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 A k a d . 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).
NOTES
1320
boron hydrides would be anticipated. In diborane4 the two borons are connected by a pair of hydrogen bridges; thus the molecule can be regarded as composed of only BH, units, hence no B-B bonds. Such BHs units are capable of reacting with water3 or alcohols2 to yield one molecule of hydrogen per hydridic hydrogen as shown in equation 1 BzHa
+ 6ROH +2B(OR)3 + GHz
(1)
In higher boron hydrides the molecules contain B-B bonds in addition to B-H bonds. For example, in the structure of tetraborniies (Fig. 1) two
Fig. 1.-Graphic
representation of molecular structure of tetraborane.
borons form a direct B-B bond while the other two borons are joined to this B-B unit through hydrogen bridges. Terminal hydrogens are attached to each boron as shown. The net effect is that two of the boroiis resemble BHs units (dotted circles, Fig. 1). In general, as the number of borons in the boron hydride increases, the greater the number of B-B bonds present. The question now arises as to what happens when water or alcohol attacks these higher molecular weight boron hydrides. From studies on hydrolysis6 and alcoh01ysis~J~~ the ultimate products are found to be the same as those obtained from dibornne; but somewhere in the process more molecular hydrogen forms than corresponds to the number of hydridic hydrogens present in the boron hydride, as shown in the equations B4Hio B:,Hs BioH14
+ 12ROH +4B(OR)s + llHz + 30ROH -+- 10B(OR)3+ 22H2
+ 15ROH + 5B(OR)s + 12Hz
(2) (3) (4)
The number of moles of hydrogen in excess of the number of hydrogens in the boron hydride represent the number of €3-B bonds that must be broken, and, as shown by the above equations, two ROH molecules ultimately are required for each of these B-B bonds. Thus, although the terminal R-H bonds are expected to react similarly to those in diborane, the presence of B-B bonds clearly introduces a new element. Experiments using isotopically labeled reagents reveal that alcoholic protons are converted into hydridic hydrogens when B-B bonds are rupt,ured. Experimental Reagents.-Diborane and deuteriodiborane were prepared9 by the reaction of boron trifluoride with lithium 1.
(4) R. P.Bell and H. C. Longuet-Higgins, Proc. Roy. Sac. (London) 11188, 357 (1945).
(5) C. E. Nordman and W. N. Lipscomb, J . Am. Chern. Soc., 76, 4116 (1953). (6) I. Shapizo and H. G. Weiss, ibid., 76, 6020 (1954). (7) H. C.Beachell and T. R. Meeker, ibzd., 78,1796 (1958). (8) 3H. C.Beachell and W. C. Schar, ibail., SO,,2943 (1958). (9) I. Shapiro, H.G. Weias, M. Schmich, S. Skolnik and G. 8.L. klmith, ibid., 74,901 (1952).
Vol. 63
aluminum hydride or lithium aluminum deuteride (obtained from Metal Hydrides, Inc., Beverly, Mass.). Tetraborane and pentaborane were fractionated from the pyrolysis products of diborane, and identified by infrared and mass spectral analysis. Ethanol was purified by refluxing over and distilling from anhydrous calcium oxide. Deuterated ethanol (CzHbOD) was obtzined from Merck and Co., Limited, Montreal, Canada. 2. Apparatus.-Standard high vacuum apparatus was used for prepamringand handling the boron hydrides. Infrared spectra were obtained with a Perkin-Elmer Model 21 spectrophotomet.er equipped with sodium chloride optics. The standard 5-cm. gas cell was modified to include a mercury manometer and a side arm closed by a (self-sealing) silicone plug through which the reagents could be injected int,o the cell. 3. Procedure.-All experiments were carried out a t room temperature. The appropriate isotopic species of diborane, tetraborane or pentaborane was introduced into the infrared gas cell at a measured pressure, and its spectrum was taken. Then the isotopically labeled ethanol was injected in incremental amounts through the self-sealing silicone plug by means of a 20-gage double-ended hypodermic needle whose other end was attached to the ethanol reservoir. The reservoirs also were equipped with silicone plugs and were manipulated in such a manner that only the content. of the internal volume of the needle was injected a t any one time. Although the reservoir, and consequently the needle, contained the reactant as a liquid, the reactant vaporized readily as it entered the cell due to the low pressure therein. An infrared spectrum was obtained immediately after each injection and again after standing for one-half hour. Negligible changes in spectra occurred on standing. The volume of the hypodermic needle was sufficiently small so that each increment of reagent consumed only a small portion of the boron hydride.
Results The incremental addition of either isotopically normal or deuterated ethanol to isot,opically normal diborane resulted in the progressive formation of diethoxyborane, HB(OC2Ha)2,which subsequently reacted with addit,ional ethanol to form triethoxyborane. Substantially all of the diborane was converted to diethoxyborane before any triethoxyborane was detected. When deuterated diborane was treated with ethanol, the only intermediate detected was DB(OCzH&. The various isotopic species of the ethoxyboranes were easily identified from their infrared spectra; the complete vibrational assignments of these compounds are being reported separately.l0 When ethanol was added to excess tetraborane or pentaborune, HB(OC2H5)2 was found as a product; however, when C2HBODwas added to these higher boron hydrides, both HB(OC2H& and DB(OCzH& were found. In the case of tetraborane the concentration of the protonated intermediate was approximately twice as great as that of the deuterated intermediate; with pentaborane the relative amounts of the two intermediate species were nearly the same. The respective ratios of the two species were maintained for each incremental addition of the ethanol-d. Additionally, an appreciable amount of triethoxyborane was observed even though the amount of ethanol added was comparatively small with respect to the boron hydride. Discussion The foymation of DB(OC2H& from C2HbOD and tetraborane or pentaborme, and the absence of this compound in the case of diborane, show that (10) W. J. Lehmann, H. G. Weiss and I, Shapiro, J. Chsm. Phys., in pr’esa.
August, 1959
NOTES
a deuteride is created from the alcoholic deuterium during the breaking of the boron-boron bond. The ethoxy group apparently attaches itself to one boron atom and the deuterium goes to the other boron atom, vix.
DISSOCIATION CONSTANT O F XANTHIC ACID AS DETERMINED BY SPECTROPHOTOMETRIC METHOD BY I. IWASAKI A N D S. R. B. COOKE
>B-B
B-OCzHS + DB
