Separation and acid equilibria of xylenol orange and semi-xylenol orange

Talanta. 1967. Vol. 14. PP. 1293 to 1307. Pcrgamon Press Ltd. Printed in Nortlmn Ireland

SEPARATION AND ACID EQUILIBRIA OF XYLENOL ORANGE AND SEMI-XYLENOL ORANGE MITSUMASAMURAKAMI, TAKASHIYOSHINOand SHIRO HARASAWA Department

of Chemical Technology, Faculty of Engineering, University, Tokiwadai, Ube, Japan

Yamaguchi

(Received 15 February 1967. Accepted 29 March 1967) Summary-A mixture of Xylenol Orange (X0) and Semi-Xylenol Orange @X0) was chromatographed on a cellulose column aud ionexchanged with Diaion SK-l resm. X0 and SXO in the acidic forms were titrated with sodium hydroxide to determine the basicities and the acid formation constants. The absorption spectra of X0 and SXO were measured over a wide pH range, and were used for the calculation of acid formation constants, molar absorptivities, and the effect of ionic strength on the activity of X0. The purity of a commercial X0 was measured by absorption spectroscopy, and it was found that the sample contained 36-3 % of X0 and 17.2 % of SXO. Pure X0 and SXO form a 1: 2 and a 1: 1 complex respectively with Zn(II). On the basis of these data the ionic structure of X0 and SXO have been compared with those of Cresol Red and iminodiacetic acid, and discussed.

As PARTof an investigation on the chelates formed between sulphonphthalein derivatives and metal ions, the purification and some physico-chemical properties of Xylenol Orange (X0) and Semi-Xylenol Orange (SXO) were studied, and the structures were cotmrmed. Previous workers l3 have reported that X0 has been synthesized from Cresol Red, iminodiacetic acid and formaldehyde by the Marmich condensation, and the structure was supposed to be 3,3’-bis [N,N’-di(carboxymethyl)aminomethyl]-ocresolsulphonphthalein. So far as is known, however, the puritication of this compound has never been successful, so that the mole ratio, suitable pH range, wavelength of maximum absorption, molar absorptivity and stability constant have been uncertain in the case of the chelate of X0 and a metal ion such as Zr(IV),4-7 Th(IV),*ps or Fe(III).lO-U Olson and Margerum have pointed out that SXO could be isolated from a mixture with X0 by paper chromatography.3 In the present work cellulose column chromatography and ion-exchange were used for separation of X0 and SXO. The purity of X0 and SXO separated by these methods was nearly 100 % and the purity of each X0 used in other work4*s,12-23could be evaluated by comparison of the data. EXPERIMENTAL Apparatus

A Toadenpa pH meter, Model HM-5A, was used. Standard butfer solutions (phthalate, phosphate, borate, O*lM hydrochloric acid and O*lM sodium hydroxide) were used for calibration. All the absorption measurements were made with a Shimadxu Model SV-SOAL spectrophotometer, with a l-cm cell. Toyo Roshi No. 52 paper was used for paper and cellulose column chromatography. Metals contained as impurity in the paper were almost all removed by developing with a hydrochloric acid-acetone solution. The cellulose column was prepared by shaking the paper with hot 1M nitric acid and packing the slurry. 7

1293

1294

MITSUMASA

MURAIGW,T.&%srir YOSWINO and Smno HARASAWA

Sodium hydroxide solutes, O+lM, Carbonatefree. Bulspersolutions. The following buffer solutions were used, adjusted to the vahre required.

pH 95-14: potassium hydroxide sohrtion pH 8-11: 1M ammonia-U4 ammonium nitrate pH 3-95: l&f veronal-1M acetic acid-1M potassium hydroxide pH 3-65: 1M hexamine-lA4 nitric acid pH l-3: nitric acid pH (I&) 0.5 : sulphuric acid The reagents were analytical grade materials. Synthesis of X0 and SXO These were synthesized by the Mannich condensation.l-a o-Cresol Red (1.91 g; 5 x 1O-smole), 37% formaldehyde (l*OOml; 1.2 x lo-* mole), iminodiacetic acid (1.33 g; 1 x ltVa mole), and

sodium hydroxide (1 g) were dissolved in glacial acetic acid (50 ml). The mixture was heated at 63-G”. After 10 hr, the solvent was distilled off under reduced pressure. Recrysta~~~zat~on from a polar solvent

Recrystallization of X0 and SXO from akoho1, ketones, and esters was unsuccessful. From ethanol-sodium acetate solution, X0 was precipitated, but part of it was decomposed to a red compound which formed no chelates with metal ions. Separation by column chromatogaphy and ion-exchange

_The synthesized X0 was chromatographed on alumina, silica gel, cation-exchange resin, and cellulose. On alumina and silica ael X0 was decomnosed. and from the ion-exchange resin a part of the X0 could not be eluted. TheYmixture of X0 atid SXO was completely separatzd on a o&lose colnmn by butanol saturated with 10% acetic acid. The elution order was: an unknown white compound, Cresol Red, sodium ions, SXO, X0, and iminodiacetic acid. The solvent was distilled off from each fraction under reduced pressnre. The SXO and X0 were the disodium and trisodlum salt respectively. The SXO (1 g) was run through a column of Diaion SK-l lOGmesh cation-exchange resin (IO-20 mequiv). The effluent solvent was distilled under reduced pressure and the residue was dried in a vacuum desiccator for two weeks. The compound was the free acid form of SXO, m.p. 201-204” (decomp.). Found: C, 57.6%; II, 5.0%; N, 26%; C&H,,OeNS.H,O requires: C, 57.24%; H, 4.99%; N, 257%. The ion-exchange method used for X0 containing sodium ions was virtuahy identical with that described for SXO, but the acid form of X0 was again chromatographed and ionexchanged to remove iminodiacetic acid CompIetely. The product had m.p. 274-277’ (decomp.). Found: C, 523%; H, 5.2%; N, 41%. C81H8POllNlS.2HP0requires: C, 5254%; H, 5.11%; N, 3.95%. Potentiometric titration The acid form of X0 (67.3 mg) was dissolved in 45 ml of water and 5 ml of 1M potassium nitrate,

and the solution was titrated with 0*1&fsodium hydroxide at 25 & O-l”, under nitrogen. titrations were performed with the acid form of SXO and a commercial X0 (Dotite X0).

Similar

Absorption spectra

To a 25-ml volumetric flask, 1 ml of l-25 x lo-*M X0 or SXO solution, 0.5 ml of the buffer solution, and 2 ml of 1M potassium nitrate were added and diluted to the mark with water. The absorption spectrum of the solution was measured at room temperature. When the solution had only a small buffer action, it was measured under nitrogen so that the pH error might be below 0.03 within the range of pH 2-10. RESULTS

AND

DISCUSSION

The synthesisand separationof X0 and SXO The removal of iminodiacetic acid and SXO from impure X0 is diEcult by means of recrystallization, and what is worse, iminodiacetic acid and SXO form chelates with many metal ions. Table I shows that X0 is decomposed by methanol, ethanol and propanol and that the Rf value on a cellulose column is related to the number of

Developer

No.

CH,OH : 20 % AcOH (4: 1) CPHIOH: 20% AcOH (4:l) n-CJ-Z,OH saturated with 20% AcOH n-C,H,OH saturated with 10% AcUH n-C,tr,oH saturated with 10% AcOH crr,caoc,rrS saturated with 20% AcOH

x0,

SXO,

.a

Rf

CresofRed. Rf

Other compounds, Rt

O-O*75 0*7-@9

0.8-1.0

Q-O*95 0%1.0

0%1.0

Pu$e decomp. product * Red dwomp. product, 0.6 l$pT decomp. product,

0.7-l*O

Red decdmp. product, O-4 Fu$e dec-omp. product,

04-M%

@4-M

O*O!L@ 1

@6-w

@3-w*

0*6+9*

Iminodiacetic acid, i?*O3-@07 rmirlodiwj& acid, @owl3 O-&-1*0*

@5-@?5

0.7-0.95

09-1-O

O%l~O

AcOH = acetic acid. When hydrochloric acid was used in place of acetic acid, the development was lass perfect. * Samples in the free acid form,

carboxyl groups in the molecule and to the number of sodium ions. Cresol Red and SXO were separated on a cellulose column from the sodium salts of X0, and X0 and iminodiacetic acid were separated from the acid form of SXO. The purities of the products were established by elemental analysis, titration, paper c~omato~aphy, and absorption spe&ra. SXO was easily synthesized at 55” with the theoretical amount ofst~~~mate~als_ Culczdaiion of ~~id~or~tio~

~o~t~~t~ from the@3 tit~at~~~curoe

The acid formation constant is more suitable than the acid dissociation constant for discussion over a wide pH range The constants are calculated by the methods of Rjerrum” and Block ei alF6 As the acid is of the HNI type, then Hi++1fl-*

HIW+,

H+ + HIW-“L- +

H2I(A’-2)-

, _ . . ,

H+

n’ = Gr -

W+l+ PWiG

+

hv-tt~

= $, J,,K,,

J, = (n - I?)[H+l” c, = Total concentration c, = Total concentration

(1)

(4) (5)

of the acid of protons

5 = Mean number of protons in the acid kl, k,, . . . , kN z= Acid formation constants Ks=k2k2...kx

I- +HNI

1296

MITSUMASA

MURAKAMI,TAICASHI YOSHINOand SHIROHARA~AWA

[H+]ismeasuredpotentiometrically, C’,and Cn are calculatedfrom the pH titration curve, and then the acid formation constants are calculated from equations (4) and (5). The concentration of free protons is corrected for the activity coefficient, which is measured by pH titration of nitric acid under the same conditions. The pH titration curves of X0 and SXO are shown in Fig. 1. The curves show the acid forms of X0 and SXO to be H,XO and H$XO as might be expected. Within the titration range O-3 ml, the equilibria of X0 are those of a strong acid corresponding to HsI. From equations (3) and (4), an initial value of 1.092 was obtained for fi

I

I

I

I

I

3

I

4

I 5

I 6

O.O,2M FIG.

I-67.3

l.-pH

mg of HIX0.2HIO;

M NaOH, ml titration curves, at 25.0 f 0.1%

II-52.8 mg of H,XO.H,O; 111-71.7 mg of Dotite X0; each in 50 ml of O.lM IWO,.

(i.e., for an untitrated solution), which showed the existence of HaX03-, HdXO*-, and H,XO-. From equations (4) and (5), log k4 = 2.85 f 0.06 and log k5 = 2.32 f@15 were calculated. Over the titration range 3-5 ml the solution will contain HXO&, HaX04-, and HsX03-. The equilibria correspond to those of H,I and at 4.30 ml titration A = O-606, which shows the existence of HXO&. For the equilibria, log kg = 10.39 f 0.05 and log k3 = 6.67 f 0.03 were calculated. The calculation of the acid formation constants of SXO is virtually identical with that of X0. Log kl = 10.90 & O-15, log kz = 7.44 -& 0.03, and log k, = 2.60 & 0.06 were calculated for the equilibria between SX04-, HSX03-, H$X02-, and H,SXO-. In this report all the constants are mixed constants and the accuracy of each was estimated by considering the accuracy of the pH titration and the absorption measurements. Calculation of acid formation constants from absorption spectra Both X0 and SXO have a variation in colour over a wide pH range. The concentration of each species is determined from its absorbance. Between pH 2 and 5, however, X0 or SXO have identical absorption curves, so the pH method is used for this region. When the equilibria shown iu equations (l), (2) and (3) are in existence,

Xylenol Orange and Semi-Xylenol Orange

1297

the absorbances should be in accordance with the equation (6). A==$ en,r [H,P-“‘-1 n=o

(6)

From equations (2), (3) and (6) we obtain A - Cgs, = 5 J,,‘klk2 . . . . kN n=l

(7)

J,,’ = (CseHIz - A)[H+]”

(8)

A = Absorbance E = Molar absorptivity J,,’ = A parameter used to calculate the acid formation constant. Acid formation constants are calculated from equations (4), (7) and (8) used as simultaneous equations. The calculation does not necessitate knowledge of Ce and [H,I(N--n)-], but A, [H+], and Gen,r will suffice so long as Ce is constant. If G&n,r cannot be measured, the constants containing it are calculated for many values of A and [H+], and Gan,r and the acid formation constants are derived from them by iterative calculation. The absorption spectra of 1.001 x IOdM SXO and 8.05 x 10-6M X0 below pH 2 are shown in Figs. 2,3 and 4. Figure 4 also shows the curves calculated from the constants determined in the course of this work. Acidity below pH 1 is indicated by the Hammett function Ho.26*27From pH 2 to Ho O-35the absorption of SXO gradually increases at 510 rnp and below Ho O-35 SXO has strong absorption at 510 rnp and an isosbestic point at 470 rnp. The equilibria may be among H,SXO, H,SXOf, and H,SX02+. From the equations above, &n,sXo = 1.54 x l@, log k, = O-53 f 0.03, and log k6 = -0.65 If O-05 were calculated, using C&n,aXO = O-050, Ceen,aXo = O-670, and A = O-105 (Ho O-67), O-201 (Ho 0*045), and O-565 (Ho -1.24) at 510 rnp. On the other hand the absorption spectra of X0 show three equilibria below Ho O-5. The absorbance increases at 450-490 m,u in regard to the first equilibriumandat 515mp in regard to the second equilibrium near Ho - 1. At 480 rnp, ~n,*~ = l-78 x l@, log k7 = -1.04 f 0.05, and log k8 = -2.29 4 O-08were calculated for the equilibria between HsXO, H,XO+, and H,X02f. The absorbances between Ho -0.86 and -5 were corrected by means of k, and k8. By using the corrected values, ~?,~o = 6.45 x 104, log k, = -1.83 & 0.06, and log ks = -3.32 + 0.08 were obtained for the equilibria of H,XO+, H,X02+, and HgXOa+. The absorption spectra of SXO between pH 3.7 and 14 are shown in Fig. 5. Near pH 7, &nsxo = 5.58 x 104 and log k, = 7.47 f O-03 were obtained from the pH value corresponding to the mid-point of the absorbance increase at 573 rnp as the pH was raised. Above pH 9 the absorption increases gradually with the addition of alkali, and log kl = lo-90 f O-15 was obtained from the pH value of the mid-point of the absorbances corrected for ensxo and k,. The absorption spectra of X0 between pH 1 and 14 shown in Figs. 6 and 7 are similar to those obtained by gehak and KijrbPs but the absorbances are about one and a half times as large. The calculations for X0 were carried out as described above, and the results are shown in Table I.

1298

TAKAW YOSJSDIO and SHIROHARASAWA

MITSUMA~A Mm,

0.6 -

0.5-

04t!

go-

02-

I

I

400

FIN. 2.-Absorption

I

I

450 500 Wavelength,rnp

spectra of SXO (1GOl x 10-6M in l-cm cells, from Ho = -2.54 to pH - 2.55).

0.6-

400

450 wavelength,

FIN. 3.-Absorption

500

550

6CX

mp

spectra of X0 8.05 x lO+M in l-cm cells, from Ho = -550 to t1.50.

Xylenol Orange and Semi-XylenoI Orange

-

pH--+-----H, FIG. 4.--Effect

I-Cresol

1299

of & On absorbance.

Red, 1.000 x W6M at 520 rnp; II-SXO, l%lOl x 10+&f 111--X0, 8.05 x IO-*A4 at 515 m,u.

at 510 m@;

0.6

0.5

Wavelength,

FIG. 5.-Absorption

m,u

spectra bf SXO (l+JOI x lO+W in I-cm cells, ,Y = O-1, from pH 3.74 to 13.48).

1300

MITSUMASA

MIJRAKAMI,TAKASHIYOSHINOand SHIRO HARASAWA

400

FIG. 6.-Absorption

450

500

550

600

spectra of X0 (9.20 x 10-6Min l-cm cells, ,U = 0.1, from pH 1.68 to 9.38).

400

450

500

560

600

Wavelength, rnp FIG. 7.-Absorption

spectra of X0 from pH 10.37 to 142 (conditions

as in Fig. 6).

Xylenol Orange and Semi-Xylenol Orange

1301

Effect of ionic strength on the activity of X0 If the equilibrium between red X0 and orange X0 is that between H,XO* HaXoS-, the equation will be describedaB by A log ka = log (YH,XO/YH,X& - log (YH,x~/YH,x~)~.

and

(9)

y = Activity coefficient of the ion indicated by subscript A log k3 = Difference between the apparent and true acid formation constant Subscripts x and o = Actual and infinitely dilute solution respectively. When the Debye-Htickel limiting law holds good (,u < O*Ol),equation (9) becomes A log k3 = (3a - 4”) x O-509 6

= -3.5 4.

(10)

The acid formation constants were obtained spectrophotometrically in this way. The results, and data for Cresol Red for comparison,as are shown in Fig. 8. The slope is similar to that of equation (10). Cresol Red is a dibasic acid, and gives a slope of -1.5. This shows that the activity coefficient of X0 ion can be calculated from the Debye-Htickel equation, that the equilibrium near pH 7 is between HsXo4- and H,XOS-, and that the formation constants of X0-metal chelates are affected by the ionic strength.sO The equilibria of SXO The wavelengths of absorption maxima and the formation constants of X0, SXO, Cresol Red and iminodiacetic acid are shown in Table II. On the alkaline side the equilibrium between the red SXO and yellow SXO corresponds to the dissociation of the hydroxyl group. 31 Above pH 10 the molar absorption of SXO increases gradually, but not that of Cresol Red, so that log kl corresponds to log k = 9.65 for iminodiacetic acid. Between pH 2 and 5 the colour of the solution has not changed, and log k3 and log k4 are similar to those of the carboxyl groups. Below pH 2 the two constants corresponding to those of the quinone and sulphonic acid groups= are lower than the constants for Cresol Red (log k = l*OO). The constant observed by Olsen and Margerum3 is compared with log k, and log k, calculated by us. All the equilibria of SXO are shown in Fig. 9. The equilibria of X0 The equilibrium constants of X0 obtained by Rehik and KijrbF are different from ours on the acidic side but similar on the alkaline side. This shows that their sample might have contained about 30 % of iminodiacetic acid and a small amount of SXO. The three constants obtained in strongly acidic solution are based on the protonations of the carboxyl, quinone, and sulphonic acid groups, and correspond to the three constants of SXO (k4, k, and kg).31J2 In view of the facts it seems most reasonable to conclude as follows. (1) SXO and X0 have one and two di(carboxymethyl)aminomethyl groups respectively. (2) The acid formation constants of SXO and X0 are similar to those of Cresol Red and iminodiacetic acid. (3) The protonations of the sulphonic acid and quinone group of

434

H,XO*-

578

582

HX05-

X0’-

0.03

6.54 f 0.05

3.66 k 0.25

6.09 & 0.04

2.62 f

f 0.05

f 0.06

f 0.08

12.23 rt 0.05

10.56 f 0.09 10.39 f 0.05 *

6.67’p 0.03;

6.74 f

2.85 & 0.06*

2.32 f 0.15.

<1.5*

-1.04

-1.83

-3.32

log k

Equilibrium constant

l Data measured by means of pH titration; t Data obtained near absorption maximum.

578

H,XO’-

H,XOS-

439

H6XO-

H,XO

l-78 f OGlt

4807

H,XO+

0.15

6.54 f

515

x IO-’

H,XOa’

&

8.08 f 0.06

v

Amsx

Absorptivity

515

Ion

Wavelength

Xylenol Orange

576

573

431

443

510 t

510

v

1max

6.20 + 0.03

5.58 f 0.03

2.54 f 0.03

1.54 f 0.03t

0.05

x lo-’

6.69 f

E

Absorptivity

Orange

the rest by means of spectrometry.

SXO’-

HSXO*-

H,SX02-

HsSXO-

H,SXO

H,SXO+

H,SXOa+

Ion

Wavelength

Semi-Xylenol

IMINODIACETIC

f 0.05

10.90 f 0.15 10.90 f 0.158

I.47 f 0.03 744 f 0.03.

2.60 f 0.06f

<1.5*

0.53 f 0.05

-0.65

log k

Equilibrium constant

ACID

CR’-

HCR-

H&R

H&R+

Ion

512

435

520

v

Lmsx

Wavelength

x lo-’

4.97 & 0.04

1.80 f 0.03

5.00 f 0.05

E

Absorptivity

Cresdl Red

7.95 f 0.03

1G3 f 0.05

log k

Equilibrium constant

IDA8-

HIDA-

HJDA

H,IDA+

Ion

acid

9.65 & 0.05*

2.75 f O.OS*

logk

Equilibrium constant

Iminodiacetic

FORMATIONCONSTANTS,WAVELENGTHSOF AB~~RORPTION MAXIMA AND MOLAR AB~ORPTIWTILSOF X0, SXO. CRESOLRED, AND

H,XOa’

--

TABLE IL-ACID

1304

MITRJMASAMURAKAMI,‘I’AKAWIIYOSHINO and Smo

FIG.

9.-Equilibria

2.5 FIG. lo.--Plots

I-X0,

HAWAWA

of SXO.

3 PH

of fiexpand curve of I?AC against PH.

shown as H,(I&XO);

II-SXO,

shown as H,(H&XO).

1305

Xylenol Orange and Semi-Xylenol Orange

0.6

400

550

450

Wavelength,

60(

mp

FIO. Il.-Absorption spectra of pure X0, pure SXO and Dotite X0. At pH 3.11, p = 0.1; I-X0; II-SXO; III-Dot&z X0. In l+UkfH,SOI; I’-X0; II’-SXO; III’-Dotite X0. (X0-1.908 x lo-Sk& SXO-1.928 x 10-6M, Dotite X0-2+0 x 10-5M).

Molefroctii

of Zn

FIG. 12.-Job’s curves for zinc complexes. tZn-X0, [Zn] + [x0] = 3.86 x W5M, p = 0.1, pH 6.21, l-cm cells at 573 q; 0-ZIPSXO, [Zn] + [SXO] = 3.88 x IOJM, ~1 = 0.1, pH 6.30, l-cmcels, at 500 w; A-Zn-impure X0, lo [Zn] -t [x0] = 5 x 10-W, p = O-04, pH 6.0, l-cm cell, at 574 w.

1306

MITSUMA~AMURAKAMI, TAICA~HIYO~HINOand SHIRO HARASAWA

used was only 66 % of that found by us. Impure X0 and SXO may contain 30-50 % of iminodiacetic acid which is difficult to remove by means of recrystallization. Figure 12 shows that X0 and SXO form 1:2 and 1: 1 chelates respectively with Zn(I1) (i.e., XOZn, and SXOZn), but ktudlar and Janougek’s curvea shows a 1: 1 chelate. Although many papers have claimed that Methylthymol B1ue35-ss and X07~10~1pso~a3~30~34.39-41 form 1: 1 chelates with many metals, it now seems that X0 forms at least some 1:2 chelates. R&arm&On a chromatographie un melange de XyRnol Orange (X0) et de Semi-Xylenol Orange (SXO) sur une colonne de cellulose puis pro&l6 a l’echange d’ions avec la r&sine Diaion SK-l. On a titre X0 et SXO sous formes acides par la soude pour determiner les basicites et les constantes de formation d’acide. On a mesurb les spectres d’absorption de X0 et SXO dam un large domaine de pH et les a utilis& pour le calcul des constantes de formation d’acide, des absorptions’ moleculaires et de l’effet de la force ionique sur l’activite de X0. On a mesure la purete dun X0 commercial par spectroscopic d’absorption et a trouve que l’echantillon contenait 36,3 % de X0 et 17,2 % de SXO. X0 et SXO purs forment des complexes 1: 2 et 1: 1 respectivement avec Zn (II). Sur la base de ces don&es, on a compare la structure ionique de X0 et SXO a celles du Rouge de Cresol et de l’acide iminodiacetique et en discute. ZusammenIhssung-Ein Gemisch von Xylenolorange (X0) und SemiXylenolorange (SXG) wurde an einer Celluloses&rle chromatographiert und mit Diaion SK-l dem Ionenaustausch unterworfen. X0 und SXO wurden in saurer Form mit Natriumhydroxid titriert, urn Basizitlten und Dissoziationskonstanten zu bestimmen. Die Absorptionsspektren von X0 und SXO wurden in einem gro!Jen pH-Bereich gemessen und zur Berechnung der Dissoziatio&konst&rten, der -molaren Extinktionskoeffizienten und des Elntlusses der Ionenstiirke auf die Aktivitat von X0 herangezogen. Die Reinheit von kiiuflichem X0 wurde durch Absorptionsspektrometrie geprilft; die Probe enthielt 36,3%X0 und 17,2% SXO. ReinesXOundSXObildeneinen1:2-bzw. 1 :l- Komplex mit Zink(I1). Auf Grund dieser Daten wurde die Ionenstruktur von X0 und SXO mit der von Kresolrot und Iminodiessigs&rre verglichen und diskutiert. REFERENCES 1. 2. 3. 4. 2: 7. ;: 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.

J. K&b1 and R. Plibil, Chem. Znd. (London), 1957,233. E. M. Urinovich, USSR Patent 132234, Oct. 5, 1960; C/rem. Abstr., 1960.55, 11370. D. C. Olson and D. W. Margerum, Anal. Gem., 1962,34,1299. K. L. Cheng, Takmta, 1959,2,266. A. K. Babko and V. T. Vasilenko, Zavodsk. Lab., 1961 27,640. K. L. Cheng, Anal. Chim. Acta, 1963,28,41. B. Bud&SW, Collection Czech. Chem. Commun., 1963,28,1858. B. I. Nabivanets and L. N. Kudritskaya, Ukr. Khim. Zh., 1963,29, 1198. M. Otomo, Japan Analyst, 1965,14,229. K. L. Cheng, Talanta, 1959,3,147. B. Bud&%lnskf, Z. Anal. Chem., 1962,188,266. M. Otomo, Bull. Chem. Sot. Japnn, 1963,36,137. Zdem, ibid., 1963,36,140. Zdem, ibid., 1963,36,1577. Zdem, ibid., 1965,38,624. H. Onishl and N. Ishiwatari, ibid., 1960,33,1581. N. Ishiwatari and H. Onishi, Japan AnaZyst, 1962,11,576. N. Ishiwatari. H. Nagai and Y. Hida, ibid., 1963,12,603. A. I. Busev and I. G. Tiptsova, Zh. Analit. Khim., 1960, 15, 655.

Xylenoi Orange and Semi-Xylenol Orange

1307

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