Sulphonated azo-dyes as extractive metallochromic reagents

Tolrmm, Vol. 20, pp. 417420.

Pergamon Press, 1973. Printed in Great Britain

SULPHONATED AZO-DYES AS EXTRACTIVE METALLOCHROMIC REAGENTS (Receiued

f 4 August I 972, Accepted 6 October 1972)

The metallochromic properties of azo-dyestuffs, particularly those containing o,o’-dihydroxy groups, are well known and many of these reagents have found application in the complexometric titration of metals.’ Examples of their use for the spectrophotometric determination of metals have also appeared,2 but in general these reactions are non-selective. Selectivity or specificity may be achieved by the use of appropriate masking agents. Furthermore, in some instances the use of an az.o-dye as a spectrophotometric reagent is prevented by similarity in the colours, and consequently, in the absorption spectrum of the metal complex and the reagent itself. For practical purposes it is convenient if the molecule contains at least one suiphonic acid group to make the reagent soluble in water. If more than one sulphonic acid group is present, the tendency of the reagent to form extractable ion-aviation complexes is reduced. With the hope of improving the selectivity and sensitivity of such reactions we, as well as previous workers in the Laboratory,3 have investigated the possibility of extracting the metal complexes of a number of representative sulphonated o,o’-dihydroxyazo-dyes into chloroform as the ion-association complexes formed with a quaternary ammonium cation. In the present work the pH range between I.0 and 12.0 was investigated. In acid solution (_ < pH 1) dissociation of sulphonic acid groups is suppressed and it is probable that the reagents and their metal complexes will be extracted even in the absence of a large cation. The number of possible substitutions of azo-dyes is very large, but o,o’-dihydroxy mono-azo dyes may be classified conveniently according to the number of aromatic rings present and further, for the naphthyl series, by the position of the azo-substitution. Thus, the parent compounds are I II III IV V VI

2,2’-azodiphenol 2-(~-hydroxy-I’-naphthyl~o)p~nol 2-( I ‘-hydroxy-2’-naphthyl~)p~nol 2,2’-dihydroxy-1 ,I ~-~onapht~lene

l,2’-dihydroxy-2,I’-azonaphthalene l,l’-dihydroxy-2,2’-azonaphthalene

Some readily available monosulphonated A B C D E

F G

S-C1,4’-OH,3-SOaH5-SO,Na-II 5-CH3,4’-SOaH5-OH,S-S03Na-III 4-SOAH-IV 4-SOaH-V 6-NO&SOsH-V

derivatives of I-V were investigated,

oiz.

Colour Index No.

Commercial name

Mordant Red 72 15670 f6500 15705 14640 14645

Lumogallion Acid Alizarin Violet (N) Calmagite Chrome Fast Black PV Calcon, Eriochrome Blue Black R Eriochrome Blue Black B E&chrome Black T

Two closely related reagents H

I

S-Cl&‘-OH,3’,6’-SOaNa-III 2-(2’-Hydroxy-I’-naphthylazo)-3-methyl5-phenyl-l-hydroxylpyrazole&sulphonic acid

16680 18760

Eriochrome Eriochrome

Blue SE Red B

were also examined. Systematic classification of dyes with two azo linkages is more complicated, but three examples of this class which have found application in spectrophotometric analysis were also studied. K L M

Acid Alizarin Black SN Fast Sulphon Black F Cal&chrome

21725 26990 417

418

SHORT COMMUNICATIONS EXPERIMENTAL

Reagents

Acetate (pH 1.1-52). phosphate (6.1) and borate (7.5-12.0) buffers were prepared to cover the pH range 1-12 and their ionic strength was adjusted to 0.3 with sodium perchlorate. Metal ion solutions (O.lM) were prepared, from the perchlorates where possible. Dye solutions nominally 4 x 10w4M were prepared by dissolving the theoretical amounts of the solids in distilled water. No attempts were made to purify the commercial products. Solutions of the quatemary ammonium salts (O.lM) were prepared by dissolving Aliquat 336 (methyltricaprylylammonium chloride) (General Mills, Chemical Division, Kankakee, Illinois) or tetrahexylammonium iodide in chloroform. The latter solution was converted into the perchlorate form by shaking three times with an equal volume of 10% sodium perchlorate solution. Procedure

Qualitative tests were made of the reaction of a given reagent with 20 selected metal ions, viz. Al, Bi(lll), Ca, Cd, Co(H), Cu(II), Fe(III), La, Mg, Mn(II), Mo(VI), Ni(II), Pb(II), Pd(Il), Sn(lV), U(VI), V(IV), W(V1). Zn and Zr(IV) at each of eleven pH values by addition of one drop of 0.1M metal ion solution to a test-tube containing 1 ml of 4 x 10m4M reagent solution and 3 ml of the appropriate buffer solution. After thorough mixing, a few minutes were allowed for reaction before the colour was noted. One ml of quaternary ammonium salt solution (0.05 or O.lM) was added, the mixture was agitated vigorously for a few seconds and, after settling, the colour of each phase was noted. Reactions giving interesting colour changes were carried out semiquantitatively (again with an excess of metal ion over reagent) and the spectrum of the metal complex as well as of the reagent alone was plotted in the visible region for the aqueous phase or for the organic phase after extraction, as appropriate. Reactions appearing to have analytical possibilities, i.e., giving a large shift in absorption maximum and an intensely coloured metal complex, were then further investigated by preparing a Beer’s law plot to test the sensitivity under the reaction conditions used. RESULTS

It will be appreciated that in qualitative tests the recognition of a potentially useful reaction is very subjective. The further characterization of a given reaction in terms of sensitivity and selectivity is necessary to achieve objectivity. The present survey has, however, confirmed previous workers’ findings that o,o’-dihydroxyazo dyes react with many metal ions in aqueous solution under various pH conditions, e.g., Mo(VI) with almost every reagent in acid solution; Cu(I1) with reagents B, F and K at pH 14; Zr(IV) with A, B and Hat pH l-4; Fe(lI1) with A, B, D, F, H, and J at pH l-5; V(IV) with B, D, F, G, H, J, K and Mat pH 3-6; U(VI) with F, G, H, and K at pH 4-5; several transition metals and La(II1) with K and L at around pH 7; Ca and Mg with B, C, D, F, H, and M in alkaline solution. In several instances these reactions are best suited to spectrophotometric application by measurement of the decrease in absorbance at a given wavelength upon complex formation and have already been used in this manner.4*S The formation of an extractable species depends upon neutralization of the negative charge of the metal complex by ion-association with one or more quatemary ammonium cations. At low pH only the sulphonic acid groups are dissociated, the hydroxyl groups ionize successively as the pH is increased. Thus at higher pH more quaternary ammonium ions are needed to achieve neutralization of charge. The reactions of the o,o’-dihydroxyazo dyes after extraction are summarized in Table 1 in which each reagent is represented by the letters assigned to it above. Entries appear for all conditions under which there was a significant difference between the colour of the organic phase with a metal present and that for the reagent alone. No extractable complexes were formed by reagents L and M. indicating that the presence of three or more sulphonic acid groups prevented charge-neutralization under these experimental conditions. Bi(lII), Ca, Cd, La(lII), Mg, Pb(l1) and Zn formed no extractable complexes coloured differently from the reagent. These tests were done with an excess of metal over reagent so that in some instances, although complex formation occurred, the reaction would not be applicable to spectrophotometric analysis. Several reactions, however, did appear to be worthy of consideration for spectrophotometry and a rapid examination was made to obtain an estimate of the sensitivity of a number of these without rigorous optimization of conditions. These results are shown in Table 2. The reaction of aluminium with Calmagite at pH 8.6 has been studied more thoroughly as a spectrophotometric method.6 Conclusion

The investigations described herein have shown that several monosubstituted o,o’-dihydroxyazo dyes form coloured metal complexes which are extractable into chloroform as ion-association complexes with a quaternary ammonium cation. These reactions may offer advantages in selectivity and sensitivity over existing spectrophotometric methods based on metal-azo-dye complexation.

SHORT COMMUNICATIONS

419

Table 1

Metal ion

2.0

1.1

AI(III)

3.0

-

D, K

E

.--

cow

Fe(II1)

D, F, H, J, K

6.1

10.0

11.1

12.0

B, C

8, C B, C B, C

B, C,

C, J, K

J, K

c

c

c

c

c

IC

c

c

c

C, J

C

C

-!-

C

._

._---_

E

B, C, F,JJ

E

_---_

._--E, F, J

8.6

E. K

_

A, B, C, D, E, F, G, K

Ni(I1) Pd(lI)

7.5

._---_

..

Mo(VI)

-

._

E, J

E, F, J

Mn(II)

A, B, E, K

SnW) /

_

B, C, E, B, C, E. F, G, K F, G, K . -_

---_

. .--

.----

_

.

B, C, E

B, C

_.

1

-.

V(IV)

A, K

WW

A, B, D, E, F. K

K K

IK F, K

_.--

Zr(IV)

-

E, F

__ A, 4 D, F, E G, H, K . ---

Cu(II)

UW)

PH 5.2

4.2

B, E, F

E, F

_.

t“,F _---

c ---K __ _---_ G F, J 1E r; G 1F _. _---E, E G, E, F, G, C, E, F, C,J J, K J, K J _---__---

__---

1F, H

K

IC,F

I

K

.----

Table 2

Metal

Mo(W

Mo(VU Mo(VI) W(VI) ClJ(II) Pd(I1) Fe(III) Co(II) Co(II) Co(U) Al(III) Al(III)

Department of Chemistry University of Arizona Tucson, Arizona 85721, U.S.A.

Reagent

pH

B C K B B B K C B B E C

1.1 1.1 1.1 1.1 1.1 1.1 1.1 4.2 5.2 8.6 8.6 8.6

Wavelength, nm 570 575 610 570 570 570 610 580 570 570 570 580

c, hnole-l~cm-’ 6.5 6.0 12-o 7.0 5.5 5.5 18.0 8.0 24.0 25.0 29.0 40.0

x x x x x x x x x x x x

IO3 10” 103 103 103 103 lo3 10’ lo3 10’ lo3 10’

COLIN WOODWARD HENRY FREISER

C, I=

420

SHORT

COMMUNIC4TlONS

REFERENCES

1. R. Pi?bif, Adytkxzi Applications of ELITA and Reiated Co~pauds, Pergamon, Oxford, 19f2. 2. ID. F. Bohz and M. 0. Melton, A&. C&m., I966,38,317R. 3. N. Suzuki (1965) and F. T. Ashizawa (1966). University of Arizona, unpublished observations. 4. M. Hosain and T. S. West, Anal. Chim. Acttz, 1965, 33, 164. 5. A. M. Cabrera and T. S. West, Anal. Chem., 1963,35, 311 6. C. Woodward and H. Freiser, Talanta, 1968, 15, 321.

W-A survey has been made of analytically useful extractabte ion-pair compiexes that are formed by !he use of a series of metallochromic indicator-metal complexes in conjunction

with quaternary ammonium ions. The reagents were D,U’-dihydroxyazo dyes and azo-oxines. Zw--Es

wird eine t)bersicht fiber analytisch niitzliche extrahierbare Ionenpaarkomplexe gegeben, die aus einer Reihe von Metallfarbindikator-Metall-Komplexen mit quart&en Anunoniumionen gebildet werden. Die Reagentien waren o, o’-Dihydroxyazofarbst&e und Azooxine. %am&-Un a efWu& tme etude de complexes paires d’ions extractibles, ana~~~quement utiSes, qui sent form&s par f’emploi d’une s&ie de complexes indicateur m~talI~hrome-metal conjointernent a des ions ammonium quaternaires. Les reactifs sont des colorants o, o’-dihydroxyazo et des azo-oxina.

~-~~-ACETYL-l,3-INDANDI~NE-~-HYDR~~NE}TR~ALKYLAMMONIUM IODIDES AS A NEW GROUP OF REAGENTS THE CARBONYL GROUP

FOR

(Received 8 September 1972. Accepted 23 October 19’72) Braun and Mossher’ introduced Idiphenyfa~etyl-1,3-indandione-I-hydrazone as a reagent for characterization of carbonyl compounds. Aldehydes and ketones react with the hydrazone to give Ruorescent a&es having sharp and welt spaced melting points. Brandt and Cheronis’ showed that concentrations of these azines as low as IfX9M could be detected spectrophotometrically. Mosber, Bechara and Pozomek’ indicated the use of the reagent and its analogues for identification of various classes of organic compounds such as amines, alcohols, anhydrides, hydrazines and ortho-esters. The potential usefulness of these reagents appears to be due to the 2-acetyl-1,3-indandione nucleus. The present paper deals with the investigation of quarternary ammonium derivatives of these reagents6 which have been found to react with afdehydes, ketones and ketoacids, but not with alcohols. amines and non-keto carboxyiic acids. EXPERfMENTAL

2-Acetyt-1,3-indandiono was obtained by Claisen condensation of dimethyl phthafate with acetone in the presence of sodium methoxide according to the method reported by Kilgore.5 Preparation of N-(2-acetyl-f ,3-indandione)trialkylammoniumiodides 2-Acetyl-~,3-jn~nadione was quatemized with an appropriate tertiary amine and iodine in methanoiic mediumV4 The compounds prepared were the trimethyl {m-p* 221-223’7, triethyl (m.p_t3f-i32”)S tripropyi (210” dec.) and tributyl (mp. 52-53”) derivatives.