml. water adsorbed after 1, 2, 4, 6 and 10 minutes, respectively, the process continuing until 35.5 ml. had been adsorbed at 200 minutes. On pre-adsorbing 0.52 ml. H2 (run 21P, a t PO = 28.6 cm. DBP, 100') 5.20, 5.35, 5.44, 5.45 and 5.45 ml. of water were adsorbed after 1 , 2 , 4 , 6 and 10 minutes, respectively. Pre-adsorption of 1.5 ml. Hz in run 24P (Po= 23.7 om. DBP, 100') or 3.2 ml. H2 in run 19P (Po= 21.1 cm. DBP, 100') decreased the amounts adsorbed after 1, 5 and 10 minutes to 3.82, 4.33 and 4.44, and to 3.35, 3.76, and 3.83 ml., respectively. Complete inhibition of hydrogen adsorption occurred of pre-adsorbing water vapor. For example, on adsorbing HZat PO = 46 cm. DBP at 100" on top of 23 ml. adsorbed water, no absorption but a desorption of about 0.05 ml. of gas was noted. An adsorption of about 0.05 ml. HZ occurred on ZnO containing 7.5 ml. of pre-adsorbed water. These inhibitions are similar to those detected by Taylor and Sickman and Burwell and Taylor. Such great inhibitions must obviously be due to effects other than simple geometric surface coverage, and reflect the great sensitivity of the ZnO surface to pre-treatment. Similar great changes in the nature of the surface due to insufficient degassing, or to thorough degassing resuIting in reduction, may be inferred from the CO adsorption experiments.
Vol. 63
urements could be made satisfactorily with contact times less than 6 hours. The resin used was Dowex 5OW-X8, 50-100 mesh, B light yellow bead-t,ype sulfonated polystyrene with 8% nominal crosslinking. It was washed, converted to the hydrogen form and air-dried before use. The exchange capacity was 5.18 meq./g. dry H-resin; the water uptake on swelling, 1.20 g./g. dry H-resin as determined by blotting the wet resin with filter paper, placing in a bottle and weighing, then drying and reweighing.' ( a ) The Ion-exchange Equilibrium.-Measured weights of H-resin were stirred with known volumes of a solution of mercuric perchlorate containing perchloric acid to prevent hydrolysis. Samples of solution were withdrawn at intervals and analyzed. After 1-2 hours the mercuric ion concentration showed no further change. Aft,er 4-5 hours the solution was separated from the resin. The resin was caught on a sintered glass filter, washed with about 20 ml. of water, and its replaceable hydrogen ion content determined by transferring the resin to a beaker! adding water and 2 g. of potassium bromide, then titrating potentiometrically. The potassium ions displace H + and Hg++ from the resin, the bromide ions complex Hg++ and prevent its hydrolysis. The hydrogen ion content of the solution was found by potentiometric titration after adding potassium bromide or chloride. The mercuric ion content was found by titration with "Versene"2 or, if very small, by dithiaone.
The equilibrium quotient of the reaction 2H Res
+ Hg++
Hg Resz
+ 2H+
mas computed as (meq._ Hg++), K = _ - x~g. resin (meq. H+)?
(meq. H+),2 (rneq. Hg++), x ml. soln.
The subscripts r and s refer t,o resin and solution. Grams of resin are on the dry basis; the solution volume was corrected for the water taken into the swollen resin beads, since it was verified that electrolyte was excluded due to the Donnan equilibrium. Data for 0 and 25" are presented in Fig. 1, K being plotted against the equivalent fraction of mercury in the resin. The data a t each temperature are for a constant equivalent concentration in the solution 0.137 N in every case. Since the equivalent fraction of mercury in the solution was never more than 0.27 (the maximum for the 0" series) and was usually very much less, the ionic strength was approximately constant. The hydrolysis of the mercuric ion should be less than 2% since the acid normality a t equilibrium was a t least 0.1.3 The data show that the selectivity of the resin REACTIONS OF MERCURY (11) WITH A for mercury increases with the proportion of metal ions in the resin, which seems to be characteristic CATION-EXCHANGE RESIN of the divalent heavy metal ion-hydrogen ion esB Y H. F. WALTONAND J. M. MARTINEZ changes so far studied in our laboratory. Similar University of Colorado, Boulder, Colorado increases of selectivity with metal ion loading have Received November .??4f1868 been found in certain cases by Bonner and coAs part of a study of the behavior of heavy metal w o r k e r ~ . ~Complete thermodynamic treatment ions in cation exchange, we have investigated the of the data is not possible without knowledge of the reaction of a sulfonated polystyrene exchanger with activity coefficients in solut.ion; on the assumption solutions containing mercuric perchlorate and per- that these do not change with temperature, AH = chloric acid. Two distinct reactions occurred : 1160 cal. for a gram-equivalent of pure H-resin the normal exchange of hydrogen ions and mercuric reacting to form a gram-equivalent of pure Hgions, which was complete in an hour or so under (1) 0.D. Bonner, W. J. Argersinger and A. W. Davidson, J . Am. avera.ge conditions, and a reaction of the mercuric Chem. SOC.,74. 1044 (1952). salt with the hydrocarbon matrix of the resin, which (2) G. Schwarsenbach. "Die Komplexometrische Titrationen." 1956, was slower and continued over several days. At p. 82. (3) S. Hietanen and L. G. SillBn, Acta Chem. Scand., 6 , 747 (1952). GOo this secondary reaction was fast enough to 0.D. Bonner, THISJOURNAL,69,719 (1955): 0. D. Bonner and interfere with the measurement of the ion-exchange F. (4) L. Livingston, ibid., 60, 530 (1956); 0. D. Bonner and L. L. Smith, equilibrium; a t 25' and below, equilibrium meas- ibid., 61, 326 (1957).
3
1319
NOTES
August, 195'3 I
I
I
I
5.0
K, 4.0
Mercuric ions mere released slowly and very incompletely (about 0.2 meq. per gram resin) when the resin was extracted with 2 N sulfuric acid. Aqueous potassium iodide removed more mercury from the resin but, even so, only a fract,ion of t,hs mercury could be extracted. The heavily mercursttetl rcain was of a darker color than the hydrogen resin and took up less water on swelling. A sample, powdered and pressed into n pellet with solid potassium bromide, showed strong infrared absorption a t 8.6 p ; this band was absent in the original hydrogen resin, and wns not found in a spectrum of phenyl mercuric acetate which was run for comparison. The mode of reaction of mercuric ions with the resin is uncertain, but it seems that mercury displaced hydrogen in ionic form from the aromatic rings, perhaps in the manner -CH-CH*-
3.o I
-
I I I I 0.2 0.4 0.6 0.8 EQUIVALENT FRACTION Hg-RESIN ,
Fig. 1.
resin. This was computed using the graphical in tegration method of Chines and Thomas.6 (b) The Secondary Reaction.-When resin was stirred a t 60" with a solution containing enough niercuric ions to be nearly equivalent to the exchangeable hydrogen ions in the resin, the mercuric ion concentration fell continuously for several days, finally dropping below molar. When the resin was separated and titrated with base after addition of potassium bromide as described above, much more replaceable hydrogen ions were found in the resin than could be explained by normal cation exchange. A typical expcriment yielded the following data: H-Resin taken, 1.581 g. (air-dry) = 6.62 meq., solution taken, 50.0 ml., containing 5.87 meq. Hg(C10& and 1.10 meq. HC104. After stirring a t 60" for 110 hours, the solution contained 0.0029 meq. Hg++ and 6.80 meq. H+. The resin contained 3.96 meq. replaceable H+. I n this example 2.96 meq. of acid was formed during the experiment. In other tests resin was stirred with a considerable excess of niercuric perchlorate a t 80-85". After 48 hours the mercury content of the solution was still falling, although the total normality remained unchanged. The resin had absorbed over 15 meq. of mercury per gram (dry basis), or over three times the normal exchange capacity. No replaceable hydrogen ions were found in such resins; on the contrary, a very small amount of strong base was liberated when the resin was removed and stirred with potassium bromide. No sulfate ions were found in the solutions, suggesting that the sulfonic acid groups of the resin remained intact. No soluble mercurous salt was detected, though a very small amount of mercurous bromide was formed when the mercurated resin was stirred with aqueous potassium bromide. (5) G. L. Gaines and H. C . Thomas, J . Cham. Phys., 21. 714 (1953)
-GH-CHr
$Oa-H +
Such a reaction is like the mercuration of toluene by mercuric perchlorate reported by Klapproth and WestheimerO and could explain the uptake of one mercury atom per aromatic ring. Uptake of mercury proceeded beyond this stage wit,hout perchlorate ions entering the resin; this suggests that additional mercury atoms formed bridges between aromatic rings. A reaction of this type was noted by Miles, Stadtman and Kielley' who crosslinked a phenol-formaldehyde polymer by reaction with mercuric acetate. Such bridging would account for the reduced water uptake on swelling and may nccouiit for the infrared band a t 8.6 p . Acknowledgments.-This work was supported by the U. S. Atomic Energy Commission, Contract No. AT(l1-1)-499. Thanks are due to M. G. Suryaraman for assistance. (6) W. J. Klapproth and F. H. Westheimer, J . A m . Cham. Soc., 72, 4461 (1950). (7) H. T.Miles, E. R. Stadtman and W. W. Kielley. ibid., 76, 4051 (1954).
ALCOHOLYSIS OF BORON-BORON BONDS TO FORM HYDRIDES BY I. SHAPIRO* AND H. G. WEISS Research Laboratory, Olin Mathieson Chemical Corporation, Pasadena, California Received November $9,1968
The recently proposed mechanism for the alcoholysis of pentaboranel is surprisingly similar to that proposed for d i b ~ r a n e . ~yet J from structural considerations a more complex mechaiiism related to the breaking of boron-boron bonds in the higher
*
B o x 24231. Los Angeles 24, California. (1) A. F. Zhigaoh, E. B. Kazakova and R. A. Kigel, Dolclady Akad. N a u k SSSR, 106,69 (1956). ( 2 ) A. B. Burg and H. I. Sohlesinger, J . Am. Chem. SOC.,55, 4020 (1933). (3) H. G. Webs and I. Shapiro, $bid., 76, 1221 (1953).
