Fractional sublimation of some metal chelates of thenoyltrifluoroacetone

Atwlytica

Chimka

Rcta

Efbcvicr Publishing Compnny, Amsterdam Printed in The Ncthcrlanmds

FRACTIONAL SUBLIMATION THENOYLTRIFLUOROACETONE

OF

SOME

METAL

CI-IBLATES

OF

The initial work of BERG AND TRUEMPER~-3 and BERG ANT) DOWLING~ confirmed the general volatility of the metal chelates of the @-diketones. BERG AND HARTLACESthen reported the separation of a number of mixtures of metal /?dikctone chelates by a vacuum fractional sublimation technique which they devcloped. More recently, BERG AND CHIANG 8.0 reported on the volatility and fractional sublimation of the dipivaloylmetl~ane chelates of the lantlranide and related elements. The /I-diketones which have been investigated most extensively in these studies arc listed in Table I. These investigations have indicated that thechelates of acctylacetone TABLE

I

/?-DIKBTONES

XNVRSTYGATED -_.___--

--VP

.-

sy ,,lb;;r

UP;1 C 9hatnc

Nonle

1

ncetylacctonc Trifluoroacctylacctonc Hexafluoroacctylacctonc Boazoyfacetono Benzoyltri~uoroacetonc Dipivaloylmcthanc

2,4-i~entnncdionc

I, 1, x -Trifluoro-z,Li_pcntancdione r,I,t,5,5,5-Ncxafluoro-2,4-pcntancdiono I-Phonyl-x,3-l>utanedione I-P~cnyl-4,4,4-triauoro-r,j-butrinedionc 2,2,b,G-Tctramcthyl-3,S_heptancdionc

EAA HFAA EA

BPM

provided the most satisfactory separations and that the /%dikctones which contained aromatic groups did not lead to favorable results, although many of these chelates were volatile. For example, the chelates of benzoylacetone and benzoyltrifluoroacetone generally recrystallized in diffuse zones of microcrystals or condensed as liquids, and good separations were not possible. In addition, benzoylacetone formed few volatile chelates. It would be advantageous, however, to use the aryl /?-diketonates in fractional sublimation separation methods for several reasons, First, these chelates form very insoluble complexes in aqueous systems. This would result in more complete and easier separations of the metals from their initial environment. Second, the aryl chelates are usually more stable than those of the aliphatic @diketones, Such stability would be helpful under the experimental conditions of fractional sublimation. Third, * Present address: Ky.. qrora, U.S.A.

Department

of Chemistry,

Vifla

Madonna

College,

Asal.

P.O.

Box

46, Covin@on,

Chim, Acta, 42 (xgG8) 207-212

B.

208

W.

BERG.

an increase in separation of t.lJc recrystallized zones might 1x2anticipated. trifluoroacetonc (T’TA ; x-(z-thencJyl)-4,4,4-trifluoro-r,Q-l>utancdione)

K. I’. REED

Tlicnoyl-

readily with mctai ions in aqueous solution, and forms chelates which are both quite stable and insolul~lc in water. TTA combines the effects of the tliienyl group, wfliclk is aromatic, and tlJc triflu~)ro~i~ctl~yl group which has been clcmonstrnted by l31-m~ ~NI> xW-LACE to cnhancc the volatility of the j%clikctonc cklatcs. Tlic cllclatcs of TTA have lxcn well characterized and have been demonstrated to he volatilcl-:J. The extension of fractional sublimation separation studies to incluck the chclatcs of TTA is both logical and warranted.

reacts

The schematic diagrams for the sublimation apparatus employed in these stuclics and the specifications, construction details and operating procedures were 33ricfly, the apparatus consists of a pyrcx tube I’CPOI-tCd by hIlG AND ~rARTl.AGEG. (x2 mm 0.d.; lcngtli 120 cm) along which a nearly linear tcmpcraturc graclicnt is maintained. The pressure inside the tube is held at approsimatcly I mm Hg by means of an air throttle-valve at the hot end of the tube, while a vacuum is applied at the cool end. Sampies are introduced in small aluminum boats at the hot encl before the pressure is recluced. The sublimed chelate is entrained in a stream of air and passed through the tube until recrystallization occurs. The recrystallizecl chelate usually is found in discrete zones in the sublimation tube, The temperature range which corresponds to this zone is defined as the recrystallization zone temperature. The chelatc can be removed from the tube by cutting the tube into appropriate scgmcnts and scraping out the chelate, or by dissolving the comples in a suitable solvent. The recovery calculations are deterlllined on the basis of the weight lost by the sample on sublimation. Since the chelates are for the most part all stable at the temperatures involved in the sublimator and since no traces of the sublimed &elate could be found anywhere else in the apparatus, the recrystallized zone was assumed to contain all the chelate which was volatilized. In the case of the chelates which decomposed as they sublimed, the yielcl was determined by recovering and weighing the chelate.

The metal chelates of TTA were prepared according to the method of BERG An escess of a hot 5% aqueous solution of the metat nitrate (except for l3e) was added to IO ml of a hot 1% ethanolic solution of TTA and immediately buffered with sodium acetate. If precipitation did not occur on cooling, the solution was evaporated on a steam bath until the first indication of the separation of solid, and then cooled. The precipitates were filtered, washed with water and air-dried. The

AND

‘rRURMPER3,

R~nai.Cl&%.

Acta,

42

(rgG8)

207-222

FIIACTIONAI.

SUIJLIMATION

OF

METAL-TTA

CHIZATES

209

chelates were purified by recrystallization from the minimum amount of boiling etlxmol. The beryllium chelate was prepared by shaking 50 ml of a 5% aqueous solution of beryllium chloride with 5 g of sodium acetate and 40 ml of a r% solution of TTA in ether. The dicthyl ether layer was separated, washed with water until neutral, dried over sodium sulfate and evaporated to dryness. The crude product was recrystallized from ethanol as above. The chelates were characterized by their melting points when possible, and all were confirrncd by their infrared spectra.

The sublimatittn recrystallization xonc data and the recovery data for the TTR chelates arc summnrizccl in Table II. An esamination of these data shows that the chelates of TTA formed well-defined crystalline zones, and when no decomposition occurred, the recovery of the chelates was quite good, often quantitative, The

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sublimation.

chelates of iron(f1) and mangancscfI1) were not volatile and the chclate of cadmium was only slightly volatile. The chelates of L~ranyl(II), zirconium, lead(H), and chromium(II1) decomposed during the sublimation process, even tvhen lower sublimator temperatures were employed. Even though decomposition accompanied the sublimation of these complexes, some recovery of the pure chelate was found. The sublimation recrystallization temperatures for the TTA chelates are graphically presented in Fig, x, Rlznl. Cfrim. Acta,

42 (~968)

207-212

II. W.

210

BERG,

K. P. REED

The recrystallization zone temperatures of the chelates of TTA are compared to those of the acetylacetonates ancl the benzoyltrifluoroacetonates in Table III. The cliffercnces between the highest temperatures of the recrystallization zones indicate in a qualitative way the case with which a given separation may be effected. For most metal chelates, the differences between these temperatures are found to be most advantageous in the case of the acetylacetonates. However, some separations are possible with the chelates of TTR which are not possible with the chelates of acetylm

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TEMPERATURE Fig. I. Sublimation

COMDARISON OB VARIOUS

iorr

M&t

c I80

rccrystdlizntion

totnpcrnturcs

OF TIIII; RBCRYSTALLIZATION hlt3TAL Clft.3LAT15S 017 TTA,

Bl'A

TTA

AR

BTA

x80-170 t 75-t@ * 75-145 I GS-rG0 t Go-r45 155-127

137-x t 7 II r-88 14x-120 t&-1 14 St-60

Liquid Liquid Liquid 128-120 Liquid

102-77

t

Fo(II) Mn(I1) Tl(II1) Cr(II1) Zn(I1) Bc(l1)

Not volntilc Not volatile

-

138-x18

I OG-so 3fht 31-15

$2-138 x52-125

-

X47-110 145-x23 x40-1x2

I35-I~3 134-90

127-102 Ckimz.

various motnl z-thcnoyltrifluoroncctonatas.

TEMPEI~ATUROS

hi\ AND

Pd(I1) Pb(II) Co(I1) Cu( II) FcfTIT)

And.

ZONE

for

Acta,

42

t33-ro3 Liquid

94-74

88-67 102-82 8$&.5

(x968) 207-212

r26-101

Liquid

W-70

Liquid I x9-103 97-7 1

FRACTlONAL

SUBLIMATION

OF METAL-TTA

CHELATES

2x1

acetone. For example, iron(II1) can be quantitatively separated from Al(IIX), M&II), Ni(If), Mn(II), and Fe(II) by fractional sublimation of their TTA chelates, but not their acetylacetonates. On the other hand, M&II), Al(III), Zn(I1) and Be(I1) can be separated as the acetylacetonatcs but not as the chelates of TTA. The effect of the thienyl ring on chelate volatility can be shown by comparing the sublimation results of the TTA chelates with the benzoyltrifluoroacetonates. Many of the chelates of BTA condensed as liquids and were not suitable for sublimation studies, whereas the volatile chelates of TTA crystallized in well-defined zones. Also, the chelates of TTA were less volatile than the corresponding ones of BTA. The combination of the thienyl group and the trifluoromethyl group in TTA apparently strikes a balance in which the trifluorometl~yl group increases the volatility of the diketone while the thienyl group contributes to the formation of crystalline sublimates. One may conclude from the recrystallization zone data that many chelates of 'JTA are sufficiently volatile and stable to be fractionally sublimed in vacuum and recovered with high yields. The differences in the recrystallization zone temperatures observed among the chetates studied indicate that a number of mixtures can be resolved by the fractional sublimation of the TTA chelates. Still, the best overall separability of metal chelates by fractional sublimation has been found with the acetylacetonates. The results with the TTA chelates compare quite favorably with, and in some respects are superior to, the results reported for the chelates of trifluoroacetylacetone, he~afluoroa~etylacetone and benzoylacetone. Faculty

This work was supported in part by a National Fellowship awarded 1C.P.R.

Science

Foundation

Science

SUM MARY

Studies on the fractional sublimation of various metal #5.diketone chelates have been extended to include the chelates of thenoyltrifluoroacetone (‘PTA). Many of the common metal chelates were found to be stable, to sublime readily, and to form well-defined zones in the vacuum fractional sublimator. Of the 17 chelates reported only those of manganese(I1) and iron were not volatile. The chelates of UO2(11), Zr(IV), Pb(II), and Cr(II1) partially decomposed during sublimation and their recovery was incomplete. The recovery of the sublimed chelates of Ni(II), Mg(II), Al(III), Pd(II), Co(II), CufIl), Fe(III), Tl(III), Zn(I1) and Be(II) ranged from 87 to x00%, with most recoveries being quantitative, The sublimation recrystallization zone temperatures of the various chelates are compared to those of the metal acetylacetonates and the benzoyltrifluoroacetonates; in general, the metal chelates of TTA sublime more readily than those of benzoyItrifluoroacetone but are potentially less useful for fractional sublimation separations than the corresponding metal acetylacetonates. Even so, a quantitative separation of iron(II1) from Ni(II), Al(III), Mn(XI), and Fe(II) is proposed that depends upon the fractional sublimation of the TTA chelates. R&SUM&

Une dtude est faite sat la sublimation

fractionnde de divers chelates mritalliques Anat, Chim, Acta, 42 (1968)

207-222

212

1%. w.

BERG,

I<.

P.

KEEI)

clc P-clic&onc comprenant ~galemcnt les chdlntcs clc thdnoyltrifluoroacCtone (vmq. La plupart clcs chhtcs
der fraktionicrten Sublimation verschicdencr Metall-& Untcrsuchungcn Dil~et~n-Cl~elate wurcle auf die Cfuhtc von ‘~l~cnoyltrifluoroacct~~n (TTA) ausgcdehnt, Viele clcr gcbriiulichen Metallchelate sincl stabil, sublirnieren sclmell uncl bilclen wohlclefinierte %onen im Vakuumsublimator. Von den 17 Cllclaten, iiber die berichtet wird, sind nur die von Mangan(I1) uncl Eisen(l1) nicht fltichtig. Die Chelatc von UOQI), %r(XV), Pb(fl) und Cr(II1) zersctzen sich wsihrcnd cler Sublimation teilweisc und sind nur unvollsthdig wiederzugewinnen. Die Ausbcuten cler sublimicrtcn Chelate von Ni(II), Mg(II), Al(III), Pd(II), Co(II), CufFI), l~e(III), Ti(III), %n(II) und 13c(II) licgen r,wischen 87 uncl 100% uncl sind meist quantitativ. Im allgetneinen sublitnicren die Chclatc von ‘I’TA sclmeller als die von Benzoyltrifluoroaccton, sic sincl jcdoch ~ll~~li~l~erweise flir eine l’rennung clurch fraktionierte Sublimation weniger gee&et als die cntsprechcnclen M&all-Acetylacetonate. Eine cluuntih-ttive ‘l’rcnnqng clos Eiscn(II1) von Ni(II.), Al(III), Mn(I1) uncl Fc(Il), die auf clcr fraktiothrten Sublimation dcr TTA-Cl&ate bcruht, wird vorgeschlagen.