Spectrophotometric determination of palladium using 4-methyl-l ,2-cyclohexanedionedioxime

VOL. 21 (1959)

M. OOSTXNG

308

J-J.A. Bew~cx, Awd; Clrcm.. 24 (1952) 1826. I,. Mour,~ AND T). W. HAWLEY, A?iar. C/rem., 25 (1953) t36~). 3 1’~. MO~~LLIU~, Ind. 6~g. C&m., Anal. Ed., rg (I 943) 3464 f-1. J. CLULISY, R?zafyst, 79 (1954) 567. 5 P. A. I'OHL AND Ft. 1)RMMEL, .d?lUf. Cbi?it. LtGkC, IO (1954) 554. n 13. HtjK, Sums/c licnz. Tidskr., Gg (1953) 106. 7 17. 13. S~xDrsu., /tad. Eng. Chom., Anal. Ed., FI (1936) 336. H J. Fr.~cc;, Ovgnnic ihq,~~~ts, Tntcrscicncc Publishers, Inc., New York 1948. IJ I. &I. KOLTIIOI:P AND I;. n. SANURLL. J. Am. CJrcvr. Sm., 03 (194:) rc)oG. ‘1’ N. 1.t. JCURMAN, w, 13. IMASON AND J. S. ~‘iX0i.A. ,d rlttf Chctn. ‘2 I (I()& 13’3. ‘1 f:. 13. SANUfSLL AND f'fi.J-I. CUMMtNGS, adtrd c&W., 21 (1949) 1356. 1% G. f.1. ~OHRISON AND 1-i. J:H~ISISH, .%~vclif ihtvrrctiail in ~~utfyticcd CktniStYy, John SCJIIS 1nc., New York 1957. J:J 13. IRVING ANI) I<. J. I'. WILLIAMS,,/. C/rem. Sm., (19q~) 18+r. 1 0.

A.

KRNYON

2 L. SILVERMANN,

AND

I
February

\vikFy

zoth,

&

xg5cj

SPECTI~OPHO’l+OMETRIC DETERMINATION OF PALLADIUM USING 4-ME’I’HYL-1,2-CYCLOF-Ii3XANEl~IONEDIOXIME* Cl-JARLI
ft3r A tottric licsenrch

V. J~ANIiS

AND

RONNIE

nnd I&#xirtr~x3zt of Chemistry,

V. Slttl’I’H

Iowa State

College,

cf mcs,

Iowa

(U.S..4

.)

INTRODUCTION

Many reagents hnvc hccn proposed for the spectroI~Ilotometric ci~termination of palladium. ‘I’hc reducing properties of mercury(I) Noride have been used to dctermine submicrogram quantities of palladium by observing the color and opaqueness of the palladium metal clcl~ositccl on the mercury(I) chloriclc~. 2, Palladium has also been clctcrmincd by estimating its catalytic cffcct on the reduction of nickcl(I1) by sodium llyI>oI~hosI,llite3. Wydrohromic acid4, iodide”-8, tin(E1) chloride+, and thiocyanatcl”. 11 have also been suggcstccl as colorimctric rcngcnts. Some of the organic rcagcnts which have been reported for the dctcrmination of pallaclium arc : 4-siitrosorcsorcinoll”, p-climcthylan~inol~cnzylidcncrl~odanin~~~~ 14, compounds containing the +tlitrosoamino groups16-17, 2-mcrcapto-4,5-dinxthylthiaxoliR, x-nitroso-2-nnphtIlol~~, 2-nitroso-s-naphtholz”, rubcanic acid”-‘, cthylcnccli~~minctctrnacctic acid (EI)?‘A)*2, thiourcaa3, and substituted acety1cxxs23. Various osimcs have also been rcportcd for the calorimetric cictermination of palladiuma+“7. Many of the rcagcnts mcntionccl above do not possess all the dcsirccl propcrtics of an idcal colorimctric rcagcnt~“, SOGAN~ AND ~~~IATTACHAI~YYA~Q have proposed ~-l~ydrc~sy-x-~-s~ilf~~ti~~tophcnyl-~-~~l~cnyltri~~in~ as a colorimctric rcagcnt for palladium, ancl they report it to bc better and more idcal than any of the rcagcnts mcntioncd previously in the litcraturc. Recently ~~~~UMDAR AND CHAKRABARTT\+ suggestod 2,5-dimorcaI,to-1,3,~-thiodiazole (13ismuthiol I)30 and s-mcrcapto-3-phcnyl2-thio-1,3,4-thiodiazolonc-2 (13ismuthiol II) 31 as new rcagcnts for tlic dctcrmination. * Contribution No. 724. Work Energy Commission. flefevences p. 31x

was pcrformecl

in the Ames Laboratory

of the U.S. Atomic

VOL.

21 (1959)

SPECTROPHOTOMETRY

OF

I’d

309

KODAMAse used o-nitrosoresorcinol monomethyl ether as a colorimctric reagent for palladium and rhodium. Palladium is heated with perchloric or sulfuric acid until fumes arc evolved. The solution is transfcrrcd to a scparatory funnel and cstractcd with chloroform, The absorbance of the chloroform phase is measured at 420 m/r. A procedure employing nickel or potassium clialkyl- and ciiarylditliiopl~osphates for the determination of palladium was published by BUSEV AND IVANIUTIN~~. The complcs formed is insoluble in strong acids such as hydrochloric or sulfuric, but can bc extracted with chloroform or carbon tctrachloridc. The maximum absorption of the complex in carbon tetradhloride is at 295 m&t and is used for spcctrophotomctric determinations in the range of 0.014-0.090 mg Pcl/25 ml ; howcvcr, the absorbance of more concentrated solutions (0.x6-x.1 nig IV/25 ml) is mcasurccl sI~ectrol~hotonictritally at 340 mbt. . Although the reactions of palladium with vie-diosimcs have bcon known for a Iong time, very few colorimctric methods have been published employing them. ‘l’l~osc 25.“fie34, dimethylglyoximc~fi, ant1 dioximes which have been used arc methylglyoximc c.-furildioxime36. 4-Methyl-x ,a-cyclohc%ancclioncdioximc (4-mcthylnioximc) can be easily prcparodJ7 and has been reported to be an cxccllent gravimctric reagent for pallaclium38. The purpose of this study was to dctcrminc the merits of this compound as a colorimctric reagent. APPARATUS

ANI)

REAGEXTS

Absorbance mensuremcnts wcr(: made with a Beckman Model UU sI’ectropllotoarctcr using r-cm silica cells. A Gary Modci I.2 recording spcctrophotomctcr was used to scan the spectra of the complexes and reagents. A Beckman Model G psr meter was used for pn stndics. The volumetric glassware employed was Kimblc Normax and Pyrex class *‘A“, q-Methyl-r ,z-cycloand a satnratcd aqwous hcxancdioncdioximc: this compound was prcparcd in this laboratorys’ solution was used. Standard palladium solution : a solution was prcparccl by dissolving 0.8236 g of reagent-grade palladium chloride in hydrochloric acid nntl diluting to z 1. This solution was standardiwd gravimetrically using I ,z-cyctohcxancdioncdioxime according to the proccdnrc of molts/l. VOTISR, BANKS. AND XArcr~t 33. The concentration of palladium was found to bc 2.1 x-10-3 Buffer solution : R hydrochloric acid-potassium chloride buffer solution was prcparctl by mixing 5.30 ml of 0.2 N HCl and 25 ml of 0.2 N KC1 solutions and diluting to IOO ml. Other cllcmicals used wcrc reagent-gmtlc quality. ESPERIMESTAL

WORK

HOOKER*” found that palladium could bc dctcrmined by the suspcnsion-spectrophotometric method proposed by FERGUSON AND BAKKS~’ for the determination of nickel. Gum arabic is added to the solution to stabilize the suspension of the prccipitatc. Highly colored ions seriously interfcrc in this method. However, if gum arabic is omitted and the precipitate allowed to form and then cxtractecl, a very scnsitivc method results. The precipitate of bis (4-mcthylnioximato-S,W) palladium(I1) was found to bc soluble in chloroform and to have an absorption band at 280 m/t. Ncithcr 4-mcthylnioxime nor chloroform shows appreciable absorption at this wavclcngth. For optimum extraction the p?l of the aqueous phase should be between 0.7 and 5.0. The solution should be prepared 60 min prior to extraction. It was observed that the chloroform phase was stable for only 3 h after being equilibrated with an aqueous phase which was adjusted to pn 2 with hydrochloric acid. However, if the aqueous phase is adjusted to pn z with a hydrochloric acidpotassium chloride buffer, the chloroform phase remains stable for more than 24 h.

Xeferetrces

9. 3rr

C. V. IMNKS,

310

I<. V. SMITII

VOL.

21 (ICJj())

pl~asc containing 2.5-250 /4,gof palladiun1 is transfcrrccl to a x25-ml bcrlkcr and acljustcd to approximately prr 2 using tlic 1lydroChloriC acid-potassium chloritlc buffer. ‘I’hc solution is then traJlsfcrrct1 to a x25-ml scparatory funnel, one ml of the saturatccl solution of 4-Jncthylnioximc is acldccl, and the solution allowed to stancl for 1 11. ‘I’lic aqueous phase is then cxtractccl wit11 three y-ml portions of chloroform. ‘1’1~ extracts arc con~binccl, transfcrrccl to a 25-ml volumetric flask, and clilutcd to volume with clJloroform. As a clrying agent, 0.5 g of anhydrous sodium sulfate is ~~ticlccl. ‘I’l~e absorbance of tlJc chlorofortn phase is mcnsurccl against chloroform at by rcfcrcncc 280 m/r. using I-cm silica ~11s. ‘I’hc ainount of pallaclium is clctcrminccl to a calibration curve. An

nc~uc&*s

TlJc cxtractiori-sl~cctroplJotoJnctric methocl cliJninatcs the intcrfcrencc of many of tllc highly colorccl iorls which cause trouble in tlic suspension-spcctroplJotometric method. I-lowcvcr, as iJi the cast of tlic suspension-spcctrophotomctric method, tlJc following ions wcrc found to intcrfcrc when prcscnt: ruthcniun~(III), coppcr(II), cobaIt(II), iron( t I), and iron(I 1 I). Successful masking agents wcrc found in all cases csccpt ruthcniuni. Microgram but not milligram quantities of coppcr(I1) may bc maskccl with thioglycolic acid. Intcrfcrcncc from cobalt can bc climinatcd by conversion to the hcxacyanocobultate(II1) complex. Iron(I1) can bc oxidiacd to iron(II1) and cd~nplc.xccl with citlicr tartratc, l~liosl~liatc, or fluoriclc ; fluoriclc was found to bc the Jnost cffcctivc maskirig agent. DISCUSSION

One of the outstanding propcrtics of the substituted niosimcs is the high solubility in chloroform of tlic his (?lic-clioximato-N,N’)mct,al(II) complescs containing palladium and Jlickcl. ‘I’hcrcforc, the cluantitativc cxtractioll of thcsc cornplcxcs into chloroform ancl a subscclucnt sl~cctrol~lJoton~etric clctcrrnination is possible. 4-Mcthylnioximc has scvcral uclvantagcs over otllcr reagents for tllc spcctrophotomctric clotcrJnination. Tlic pJr at wliich tlic complcs is forJnccl and cxtractccl is not critical, the con~plcs is readily cxtractccl illto chloroform, the chloroform solution is stable for Jnorc than 24 11, and great sensitivity can bc acl~icvccl. Irdcrfcrcncc by highly colored, cstractablc rutlwnium

ions is easily nvoidccl by using rcaclily nvailablc must bc nbscnt when pallaclium is clctcrmined.

masking

The molar absorptivity of the bis(4-mcthylniosimato-N,N’)palladiuJl~(II) was cnlculatccl from tllc calibration curve and found to bc 1.51.10~ cliloroform at 280 mfc.

agents;

only

complex l/molts-cm in

9

SU,MMhRY A proccdurc

for tlw

tlctcrnlitlrrtion of pnllndium with J)-nictllyl- c,z-cyclohcx;rncdiollctlioxin~c

by nn extraction-spcctrophotomctric mcthocl has been ~lcvclopccl. Intcrfercnce by coppcr( I I), cobnlt(Il), iron(H), or iron(II1) can bc climinrrtcd by suitable muking agents. Ruthenium(ll1) must bc absent or scparatcd prior to tlro tlctcrminntion of pnllaclium. The molar nbsorptivity of the bis(~-methyl-~,z-cyclohcx~tncclionctlioxim;rto-N,N’) pdlnclium(II) complex has been cnlculatcd and found to bc 1.51-104

h2feYct1cc.5p. 3x1

l/moles-cm

in chlorofortn at 280 mp.