R. MATHUR, E. D. BECKER, R. B. BRADLEY, ASD N. C. LI
2190
8B. If the spin lattice relaxation time of the proton interacting with the unpaired electron is Tp, the probability for the relaxation process with the relaxation time TZ, is =
T,
(1 -
&)
r =
-Tz1+ - 1
T21
Vol. 67
=1+-
Tp - 1
1 TP TP The value of r estimated from Fig. 7B and 7C is approximately 4; therefore Tz = 3Tp 1in this case. Acknowledgment.-The author wishes to thank Prof. W. Gordy for his interest in this work, and also wishes to thank Dr. D. J. Ward, who read this manuscript. I
+
where T z is the spin lattice relaxation time. Therefore, the ratio, T , of intensities of the stronger and the weaker lines is
PROTON MAGNETIC RESOSANCE STUDIES OF HYDROGEN BONDING OF BEXZENETHIOL KITH SEVERAL HYDROGEN ACCEPTORS BY R ~ ~J I A T H IEDKIN R , ~ ~D. BECKER, ROBERT B. BRADLEY, AKD XORMAK C. L I ’ ~ Satzonal Institute o j Arthritis and Metabolic Diseases, Xational Institutes of Health, Bethesda, Xarylancl Received April 8, 196s Proton magnetic resonance studies are reported of hydrogen bonding between the S-H proton of benzenethiol and the hydrogen acceptors dimethylformamide, pyridine, x-methylpyrazok, tributyl phosphate, and benzene, all in C c 4 solution. Data on the variation of the chemical shift of the S-H proton as a function of the concentration of hydrogen acceptor are treated graphically in a manner which permits the determination of both the hydrogen bond shift, A,, and the equilibrium constant for formation of a 1:1 complex, K. The enthalpy change on hydrogen bond formation was determined from the variation of K with temperature. For the benzenethiol-dimethylformamide system, for which the most complete results were obtained, A, appears to be independent of temperature over the range - 12 to 68’.
While much work has been done on thermodynamic studies of hydrogen bonding of phenol with a variety of hydrogen acceptors,?-’ relatively little has been published on similar studies involving the sulfur analog, benzenethiol. Copley, et CZZ.,~ showed by heats of mixing t’hat beiizenethiol interacts with several proton acceptors, and Josieii, et al.,9 demonstrated similar interactions by changes in infrared spectra. Except for studies by Spurr and Byers’O on the dimerization equilibrium, apparently no results have been published giving equilibrium constants or enthalpies for benzenethiol interacting with various hydrogen acceptors. This paper presents the results of thermodynamic studies, using the proton magnetic resonance (p.m.r.) method, on hydrogen bonding involving benzenethiol. For t’he hydrogen acceptors, we have chosen 11,S-dimethylformamide, t’ributyl phosphate, pyridine, K-methylpyrazole, and benzene to serve as models for hydrogen bonding of -SH to the carbonyl oxygen, phosphoryl oxygen, organic nitrogen bases, and an aromatic n-electron system, respectively. (A (1) (a) Research assistant on a U. S. Atomic Energy Commission contract, S o . AT (30-1)-1922, and on a National Science Foundation grant, No. G21532, both w-ith Duquesne University; guest worker, National Institutes of IYealth; (b) Visiting Scientist: Duquesne University, Pittsburgh 19, Pennsylvania. (2) G. C. Pimentel and A. L. McClellan, “The Hydrogen Bond,” W.H. Freeman and Co., San Francisco, Calif., 1960. (3) R. West, D. L. Powell, L. S. Whatley, M. K. T. Lee, and P. von R. Schleyer, J . Am. Chem. Soc., 84, 3221 (1962). ( 3 ) M.D. Joesten and R. S.Drago, ibid., 84, 2696 (1962). ( 5 ) A. K. Chandra and 8 . Banerjee, J . P h y s . Chem., 66, 952 (1962). (6) H. Baba a n d S. Suzuki, J . Chem. Phys., 85, 1118 (1961). (7) M. D. Joesten and R. S. Drago, Abstracts, 142nd Xational Meeting of the American Chemical Society, Atlantic City, N. J., September, 1962, p. 6T. (8) RI. J. Copley, C. 8. Marvel, and E. Ginsberg, J . Am. Chem. Soe., 61, 3161 (1939). (9) A I . L. Josien, P. Iliaabo, and P.Sanmagne, RdZ. d o c . c h i m . Pranrp, 428 (1957). (10) R . A . *purr and H. I”. Hyers, .I. f’1ru.s. Chem., 62, ~123(19.58).
few measurements were also made with diphenylether, but there was virtually no shift in the SH frequency.) Experimental Materials.-A pure sample of ?j-methglpyrazole was kindly given by Dr. Hans Reimlinger of the Vnion Carbide-European Research Associates. Benzenethiol (BT), tributyl phosphate (TBP), and dimethylformamide ( D M F ) were Eastman Organic chemicals. BT was distilled in an atmosphere of nitrogen just before use. TBP was washed with 1 M HC1, then with 1 M NaOH, and finally with distilled water until the organic layer was clear and the washings neutral. The washed product was distilled under reduced pressure. Distilled pyridine and benzene were kept over Linde Molecular Sieve. DMF and carbon tetrachloride were dried over phosphorus pentoxide in an evacuated desiccator. Preparation of Samples.-Samples were prepared and transferred to 5-mm. precision n.m.r. tubes in an atmosphere of nitrogen and were kept in the dark. Solutions were made up at room temperature by weighing the requisite amount of the hydrogen acceptor in 10-ml. volumetric flasks, adding 1 ml. of a freshly prepared BT stock solution (about 0.5 J!f in CCL), 1.66 ml. of a CCll solution which contained 30 p.p.m. HC1,11 and enough CC14 (containing about 1% tetramethylsilane) to reach the 10-ml. mark. The n.m.r. tubes containing the solutions were immersed in liquid nitrogen, evacuated, and sealed. The molarity of the solutions, a t temperatures other than room temperature, was calculated from the change in density with temperature of carbon tetrachloride. P.m.r. Measurements.-P.m.r. spectra at 26 i 1” were obtained with a Varian Associates Model A-60 n.m.r. spectrometer, together with a 12-in. magnet system and super stabilizer. -4 sweep width scale of 50 c.p.s. was used. For other temperatures, a S’arian HR-60 n.m.r. spectrometer was used, in conjunction with a V-4340 variable temperature probe. Temperatures (11) HCl was added to bring about rapid proton exchange and to ensure a sharp S H peak. Preliminary experiments indicated t h a t the presence of this quantity of HCI ( 5 p.p.m. in the final solution) did not alter the SH frequency; e.g., three solutions each 0.05 Jf in B T and 0.56 A! in D M F , and containing 1, 5 , and 10 p.p.m. of HCI had SH frequencies of 209.11, 209.13 209.03 c.P.s., respectively. The latter two lines were sharp: the former was not. (The amount of water introduced b y addition of HCI (aq.) wab only 5 X 10-374 and is considered negligible.)
of the samples were determined to h0.2" with a copper-constantan thermocouple immediately prior to the p.m.r. measurements. During the running of the spectra the temperature remained constant to within rtO.2", as indicated by an auxiliary thermocouple placed in the inlet nitrogen stream. Chemical shifts of the -SH signal in benzenethiol were measured with respect to tetramethylsilane used as an internal standard and are quoted as c.p.s. All lines are downfield from TMS. A side band of the tetramethylsilane was placed before and after the -SH resonance peak at a separation of 10-15 c.p.s. The sideband frequencies were measured by means of audio oscillators and a frequency counter. For each solution six spectra were recorded and then averaged. (To compensate for possible field drift in the HR-60, three were upfield and three downfield scans.) The reported shifts are accurate to a t least 0.1 C.P.S. for the A-6 experiments and 0.2 C.P.S. for the HR-60 runs. Becker12 has shown that in the presence of high concentrations of aromatics the frequency of an internal reference compound is very markedly altered. For this reason, when benzene or pyridine is used as the hydrogen acceptor to benzenethiol, correction for the frequency shift of tetramethylsilane must be applied t o the observed frequency of -SH. The internal reference shifts were determined with respect to cyclohexane in a sealed capillary placed in the n.m.r. tube. In order to measure the chemical shift of tetramethylsilane relative to the external reference, a side band of cyclohexane was placed before and after the tetramethylsilane signal, in the manner described for the determination of the -8H frequency, V S H . This observed shift, YTMS (obsd. 1, must be corrected for change in magnetic susceptibility of the solution by meana of the standard relationx3 YTMS
' 1
HYDROGEN BOKDIXG OP' BENZENETHIOL
Oct., 1963
(COT.)-.
YTMS
(obsd.)
25 20
2191
N
-I$
0
X
or
I
I
1
I 4
I
2
0
l/d . Fig. I .-Benzenethiol-dimethylformamide. See text for definitions of symbols; temperatures as follows: 0 , -12"; 0 , 8"; 0 , 2 6 " ; 0,48"; 8 , 68".
Q = 2n/3 X
(KO- K ) X 60 X 1C6
(1) 30
where Y is frequency in c.P.s., R is the volume magnetic susceptibility in c.g.s. unit, and the subscript 0 refers to a solution in which the concentration of benzene or pyridine is zero. In order to obtain the values of K , we have assumed an additivity The values of K law for the volume magnetic sus~eptibilities.~~
TABLE I CORRECTIONS FOR FREQUESCY SHIFTS IN THE PRESENCE OF BEKZENE OR PYRIDISE Conen. of benzene, ;M
0.000 ,931 1,364 1.775 2.325
N
0
X
-I$-
2o
10
0 0
-K
x
108,
c.g.s.
Q,
O.P.8.
0,692 0 ,685 -0.9 ,683 -1.1 ,680 -1.5 .677 - 1.9
nT?dS,a
VTMS.
obsd.
cor.
70.6 74.1 75.8 77.2 79.0
70.6 73.2 74.7 75.7 77.1
2
1
3
4
I
70.6
obsd.
195.0 192.2 191.1 189.9 188.9
195.0 189.6 187.0 184.8 182.4
70.6 0 195.0 70.9 0 . 3 198.6 71.1 . 5 199.4 71.3 .7 201.1 72.4 1.8 205.3 as external ref., 26'.
195.0 198.3 198.9 200.4 203.5 ,7 This
0
2.6 4.1 5.1 6.5
6
cor.
Fig. 2:-
Benzenethiol-pyridine.
Coded As in Fig. 1; in addition, 0 , -20".
I
I
I
1
'
I
Concn. of pyridine,
-
M
0.000 .692 0 70.6 .224 .691 -0.2 71.1 .266 .690 - .2 71.3 .376 .689 - . 3 71.6 ,637 .688 - . 5 72.9 a This value us. cyclohexane value us. TMS internal ref., 26".
( X lo6) for beinzene, carbon tetrachloride, benzenethiol, and pyridine are taken to be -0.617,14 -0.692,15 -0.693,16 and - 0.61 1,I7 respectively. The frequency shifts of tetramethylsilane, corrected for change in magnetic susceptibility of solution in the manner described above, were determined at room temperature only and are as(12) E. D. Becker, J . Phys. Chem., 63, 1379 (1959). (13) J. A. Pople, W. G. Schneider, and H. J. Bernstein, "High Resolution Nuclear Magnetic Resoanance," McGraw-Hill Book Co., Inc., New York, N. Y . , 1959. (14) V. C. G. Trew, Trans. Faraday Soc., 49, 604 (1953). (15) C. M. French and V. C. G. Trew, ibid., 41, 439 (1945). (16) A. Fava and A. Iliceto, Ric. Sci., 24, 1652 (1954); Chem. Abstr., 49, 6673 (1955). (17) B. K. Singli, 0. h'. P'erti, AI. Singh, and S. L. Aggarwal, Proc. I n d i a n Acad. S c i . , 29A, 309 (1948); Chem. Ahstr., 43, 8768 (1949).
, 0
2
4
6
I
4
Fig. 3.-Benzenethiol-tributyl
phosphate; coded as in Fig. 1.
sumed to be the same for other temperatures.xs These values are subtracted from the observed frequency of -SH in the presence of benzene or pyridine, in the manner shown in Table I.
Calculation of Equilibrium Constants Let the equilibrium be represented by
BT
+ D = BT - D
(2)
(18) Some support: for this assumption was obtained from a measurement of the frequency of T b I S with respect to external cyclohexane for a solution ' 8 The valixes obtained, 0.05 .M in B T and 0.93 .M in benzene a t 26 and . 74.1 and 74.0 c.P.s., agree w i t h i n probable error.
R.~ I A T H CE.RD. , BECKER, R. B. BRADLEY, AXD K.C. LI
2102
___-_
680
Vol. 67
TABLE I1 Benzenethiol-dimethylformamide
----
,--26°-~
-----480---
-'8-7
120----
,----
d
Yobad
d
hbsd
d
%bad
d
vabsd
d
Yobsd
0.152 .176 .244 .433 ,584 .780 .953
196.9 197.5 198.5 202.1 204.5 207.8 211.1
0,156 .180 .250 ,444 .598 .799 .977
197 8 198.7 200.1 204.3 207.3 211.2 214.4
...
0.167 .194 .268 .477 .643 .859 1.05
203.6 204.8 207.6 214.9 220.8 226.8 231.0
...
...
200.9 202.2 204.1 210.4 215.2 220.2 224.4
217.7
1.4SO
220.1
199.6 201.2 202.3 207.5 211.3 215.8 219.6 223.4 228.8
0.163 .189 .262 .466 ,628 ,839 1.030
1.446
0.160 ,186 .257 .446 .615 .822 1.004 1.208 1.523
1.551
233.1
1.59
242. .5
~
...
...
...
Benzenethiol-pyridine 26'
-
d
vobsd
POOP
d
0.224 .266 ,376 .637 .864
198.6 199.4 201.1 206.3
198 3 198.9 200.3 203.6
0.229 ,271 ,382 .649 .877
...
...
-----
-26
%bsd
200.0 200.0 202.3 206.0 209.4
- 200----.
,
-120-d
vobsd
0.235 .278 .392 .667 .909
202.5 203.6
YDOI
200.4 201.0 203.2 207.7 211.7
--
-o-
,
80-----
I
d
Yoor
202.1 203.1
...
212.6 217.1
--
...
0.237
Yobsd
%or
203.4
203.0 207.2
...
...
...
.397
208.1
210.8 214.8
..*
...
.917
220.2
218.0
...
...
Benzenethiol-benzene 7---8°-
d
Uobsd
Yoor
d
vobsd
VOW
0.454 ,931 1.364 1.775 2.325
193.4 192.3 191.1 189.9 188.9
191.6 189.6 187.0 184.9 182.4
0.464 .951 1.393 1.812 2.374
193.8 192.3 191.0 189.9 188.3
192.1 189.3 186.9 184.8 181.8
-
.-----120----1 d
0.474 .973 1.425 1.855 2.429
vobsd
voor
194.4 192.4 190.8 189.3 187.8
192.6 189.7 186.7 184.3 181.3
Benzenethiol-S-methylpyrazole ---260--
480----
d
0.310 .660 ,967 1,378 -__. -263--
d
0.117 .I50 .227 .336 .383 .463
Y'bEtl
190,s
201.7 205.1 209.4 210.1) 214.2
d
bb,d
197.6 201.0 203.7 206.8
vobsd
0.319 ,678 .994 1.416
199.1 203.3 206.7 210.7 -.----.-120-
~
d
uobsd
0.328 ,693
200.6 205.9
... 1,446
--_
Uenzenethiol-tributylphosphate -----go---
8'
7
Benzenethiol (no base) T,"C.
d
%bad
d
Uobsd
0.119 ,153 ,231 ,343 .391 ,473
201 8 203.4 207. ti 212.ti 214.9 216.5
0.122 .l57 ,237 ,352 .400 .484
204.4 306.3 211.5 217.6 220.2 223.3
Here benzenethiol, BT, forms an adduct with D, the hydrogen acceptor or electron donor. KO consideration is given to the hydrogen-bonded form in which two BT molecules are associated with one D molecule, because in our experiments the concentration of D is always greater than that of BT. The equilibrium constant K is expressed by the equation (3)
where b is total concentration of BT in moles/l., kept constant at about 0.05 114, f is the equilibrium concentration of free or uncomplexed BT, and d is the total concentration of the electron donor, 0.1 to 2 M. Since hydrogen-bonding equilibria usually involve very rapid reactions, we may assume the observed frequency of SH in BT to be the weighted average of the characteristic frequencies of the free and complexed BT (respectively, vi and vc j . Thus
where A,
= vo
214.7
Yf
-20 - 12 8 26 48 68
196.8 196.4 195.4 195.0 194.3 193.6
- vf. By introducing eq. 3, eq. 5 becomes
v - vi =
Kf(d- 6
+ f)A&
When d >> b [or less stringently, when d >> ( b - f)], the following equation may be derived, by rearranging eq. 6 and reintroducing eq. 3 - -1- - - 1 1 v - vi K A, d
+ -A,1
(7)
From eq. 7, a plot of l/(v - vf) vs. l/d yields a straight line, from which the values of Ac (= v, - vf) and K can be determined separately. The value of vf is the measured frequency of SH in B T in the absence of any hydrogen acceptor. (The extremely small amount of self-association of BT is discussed later.)
Results Figures 1-5 are plots of l l ( v - vf) us. l j d for BT bonding to DMF, pyridine, N-methylpyrazole, TUP, and benzene, respectively, at different temperatures. The experimental frequency &ta are given in Table
HYDROGEN BONDISG OF BENZENETHIOL
Oct., 1963
I
11. Initial plots of the datg for the system BT-DAIF, the one studied most extensively, showed no systematic variation of the intercept, henoe of A,, with teniperature. (The random variation, an average deviation from the mean of about 5 c.P.s., is discussed below.) To determine Ac more accurately for the five systems investigated, the data a t 26" were fitted to a straight line by a least squares calculation; these are the lines for 26" shown in the figures. The lines given for other temperatures were obtained visually, maintaining the same intercept as a t 26". The values of & and K , obtained from the intercepts and slopes of these lines, are summarized in Table 11. (See Discussion below for limits on the accuracy of these quantities.) Figure f? gives plots of log R us. 1/T for BT hydrogen bonded to the hydrogen acceptors. The enthalpies of hydrogen bond formation are obtained from the slopes of these lines and are included in Table 111. 'rHERhlODYNAAllC
Pyridine N-Methylpyrazole
TBP
I
I
'
- 2 G - '
'
'
'
5
0
I
>d
'
Fig. 4.-Benzenethial-benzene;
coded as in Fig. 1.
I
I
I
I
t 25t
4I
P
/
30
i I
TABLE 111 DATAFOR BT HYDROGEN BONDING TO HYDROGEN ACCEPTORS
Hydrogep acGeptor
DMF Benzene
2 193
,-------&,---'C.p.s. P.p.m.
70 90 110 130 -150
1.2 1.5 1.8 2.2 -2.5
KZSO, l./mole
0.22 .I4 .43 .24 .039
-AH, kcal./mole
2.4 2.1 2.0 1.8 0.5
Discussion Comparison with Phenol.-The values of -AH and K given in Table I1 are much smaller than those for the same hydrogen acceptors interactilia with phenol. For example, typica,l values for -AH and K, respectively, are 6.1 kcal./mole and 64 I./mole for phenolDMF4; 6 kcal./mole and 77 I./mole for phenolpyridine6; and 0.37 l./mole (K200, only, available) for phenol-benzene.2 Since solvents and conditions differ, these data should not be compared quantitatively, but they suffice to show the weakness of the BT H-bonding interaction relative Lo its oxygen analog. The smaller H-bonding shift observed in the infrared in the S-H stretching frequency,g compared with that of 0-H in phenol, is in accord with this result. Treatment of Data.-The method devised here (eq. 7)19 for determination of K and A, is, of course, generally applicable to systems where only 1:l coinplexes are formed and where d >> ( b - f). I n the present work the principal limitation in the accurate determination of these quantities arises from the small value of the ordinate intercept, l/&. Thus, the values quoted for K and Ac must be regarded as possibly subject to considerable error, especially in the systems where corrections were made for aromatic shifts.21 The values of AH, on the other hand, are considered to be much more reliable, since a change in the intercept would not appreciably affect the determination of AH. The variance of the points in Fig. 6 indicates (19) I t is intereciting t o note that this equation is identical in form with that derived b y Eaba and Suzuki2o for treatment of ultraviolet spectral (lata, except for replacement of ultraviakt extinction coefficients by p.m.r. frequency shlfts. It also has some simikrities t o the method employed by S p u n and Byers.10 (20) H. Baba a n d S. Suzulci, J . Chem. Phus., 36, 1118 (1961). (21) If rorrections are not made for sluft of the internal reference in the pyridine a n d benzene systems, the data are more scattered, and the intercepts appear to be near zero, iinplying a A. qf the order of 2000 c.P.s., which we regard as unreasonable.
I I
I
I
I
1
2
3
4
5
lid.
Fig. 5.-Benzenethiol-h'-methylpyrazole;
I
I
I
I
I
I
68
48
2826
8
II
I
coded as in Fig. 1.
I
I
-12
-20
0.7
0.5
Y
0.2
0.I
I
T(OC.).
Fig. 6.-Plot of log K us. 1/T, for benzenethiol interacting with the following hydrogen acceptors: 0 , diniethylformamide; 0, pyridine; a,tributyl phosphate; 0 , benzene; 0 , N-methylpyrazole. Ordinates for benzene curve have been multiplied by 10. Points for dimethylformamide and pyridine at 8 " coincide.
that the uncertainty in the value of AH for BT-DhIF is about 0.05 kcal./mole, while that for the other systems is about 0.2 kcal./mole, since less extensive data have
ROBERT L. SCRUGGS, TAIKIM,AKD NORMAKC. LI
2194
been obtained for these systems. The value of AH for the BT-benzene system is subject to the largest uncertainty, since the values of K are small and the susceptibility corrections are relatively large. It is apparent from eq. 7 that the lines caii be extrapolated to an intercept with the abscissa at l / d * (d* < 0) and that K = -l/d*. We found that this treatment offered no advantage because of the steep slopes occasioned by the small values of K: in other systems with somewhat larger values of K , this extrapolation might prove superior. Self-Association and dvf/dT.-uf, the SH frequency in the absence of hydrogen acceptors, was found to be slightly temperature dependent, with an average dvfldT = 0.03 c.p.s./degree over the range -12 to 68”. We believe that this small variation is due to changes with temperature in the extent of self-association of BT. From the equilibrium constant for dimer formation a t room temperature10 one can calculate that a t 0.05 M only 0.2% B T is associated, thus justifying our initial implicit assumption that self-association can be neglected in determining K . Changes with temperature in even this small amount of dimerization may well cause the sniall alteration in vi. We have, of course, taken this self-association into account by using for the determination of K a t each temperature the value of vi found at that temperature. Additional corrections, of the type used, for example, in the study of alcoholbase iiiteractions,22 are needed only where self-association is much greater. Temperature Independence of A,.-Our finding that the ordinate intercepts, (l/A,), of the plots for BTDAIF (Fig. 1) are apparently independent of temperature lends support to the critical assumption made in treating p.m.r. data for some other systems that the (22) E D. Becker, Spectrochzm Acta, 17, 436 (1961).
Vol. 67
hydrogen bond shifts do not vary with temperature.23,24 The results for the other systems that we studied are consistent with a temperature-independent Acr but for these systems the data are not extensive enough to really furnish additional proof of the constancy of Ac. Correlation of A, with AH.-Considerable interest has attached to correlations between AH for H-bond formation and various spectral properties, such as infrared frequency shifts2.’ and intensity changesz2and p.m.r. frequency shifts (in our terminology, Ac).23 I n benzene the ring current effect dominates the sign and magnitude of Ac.25 For the other four systems, the data in Table I11 can be correlated surprisingly well, but with a relation such that the largest value of -AH correlates with the smallest value of A,, in contrast to our expectation. This is reminiscent of the similar correlation found between AH and infrared frequency shift for phenol bonding to various hydrogen acceptors, which is opposite in direction to the normally expected infrared correlation.2 Because of the limited number of p.m.r. data available for the B T systems, the limited range of AH, and the very significant possibility of error in determining A, for these systems, we believe that this apparent correlation between AH and A, is suggestive, but not definitive. However, the method of data treatment developed here may well be applied to more strongly H-bonded systems (e.g., involving phenols or alcohols) to provide very accurate values of A H and A . , which can be used to test such correlations. (23) C. XI. Huggins, G. C. Pimentel, a n d J. N. Shoolery, J . Chem. Phys., 25, 1244 (1955). (24) J. C. Davis, Jr., K. S.Pitser, a n d C. N. R. Rao, J . Phys. Chem., 64, 1744 (1960). (25) With the model of Johnson a n d Bovey [J. Chem. Phys.. 29, 1012 (1958)l we calculate t h a t the S-H proton would experience an upfield shift of 150 C.P.S. if i t approached on the sixfold axis of benzene to a distance of about 2.6 .&. from the plane of the ring.
NUCLEAR MAGNETIC RESONANCE AND SOLVENT EXTRACTION STUDIES. I. COMPLEXES INVOLVING THENOYLTRIFLUOROACETONE AXD SOME NEUTRAL ORGANOPHOSPHORUS ESTERS BY ROBERT L. SCRUGGS,~“ TAI KIM,^"
AND
NORMAN C.
L1lb
National Institute of Arthritis and Metabolic Diseases, National Instatutes of Health, Bethesda, Jfaryland, and Deprtrtrnent of Chenzistry , Duquesne Unizersity, Pittsburgh, Pennsylvanza Received Aprd 8, 1063 The proton magnetic resonance and phosphorus nuclear magnetic resonance methods have been used t o demonstrate that the extent of interaction between thenoyltrifluoroacetone (HB) and tributyl phosphate or tri-n-butoxyethyl phosphate (1,)and between zinc nitrate and tri-n-butoxyethyl phosphate is slight. Solvent extraction methods have been uaed to obtain equilibrium constants for the reactions: Zn*+(aq) 2HB(org) = ZnAs(org) ZH-(aq); Zn2-(aq) %HS(org) L(org) = ZnAaL(org) 2H+(aq); and ZnAq(org) L(org) = ZnA*L(org). The synergistic effect of a mixture of HA and L on the extraction of Zn(I1) is postulated to be due to the replacement of the aquo metal-thenoyltrifluoroacetone complex, ZnAZ.Ha0, by the more hydrophobic Zn&L complex.
+
+
+.
The word “synergisin” was first used by Blake, a greatly enhanced extraction of uranium from aqueous solut’ioii by a mixture of an acid dialkyl phosphate and certain et a1.,2 to describe the phenonienon of
(1) (a) Research assistant on a U. S.Atomic Energy Commission contract, No. AT(30-1)-1922 with Duquesne University; (h) Duquesne University, Pittsburgh, Pennsylvania: part of this work was done while Visiting Scientist a t the National Institutes of Health. (2) C . A . Blake, C . P.Haes, C. If. Coleinan, a n d J. C. I\-hite, P i o c . Iflte:11.
ns77ei’a, is, ism ( 1 ~ s ) .
C U ~ ~ , T .i+ncefui [ L S ~ Sni. ~ : ~ ~ ~ . y ~ 1068, ~ ,
+
+
+
phosphorus esters, the resulting mixture giving a better extraction than either the acid or neutral phosphate alone. More recently, several authors have found synergism in systems wherein the acid dialkyl phosphate is replaced by thenoyltrifluoroacetone (HA).3,4 As yet, however, there is not sufficient understanding of the (3) H. Irving a n d D. N. Edgington. PTOC.Chem. S o c . , 360 (19.59); .I. Inow. S u c l . Chem., 20,314 (1961); 21, 169 (1961). (?) T. \’. Herrly, ihid., 19,314, 328 (1961).
