86

Cx.PRABttAKARI~AOand A. R. VASVDEVAMVRTHr

Bd. 177

U m die verschiedenen Phasen der Hydrolyse auch nur halbquantitativ erkl~ren und die sich w~hrend der Hydrolyse abspielenden ehemisehcn Prozesse aufdeeken zu k6nnen, sind jedoch noeh zahlreiche Untersuchungen notwendig. Zusammenfassung

Verfasser bcs~immten mit Hilfe ihres bereits friiher ver6ffentlichten Verfahrens den Ammoniak-, Cyanid-, Nitrit- und Nitratgehalt der unter identischen ]3edingungen hergestellten alkalischen Itydrolysate einiger Salpeters~iureester (Glycerintrinitrat, PentaerythrittetraIfitrat, ,,Nitrost/~rke" und ,,Nitrocellulose") und bereehneten das wechselseitige Verh/iltnis des Nitrat- uud Nitrit-Stickstoffs in diesen Hydrolysaten. I m Mittel betrug das Verh/~ltnis beim Pentaeryth~ittetranitrat 1:0,83, beim Glycerintrinitrat und bei der Nitrost~rke 1 : 2 , 1 4 und bei der Nitrocellulose 1:1,46. I m Gegensatz zu den fibrigen untersuchten ,,Nitrok6rpern" konnte im Hydrolysa~ des Pentaery~hrittetranitrates kein Cyanid nachgewiesen werden. Die Analyseergebnisse sind zur Charakterisierung der ,,Nitrok6rper" geeigne~. Literatur I SCHULEK, E., K. BURGERU. •. FEH~R: diese Z. 167, 28 (1959). -- 2 SCHULEK,

E., K. BURGEIr U. NI. FEH~R: diese Z. 167, 423 (1959). -- 3 Se~ULEK,E., u. B. KER~,N~: Pharmaz. Zentralhalle Deutschland 73, 241 (1932). Prof. Dr. E. SCHULEK,Budapest VIII., l~uzeum-kSrfit 4/b (Ungarn)

Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore, India

Cerimetry in Nonaqueous Media By G. PR~HAKAR RAO and A. R. VASUDEVA MURTHY

(ReceivedJune 20, 1960) Titrations in nonaqueous media have been so far mostly confined to neutralisation reactions. This versatile technique has not been applied extensively as an analytical tool to study the oxidation reduction reactions. There is very little information in literature covering this fieldS,% Preliminary experiments carried out b y the present authors indicated t h a t a solution of a cerie salt in aeetonitrile could oxidize quantitatively a solution of xanthate in the same solvent. An analytical method could be developed on the basis of this observation which is described in this short communication.

1960

Cerimetry in Nonaqueous l~ledia

87

Standard Ceric Solution. A deci-normal solution (or of any other suitable strength) of eeric ammonium nitrate was prepared by dissolving the appropriate quantity of pure salt in acetonitrile and making up the solution in a standard volumetric flask. The solution is coloured orange red. I t is stored in coloured glass stoppered bottles and kept in a dry chamber. The strength of such a solution can be checked by the following method: An aliquot of ceric ammonium nitrate in aeetonitrile solution was run down into acidified potassium iodide solution and the liberated iodine was titrated with standard thiosulphate using starch as indicator towards the end point of the titration. The strength of the standard ccric solution obtained by this method was found to be 0.04950 iN. This procedure was found to be satisfactory. I t was reported ~ that the presence of cerous salt would catalyse the oxidation of hydroiodic acid by the dissolved oxygen in aqueous solution. So it is preferable to avoid such errors by removing the dissolved air by bubbling nitrogen to expel the dissolved oxygen. Standard Xanthate Solution. A pure sample of potassium ethyl xanthate was prepared by the standard method described in literature s by digesting a known amount of carbon disulphide in freshly prepared alcoholic potash. The purity of the sample was checked up by iodine1, 6 and chloramine-T 7 methods. A known amount of xanthate (5--25 nag) was dissolved in aeetonitrile (10--15 ml) and used for titration with ceric solution. Titration Procedure. The standard ceric solution was run down from a micro burette duly protected from atmospheric moisture by drierite guard tubes. The titrant was taken in a suitable conical flask into which the oxidant was added. During the titration the orange yellow colour of the ceric salt disappeared instantaneously and a white precipitate separated out and settled down at the bottom. This precipitate on analysis was found to be cerous salt. At the end point the solution attained a light yellow colour of ceric solution and the end point was quite sharp. There was no difficulty in locating the end point. The results of a few representative experiments are given below:

Table 1

~o.

l~[oles o f xanthate taken

I~oles o f ceric a m m o n i u m nitrate consumed

. i0-~

Error ~

9 10-8

25.84 51.69 77.56 103.4

25.64 52.50 78.14 103.8

--0.77 1.5 0.7 0.4

I t c a n be seen f r o m t h e r e s u l t s t h a t for e v e r y o n e m o l e o f x a u t h a t e u s e d o n e m o l e o f ceric s a l t w a s c o n s u m e d . T h e p r o b a b l e p r o d u c t o f t h e o x i d a t i o n is d i x a n t h o g e n a n d t h e r e a c t i o n m a y be r e p r e s e n t e d as follows : 2 S = ,C(/SK ~ O E t - ~- 2 Ce(N08) a -+ S = C - S - S - C -----S -t- 2 K N O a + 2 C e ( N 0 3 ) 3

I

OEt

I

OEt

T h e d i x a n t h o g e n p r o d u c e d in t h i s r e a c t i o n was n o t o x i d i z e d f u r t h e r . This was confirmed by a separate experiment where in a known amount o f d i x a n t h o g e n ( p r e p a r e d a c c o r d i n g t o t h e m e t h o d of DESAINS 2 w a s t a k e n

88

G. P~ABUAKA~gAO et al. : Cerimetry in Nonaqueous Media

Bd. 177

in acetonitrile. Such a solution did not consume any oxidant. Thus quantitative estimation of xanthate could be done by this method at comparatively low concentrations within an accuracy of • 1.5%. However, it has to be pointed out that if the xanthate taken is in larger quantities the precipitate separated ~dll be larger in quantity and also the dixanthogen produced will be in larger concentration and mask the end point and the end point appears at an earlier stage than the theoretically required amount for complete titration. For instance the following values were obtained when larger amounts of xanthate were taken for estimation. Table 2 ~[oles of x a n t h a t e taken

Moles of x a n t h a t e found

9 10-~

.10-6

354.6 517.8 615.3

336.6 481.2 564.3

Therefore larger concentrations are to be avoided. Among the eerie salts tried eerie ammonium nitrate was found to be the best solute in acetonitrilc. The strength of the eerie solution in this solvent was observed to be quite stable even for several days. For example the titre value against standard thiosulphate of a typical standard solution remained same within the limits of experimental error as indicated by the following data. Table 3 Days

Titre value against thiosulphate

0

1

[

2

3

4

15

!5.13

5.13

5.13

5.10

5.10

5.10

Ceric ammonium nitrate in acetonitrile is superior to other eerie solutions in nonaqueous media described in literature9 O. N. H~SSVARK and K. G. S T O ~ ~ have used ceric ammonium nitrate in acetic acid for titration of oxalic acid and found that the solution is not stable even for 24 hrs. Moreover the preparation of the reagent is difficult as the salt is not easily soluble in the medium prescribed. In the case of the reagent described in the present investigation it is free from any of these limitations and is decidedly more suited for a general oxidation reaction. Other physieo chemical methods of studying these reactions with various types of reducing agents in nonaqueous media are in progress9 The authors wish to express their grateful thanks to ProL M. 1~. A. I~AOfor his keen interest in the work9

1960 SZEKEgESU. BAK.~CS-POLG~,g: Alkalicarbonat neben Alkalihydroxyd

89

References 1 DELACHA~AL,B., and A. MEg~ET: Ann. Chim. Phys. 12, 108 (1877). -" DESAINS:Cf. Beilsteins tIandbuch der 0rganischen Chemic, Vol. III, p . 2 1 4 . a FOSTE~g,L. S. : Dept. of Mining and Metallurgy Res. Tech. Paper No. 2 ppn. of Xanthates and Thiocarbonates (1927). (cited from Gandin's Text Book on Flotation, p. 224). -- 4 FVRMA_~,N. H., and J. I-L W~LLAeE: J. Amer. chem. Soc. 53, 1283 (1931). -- 5 ttI~SVAnX, O.N., and K. G. STO~: Analyt. Chemistry 28, 334 (1956); cf. Z. analyt. Chem. 153, 313 (1956). -- 6 MATUSZAK,M. P.: Ind. Engng. Chem., anal. Edit. 4, 98 (1932) ; cf. Z. analyt. Chem. 96, 459 (1934). -- ~ MV~THu A. g. VASVDEVA and V. l~. SATYA~AgA~A~ I~AO: Talanta 1960 (under publication). -- s To3~15~, 0., and A. HEYgOVSK~: Collect. ezeehoslov, chem. Commun. 15, 997 (1950). -- 9 TONIS~K, O., and J. V~I~e~A: Collect. czechoslov, chem. Commun. 16, 113 (1951); cf. Z. analyt. Chem. 137, 215 (1952/53).

Dr. A. t~. VASVDnVAMVgWHY, D. Sc., Dept. of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore-12 (India)

Aus dem Chemischen Institut der Hochschule fiir Veterin~rwissenschaften, Budapest

Bestimmung yon Alkalicarbonat neben Alkalihydroxyd Von •. SZEKERES und E. BAKACS-POL6~R (Eingegangen am 20. Juni 1960)

I n einer friiheren M i t t e i l u n g l , s h a b e n wir ein Verfahren zur Bestimm u n g y o n A l k a l i h y d r o x y d n e b e n A l k a l i c a r b o n a t beschrieben, das ebenso wie eine i n d e n l e t z t e n J a h r e n mitgeteilte weitere Methode 2 n u t d a n n eine zuverlfissige A n a l y s e d u r c h z u f i i h r e n gestattet, w e n n die zu prtifende L6sung eine im Verh~iltnis zur K o n z e n t r a t i o n der C a r b o n a t i o n e n hohe H y d r o x y l i o n e n k o n z e n t r a t i o n besitzt. U n s e r ~m folgenden beschriebenes Verfahren bJetet demgegeniiber deR Vorteil, d a b es bei allen willkiirlieh gews M o l k o n z e n t r a t i o n e n tier H y d r o x y l - u n d C a r b o n a t i o n e n geniigend genaue R e s u l t a t e liefert. Wie iiblieh sind 2 T i t r a t i o n e n d u r c h z u f i i h r e n : 1. Der G e s a m t a l k a l i g e h a l t wird a u f b e k a n n t e Weise aeidimetrisch i n Gegenwart y o n M e t h y l o r a n g e als I n d i c a t o r ermittelt. 2. Z u r B e s t i m m u n g der C a r b o n a t i o n e n wird der zu priifenden LSsung eine gemessene iibersehiissige Menge einer S t r o n t i u m n i t r a t l S s u n g b e k a n n t e r K o n z e n t r a t i o n zugefiigg. Das S t r o n t i u m e a r b o n a t f/illt n a e h kurzer Zeit k r i s t a l l i n aus. Der i n L 6 s u n g verbliebene Teil des S t r o n t i u m s wird n a e h Z u g a b e y o n ) [ t h a n o l m i t A D T A - M a g l 6 s u n g in Gegenwart y o n M e t h y l t h y m o l b l a u als I n d i c a t o r titriert. M a n k a n n die B e s t i m m u n g aueh m i t einer B a r i u m n i t r a t l 6 s u n g durchfiihren, doeh ist der I n d i c a t o r U m s e h l a g bei A n w e n d u n g y o n S t r o n t i u m n i g r a t besser siehtbar.