1274
T'ol. 65
NOTES
POLARIZATIONS A S D
Compound
--70
Calcd.
ZnClp(C6HsN) 24.08 ZnClp(CK-CH~C'SHJ)~ 21.99 ZnCls(pCH3CjHJ)z 21.99 ZnCl&CH&$H4N) ZnCl2( Y - C H ~ C ~ H ~ N ) ~ 21.99 ZnClz(I.'t3P)2 19.03 BCl,( C,HsS) 54 18 Extrapolated values (ufp = 0).
c1-
TABLE I ELECTRIC L f O M E S T S AT 25' P
Found
Solvent
1OOw/z
AD/u,/2
Ad/uf2
23.90 21.45 21.90
D
0.17-0.56 .18- .43 .18- .86 .50- .79 .35- .86 .33-1.06 .30-0.93
36.2 30.7 35.5 31.0 37.0 1 7 1" 31.5"
0.32 .24
21.70 19.17 53.58
D D B I) B H
Boron trichloride-pyridine n-as prepared by mixing carbon tetrachloride solutions of pyridine and boron trichloride. The product was dissolved in benzene and reprecipitated by the addition of petroleum ether. Triethylphosphine was prepared by the reaction of ethylmagnesium bromide with phosphorus trichloride; after hydrolysis the product was distilled in an atmosphere of nitrogen and added to an aqueous solution of zinc chloride to yield dichlorobis-( triethylphosphine)-zinc. The precipitate %-as washed with ether and dried over sulfuric acid. C.P. benzene was refluxed over phosphoric anhydride and distilled. Dioxane was purified by the method described by Fieser.2 The product was distilled from sodium. Dielectric constant and density measurements and calculations of electric moments were carried out as in previous ~ o r k . 3 With the exceptions noted, the dielectric constant/ w i g h t fraction ratios listed in Table I are average values. The refractions were taken as the sum of the values for the base and the metal chloride. A value of 19 ml. was estimated for zinc chloride from the refractions listed for magnesium, cadmium and mercury chlorides in Landolt-Bornstein.' The 'distortion polarizations were taken as 1.10 .TI RD.
Discussion The agreement bet'ween the values obtained for the moment of dichlorobis-(P-picoline)-zinc in benzene, 9.53, and in dioxane, 9.54, indicates that dioxane exerts no specific solvent effect on t'he moments of these addition compounds. The moment's of the zinc chloride complexes are in t'he expected order: ypicoline > p-picoline > pyridine > a-picoline. The difference between the moments obt'ained for the a-picoline and pyridine complexes, 0.55 Debye, is equal to the calculated difference for these tet'rahedral molecules. It is not possible to make quantitative calculations of the moments of t'he a- and I!-picoline complexes as these values depend on the :favored (unknown) relative orientations of the pyridine rings, which are affect'ed by t'he steric requirements of the methyl groups. The moment3 observed for dichlorobis-(triet,hylphosphine)-zinc, 7.57, compares to the value 10.7 reported by Jensenj for dichlorobis-(triethylphosphine)-platinum(I1). Taking into account the configurations of these complexes, tetrahedral for zinc and cis square planar for platinum, the sum of the R3P-Zn and Zn-C1 moments is 6.58, compared to 7.57 for the sum of the R&Pt and I't-C1 vectors. This difference, 1.0 Debye, is not surpi*ising in the light of the greater stability of the platinum complexes compared to those of zinc. It' is expected that, the P-Pt u-bond
.26
.35 .22 .32 35
P9m
1807 1695 1948 1943 2030 1285 1200
Pu
74 85 85 85 85 110
51
Debyes
9 8 9 9 9 7 7
20 & 0 04 86 + 04 54 i 04 53 i 04 75 d= .1 57 1 50 i. 04
*
mill have a greater covalent character and therefore a greater polarity than the P-Zn bond. The difference suggests that there is no appreciably greater double bond character (which decreases bond polarity) in the phosphorus-to-platinum than in the phosphorus-to-zinc bond. The moments obtained reveal an anomaly in the relative polarities of zinc complexes and boron complexes. The moments of boron trichloridetrimethylamine and boron trichloride-trimethylphosphine are 6.23 and 7.03, respectively.'j These values indicate that the P-B bond is more polar than the N-B bond. It is not possible t o determine the moment of a dichlorobis-(trialky1amine)-zinc complex because of solubility limitations. The moment of boron trichloride-pyridine is 1.27 Debyes larger than that of boron trichloridetrimethylamine. If this difference (multiplied by 1.15 for the tetrahedral bis complex) holds also for the addition compounds of zinc chloride, the moment of dichlorobis-(triethylamine)-zinc is expected to be 7.8, compared to the observed moment of dichlorobis-(triethylphosphine) -zinc, 7 3 7 . This indicates that the P-Zn bond is slightly less polar than the S-Zn bond. Partiai I'=Zn double bond character could account for this, but zinc is not expected to use electrons from its completed third shell in forming n-bonds. ( 6 ) G. A I , Phillips, 1. S. Hunter and L E. Sutt i n I C h e m S o c , 146 (1945).
THE EFFECT OF UREA O S T H E COSFIGURATION OF POLYT'ISYLPYRROLIDOSE BY IRVING A I . KLOTZ AND JOEL It7, R r
,>ELL
Department of Chemistry, Sorthicestern Unzversity I.-z n?islon Illinois Received Januaru 6 , 1961
The synthetic polymer poly\-iii\-lpyrrolidone (PT'P) mimics protein behavior in a numbe? of
1
(2) L. Fieser, "Experiments in Organic Chemistry," D. C . Heath and Co., Boston, Mass.. 1911, p. 369. cCusker and H. S.Xakowski, J . Am. Chem.
respects. For example it form? cvmpleses u-ith many types of small m~leciile,~-.' although u-ith
Soc., 79, 5188 ( 1 9 5 7 ) . f.1) Lmdolt-Bornstein,
(1) H. Bennhold and R . Schubert, Z. g e s . E r p t l . M e d . . 113, 722 (1943). ( 2 ) C. Wunderly, Arztl. Forsch., I , I , 29 (1950). (3) W.Scholtan, Makromol. Chem., 11, 131 (1953).
"Physikalisoh-Chemische Tabellen," wards Bros., -4n.n Arbor, Mich., 1943, vol. 2. ' 5 ) K. -4. Jenaen, 2. anorg. allgem. Chem., 229, 225 (1936).
Fd-
XOTES
July, 1961 only about one-third the affinity shown by serum a l b ~ r n i n . ~Likewise it shifts the pKa of a covalently-linked acid-base substituent in t'he same direction as is observed with corresponding protein ~onjugat'es.~ Furthermore, with the PVP conjugate, as with those of proteins, the addition of urea to the a,queous solution decreases markedly the shift in acidity c ~ n s t ' a n t ~ . ~ Urea is a well-known protein denaturant and produces mar'ked changes in macromolecular configurat'ion of proteins. The intrinsic viscosity of ovalbumin (molecular weight 44,000) for example, changes from 0.043 (g./100 c,c.)-I for t'he native protein6 to 0.21 for t'he protein in 7.5 M urea.' It sl3emed of interest, t'herefore, to examine t'he effect of urea on the viscosity and henre configuration, of polyvinylpyrrolidone. Experimental Viscosities were measured in a standard Ostwald viscometer whose water outflow time was 110 see. Before each measurement, the viscometer was cleaned with warm chromic acid solution, rinsed throughly with distilled water and dried with a stream of dry air. It was mounted carefully with the same chmp in the same position in a water-bath a t 25' and its vertical alignment was checked with a plumb line. Outffow times for a given solution checked within 10.03 sec. or betti?r. Stock solutions were prepared containing 4y0 polyvinylpyrrolidone in water and in 8 M urea, respectively. These were diluted with corresponding solvent to prepare more dilute so1ut:ions of the polymer. All solutions were filtered before use. Five-ml. samples were added carefully a t the bottom of the bulb of the viscometer to prevent the formation of bubbles. Densities of the solutions were measured with a Westphal balance. Measured viscosities, Q, were converted to reduced viscosities n r e d , according to the equation (S/QO) - 1 Sred =
Discussion It is of interest to note first that the intrinsic viscosity l : ~ ] , where =
4 ;
3 0.10 i
2 3 4 (PVP). Fig. 1.-Reduced viscosity of polyvinylpyrrolidone as a function of concentration in g. per 100 ml.: 0, in water; 0 , in 8 .If urea in water. 1
for a decrease in the degree of hydration of the macromolecule. In regard to comparisons of the behavior of proteins with that of polyvinylpyrrolidone, these viscosity experiments lead to two interesting conclusions. First it is evident that interactions such as binding of ions or masking of the reactions of conjugated groups can occur with a macromolecule having a relatively random configuration such as is found for PVP. Secondly urea may perturb these interactions of PT'P even though it does not produce a major change in macromolecular configuration. These observations are directly relevant to the molecular interpretation of corresponding interactions of protein macromolecules.6
C
where qo is the viscosity of the solvent free of polymer and c is the concentration of polymer in g. per 100 ml. of solution. Reduced viscosities for polyvinylpyrrolidone in water and in urea are plotted in Fig. 1.
h1
1275
lim
c+o
(Qrtd)
for polyvinylpyrrolidone in water is 0.225 (g,/ 100 ml.)-I Jvhich is of the same order of magnitude as that of denatured ovalbumin.' The average molecular weiglit of the sample of polyvinylpyrrolidone used is 40,000,* compared to 44,000 for ovalbumin. Hence even in water, polyvinylpyrrolidone is in a relatively loose configuration. It is not surprising therefore that urea has very little effect on t'he intrinsic viscosity of polyvinylpyrrolidone, the value dropping slightly, to 0.215. Such a drop is small and probably within experimental error, but it is of interest t'o note that the change wi.th urea is in the direction to be expected M. Klotz and J. Ayerc, unpublished experiments. ( 5 ) I. ,If. IClotz and Y. H. Stryker. J . A m . Chem. Soc., 82, 5169 (1960). (6) A. Polson, Kolloid Z., 88, 5 1 (1939). (7) H. K. Frensdorff. &I. T. Watson and W. Kauemann, J. An. Chem. Soc., 76, 5167 (1953). (8) "PVP, Polyvinylpyrrolidone," Bulletin P-100, General Aniline (4) I.
a n d Film Corp., New York, N. Y.,1951.
THE DISSOCIATION PRESSURE OF GALLIUM ARSENIDE BY V. J. LYONS ASD V. J. SILVESTRI I B M Research Laboratory, Poughkeepsze .Veu York Receaved J a n u a r y 7, 1961
Gallium arsenide thermally dissociates to the constituent elements and two previous investigations of the reaction equilibria have been reported. The solid-liquid-vapor equilibria were studied by van den Boomgaard and Schol' over the range 781 to 1237'. Goldfinger and Drowart2 have reported a mass spectrometric study of the vapor species resulting from thermal dissociation of the compound in the range 758 to 863'. The purpose of this work was to re-examine the reaction in a temperature range below the compound melting point because of the inconsistency in the reported data. Since the vapor pressure of arsenic is several orders of magnitude greater than that of gallium the dissociation pressure of GaAs is essentially equal to the arsenic pressure in equilibrium with the compound. The method used to measure the equilibrium arsenic pressure was the visual observation of the arsenic dew-point in a sealed tube containing solid Gails. The applicability of the method to decomposing solids has been demonstrated, and the more general details of the experimental procedures have been described (1) J. van den Boomgaard and K. Schol, Phillips Res. R e p . , 12, 127 (1957). (2) P. Goldfinger and J. von Drowart, J . G'hem. Phps., 68, 721 (1968).
