Indian Journal of ChemistryVol. 23A, March 1984, pp. 248-249

Hydrazine Carbothioamide 2-[(4-Hydroxy-3-methoxyphenyl)methylene] as aSelective Reagent for Mercury(lI)

K N THIMMAIAH*, H SANKE GOWDA & MAQBOOLAHMED

Department of Post-graduate Studies & Research in Chemistry,University of Mysore, Manasagangotri, Mysore 570006

Received 22 February 1983; revised 26 AprU1983;accepted 28 October 1983

Hydrazine carbothioamide 2-((4-hydroxy-3-methoxyphenyl)me-thylene] is proposed as a selective reagent for the rapidspectrophotometric determination of mercury(II). The reagentinstantaneously forms an orange yellow coloured I: 2 complex inalkaiine medium at room temperature. The complex exhibits anabsorption maximum at 402 nm with a molar absorptivity of \.37x 104 litre mol- 1 em' I. Beer's law is valid over the concentrationrange of 0.1-9.5 ppm of Hf(II).

Mercury is an health hazard in places where themercury/electrolytic cells operate. The volumetric andgravimetric methods are rather time consuming andseldom applicable to microgram quantities+". Alimited number of reagents available for thespectrophotometric determination of mercury sufferfrom one disadvantage or the other. Hydrazinecarbothioa mide 2- [( 4-h ydroxy- 3-methox y-phenyl)methylene] (HCHMM) was prepared byGuha-Sircar et al? who used it as a reagent for thedetection of few metal ions. In this note we report theusefulness of HCHMM, as a sensitive and selectivereagent for the rapid spectrophotometric de-termination of mercury(II).

The stock solution of mercury(II) was prepared bydissolving mercury(II) chloride ( 1 g, A R) in 0.1 Mhydrochloric acid (I litre) and the solution wasstandardized by the potassium iodate method".HCHMM was prepared by the reaction of hydrazinecarbothioamide with vanillin and was purified by therecommended method". A 0.3% solution ofHCHMMwas prepared in 85~~ aq. ethanol (v/v).

Solutions of diverse ions of suitable concentrationswere prepared using analytical grade reagents.

A Beckman spectrophotometer, model DB withmatched I em silica cells was used for absorbancemeasurements.

ProcedureTo an aliquot of the stock solution containing 5-

237.5 pg of mercury(II), was added ethanol (6 ml),HCHMM (3ml, 0.3%) and sodium hydroxide (I M,

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3.5 ml) and the resulting solution was diluted to 25 mlwith doubly distilled water. It was mixed well and theabsorbance measured at 402 nm against a reagentblank prepared in the same manner. The amount ofmercury was then deduced from the standardcalibration graph.

HCHMM instantaneously forms an orange yellowcomplex with mercury(II) in acid medium (HCI,H2S04, CH3COOH or H3P04) as well as in alkalinemedium at room temperature (27°C). However, thecomplex is stable in acid medium for less than 2 min;while it is stable for I hr in alkaline medium, hence thealkaline medium was chosen. The complex givesmaximum absorbance in the NaOH concentrationrange of 0.08 to 0.24 M. Hence, all studies wereconfined to 0.14 M sodium hydroxide. The effectiveethanolic concentration is 28-72 % (vIv). Below thisalcoholic range turbidity is obtained while above thisrange maximum absorbance is not attained. Hg(II)-HCHMM system absorb maximally in the region 400-404 nrn: at this wavelength the absorption due to thereagent and Hg(II) solution is negligible. A twenty-one-fold molar excess of the reagent over mercury (II) isrequired in order to obtain maximum absorbance. Theabsorbance readings are constant in the temperaturerange 5-400C. Above 40°C the absorbance graduallydecreases The order of the addition of reagents was notcritical.

The I {g(Il)-HCHMM complex obeys Beer's lawover the concentration range of 0.2-9.5 ppm ofmercury. The optimum concentration rangeevaluated by Ringbom's method is 0.5-9.3 ppm. Themolar absorptivity is 1.37 x 104 litre mol ? em -I andSandell's sensitivity is 14.6ngcm -2. The standarddeviation calculated from 10 determinations insolutions containing 4ppm of rnercuryfll) each is 0.006ppm. Errors are in general about ± 2:%;.

Job's method of continuous variation":" and molratio" method indicate the formation of 1:2 complex(metal-ligand) having a log K value of 6. 7 at 2rc. Ionexchange experiments indicate that the complex iscationic in nature.

The following amounts (J1g/ml) of foreign ions werefound to give less than 2~<>error in the determination of4 pg of mercurytl l) per ml. Sb(III) 60, Curll) 1.8, Ag(n15, Ru(Un 16, Os(VIIn 15, Jr(IIn 10, Pb(ln 120, Bi(IIn12, Bi(IIn 36**, Fe(III) 40, Fe(IIn 71t. Ni(In 1.5, Ni(In2.5*, zenn 118, Zn(m 140*, Rh(IIn 12, Pt(IY) 14,Pt(IY) 20t, Pd(IJ) 1.4, Pd(II) 1.6**, Co(In 10.4, Au(IIn14, Au(HI) 20**, Ti(IY) I, Cr(VI) 20, Mn(In 2, W(VI)1449, Cd(In 45, C<1(1n 140**, Se(In 118, As(IIn 146,

fluoride 10800, chloride 67000, bromide 96000, iodide5600, nitrate 9600, sulphate 9600, phosphate 860,acetate 5600, citrate 7600, and EDT A 440. Manycations and anions do not interfere. Interference fromplatinum metals and other cations could be reduced byusing citrate*, phosphate** and EDT At as maskingagents.

The method was extended to the determination ofmercury in synthetic mixtures corresponding tominerals, alloys and chlorite cell liquors. The resultsobtained were quite satisfactory.

ReferencesI Coetzee J F. Mercury: Treatise on analytical chemistry, Vol. 3,

NOTES

edited by I.M. Kolthoff & P.J. Elving (Interscience, NewYork), 1961,231.

2 Kodama K, Methods of quantitative inorganic analysis(Interscience, New York), 1963, 150.

3 Guha-Sircar S S & Satyabadi Satpathy, J Indian chem Soc. 31(1954) 450.

4 Vogel A I. Quantitative inorganic analysis (The ELBS &Longmans, London), 1975, 377.

5 Bernstein J, Yale H L, Loosee K, Holsing M, Martins J & LoU WA, J Am chem Soc, 73 (\951) 906.

6 Job P. Justus Lieligs Ann Chern, 9 (1928) 113.

7 Irving H & Perce T B, J chem Sac, (1959), 2565.

8 Yoe J H & Jones A L, lnd Engng Chern, Anal Ed, 16 (1944) Ill.

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