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Differentiation of Strong Acids by Conductometric Titration in Glacial Acetic Acid.

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Differentiation of Strong Acids by
Conductometric Titration in Glacial Acetic Acid
By Dr. B. Sansoni
Chemisches Institut der Universitat Marburg/Lahn
Strong acids are buffered by water to the acid strength of
the hydroxonium ion OH3@,so that titration of a mixture of
HClO4, H2SO4, H N 0 3 , and CCI3COOH with O H @ ion
produces only a single end-point. On the other hand, in
glacial acetic acid which is a substantially more weakly basic
solvent, the solvated hydrogen ion CH3COOHz0 is more
acidic than OH30 in water, and an equilibrating buffer effect
begins only at correspondingly higher acid strength. In
glacial acetic acid, HC104, H2S04 (first dissociation stage),
p-CH3-C6H4-S03H1 and HCL have p K values of 4.87,
7.24, 8.46, and 8.55, respectively, and according to other
data [ I ] , the relative strengths of 0.005 N HC104, HBr,
H2S04, HCI, and HNO3 are 400:160:30:9:1. These differences in acid strength, as well as the differing tendencies of
the individual acids to undergo ion association to ion pairs
or triple ions [2], make it possible to achieve conductometric differentiation of strong acids in glacial acetic acid.
Titration of H2S04 in glacial acetic acid yields two distinct
equivalence points corresponding t o HSO4@ and SO420 ;
differentiation of binary mixtures, for example of H2S04 and
HCI, is also possible [3]. Conductometric titration with 0.5 M
sodium acetate in glacial acetic acid can be used to differentiate complex mixtures of strong acids. The apparatus used
entailed a high-precision bridge with logarithmic indicating
amplifier (Type WBR TAV) and unplatinized Pt-electrodes,
and measurements were made in analytical grade glacial acetic
acid (0.1-0.2 7; H20) in an adjustable cell at 20.0 = 0.1 "C
with exclusion of moisture. The mixtures HC104/HzS04/
HS04;', HC104/HN03, H2S04 HBr/HS04. HC104/HzS04/
HNOj/HSO? and HC104/H2S04/HNO~/HSO~/CC13C0OH
all gavereproducible, analyticall yevaluable points of inflection.
Finally, as many as six points of inflection are recognizable
i n the titration of the mixture HC104/p-CH3-CaH4-S03H/
H2SO?/HNO~/HSO4@/CCI3COOH(Fig. 1).
acids as impurities (from Messrs. Riedel De Haen), gave
four points of inflection.
Corresponding titrations in propionic acid with sodium
propionate proceeded unfavorably; probably both the acidity
and dissociation are too low in this case. Formic acid also
proved unsuitable; it is, of course, a stronger acid than glacial
acetic acid, but its high autoprotolysis constant (1.0 x 10-6,
cf. acetic acid: 3.5 x 10-15) [I], indicates a very high basic
strength. This produces a buffering effect similar to that which
occurs in water.
Received, December 3rd, 1963
[Z 634/466 1El
German version: Angew. Chem. 76, 184 (1964)
[*] Part 4 of a series on Separations in Non-aqueous Solvents;
Part 3: Angew. Chem. 75, 418 (1963); Angew. Chem. internat.
Edit. 2, 615 (1963). Work carried out in collaboration with the
following students: U.Murowski, H.-B. Kuhnhen, B. Berrang, H .
Arold, H . Cunrze, and E. Sebastiani and reported in a lecture in
March 1963 at the H. C. 0rsted Institute, University of Copenhagen (Denmark).
[l] S. Bruckenstein and I. M . Kolthoff in I. M . Kolthqff;Ph. J .
Elving, and B. B. Sandell: Treatise on Analytical Chemistry. The
Interscience Encyclopedia Inc., New York 1959, part I, Vol. 1,
p. 475.
[2] R . M . Fuoss and C. A . Kraus, J. Amer. chem. SOC.55, 2387
(1933); R. Stolz, Ph. D. Thesis, Universitat Marburg, 1963.
[3] ti. Jander and G . Mass, Fortschr. chem. Forsch. 2, 619
(1953); T. Higuchi and C . R . Rehm, Analytic. Chem. 27, 408
(1955); A . M . Shodkin and N . A . Izrnailov, Zh. obshch. Khim. 20,
39 (1950).
[4] D . B. Bruss u. ti. E. A . Wild, Analytic. Chem. 29, 232 (1957):
W. Stuck, Z . analyt. Chem. 177, 338 (1960).
Reaction of Potassium Xanthate with
Diaryldichloromethanes, a New Thioketone
Synthesis I*]
By Prof. Dr. A. Schonberg and Dipl.-Chem. E. Frese
FakultPt fur allgemeine Ingerieurwissenschaften
der Technischen Universitlt Berlin (Germany)
Diaryldichloromethanes (f) react with one equivalent of
potassium xanthate to give diarylchloromethyl xanthates ( 2 ) ,
which cannot be isolated; these decompose exothermically
according to Equation (1) to form thioketones (3) and 0ethyl chlorothioformate. The reaction in boiling petroleum
(b.p. 10O-14O0C) or in hot dimethylformamide, in which
potassium xanthate is readily soluble, is complete in ca. 1 h ;
at room temperature, it requires ca. 24 hours. The yields of
the resultant thioketones, which were shown by melting-point
determination and analysis to be almost pure, are consistently
greater than 90 %.
05M NaOAc[mll-
Fig. 1. Conductometric titration of a mixture of 0.69 mmole of HClO4
(70 %)/0.78 mmole of p-CHs-C&-SO~H/l.05
mmole of HzSO4
(97 %)/1.23 mmole of HNO, (100 %)/0.62 mmole of CC1,COOH in
99 nil of glacial acetic acid 4- 1 ml of water with 0.5 M CHsCOONa.
experimental measurements.
- - _ _ _ - - _theoretical equivalence points.
Curve I (left-hand ordinate) H [lO4mho cm-11.
Curve I1 (right-hand ordinate) scale degrees (measurements were a
nonlinear function of x ) .
Examples of compounds prepared by this route are p,p'-dimethoxythiobenzophenone, xanthione, and I-thioxanthione,
and the previously unknown deep blue-green, solid 1,4-bisthiobenzoylbenzene, m.p. 140- 142 "C.
R\ /C'
The sequence of equivalence points generally corresponds
roughly to the acid strengths is glacial acetid acid. The best
conditions were obtained with the addition of about 1 %
water. 'Figure 1 shows the most extensive differentiation of
strong acids known to us that has',been obtained using acidbase titrations [4]. A mixture of the acids CH2CICOOH/
CHC12COOH/CC13COOH gave three equivalence points;
commercial H4P207, containing mono- to pentaphosphoric
Angeiv. Chern. ititernat. Edit. / Vol. 3 (1964) 1 No. 3
i Cl-CS-OCzH5
2 I<S-CS-OC,f!S
\S -C
S-OC *H5
f 1)
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acid, titration, strong, differentiation, acetic, glacial, conductometric
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