1562
C. D. MILLER,R . C. MILLERAXD IV. ROGERS, JR.
Vol. '30
KH"' = 0.25 =t 0.09 at 22") two valuesof K ~ ~ a tTable V gives the PKs (where $K = -log K ) of 22" can be calculated from the usual thermody- several of the acids analogous to H,Se. namic equations and the assumptions that (a) the Assuming a simple electrostatic model, one obactivity coefficients of NaHSe and KazSe in these tains the equations solutions are the same as those of NaOH and NanpK, 3 3 = SO4, respectively, at the ionic strength of the solu7 r tions, and (b) Latimer's estimates of the entropies of HSe- and Se=, namely, 22 and 0 e.u., respecPA', = -c tively, are correct. These calculations give, from the measurements at 0.5", K? = 10-14.5*n.4 where C is a constant, z1 and z2 are the charges on a t 22", where the limits of error come from the h i - the ions. and r is the bond length of the atoms. On its of error of the original measurement and my es- the basis of this model one would expect that pK1, timate of the reliability of the above assumptions. PK, and PK, - ~ Kwould I increase from the heavier The measurement a t 22' gives Kn0= 10-15.9* O.'. members of the series to the lighter members. If both measurements are taken into account with This does not occur. The discrepancy is shown their estimated limits of error, the best value is most distinctly by pK, - pK1, where the value is probably K = 10-1j." 0 . 6 , lower for H,S than for either H2Teor H2Se. Therefore, on the basis of this model, one would conclude TABLE Tthat the value of K 1for H,S is anomalous. The asXCID COSSTAXTS OF H2.1 signment of partially covalent character to the Compound ~ K I @Kz ZIG-~KI Ref. bonds does nothing to help resolve this anomaly. HzO 15.7 Acknowledgment.-I wish to express my ap5.9 11,12 7.0 12.9 HzS preciation to Professor Richard E. Pornell and 3.6 15 HzSe 11.4 ti, 7 to Professor Robert E. Connick for their many help2.6 11 H2Te 8 4 7,3 ___-ful suggestions in connection with this work, which (10) \V, 52. Latimer, "Oxidation Potentials," Pret:ticv-€€dl, S r i v was performed under the auspices of the U. S. York, S.Y . , 1953. Xtoniic Energy Commission. (11) H. Kubli, Helu. Chzm. A c t a , 29, 1962 (194G).
c
BERKELEY, CALIFORNIA
(12) N. Konopick and 0 . Leberl, .\fa?zatsh. Cheiii., 80, 781 (1949).
[COSTRIHUTIOS FROM THE I)F,PARTLIENT O F CHEMISTRY,
Phosphine Oxides. BY C A R O L I N E
D.
V.
TEMPLE USIVERSITT]
Intra- and Intermolecular Association1
hIILLERIEa3 ROBEKT C L A Y &!ILLER3 AND W I L L I A M
ROGERS, JR.
RECEIVED SEPTEMRER 27, 1957 >P---c< -111
iiitrarnolecular hydrogen bond of the type
4 9 '. i
0
has beeti found in certain a-hydroxy phosphoryl compounds.
1% The strength of this bond has been related to the negativity of the phosphoryl oxygen. n'hen the phosphoryl is extremely polarized, as in the phosphine oxides, an interinolcculnr association is also observed. This is probably a dipole-dipole interaction of these phosphoryl groups.
The spectra of a number of phosphoryl compounds have appeared recently in the literature, and various assignments have been made, both empirically and theoretically. The effect of electronegativity of the substituents on the phosphoryl stretching frequency has been shown,.1,5and the existence of hydrogen bonding phenomena involving the phosphoryl group has been d e m ~ n s t r a t e d . ~Anal,~ ( 1 ) Presented a t t h e Meeting of t h e American Chemical Society For t h e fourth paper in this series, aee R. C Miller, C. D . Miller. W. RoRera and L. A. Hamilton, TIIISJ O U R N A L , 79, 424 11967). ( 2 ) Abstracted in p a r t from t h e dissertation submitted by C . D . M. to rhe Temple University Graduate Council in partial fulfillment of the requirements for t h e degree of Doctor of Philosophy-. (3) Experimental Station, E . I. d u P o n t d e N e m o u r s Co., R'ilrnington, Delaaare. (4) L . W.Daasch and D . C. Smith, A n a l . C h e w . , 23, 853 (1951). ( 5 ) J . V . Bell. J . Heisler, H. Tannenbaum and J. Goldenson, THIS TOVRNAI, 76, 5183 (1954). (13)G. h1. Kosolapoff and J. F. McCullough, i b i d . , 73, 5392 (1951). (7) E. Halpern, J . B o ~ i c k ,H. Finegold and J . Goldenson, ibid.,77, 4472 (1955) at S f w York, N. Y., September lY57
ogous relationships involving the carbonyl group have received somewhat more attention * and, with the exception of the steric differences of the tetrahedral phosphorus atom of the phosphoryl from the planar carbon atom of the carbonyl, there exists a iiotable similarity. Recent work a t this Laboratory has resulted in the synthesis of several new classes of organophosphorus compounds, whose spectra have also been recorded, from which certain information concerning their structure and properties may be deduced. Chronologically the first, and structurally the simplest, of these are the disubstituted phosphine oxides, KJ'(0)H. Prior t o their general synthesis,8 such compounds were tentatively classed as trivalent phosphinous acids, R*P-OHg. However, the presence of strong P-H absorption a t 2335 cm.-' ( 8 ) R. H . Williams and L. A . Hamilton, ibid., 74, 5418 (1952). (9) G. >,I. Kosolapoff, "Organophosphorus Compounds," John W l e y and Sons, Inc., X e w York, N. Y., 1950.
INTRAAND INTERMOLECULAR ASSOCIATION OF PHOSPHINE OXIDES
April 5, 1958
and a P-tO absorption at 1190 an.-', together with the absence of any absorption which could reasonably be assigned to an 0-H stretching mode (except, perhaps, for a slight shoulder near 2700 cm.-l) is strong evidence that these compounds exist as the tetravalent form, predominantly if not exclusively. An interesting detail of the spectra of these compounds is the unmistakable shift of the phosphoryl absorption from 1150-1155 cm.-' in the solid state to 1190 cm.-l in carbon disulfide solution. An intermolecular association is strongly indicated; it is not, however, the most obvious, since the P-H R
/ . . .O c P-R \
\
R-P-H. I(
Y
9
% 6.0
1 -
Y
E
I
5
-3
5.5
I I
-
R
H
0
frequency decreases, rather than increases, upon solution (2335 cm.-l in solid state; 2283 cm.-l in carbon disulfide solution). Similar evidence for intermolecular association of the phosphoryl group of trialkyl phosphine oxides is observed. Solution of tri-n-octylphosphine oxide in carbon disulfide produces an increase in frequency from 1142 to 1170 em.-' This almost certainly can be attributed t o dipole-dipole association of the phosphoryl groups. \s,
6.5
1563
-p-o.
s-
/
6+ 6-
. . . . .p-0
/I\
The association of the disubstituted phosphine OXides is probably similar, and the shift of the P-H stretching frequency can be interpreted as reflecting the change of electron affinity of the phosphorus atom in the associated and non-associated states. While the number of compounds containing P-H groups which we have examined is too limited t o draw any firm conclusions, it seems t o be generally true that the P-H frequency varies with the nature of the other substituents upon the phosphorus in the same sense as does the phosphoryl. The rather wide (for an X-H type vibration) range of P-H absorption from compound to compound has been noted by BellamyI0 without any explanation. Available data from this Laboratory and from the literature for the P-H frequency in tetravalent species are listed in Table I. Plotting these frequencies against the sum of the phosphoryl shift constants5 of the other two substituents, excluding the oxygen, gives a smooth curve, as shown in Fig. 1. Trivalent species would not be expected t o obey this relationship.
2350
2300
2400
v P-H, an.-'. Fig. 1.-Variation of P-H stretching frequency.
From simple, symmetrical trisubstituted phosphine oxides, consideration was next directed to the dialkyl a-hydroxyalkylphosphine oxides, whose synthesis recently was reported. Absorption data for these compounds are given in Table 11. These compounds showed a strong phosphoryl absorption a t 1100-1140 cm.-' in the crystalline state which increased to 11600-1165cm.-l in carbon disulfide solution. In addition, these compounds exhibit a characteristic, strong, well-defined absorption near 3050-3100 cm.-l which shifted only slightly (30903150 cm.-l) upon dissolving in carbon disulfide and whose frequency was thereafter independent of concentration a t successive dilutions t o 0.01 M . The assignment of this as a hydroxyl stretching frequency was confirmed by deuteration of several examples by recrystallization from DpO-dioxane solution. Exchange was incomplete, but 0-D absorption was observed as expected a t 2340 em.-'. By coincidence, this is very nearly the frequency of the P-H in the parent disubstituted phosphine oxide. There was no evidence, either chemical or spectroscopic, of decomposition during deuteration. Moreover, decomposition in this medium might be expected t o yield P-D rather than P-H groups. These data indicate that the hydrogen bonding of the hydroxyl is primarily intra.molecular as >P-c
