Indian Journal of Chemi stry Vo l. 44A, August 2005. pp. 1625-1630 --

Extraction spectrophotometric determination of micro amounts of palladium(lJ) in catalysts

S H Gaikwad, T N Lokhande & M A Anuse* _ . - -Analytical Chemistry Laboratory, Department of Chemistry,

Shi vaji University, Kolhapur 416 004.Jndia

Email : mansinganuse@yahoo.com

Received 5 December 2003; revised 24 March 2005

A new reagent, 4-(Y-furalideneimino)-3-methyl-5-mercapto-1.2,4-triazole, has been synthesized and used as a chromogenic reagent for palladium(II) . Palladium(lI) has been extractt:d as a yellow complex (1..,,",. 410 nm) from an aqueous solution at pH 5.4 with FIMMT in n-butanol. The molar extinction coefficient and Sandell's sensitivity are 1.4 x l03 L mor l cm-I and 0.073 J1.g cm-2,

respectively. The effects of pH. reagent concentration, solvent, shaking ti.lne and stability of the complex have been studied. The complex system confirms to Beer' s law over the range 5-50 ppm of palladium(II ) with optimum range l7-50 ppm of the metal as evaluated from Ringbom' s plot. The tolerance limit for many metal ions has been determined. The method has been applied successfully for the determination of palladium(II) in synthetic mixtures corresponding to alloys and palladium(lI) in various hydrogenation catalysts.

IPC Code: C07D249/08 ; C07F I 5/00; GOIN21/00

The development of efficient techniques for the recovery of valuable metals in industrial wastes are of interest due to the resource scarcity and hazards these metals might cause to the global environment. Of the valuable metals , precious metals are known to possess unique physical and chemical properties that are suitable for manufacturing industrial materials such as catalysts, electrical and cOlTosion- resistant alloys, etc . In most of the wastes, the amount of target metal is often low as compared to a primary source and thus a separation IS very difficult l.2 . Therefore, it IS

necessary to develop an efficient method of estimation for such valuable metals like palladium.

The sulphur containing ligands form more stable complexes with palladium(lI), because platinum group metal s behave as 'soft' acids while sulphur containing ligands behave as 'soft' bases. Some sulphur containing ligands such as substituted thioureas3

-8

, 2-arylthio-p-n i troacetophenone9, thio­

semicarbazones l o-II

, 2,2'-dithiodianiline I2, have been

reported for spectrophotometric determination of palladium(ll) from associated elements, but these suffer from lack of selectivity and are time­consuming.

Palladium(lI) does not react with some organic reagents at room temperature. Complexation has been reported at an elevated temperature by heating the reaction mixture in hot water bath. With, 3-(2'­thiazolylazo)-2,6-diaminopyridine I3 (90°C for 35 min), 2,6-dibromo-4-carbox',' Jenzene diazoamino­benzene-l,lO-phenanthroline I4 (80°C for 5 min) and 1-(5-bromo-2-pyridylazo )-2-naphthol-6-sulfonic acid l5 (lOO°C for 3 min), while waiting period has been recommended for full colour development in the case of, pyrogallol red - H20 2

16 (4-5 min).

Azo compounds such as, 1,9-bis (4-antipyrinyl­azo )-purinedione 17, 5-(5-nitro-2-hydroxyphenylazo) rhodanine 18, 5-(5-nitro-2-pyridylazo )-5-dimethyl-aminoaniline l9

, 2-tetrazolylazo-5-diethylaminophe-nol2o, 2-(2 '-thi azol y lazo)-5-dimethylami no-benzoic acid21 and 2-(5-nitro-2-pyridylazo)-5-(N-propyl-N-3-sulfopropylamino-phenol22

. The methods involved a number of steps for stabilizing the complex, critical pH range also many metal ions interfere.

Direct spectrophotometric determination of metal ion without involving extraction has been reported with, sodium isoamylxanthate23

, p-dimethylamino­benzylidene rhodanine24

, nitroso-R-salt25, methdil­

azinehydrochloride26, 2,2'-dipyridyl-2-pyridylhydra­

zone27 and potassium iodide28. While these methods

are rapid and simple, separation of the metal ions is not achieved by using such procedures.

In the present work, 4-(2' -furalideneimino )-3-methyl-5-mercapto-l ,2,4-triazole has been proposed as a spectrophotometric reagent for palladium(Il). Palladium(II) reacts with FlMMT instantaneously and forms yellow coloured complex at room temperature. The optimum conditions for maximum colour development, sensitivity, selectivity of the method and effect of presence of various ions on the accuracy of the method has been investigated. The method has been applied for analysis of palladium(II) in syntheti c mixtures and palladium bearing hydrogenation catalysts.

Experimental Absorbance measurements were made on a Elico

digital spectrophotometer (model CL-27) with 1 em quartz cells. The pH measurements were carried out using Eli co digital pH-meter (model LJ-120).

A stock solution of palladium(Il) was prepared by dissolving 1 g of palladium chloride hydrate (Johnson Matthey, UK) in dilute Analar hydrochloric acid 1 M, diluting to 250 mL with doubly di still ed water and standardi zed by literature method. Working solution of 100 /-!g/mL was made by proper dilution of the stock solution .

The li gand was prepared in three steps2'.1: Firstly , thiocarbohydrazide was prepared. Then a mixture of thiocarbohydrazide and glacial acetic acid was refluxed for 4 hours to obtain 3-methyl-4-amino­mercapto-l ,2,4-triazole.

Preparation of reagent FIMMT29

To get the li gand, a mixture of 3-methyl-4-amino-5-mercapto-l,2,4-triazole (2.6 g) and 2-furfural (1.36 mL) in 50 mL of alcohol containing 3 drops of glacial acetic acid was refluxed for 3-4 h (Scheme I). The product obtai ned was separated and recrystall ized from hot ethanol. Faint yellow coloured need les were obtained (m.pt. 165°C). The purity of the FIMMT was checked by thin layer chromatography. [Anal: Mol wt =208.24. Calc for CsHsN40S: C, 46.14; H, 3.87 ; N, 26.9 1; 0, 7.68; S, 15 .49. Found: C, 46. 16; H, 3.86; N, 26.92 ; 0, 7.63; S = 15.531.

The absorption spectrum of HMMT in ethyl alcohul showed that the reagent exhibits sharp absorpti on maximum at A"m 360 nm, with molar ext inction coefficient 50.0 L mor ' cm·' . Free li gand ex ist in thiol-thione tautomeric forms as indicated by

+ fA AI:'~" ~ o CHO

2- furfural

Scheme 1

4.(:2' -fu ra I iucnei mi IlO)- .\ -m~t hy 1-5-

l1l~n::lpl (l - 1 .2 .4-tri azn l e (F IMMT )

( r hiollorlll )

1l

(Thio llc form)

presence of IR bands at 3119, 3272, 3448 (NH and SH) . The peak at 1601 for C=N and for - 0 - group peak was observed at 1099 cm-' , whi Ie for >C=S (thione) group there was a peak at 761 em· l

. PMR spectra of FIMMT in DMSO-d6 showed 0 values, 2.24 (3 H, S, = C-CH3), 2.3 (3 H, S, isomeric = C -CH3), 5.65 (J H, S, Furan ring), 7.04 (I H, S, Furan ring), 7.68 ( IH, S, Furan ring), 10.11 (IH, S, N\-I) and 13.46 (I H, S, S\-I).

The solution of 4-(2'-furalideneimino)-3-methyl-5-mercapto-l ,2,4-triazole (FIMMT) (0.0 IS M) was prepared by dissolving 0.312 g in 100 mL disti li ed /'I.-butanol.

Buffer solution of pH (5.4) was prepared by mixing 88 mL of acetic acid (0.2 M) and 412 mL of sodium acetate (0.2 M) and diluted to 1000 mL with doubly disti li ed water.

Solutions of various metal ion were prepared by dissolving the salts of the metal s in di stil led water or in suitable dilute ac ids and making up tu the known volume. The solutions of anions were prepared by dissolving the alkali metal salts in water. All the solvents and reagents were of analyti ca l reagent grade. Doubly distilled water was used throughout the work.

Recommended procedure

An aliquot of solution contall1lng 300 /-!g of palladium(ll) was diluted with acetate buffer (p\-l 5.4) solution LIp to the mark in 25 mL calibrated flask. The so lution was transferred into a 125 mL separatory funnel, followed by addition of 10 mL 0.015 M FIMMT in It-butanol. The two phases were equilibrated for a few seconds. The organic extract was collected over anhydrous sodium sulphate ( I g) to remove the traces of water, transferred to a 10 mL flask and volume made up to the mark with It-butanol. The absorbance of the extracted complex was measured at Am", 410 nm against a reagent blank prepared in the same way but without the addition of palladium(IJ). Unknown amount of palladium(IJ ) was determined from the calibration curve.

Results and discussion The absorption spectrum of the palladium (H)­

FIMMT complex in l1-butanol was studied over the wavelength range 340-560 nm. The yellow coloured complex exhibited absorption maximum at 410 nm where reagent shows negligible absorprion.

Extraction behaviour of the palladium(H)-FIMMT complex in terms of absorbance was in vestigated over

• (

\ J

r

NOTES 1627

the pH range 1-10, keeping all other conditi ons constant. The wavelength of maximum absorbance and the absorbance at the wavelength maximum remained unchanged from pH 4.8-6.5 and thus rigid contro l of p H during co lour fo rmati on was not necessary. The nature of the spectral curves remained constant indi cating the fo rmati on of onl y one spec ies of pall adium(J[) compl ex under these conditions. In the recommended procedure a sodium acetate-acetic ac id buffe r of p H 5.4 gives sati sfactory p H cont ro l and does not interfe re in the determination in any way.

T he effec t of excess of reagent on the intensity of colour was also studied. It was found that minimum 10-fo ld excess of the reagent was required for full colour development. However, fifty-fold molar excess of reagent was recommended in the general procedure . The colour develops instantaneously by equilibrating the two phases and remains stable fo r more than 24 h.

The ex tracti on of the complex into Il-butanol was fo und to be very rapid and no change was observed in the extent of extraction when the shaking time was vari ed in the range of 10 s -30 min .

Various organi c sol vents were examined fo r the ex traction of pali adium(JI)-F rMMT complex. It was observed that the absorbance values increased in the order: carbon tetrachloride < chlorofo rm < xylene < to luene < benzene < 1,2-di chloroethane < MIBK < iso-amyl alcohol < iso-butyl alcohol = n-butanol. As Il-butanol was much cheaper than iso-butyl alcohol, it was used for further studies.

The system adheres to Beer's law in the range 5-50 ppm of paliadium(lI) with optimum range of 17-50 ppm of the metal as evaluated from Ringbom's plot. The molar absorpti vity calcul ated over the range studied was 1.4 x 103 L mol'l cm-I

, whil e Sandell 's

sensitivity was 0 .073 Ilg cm-2. The average relative standard devia tion as determined of a seri es of measurements made according to the optimum conditions is in the range ± 0.55-1.0%.

The compositi on of the ex tracted species , was found to be Pd(II): FIMMT:: 1: 1 by the molar-ratio method using equimol ar soluti ons of pa ll adium(lI) and the FIMMT of concentration 9.39 x 10-4 M. A 10-fo ld excess of reagent was required for full complexati on.

In Job's method of continuous variations, the plot of absorbance versus mo le fraction [MlM+L] indicates the fo rmati on of a complex with a paliadium(U): FIMMT ratio of I : I .

The compositi on of the complex was also conf irmed by using log 0 - log C plots. T he graph of log D[ Pd( lI )J versus log C [FIM MT[ at fixed pH (4.5) was linear with slope of 1.3. Hence, the probabl e composition of ex tracted species in n-butanol was fo und to be 1: I, [Pd(U): FIMMT] as shown in the structure (I ), which is analogous to that reported elsewhere for noble meta ls.\o.

T he effect of various fo reign ions on ex traction of 300 Ilg of pa ll adium(lI) with the proposed reagent was investi gated following the recommended procedure. Initi all y foreign ion was added to the paliadium(U) soluti on in large excess ; 200 mg fo r anions and 25 mg fo r cations. When interference was found to be intensive, the tests were repeated wi th success ively smaller amounts of fo reign ions. ' The tolerance limit o f an ion was taken as the max imum amount (mg) causing an erro r of not greater than ± 2% in the absorbance value, (T able 1). Most of the common cations and anions were tolerated even when present in large amounts. T he only species showing interference in the procedure were Cu(JI), Mn(V II), Cr(VI), thi osulphate and thi ourea. However, the interference o f Cu(l£) was e liminated by maski ng with EDT A. Thiourea and thi osulphate form very strong compl exes with paliadium(Il) because pl atin um group meta ls belongs to the soft acids whi ch possess a strong affinity to li gands contai ning donating type sulphur atoms whi ch acts as a soft bases.

Determination of palladium(II) in synthetic solution and real samples

To ascertain the selectivity of the reagent, the method was successfully used for the determinati on of paliadium(Il) in alloys. Syntheti c solution simil ar to those of the alloys of pall adium(IJ) were prepared and the amount determined fo llowing the recommended procedure . Results obtained are su mmari sed in Table 2.

(I )

1628 INDIAN J C HEM, SEC A. AUGUST 2005

Table I - Effect of di verse ions on the extractive spectrophoto metri c determin ation of pallad ium(H). [Pd(lI ) = 30 ppm: pH = 5.4 (acetate buffer); FIMMT = 10 mL 0.015 M: Solvent = Il-butano lj .

Io n Added as Amt to lera ted Ion Added as Amt to lerated (mg) (mg)

Bromide KBr 200 Ir(lI l ) IrO , 1.5

EDTA Na:! EDTA 100 Pt(lY) H2PtCI6 1.5

Oxalate Oxalic ac id 100 Au(lIl) HAuC I4.4H2O 1.5

Thiocyanate Amill. th iocyanate 100 Ag(l) AgNO, 0 .5

Iod ide Pot. iod ide SO Bi(lIl ) BiCI, 7

Tartr:lte Sod. tartarate 100 Sn(lI) SnCll IS

Cit rate C itric acid 100 Pb(ll) Pb(N01h IS

Fluoride Amm. fluoride 100 Se(JY) Se02 5

Acetate Sod. acetate 100 Te(lY) Na2Te03 5

Ti(lY ) K2TiF6·HzO 3 U(YI) UOl(NO,h 10

\f(V) NH4YO). Hp 10 Th(IY) Th(NO, )4 10

Cr(lll) CrCI, 8 La(IIl ) LaCI,.7H2O

Mn(II) MnC I:!. 6H2O 8 Re(Y U) KRe04 2

Fc(lIl) FeCI , 5 Mo(Y I) (NH4)c,M070:!4.2H20 4

Co(ll ) CoC12·6H20 5 Zr(lY) ZrOCl z·8HzO 5

Ni(ll ) NiCI2·6H2O 6 Be(Il) BeS04·2 HzO 15

Cu(I1)" CuCI2·2H2O 4 Mg(II) MgClz·2HzO 15

Zn{II) ZnCI :! 8 Ca(ll) CaClz·2H zO 10

Cd(II ) CdC lz.2 '/2 H2O 10 Sr(ll) SrCl z.6HzO 10

Hg( II ) HgC I2 2 Ba(ll) BaClz·2Hp 10

AI(lII) AICI3 10 Sb(lll ) Sb20 3 10

Ga( lJI ) GaCl , 2 Rh(llI) RhCI,

In (JII ) InCl .1 2 Os(YIII) OS04

T I( lll ) T I2O) 2 Ru(lll ) RuC I, 1.5

" Masked with 100 mg EDT A

Table 2 - Analysi s of Pd(ll) in syntheti c mi xtures corresponding to a lloys and catalyst samples

Synthetic mixtures correspondi ng to Compos iti on Pd(II) taken Recovery RSD sa mples (%) (!.lg) (0/0) (%)

Allovs t

Low melting dental alloy Pd. 34 ; Au. 10; Co, 22; Ni , 34 300 99.85 0. 16

Sti bio palladi -nite mineral Pd , 75;Sb, 25 300 99.62 0.4

Jewellery a lloy (Pd-Au alloy) Pd. SO: Au. SO 300 99.73 0.24

Oakayall oy Pd . 18.2; Pt. 18.2 ; Ni. 54.2: V. 9. 1 300 99.59 0.43

Pd -ClI a lloy Pd. 60: C u". 40 300 99.79 0 . 130

Go lden co lou red s il ver alloy resistant Pd. 25.5; In . 21: C u. 18: Ag,35 300 99.88 0. 14 10 tarnish ing

(Coli/d. )

NOTES 1629

Table 2 - Analysis of Pd(H) in synthetic mixtures corresponding to alloys and catalyst samples - COI//d.

Synthetic mixtures corresponding to samples

Cawlys f s{lIllplei

Composition (%)

Hydrogenation catal yst (Pd o n BaS04 10%) Merck

Lindlar Hydrogenation catalyst (Pd on CaCO, 5%) Merck

Lindlar Hydrogcnatio n catalyst (Pd o n CaCO, 10%) Merck

Hydrogenation catalyst (Pd on asbestos 10%)(S.D. Fine Chern. Ltd.)

Hydrogenation catalyst (Pd o n asbestos 5%)(S. D. Fine Chern. Ltd. )

Hydrogenation catalyst (Pd on asbestos. 10%)(S.D. Fine Chern. Ltd. )

t Average of six determinations

:; Average of five determinatio ns

a Masked with 100 mg EDTA

In order to confirm the usefulness of the proposed method, it was applied to the determination of palladium in the palladium catalysts. The catalyst sample was prepared by literature method3

!.32 : To prepare a solution of palladium catalyst, the sampl e (0.1 g) was dissolved in aqua regia. The solution was evaporated to nearly dryness with the addition of three 5 mL portions of concentrated hydrochloric acid to remove the oxides of nitrogen and extracted with 10 mL (l M) hydrochloric acid. The solution was filtered if necessary and diluted to 100 mL with doubly di stilled water. An appropriate aliquot of the solution was taken for the analysis of pall adium content. The results given in T able 2 show that the amount obtained by the proposed method is in good agreement with certified values .

Acknowledgement One of us (S HG) is grateful to the University

Grants Commjssion, New Delhi , for providing financial assistance

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