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Syntheses and spectrophotometric studies of azo dyes containing m-dimethylaminophenol as analytical reagents
Analytica Chimica Acta, 66 (1973) 397--409 © Elsevier Scientific P u b l i s h i n g C o m p a n y , A m s t e r d a m - Printed in T h e N e t h e r l a n d s
SYNTHESES AND SPECTROPHOTOMETRIC CONTAINING m-DiMETHYLAMINOPHENOL REAGENTS
STUDIES OF AZO AS A N A L Y T I C A L
397
DYES
SHOZO SHIBATA, MASAMICHI FURUKAWA and KYOJI TOEI* Government Industrial Research Institute, Nagoya, Kita-ku, Naaoya (Japan)
(Received 1st February 1973) D u r i n g t h e p a s t t w e n t y years, the a n a l y t i c a l a p p l i c a t i o n of 2 - p y r i d y l a z o c o m p o u n d s h a s b e e n s t u d i e d extensively. T w o r e p r e s e n t a t i v e s o f this g r o u p , l-(2p y r i d y l a z o ) - 2 - n a p h t h o l ( P A N ) a n d 4 - ( 2 - p y r i d y l a z o ) r e s o r c i n o l ( P A R ) , have p r o v e d to be very versatile r e a g e n t s for m e t a l s 1. A l t h o u g h n e i t h e r r e a g e n t is selective as a c h r o m o g e n i c a g e n t o r a n e x t r a c t a n t , n e w selective 2 - p y r i d y l a z o d e r i v a t i v e s have b e e n p r o p o s e d by several w o r k e r s . M u c h o f the i m p o r t a n t w o r k o n t h e s e derivatives has b e e n c a r r i e d o u t in Russia, in p a r t i c u l a r by T a l i p o v z a n d G u s e v 3 a n d coworkers. In a s e a r c h for n e w sensitive a n d selective reagents, a t h o r o u g h s t u d y o f s o m e azo c o m p o u n d s c o n t a i n i n g _C-substituted p y r i d i n e has b e e n m a d e 4-v. A t the p r e s e n t time, t h e m a i n p u r p o s e o f t h e w o r k is to p r e p a r e sensitive o r g a n i c r e a g e n t s w h i c h h a v e m o l a r a b s o r p t i v i t i e s o f the o r d e r o f 105 for different m e t a l s . As is well k n o w n , s u c h o r g a n i c r e a g e n t s were very rare until a few y e a r s ago. In p r e v i o u s p a p e r s 8.9 t h e a u t h o r s have a l r e a d y r e p o r t e d t h a t o n e o f these c o m p o u n d s , 4 - [ ( 5 - c h l o r o - 2 - p y r i d y l ) a z o ] - l , 3 - d i a m i n o b e n z e n e , possesses very high sensitivity for c o b a l t ; t h e m o l a r a b s o r p t i v i t y o f t h e c o b a l t c o m p l e x beirlg 1 . 1 3 - l 0 s 1 mol-1 cm-1. Moreover, the 4-(2-pyridylazo)-l,3-diaminobenzene and 4-(5-bromo2 - p y r i d y l a z o ) - l , 3 - d i a m i n o b e n z e n e r e a g e n t s also e x h i b i t r e m a r k a b l y h i g h sensitivity for c o b a l t , t h e m o l a r a b s o r p t i v i t i e s b e i n g 1.07-105 a n d 1.17-105 1 real - I c m -1, respectively i°'xl. I n t h e case o f t h e s e r e a g e n t s t h e p - a m i n o g r o u p o p p o s i t e t h e azo g r o u p m a y play a v e r y i m p o r t a n t role in t h e h i g h m o l a r a b s o r p t i v i t y a n d stability o f t h e m e t a l c o m p l e x . T h e r e f o r e , o n e w o u l d e x p e c t to o b t a i n n e w h i g h l y sensitive r e a g e n t s for m e t a l s by i n t r o d u c i n g t h e d i m e t h y l a m i n o g r o u p , w h i c h is a s t r o n g l y e l e c t r o n - d o n a t i n g g r o u p , in t h e p a r a p o s i t i o n next to t h e a z o g r o u p . I n t h e p r e s e n t p a p e r , t h e p r e p a r a t i o n o f fifteen a z o derivatives ( f o r m u l a e 1-15) o f m - d i m e t h y l a m i n o p h e n o l , a n d t h e c o l o u r r e a c t i o n o f these r e a g e n t s with s o m e m e t a l i o n s in a q u e o u s solution are reported. It w a s f o u n d , a s e x p e c t e d f r o m t h e c o m p o s i t i o n , t h a t these h e t e r o c y c l i c azo d e r i v a t i v e s a r e very sensitive c h r o m o g e n i c reagents. F u r t h e r m o r e , p y r i d y l a z o c o m p o u n d s f o r m e d t h e m o s t sensitive c o l o u r c o m p l e x e s . F o r e x a m p l e , t h e m o l a r absorptix, ities o f t h e c o p p e r , zinc a n d nickel c o m p l e x e s o f 2 - [ 2 - ( 5 - b r o m o p y r i d y l ) a z o ] - 5 - d i m e t h y l a m i n o p h e n o l w e r e f o u n d to be 1 . 0 , 1.33 a n d 1.28.105 1 real -1 c m - 1, respectively. * Present address: Okayama University, Tsushima, Okayama, Japan.
398
S. SHIBATA, M. F U R U K A W A , K. T O E I
oH
(~R
OH S
~ R HO3S
H.C
R
S oR O2N
R O2N
. .37 -==° =j-C3-=
i
EXPERIMENTAL
Reagents Standard metal solutions. A h i g h - p u r i t y m e t a l (99.999~o) was dissolved in n i t r i c acid ( i + 1) o r h y d r o c h l o r i c a c i d (1 + 1), a n d 10 ml o f p e r c h l o r i c a c i d was a d d e d . T h e m i x t u r e was e v a p o r a t e d u n t i l f u m e s o f p e r c h l o r i c acid a p p e a r e d . After cooling, the s o l u t i o n was d i l u t e d to 1 1 with distilled w a t e r a n d a 10-2 M s o l u t i o n w a s finally p r e p a r e d . Buffer solutions. 0.2 M Acetic a c i d - 0 . 2 M s o d i u m acetate, 0.2 M a m m o n i a - O . 2 M a m m o n i u m chloride, a n d d i l u t e d h y d r o c h l o r i c a c i d were u s e d for p H a d j u s t m e n t . 10-a M Reagent solutions. A n e t h a n o l i c o r a q u e o u s s o l u t i o n was p r e p a r e d f r o m t h e p u r e m a t e r i a l s (see below). T h e solutions were stable for several m o n t h s if stored in a n a m b e r bottle. O r g a n i c solvents w e r e purified b y the usua, m e t h o d s . All t h e o t h e r r e a g e n t s used were m a d e f r o m h i g h - p u r i t y m a t e r i a l s or purified reagents, a n d all s o l u t i o n s were p r e p a r e d with redistilled water.
Apparatus E l e m e n t a l a n a l y s e s w e r e m e a s u r e d with a M o d e l M T - 2 Y a n a g i m o t o C£-INcorder. A b s o r b a n c e c u r v e s a n d i n f r a r e d spectra w e r e m e a s u r e d w i t h a M o d e l 323 Hitachi r e c o r d i n g s p e c t r o p h o t o m e t e r with l-era cells a n d a H i t a c h i G 3 i n f r a r e d r e c o r d i n g s p e c t r o p h o t o m e t e r . A H i t a c h i - H o r i b a M 5 - t y p e glass e l e c t r o d e p H m e t e r was used.
Preparation o f reagents T h e r e a g e n t s w e r e p r e p a r e d b y c o u p l i n g m - d i m e t h y l a m i n o p h e n o l with t h e a p p r o p r i a t e d i a z o t a t e in a q u e o u s o r a l c o h o l i c solution. 2-[1-(2-Hydroxyphenyl) azo]-5-dimethylaminophenol (1). o - A m i n o p h e n o l (0.54 g) was dissolved in 25 m l o f 0.5 M h y d r o c h l o r i c acid, a n d d i a z o t i z e d a t 0-5 ° with s o d i u m n i t r i t e s o l u t i o n by the usual m e t h o d , m - D i m e t h y l a m i n o p h e n o l
; m - D I M E T H Y L A M I N O P H E N O L DERIVATIVES O F AZO DYES
399
(0.7 g) was dissolved in 25 ml of 1 M s o d i u m h y d r o x i d e solution, and the diazo s o l u t i o n was a d d e d dropwise to this solution at 0-5 °, after which the mixture was s h a k e n for a bout 2 h. T h e mixture was left overnight an d then neutralized, an d the precipitated crude materials were filtered. The precipitate was dissolved in small portions of dilute sodium hydroxide solution a n d reprecipitated from neutral aq u eo u s ethanolic solution (14-3). The dark red needles o b t a i n e d sublimed at about 175 °. Analysis. C x , H 1 5 N 3 0 2 requires: 65.05~/o C, 5.99/0 H, 16.3~o N ; found: 65.19/o C, 6.0% H, 16.69/o N. 2-f l-(2-Hydroxy-5-sulfophenyl)azoJ-5-dimethylaminophenol (2). This was .... prepared by treating t he 2-aminophenol-d-sulfonic acid (0.94 g) with m-dimethyla m i n o p h e n o l (0.7 g) in the above man n er. Red-purple needles were obtained, Analysis. C x , H 1 5 N 3 O s S requires: 49.89/o C, 4.59/0 H, 12.459/o N ; found: 45.2~/o C, 5.4% H, 10.8% N. 2-f l-(2-Hydroxy-5-methylphenyl)azoJ-5-dimethylaminophenol (3). This was p r e p a r e d by treating t h e 2-amino-4-methylphenol (0.65 g) with m-dimethylaminop h e n o l (0.7 g) in the a bove manner. The orange-red needles obtained sublimed at 190 °. Analysis. C I s H x 7 N 3 0 2 requires: 66.4% C, 6.39/o H, 15.5% N ; found: 66.19/o C, 6.5% H, 15.69/o N. 2-[1,(2-H ydroxy-5-nitrophenyl)azoJ-5-dimethylaminophenol (4). 2-Amino-4nitrophenol (0.7 g ) w a s dissolved in 10 ml of 1 M sodium hydroxide solution and 20 ml of 1 M hydrochloric acid solution was a d d e d with vlgor0us stirring; a fine precipitate was formed. Diazotization an d coupling were almost the same as described for (1). D a r k yellow-brown needles were formed. Analysis. C 1 4 H x , N 4 0 4 requires: 55.69/0 C, 4.79/0 H, 18.5% N ; found: 54.69/0 C, 4.5% H, 16.0% N. 2-[1-(2-Hydroxy-3,5-dinitrophenyl) azoJ-5-dimethylaminophenol (5). S o d i u m nitrite (0.7 g) was dissolved in 10 ml of ,-nno~.ntrated sulfuric acid and 2-amino4,6-dinitrophenol ( 2 g) was added at 0-5 °. After diazotization, the yellowish diazo solution was p o u r e d on to ice a n d the precipitated diazonium c o m p o u n d was filtered. This d i a z o n i u m salt was su sp en d ed in a small a m o u n t of water. T h e coupling p r o c e d u r e was the same as for (1). A d a r k b r o w n a m o r p h o u s precipitate was formed. Analysis. C14HxaNsO 6 requires: 48.49/o C, 3.89/0 H, 20.29/0 N; found: • 46.09/0 C, 3.39/0 H, 18.49/o N. 2-[1-(2-Carboxyphenyl) azo.]-5-dimethylaminophenol (6). This was prepared by treating t h e o-aminobenzoic acid (0.68 g) with m-dimethylaminophenol (0.7 g) as described for (1). The crude precipitate was reprecipitated from concentrated hydrochloric acid; the dark red needles sublimed at 250 °. Analysis. C 1 5 H t s N a O a - 2 H C I requires: 50.39/0 C, 4.259/0 H, 11.7~o N ; f o u n d : 48.79/0 C, 5.8~ H, 11.5% N. 2-[1-(2-Carboxymethoxyphenyl)azoJ-5-dimethylaminophenol (7). 2-Nitrophenoxyacetic acid (3 g) was dissolved in 25 ml of 0.5 M sbdium hydroxide solution, a nd the mixture was heated on a water bath. I r o n ( I I ) Sulfate (6 g) was a d d e d a nd t he mixture was heated for 2 h. Iron was precipitated by addition of ethanol a n d filtered, a n d the filtrate was then e v a p o r a t e d to remove the ethanol. Precipitated 2-aminophenoxyacetic acid was filtered off. The reagent was prepared by treating t h e 2-aminophenoxyacetic acid (1.6 g) with m-dimethylaminophenol (1.4 g) as described for (I). A dark b r o w n a m o r p h o u s p o w d e r .was formed. Analysis. C16HxTN304 requires: 60.99/o C, 5.49/0 N, 13.39/o N ; found: 57.8% C, 5.4% H, 12.49/o N. 2-[1-(2-Arsonophenyl)azoJ-5-dimethylaminophenol (8). T h i s w a s prepared by
4OO
S. S H I B A T A , M. F U R U K A W A , K. T O E I
t r e a t i n g the 0 - a m i n o b e n z e n e a r s o n i c acid (1.08 g) with m - d i m e t h y l a m i n o p h e n o l (1.37 g) as described for (1). B r o w n needles w e r e formed. Analysis. C~4H16NaO4As r e q u i r e s : 46.0~/o C, 4.4?/o H, 11.5~/o N ; f o u n d : 39.2~/o C, 4.3% H, 9.8~/o N. [2-[1-( 2-H ydroxy-4-sulfonaphthyl) azoJ-5-dimethylaminophenol (9,). Small a m o u n t s of w a t e r w e r e a d d e d to 1 - a m i n o - 2 - n a p h t h o l - 4 - s u l f o n i c a c i d (1.2 g) to f o r m a paste, a n d c o p p e r sulfate (0.12 g) in small a m o u n t s o f water w a s a d d e d t o this paste, w h i c h was then diazotized by s o d i u m nitrite (0.7 g) solution. The d i a z o t i z e d m i x t u r e was filtered, c o n c e n t r a t e d h y d r o c h l o r i c acid w a s a d d e d to the filtrate, a n d the precipitated d i a z o n i u m salt was filtered. T h e c o u p l i n g p r o c e d u r e was t h e s a m e as d e s c r i b e d for (1). D a r k b r o w n a m o r p h o u s crystals were formed. Analysis. C x s H x T N 3 O s S requires: 55.8~/o C, 4.4?/o H, 10.8~/o N ; f o u n d : 48.9% C, 4.7~/o H, 8.5% N. 2-[8-QuinolylazoJ-5-dimethflarninophenol (DMQAP; 10). This was p r e p a r e d by t r e a t i n g the 8 - a m i n o q u i n o l i n e (0.9 g) w i t h r n - d i m e t b y l p h e n o l (0.7 g) as d e s c r i b e d for (1). T h e crystals o b t a i n e d s u b l i m e d at 205 °. Analysis. C 1 7 H 1 6 N 4 0 r e q u i r e s : 69.8~/o C, 5.5% I-/, 19.2% N ; found: 70.0~/o C, 5.5% H, 19.4~,o N. 2-(2-Thiazolylazo,)-5-dimethylarninophenol (DMTAP; 11) l z. S o d i u m nitrite (0.7 g) was d i s s o l v e d in 10 ml of c o n c e n t r a t e d sulfuric acid, a n d the s o l u t i o n was c o o l e d to 0-5 °. Glacial acetic acid (8.5 ml) a n d p r o p i o n i c acid (1.5 ml) w e r e a d d e d to this solution followed b y 2 - a m i n o t h i a z o l e ( 1.0 g). m - D i m e t h y l a m i n o p h e n o l ( 1.4 g) was dissolved in 20 ml of ethanol, a n d c o u p l i n g was d o n e w i t h the a b o v e d i a z o n i u m m i x t u r e at 0-5 ° . T h e d a r k purple needles o b t a i n e d s u b l i m e d at 175 ° . Analysis. C l l H 1 2 N a O S requires: 53.2% C, 4.9~/o H, 22.6~/o N ; found: 53.4% C, 4.8~o H, 22.6~/o N . 2-E2-(5-Nitrothiazolyl)azoJ-5-dimethylaminophenol (12). T h i s was p r e p a r e d by t r e a t i n g the 2 - a m i n o - 5 - n i t r o t h i a z o l e (1.4 g) with r n - d i m e t h y l a m i n o p h e n o l ( 1.4 g) as d e s c r i b e d for ( 1 l ) ( m . p . 172% d a r k p u r p l e a m o r p h o u s crystals). Analysis. C l l H l x N sO.zS requires: 45.0~/o C, 3.8~/o H, 23.9~/o N ; f o u n d : 43.6~/o C, 4.2~/o H, 16.7~/o N. 2-(2-Pyridylazo)-5-dimethylaminophenol (DMPAP; 13). T o a s o l u t i o n o f 2.1 g of clean s o d i u m in 10 m l of absolute ethanol, 2 - a m i n o p y r i d i n e (5 g) in 30 ml of a b s o l u t e ether w a s added, and the mixture w a s refluxed for 1 h u n d e r an a t m o s p h e r e of n i t r o g e n . T h e n , 5 ml of isopentyl nitrite was a d d e d , a n d refluxing was c o n t i n u e d for an a d d i t i o n a l 2 h. O n cooling, the d i a z o n i u m salt p r e c i p i t a t e d a n d was filtered off a n d dried in a v a c u u m desiccator. T o a s o l u t i o n o f m - d i m e t h y l a m i n o p h e n o l (0.7 g) in 20 ml o f absolute ethanol, the d i a z o n i u m salt (2.2 g) in 10 ml of absolute e t h a n o l was a d d e d at 0 - 5 °, a n d c a r b o n d i o x i d e was passed t h r o u g h the solution. T h e c r u d e m a t e r i a l was recrystallized from e t h a n o l - w a t e r mixture. T h e d a r k red needles o b t a i n e d s u b l i m e d at 174 °. Analysis. C a 3 H x 4 N 4 0 requires: 6 4 . 5 ~ C, 5 . 8 ~ H, 23.1~/o N ; f o u n d : 6 4 . 5 ~ C, 5 . 8 ~ H, 2 1 . 1 ~ N . 2-[2-(5-CMoropyridyl) azoJ-5-dimethylaminophenol (5-CI-DMPAP ; 14). T o a s o l u t i o n o f 2.1 g of s o d i u m a m i d e in 30 ml of a b s o l u t e ethanol, 2 - a m i n o - 5 - c h l o r o p y r i d i n e (6.5 g) was a d d e d , a n d the m i x t u r e was refluxed for 1 h u n d e r an a t m o s p h e r e o f nitrogen. Then, 5 ml of" isopentyl nitrite was a d d e d to the .mixture a n d refluxing was c o n t i n u e d for a n a d d i t i o n a l 2 h. O n cooling, the d i a z o n i u m salt p r e c i p i t a t e d a n d was filtered off a n d d r i e d in a v a c u u m desiccator. T o a solution o f m - d i m e t h y l a m i n o p h e n o l (1.4 g) in 20 ml o f a b s o l u t e e t h a n o l , the d i a z o n i u m salt (1.7 g) in 10 ml of a b s o l u t e e t h a n o l was a d d e d at 0-5 ° in a s t r e a m
m-DIMETHYLAMINOPHENOL
DERIVATIVES
OF AZO
401
DYES
of c a r b o n dioxide. T h e c r u d e m a t e r i a l was recrystallized from e t h a n o l - w a t e r m i x t u r e ( 1 + 1). T h e d a r k red needles o b t a i n e d s u b l i m e d at 190 °. Analysis. C I a H x a N 4 O C 1 requires: 56.4~/~ C, 4.7~/o H, 20.2~o N ; f o u n d : 5 6 . 7 ~ C, 4.7~/o H, 20.1~/o N . 2-[2-(5-Bromopyridyl) azo]-5-dimethylaminophenol (5-Br-DMPAP; 15). This was p r e p a r e d by treating the 2 - a m ' i n o - 5 - b r o m o p y r i d i n e (10 g) with the m-dimethyla m i n o p h e n o l (0.7 g) as d e s c r i b e d for (14). T h e d a r k red needles o b t a i n e d s u b l i m e d at 190 °. Analysis. C x a H 1 3 N 4 O B r requires: 48.6~o C, 4.1~/o H, 17.4~o N ; f o u n d : 48.6~/o C, 3.9~o H, 17.2~ N . RESULTS
AND
DISCUSSION
Colour reactions with some metals T h e chelate c o m p o u n d s are easily p r e p a r e d by a d d i n g a few d r o p s of a s o l u t i o n of the reagent in a l c o h o l o r water, to a solution of a heavy metal. The c o l o u r r e a c t i o n s with s o m e m e t a l s at the o p t i m a l p H values are listed in T a b l e I. T h e chelating r e a c t i o n s of reagents 6, 7 a n d 8 c o u l d not be detected visually. TABLE
I
COLOUR
REACTIONS
WITH
SOME
METAL
IONS*
Reagent
Reagent
A I a÷
C d 2+
C o 2+
C u 2+
F e a+
L a a÷
M g 2÷
M n 2+
N i 2+
p b 2+
Z n 2+
y-O y-O y-O p-R R Y y-O Y r-P y-O O p-B Y Y Y
-R R r-P p-R . . . --------
O O y-R r-P p-R
r-P p-R R r-P p-R
r-P y-R ~-P r-P p-R
Br Y Br Br Br
O -r-P r-P -. . . b-P -P b-P r-O r-P r-P
O -y-R r-P -. . . ----r-O r-P r-P
r-P R P P p-R
r-P O p-R O p-R
r-P r-P r-P r-P p-R
r-P O R r-P p-R
---b-P r-P r-P r-P
P r-P r-P b-P r-P r-P r-P
1"i0.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
. . .
. . . -r-O r-P b-P r-P r-P r-P
. . . b-P r-P P b-P P P P
. . . P r-P P b-P r-P r-P r-P
. . . b-P Br P b-P r-P r-P r-P
. . .
. . . b-P r-P r-P b-P R r-P r-P
. . . P r-P r-P P r-P r-P r-P
O = O r a n g e , P = P u r p l e , R = R e d , Y = Y e l l o w , B = B l u e , B r ---- B r o w n , b = b l u i s h , p = p u r p l i s h , r - - r e d d i s h , y = yellowish, -- not detectable.
T h e d e t e c t i o n limits of s o m e r e a g e n t s w e r e then studied m o r e quantitatively. T h e c o l o u r s of a s e r i e s ' o f solutions c o n t a i n i n g k n o w n a m o u n t s of metals ( a d d e d by a E p p e n d o r f m i c r o p i p e t t e ) , a d r o p o f dye solution, 0.5 ml of p H 10 buffer s o l u t i o n a n d 0.5 ml of water, were o b s e r v e d visually against a reagent blank. T h e d e t e c t i o n limits o b t a i n e d are s h o w n in T a b l e II. F r o m these results, subsequent studies w e r e c a r r i e d o u t with reagents 10, 11, 13, 14 and 15.
Acid dissociation behaviour All the reagents w e r e sparingly soluble in Water, but soluble in various
402
S. S H I B A T A , M . F U R U K A W A ,
K. T O E I
T A B L E II THE DETECTION
LIMITS FOR SOME
METALS"
Reagents
Co(ll)
Cu(lI)
Ni(ll)
,Zn(II)
I 2 3 4 5 9 I0 11 12 13 14 15
0.3 0.6 0.3 1.2 0.3 0.3 0.3 0.3 0.3 0.03 0.09 0.09
0.3 0.6 0.3 0.6 0.3 0.3 0.9 0.3 0.6 0.03 0.06 0.06
0.3 0.6 0.6 0.6 0.3 0.3 0.3 0.3 0.3 0.03 0.03 0.03
0.6 (1.9 0.6 1.2 0.3 0.6 0.9 0.3 2.1 0.03 0.06 0.06
" C o n c e n t r a t i o n s are given in itg m l - t
organic solvents, including ethanol, methanol, MIBK, benzene and chloroform. These reagents showed acid-base indicator properties and were yellow in weak acidic and neutral solution but orange-red in strongly alkaline solution. Four species of these reagents, HaL 2+, H2 L+, HL and L - , are involved in its acid-base behaviour. For example, the four forms of D M P A P involved in its acid-base behaviour are related by the following equilibria."
N ( C H 3 ) 2'
N=N
N(CH3) ~
rq=N
HO
HO
DKa3 'N(CH3) 2
HO
-O
The acid-base equilibria of D M P A P may be formulated: Ka 1
• H2 L+ +H
HAL2+
+
(1)
Ka2
H2 L+ HL
~a3
" HL +H +
(2)
"L-
(3)
+H +
The three acidity constants for D M P A P are then defined by K,,t = [H2L+] [ H + ] [HaL 2+]
(4)
m-DIMETHYLAMINOPHENOL
403
DERIVATIVES OF AZO DYES
Ka 2 = [ H L ] [ H +] ... [H2L +] Kaa----
(5)
[L-][H +] [-HL1
(6)
T h e s e associated e q u i l i b r i a can be calculated i n d e p e n d e n t l y because the steps were sufficiently separated. T h e a c i d dissociation constants d e t e r m i n e d are r e p o r t e d in T a b l e III, w h e r e p K . 2 refers to the dissociation of the d i m e t h y l a m i n o group, a n d P K . a refers t o the d i s s o c i a t i o n o f the h y d r o x y group. T h e p K . 1 value is below p H 1. T h e p K . 2 values of the d i m e t h y l a m i n o g r o u p increase in the o r d e r D M T A P < DMQAP< 5-C1-DMPAP~S-Br-DMPAP< D M P A P , a n d the p K . 3 values of the h y d r o x y g r o u p i n c r e a s e in the o r d e r D M T A P < 5 - C I - D M P A P _ = 5 - B r - D M P A P < D M P A P < D M Q A P . T h e w a v e l e n g t h of m a x i m a l a b s o r b a n c e a n d the m o l a r absorptivity of e a c h species in a q u e o u s 409/0 (v/v) m e t h a n o l solution are s h o w n in T a b l e IV. T h e shift o f m a x i m u m Wavelength from neutral t o basic species increases in the o r d e r D M Q A P < D M T A P < D M P A P < 5 - C I - D M P A P < 5 - B r - D M P A P . Therefore, a m o n g these reagents 5 - B r - D M P A P w o u l d be expected to be the best c h r o m o g e n i c reagent for metals. T A B L E III ACID DISSOCIATION CONSTANTS SOLUTION
O F R E A G E N T S IN A Q U E O U S
40~% (v/v) M E T H A N O L
( g = 0 . 1 KCI, 25 ° ) Reagents
DMTAP DMQAP DMPAP 5-CI-DMPAP 5-Br-DMPAP
(11) (10) (13) (14) (15)
pKat
PKa2
PKa3
< < < < <
2.8 3.1 3.6 3.4 3.4
9.9 13.1 12.1 11.6 11.6
1 1 1 1 1
T A B L E IV ABSORPTION MAXIMA OF REAGENTS AND MOLAR ABSORPTIVITIES° ( A q u e o u s 40?/o ( v / v ) m e t h a n o l solutions) Reagents
DMQAP DMTAP DMPAP 5-CI-DMPAP 5-Br-DMPAP
p H ,,, 1
pH ~ 6
N a O H ~, O.I M
~max
~
~'~x
£
~max
8
504 540 524 465 466
4.6 6.1 2.2 4.7 4.7
478 502 435 440 AA.A
4.5 4.6 3.0 4.6 4.7
490 524 494 508 510
2.6 4.1 3.0 4.6 4.7
2 ~ z is given in nm. All m o l a r absorptivities are given as '. 10 4 1 m o l - t c m - l .
S. S H I B A T A , M. F U R U K A W A , K..T O E I
404
,4bsorptiotz spectra T h e c o m p l e x e s o f these r e a g e n t s w i t h metals are n o t soluble in water b u t soluble in a q u e o u s o r g a n i c solvents. In this paper, t h e a b s o r p t i o n spectra in a q u e o u s 50~/o (v/v) e t h a n o l s o l u t i o n w e r e studied. T h e a b s o r p t i o n spectra o f the copper, nickel, cobalt, a n d zinc chelates o f the five r e a g e n t s are s h o w n in Figs. 1-5. T h e a b s o r p t i o n m a x i m a o f each m e t a l chelate are also s h o w n in Table V:"
1.2
1.2 /
1.0
~
~
1.0
8 0.8
38 =~ 9.6
"...N i ".%.
o6
o
0.4
"%~
c
~ 0.4
'.. k % %%
J2
'..Ni ~
400
450 500 Wovel en gth, n rrl
/
0.2
550
600
400
/.:;;-'/"cu
\
450 500 550 Wuveleng th, n m
N'%.. ", 600
650
Fig. I. A b s o r p t i o n spectra of D M Q A P - m e t a i chelates in aqueous 50% (v/v) ethanol. Reagent 2.5. I 0 - 5 M. (Ni pH 8, Zn pH 10, Co pH 8.5) 1.75- 10 -5 M reagent plus 0.75.10 -5 M metal. (Cu p H 8) 1.5.10 -5 M reagent plus 1.0.10 -5 M copper v s . water blank. 1-cm cells. Fig. 2. A b s o r p t i o n spectra of D M T A P - m e t a l chelates in aqueous 5 0 ~ (v/v) ethanol. Reagent 2 . 5 . 1 0 - 5 M. (Ni, Zn, C o pH 8) 1.75.10 -5 M reagent plus 0.75" 10 -5 M metal. (Cu, pH 8) 1.25.10 - 5 M reagent plus 1.25- 10- 5 M copper v s . water blank, l-cm cells. 1.2 1.0
°t
R
8 o8 c~
N!..
~ 0.8
"\
o.6 o
~ 0.6
%"~ C O
'< 0.4
",
o,
\
0.2
• •
/ -_. ) , , . _ 400
450 500 550 Wcivelength0 n m
600
\
~.
\k
%%
,,
.
650
400
4,50 500 550 600 WcIvelength, nm Fig. 3. A b s o r p t i o n spectra of D M P A P - m e t a l chelates in aqueous 50% (v/v) ethanol. Reagent 2.5. I 0 - 5 M. (Zn pH 11, Ni pH 9) 1.75-10 -5 M reagent plus 0.75.10 - s M metal. ( C u pH 11, Co pH 9) 1.875.10 -5 M reagent plus 0.625.10 - 5 M metal. ( C u * pH 6) 1.25" 10 - s M reagent plus 1.25.10 -5 M copper cs. water blank. 1-cm cells. "Fig. 4. A b s o r p t i o n spectra of 5 - C I - D M P A P - m e t a l chelates in a q u e o u s 5 0 ~ (v/v) ethanol. Reagent 2.5.10 -5 M. ( Z n pH 11, Ni pH 10, C o pH 10, C u p H 11) 1.75-10 -5 M reagent plus 0.75.10 -5 M metal. (Cu* pH 4.5) 1.25.10 -5 M reagent a n d meta.l v s . water blank. 1-era cells.
650
m-DIMETHYLAMINOPHENOL
405
D E R I V A T I V E S O F A Z O DYES
1.2
O.8 o
0.6
/
400
450 500 550 600 650 Wovelength, nm Fig. 5. A b s o r p t i o n spectra o f 5 - B r - D M P A P - m e t a l chelates in aqueous 50~ (v/v) ethanol. Reagent 2.5.10 -5 M. (Zn, Ni, Co, pH 8, Cu pH 10) 1.75. I0 -5 M reagent plus 0.75"10 -5 M metal. (Cu* pH 4) 1.25.10- 5 M reagent and metal us. water blank, l-cm cells.
TABLE V A B S O R P T I O N M A X I M A O F C H E L A T E S (nm)" Reagents
Cu
Co
DMQAP DMTAP DMPAP 5-CI-DMPAP 5-Br-DMPAP
515 560 515, 540, (530) b 530, 550, (555) 530, 550, (555)
545, 570 546, 550, 555,
515 5;70 585 590
Ni
Zn
535, 505 535 520 520, 552 520, 552
528, 535 510, 518, 570,
505 534 550 552
" In a q u e o u s 50~,~ (v/v) ethanol solution measured against water, b Between brackets 1:1 chelate.
A l t h o u g h the wavelength shifts on chelation of the quinolylazo and thiazolylazo i'eagents are small (50-60 nm), those for the pyridylazo reagents are very large (110-120 nm). The absorption s p e c t r a of the halogen-substituted pyridylazo reagents show two absorption peaks clearly, except in the case of copper. The 1:1 copper chelate has only one absorption peak, although the 1:2 copper chelate has two peaks.
Effect of pH F o r evaluation of the optimal p H values for determinations of copper, nickel, cobalt a n d zinc, the effects of pH on the absorbance were studied with the results : s h o w n in Fig s. 6-10. In the cases of cobalt, zinc a n d nickel, the absorption spectra did no t change over the whole range, so that obviously only one type' of chelate is formed. C o p p e r chelates of D M P A P and its halogen-substituted reagents having 1 : 1 a n d 1:2 copper-ligand ratios were as s u med to be formed at low pH and at high pH, respectively. The optimal p H and wavelength with mo lar absorptivity a n d sensitivity for the determination of cobalt, nickel, zinc and copper are shown in Table VI.
Nature of complex T h e empirical formulae of the c o l o u r e d complexes were d e t e r m i n e d by the
406
S. SHIBATA, M. F U R U K A W A , K. T O E I
Q8
Q8 (30
0.6
Ni
-
Ni
•
•
z.
g
g ~ o4
o4 O2
0
2
4
6
8
10
.
12
2
2
4
pH
~
6 DH
8
10
Fig. 6. Effect of p H on a b s o r b a n c e of D M Q A P - m e t a i chelates. Reagent 4.4.10 -5 M. Co, Z n a n d Ni I. 10 - 5 M, C u 0.75.10 - 5 M vs. reagent blank. 1-crn cells. Fig. 7. Effect of p H o n a b s o r b a n c e of DMTA13-rnetal chelates. Reagent 1.10 - a M. Zn, N i a n d Cu 1 • 10 - 5 M, Co 0.8.10 - 5 M vs. reagent blank. 1-crn cells.
1.0
Zn
1.0 Zn
o8
N~
9~ ' - ° - - < ~
~ O8
0.6 ~
o
~ Q4
0.4 0.2
0.2 2
4
6
8
10
pH
2
4
6 • 8 pH
10
12
Fig. 8. Effect of p H on a b s o r b a n c e of D M P A P - m e t a l chelates. Reagent 5.1 • 10-5 M. Metals 7.5.10 - 6 M vs. reagent blank, l-cm cells. Fig. 9. Effect of pH o n a b s o r b a n c e of 5 - C I - D M P A P - r n e t a l chelates. Reagent 5.10 - 5 M. Metals 7.5.10 - 6 M us. reagent blank. 1-cm cells.
Zn
1.0
Ni
c= c~ r'~
,7
~- 0.6 o <
0.4 0.2 !
2
4
6
8
10
pH
Fig. I0. Effect of pH on a b s o r b a n c e of 5-Br-D" i P A P - m e t a l chelates. Reagent 4.0- 10-5 M. Metals 7.5" 10 - 4 M v s . reagent blank. 1-cm cells.
m-DIMETHYLAMINOPHENOL
DERIVATIVES OF AZO DYES
407
T A B L E VI THE OPTIMAL pH VALUES AND WAVELENGTHS S O M E M E T A L S I N A Q U E O U S 50~o (v/v) E T H A N O L
Reagent
Metal
Optimal p H
WITH MOLAR ABSORPTIVITIES OF
Molar absorpSensitivity tivity (lzg cm.-2) ( - 10 ~ l tool- j cm. i )
Optimal analyticai wavelengtl¢' ( n m )
DMQAP
Co Ni Cu Zn
5.0-11.0 6.0-I 1.0 4.0-9.0 9.5-11.0
7.2 5,6 3,4 5.6
0.00082 0.0011 0.0019 0.0012
547 535 520 528
DMTAP
Co Ni Cu Zn
5.5-8.5 5.5-8.5 4.0-8.0 7.5-9.5
7.4 6,9 4.1 6,7
0.00080 0.00084 0.0015 0.00097
575 558 564 '556
DMPAP
Co Ni Cu b Cu Zn
5.0-10.0 5.0-10.5 4.0-6.0 10.0-10.5 7.0-9.5
7.7 9,8 5.3 8.3
0.00077 0.00060 0.0012 0.00077
11.2
0.00058
574 545 555 545 538
Co Ni Cu b Cu Zn
3.0-10.5 4.5-10.0 2.0-6.0 9.5-10.5 8.5-10.5
Co Ni Cu b Cu Zn
3.0-10.0 4.5-10.0 2.0-6.0 9.0-10.0 7.5-10.0
5-CI-DMPAP
5-Br-DMPAP
8.5
0.00069
12.I
0.00049
6.1
0.0010
10.2 12.2
0.00062 0.00054
8.8
0.00067
12.8
0.00046
6.1
0.0010
10.0 13.3
0.00064 0.00049
586 556 556 554 550 588 558 558 555 552
a Against r eag en t blank, b 1 : 1 complex.
c o n t i n u o u s v a r i a t i o n s m e t h o d at the o p t i m a l p H a n d w a v e l e n g t h . I n the case of c o p p e r , t h e c u r v e s i n d i c a t e d the f o r m a t i o n o f a 1:1 c o m p l e x at p H 3 a n d a 1:2 c o m p l e x at p H 10 except w i t h D M Q A P , w h i c h f o r m e d o n l y a 1:2 c o m p l e x with c o p p e r . I n t h e cases o f nickel, c o b a l t a n d zinc, o n l y 1 : 2 c o m p l e x e s were f o r m e d w i t h all reagents. Solvent e x t r a c t i o n
T h e highly coloured complexes f o r m e d with metals u n d e r various conditions are useful for t h e d e t e r m i n a t i o n o f c e r t a i n metals. T h e s e c o l o u r e d c o m p l e x e s are s o l u b l e in v a r i o u s o r g a n i c solvents. S o m e results are s h o w n in T a b l e VII. Conclusions Although these reagents are rather unselective, analytical conditions can improved by a judicious choice of pH, solvent, or masking agents. Anyway, photometric reagents, these compounds seem to be promising because of the markably high molar absorptivity and large bathochromic shifts produced
be as reon
'408
S. SHIBATA, M. F U R U K A W A , K. TOEI
TABLE
VII
EXTRACTABILITY
OF
METAL
CHELATES
IN
VARIOUS
ORGANIC
Metals
Solvents
DMTAP
DMQAP
DMPAP
Co
MIBK 1,2-Dichioroethane Benzene MIBK 1,2-Dichloroethane Benzene MIBK 1,2-Dichioroethane Benzene MIBK 1,2-Dichloroelhane Benzen.e.
+ -+ + + -4+ + + + + +
:F -+ + + + + + + + + +
:F + =F --t-___ + + + + +
Cu
Ni
Zn
a +
very
w e l l , . _--4- w e l l , ~,: n o t
well,
SOLVENTS*
5-CiDMPAP + + :F --4-+ + + + + +
5-BrDMPAP + + _+ _+ _ -+ + + ::F :F
-- bad.
c h e l a t i o n . F u r t h e r w o r k o n the s o l v e n t e x t r a c t i o n a n d analytical a p p l i c a t i o n o f t h e s e r e a g e n t s for d e t e r m i n a t i o n o f m e t a l s is n o w in p r o g r e s s . SUMMARY
Fifteen azo d y e s c o n t a i n i n g the m - d i m e t h y l a m i n o p h e n o l g r o u p were synthesized, a n d their a n a l y t i c a l p o t e n t i a l for the d e t e r m i n a t i o n o f m e t a l s w a s s t u d i e d s p e c t r o p h o t o m e t r i c a l l y . A m o n g these reagents, the h e t e r o c y c l i c azo d e r i v a t i v e s are m o s t suitable as c h r o m o g e n i c reagents. T h e best r e a g e n t s are t h e 2 - p y r i d y l a z o c o m p o u n d s . T h e s e c o m p l e x e s with c o p p e r , zinc a n d n i c k e l s h o w m o l a r a b s o r p t i v i t i e s o f t h e o r d e r o f 100,000. F o r e x a m p l e , t h e 2 - [ 2 - ( 5 - b r o m o p y r i d y l ) - a z o ] - 5 - d i m e t h y l a m i n o p h e n o l c o m p l e x e s w i t h c o p p e r , zinc a n d nickel s h o w m o l a r a b s o r p t i v i t i e s o f 1.0, 1.33 a n d 1 . 2 8 - l 0 s 1 m o l -x e r a - 1 , respectively. I n these reagents, the p a r a s u b s t i t u t e d d i m e t h y l a m i n o g r o u p n e x t to t h e a z o g r o u p s e e m s to p l a y a n i m p o r t a n t role in a c h i e v i n g h i g h m o l a r a b s o r p t i v i t y a n d stability o f t h e metal "complexes. RI~SUMI~
Q u i n z e c o l o r a n t s a z o i q u e s r e n f e r m a n t le g r o u p e m e n t m - d i m 6 t h y l a m i n o p h 6 n o l o n t 6t6 synth6tis6s; o n e x a m i n e a u s p e c t r o p h o t o m 6 t r e l e u r possibilit6 d ' u t i l i s a t i o n p o u r le d o s a g e des m 6 t a u x . Les c o m p o s 6 s 2 - p y r i d y l a z o c o n s t i t u e n t les m e i l l e u r s r6actifs; les c o m p l e x e s o b t e n u s avec cuivre, z i n c et nickel p r 6 s e n t e n t des coefficients d ' e x t i n c t i o n m o l a i r e de l'ordre de 100,000; o n a p a r e x e m p l e des valeurs de 1.0, 1.33 et 1.28- 105 1 m o l - 1 e r a - 1 r e s p e c t i v e m e n t p o u r les c o m p l e x e s d u cuivre, d u zinc et d u nickel avec le 2 - [ 2 - ( b r o m o - 5 - p y r i d i l ) a z o ] - 5 - d i m 6 t h y l a r n i n o p h 6 n o l . Le g r o u p e d i m 6 t h y l a m i n o en par a p a r r a p p o r t au g r o u p e azo semb!e j o u e r u n r61e i m p o r t a n t s u r l ' e x t i n c t i o n m o l a i r e 61ev6e et la stabilit6 d e s c o m p l e x e s m6talliques.
m - D I M E T H Y L A M I N O P H E N O L D E R I V A T I V E S O F AZO DYES
409
ZUSAMMENFASSUNG
Es wurden f'tinfzehn Azofarbstoffe dargestellt, die die m-Dimethylaminophenol-Gruppe ¢nthielten; ihre analytische Anwendbarkeit f'tir die Bestimmung von Metallen wurde spektrophotometrisch untersucht. Von diesen Reagenzien eignen sich die heterocyclischen Azoderivate besonders als chromogene Reagenzien. Die besten sind die 2-Pyridylazo-Verbindungen. Deren Kornplexe mit Kupfer, Zink und Nickel haben molare Extinktionskoeffizienten in der Gr/Sssenordnung yon 100,000. D i e molaren Extinktionskoeffizienten der Komplexe yon z.B. 2-[2-(5-Brompyridyl)azo]-5-dimethylaminophenol rnit Kupfer, Zink und Nickel sind resp. 1.0, 1.33 und 1.28. l0 s 1 m o l - 1 c m - 1. Bei diesen Reagenzien scheint die p-substituierte Dimethylamino-Gruppe gegeniJber der Azo-Gruppe eine wichtige Rolle hinsichtlich eines hohen molaren ExtinktionskoelTlzienten und der Stabilit~it der Metallkomplexe zu spielen. REFERENCES I S. Shibata, in H. Flaschka and A. J. Barnard, Jr., Chelates in Analytical Chemistry, Voi. IV, M. Dekker. New York, 1972, p. 1-232. 2 Sh. T. Tali ~ov, V. S. Podgornova and S. N. Kosolapova, Zh. Anal. Khim., 24 (1969) 409. 3 S. I. G u s e v I. N. G l u s h k o v a and L. A. Ketova, Zh. Anal. Khim., 24 (1969) 993. 4 S. Shibata K. Goto and E. K a m a t a , Anal. Chim. Acta, 45 (1969) 279. 5 S. Shibata M. Furukawa, E. K a m a t a and K. G o t o , Anal. Chim. Acta, 50 (1970) 439. 6 S. Shibata M. F u r u k a w a a n d S. Sasaki, Anal. Chim. Acta, 51 (1970) 271. 7 S. Shibata M. F u r u k a w a a n d Y. Ishiguro, Mikrochim. Acta, (1972) 721. 8 S. Shibata M. Furukawa, Y. Ishiguro and S. Sasaki, Anal. Chim. Acta, 55 (1971) 231. 9 S. Shibata. M. F u r u k a w a a n d K. Goto, Colloq. Spectrosc. Int. X V I , Heidelberg, 1971, Preprints, Vol. 1, p. 114. 10 S. Shibata, Bunseki Kagaku, 21 (1972) 551. 11 S. Shibata, E. K a m a t a a n d M. Furukawa, Int. Congress on Analyt. Chem., LU.P.A.C., Kyoto, April, 1972, Abstracts p. 393. 12 J. Minczewski and K. Kasiura, Chem. Anal. (Warsaw), I0 (1965) 21.
SYNTHESES AND SPECTROPHOTOMETRIC CONTAINING m-DiMETHYLAMINOPHENOL REAGENTS
STUDIES OF AZO AS A N A L Y T I C A L
397
DYES
SHOZO SHIBATA, MASAMICHI FURUKAWA and KYOJI TOEI* Government Industrial Research Institute, Nagoya, Kita-ku, Naaoya (Japan)
(Received 1st February 1973) D u r i n g t h e p a s t t w e n t y years, the a n a l y t i c a l a p p l i c a t i o n of 2 - p y r i d y l a z o c o m p o u n d s h a s b e e n s t u d i e d extensively. T w o r e p r e s e n t a t i v e s o f this g r o u p , l-(2p y r i d y l a z o ) - 2 - n a p h t h o l ( P A N ) a n d 4 - ( 2 - p y r i d y l a z o ) r e s o r c i n o l ( P A R ) , have p r o v e d to be very versatile r e a g e n t s for m e t a l s 1. A l t h o u g h n e i t h e r r e a g e n t is selective as a c h r o m o g e n i c a g e n t o r a n e x t r a c t a n t , n e w selective 2 - p y r i d y l a z o d e r i v a t i v e s have b e e n p r o p o s e d by several w o r k e r s . M u c h o f the i m p o r t a n t w o r k o n t h e s e derivatives has b e e n c a r r i e d o u t in Russia, in p a r t i c u l a r by T a l i p o v z a n d G u s e v 3 a n d coworkers. In a s e a r c h for n e w sensitive a n d selective reagents, a t h o r o u g h s t u d y o f s o m e azo c o m p o u n d s c o n t a i n i n g _C-substituted p y r i d i n e has b e e n m a d e 4-v. A t the p r e s e n t time, t h e m a i n p u r p o s e o f t h e w o r k is to p r e p a r e sensitive o r g a n i c r e a g e n t s w h i c h h a v e m o l a r a b s o r p t i v i t i e s o f the o r d e r o f 105 for different m e t a l s . As is well k n o w n , s u c h o r g a n i c r e a g e n t s were very rare until a few y e a r s ago. In p r e v i o u s p a p e r s 8.9 t h e a u t h o r s have a l r e a d y r e p o r t e d t h a t o n e o f these c o m p o u n d s , 4 - [ ( 5 - c h l o r o - 2 - p y r i d y l ) a z o ] - l , 3 - d i a m i n o b e n z e n e , possesses very high sensitivity for c o b a l t ; t h e m o l a r a b s o r p t i v i t y o f t h e c o b a l t c o m p l e x beirlg 1 . 1 3 - l 0 s 1 mol-1 cm-1. Moreover, the 4-(2-pyridylazo)-l,3-diaminobenzene and 4-(5-bromo2 - p y r i d y l a z o ) - l , 3 - d i a m i n o b e n z e n e r e a g e n t s also e x h i b i t r e m a r k a b l y h i g h sensitivity for c o b a l t , t h e m o l a r a b s o r p t i v i t i e s b e i n g 1.07-105 a n d 1.17-105 1 real - I c m -1, respectively i°'xl. I n t h e case o f t h e s e r e a g e n t s t h e p - a m i n o g r o u p o p p o s i t e t h e azo g r o u p m a y play a v e r y i m p o r t a n t role in t h e h i g h m o l a r a b s o r p t i v i t y a n d stability o f t h e m e t a l c o m p l e x . T h e r e f o r e , o n e w o u l d e x p e c t to o b t a i n n e w h i g h l y sensitive r e a g e n t s for m e t a l s by i n t r o d u c i n g t h e d i m e t h y l a m i n o g r o u p , w h i c h is a s t r o n g l y e l e c t r o n - d o n a t i n g g r o u p , in t h e p a r a p o s i t i o n next to t h e a z o g r o u p . I n t h e p r e s e n t p a p e r , t h e p r e p a r a t i o n o f fifteen a z o derivatives ( f o r m u l a e 1-15) o f m - d i m e t h y l a m i n o p h e n o l , a n d t h e c o l o u r r e a c t i o n o f these r e a g e n t s with s o m e m e t a l i o n s in a q u e o u s solution are reported. It w a s f o u n d , a s e x p e c t e d f r o m t h e c o m p o s i t i o n , t h a t these h e t e r o c y c l i c azo d e r i v a t i v e s a r e very sensitive c h r o m o g e n i c reagents. F u r t h e r m o r e , p y r i d y l a z o c o m p o u n d s f o r m e d t h e m o s t sensitive c o l o u r c o m p l e x e s . F o r e x a m p l e , t h e m o l a r absorptix, ities o f t h e c o p p e r , zinc a n d nickel c o m p l e x e s o f 2 - [ 2 - ( 5 - b r o m o p y r i d y l ) a z o ] - 5 - d i m e t h y l a m i n o p h e n o l w e r e f o u n d to be 1 . 0 , 1.33 a n d 1.28.105 1 real -1 c m - 1, respectively. * Present address: Okayama University, Tsushima, Okayama, Japan.
398
S. SHIBATA, M. F U R U K A W A , K. T O E I
oH
(~R
OH S
~ R HO3S
H.C
R
S oR O2N
R O2N
. .37 -==° =j-C3-=
i
EXPERIMENTAL
Reagents Standard metal solutions. A h i g h - p u r i t y m e t a l (99.999~o) was dissolved in n i t r i c acid ( i + 1) o r h y d r o c h l o r i c a c i d (1 + 1), a n d 10 ml o f p e r c h l o r i c a c i d was a d d e d . T h e m i x t u r e was e v a p o r a t e d u n t i l f u m e s o f p e r c h l o r i c acid a p p e a r e d . After cooling, the s o l u t i o n was d i l u t e d to 1 1 with distilled w a t e r a n d a 10-2 M s o l u t i o n w a s finally p r e p a r e d . Buffer solutions. 0.2 M Acetic a c i d - 0 . 2 M s o d i u m acetate, 0.2 M a m m o n i a - O . 2 M a m m o n i u m chloride, a n d d i l u t e d h y d r o c h l o r i c a c i d were u s e d for p H a d j u s t m e n t . 10-a M Reagent solutions. A n e t h a n o l i c o r a q u e o u s s o l u t i o n was p r e p a r e d f r o m t h e p u r e m a t e r i a l s (see below). T h e solutions were stable for several m o n t h s if stored in a n a m b e r bottle. O r g a n i c solvents w e r e purified b y the usua, m e t h o d s . All t h e o t h e r r e a g e n t s used were m a d e f r o m h i g h - p u r i t y m a t e r i a l s or purified reagents, a n d all s o l u t i o n s were p r e p a r e d with redistilled water.
Apparatus E l e m e n t a l a n a l y s e s w e r e m e a s u r e d with a M o d e l M T - 2 Y a n a g i m o t o C£-INcorder. A b s o r b a n c e c u r v e s a n d i n f r a r e d spectra w e r e m e a s u r e d w i t h a M o d e l 323 Hitachi r e c o r d i n g s p e c t r o p h o t o m e t e r with l-era cells a n d a H i t a c h i G 3 i n f r a r e d r e c o r d i n g s p e c t r o p h o t o m e t e r . A H i t a c h i - H o r i b a M 5 - t y p e glass e l e c t r o d e p H m e t e r was used.
Preparation o f reagents T h e r e a g e n t s w e r e p r e p a r e d b y c o u p l i n g m - d i m e t h y l a m i n o p h e n o l with t h e a p p r o p r i a t e d i a z o t a t e in a q u e o u s o r a l c o h o l i c solution. 2-[1-(2-Hydroxyphenyl) azo]-5-dimethylaminophenol (1). o - A m i n o p h e n o l (0.54 g) was dissolved in 25 m l o f 0.5 M h y d r o c h l o r i c acid, a n d d i a z o t i z e d a t 0-5 ° with s o d i u m n i t r i t e s o l u t i o n by the usual m e t h o d , m - D i m e t h y l a m i n o p h e n o l
; m - D I M E T H Y L A M I N O P H E N O L DERIVATIVES O F AZO DYES
399
(0.7 g) was dissolved in 25 ml of 1 M s o d i u m h y d r o x i d e solution, and the diazo s o l u t i o n was a d d e d dropwise to this solution at 0-5 °, after which the mixture was s h a k e n for a bout 2 h. T h e mixture was left overnight an d then neutralized, an d the precipitated crude materials were filtered. The precipitate was dissolved in small portions of dilute sodium hydroxide solution a n d reprecipitated from neutral aq u eo u s ethanolic solution (14-3). The dark red needles o b t a i n e d sublimed at about 175 °. Analysis. C x , H 1 5 N 3 0 2 requires: 65.05~/o C, 5.99/0 H, 16.3~o N ; found: 65.19/o C, 6.0% H, 16.69/o N. 2-f l-(2-Hydroxy-5-sulfophenyl)azoJ-5-dimethylaminophenol (2). This was .... prepared by treating t he 2-aminophenol-d-sulfonic acid (0.94 g) with m-dimethyla m i n o p h e n o l (0.7 g) in the above man n er. Red-purple needles were obtained, Analysis. C x , H 1 5 N 3 O s S requires: 49.89/o C, 4.59/0 H, 12.459/o N ; found: 45.2~/o C, 5.4% H, 10.8% N. 2-f l-(2-Hydroxy-5-methylphenyl)azoJ-5-dimethylaminophenol (3). This was p r e p a r e d by treating t h e 2-amino-4-methylphenol (0.65 g) with m-dimethylaminop h e n o l (0.7 g) in the a bove manner. The orange-red needles obtained sublimed at 190 °. Analysis. C I s H x 7 N 3 0 2 requires: 66.4% C, 6.39/o H, 15.5% N ; found: 66.19/o C, 6.5% H, 15.69/o N. 2-[1,(2-H ydroxy-5-nitrophenyl)azoJ-5-dimethylaminophenol (4). 2-Amino-4nitrophenol (0.7 g ) w a s dissolved in 10 ml of 1 M sodium hydroxide solution and 20 ml of 1 M hydrochloric acid solution was a d d e d with vlgor0us stirring; a fine precipitate was formed. Diazotization an d coupling were almost the same as described for (1). D a r k yellow-brown needles were formed. Analysis. C 1 4 H x , N 4 0 4 requires: 55.69/0 C, 4.79/0 H, 18.5% N ; found: 54.69/0 C, 4.5% H, 16.0% N. 2-[1-(2-Hydroxy-3,5-dinitrophenyl) azoJ-5-dimethylaminophenol (5). S o d i u m nitrite (0.7 g) was dissolved in 10 ml of ,-nno~.ntrated sulfuric acid and 2-amino4,6-dinitrophenol ( 2 g) was added at 0-5 °. After diazotization, the yellowish diazo solution was p o u r e d on to ice a n d the precipitated diazonium c o m p o u n d was filtered. This d i a z o n i u m salt was su sp en d ed in a small a m o u n t of water. T h e coupling p r o c e d u r e was the same as for (1). A d a r k b r o w n a m o r p h o u s precipitate was formed. Analysis. C14HxaNsO 6 requires: 48.49/o C, 3.89/0 H, 20.29/0 N; found: • 46.09/0 C, 3.39/0 H, 18.49/o N. 2-[1-(2-Carboxyphenyl) azo.]-5-dimethylaminophenol (6). This was prepared by treating t h e o-aminobenzoic acid (0.68 g) with m-dimethylaminophenol (0.7 g) as described for (1). The crude precipitate was reprecipitated from concentrated hydrochloric acid; the dark red needles sublimed at 250 °. Analysis. C 1 5 H t s N a O a - 2 H C I requires: 50.39/0 C, 4.259/0 H, 11.7~o N ; f o u n d : 48.79/0 C, 5.8~ H, 11.5% N. 2-[1-(2-Carboxymethoxyphenyl)azoJ-5-dimethylaminophenol (7). 2-Nitrophenoxyacetic acid (3 g) was dissolved in 25 ml of 0.5 M sbdium hydroxide solution, a nd the mixture was heated on a water bath. I r o n ( I I ) Sulfate (6 g) was a d d e d a nd t he mixture was heated for 2 h. Iron was precipitated by addition of ethanol a n d filtered, a n d the filtrate was then e v a p o r a t e d to remove the ethanol. Precipitated 2-aminophenoxyacetic acid was filtered off. The reagent was prepared by treating t h e 2-aminophenoxyacetic acid (1.6 g) with m-dimethylaminophenol (1.4 g) as described for (I). A dark b r o w n a m o r p h o u s p o w d e r .was formed. Analysis. C16HxTN304 requires: 60.99/o C, 5.49/0 N, 13.39/o N ; found: 57.8% C, 5.4% H, 12.49/o N. 2-[1-(2-Arsonophenyl)azoJ-5-dimethylaminophenol (8). T h i s w a s prepared by
4OO
S. S H I B A T A , M. F U R U K A W A , K. T O E I
t r e a t i n g the 0 - a m i n o b e n z e n e a r s o n i c acid (1.08 g) with m - d i m e t h y l a m i n o p h e n o l (1.37 g) as described for (1). B r o w n needles w e r e formed. Analysis. C~4H16NaO4As r e q u i r e s : 46.0~/o C, 4.4?/o H, 11.5~/o N ; f o u n d : 39.2~/o C, 4.3% H, 9.8~/o N. [2-[1-( 2-H ydroxy-4-sulfonaphthyl) azoJ-5-dimethylaminophenol (9,). Small a m o u n t s of w a t e r w e r e a d d e d to 1 - a m i n o - 2 - n a p h t h o l - 4 - s u l f o n i c a c i d (1.2 g) to f o r m a paste, a n d c o p p e r sulfate (0.12 g) in small a m o u n t s o f water w a s a d d e d t o this paste, w h i c h was then diazotized by s o d i u m nitrite (0.7 g) solution. The d i a z o t i z e d m i x t u r e was filtered, c o n c e n t r a t e d h y d r o c h l o r i c acid w a s a d d e d to the filtrate, a n d the precipitated d i a z o n i u m salt was filtered. T h e c o u p l i n g p r o c e d u r e was t h e s a m e as d e s c r i b e d for (1). D a r k b r o w n a m o r p h o u s crystals were formed. Analysis. C x s H x T N 3 O s S requires: 55.8~/o C, 4.4?/o H, 10.8~/o N ; f o u n d : 48.9% C, 4.7~/o H, 8.5% N. 2-[8-QuinolylazoJ-5-dimethflarninophenol (DMQAP; 10). This was p r e p a r e d by t r e a t i n g the 8 - a m i n o q u i n o l i n e (0.9 g) w i t h r n - d i m e t b y l p h e n o l (0.7 g) as d e s c r i b e d for (1). T h e crystals o b t a i n e d s u b l i m e d at 205 °. Analysis. C 1 7 H 1 6 N 4 0 r e q u i r e s : 69.8~/o C, 5.5% I-/, 19.2% N ; found: 70.0~/o C, 5.5% H, 19.4~,o N. 2-(2-Thiazolylazo,)-5-dimethylarninophenol (DMTAP; 11) l z. S o d i u m nitrite (0.7 g) was d i s s o l v e d in 10 ml of c o n c e n t r a t e d sulfuric acid, a n d the s o l u t i o n was c o o l e d to 0-5 °. Glacial acetic acid (8.5 ml) a n d p r o p i o n i c acid (1.5 ml) w e r e a d d e d to this solution followed b y 2 - a m i n o t h i a z o l e ( 1.0 g). m - D i m e t h y l a m i n o p h e n o l ( 1.4 g) was dissolved in 20 ml of ethanol, a n d c o u p l i n g was d o n e w i t h the a b o v e d i a z o n i u m m i x t u r e at 0-5 ° . T h e d a r k purple needles o b t a i n e d s u b l i m e d at 175 ° . Analysis. C l l H 1 2 N a O S requires: 53.2% C, 4.9~/o H, 22.6~/o N ; found: 53.4% C, 4.8~o H, 22.6~/o N . 2-E2-(5-Nitrothiazolyl)azoJ-5-dimethylaminophenol (12). T h i s was p r e p a r e d by t r e a t i n g the 2 - a m i n o - 5 - n i t r o t h i a z o l e (1.4 g) with r n - d i m e t h y l a m i n o p h e n o l ( 1.4 g) as d e s c r i b e d for ( 1 l ) ( m . p . 172% d a r k p u r p l e a m o r p h o u s crystals). Analysis. C l l H l x N sO.zS requires: 45.0~/o C, 3.8~/o H, 23.9~/o N ; f o u n d : 43.6~/o C, 4.2~/o H, 16.7~/o N. 2-(2-Pyridylazo)-5-dimethylaminophenol (DMPAP; 13). T o a s o l u t i o n o f 2.1 g of clean s o d i u m in 10 m l of absolute ethanol, 2 - a m i n o p y r i d i n e (5 g) in 30 ml of a b s o l u t e ether w a s added, and the mixture w a s refluxed for 1 h u n d e r an a t m o s p h e r e of n i t r o g e n . T h e n , 5 ml of isopentyl nitrite was a d d e d , a n d refluxing was c o n t i n u e d for an a d d i t i o n a l 2 h. O n cooling, the d i a z o n i u m salt p r e c i p i t a t e d a n d was filtered off a n d dried in a v a c u u m desiccator. T o a s o l u t i o n o f m - d i m e t h y l a m i n o p h e n o l (0.7 g) in 20 ml o f absolute ethanol, the d i a z o n i u m salt (2.2 g) in 10 ml of absolute e t h a n o l was a d d e d at 0 - 5 °, a n d c a r b o n d i o x i d e was passed t h r o u g h the solution. T h e c r u d e m a t e r i a l was recrystallized from e t h a n o l - w a t e r mixture. T h e d a r k red needles o b t a i n e d s u b l i m e d at 174 °. Analysis. C a 3 H x 4 N 4 0 requires: 6 4 . 5 ~ C, 5 . 8 ~ H, 23.1~/o N ; f o u n d : 6 4 . 5 ~ C, 5 . 8 ~ H, 2 1 . 1 ~ N . 2-[2-(5-CMoropyridyl) azoJ-5-dimethylaminophenol (5-CI-DMPAP ; 14). T o a s o l u t i o n o f 2.1 g of s o d i u m a m i d e in 30 ml of a b s o l u t e ethanol, 2 - a m i n o - 5 - c h l o r o p y r i d i n e (6.5 g) was a d d e d , a n d the m i x t u r e was refluxed for 1 h u n d e r an a t m o s p h e r e o f nitrogen. Then, 5 ml of" isopentyl nitrite was a d d e d to the .mixture a n d refluxing was c o n t i n u e d for a n a d d i t i o n a l 2 h. O n cooling, the d i a z o n i u m salt p r e c i p i t a t e d a n d was filtered off a n d d r i e d in a v a c u u m desiccator. T o a solution o f m - d i m e t h y l a m i n o p h e n o l (1.4 g) in 20 ml o f a b s o l u t e e t h a n o l , the d i a z o n i u m salt (1.7 g) in 10 ml of a b s o l u t e e t h a n o l was a d d e d at 0-5 ° in a s t r e a m
m-DIMETHYLAMINOPHENOL
DERIVATIVES
OF AZO
401
DYES
of c a r b o n dioxide. T h e c r u d e m a t e r i a l was recrystallized from e t h a n o l - w a t e r m i x t u r e ( 1 + 1). T h e d a r k red needles o b t a i n e d s u b l i m e d at 190 °. Analysis. C I a H x a N 4 O C 1 requires: 56.4~/~ C, 4.7~/o H, 20.2~o N ; f o u n d : 5 6 . 7 ~ C, 4.7~/o H, 20.1~/o N . 2-[2-(5-Bromopyridyl) azo]-5-dimethylaminophenol (5-Br-DMPAP; 15). This was p r e p a r e d by treating the 2 - a m ' i n o - 5 - b r o m o p y r i d i n e (10 g) with the m-dimethyla m i n o p h e n o l (0.7 g) as d e s c r i b e d for (14). T h e d a r k red needles o b t a i n e d s u b l i m e d at 190 °. Analysis. C x a H 1 3 N 4 O B r requires: 48.6~o C, 4.1~/o H, 17.4~o N ; f o u n d : 48.6~/o C, 3.9~o H, 17.2~ N . RESULTS
AND
DISCUSSION
Colour reactions with some metals T h e chelate c o m p o u n d s are easily p r e p a r e d by a d d i n g a few d r o p s of a s o l u t i o n of the reagent in a l c o h o l o r water, to a solution of a heavy metal. The c o l o u r r e a c t i o n s with s o m e m e t a l s at the o p t i m a l p H values are listed in T a b l e I. T h e chelating r e a c t i o n s of reagents 6, 7 a n d 8 c o u l d not be detected visually. TABLE
I
COLOUR
REACTIONS
WITH
SOME
METAL
IONS*
Reagent
Reagent
A I a÷
C d 2+
C o 2+
C u 2+
F e a+
L a a÷
M g 2÷
M n 2+
N i 2+
p b 2+
Z n 2+
y-O y-O y-O p-R R Y y-O Y r-P y-O O p-B Y Y Y
-R R r-P p-R . . . --------
O O y-R r-P p-R
r-P p-R R r-P p-R
r-P y-R ~-P r-P p-R
Br Y Br Br Br
O -r-P r-P -. . . b-P -P b-P r-O r-P r-P
O -y-R r-P -. . . ----r-O r-P r-P
r-P R P P p-R
r-P O p-R O p-R
r-P r-P r-P r-P p-R
r-P O R r-P p-R
---b-P r-P r-P r-P
P r-P r-P b-P r-P r-P r-P
1"i0.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
. . .
. . . -r-O r-P b-P r-P r-P r-P
. . . b-P r-P P b-P P P P
. . . P r-P P b-P r-P r-P r-P
. . . b-P Br P b-P r-P r-P r-P
. . .
. . . b-P r-P r-P b-P R r-P r-P
. . . P r-P r-P P r-P r-P r-P
O = O r a n g e , P = P u r p l e , R = R e d , Y = Y e l l o w , B = B l u e , B r ---- B r o w n , b = b l u i s h , p = p u r p l i s h , r - - r e d d i s h , y = yellowish, -- not detectable.
T h e d e t e c t i o n limits of s o m e r e a g e n t s w e r e then studied m o r e quantitatively. T h e c o l o u r s of a s e r i e s ' o f solutions c o n t a i n i n g k n o w n a m o u n t s of metals ( a d d e d by a E p p e n d o r f m i c r o p i p e t t e ) , a d r o p o f dye solution, 0.5 ml of p H 10 buffer s o l u t i o n a n d 0.5 ml of water, were o b s e r v e d visually against a reagent blank. T h e d e t e c t i o n limits o b t a i n e d are s h o w n in T a b l e II. F r o m these results, subsequent studies w e r e c a r r i e d o u t with reagents 10, 11, 13, 14 and 15.
Acid dissociation behaviour All the reagents w e r e sparingly soluble in Water, but soluble in various
402
S. S H I B A T A , M . F U R U K A W A ,
K. T O E I
T A B L E II THE DETECTION
LIMITS FOR SOME
METALS"
Reagents
Co(ll)
Cu(lI)
Ni(ll)
,Zn(II)
I 2 3 4 5 9 I0 11 12 13 14 15
0.3 0.6 0.3 1.2 0.3 0.3 0.3 0.3 0.3 0.03 0.09 0.09
0.3 0.6 0.3 0.6 0.3 0.3 0.9 0.3 0.6 0.03 0.06 0.06
0.3 0.6 0.6 0.6 0.3 0.3 0.3 0.3 0.3 0.03 0.03 0.03
0.6 (1.9 0.6 1.2 0.3 0.6 0.9 0.3 2.1 0.03 0.06 0.06
" C o n c e n t r a t i o n s are given in itg m l - t
organic solvents, including ethanol, methanol, MIBK, benzene and chloroform. These reagents showed acid-base indicator properties and were yellow in weak acidic and neutral solution but orange-red in strongly alkaline solution. Four species of these reagents, HaL 2+, H2 L+, HL and L - , are involved in its acid-base behaviour. For example, the four forms of D M P A P involved in its acid-base behaviour are related by the following equilibria."
N ( C H 3 ) 2'
N=N
N(CH3) ~
rq=N
HO
HO
DKa3 'N(CH3) 2
HO
-O
The acid-base equilibria of D M P A P may be formulated: Ka 1
• H2 L+ +H
HAL2+
+
(1)
Ka2
H2 L+ HL
~a3
" HL +H +
(2)
"L-
(3)
+H +
The three acidity constants for D M P A P are then defined by K,,t = [H2L+] [ H + ] [HaL 2+]
(4)
m-DIMETHYLAMINOPHENOL
403
DERIVATIVES OF AZO DYES
Ka 2 = [ H L ] [ H +] ... [H2L +] Kaa----
(5)
[L-][H +] [-HL1
(6)
T h e s e associated e q u i l i b r i a can be calculated i n d e p e n d e n t l y because the steps were sufficiently separated. T h e a c i d dissociation constants d e t e r m i n e d are r e p o r t e d in T a b l e III, w h e r e p K . 2 refers to the dissociation of the d i m e t h y l a m i n o group, a n d P K . a refers t o the d i s s o c i a t i o n o f the h y d r o x y group. T h e p K . 1 value is below p H 1. T h e p K . 2 values of the d i m e t h y l a m i n o g r o u p increase in the o r d e r D M T A P < DMQAP< 5-C1-DMPAP~S-Br-DMPAP< D M P A P , a n d the p K . 3 values of the h y d r o x y g r o u p i n c r e a s e in the o r d e r D M T A P < 5 - C I - D M P A P _ = 5 - B r - D M P A P < D M P A P < D M Q A P . T h e w a v e l e n g t h of m a x i m a l a b s o r b a n c e a n d the m o l a r absorptivity of e a c h species in a q u e o u s 409/0 (v/v) m e t h a n o l solution are s h o w n in T a b l e IV. T h e shift o f m a x i m u m Wavelength from neutral t o basic species increases in the o r d e r D M Q A P < D M T A P < D M P A P < 5 - C I - D M P A P < 5 - B r - D M P A P . Therefore, a m o n g these reagents 5 - B r - D M P A P w o u l d be expected to be the best c h r o m o g e n i c reagent for metals. T A B L E III ACID DISSOCIATION CONSTANTS SOLUTION
O F R E A G E N T S IN A Q U E O U S
40~% (v/v) M E T H A N O L
( g = 0 . 1 KCI, 25 ° ) Reagents
DMTAP DMQAP DMPAP 5-CI-DMPAP 5-Br-DMPAP
(11) (10) (13) (14) (15)
pKat
PKa2
PKa3
< < < < <
2.8 3.1 3.6 3.4 3.4
9.9 13.1 12.1 11.6 11.6
1 1 1 1 1
T A B L E IV ABSORPTION MAXIMA OF REAGENTS AND MOLAR ABSORPTIVITIES° ( A q u e o u s 40?/o ( v / v ) m e t h a n o l solutions) Reagents
DMQAP DMTAP DMPAP 5-CI-DMPAP 5-Br-DMPAP
p H ,,, 1
pH ~ 6
N a O H ~, O.I M
~max
~
~'~x
£
~max
8
504 540 524 465 466
4.6 6.1 2.2 4.7 4.7
478 502 435 440 AA.A
4.5 4.6 3.0 4.6 4.7
490 524 494 508 510
2.6 4.1 3.0 4.6 4.7
2 ~ z is given in nm. All m o l a r absorptivities are given as '. 10 4 1 m o l - t c m - l .
S. S H I B A T A , M. F U R U K A W A , K..T O E I
404
,4bsorptiotz spectra T h e c o m p l e x e s o f these r e a g e n t s w i t h metals are n o t soluble in water b u t soluble in a q u e o u s o r g a n i c solvents. In this paper, t h e a b s o r p t i o n spectra in a q u e o u s 50~/o (v/v) e t h a n o l s o l u t i o n w e r e studied. T h e a b s o r p t i o n spectra o f the copper, nickel, cobalt, a n d zinc chelates o f the five r e a g e n t s are s h o w n in Figs. 1-5. T h e a b s o r p t i o n m a x i m a o f each m e t a l chelate are also s h o w n in Table V:"
1.2
1.2 /
1.0
~
~
1.0
8 0.8
38 =~ 9.6
"...N i ".%.
o6
o
0.4
"%~
c
~ 0.4
'.. k % %%
J2
'..Ni ~
400
450 500 Wovel en gth, n rrl
/
0.2
550
600
400
/.:;;-'/"cu
\
450 500 550 Wuveleng th, n m
N'%.. ", 600
650
Fig. I. A b s o r p t i o n spectra of D M Q A P - m e t a i chelates in aqueous 50% (v/v) ethanol. Reagent 2.5. I 0 - 5 M. (Ni pH 8, Zn pH 10, Co pH 8.5) 1.75- 10 -5 M reagent plus 0.75.10 -5 M metal. (Cu p H 8) 1.5.10 -5 M reagent plus 1.0.10 -5 M copper v s . water blank. 1-cm cells. Fig. 2. A b s o r p t i o n spectra of D M T A P - m e t a l chelates in aqueous 5 0 ~ (v/v) ethanol. Reagent 2 . 5 . 1 0 - 5 M. (Ni, Zn, C o pH 8) 1.75.10 -5 M reagent plus 0.75" 10 -5 M metal. (Cu, pH 8) 1.25.10 - 5 M reagent plus 1.25- 10- 5 M copper v s . water blank, l-cm cells. 1.2 1.0
°t
R
8 o8 c~
N!..
~ 0.8
"\
o.6 o
~ 0.6
%"~ C O
'< 0.4
",
o,
\
0.2
• •
/ -_. ) , , . _ 400
450 500 550 Wcivelength0 n m
600
\
~.
\k
%%
,,
.
650
400
4,50 500 550 600 WcIvelength, nm Fig. 3. A b s o r p t i o n spectra of D M P A P - m e t a l chelates in aqueous 50% (v/v) ethanol. Reagent 2.5. I 0 - 5 M. (Zn pH 11, Ni pH 9) 1.75-10 -5 M reagent plus 0.75.10 - s M metal. ( C u pH 11, Co pH 9) 1.875.10 -5 M reagent plus 0.625.10 - 5 M metal. ( C u * pH 6) 1.25" 10 - s M reagent plus 1.25.10 -5 M copper cs. water blank. 1-cm cells. "Fig. 4. A b s o r p t i o n spectra of 5 - C I - D M P A P - m e t a l chelates in a q u e o u s 5 0 ~ (v/v) ethanol. Reagent 2.5.10 -5 M. ( Z n pH 11, Ni pH 10, C o pH 10, C u p H 11) 1.75-10 -5 M reagent plus 0.75.10 -5 M metal. (Cu* pH 4.5) 1.25.10 -5 M reagent a n d meta.l v s . water blank. 1-era cells.
650
m-DIMETHYLAMINOPHENOL
405
D E R I V A T I V E S O F A Z O DYES
1.2
O.8 o
0.6
/
400
450 500 550 600 650 Wovelength, nm Fig. 5. A b s o r p t i o n spectra o f 5 - B r - D M P A P - m e t a l chelates in aqueous 50~ (v/v) ethanol. Reagent 2.5.10 -5 M. (Zn, Ni, Co, pH 8, Cu pH 10) 1.75. I0 -5 M reagent plus 0.75"10 -5 M metal. (Cu* pH 4) 1.25.10- 5 M reagent and metal us. water blank, l-cm cells.
TABLE V A B S O R P T I O N M A X I M A O F C H E L A T E S (nm)" Reagents
Cu
Co
DMQAP DMTAP DMPAP 5-CI-DMPAP 5-Br-DMPAP
515 560 515, 540, (530) b 530, 550, (555) 530, 550, (555)
545, 570 546, 550, 555,
515 5;70 585 590
Ni
Zn
535, 505 535 520 520, 552 520, 552
528, 535 510, 518, 570,
505 534 550 552
" In a q u e o u s 50~,~ (v/v) ethanol solution measured against water, b Between brackets 1:1 chelate.
A l t h o u g h the wavelength shifts on chelation of the quinolylazo and thiazolylazo i'eagents are small (50-60 nm), those for the pyridylazo reagents are very large (110-120 nm). The absorption s p e c t r a of the halogen-substituted pyridylazo reagents show two absorption peaks clearly, except in the case of copper. The 1:1 copper chelate has only one absorption peak, although the 1:2 copper chelate has two peaks.
Effect of pH F o r evaluation of the optimal p H values for determinations of copper, nickel, cobalt a n d zinc, the effects of pH on the absorbance were studied with the results : s h o w n in Fig s. 6-10. In the cases of cobalt, zinc a n d nickel, the absorption spectra did no t change over the whole range, so that obviously only one type' of chelate is formed. C o p p e r chelates of D M P A P and its halogen-substituted reagents having 1 : 1 a n d 1:2 copper-ligand ratios were as s u med to be formed at low pH and at high pH, respectively. The optimal p H and wavelength with mo lar absorptivity a n d sensitivity for the determination of cobalt, nickel, zinc and copper are shown in Table VI.
Nature of complex T h e empirical formulae of the c o l o u r e d complexes were d e t e r m i n e d by the
406
S. SHIBATA, M. F U R U K A W A , K. T O E I
Q8
Q8 (30
0.6
Ni
-
Ni
•
•
z.
g
g ~ o4
o4 O2
0
2
4
6
8
10
.
12
2
2
4
pH
~
6 DH
8
10
Fig. 6. Effect of p H on a b s o r b a n c e of D M Q A P - m e t a i chelates. Reagent 4.4.10 -5 M. Co, Z n a n d Ni I. 10 - 5 M, C u 0.75.10 - 5 M vs. reagent blank. 1-crn cells. Fig. 7. Effect of p H o n a b s o r b a n c e of DMTA13-rnetal chelates. Reagent 1.10 - a M. Zn, N i a n d Cu 1 • 10 - 5 M, Co 0.8.10 - 5 M vs. reagent blank. 1-crn cells.
1.0
Zn
1.0 Zn
o8
N~
9~ ' - ° - - < ~
~ O8
0.6 ~
o
~ Q4
0.4 0.2
0.2 2
4
6
8
10
pH
2
4
6 • 8 pH
10
12
Fig. 8. Effect of p H on a b s o r b a n c e of D M P A P - m e t a l chelates. Reagent 5.1 • 10-5 M. Metals 7.5.10 - 6 M vs. reagent blank, l-cm cells. Fig. 9. Effect of pH o n a b s o r b a n c e of 5 - C I - D M P A P - r n e t a l chelates. Reagent 5.10 - 5 M. Metals 7.5.10 - 6 M us. reagent blank. 1-cm cells.
Zn
1.0
Ni
c= c~ r'~
,7
~- 0.6 o <
0.4 0.2 !
2
4
6
8
10
pH
Fig. I0. Effect of pH on a b s o r b a n c e of 5-Br-D" i P A P - m e t a l chelates. Reagent 4.0- 10-5 M. Metals 7.5" 10 - 4 M v s . reagent blank. 1-cm cells.
m-DIMETHYLAMINOPHENOL
DERIVATIVES OF AZO DYES
407
T A B L E VI THE OPTIMAL pH VALUES AND WAVELENGTHS S O M E M E T A L S I N A Q U E O U S 50~o (v/v) E T H A N O L
Reagent
Metal
Optimal p H
WITH MOLAR ABSORPTIVITIES OF
Molar absorpSensitivity tivity (lzg cm.-2) ( - 10 ~ l tool- j cm. i )
Optimal analyticai wavelengtl¢' ( n m )
DMQAP
Co Ni Cu Zn
5.0-11.0 6.0-I 1.0 4.0-9.0 9.5-11.0
7.2 5,6 3,4 5.6
0.00082 0.0011 0.0019 0.0012
547 535 520 528
DMTAP
Co Ni Cu Zn
5.5-8.5 5.5-8.5 4.0-8.0 7.5-9.5
7.4 6,9 4.1 6,7
0.00080 0.00084 0.0015 0.00097
575 558 564 '556
DMPAP
Co Ni Cu b Cu Zn
5.0-10.0 5.0-10.5 4.0-6.0 10.0-10.5 7.0-9.5
7.7 9,8 5.3 8.3
0.00077 0.00060 0.0012 0.00077
11.2
0.00058
574 545 555 545 538
Co Ni Cu b Cu Zn
3.0-10.5 4.5-10.0 2.0-6.0 9.5-10.5 8.5-10.5
Co Ni Cu b Cu Zn
3.0-10.0 4.5-10.0 2.0-6.0 9.0-10.0 7.5-10.0
5-CI-DMPAP
5-Br-DMPAP
8.5
0.00069
12.I
0.00049
6.1
0.0010
10.2 12.2
0.00062 0.00054
8.8
0.00067
12.8
0.00046
6.1
0.0010
10.0 13.3
0.00064 0.00049
586 556 556 554 550 588 558 558 555 552
a Against r eag en t blank, b 1 : 1 complex.
c o n t i n u o u s v a r i a t i o n s m e t h o d at the o p t i m a l p H a n d w a v e l e n g t h . I n the case of c o p p e r , t h e c u r v e s i n d i c a t e d the f o r m a t i o n o f a 1:1 c o m p l e x at p H 3 a n d a 1:2 c o m p l e x at p H 10 except w i t h D M Q A P , w h i c h f o r m e d o n l y a 1:2 c o m p l e x with c o p p e r . I n t h e cases o f nickel, c o b a l t a n d zinc, o n l y 1 : 2 c o m p l e x e s were f o r m e d w i t h all reagents. Solvent e x t r a c t i o n
T h e highly coloured complexes f o r m e d with metals u n d e r various conditions are useful for t h e d e t e r m i n a t i o n o f c e r t a i n metals. T h e s e c o l o u r e d c o m p l e x e s are s o l u b l e in v a r i o u s o r g a n i c solvents. S o m e results are s h o w n in T a b l e VII. Conclusions Although these reagents are rather unselective, analytical conditions can improved by a judicious choice of pH, solvent, or masking agents. Anyway, photometric reagents, these compounds seem to be promising because of the markably high molar absorptivity and large bathochromic shifts produced
be as reon
'408
S. SHIBATA, M. F U R U K A W A , K. TOEI
TABLE
VII
EXTRACTABILITY
OF
METAL
CHELATES
IN
VARIOUS
ORGANIC
Metals
Solvents
DMTAP
DMQAP
DMPAP
Co
MIBK 1,2-Dichioroethane Benzene MIBK 1,2-Dichloroethane Benzene MIBK 1,2-Dichioroethane Benzene MIBK 1,2-Dichloroelhane Benzen.e.
+ -+ + + -4+ + + + + +
:F -+ + + + + + + + + +
:F + =F --t-___ + + + + +
Cu
Ni
Zn
a +
very
w e l l , . _--4- w e l l , ~,: n o t
well,
SOLVENTS*
5-CiDMPAP + + :F --4-+ + + + + +
5-BrDMPAP + + _+ _+ _ -+ + + ::F :F
-- bad.
c h e l a t i o n . F u r t h e r w o r k o n the s o l v e n t e x t r a c t i o n a n d analytical a p p l i c a t i o n o f t h e s e r e a g e n t s for d e t e r m i n a t i o n o f m e t a l s is n o w in p r o g r e s s . SUMMARY
Fifteen azo d y e s c o n t a i n i n g the m - d i m e t h y l a m i n o p h e n o l g r o u p were synthesized, a n d their a n a l y t i c a l p o t e n t i a l for the d e t e r m i n a t i o n o f m e t a l s w a s s t u d i e d s p e c t r o p h o t o m e t r i c a l l y . A m o n g these reagents, the h e t e r o c y c l i c azo d e r i v a t i v e s are m o s t suitable as c h r o m o g e n i c reagents. T h e best r e a g e n t s are t h e 2 - p y r i d y l a z o c o m p o u n d s . T h e s e c o m p l e x e s with c o p p e r , zinc a n d n i c k e l s h o w m o l a r a b s o r p t i v i t i e s o f t h e o r d e r o f 100,000. F o r e x a m p l e , t h e 2 - [ 2 - ( 5 - b r o m o p y r i d y l ) - a z o ] - 5 - d i m e t h y l a m i n o p h e n o l c o m p l e x e s w i t h c o p p e r , zinc a n d nickel s h o w m o l a r a b s o r p t i v i t i e s o f 1.0, 1.33 a n d 1 . 2 8 - l 0 s 1 m o l -x e r a - 1 , respectively. I n these reagents, the p a r a s u b s t i t u t e d d i m e t h y l a m i n o g r o u p n e x t to t h e a z o g r o u p s e e m s to p l a y a n i m p o r t a n t role in a c h i e v i n g h i g h m o l a r a b s o r p t i v i t y a n d stability o f t h e metal "complexes. RI~SUMI~
Q u i n z e c o l o r a n t s a z o i q u e s r e n f e r m a n t le g r o u p e m e n t m - d i m 6 t h y l a m i n o p h 6 n o l o n t 6t6 synth6tis6s; o n e x a m i n e a u s p e c t r o p h o t o m 6 t r e l e u r possibilit6 d ' u t i l i s a t i o n p o u r le d o s a g e des m 6 t a u x . Les c o m p o s 6 s 2 - p y r i d y l a z o c o n s t i t u e n t les m e i l l e u r s r6actifs; les c o m p l e x e s o b t e n u s avec cuivre, z i n c et nickel p r 6 s e n t e n t des coefficients d ' e x t i n c t i o n m o l a i r e de l'ordre de 100,000; o n a p a r e x e m p l e des valeurs de 1.0, 1.33 et 1.28- 105 1 m o l - 1 e r a - 1 r e s p e c t i v e m e n t p o u r les c o m p l e x e s d u cuivre, d u zinc et d u nickel avec le 2 - [ 2 - ( b r o m o - 5 - p y r i d i l ) a z o ] - 5 - d i m 6 t h y l a r n i n o p h 6 n o l . Le g r o u p e d i m 6 t h y l a m i n o en par a p a r r a p p o r t au g r o u p e azo semb!e j o u e r u n r61e i m p o r t a n t s u r l ' e x t i n c t i o n m o l a i r e 61ev6e et la stabilit6 d e s c o m p l e x e s m6talliques.
m - D I M E T H Y L A M I N O P H E N O L D E R I V A T I V E S O F AZO DYES
409
ZUSAMMENFASSUNG
Es wurden f'tinfzehn Azofarbstoffe dargestellt, die die m-Dimethylaminophenol-Gruppe ¢nthielten; ihre analytische Anwendbarkeit f'tir die Bestimmung von Metallen wurde spektrophotometrisch untersucht. Von diesen Reagenzien eignen sich die heterocyclischen Azoderivate besonders als chromogene Reagenzien. Die besten sind die 2-Pyridylazo-Verbindungen. Deren Kornplexe mit Kupfer, Zink und Nickel haben molare Extinktionskoeffizienten in der Gr/Sssenordnung yon 100,000. D i e molaren Extinktionskoeffizienten der Komplexe yon z.B. 2-[2-(5-Brompyridyl)azo]-5-dimethylaminophenol rnit Kupfer, Zink und Nickel sind resp. 1.0, 1.33 und 1.28. l0 s 1 m o l - 1 c m - 1. Bei diesen Reagenzien scheint die p-substituierte Dimethylamino-Gruppe gegeniJber der Azo-Gruppe eine wichtige Rolle hinsichtlich eines hohen molaren ExtinktionskoelTlzienten und der Stabilit~it der Metallkomplexe zu spielen. REFERENCES I S. Shibata, in H. Flaschka and A. J. Barnard, Jr., Chelates in Analytical Chemistry, Voi. IV, M. Dekker. New York, 1972, p. 1-232. 2 Sh. T. Tali ~ov, V. S. Podgornova and S. N. Kosolapova, Zh. Anal. Khim., 24 (1969) 409. 3 S. I. G u s e v I. N. G l u s h k o v a and L. A. Ketova, Zh. Anal. Khim., 24 (1969) 993. 4 S. Shibata K. Goto and E. K a m a t a , Anal. Chim. Acta, 45 (1969) 279. 5 S. Shibata M. Furukawa, E. K a m a t a and K. G o t o , Anal. Chim. Acta, 50 (1970) 439. 6 S. Shibata M. F u r u k a w a a n d S. Sasaki, Anal. Chim. Acta, 51 (1970) 271. 7 S. Shibata M. F u r u k a w a a n d Y. Ishiguro, Mikrochim. Acta, (1972) 721. 8 S. Shibata M. Furukawa, Y. Ishiguro and S. Sasaki, Anal. Chim. Acta, 55 (1971) 231. 9 S. Shibata. M. F u r u k a w a a n d K. Goto, Colloq. Spectrosc. Int. X V I , Heidelberg, 1971, Preprints, Vol. 1, p. 114. 10 S. Shibata, Bunseki Kagaku, 21 (1972) 551. 11 S. Shibata, E. K a m a t a a n d M. Furukawa, Int. Congress on Analyt. Chem., LU.P.A.C., Kyoto, April, 1972, Abstracts p. 393. 12 J. Minczewski and K. Kasiura, Chem. Anal. (Warsaw), I0 (1965) 21.