Indian Journal of ChemistryVol. 23A, May 1984, p: 448

Potentiometric Titrations with Anti-mony (V) Chloride in Non-aqueous Medium

A V NAIDU, C V RAJESWARI & P R NAIDU·

Department of Chemistry, Sri Venkateswara University,College of Engineering, Tirupa ti 517 502

Received 29 July 1983; revised and accepted 29 December 1983

Antimony (V) chloride in methyl ethyl ketone medium has beenused as a titrant for the potentiometric determination of urotropine(hexamine), 3-picoline, dibutylamine, cyclohexylamine, pyrrolidine,4-aminopyridine, and piperidine. The results show thatsemimicro quantities of the nitrogen bases can be determinedaccurately employing antimony (V) chloride as a titrant.

A survey of the literature shows that the Lewis acidshave been used only to a limited extent as titrants innon-aqueous media 1-5. The present work has beentaken up to study the use of antimony (V)chloride as atitrant for the determination of nitrogen bases such asurotropine (hexamine), 3-picoline, dibutylamine,cyclohexylamine, pyrrolidine, 4-aminopyridine andpiperidine in non-aqueous media.

Potentiometric determination of hexamine withantimony (V) chloride was carried out in threecommonly used solvents, namely, acetic acid,chloroform and methyl ethyl ketone (M EK). ME K hasbeen found to be the best solvent because it gives thebest potential jump, dissolves a wide variety ofmaterials, is sufficiently weakly acidic to permit thetitration of very weak acids and is sufficiently weaklybasic to be good differentiating solvent as reported byHarlow et al,", Hence MEK was chosen as the solventfor all further titrations.

All the reagents used were of AR grade. The solventMEK was dried over anhydrous potassium carbonatefor 24 hr and then distilled using a fractionatingcolumn. The liquid bases were purified by standardmethods 7. The purities of the solvent and the liquidbases were checked by comparing the measureddensities (using a bicapillary pycnometer reported byNaidu and Krishnan'') with those reported inliterature. The purity of the solid bases was ascertainedby their melting points.

A stock solution of antimony (V) chloride (I M) wasprepared by mixing ice-cooled antimony (V) chloride(7 ml) with the ice-cooled MEK (50 ml). The stocksolution was further diluted with the solvent to obtaina solution of desired concentration. The acid solutionwas standardised potentiometrically using a standardsolution of sodium acetate. The sodium acetatesolution was prepared by dissolving an accuratelyweighed quantity of the salt in the minimum quantity

448

Table l+-Results of Potentiometric Titration of SomeNitrogen Bases Against Antimony (V) Chloride

Base Amount (mg) Difference

Taken Found (mg)

Urotropine 59.0529.5254.2627.1338.2419.1235.3317.6638.0819.0441.7420.8648.3323.96

58.4329.5454.0027.2238.5919.4435.0017.5237.3719.1442.1220.8148.4224.16

-0.620.02

-0.260.090.350.32

-0.33-0.14-0.71

0.100.35

-0.050.090.20

3-Picoline

Dibutylamine

Cyciohexylamine

Pyrolidine

4-Aminopyridine

Piperidine

of acetic acid as the salt was not freely soluble in MEK,and then it was diluted with MEK. The presence ofsmall amounts of acetic acid did not interfere with thetitration". Weighed samples of the bases weredissolved directly in the solvent.

The end point was located potentiometrically usingan Elico digital pH -rneter fitted with a glass-saturatedcalomel electrode assembly. The volume of the titrantcrresponding to the end point was determined by thecalculation method 10. In all the cases the base to acidmole ratio was found to be I: I.

The titration results are presented in Table I. Theresults of the investigation show that solution ofnitrogen bases of the order of I x 1 -2 M can besuccessfully titrated with antimony (V) chloride withan accuracy of ±2% in non-aqueous medium. Theaccuracy of the results presented here parallels thatobserved using chlorosulphonic acid as a titrant 1 .

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