April 20, 1959
110FOR TRIFLUOROACETIC SOLUTIONS
of 0.005 ml. were used. The @-alcoholhad a longer retention time than the a-isomer. A . (Me:3SiC2H,)sB.-In one run the alcohol mixture resulting from the oxidation of the triorganoborane was distilled, giving an 88% yield of mixed a- and @-Me8Si(CtH& OH, b.p. 02-75' (42 mm.). Anal. Calcd. for CsH140Si: C, 50.78; H, 11.93. Found: C, 50.83; H , 12.06. The results of a number of representative runs are summarized below a-Alcohol, mole l;h
Conditions of hydroboration
NaBHd-AlCla, 20 hr. a t room temp. NaBIII-AlClr, 2 hr. a t room temp., 1 hr. at GOo hTaBH,-AlCls, 3 lir. a t room temp., 8 hr. a t 150' MeaN.BHa,22 hr. a t 70-80"
@-Alcohi>l, mule Yo
37
G3
33
67
37 34
63 66
The similar ratios of a- to 8-trirnethylsilylethanol obtained in these reactions, in which the thermal history of the reactions covers a fairly wide range, makes the possibility that thermal rearrangements occurred in the direction MsSiCHMe-B + Me&3iCH2CHZ-B, similar to those reported by Hennion, et al.," and by Brown and RaoI8, seem urd ikely . B. 1 :1.6 Hydroboration Reaction Products.-Oxidation of the products of the 1: 1.6 hydroboration reaction described above are summarized below. The (Me3SiC2H4)zBOC2Haobtained, 12.8 g. (0.0495 mole), w3s oxidized in the usual manner using l.G g. NaOH in 50 (17) G . F. Hennion, P. A , McCusker, E. C . Ashby and A. J. Rutkowski, IS JOURNAL, 79, 5190 (1957). (18) H. C. Brown and B. C. Siibha Rao, J. Org. C h ~ , n . ,22, 1130 (19ni).
OF SULFURIC A N D
HYDROFLUORIC ACIDS
1847
ml. of cthanol and 14 g. of 3oY0 hydrogen peroxide to give 10 g. of mixed alcohols. Gas chromatographic analysis showed the mixture to consist of 70.470 a-trimethylsilylethanol and 29.7% &trimethylsilylethanol. The (MeaSiCzH,jsB, 8.8 g. (0.028 mole), was oxidized using 1.5 g. of NaOH in 50 ml. of ethanol and 13 g. of 30% H2O2 to give 8.1 g. of a mixture containing 42.870 of the a-alcohol and 57.1% of the @-alcohol. Similarly, the [(MQS~CZH~)ZB]ZO, 6.3 g. (0.014 mole), was oxidized in solution with 1.0 g. of NaOH in 35 ml. of ethanol by 8 g. of 30% H Z O ~yielding , 5 g. of mixed alcohols (40.5% a-alcohol and 59.4Y0 @-alcohol). Thus the boron compounds obtained in this experiment contained a total of 0.128 mole of MeaSiCHMe- groups and 0.112 mole of Me&CH*CHrgroups, giving an over-all distribution of 53.4% a-trimethylsilylethyl groups and 46.670 of the 8-isomer. Hydroboration of Trimethylvinyltin.-Atternpted hydroboration of trimethylvinyltin with the NaBHrAlCla reagent gave a product having a characteristic organoboranelike odor that caused ignition when poured on cloth or paper. Attempted distillation resulted in decomposition. Oxidation of the crude trimethylvinyltin hydroboration product by the usual procedure also resulted in decomposition and no organotin-alcohol could be isolated.
Acknowledgments.-This work was supported in part by the United States Office of Naval Research and may be reproduced in whole or in part for any purpose of the United States Government. The author is indebted to Professor J. S. Waugh and Dr. S. Castellano for determination and interpretation of the NMR spectra, and to Mr. Harold Ward for carrying out gas chromatographic analyses. CAMBRIDGE 39, MASS
[CONTRIBUTION FROM ARGONNENATIONAL LABORATORY]
The Hammett Acidity Function Ho for Trifluoroacetic Acid Solutions of Sulfuric and Hydrofluoric Acids BY HERBERT€1. HYMAN A N D RONALD A. GARBER RECEIVED OCTOBER 17, 1958 The Ho values of mixtures of HSOI and trifluoroacetic acid, as well as HF and trifluoroacctic acid, have been measured over the entire range of compositions. The values found are related t o those found for aqueous systems, displaced as expected due to the higher acid strength of trifluoroacetic acid.
Introduction Some interest has been shown in this and other laboratories in non-aqueous highly acid media. Trifluoroacetic acid has rather good solvent properties for many organic molecules, is readily available as a rather pure anhydrous chemical and is completely miscible in all proportions with some stronger acids such as H2S04,HCIOl and HF. The Hammett acidity function has been correlated with other phenomena of interest involving proton mobility.2 The HzSO4-trifluoroacetic acid system has been used to investigate the effect of increasing acidity on the hexamethylbenzene spectrum, and values were given for a Hammett function Ho calculated using hexamethylbenzene as the indicator.s This hydrocarbon is a different type of proton acceptor than is usually used as a Hammett
indicator and as would be true of any indicator, is useful only in a narrow acidity range. This paper gives the acidity of the entire trifluoroacetic acid, sulfuric acid system obtained by using the conventional Hammett indicators. Since systems exist in which the sulfonating behavior of sulfuric acid systems is undesirable, the HF-trifluoroacetic acid system was also investigated. Mixtures containing high concentrations of perchloric acid are too oxidizing to be useful as simple acidic solvents and were not investigated. The data of Dallinga and Kok discussed by were not known to us a t the Mackor, et time this program was initiated. Over the range of concentrations reported, the results are in good agreement. Experimental
(1) Based o n work performed under the auspices of the U. S. Atomic Energy Commission. (2) L. P. I-Iammett, Chcm. Reus., 16, 67 (1935); "Physical Organic Chemistry," McGraw-Hill Rook C o . , New York, N. Y . , 1940. (3) hl. Kilpatrick and H. H. Hymau, T H I S JOUHNAL, 80, 77 (1958).
Materials.-The iiidicators used were Aldrich Chemical Company products sold for use as Hammett indicators. They were used as received. Trifluoroacetic acid is now (4) E. L, hiackor, P. J. Smit and J. H. van der Waals, Trans. Faraday Soc., 63, 1309 (1957).
_. 1 ~
1
Zfu 1 ~ \ - ~2 i r 1, w \~
~
TABLE I SULI:URIC .le111 SOLLTIOSS IN
FOR
?rI< IFL U O R O ACE 1'I C .IC I D ir,so,,
- [lo
.ii
I!idicntd'
1
s;
3.03 5.90 5.72 n .0 1 7.33 8.07
0
nln
11
117.5
I!, .31 .';
:4
S . Sii
;.
I;:
9 2,;
!)
;;,-I
1k
!Ili
< I , ;j3 0 (i1
11;
5::
n s5
I> 711
11.1 0
a
I1
I1 I1
b c c'
t
C
c
e 2 , ~ - l ~ i ~ l i l ~ i r c i - l j - i i i : ~ ~ : i i ! i ! /i)i?i i ~ ~ ,= --3.32; (IJ i t r ~ ~ ~ i i i l i n/>I< c , = -4.5:;; (c I ij-l~riiii~o-L',.l-ditiitro, i i i i l i i i e , pi? = -1i.71; ((1) ~ i i i l l i r . I q ~ i i i i ( i i i epK , = -S.27; ( e l t r i i i i t r w i i i ! i i i e , ,hi< = -9.41.
tlic iiiiddle raiige of suliuric acid conccntrutiori, rju;ilitati\-c changes a r e t:ikirig place :~ndthe acidit>-rises slowly iiutil cii:e is well into the region n.Iic1-c tlic suliiiric :tcitl is the major component. ,. I lie cfl(3c.t of :itlcliiig trifluoroncetic acid at this ;) r JIX , I i - t i t bii:it
