Dec 5, 2003 - using Elico digital pH-meter (model LJ-120). A stock solution of palladium(Il) was prepared by dissolving 1 g of palladium chloride hydrate ( ...
Indian Journal of Chemi stry Vo l. 44A, August 2005. pp. 1625-1630
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Extraction spectrophotometric determination of micro amounts of palladium(lJ) in catalysts
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S H Gaikwad, T N Lokhande & M A Anuse* _ . Analytical C hemistry Labo ratory, Department of Chemistry, Shi vaji University, Kolhapur 416 004.J ndia Email : mansinganuse @yahoo.com
Received 5 December 2003; revised 24 March 2005 A new reagent, 4-(Y-furalideneimino)-3-methyl-5-mercapto1.2,4-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 l0 3 L mor l cm-I and 0.073 J1.g cm-2 , respecti vely. The effects of pH. reagent concentration, solvent, shaking ti.lne and stability of th e 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 thioureas 3-8 , 2-arylthio-p-n itroacetophenone 9 , thiosemicarbazones l o- II , 2,2'-dithiodianiline I 2 , 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 - H 20 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-dimethylaminoaniline l9 , 2-tetrazolylazo-5-diethylaminophe2o nol , 2-(2 '-thi azol y lazo)-5-dimethylami no-benzoic acid 21 and 2-(5-nitro-2-pyridylazo)-5-(N-propyl-N-3sulfopropylamino-phenol 22 . 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-dimethylamino25 benzylidene rhodanine 24 , nitroso-R-salt , methdil26 azinehydrochloride , 2,2'-dipyridyl-2-pyridylhydrazone27 and potassium iodide 28. 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 )-3methyl-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 meas urements were made on a Elico digital spectrophotometer (model CL-27) with 1 em quartz cells. The pH meas urements were carried out using Eli co digital pH-meter (model LJ-120). A stock solution of pall adium(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 ga nd was prepared in three steps2'.1: Firstly , thiocarbohydrazide was prepared. Then a mixture of thiocarbohydrazide and glaci al acetic acid was refluxed for 4 hours to obtain 3-methyl-4-aminomercapto-l ,2,4-triazole. Preparation of reagent FIMMT 29
To get the li gand, a mixture of 3-methyl-4-amino5-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 (Sc heme I). The product obtained was separated and recrystall ized from hot ethanol. Faint ye llow coloured need les were obtai ned (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 eth yl alcohul showed th at the reagent ex hibits sharp abso rpti on max imum at A"m 360 nm, with molar extinction coefficient 50.0 L mor ' cm·'. Free li gand ex ist in thiol-thione tautomeric forms as indi cated by
+
fA o
AI:'~"~
CHO
2- furfural
4.(:2' - fu ra Iiucnei miIlO)- .\ - m~ t hy 1-5l1l ~ n: :lpl (l - 1 .2 .4-tri azn l e (F IMM T )
( r hiollorlll )
1l
(Thi o llc form )
Scheme 1
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, iso meric = C CH 3), 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-5mercapto-l ,2,4-tri azole (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.
• (
\ J
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 th e addition of palladium(IJ). Unknown amount of pall adium(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 th e palladium(H)-FIMMT complex in terms of absorbance was in vestigated over
r
NOTES
the pH ran ge 1-10, keeping all other conditi ons constant. The wavelength of maximum absorbance and the absorbance at th e wavele ngth maximum remain ed un changed from pH 4.8-6.5 and thu s ri gid contro l of p H during co lour fo rmati o n was not necessary. T he nature of the spectral curves remained constant indi cating the fo rmati on of onl y o ne spec ies of pall adium(J[) co mpl ex under th ese conditi ons. In the reco mmended 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 determin ation in any way. T he effec t o f excess of reagent o n the intensity of colour was also studied. It was found that minimum 10-fo ld excess of the reagent was required for full co lour development. Howe ver, fifty-fold molar excess of reagent was recommended in the general procedure . The co lour develops instantaneously by equilibrating the two ph ases and remains stable fo r more th an 24 h. The ex tracti on of the co mpl ex into Il-butano l was fo und to be very rapid and no change was observed in the extent of extraction w hen the shaking time was vari ed in the range of 10 s -30 min . Vari ous organi c sol vents were examined fo r the ex traction of pali adium(JI)-F rMMT co mplex. It was observed that the absorbance values increased in the order: carbo n tetrachloride < chlorofo rm < xylene < to luene < benzene < 1,2-di chl oroeth ane < MIBK < iso-amyl alcoho l < iso-butyl alcohol = n-butano l. As Il-butanol was much cheaper th an iso-butyl alcoho l, it was used for further studi es. Th e system adheres to Beer's law in the range 5-50 ppm of pali adium(lI) with optimum range of 17-50 ppm of the metal as evalu ated from Ringbom's pl ot. The molar absorpti vity ca lcul ated over the range studi ed was 1.4 x 103 L mo l'l c m-I , whil e Sandell 's sensiti vity was 0 .073 Ilg cm-2 . Th e average relative stand ard dev ia tio n as determined of a seri es of measurements made accordin g to the optimum conditi ons is in the range ± 0. 55-1.0% . T he co mpos iti on of the ex tracted spec ies , was fo und to be Pd(II): FIMMT:: 1: 1 by the molar-rati o method using equimol ar so luti ons of pa ll adium(lI) and th e FIMM T of concentrati o n 9.39 x 10-4 M. A 10fo ld excess of reagent was required for full complexati on.
1627
In Job's method o f continuous variation s, the pl ot of absorbance versus mo le fracti o n [MlM+L] indicates the fo rmati on of a complex with a pali adium(U): FIMMT ratio of I : I. T he compos iti o n of the co mpl ex 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 co mpos iti o n of ex tracted spec ies in n-butano l was fo und to be 1: I, [Pd(U): FIMMT ] as show n in the structure (I ), whi ch is analogo us to th at reported elsewh ere for noble meta ls.\o. T he effect of vari ous fo reign io ns o n ex tracti on o f 300 Ilg of pa ll adium(lI) with the proposed reagent was investi gated following the reco mmended procedure. Initi all y foreign io n was added to the paliadium(U) so luti on in large excess ; 200 mg fo r ani ons and 25 mg fo r cation s. Wh en interference was found to be intensive, the tests were repeated wi th success ively small er amounts o f fo reign io ns. ' The tol erance 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 abl e 1). M ost of the commo n cations and anion s were tolerated even when present in large amounts. T he o nly spec ies show in g interference in the procedure were Cu(JI), Mn (V II), Cr(VI ), thi os ulph ate and thi ourea. However, the interfere nce o f C u(l£) was e liminated by mas ki ng with EDT A. Thi ourea and thi os ulph ate form very strong compl exes with paliadium(Il) because pl atin um gro up meta ls belo ngs to the soft acids whi ch possess a strong affinity to li gands contai ning donatin g type sulphur ato ms whi ch acts as a soft bases. Determination of palladium(II) in synthetic solution and real samples
To ascertain the se lectivity o f th e reagent, the method was successfully used for the determin ati on of pali adium(Il) in all oys. Syntheti c solutio n simil ar to those of the all oys of pall adium(IJ) were prepared and the a mount determined fo ll ow ing the recommended procedure . Results obtained are su mma ri sed in Table 2.
(I )
1628
INDIAN J C HEM, SEC A. AUGUST 2005
Table I - Effect of di verse ions on the extractive spec trophoto metri c determin ati o n 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
Ad ded as
Amt to lera ted (mg)
Ion
Added as
Amt to lerated (mg)
Bromide
KBr
200
Ir(lI l )
IrO ,
1.5
EDTA
Na:!EDT A
100
Pt(lY)
H2 PtCI 6
1. 5
Oxalate
Oxalic ac id
100
Au(lIl)
HAu C I4.4H 2O
1.5
Thiocyanate
Am ill. th iocyanat e
100
Ag(l)
AgNO,
0 .5
Iod ide
Pot. iod ide
SO
Bi(lIl )
BiCI,
7
Tartr:lte
Sod. tartarate
100
Sn(lI)
SnCl l
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 )
K 2TiF6 ·H zO
3
U(YI)
UOl(NO,h
10
\f(V)
NH 4YO). Hp
10
Th(IY)
Th(NO, )4
10
Cr(lll)
CrCI,
8
La(IIl )
LaCI,.7 H2O
Mn(II)
MnC I:!. 6H 2O
8
Re(Y U)
KRe04
2
Fc(lIl)
FeCI ,
5
Mo(Y I)
(NH4)c,M 070:!4.2H20
4
Co(ll )
CoC12·6H 20
5
Zr(lY)
ZrOCl z·8 H zO
5
Ni(ll )
NiCI 2·6H 2O
6
Be(Il)
BeS04·2 HzO
15
C u(I1)"
CuC I2·2H 2 O
4
Mg(II)
MgC lz·2H zO
15
Zn{II)
ZnCI:!
8
Ca(ll)
CaCl z·2H zO
10
C d(II )
CdC lz.2 '/2 H2O
10
Sr(ll)
SrCl z.6H zO
10
Hg( II )
HgC I2
2
Ba(ll)
BaCl z·2 Hp
10
AI(lII)
AICI 3
10
Sb(lll )
Sb 20
Ga( lJI )
GaCl ,
2
Rh(llI)
Rh C I,
In (JII )
InCl .1
2
Os(YIII)
OS04
T I( lll )
T I2O)
2
Ru(lll )
Ru C I,
10
3
1. 5
" Masked w ith 100 mg EDT A Table 2 -
Analysi s of Pd(ll) in sy nth eti c mi xtures co rres po ndin g to a ll oys and catal yst samples
Syn th etic mixtures correspondi ng to sa mpl es
Allovs
Co mpos iti on ( %)
Pd(II) taken (!.lg)
Recovery (0/0)
RSD
0. 16
(%)
t
Low meltin g dental all oy
Pd. 34 ; Au. 10; Co, 22; Ni , 34
300
99.85
Sti bio palladi -nite min eral
Pd , 75;Sb, 25
300
99.62
0.4
Jewe llery a ll oy (Pd-Au all oy)
Pd. SO: A u. 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 all oy
Pd. 60: C u". 40
300
99.79
0 . 130
Go lden co lou red sil ver all oy resistant 10 tarnish in g
Pd. 25.5; In . 21: C u. 18: Ag,35
300
99.88
0. 14 (Coli/d. )
NOTES
Tab le 2 -
1629
Ana lysis of Pd(H) in synthetic mixtures correspo ndin g to all oys and catalyst sa mples -
Synt hetic mixtures corresponding to sampl es
COI//d.
Pd(ll) taken (I-lg)
Recovery (%)
RSD (%)
Hydroge nati o n ca tal yst (Pd o n BaS0 4 10%) Merck
300
99.73
0.24
Lindlar Hydrogenatio n catalyst (Pd o n CaCO, 5%) Merck
300
99.65
0.39
Lindlar Hydrogcnati o n catalyst (Pd o n CaCO, 10% ) Merck
300
99 .62
0.4 1
Hyd roge nation catalyst (Pd o n asbestos 10%)(S.D . Fine C hern. Ltd.)
300
99.49
0.56
Hydroge nation catalyst (Pd o n asbestos 5%)(S. D. Fine C hern. Ltd. )
300
99 .58
0.45
Hydrogenation catalyst (Pd on asbestos. 10%)(S.D. Fine Chern. Ltd. )
300
99.49
0 .56
Composition (%)
Cawlys f s{lIllplei
t
Average of six determinations
:; Average of five determinati o 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 method 3 !.32 : To prepare a solution of palladium catalyst, the sampl e (0.1 g) was di ssolved 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 so lution was filtered if necessary and diluted to 100 mL with doubl y di stilled water. An appropriate aliquot of the so lution was taken for the analysis of pall adium content. The res ults given in T able 2 show that the amount obtained by the proposed method is in good agreement with certified values .
5
Ding Guosheng & Ma Donglan, Fenxi Hallxue. 29 (200 I ) 740.
6
Ma Do nglan, Li Ying, Li Jianpin g & Wang Yulu , Yejil/ Fel/xi. 20 (2000) 10.
Acknowledgement One of us (S HG) is grateful to the University Grants Commjssion, New Delhi , for providing financial assistance
7 8
C haudhu ri S P & Shome S C. J Illdian Chem Soc, 74 ( 1997) 554.
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Gojare P T, Ga ik wad S H & Anuse M A, Res J Chelll Environ. 5(200 1) 5 1.
10
Salinas Franc isco, Esp inosa Anuciacion. Lopez Letici a & Lopez Pedrolui s, Chelll Anal, 46 (200 I) 239.
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Murthy G Y R & Reddy T S, Talallta . 39 ( 1992) 697.
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Gho li va nd M B & Nozari N, '(alal/ta , 52 (2000) 1055 .
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Toral M I, Richter P. Lara N. Escudera M T & Soto C. AI/al Left, 33 (2000) 93 .
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Mao Xueqin, Tang Fulo ng & l in Q in gping. Fel/xi HUClxue. 20 ( 1992) 95 1.
16
Ensati A A & Keyvanfard M. Specfmchilll AC/a. 58A (2002) 1567 .
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Wang Yingxiang & Wang Zunpen. Fel/xi HU(Lrue. 28 (2000) 1188.
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