NOTES
Jan., 1960
Discussion Figure 1 illustrates the application of equation 4 to several weak bases; the indicator was p-naphtholbenzein. Another point, lying off the graph, falls on line 5. The linear relationship appears to hold for these data, all of which were obtained in acetic acid solutions 0.018 M with respect to mater. Phenobarbital shows no basic properties in this system. Table I lists the perchlorate formation conqtants for all of the indicators and weak bases as determined by the methods outlined here. The table also includes some values for stronger bases (acetamide, urea, 2,6-dimethyl-a-pyrone, thiourea and caffeine) which were evaluated via the exchange constants (Kex = K:HA/K7H") of these bases as determined by the so-called modified type I1 photometric t i t r a t i ~ n . The ~ uncertainties given are based upon an assigned uncertainty of 0.05 X lo5 in the value for p-naphtholbenzein and upon the relative precision of the exchange constants, about 5%. The accuracy of the constants for the weaker bases is a rough estimate only. Because of the graphical treatment of data, a quantitative evaluation of the errors is difficult. TABLE I PERCHLORATE FORMATION CONSTANTS FOR SOME BASESA N D INDICATORS IN ACETICACID Compound
Salicylamide Benzamide Acetanilide Acetophenetidin Acetamide Urea Dimethylpyrone Thiourea Caffeine Sudan I11 Nile Blue A p-Naphthol benzein Malachite Green
@HClO4
4 . 8 f 0 . 4 X 101 7 1 f .5 X 102 9.2 f .5 X 102 3 . 2 =t . 6 X 108 1.1 f . 2 x 104 85* .7x104 1 . 4 f . 3 X 106 1.5 . 2 x 105 2.4 f .5 x 105 9.1 f .5 x 108 3.9 . 6 X lo4 1.1 .05 x 106 1.8 .2 x 106
* * *
The constant for acetophenetidin was found by the method given here and also by the modified type I1 technique; agreement was within the uncertainty given in Table I. Constants such as those in Table T are rapidly evaluated; the use of photometric titrations for the determination of Q promotes the simplicity of the operation. Such salt formation constants permit convenient and quantitative examination of such very weakly basic compounds as amides; the correlation of amide basicity with other amide reactions or with structure is presently limited by the few reliable values of amide basicities available. The data of Table I suggest that the base strength of unsubstituted amides may be compared usefully with the acid strength of the corresponding acids; nearly the same effects are operative in both cases. Thiourea seems to be a stronger base than urea according to the perchlorate formation constants; this is contrary to the situation in water or metha n ~ l .This ~ reversal may be due to a very specific (8) K. A. Connors, Ph.D. The&, University of Wiaconsin, 1959. (9) R. G.Pearson and J. Tucker, J . Am. Chem. SOC.,71,749 (1949).
181
solvation effect or to the dependence of the salt formation constant on the dissociation constants of the acid HA and the salt BHA.l0 In some preliminary experiments the effect of benzene on salt formation in acetic acid has been studied. The system was p-naphtholbenzeinwater; equation 2 was employed. The ratio K W H A (i.e., the slope of the 1/& us. C H ~ O plot) increases linearly with decreasing dielectric constant over the benzene mole fraction range 0.000 to 0.491 (the dielectric convtant changes from 6.20 to 2.83 in this range)." The data are not sufficiently accurate to obtain reliable values of the individual constants. This increase in perchlorate formation constant may be the result of increased extent of formation of higher ionic aggregates. (10) T. Higriohi and C. R. Rehm, Anal, Chem., 27, 408 (1955). (11) C. P. Smyth and H. E. Rogers, J . Am. Chrm. Soc., 6 2 , 1824 (1930).
NOTE ON T H E MOLECULAR WEIGHT DEPENDENCE OF BLENDING EFFECTS ON THE STRESS-RELAXATION BEHAVIOR I N POLYVINYL ACETATE FILM BY KAZUHIKO NINOMIYA~ AND MICHITARO SAKAMOTO Physical Chemietry Laboratow, Department of Fisheries, Kyoto Uniuersily. Maimru, Japan Received August 7, 1969
Recently it was shown experimentally for polyvinyl acetate2 and polyi~obutylene~ that in the rubbery region the relaxation modulus of a blend consisting of two fractionated components could quantitatively be represented in terms of those of the components by Ebdl)
=
wiEi(t/Xi) -I-W z E d t / X ? ) w1 wa = 1
+
(1)
Here Ebl(t) and E i ( t ) represent, respectively, the relaxation moduli of the blend and its i-th component (i = 1, 2), and wi is the weight fraction of the i-th component. The constant X i was expected to be equal to tke ratio of the number-average molecular weight, n/fnhl, of the blend to that of the i-th component, h4ni,2 i.e. xi
%nbl/%ni
(2)
However, no experimental data for were available for the polymers to test the validity of equation 2. Recently osmotic measurements for the polyvinyl acetate specimens used in the previous work2 were carried out to determine the values of M n for those. The present note is essentially concerned with tests of validity of equation 2 made with these experimental data for M,. Experimental Sam les used for osmotic pressure measurements were FVI, JVII, FIX, FX, F X I and FXIII (for their details, see Table I in ref. 2, and also Table I in ref. 4). The measurements were made in acetone solutions of those samples at 26.0°, by the Schulz-Wagner type osmometers6 (1) The Japan Synthetic Rubber Co. Ltd., Yokkaichi Plant, Yokkaichi, Japan. (2) K.Ninomiya, J . Colloid Sci., 14,49 (1959). (3) H.Leaderman and K. Ninomiya. in preparation for publication. (4) K. Ninomiya and H. Fujita, J. Colloid Sci., 13, 204 (1957).
182
Vol. 64
NOTES I
I
0
1
the second virial coefficient At. The values of iVn for six blends, A, C, D, F, G and H (for their designations, see Tabje I in ref. 2) were calculated from the values of Mn for the fractions and their weight compositions in respective blgnds, and are given in Table I. The value of M n b l / M n i was calculated for each of the six blends and was plotted against the value of the corresponding Xi on a loglog graph in Fig. 2 . It is apparent from Fig. 2 that equation 2 only approximates the tangent at the coordinate origin and that the plots deviate progregively- from the predicted relation as the ratio M n b l / M n i is more apart from unity. It was found that the data can be represented well by log xi = ( 1 p [(Gnz/Grtl)- 111log (-@nbl/Gni) (3) for
+
an2
01
0 Fig. 1.-Plots
@
I
I
0.5 1 .o c (g./100 ml.). of T / C us. c for six polyvinyl acetate fractions in acetone at 26.0'.
> Gal
where p is a constant. The value of p for this case was 0.25. Table I1 compares the observed values of log A; with those calculated in terms of equation 3, where p = 0.25. As seen in Table 11, both the observed and calculated values of log Xi agree fairly well with one another for each blend. It is of interest to observe that Xi can be expressed in terms of an equation which contains only numberaverage molecular weights for both blend and its components. The authors wish to thank Professor H. Fujita of Kyoto University for showing interest in this work. TABLE I
an,
XVMBER-AVERAGE MOLECULAR WEIGHTS, OF POLYVINYL ACETATE FRACTIONS A N D BLENDS. SECOND VIRIAL A? (mL3mole g.-2) OF FRACTIONS IN ACETONE COEFFICIENT, ~~26.0' Fraction
anx 10-5 x 104
Blend Ai" x 10-5
FVI
FVII
FIX
FX
FXI
FXIII
1.0 5.* A 3.8
0.90 5.a
1.5
3.5
7.6
s.4 D
1.8
1.2
5.2 G 1.2
5.1
C
2.3 5 1 F 1.4
H 2.8
TABLE I1 COMPARISON OF VALUES OF
LOO X i
OBSERVED A N D CALCU-
LATED
Blend
logx,
-0.5
0.0
+0.5
log (lgnbl/Gni). Fig. 2.-Doubly logarithmic plots of X i us. E+/@,,$ for six polyvinyl acetate blends; dashed line indicates the relation of equation 2. fitted with semi-permeable membranes of du Pont Cellophane 6006; the conditioning of the membrane was made in 30% aqueous solution of sodium hydroxide.
Results and Discussion Figure 1 shows the usual plots of TICus. c for the six polyvinyl acetate fractions. The value of Mn for each fraction, determined from its intercept on the ordinate, is given in Table I, together with (5) F. Daniels, et al., "Experimental Physical Chemistry," Fifth Edition, McGraw-Hill Book Co. New York, N. Y., 1956, p. 218. (6) This was furnished from the University of Wisconsin through the kindness of Professor John D Ferry.
loax'(
{ d~:; obsd. odd.
A +0.83 -t .80
C D +0.60 +O.OO
+
.09
.68 .62
-
.13 .I1
-
+
.66 -1.58 -1.68
-
F f0.24
+
-
.28 .32 .29
G +0.13 .17 .42
+
-
.40
H +0.06
+ -
.09 .09 .ll
POLARIZABILITIES IN BORONCONTAINING BONDS AND OCTETS BYHANSWEIDMANN AND HOWARD K. ZIMMERMAN, JR. Depariment of Chemislr2/, Agricultural and Mechanical College of Tezas, College Stalzon, Tezas Received August 10,1969
X recent paper by Christopher and Tully' presents octet refractivities for B :0 .. :C and B :Cl : structural elements, as well as bond refractivities for B :C when the carbon is either aliphatic or aromatic. This work mas based entirely upon refrac(1) P. BZ. Christopher and T. J. Tully, J . A m . Chem. Soc., 80, 6516 (1958).
