Titrations with extractive end-points

Titrations with extractive end-points

546 ANALYTICA TITRATIONS WITH III. THE CIIIMICA E~YTRACTIVE IODINE VOL. 13 ACTA (1955) END-POINTS TITRATION LY ChwtisIry Schoul, Unrvcrs...

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546

ANALYTICA

TITRATIONS

WITH III.

THE

CIIIMICA

E~YTRACTIVE IODINE

VOL. 13

ACTA

(1955)

END-POINTS

TITRATION

LY

ChwtisIry Schoul,

Unrvcrsily

of Sydney.

Sydrrcy, N.S. W. (Arrshlia)

and ‘L’lic tril~hctiylmctliylarsonium cation hns 1~~7 appliccl to pcrmang:inatcl, ‘J’flis paper deals with its npplidiChromatc2 titrations, using cstrxtivc cd-points. cation (as tripl~cnylmcthyl~~rs0nium iotliclc) to the titration of arscnitc ilnd thiosulphatc with iotlinc, and the rcvcrsc’. A convcnicnt mcthocl of estimating iodine is by titration with stanclarcl thiosul‘I’hough the blanks for N/r0 iodine arc lJl’i1t.C or arscnitc, using starch as indicator. ncgligiblcS tllc use of starch xi indicator suffers from a nuinhcr of clisntlvnntngcs, the chief being: (I) It gives a water-insolul~lc complcs with ioclinc. (I I) Thcrc is il drift cd-point, which is murkccl when the solutions arc dilute. (III) ‘I’hc end-point is not visible in tlic prcscncc of li\rgC quxntitics of colourccl ions. (IV) Starch CilllIlOt solutions nor strongly i1CiC.lsolutions clue to hydrolysis. lx cmployccl in ;tlcoholic Estraction of ioclinc into Cilrb0n tctracliloriclc or chloroform at the cd-point is an illtC9YliltivC! mctliocl of titration 4. IJOtcntiOmctric clctcrminiition of tlic end-point but not in the ilrscnitc/ioClinc is successful in the tl~iosull~li~~tc/iocliii~ titrntion4*“, titrzition, as the rcclos potcntiztls of osiclant illIt rccluctant arc too close. Colourccl solutions may 1x2 titriltccl with iodine using the lx~tcntiomctric mcthocl, using tryl)flilvin as inclirXtor7 or CXtrilcting or visually, the iodine with carbon of colourecl tctrxliloriclc. In tliis l)i1lX!r, ;i new nicthotl is suggcstccl for the titration solutions wit11 ioclinc, in which tllc cncl-point is indicated by the cstrilction of ycllowbrown Pli,MrAsI, into an 0rg;niiic solvent layer. Tliis mcthocl is i\l>lJliCablC to the arscnitc titration, tlicrc is no limit to the clcldh of colour of the aclucous layer, and the I’li,,MeAsI, is non-volatile.

‘I’ril~liciiyIii~ctl~ylarsonium tri-iocliclc, lJli~,lIcAsI,( I) has Ix~2n prclx&cl nccording to S*rEIs IiUI’l: t\\sIJ SCIIWI~N” ancl also by the idClitiOl1 of ioclinc to tril~licnylmctliyl;~rsoiiium iotliclti. (1) is insoluhlc in ether and water but rcuclily solul~lc in chloroform, ctliylcnc clicl~loriclc, tctriKl~l0r0Ctlln~lc, carbon tctra.cliloriclc, clilorlxnzcnc imcl boiling illCOllOl. Iodine titrations with (I) us indicator arc similar to the ycrmanganatel and clichroRcfcroms

f~. 5.~3.

VOL.

13 (r9s5)

TITRATIOSS

WITH

ESTRACTIVE

END-POINTS.

III

547

+ ion is added as a rO/Jaqueous solution mate 2 titrations, except that the Ph,McAs, of PhJIcAs I. The yellow-brown colour of (I) in the organic layer is readily seen against a white background and is not affected by colourcd ions in tllc nqucous layer. The method was al>pliccl to the titration of nrscnitc (Table I) and thiosulphatc (Table II) with iodine solutions (:Y/ro, X’/zo and .\‘/xoo). Hlanks were ncgligihlc for The rcvcrsc titrations wcrc N/r<), o.02 ml for N/~o and o.04 ml for N/xoo iodine. also successful, the end-point being indicatccl by thr disaplxarancc of colour in the iodine: o.04 ml ; organic layer. The blanks were similar (X/TO ioclinc: o.or ml ; N/go ml). Large concentrations (up to 200 : 1) of chromium (I I I), nickel N/rw iodine : 0.4 (II), cohult(II) and mangancsc(II) were without effect in titrations ot thiosull~hntc of arscnitc with iodine, nickel with iodine (Table I). In the cast of titrations (I I), mangancsc( I I) and cobalt (1 I) were lxccipitntcd, probably as basic carbonates. These precipitates fell into the organic layer, making it impossible for the end-lloint to bc obsc*rvcd; chromium(I1 I) did not prccil)itatc and did not intcrfcrc: (‘l’ablc II). Coppcr(I I) ions liberate iodine from the iodide ions In-escnt” and so wc’rc: not tcstccl for interfcrcncc. Chloroform, carbon tctrachloridc and chlorbc~nzcnc2 were SiltiSfilCtOry extractants for (I), Ijut the pilrtition coefficient of cthylcnc! it;ltc~l cuprous layer. Attempts to filter off the culx-ous iotliclc Ixnforc titration were not successful.

In

all

C~SCS 25 ml alqr~ots of solution wcrc ppcttccl intc~ tlw flask nntl then tlm I’!:. rqucow, (Cl.5 ml) iltltlctl, togctlicr wltli 5 nil c,f ~l~lorof~~rnl or cxrlmri tchxchlorrclc. The conclltions of prl anti volunic wcrc Iclcntlcal with tliuvc tlcstrll~ctl for the stnntlertl nrscnltcll ant1 th10Sll~~lhatC'2 tltr~ltlcJllS. ‘I’hc intcrfcriii~ cations wcrc atlclcti iis tllcir Sllll>~liltC\ dissolvC~l iii wutcr (CU. loo ml). l'11c itrthnc suluticm was iLtItIc!Il tlropwac with hllaklng near the Cntl-plJlnt. wliiclr WILS intlicxtctl by the cok~urlc*ss orgnntc layer turning yellow-brown. Pll,hlCASl

l’ripl~enylrrreflrylurso,lrrc,n fri-lodicfc (I) I 131~ ;\lcAs I,. ‘I’hln was ina& by two mcthotls. xtldition of iodine in dry (i) Prcpnrctl according to SCILINICOPI: AND SCI~WI~N~ by the clropwhc light pctrolcnm to triphcnylnrslnc in dry llgllt pctmlcum.‘I’hc rcsnltlnfi unstable tlr-~otlo trlphcnylarliinc was then rcfluxctl with methyl iodide for 3 Ilout-h. On cooling the tri-ioclitlc scpnratccl as a brown oil which boun crystalhzctl. I'll,hS I'11:,As12

Ovcmll

+

I,-----r

I'll,ASl,

NC1 -> I’h,hlC,\~l, yield = 54:;. +

(I) was rccrystillllzctl from nqilcolis nlcolid, as lustrous In-own Icdlcts, ni.p 107-8’ (cl), Iltcriltll~c" rcporte m.p. 107~ (cl). (ii) I’ri~~hcnylmctli~l~rso~iium iotlitlc (9.0 g) was tlissolvctl in nlcol~~l (100 ml) ilntl iotlinc (3.x g) in alcohol (loo ml) ndtlccl tlropwisc to the hiling solution. iLlId tlicn tllc MJllltion rcfluxctl fur 30 minutes. \Vatcr wi\S :ddcci to the boiling soliition and Ict cod. Brown Jcaflcts of (1) scprrratctl. Refererrces p. 543.

N. /iA. GIBSOE;,

548

(I) was ~olloctcd, washctl with ro~-90 (d). TIE molting point

fE. A.

VOL.

WHITE

aqucou~ alcohol and recrystalliaed was not deprcsscd with a sample

of

from (I)

13 (rQj5)

aqueous alcohol, m.p. made by method (I).

Ph,;MeAsI -/- I2 -> l?h,MeAsI, yield = 9GX. Ik!

iO&:YC

\VitS

Clf&XtnirKXl by

tflc

Ill~thOd

‘I)WYOR

Of

AND

1 = 54.2x%, L~II~MoAsT~ rcquircs:

NYfiOLbt

=.

54.15% I = 54.25Y,.

1~0ur1d:

N/x0, iV/.y~ and N/r00 solutions of iodine IQ, arsenitell and thiosulphatelG pared. Solvent: Carbon tctrachloridc (5 ml) Volume of r(/, Ph,McAsI solution = 0.5 ml TABLE N/to,

N/so

Uin

. -__

ion: rodrtts

l’otmtbnctric _--_

of todtne

100:x

N/IO

200:x

N/so

NISJ

due to colourcd

N/lo,

_ Z~~rJrriteg iom

-._

___

25.20

25.2

24.49 24.89

24.49 24.91

25.21

25.20

24.50 24.90 25.21

24.49 24.89

Cr-l-n Cr-+-3 Cr+” **

.

25.2

I

24.48 24.9: 25.23

1

_._I..

.

arscnite

II solutions

(25

ml) with iodine.

-

___.__.

Mean titration (mr) Starch Ext*activs

Concmtration of dodwm

I__-

.

ions present.

--__

---.

._-- _.

._

_-__.__ _

Molar mtio ion: iodine

.. ..

_.--____

N/go and Njroo

-__-

Starch

-

24.48 24.92 25.19 24.50 24.9 I

N/r00

TABLE -_-._

Extracliva

~___

-_

not visible,

mcthotl

-_._.......--

(ml)

Iv110

Nf5o Njroo N/IO N/SO N/x00

-.

:Clrafbn

24.47 24.91 25.20 24.50 24.91

Nl IOO N/IO

zoo:1 200:x x00:1 200:x 200:x x00:x 200:x 200:x

End-point

Mean

_ _- __-__--

-- .

Ioo:x

._.-- _ ..____ _

__.-

Concentrafion

zoo::

l.

I

and N/r00 sodium thiosulphatc (25 ml) with iodine. Results by cxtractivc cc~mparctl with those by potcntiomctric’,G and starch indicator methods.

._. .--.--...---____ __“__ fnte?J#tinp &10&tralio .._ -.

were prc-

.____-_

100:1

N/IO

25.12

zoo:1 200:x

N/so

25.24 25.17

N/x00

25.121. 25.23**

25.18**

__

Trtratron results in absence of chromium(II1) seen when chromium(II1) was prcsont.

ions; as in Table

I the end-point

could

not

be

hCKNOWX.EDCEMENT

The

authors

Referettccs

wish to gratefully

p. 549.

aclcnowlcdgc

a grant

from

the Commonwealth

Rcscarclr

Fund.