4436
J. B. CONANT AND T. H. WERNER
Vol. 52
pared by benzoylation of 5-amino-8-hydroxyquinoline showed no depression. Moreover, by hydrolysis with hydrochloric acid (20%) the formation of benzoic acid could be ascertained by the mixed melting point method. Anal. Subs., 3.066: Nz, 0.290 (24', 766 mm.). Calcd. for ClsHIPOZN~:N, 10.61. Found: N, 10.63. Acid sulfate gave yellow columns from alcohol; m. p. 221-222' (decomp.). S-Benzoyloxyquinoline.-The benzoylation of 8-hydroxyquinoline with benzoyl chloride was carried out in the presence of pyridine in the cold; yield, 90% of the theoretical after recrystallization. It forms in colorless tables from alcohol; m. p. 122-122.6'. This compound was prepared first by Bedall by the interaction of 8-hydroxyquinoline and benzoyl chloride at a high temperature; he found a melting point of 118-120' for his product.8 Anal. Calcd. for Cl&I1102N: N, 5.62. Found: N, 5.54. The hydrochloride was obtained by treating an ice cold ethereal solution of the free base with dry hydrogen chloride gas. It forms in colorless needles; m.p. 124'. It is easily soluble in water. Anal. Caicd. for ClsH1102N.HC1: HCI, 12.78. Found: HCl, 12.54. On submitting this hydrochloride to a Friedel and Crafts reaction, benzoic acid and 8-hydroxyquinoline could be recovered and no condensation product could be isolated.
I hereby desire to express my hearty thanks t o Professor Hata for the interest which he has kindly taken in this work and t o Mr. C. Sone for his assistance in this investigation.
Summary The preparation of 5-acetyl-, 5-chloro-acetyl- and 5-benzoyl-8-hydroxyquinoline has been reported. TOKYO, JAPAN [CONTRIBUTION FROM
THE
CONVERSEMEMORIALLABORATORY OF HARVARD UNIVERSITY 1
THE DETERMINATION OF THE STRENGTH OF WEAK BASES AND PSEUDO BASES IN GLACIAL ACETIC ACID SOLUTIONS' BY J. B. CONANT AND T. H. WERNER RECEIVED JULY 17, 1930
PUBLISRBD NOVEMBER 5, 1930
Previous papers of this series have shown that the titration of bases with strong acids in glacial acetic acid solution may be followed by means of the chloranil electrode. We have been interested in extending this study of weak bases to weak pseudo-bases of the type of triphenyl carbinol. It is only by the use of a solvent such as glacial acetic acid that these weak pseudo-bases can be studied and the oxidation-reduction systems composed of free radicals and halochromic salts can be investigated. Before continuing the study of these more strictly organic problems, it was necessary
* Bedall and Fischer, Ber., 14, 1367 (1881). For earlier papers of this 1 This is Paper 4 in a series on Superacid Solutions. series, see THIS JOURNAL, 49,3047,3062 (1927); and 50,2367 (1928).
Nov., 1930
STRENGTH OF WEAK AND PSEUDO BASES
4437
to obtain more information in regard to the factors influencing the dissociation constants of weak bases in glacial acetic acid. From the earlier work it was clear that the neutral salt concentration was an important factor. For example, the shape of the titration curves obtained by Hall and Werner2 clearly pointed to a marked effect of the changing ionic strength on the strength of the base being titrated. We shall first present in this paper certain results obtained in a Study of the effect of the ionic strength on dissociation constants of weak bases in glacial acetic acid solution. The results were obtained by two different methods. One was the electrochemical method using the chloranil electrode in exactly the manner previously described. The other method was to take advantage of the color changes which take place when crystal violet is further neutralized by the addition of strong acids. These changes have been studied in detail in water solution by Adams and Rosenstein.s Since the results obtained by the e. m. f. method with colorless bases, and by a spectrophotometric method with crystal violet, are closely related, they will be discussed together. The results obtained with crystal violet may be considered first. Adams and Rosenstein have proved that the change of color of this substance from violet through blue and green to yellow on adding strong acid, is due to the formation of the green and yellow ions which correspond to the addition of one and two protons, respectively, to the violet ion, according to the equations B + H+6 (1) violet
BH++ green
Bg€€:
+ H+e B&+++ yellow
(2)
One is thus in a position to evaluate the equilibrium constants for the first and second reactions written above (K: and K:) from spectrophotometric data. Actually, the values of KL are subject to a much greater experimental error and the agreement among them we found to be unsatisfactory, and the change of this constant with change in ionic strength was irregular, for reasons which are not entirely clear. For these reasons we shall attempt to interpret only the changes of K: with change of ionic strength, giving only an approximate value for K:. Briefly, the method consisted in measuring the extinction coefficients of solutions of crystal violet in buffer solutions of definite ionic strength to The and measured P H ( ~ * ~ ) . concentration of dye was so small (4 X 2 X molar) that its contribution t o the ionic strength could be neglected. The extinction coefficient was measured a t intervals of 10 mp from 470 to 680. From the curves thus obtained with solutions which
* Hall and Werner, THISJOURNAL, 50,2367 (1928). * Adams and Rosenstein, ibid., 36, 1452 (1914).
4.75) were used for the fundamentals of the violet form and those for the yellow were taken
-
lated on assumption of following csmpositions:
t o y agreement on the assumption of a certain composition 82 8 10 s 20 43 37 for each solution. Three typiT 1 25 74 cal curves are shown in Fig. 1 and the fundamentals finally chosen are given in Table I. It may be noted that the equation for the extinction coefficient of a particular solution at a particular wave length is Vee + GEQ Yell = e where E,, EG and er are the fundamentals and V , G and Y the fraction of the material present in the violet, green and yellow forms. Since there was no evidence of a colorless form, the sum of those fractions was taken as one. The fading, noted by Adams and Rosenstein, which was due to hydrolysis, was not evident in our work because the amount of water present was negligible. The algebraic solution of the above equation is impossible but satisfactory results may be obtained by the laborious trial and error method just described. Curve C
% Violet
% Green
% Yellow
+
Nov., 1930
STRENGTH OF WEAK AND PSEUDO
4439
BASES
Expressed logarithmically, the mass law equations for the two equilibria are @K{ PdHAa) - (log T' @Ki = PdHAo) - (log G
- log G)
(la) (24
- log Y)
The data obtained in the measurements of the values are summarized in Table I1 and the results of the spectrophotometric measurements in Table 111. TABLEI MOLECULAR EXTINCTION COEFFICIENTS X 10-8 Wave length
470 490 510 520 540 560 570 590 600 605 615 630 640 660 680
Crystal Crystal violet violet in in 0.05 M 3 M pyridine HClOi in HAC in HAC
19.0 12.4 6.15 4.20 1.50 0.42 .18 .028 .005
3.01 8.16 20.7 31.9 61.0 77.0 82.7 93.2 81.3 68.2 40.8 13.8 7.10 3.20 2.50
,..
... ... ...
... ...
Fundamentals chosen for Violet Green Yellow form form form
...
2.45 9.40 25.0 35.0 63.8 76.6 83.0 93.2 74.0 58.0 35.0 16.2 8.47 4.02 2.60
... 2.0 5.0 13 26 36 56 69 80 95 112 100 60 18
19.0 12.8 6.5 4.2 1.7 0.5 .18 .028 .005
... ... ... ... ... ...
TABLEI1 MEASUREBIENTS OF BUFFERS (a) Urea-Sulfuric Acid Buffers Soh
u1 u2 u3 u4 u5 U6 u7 U8 u12 U13 U14 U15 U16 U17 U18 u19
Concn. of base, mole/liter
% Neutral with acid
Ionic strength,
I'dHAa)
c
pK' of dTr
0.00 0.003 0.055 .37 .012 .110 .54 .016 .127 -j- .20 .028 .167 -1.00 .0375 .193 .064 -0.03 .253 .316 50 -33 .loo 75 .80 ,150 .387 (b) Urea-Perchloric Acid Buffers 0.00025 40 -0.51 0.0001 0.010 .003 50 -1.25 .0015 .039 7.2 -0.32 .0036 ,060 .05 13 .58 .0065 .05 .080 .05 39 .90 .0195 .140 .05 50 -1.12 .025 .158 .20 45 -0.52 .09 .300 50 .46 .15 .30 ,387 0.05 .20 .05 .20 .05 .20 .20 .20
6 6 32 14 75 32
+ -
-
-
-
-
base
-1.20 -0.83 .87 .59 - .52 .36 .33 - -32
-
-0.69 -1.25 -1.43 -1.41 -1.09 -1.12 -0.61 .46
-
4440
VOl. 52
J. B. CONANT AND T. H . WERNER
TABLE I1 (Conckded) Soln.
A1 A2 A3 A4 A5 A6
Concn. ofbase, %. Neutral mole/liter with add
'Yh'
PK' of
P H ( ~ Ionic ~ ~ )
base
(c) Acetoxime-Sulfuric Acid Buffers 0.00025 40 -0.25 0.0001 0 .01 .025 40 .21 .Ol .10 40 .61 .04 .10 .20 * 10 80 - .20 .08 .283 .10 80 - .24 .08 .283 .44 .30 65 .42 .195
-0.43
+ +
+ .03 + .43 ++ .40 .36 + .69
+
TABLE I11
SUMMARY OF MEASUREMENTS OF DISSOCIATION CONSTANTS OF CRYSTAL VIOLET FROM SPECTROPHOTOMETRIC DATAAT 25 O
(a) UreaSulfuric Acid Buffers Soln.
Color of solution
J?
Fraction of material as P H ( ~ * ~Violet ) Green Yellow
Concn. of crystal violet X 106
u2 u4 U1 U6 u3 U8 u5
Blue-violet Blue Blue-violet Blue-green Green-blue Green Yellow-green
0.110 $0.37 0.755 0.22 0.025 1.96 .20 .440 ,167 .40 .16 1.96 .OO .72 ,055 .17 . l l 1.96 .253 - .03 .17 .45 .38 3.92 ,127 .54 .17 .45 .38 1.96 .387 .80 ,004 .132 .864 3.92 .193 -1.00 .015 ,285 .70 3.92
U14 u12 U18 U15 U16 U17
Blue Light blue Yellow-green Green-blue Yellow-green Yellow -peen
0.060 .010
A3 A6 A2 A4 A1
Blue Green-blue Blue Green-blue Violet
+ -
(b) Urea-Perchloric Acid Buffers -0.32 0.37 0.40 0 . 2 3 - .51 .20 .40 .40 .300 - .52 .02 .32 $66 .465 .335 .080 - .58 .20 .025 .33 .140 - .90 .645 .158 -1.12 .01 .25 .74
PKI'
OK,'
-0.17 -0.57 .16 - .20 - .63 .14 .39 - . l o - .12 .61 -72 .02 .28 - .61
+ + + +
-
+
1.96 -0.29 -0.56 .51 1.96 - .21 .68 .20 3.92 .72 1.96 - .21 3.92 .22 .61 .28 .65 3.92
+
+
+
-
(c) Acetoxime-Sulfuric Acid Buffers 0.20 +0.61 0.59 0.26 0.15 1.96 $0.25 $0.37 .44 .42 .20 .43 .37 1.96 .75 .35 .10 .21 .63 .22 .15 1.96 - .25 .04 .35 - .25 .13 .46 .41 1.96 .283 .20 .08 .10 1.96 -1.26 - .15 .01 .25 .82
+ +
+ + -
+
+
Throughout this paper we have used the same arbitrary convention in regard to the placing of the P H ( ~ * scale ~ ) as that used in the previous papers of this series. The actual.numerica1 values of the #K's are therefore given in terms of the zero point of that scale. The uncertainty in the reproducibility of the PHvalues is probably about *0.02. The data given in Table 111 are plotted in Fig. 2. The smooth curves developed from the fundacorrespond to equations relating #K' and mental Debye-Hiickel Equation 3. -logy =
Az2 4 1 + B a 4
(3)
Nov., 1930
STRENGTH OF WEAK AND PSEUDO BASES
4441
Taking the dielectric constant of the medium as 10 and the temperature as 25’, the values of A and B are found to be 11.15 and 0.921 X lo8. Substituting we obtain Equation 4
- log
=
11.15 .z*
1
6
+ 0.921 X 10%
