Synthesis of new reagent 2-acetylthiophenethiocynate and its use in extraction of Pt(IV) spectrophotometrically

Article abstract of DOI:10.1002/jccs.200200032

2-Acetyl thiophenethiocynate (ATT) was synthesized and its characterization study was carried out using elemental analysis, IR and NMR techniques. The new reagent was proposed as an extradant for the development of the extractive spectrophotometric method for determination of Pt(IV) metal. The reagent complexes with the metal to produce a yellow colored complex which was then extracted into ethyl acetate at pH 11.2-11.6 having an absorption maxima at 400 nm. The thermal study showed that the extraction reactions are exothermic in nature with the reagent, and the stoichiometric ratio of Pt(IV) to 2-acetyl thiophenethiocynate in the organic phase was 1:2. The method permits separation and determination of platinum from real and binary mixtures. The separation of Pt(IV) from bivalent metal ions has been also studied.

Full text of DOI:10.1002/jccs.200200032

JournaloftheChineseChemicalSociety, 2002, 49, 207-212
207
Syn the sis of New Re agent 2-Acetylthiophenethiocynate and its Use in
ExtractionofPt(IV)Spectrophotometrically
Avinash Baliram Chaudhary, Nirupa.Shrinivasan and Rama Sadashiv Lokhande*
DepartmentofChem is try, Uni ver sity of Mumbai, Vidyanagari, Santacruz (E), Kalina,
Mumbai - 400 078, In dia
2-Acetyl thiophenethiocynate(ATT)wassynthesizedanditscharacterizationstudywascarriedoutusing
elementalanalysis, IRandNMRtechniques. Thenewreagentwasproposedasanextractantforthedevelop-
mentoftheextractivespectrophotometricmethodfordeterminationofPt(IV)metal.The reagentcomplexes
with the metal to pro duce a yel low col ored com plex which was then ex tracted into ethyl ac e tate at pH
11.2-11.6havinganabsorptionmaximaat400nm.Thethermalstudyshowedthattheextractionreactionsare
exo ther mic in na ture with the re agent, and the stoichiometric ra tio of Pt(IV) to 2-acetyl thiophenethiocynate
intheorganicphasewas1:2.Themethodpermitsseparationanddeterminationofplatinum from real and bi-
narymixtures. TheseparationofPt(IV)frombivalentmetalionshasbeenalsostudied.
INTRODUCTION
Organosulfur com pounds are clas si fied as soft bases,
tures and from real sam ples. These re agents ex tract the metal
through the sol va tion method. How ever there has been lit tle
doneonexploringthepossibilityofusingthiocynatederiva-
tives as extractants. The thin layer chro mato graphic and elec-
tro pho retic study of the chlorothiocynato com plex of plat i-
num is re ported.17 The mix ture of thiocynate and rhodamine
6Gwasusedtocarryoutspectrophotometricdetermination
of plat i num(IV) in mi cro amounts.18 Extractivespectropho-
tometricdeterminationofnoblemetalshasbeendescribed
ear lier; how ever the method adopted re quire sev eral ex trac-
tion stages for quantitve ex trac tion of plat i num(IV). To de-
velop a more ef fec tive method, by ex trac tive spec tro pho to-
metricdeterminationofplatinum(IV),itsapplicationinvari-
ouscommercialsamplesiscarriedout.
which pref er en tially re act with soft acid met als, like Pt(IV),
Pd(II), Au(III), and Ag(I) ac cord ing to Pearsen’s HSAB prin-
ci ple. When dialkalysulfides and the corresponding sulf-
oxides are em ployed for no ble met als, ex trac tions showed1
sul fides to be su pe rior to sulfoxides. On an in dus trial scale
(INCO) Pt(IV) was ex tracted by dialkyl sul fides.2 The di rect
ex trac tion of Pt(IV) was found to be very poor with 2-ethyl
hexyl phosphonic acid mono-2-ethylhexyl es ter (PC-88A),3
triphenyl phos phine (TPP),4 derivativesofthiourea,5,6 and
dithizone,7,8 in CCl4 from chlo ride me dia, and was pos si ble
onlyafterreductionofPt(IV)toPt(II)bystannouschloride.9
Theextractionofplatinum(IV)andpalladium(II)wasstudied
with amines,10 diamines,11 and TOA;12 while TOA is used on
an in dus trial scale, these all suf fer from long equi lib rium
time. The novel extractant, 3,3-diethylthietane (DETE)13
could not give a quan ti ta tive ex trac tion of Pt(IV) from chlo-
ridemedia.Thederivativesofcalix[4]arene14 are also used as
phasetransferreagentsforextractionofPt(IV)fromchloride
media.
Inthiscommunicationwepresentsynthesisofa new re-
agent and method for ex trac tion of Pt(IV) from aque ous me-
diaataparticularpHinthepresenceofvariousmetalsusing
2-acetyl thiophenethiocynate (ATT) as an extractant in ethyl
ac e tate us ing a UV-spectrophotometer at 400 nm.
EXPERIMENTAL
The ex trac tion with TOPO15 from chlo ride me dia has
also been re ported. Sev eral ox imes, semicarbazones and
thiosemicarbazones have been re ported which form com-
plexes with met als and are found use ful in com mer cial ap pli-
cations.16 These types of re agents have been used to find out
quantitativelythepercentageofcompositioninbinarymix-
Equipment
Absorbance and pH mea sure ments were car ried out on
a Shimadzu UV vis i ble 2100 spectrophotometer with 1 cm
quartz cells and a Con trol Dy namic dig i tal pH me ter with
combinedglasselectrode,respectively.
*Correspondingauthor. E-mail:lokhanders@yahoo.com

208 J. Chin. Chem. Soc., Vol. 49, No. 2, 2002
Chaudhary et al.
Synthesis of Ligand
absorbtraceamountsofwater. Theamountofplatinummetal
pres ent in the or ganic phase was de ter mined quan ti ta tively
byU.V.spectrophotometry.Thedistributioncoefficient,D,
was cal cu lated as the ra tio of the Pt(IV) in the or ganic phase
to that of the aque ous phase. Trip li cate ex per i ments and as-
says were rou tinely per formed. In gen eral, D had a stan dard
deviationof±5%. Theuncertaintyintervalwashigherforthe
very high (D > 100) or very low (D < 0.01) D val ues. The de-
ter mi na tion of plat i num(IV) in the or ganic phase was cal cu-
latedbytakingabsorbanceat400nmspectrophotometrically
and that in aque ous was de ter mined by a known method.
Themodifiedsynthesisprocedureforpreparationof
thiocynate is pro posed. The re agent 2-acetyl thiophene thio-
cynate (ATT) was pre pared ac cord ing to a mod i fied pro ce-
dure, which is de scribed in Vogel.19
2-Acetyl thiophenethiocynate (ATT) was syn the sised
as follows. In the first step the bromination of 2-acetyl
thiophenewascarriedouttakinganequimolarconcentration
and sol vent as gla cial ace tic acid and the bro mine was added
dropwise for an hour at 4 0C and then stirred for three hours
for its com plete re ac tion. The re ac tion mix ture was de com-
posed on ice and then the prod uct was sep a rated with ethyl
ac e tate by a sep a rat ing fun nel and then pro cessed. The ethyl
acetate was distilled out under vaccum leaving the bro-
minated com pound which was stirred with potassium thio-
cynate (ra tio 1:2) tak ing sol vent as DMSO at room tem per a-
ture for 8 hrs. The re ac tion mix ture was de com posed on ice
and the yel low solid which sep a rated out was recrystallised
and used for fur ther stud ies. The m.p. re corded was 97°C.
The char ac ter iza tion of the prod uct was car ried out with the
help of IR which shows stretching of C=O at 1640 and
stretch ing of SCN at 2020, NMR in CDCl3 which showsd 4.5
(2H, s, -CH2-); d 7.0-7.33 (1H, t, H4); d 7.66-8.0 (2H, m, H3
and H5) and el e men tal anal y sis re corded was C, 45.88; H,
5.88; N, 16.33; O, 12.44%. The yield of the prod uct re corded
was very low i.e 22.38%.
Reagents
The stock so lu tion of plat i num(IV) was pre pared by
dis solv ing 0.10 g ofhexachloroplatinic acid in 100 mL dis-
tilledwater.Thesolutionwasstandardized20 and a work ing
so lu tion of lower con cen tra tion was ob tained by suit able di-
lution. 2-Acetyl thiophenethiocynate (ATT) dissolved in
methanolwasusedasextractant. A0.1%solutionof2-Acetyl
thiophenethiocynate(ATT)wasusedforspectrophotometric
determinationofplatinum(IV).Alltheotherchemicalsused
wereofanalyticalreagentgrade.
RESULTS AND DISCUSSION
Extraction as the function of pH
Inordertoobtaintheoptimumextractionconditionsfor
platinum(IV)theextractionwascarriedoutatvariouspHval-
ues (2.0-12.0) (see Fig. 1) us ing 0.1 M hy dro chlo ric acid or
0.1Msodiumhydroxidesolution.Theconcentrationofplati-
num(IV) (50 mg) was taken in aq. phase and to it 2.0 mL of
ATT (0.1%) was added. The pres ence of plat i num(IV) in
120
100
80
60
40
20
0
General Procedure
Extractionexperimentswereperformedbyshakingthe
appropriateorganicandaqueoussolutionatanO/Aphasera-
tio of 1 for 10 min. The dis tri bu tion stud ies were car ried out
at 25°C, ex ceptfortheeffectoftemperature.Theinitialcon-
cen tra tion of Pt(IV) was main tained at 50mg through out the
experimentTheATTextractantformedacomplexwithplati-
num(IV), wastransferredintoaseparatingfunnel, extracted
in ethyl ac e tate (2 ´ 5 mL) and trans ferred to a 10 mL vol u-
met ric flask with some amount of so dium sul fate in or der to
7
8
9
10
pH
11
12
13
Fig. 1. Percentage extraction of complex of Pt(IV)
with ATT in ethyl ac e tate at dif fer ent pH.

2-Acetylthiophenethiocynate, ExtractionofPt(IV)
J. Chin. Chem. Soc., Vol. 49, No. 2, 2002 209
aque ous phase at dif fer ent pH was stud ied by the stan dard
method and was found that in the pH 11.2-11.6 range the
pres ence of plat i num(IV) was least. It was ob served that 0.5
mL of 0.1% ATT dis solved in meth a nol quan ti ta tively ex-
tracts plat i num from aque ous so lu tion at pH 11.2-11.6. It is
pro posed that the ni tro gen of the thiocynate func tional group
andsulphurofthiopheneinalkalinemediumhelpsinextract-
ingplatinum(IV)metalionsfromanaqueousmedium.
Table 1. Distribution Coefficient of Pt:ATT Complex in Various
Organic Solvents
Solvent
% E
D
Chloroform
n-Butanol
Toluene
Carbontetrachloride
Ethyl methyl ketone
Ethyl acetate
Hexane
25.0
10.0
0.00
0.00
45.0
99.9
0.00
62.0
0.333
0.111
0.00
0.00
0.818
999
0.00
1.631
Ef fect of equi lib rium time
Methyl isobutylketone
The in flu ence of shak ing time for the ex trac tion of
Pt(IV) was stud ied for 30 s to 120 s. The quan ti ta tive ex trac-
tion of Pt(IV) was achieved af ter 60 s with ATT. With fur ther
increaseinshakingtime,thepercentageextractionremained
quan ti ta tive. The sta bil ity of the com plex was stud ied as a
func tion of time and found that the com plex was sta ble for
72.0 h.
ent tem per a tures from 303 K to 333 K and it was found that
the ex trac tion of plat i num de creases as the tem per a ture in-
creases. The plots of log D against 1/T ´ 1000 (K) are shown
in Fig. 2. TheDH (change of enthalpy) are -6.565 kJ mol-1 for
ATTrespectivelyindicatingexothermicreaction.
Effectofreagentconcentration
Influence of diluents
Variousvolumes of 0.1% re agent so lu tion were added
tothesamplesolutioncontaining0.5mLofplatinum(stock
solution0.1mg/mL)attherespectivepHvalues. Theabsorb-
ances re mained con stant when the vol ume of the re agent so-
lu tion used was more than 0.5 mL. There fore 0.5 mL of 0.1%
con cen tra tion of the re agent was suf fi cient for com plete
quantitativeextractionoftheplatinummetalionpresentin
the aque ous phase. The ra tio of [ATT]/[Pt(IV)] was 10:1.
Thesuitabilityofthediluentswasinvestigatedusing
organic solvents such as chlo ro form, ethyl ac e tate, ethyl
methyl ketone, methyl isobutylketone, n-butanol, car bon tet-
rachloride, toluene, and hexane. The extraction of plat i-
num(IV) was quan ti ta tive with ATT when both were dis-
solvedinaqueoussolutiontakingethylacetateasdiluent(see
Table1).Ethylacetatewasusedforfurtherextractionstudies
asitgavebetterandquickerphaseseparation. Theextraction
of Pt-ATT com plex from aque ous me dia into ethyl ac e tate
was max i mum (up to 99.0%) than the other or ganic sol vents.
So ethyl ac e tate was cho sen as an ex tract ing sol vent for fur-
therstudies.
Ef fect of salt ing out agents
Thepresenceof0.1Mnitratesaltsofalkaliandalkaline
met als such as Na, K, Mg, Ca, and Ba does not show any im-
prove ment over the absorbance value of Pt:ATT ex tract (see
Table2).
The influence of temperature
The ex trac tion study of Pt(IV) was per formed at dif fer-
Nature of extracted species
The na ture of ex tracted spe cies was as cer tained from
the plot of log D vs log R from aque ous me dia Fig. 3, where
3.35
Slope = 0.3502
3.3
3.25
3.2
Table 2. Effect of Salting out Agent on Pt:ATT Complex
3.15
3.1
Nitrate salts
Absorbance at 400 nm
3.05
3
--
0.312
0.312
0.312
0.312
0.312
0.312
Barium
Calcium
Potassium
Magnesium
Sodium
2.95
0
0.2
0.4
1/T x 1000
0.6
0.8
1
Fig. 2. Ef fect of tem per a ture on ex trac tion of Pt(IV)
with ATT in ethyl ac e tate from aque ous me dia.

210 J. Chin. Chem. Soc., Vol. 49, No. 2, 2002
Chaudhary et al.
Table 4. Binary Separation of Pt(IV) with ATT in Ethyl Acetate
from Aqueous Media
logDisthedistributioncoefficientofthecomplexandlogR
is the con cen tra tion of re agent. The slope of the graph is
2.1409 for ATT. Thus the stoichiometry ra tio of metal to re-
agent was found to be 1:2 with the re agent. The com plex for-
ma tion is through ion pair mech a nism. The prob a ble struc-
ture of Pt(IV) and ATT is pro posed and the lone pair of elec-
tronsonnitrogenofthe–SCNgroupandsulphurofthiophene
playimportantrolesincomplexformation.
Platinum found (ppm)
Binary mixture
Metal taken (ppm)
Present method
Standard method
Pt (5) + Mo (5)
Pt (4) + Cr (6)
Pt (6) + V (4)
Pt (5) + Zr (5)
4.98
4.01
5.99
4.98
5.01
5.99
4.01
5.01
Each result is the average of three independent experiments.
+ 4
O
C-CH -S-C
N
2
Influence of diverse ions on percentage extraction of
Pt(IV)
S
2
Varying amounts of for eign ions were added in a fixed
amount (100 mg)ofplatinum(IV)tostudytheinterferencein
therecommendedextractionandsubsequentdetermination
pro ce dure. The tol er ance limit was set at the amount of for-
eign ions re quired to cause ±1.0%errorintherecommended
procedure. TheresultsarereportedinTable3.
Pt
Beer’s law and sensitivity
A cal i bra tion graph for these met als was con structed
under optimum conditions. The graph obeys Beer’s law
5-120 mg for plat i num. The mo lar ab sorp tivi ty and sandell
sensitivitywerecalculatedtobe0.41´ 104 L mol-1 cm-1 and
0.026 mg cm -2 ,respectively.
Separation of Pt(IV) from other pre cious metal ions
The pro posed method fa cil i tates sep a ra tion of plat i-
num(IV) from its binary binary mixture with molybde-
num(II), chro mium(II), zir co nium(II), and va na dium(V).
These metal ions do not ex tract and re main quan ti ta tively in
theaqueousphaseundertheoptimumextractionconditions
1
Slope = 2.1409
R2 = 0.9881
0.5
0
-3.4
-3.3
-3.2
-3.1
-3
-2.9
Log R
-2.8
-2.7
-2.6
-2.5
Table 5. Masking Agents Required to Suppress the Interference
of Foreign Ions
-0.5
Sr.No
Interfering Ion
Masking Agents Added
-1
1
2
3
4
5
Cu(II), Ni(II)
Pd(II)
Fe(III)
Ce(IV), U(VI)
Cr(III)
Sodium thiosulphate
Thiourea
Thiourea
Sodium fluoride
Ammonium acetate
Fig. 3. Stoichiometric ra tio of metal to re agent com-
plex of Pt(IV) with ATT in ethyl ac e tate from
aqueousmedia.
Table 3. Effect of Diverse Ions on Percentage Extraction of Pt(IV) with ATT in Ethyl Acetate from Aqueous Media. Pt(IV) = 100 mg
Foreign ion
Amount tolerable in mg
Foreign ion
Amount tolerable in mg
Foreign ion
Acetate
Amount tolerable in mg
Li(I), Na(I), K(I)
Ca(II)
Mn(II)
Ba(II)
Sr(II)
25
25
10
10
25
10
F-, Br-, I-
10
10
10
10
10
10
10
25
10
10
10
10
NO2-, NO3-
Cl-, SO4
-2
-
ClO3 , IO3-
Cynate
As(III)
Bi(III)
Al(III)
-
BrO3
SO3-2
Tartarate
S2O8-2

2-Acetylthiophenethiocynate, ExtractionofPt(IV)
J. Chin. Chem. Soc., Vol. 49, No. 2, 2002 211
Table 6. Determination of Pt(IV) from Real Samples
Standard samples
% Present
% Found
% Recovery
R.S.D
Cisplatin
Pt-wire
65.0%
99.90%
64.89%
99.81%
99.83%
99.90%
0.0408
0.0407
Each result is the average of three independent experiments.
of plat i num(IV) withtheATTsystemfacilitatingseparation
ofbivalentplatinumquantitativelybytheproposedmethod;
the re sults are in Ta ble 4. The ef fect of some com mon tran si-
tionmetalionswasstudiedandtheirinterferencewasmasked
by us ing proper mask ing agents (see Ta ble 5). It was ob-
served that the Zn(II), Zr(II), Th(IV), Ag(I) metal ions do not
interfereintheprocessofextraction.
Nomenclature:
D=Distributionratio.
%R=Percentagerecovery.
aq. = Aque ous phase.
org.=Organicphase.
s = Sec ond.
h = Hours
Theproposedmethodalsofacilitatesdeterminingplati-
num(IV) from plat i num wire and cisplatin in jec tion (see Ta-
ble 6). The con fi dence limit for 95% was cal cu lated and for
cisplatin it was ± 0.06% and for plat i num wire± 0.1%.
<Subscripts>
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Key Words
Extraction; Platinum(IV); 2-Acetyl
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