Separation of amines by ligand exchange

ANALYTICA

84

CHIMICA

ACTA

is tlic exchange of ligands coordinated to metal ions that “Ligand Excliange” in turn arc bound to a cation-cxclianging material. Thus, amine molcculcs may l)c substituted for ~Unnl~Jnia molecules in complex ions such as Ni(NHg)$+ while the of ligand cxcliangc to the metal ions remain bound to the exchanger 1. Applications clution cliromatogxqliy of amine mixtures liavc been cxplorcd in a preliminary way 2.3, The technique has many possibilities, for the nature by h’iTIIRISLJ, AND WALTON of the coordinating metal ion can bc varied as well as the nature of tlic cxcliangcr matrix. This report describes a comparison of 3 different tyl>cs of cxchangcr, each loaded with nickel(II) ions. A limitccl number of amines was used ;Incl aqueous ammonia was the cluant. Most of this work was done with arnincs labelled with carbon-x4, which makes it possible to USC very small amounts of adsorbate and hence to evaluate relative distribution coefficients and theoretical-plate licigllts. We have also been cxperimcnting with a flowing differential rcfractorneter for monitoring column effluents, and some of the data here reported were obtained with this instrument.

Materials Four atnincs labcllcd with carbon-14 were used: ctl~nnolnmine and dimcthyland Itamine, obtainccl from the New ISngland Nuclear Co., and clietlianolnminc hutylamine, obtained from Nuclear licscarch Cllcmicnls, Inc. They were diluted with water and inactive amincs to give cu. 0.01 M stock solutions with activities of about I ,uc/ml, Volumes of 0.1-0.2 ml were placed on the columns. The inactive amines (which included bcnxylaminc) were purified by distillation. Tin-cc sulfonntccl polystyrcnc resins (Dowex-so) were used, with nominal cross-linkings of 2O/“,, 4o/0 ancl So!,, The 8% cross-linkccl resin was 200-400 mesh, and the others ~a-100 mesh. A carboxylated resin (Bio-Rex 70), which is a crosslinkccl polymcthacrylic acid, was usccl in go-roo mesh size, and so was a zirconium phosphate cation exchanger. All these eXclliUlget% were obtained from the ISo-Rad Corporation, Richmond, California. Preliminary tests were also mndc with-a mncroreticulnr sulfonntccl polystyrene resin, Amberlitc X%219, kindly supplied by the Rohm and Haas Company. Tllis was unsuitable for our purpose bccausc the nickel ions (ancl also copper(I1) ions) Amal.

Cltinr.

.dlcln. 33 (rgqj)

84-00

SEPAI1ATION

OF AMINES

BY LIGANU

were displaced too readily used as cluants.

EXCHAStiE.

by the ammonium

III

85

ions in tile aqueous ammonia solutions

Col2tnr9isand analyzers The columns had IO-xz mm internal diameter and contained x0-15 ml of exchanger in bulk volume. Flow rates were generally 0.3-0.4 ml/min. In most of the tests the effluents were collected by a Vanguard fractioncollectar, Model 1000. Carbon-q activity was counted by liquid scintillation using a Packard Tri-Carb spectrometer. Benzylamine was determined by absorbance at 255 mP*

The data for YO/, cross-linked sulfonuted polystyrene resin were obtained wit11 a flowing differential refractomctcr made by IYatcrs Associates, Inc. This is designed specifically for liquid cllromato~ral’lly. It allows continuous recording of the difference in refractive inch bctwecn influcnt and effluent, and it is extraordinarily sensitive. We IUVC so far hccn unrrblc to use the fullsensitivity owing to random

fluctuations

in

rcfrnctivc

The nickel content

indcs.

was found by preparing small UScd for ligand CXChllgC, measuring their hulk volume, tllcn cluting the nickel with 2 N llydrocllloric acid and determining it by ~D’I’A titration. ‘L’hc effluents from tllc columns used in ligantl cxchangc wcrc also analyzed for nickel to estimate the leakago of nickel that occurred ‘Tliis \Vi1S done pllotolIletrici~lly using tllc dilnctllyl;LS ;lClUCOUS iUllTllOllii1 WZlS pSSCd. glyoxitne method of Ch~ssI:s A~I) 13Aswxc;s*8. C~JhInllS

of

WK.hangCr

of the various exchangers

in the! SMIlc

Way

t1S the

CdUIllnS

PH

ml

0.994M

NoOH

Fig. 1. l32tcrminirtiOll of formation constnntn for Ni( I I) ilYlt1 tlicthilnolnllrillc. clictl~anolammoni~~n~ chloriclc plus slight CXCO~H 14Cl titr;rtctl as shown. Upper 0.80 Rf in 1X1. I,owcr curve, solution is 0.50 114 in KCl, 0.0~80 A? in NiCln.

I00

curve,

ml

0.200 solution

W is

1” Arid

Chim.

Acln,

33 (rgG5) Q-go

86

A.

G.

HILL,

It.

SEI~GLI!Y,

5’. WALTON

H.

wc’rc made to cletcrmine the stabilities ‘1’0 help intcrprct tlic data, attempts of the various nickel-amine complexes in aqueous solution by the glass-clcctrodc ‘1’11~ complcxcs with dimcthylaminc and titr;ition mctllocl of (hI,VIS ASI) 13JlCIutylominc wcrc SC) unst;lMc by comparison with the prdonated forms of these amincs that nickel hyclroxicle prccipitatecl almost immccliately after the inflation point was rcachccl in titrating mixtures of nickcl(II), I-lL+(L =: ligand) and hyclrocl;loric acid with sotliurn hyclroxiclc. With dicthanol;lminc, however, curves were obt:iinctl which allowed the: first two stability constants to bc detcrminccl (Fig. I). ‘I’hc association had been mcnsured sta?)ility constnnts fol the niclcc!l(iI)-etll:Lt~olnmitlc In-cvirmsly”.

‘I’A

_..-..

131,l’

I

. ,_ _ ._.._ -

/:‘.wlllcu&w

_._- --.-..-

cJ*os.+fiJrlriJrg _____..______

--

.--. *vi

(1 rrd

-- -- . _ ..-.- ------.___._.-.___...-_--__

.^____.._.-_...-_-. .*I

c’orlll!lrl

(III JJld/Jd) .______._._. ______-_

_.._..._.

JuiJre

.-_-_

/:lllfifJJl

AVIin CrJllCJt. (A,?) .___ -.--.-.___._--_

._.-_-_...-

7JfJ!t,JJlc! ” _____

-

0.22 0.‘).+ 0..1.;

“.fJ7 O.C)7 0.07 0.x7

0.12

3.8.5

O.XX

.J.fnl

0.X8

4.3’L 1o.h

o.HH I.10

1.1.5

I..?0 I .20

1 :,?o 1 .‘JS

0. ‘2 I

ll*‘J.) 0JJ.i O.cJ.) 0.0.)

Z..}X _P--....

-

___-..

--

-_-__

.

.

_ .__.

__

__________

1’ IXctol --- tliC~tl;lilol;ililinc; ctut :G cttl;lnolnliiiilc; ttimcttiyl amino; bcnzyl I- twrlzyl~~nlinc. 1’ Elution votlltncs ;IL’c muttiptcs of ttlc bulk c,otun~n votunlc, (htk

COtUl1lll

\~Ot1lllW).

_.

=

.

.

.

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

ttir~~ctt~yl~rn~ii~c;

_

butpt

i.e. (volu~t~cpnsscctto clutc

-2 wbutyltlrc peak)/

SEPARATION

RESULTS

01’ AAIXNES

Izl’ LIGAND

EXCHANGE.

57

111

AS11 UISCUSSION

A selection of the measured peak clution volumes are given in Table I. The elution volumes arc csprcsscd as multiples of the bulk column volume with no attempt made to allow for the void volume. It is hard to evaluate the effective void fraction of the columns, since dissolved uncomplexed amine pcnctrates the resin beads along with water and ammonia, but the minimum elution volumes obtained with very weakly bound amines and high ammonia concentrations suggest that the effective void fraction is o-s-o.G, comparccl to 0.4 for uniform non-permeable spheres. It is interesting to note that the order of clution of the 4 lK-1abcllecl amines Rctwccn low cross-linked sulfonatecl polystyrene is different for different resins. of the nickcland zirconium phosphate the order is cxnctly reversed. The stabilities amine complexes in water appear to have little to do with the clution order. The 2 amincs for which reliable data are availal~lc have stability c<)nstilIIts as fo1lows: ATI :=I: 620 ancl I<:! = 45. CtlliUl0lilmillC Ir’l = 950 ant1 Kc 125; dicthanolamine Ethanolaminc shoultl bc held mcwc strongly by the nicltcl-loadccl cxchangcrs than tlictllanolaminc, and this is true for iIll CXCllil~njiCrS cxccpt zirconium pllospllatc, but the ratio of the distribution constants varies from one exchanger to another and is considerably larger than the ratio of tllc Il’r values. It sccrns tllilt the affinity of the amities for the cxclinngcr matrix is mow

0 IO 20 30 40 so i--O.94 M NH,---+--1.B

--it+ M NH, -

i EO

ml 0.77M

C

NH,

Fig. 2. ISlution 01 arninc 3nixtllrc on h’Lsulfr8nic rcnill. 2’%, crcw+linlwd, 50-f 00 nwsll. 1~ullccolumn voli~rnc, 10.6 nil; tlianwdx, I.0 tin: flow rate, 0.3 nil/nlin. Ortlcr of chition: clicthtnoltllninc, CtlliLll0lnllliIlc, tlilnctll~l~liliilC, Ln~lylnrninc. Fig. 3. Elution of ;rniinc mixture on Ni-cntl,oxylic resin, go-100 tncsh. 13ullc column Volulllc, x.+.0 ml; cliiwictcr, I,0 an; flow rate, 0.3 nll/niin. Ortlcr of clution: lx~tykuninc, ditiicthyl;lliiillc, cthnnolnminc.

A.

88

G.

HILL,

It. SElXLEY,

Ii.

I:. WALTON

important than their affinity for the nickel ions. This is very obvious with benzylamine, which is held strongly by a polystyrene-base resin but very weakly by zirand the same cffcct is noted with butylaminc. This is held strongconium phosphate, ly by the I;olystyrcne matrix but only weakly by the less carbonaceous, less “oleophilic” matrix of tile carboxylic resin, cross-linked polymctllacrylic acid. Diethanolamine i!j boUnd strongly by the c!xtremcly “llydroplliliC” or polar matrix of zirconium phosphate. Whatcvcr the reasons, the changes in selectivity orders between different exchangers are of obvious analytical interest. Elution curves for mixtures of amincs on sulfonic and carlwxylic resins arc shown in Figs. 2 and 3.

r + I+\+ i \+ +

L+7’+ s<

-

I +

= 3.5flll

I

i

liigurc 4 slicers tllc clution curve for a single amine on 8 column of carboxylic resin. It has almost iCh1 shape for a tract iUTlC)U~lC of adsorbatc and pcrnlits cvaluation of the number of thcorctical plates in the column, using the rclation7: -

0 I/

--‘

V IlllIX

2 1/N

whcrc lV is the number of theoretical plntcs, (>I’ is the half-width of the band at a concentration r/z.718 times the pcnlc value, and V ,nclxis the volume of cluant passed at t11c pcnk, corrcctccl for the void column volume. Taking the void volume as onchalf of the 1~111; volturIc, the thcorctical-plate heights were calculated for different

SEPARATIOS TA.x3I.E

OP

AMINES

BY

LIGAXD

EXCHASGE.

s9

III

II

-f3drwger

.-Intine

0

I3irliotr (brtllr

PlOll!

volio7tc colll~~r71

val7rn1es)

IIimcthyl l~imcthyl I~utyl Dirncthyl

3.Go 2.77 1.7 Zirconium phosphntc 3.2 --_-_ -..-_ 0 l’hc first two cxchnn~crs wcrc 50-100 1ncs1~.

Sulfonlc, 2’2, ‘Carboxylic

l1cigl1t

(no.)

__

1.8 1.o 1-S 5.5

--

‘Ike data are summarized in Table II; they show tliat the cnrbosylic columns. resin gives the sharpest bands and hence tlic smallest plate Iicights, while zirconium phosphate gives the largest plate heights. The bands obtained with zirconium phosphate are, moreover, decidedly unsymmetrical. One concluclcs that tlie diffusion of these amincs is fastest in the carboxylic resin (since the bead size was roughly the same as in the sulfonic resin) and slowest in the zirconium 1Aiosphatc. The concentrations of nickel and phosl~hate leached out of the exchangers by the ammonia solutions are shown in Table II 1. They are approximate only, and seem to get smdkr as more of the nickel ions in the exchangers are rcplaccd by ammonium ions.

NICKlit.

AN;)

_---_ I~sclrrmger - .-___

1’11O51’11h’l’l: ._ .-. .-... ._._._

A r,rmmitr

IZt’l’l.UI:N’E3

(lI.IOkR/~)

-..--..-comti.

._...,_..-....- ___^I-.-

.vi

CONCII.

.-... . . - .._.______-_. 2.T . I”.‘4 Sulfonic, St;/, 1.1 . If-J-4 1.x 1.2 Sulfonic, .+“/, C;Lrboxylic 2 * 10”’ 0.7 Zr phospiiatc 0.9 4 . x0-b -_____._. --..____. ._.,...-. -_._..--.- . . .-.--_ - _._._.

_

CONTlNTS:Ol~ ..-_-

-Pop-

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

cot1cIl.

..-.-

7’ 10-a

The support of the U. S. Atomic Energy Commission under Contract AT(rx-I)499 is gratefully acknowledged. One of us (A.G.H.) rcccivccl a Natioiial Science Foundation Iicllowship under the Summer lb3ciWcll Participation program. The liquid scintillation spcctrometcr was purcliascd by funds given by tlic Shell Companies, Dow Chemical Company and the University of Colorado Committee on Coordination of Researclr . SUXKhlhIiY

The clution behavior of 4 amincs, ctluinolnminc. diethanolanrine, dimcthylamine and It-butylamine, was studied on 4 cation-exchange resins and zirconium ammonia was used for clution. phosphate, all l&ded with nickel ions. Aqueous of diffcrcnt types. The Different selectivity orders were found with exchangers resin gave the sharpest bands, but 2% cross-linked carboxylic cation-exchange sulfonic resin gave the best separation of these amines. Anal.

Chirn. Acta, 33 (x965) Q-go

90

A. G. HILL,

12. SI:DGLEY,

!.I, I’. WALTON

cli&hanolaminc, dim&tliylamine et ItL’blution clc 4 amines (bthanolaminc, I~utylominc) a 6td examindc sur 4 rdsincs &A~angcuscs clc cations et phosphate de ;I,ircouium, tous char&s tl’ions nickel. L’ammoniaquc a 6td utilide pour l’dlution. 1~s auteurs ont trouvb clivers orclres clc sblcctivit& avcc Its &A~angeurs de diffdrents types. ILL r&inc carhoxylique a clonn6 142s bancks Its plus nettcs; rnh la r&he (2’vo) ;L pcrmis la mcilleure sCparation dc ccs sulfonicpc, h liaisons transvcrsulcs amincs.

Das I~lutiotlsvcrllnltcn von 4 Amincn, Atl~anolamin, Diiitllanolamin, Dimctllylamin uncl wI3utylatnin wurclc an 4 I(~ttioncnaustauschcrllarzcn uncl Zirkoniumpllospllat untersucllt, die mit Nickelioncn bcladcn wtrcn. %ur Elution wurclc wlissrigc Ammoniaklijsung hcnutxt. IIic Austauschcr xcigten vcrschiedene SclektivitLit. IIilS karlxnlsaurc I(nlionenaustuus~~~erl~~~r~ Crgilh tlic sch!irfstcn I3anclcn, tin 27&cs vcrnctztcs sulfoniscllcs Harz ergal> die lxstc ‘I’rennung dcr Amine.