Determination of cyanide in the pure state and in mixtures with organic halosulfonamides

MICROCHEMICAL

JOURNAL

Determination

34, 103- 114 (1986)

of Cyanide in the Pure State and in Mixtures with Organic Halosulfonamides

B. THIMME GOWDA,*J B. S. SHERIGARA,~AND D. S. MAHADEVAPPA~ *Department of Chemistry, Hydrocarbon Research Insiitute, University of Southern California, Los Angeles, California 90089-1661: iDepartment of Chemistry, Mangalore University, Mangalagangothri, 574 199, Mangalore, India; and $Depurtmenr of Chemistry, Manasa Gangotri, University of Mysore, Mysore 570 006, Indiu

Received June 30, 1983 Eight aryl halosulfonamides, both mono and dihalo compounds, have been prepared and characterized by recording their IR and NMR spectra and successfully used for determining cyanide in solution. The behavior of these compounds as oxidimetric analytical reagents toward CN- ion in metal salts and complexes has been investigated and general procedures for its estimation in the pure state, in the presence of halide or in cyanide and thiocyanate mixtures, have been proposed. The same procedures are also useful for computing the number of cyanide ligands present in the complexes. The results are reproducible and compare favorably with the argentometric method. The oxidation involves a two-electron change per CN- ion. % 1986 Academic Precs. Inc.

INTRODUCTION

Cyanides have a number of industrial applications such as in the extraction of noble metals, in photography, in the paper industry, and in the preparation of insecticides and various cyanogen derivatives. In view of the importance and potential hazards of these compounds, simple, rapid, and accurate analytical procedures are essential for their estimation in solution. Although there are a number of reports on the oxidation of cyanides few analytical techniques are available for their estimation in solution. The reagents so far used for their determinations include silver nitrate (.?2), alkaline KMnO, (17), iodine (17), periodate (24), lead tetraacetate (II), and some of the aromatic haloamines (11, 25). Although some of the organic halosulfonamides have been individually employed for determining cyanides on certain occasions (11, 25) general procedures for estimating CN- ion in metal salts, complexes, and mixtures, with these oxidants, are lacking. As part of our program of developing sensitive techniques for the estimation of cyanides and other important compounds in solution, the behavior of halosulfonamides as oxidimetric reagents toward CN- ion in metal salts and complexes has been investigated in this paper. Further, the paper reports methods for the estimation of cyanide ion in mixtures containing halides and thiocyanate. The following cyanides were selected in the present investigation. (1) potassium cyanide, KCN

(2) sodium cyanide, NaCN

soluble

cyanides

I

1 To whom correspondence should be addressed. Present address: Department of Chemistry. Mangalore University. Mangalagangothri. Mangalore 574 199, India. 103 0026-265X186$1.50 Copyright 0 1986 by Academic Press, Inc. All rights of reproduction in any form reserved.

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(3) silver cyanide, AgCN insoluble cyanides (4) zinc cyanide, Zn(CN), I (5) potassium dicyanoargentate(I), KAg(CN), (6) potassium tetracyanozincate(II), K,Zn(CN), I complex cyanide The chemistry of N-halo-N-sodio and N,N-dihalo aromatic sulfonamides, Cl-l3 / \ u (orIi)

+“(o’x) 0

X

where M = Na and X = Cl or Br has evinced considerable interest because they act as sources of both halonium cations and N-anions which act as both bases and nucleophiles. They interact with a wide range of functional groups in aqueous, partially aqueous, and nonaqueous media in the presence of acid or alkali. Generally monohaloamines undergo a two-electron change while dihaloamines are four-electron oxidants. The reduction products are the respective sulfonamide and NaX and HX. The following oxidants were employed in the present investigation: (1) N-chloro-N-sodio-p-toluenesulfonamide, p-CH,-C,H,SO,NClNa, well known as chloramine-T (CAT, RNClNa, where R = p-CH,-C,H,SO,) (2) N,N-dichloro-p-toluenesulfonamide, known as dichloramine-T (DCT, RNCl,) (3) N-bromo-ZV-sodio-p-toluenesulfonamide, bromamine-T (BAT, RNBrNa) (4) N,N-dibromo-p-toluenesulfonamide, dibromamine-T (DBT, RNBr,) (5) N-chloro-N-sodiobenzenesulfonamide or chloramine-B (CAB, R’NClNa, where R’ = C,H,SO,) (6) N,N-dichlorobenzenesulfonamide or dichloramine-B (DCB, R’NCl,) (7) N-bromo-N-sodiobenzenesulfonamide or bromamine-B (BAB, R’NBrNa) (8) N,N-dibromobenzenesulfonamide or dibromamine-B (DBB, R’NBr,) The chemistry of chloramine-T has been well established compared to the other oxidants (7). The redox potential of CAT/RNH* is pH dependent and decreases with an increase in the pH of the medium. Depending on the pH of the medium CAT furnishes different types of reactive species in solution (5, 12, 14, 15, 19, 28). Free chlorine has been detected in acid medium in the presence of chloride ion (12, 26). EXPERIMENTAL

All the materials used were of analar grade and triple-distilled water was used in preparing the aqueous solutions. AR potassium and sodium cyanides (Reanal, Hungary) were used without further purification, but the purity was checked by the argentometric method (32). Zinc cyanide was prepared by mixing zinc sulfate and KCN solution in a 1:2 ratio. The precipitate obtained was filtered, washed with water and dried over anhydrous calcium chloride. Silver cyanide was ob-

DETERMINATION

OF CYANIDE

ION

105

tained in a similar manner by mixing silver nitrate and KCN solutions in a 1: 1 molar ratio. K,Zn(CN), was prepared by dissolving zinc cyanide in aqueous KCN in a 1:2 molar ratio. The resulting solution was evaporated and cooled to obtain the crystals of the complex. KAg(CN), was obtained by dissolving AgCN in aqueous KCN in a 1: 1 molar ratio. The compounds were purified by recrystallization from aqueous solution and their composition was checked by elemental analysis. Metal(%) AgCN Theoretical Found

67.5 67.3 2 0.5

ZnKN), 55.7 55.9 5 0.4

KAgKN),

K,Zn(CN),

54.2 53.9 t 0.4

26.4 26.3 k 0.2

Preparation ofoxidants. Chloramine-T (E. Merck) was purified by the method of Morris et al. (19). Dichloramine-T (DCT) was prepared by the chlorination of CAT [solutions (16)], while bromination of CAT yielded dibromamine-T (DBT) (20). Partial debromination of DBT by dissolving it in 4 M NaOH gives bromamine-T (BAT) (21). Chloramine-B (CAB) was prepared by the partial chlorination of benzenesulfonamide (8) in 4 M NaOH for 1 hr at 70°C. Further chlorination produces DCB (34). Dibromamine-B is prepared by adding liquid bromine to aqueous CAB solutions (18) and BAB is obtained by the partial debromination of DBB (I). The purity of all the oxidants was checked by iodometric estimation of the amounts of active halogen present. They were further characterized by their IR (recorded on a Perkin-Elmer 298 grating infrared spectrophotometer) and Fourier transform ‘H and 13CNMR (obtained on a Bruker WH 270-MHz nuclear magnetic resonance spectrometer using TMS as the internal standard) spectra (2-4, 6, 22, 23, 30). Approximately 0.05 M solutions of the monohaloamines were prepared by dissolving requisite quantities of the solids in triple-distilled water. Solutions of dihaloamines were prepared in water-free acetic acid (glacial acetic acid containing 10% v/v acetic anhydride). All the solutions were standardized iodometrically and stored in brown bottles. The following buffer solutions were prepared as per standard methods (10): pH 1 and 2 (HCl + KCl); pH 3 (citric acid + Na,HPO,); pH 4-6 (acetic acid + sodium acetate); pH 7-9 (borax + boric acid + NaCl); pH 10 (NaHCO, + Na,CO,). Aqueous solutions (-2 mg/ml) of soluble cyanides, NaCN and KCN, and complex cyanides, KAg(CN), and K,Zn(CN),, were prepared. Aqueous KCN (0.025 M and solution should be standardized) was used as solvent for the insoluble cyanides, AgCN and Zn(CN),. Back titrations: Preliminary studies. Known quantities of the cyanide solutions

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AND MAHADEVAPPA

were added to known excess volumes of the oxidants in separate iodine flasks (with monohaloamines, the pH of the reductant solutions were adjusted to various values or made acidic or alkaline as desired prior to adding to the oxidant solutions). The reaction mixtures were set aside for various intervals of time at room temperature (-300 K) with occasional shaking. The excess oxidant in each flask left unused was determined iodometrically by back titration with standard thiosulfate. Extra care has to be taken while working with cyanides as these and their products are potentially dangerous. Aqueous starch solution (1%) was used as the indicator near the equivalence point. A typical set of preliminary results is shown in Tables 1-3. It was noted that with monochloramines (CAT and CAB) the oxidation is fast in the pH range 3-5 and slow in acid and alkaline solutions (Table 1). The two-electron stoichiometric oxidation per CN- ion was observed in 30 min with all the cyanides except silver compounds. With the latter the stoichiometric oxidation took 45 min. Oxidation of cyanides by monobromamines (BAT and BAB) is sluggish in .acid solutions and buffer solutions of pH I-10 but is rapid in alkaline solutions (Table 2). The two-electron stoichiometry per CN- was noted in 5-10 min in 0.05-0.20 M NaOH with all cyanides. The same two-electron stoichiometry per CN- was observed with dihaloamines in partially aqueous medium (oxidant solutions in water-free acetic acid and aqueous solutions of cyanides) in about 30 min (Table 3). It was further noted that the stoichiometric oxidation of Extent of Oxidation

TABLE 1 of Potassium Cyanide with Chloramine-T Solvent Media”

in Various

umole of CAT usedb/(*mole of KCN takenc Medium

5 min

10 min

20 min

30 min

0.025 M H,SO, 0.05 M H,SO, pH1 PH 2 PH 3 pH 3.5 pH 4.0 pH 4.5 pH 5.0 pH 6.0 pH 7.0 pH 8.0 pH 9.0 pH 10.0 pH 11.0 pH 12.0 pH >12

0.913 0.940 0.934 0.950 0.948 0.945 0.951 0.950 0.935 0.948 0.943 0.947 0.953 0.937 0.949 0.536 0.540

0.917 0.949 0.943 0.950 0.962 0.960 0.961 0.960 0.935 0.948 0.943 0.947 0.957 0.942 0.962 0.778 0.780

0.926 0.953 0.952 0.950 0.970 0.968 0.970 0.970 0.944 0.948 0.943 0.947 0.961 0.942 0.970 0.880 0.880

0.947 0.957 0.956 0.950 0.979 0.994 1.005 0.992 0.975 0.948 0.943 0.947 0.960 0.950 0.974 0.929 0.929

0 Number of pmole of KCN b CAT taken: c KCN taken:

electrons changing per mole of KCN is 2 x @mole of CAT used/ taken). 1098 pmole. 311 *mole.

DETERMINATION

107

OF CYANIDE ION

TABLE 2 Extent of Oxidation of Potassium Cyanide with Bromamine-T (BAT) and Bromamine-B (BAB) in Various Solvent Media in 10 Min Medium

p.mole of BAT used* pmole of KCN takenb

pmole of BAB used” pmole of KCN takenb

0.1 M HC104 0.1 M HCl 0.05 M H,SO, PH 1 PH 2 PH 3 PH 4 PH 5 PH 6 PH 7 PH 8 pH9 pH 10 0.002 M NaOH 0.02 M NaOH 0.05 M NaOH 0.10 M NaOH 0.20 M NaOH

0.055 0.062 0.039 0.061 0.052 0.071 0.069 0.089 0.068 0.397 0.851 0.990 1.000 1.005

0.045 0.055 0.045 0.065 0.060 0.040 0.060 0.055 0.070 0.070 0.095 0.080 0.445 0.710 0.840 1.000 1.000 1.000

a BAT or BAB taken: 500 pmole. b KCN taken: 153.6 pmole.

the reductants takes place within the specified time period with about a 50% excess of the oxidants. If the percentage excess is decreased relatively longer periods are required to achieve the stoichiometric oxidations. Recommended Procedures: (i) With monochloramines (CAT and CAB). Adjust the pH of the cyanide solution to 3-5 (preferably 4) with acetate buffer. Add aliquots of this solution to known volumes (-50% excess) of 0.05 M oxidant (CAT or CAB) in iodine flasks and set aside for about 30 min (45 min with silver compounds) shaking occasionally. Rinse down with about 25 ml of water, add 10 ml of 2 M sulfuric acid and 10 ml of 20% potassium iodide solution, and titrate with 0.05 M sodium thiosulfate (V, ml) to a starch endpoint. Run blanks with the same volumes of the oxidant alone (V, ml). (ii) With monobromamines (BAT and BAB). Add aliquots of the cyanide solution to known excess volumes (-50% excess) of 0.05 M oxidant (BAT or BAB) in iodine flasks containing enough sodium hydroxide to maintain an overall concentration of 0.05-0.20 N alkali. Set aside the reaction mixtures for about 10 min with occasional shaking. Complete the titrations as under (i), adding a sufficient amount of acid solution (20 ml of 2 M H,SO,). (iii) With dihaloamines (DCT, DBT, DCB, and DBB). Add aliquots of the reductant solution to known volumes (-50% excess) of 0.025 M oxidant containing about 30% acetic anhydride and set aside the reaction mixtures for about 30 min (45 min with silver compounds). Rinse down with about 50 ml of water and add 20 ml of 10% potassium iodide solution. Complete the determinations as before.

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THIMME GOWDA, SHERIGARA,

AND MAHADEVAPPA

TABLE 3 Extent of Oxidation of Cyanides by Excess Dichloramine-T (DCT) and Dibromamine-T (DBT) with Time” Time (min)

5 10 20 30 4.5 60

5 10 20 30 45 60

NaCN 365.2*

KCN 325.6*

0.438 0.467 0.493 0.500 0.500 0.504 337. lb

Dichloramine-Tc (pmole of DCT usedikmole of cyanide taken) 0.412 0.407 0.862 0.815 0.436 0.433 0.900 0.865 0.478 0.468 0.937 0.937 0.499 0.482 1.003 0.968 0.499 0.499 1.003 0.999 0.501 0.500 1.012 1.006 346.9* 323.2* 199.1* 104.76

1.696 1.833 1.971 2.004 2.004 2.016 81.44*

0.445 0.460 0.497 0.504 0.504 0.508

Dibromamine-Td (kmole of DBT usedikmole of cyanide taken) 0.447 0.456 0.900 0.897 0.476 0.464 0.919 0.924 0.497 0.472 0.956 0.976 0.501 0.487 0.994 1.003 0.504 0.503 1.003 1.003 0.504 0.503 1.003 1.009

1.850 1.909 1.968 1.998 2.005 2.013

AgCN 209.4*

Zn(CNh 199.lb

K&&N), 104.76

K,Zn(CN), 81.446

0 Number of electrons changing per mole of cyanide is 4 @mole of DCT or DBT used/p,mole of cyanide taken). * pmole of cyanide taken. c DCT taken: 320.9 pmole. d DBT taken: 547.5 kmole.

The amount of cyanide (micromoles) in the sample solution is given by 103M, (V, - VJIE, where M, is the molarity of thiosulfate and E is the number of electrons changing per molecule of cyanide; E = 2 for NaCN and KCN and E = 4 and 8 for KAg(CN), and K,Zn(CN),, respectively. Calculation of Recovery with Insoluble Cyanides (AgCN and Zn(CN)J. Add aliquots of insoluble cyanides (AgCN and Zn(CN),) in 0.025 M KCN to a known excess (-50% excess) volume of M2 molar oxidant. Set aside the reaction mixtures for different intervals of time with different oxidants as under (i), (ii), and (iii). Determine the unconsumed oxidant by iodometric titration with 0.05 N sodium thiosulfate (V, ml). Add the same aliquots of 0.025 M KCN to the same volumes of M2 molar oxidant as above under identical conditions. Titrate the unreacted oxidant, iodometrically, with 0.05 M thiosulfate (V, ml). Then the amount of insoluble cyanide (micromoles) in the sample solution is given by lo3 M,(V, - V,)/E, where E = 2 and 4 for AgCN and Zn(CN),, respectively, with M, is the molarity of thiosulfate. Direct Titrations. Direct titration of cyanide with most of the oxidants (except BAT and BAB) was found practicable in the presence of sodium acetate and potassium bromide (and acetic acid with CAT and CAB). Sodium acetate was found to catalyze the oxidations. The endpoints can be detected visually in an Andrews-type titration or by the potentiometric method. Premature endpoints were noted when the oxidant was added to cyanide solution containing acetic acid,

DETERMINATION

109

OF CYANIDE ION

possibly due to the loss of HCN. The reductant solution was added to aliquots of the oxidant solution. However, the titration assembly was designed to minimize the loss of HCN or Br, from the solutions. Recommended procedure. Take V ml of M, molar oxidant solution in a titration assembly. Add 5 ml of 1 M potassium bromide, 5 ml of 10% sodium acetate, and I ml of carbon tetrachloride (and also 5 ml of glacial acetic acid with CAT and CAB) and titrate with the cyanide solution with stirring until the bromine disappears from the organic layer. Alternatively, use potentiometric determination of the endpoint for the titration done in the same way. A potential jump of - 100-200 mV was noted for the addition of 0.05 ml of 0.025 M reductant at the endpoint. The amount of cyanide (micromoles) in the volume of cyanide solution used for the titration is lo3 E,M,V/E, where E, is the number of electrons changing per mole of oxidant; E, = 2 and 4 for monohaloamines and dihaloamines, respectively. E has the same meaning and values as before for soluble and complex cyanides. With insoluble cyanides the recovery is calculated as follows: If a ml of cyanide mixture is required for V ml of oxidant, the volume of oxidant (W ml) required for a ml of 0.025 M potassium cyanide would be W = 2 x O.O25alM,. Then (V - w) ml of the oxidant would have been used for the oxidation of the insoluble cyanide. The amount of insoluble cyanide (micromoles) in the sample is 103E, M,(V W)lE, where E is again 2 and 4 for AgCN and Zn(CN),, respectively. The reproducibility and accuracy of the results of determinations are shown in Table 4. TABLE 4 Reproducibility and Accuracy of the Results of Determination of Cyanide Ion in Metal Salts and Complexes by Arylhalosulfonamides Amount taken

Coefficient of variance (2 o/o)”

Cyanide

@mole)

CAT

DCT

BAT

DBT

CAB

DCB

BAB

DBB

AgNO,

NaCN KCN AgCN Zn(CW K&&N, K,Zn(CN),

204.0 153.6 74.7 85.2 50.2 40.4

0.5 0.4 0.6 0.5 0.6 0.3

0.6 0.3 0.7 0.6 0.7 0.4

0.3 0.1 0.6 0.3 0.3 0.4

0.6 0.6 0.7 0.6 0.7 0.5

0.5 0.5 0.7 0.6 0.7 0.4

0.5 0.4 0.6 0.6 0.4 0.4

0.0 0.4 0.6 0.4 0.5 0.2

0.6 0.4 0.6 0.4 0.5 0.2

0.6 0.5

0.5 0.6 0.4 0.5 0.5 0.5

0.6 0.5 -

-

Accuracy Range studied h-mole) NaCN KCN AgCN ZWN), K&dCN), K,Zn(CNh

40.8-1020.2 30.7-767.8 14.9-373.4 17.0-425.9 10.0-251.2 8.1-201.9

o Calculated for six trials.

Maximum error in recovery (2 %) 0.6 0.5 0.7 0.6 0.7 0.5

0.7 0.7 0.7 0.6 0.7 0.5

0.3 0.5 0.7 0.4 0.5 0.5

0.7 0.6 0.7 0.5 0.7 0.4

0.5 0.6 0.7 0.5 0.6 0.3

0.7 0.6 0.7 0.7 0.6 0.5

0.5 0.3 0.6 0.5 0.5 0.5

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The following procedures have been proposed for determining cyanide in the presence of halides and in mixtures of cyanide and thiocyanate ions. Determination of cyanide in the presence of halide. Add excess -0.5 M zinc sulfate to precipitate cyanide as zinc cyanide from a solution containing CN- and halide. Filter it off and wash the precipitate with the minimum amount of ice-cold water until free from halide. Dissolve it in 0.025 M aqueous potassium cyanide (b ml). Add the resulting solution to a known excess volume of 0.05 M oxidant under the conditions described before. Set aside the reaction mixture for about 30 min, shaking occasionally. Titrate the unconsumed oxidant with 0.05 M thiosulfate (V, ml). Add b ml of 0.025 M potassium cyanide to the same volume of 0.05 M oxidant under the same conditions as above. Determine the unreacted oxidant after 30 min by titration with the same thiosulfate (V, ml). Then the amount of cyanide (micromoles) in the test solution is 103M, (Vs - VJ2, where M, is the molarity of the thiosulfate. Estimation

of cyanide

and thiocyanate

ions in a mixture.

(i) Back titration.

Thiocyanate also undergoes quantitative oxidation with eight-electron stoichiometry with all the oxidants. Add an aliquot (x ml) of the mixture to a known excess volume 0, ml) of 0.05 M oxidant under the conditions described before to oxidize both CN- and NCS- ions. After 30 min determine the excess of the oxidant by titrating with thiosulfate (V, ml). Run a blank concurrently with the oxidant solution alone (V, ml). From another aliquot (X ml) of the original mixture, precipitate cyanide as zinc cyanide using 0.5 M zinc sulfate. Analyze the precipitate for cyanide as above (Vs2 ml) using the same volume of oxidant 0, ml). Then the amounts of CN- (P kmol) and NCS- (q kmole) in the mixture are given by P = 103M, (V, - V&/2 and q = 103M, (V, - V,)/8, respectively, where M, is the molarity of thiosulfate. Alternatively determine the amount of thiocyanate in the filtrate. Add the latter into y ml of oxidant under identical conditions. Titrate the unconsumed oxidant after 30 min with the thiosulfate (V,, ml). Then p = 103M, (V,, - V,)/2 and q = 103M,(Vs - VI,)/& If there is only enough for one sample, analyze the precipitate for cyanide and filter for thiocyanate. (ii) Direct titration. Titrate an aliquot of the oxidant solution (V,, ml) of molarity M2 against a sample solution containing a mixture of cyanide and thiocyanate (C ml) under conditions described for cyanide with visual or potentiometric endpoint. Precipitate cyanide as zinc cyanide from a C-ml aliquot of the original mixture by adding 0.5 M zinc sulfate. Then determine the thiocyanate in the filtrate as follows: Add 5 ml of 1 M potassium bromide, 5 ml of 10% sodium acetate, and 1 ml of carbon tetrachloride (and 5 ml of glacial acetic acid with CAT and CAB) and titrate with the oxidant solution with stirring until the appearance of a faint yellow color in the organic layer (V,, ml) (or use the potentiometric method for detecting the endpoint). Then the amounts (micromoles) of CN- and CNS- are given by p = 103E, - M,(V,, - I’,,)/2 and q = 103E,M2V,,/8, where E, = 2 and 4 with monohaloamines and dihaloamines, respectively. Alternatively analyze the precipitate of zinc cyanide for cyanide as before. Some typical results of the analysis are shown in Table 5. 2 After applying correction

for the solvent.

DETERMINATION

Determination

OF CYANIDE

TABLE 5 of Cyanide and Thiocyanate with Chloramine-TO

111

ION

Ions in Mixtures

Found

Taken CN-

CNS-

35.4 88.0 176.0 353.6 529.6 703.3 1056.9 1410.5

15.8 39.4 78.9 158.4 237.3 315.1 473.5 631.19

CN35.4 88.4 176.8 352.4 530.4 705.2 1053.0 1406.6

CNSe t k k 2 2 2 k

0.2 0.4 0.5 1.6 2.0 2.1 4.2 5.0

15.8 39.6 78.9 158.4 235.9 313.4 471.8 630.2

2 2 2 f k 2 2 t

0.1 0.3 0.3 0.5 0.7 0.6 1.2 2.5

a All values in p,mole.

RESULTS AND DISCUSSION

The oxidation of cyanides under the present experimental conditions has twoelectron stoichiometry per CN- ion with all the oxidants. The amounts recovered in the case of each cyanide are calculated on the basis of the above stoichiometry. Table 4 gives the reproducibility and accuracy of the results obtained in the present investigations. The top half of the table relates to the reproducibility and the bottom half to accuracy. It can be seen that the maximum error encountered is about kO.7. The present results with soluble cyanides compare favorably with the argentometric method (Table 4). There are very few reagents for the estimation of cyanides either in the pure state or in mixtures. In addition, the argentometric method is not that economical and is difficult to use with insoluble and complex cyanides. Considering the limitations of the established reagents, the proposed reagents, especially monohaloamines in general and chloramine-T and bromamine-T in particular, have advantages over them. Chloramine-T is commercially available and cheaper. The other toluene analogs can be easily prepared starting from it. The proposed reagents are also useful for the estimation of cyanide in the presence of halides and thiocyanates. In general monochloramines are best suited for the estimation of cyanide in acidic solutions and monobromamines are better reagents for the estimation in alkaline solutions. Although the dihaloamines can also be successfully used for the same purpose, they are mainly of academic interest. The usefulness of the proposed reagents for the purpose described is of the following order: CAT > BAT > CAB > BAB > DCT > DBT > DCB > DBB. The haloamines appear to be suitable substitutes for hypohalites and hypohalous acids which are very unstable. The results of back titrations were found to be more reproducible than those of direct titrations as the latter are sensitive to the loss of HCN or Br,. The effect of foreign ions and compounds on the estimation of cyanides was investigated in both direct and back titrations. A typical set of results is shown in

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AND MAHADEVAPPA

Table 6. As may be seen the common anions such as NO:, ClO;, SO:-, POj-, and F- do not interfere, but Cl-, Br-, I-, and hydrazine do interfere in the estimation. Metal salts of monohaloamines (RNXM, where R = C,H5S02 or p-CH,C,H, SO,, X = Cl or Br, and M = Na) behave like electrolytes (5) in aqueous solutions and dissociate as RNXM G (RNX)- + M+. The anions pick up protons in acid solutions to give the corresponding free acids, monohaloamines, RNHX (N-halobenzenesulfonamide or N-halo-p-toluenesulfonamide) (19) which can undergo disproportionation and/or hydrolysis (5, 13, 28). The oxidizing species in acidified haloamine solutions are RNHX, RNX,, HOX, and possibly H,OX+ (and X, in the presence of X-) and those in alkaline solutions are RNHX, HOX, RNX-, and OX-. Effect of Salts on the Oxidation

TABLE 6 of Potassium Cyanide with Chloramine-T

and Dichloramine-T

Direct titration Visual endpoint Salt (50 mg)

KCN recovered olmole)

% Deviation

Potentiometric KCN recovered OLmole)

endpoint % Deviation

Back titration KCN recovered (wale)

% Deviation

Chloramine-T KCN taken:315.7

NaF KCI KBr KI KNO, WO, KH,PO, NaClO, NJ%

317.8 313.7 317.8 31.8 317.8 317.8 317.8 315.7 8.4

+0.67 -0.63 + 0.67 - 89.93 +0.67 +0.67 + 0.67 0.00 - 97.34

KCN taken:325.4

pmole

315.7 313.7 313.7 31.4 315.7 317.8 317.8 317.8 8.4

0.00 -0.63 - 0.63 - 90.05 0.00 + 0.67 +0.67 + 0.67 -97.34

323.8 323.8 322.1 78.1 21.5 323.2 323.8 323.2 323.8 1031.5

kmole -0.49 -0.49 - 1.01 - 76.00 -93.39 -0.68 -0.49 -0.68 -0.49 +216.99

Dichloramine-T KCN taken:422.2

NaF KC1 KBr KI KNO, K,SO, KH,PO, NaClO, N-H,

421.7 421.7 420.2 63.0 421.7 423.3 420.2 421.7 171.8

-0.12 -0.12 - 0.47 -85.08 -0.12 +0.26 -0.47 -0.12 -59.31

423.3 421.7 420.2 65.6 420.2 423.3 420.2 421.7 174.9

KCN taken:346.2

pmole +0.26 -0.12 - 0.47 - 84.46 -0.47 +0.26 -0.47 -0.12 - 58.57

346.2 348.6 377.4 618.3 361.4 346.2 346.2 348.6 346.2 -

kmole 0.00 + 0.70 +9.01 +78.60 +4.39 0.00 0.00 +0.70 0.00 -

DETERMINATION

OF CYANIDE ION

113

The observed two-electron stoichiometry for the oxidation of CN- ion may be represented by the equations CN- + RNHX (or ‘/2 RNX,) + H,O -+ CNO- + RNH, (or ‘/2 RN&) + X- + H+ CN- + RNX- + H20+CNO+ RNH, + X-. In direct titrations, presumably bromine is the reaction intermediate formed from potassium bromide by the oxidants. RNHX + 2Br- + H+ + RNH, + Br, + XRNX, + 4Br- + 2H+ + RNH, + 2Br, + XCN- + Br, + Br- + CNBr The cyanogen bromide formed could be quantitatively estimated by the iodometric method (27). The presence of CNO- in the reaction products was detected by standard tests (9, 31, 33). Benzenesulfonamide formed in the reactions with benzene analogs was detected by TLC (29) (Rf = 0.88). p-Toluenesulfonamide, the reduced product of toluene analogs was detected by paper chromatography with benzyl alcohol saturated with water as the solvent and 0.5% vanillin in 1% HCl in ethanol as the spray reagent (Rf = 0.91). CONCLUSION

The proposed analytical techniques are rapid and reproducible. Substantial amounts of cyanides can be estimated by proper adjustment of reaction conditions. Furthermore the techniques are useful for determining cyanide ion in the presence of halides or thiocyanate. These procedures can also be employed for computing the number of cyanide ligands present in the complexes. The monohaloamines in general and chloramine-T and bromamine-T in particular have advantages over the established reagents and can serve as substitutes for AgNO, and hypohalites in determining cyanides. ACKNOWLEDGMENTS One of us (B.T.G.) is grateful to the Government of India, New Delhi, for the award of a National Scholarship for Postdoctoral Research Abroad. We thank the Bangalore NMR Facility, Indian Institute of Science, Bangalore, for the NMR spectra.

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