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Synthetic and analytical studies on colour reagents—IX
Short communications Talanta. 1967, Vol
14. pp 607 to 610
Pergamon Press Ltd
Synthetic and analytical
607
Printed m Northern Ireland
studies on colour reagents--IX
The reactions of phthaleinazo compounds with the alkaline earths (Received 21 October 1966. Accepted 10 January 1967) IT 1swell known that o,o’-dmydroxyazo compounds react with the alkalme earths to form stable coloured chelates m alkaline media. To find more sensitive reagents for these elements, a series of phthaleinazo compounds was synthesmed, and the linntmg concentrations for the detection of magnesium, calcium, strontium and barium were determmed. EXPERIMENTAL Synthesis of reagents Phenolphthalein, Cresolphthalem, Thymolphthalem, Phenol Red, Cresol Red and Thymol Blue were used as starting materials and the syntheses were carried out as follows:
R’
\R
Sulphonphthalein derivatives were also synthesized in the same manner, except for nitration. Nztrutzon. Phthalems were nitrated by Gatterman’s method’ (Cresolphthalem can also be nitrated by Bayer’s method*). As sulphonphthaleins cannot be nitrated by Demont’s methods the following procedure was used. The sulphonphthalem was dissolved in concentrated sulphunc acid, cooled to O”, and the calculated amount of potassmm nitrate, dissolved 111concentrated sulphurrc acid, was added dropwtse Reductzon. The theoretical amount of sodmm hydrosulphite was added httle by little to the dmttro compound m alkaline solution. The colour of the solution turned from orange through green to blue. 6
Short commumcattons
608
The blue colour mdlcated the completion of the reaction. The blue solutton was acidified wtth hydrochloric actd and filtered to remove unreacted dmttro compound. The filtrate was neutrahzed with ammonia solution to precipitate the dtammo compound. Dlazotzzation and couplmg. The dtammo compound was dtssolved in concentrated hydrochloric acid below 0”, and concentrated sodium nitrite solution was added dropwtse. Diazotmation of the two ammo groups was Judged to be complete from the amount of mtrtte consumed. As the dtammo derrvattves of sulphonphthalems are unstable, the compounds could not be prepared m the pure solid state, and the solutton obtained by the reduction was dtrectly diazottzed without any puriticatton The dtazotmed solutton was added dropwtse mto a strongly alkaline solutton contammg chromotropic acid, R-acid, or 2-hydroxy-3-naphthotc acid, below 0”. After standmg overnight at room temperature, the solution was acidtiied wtth concentrated hydrochloric acid to precipitate the phthaleinazo compound. (If the product IS not precipitated, it may be salted out, or used directly in the solution as it is ) Determrnatzon of lrmrtrng concentrations Magnesium, calcium, strontmm and barmm soluttons were prepared from magnesium nitrate, calcium chloride, strontium nitrate and barium chloride, respecttvely. The concentrations were 0 1 pg/ml for magnesmm and calcmm and 1.0 ,ng/ml for strontmm and barmm. Various pH buffer solutions were prepared from ammonia solutton, ammonium chloride and sodmm hydroxtde, m the range pH 8 5-13 5. TABLEI.-DETECTION LIMITSFOR ALKALINEEARTHS@g/ml) AT pH 11 3 Bis-dtazo component
Coupling component
-
Phenolphthalem
Phenol Red
Cresol Red
Thymol Blue
Ertochrome Black T
Cal+
Srs+
Ba”+
0*0003
0001
0.05
0 05
0001 0001
0 005 0 05
0 05 0 05
0 05 0 08
Chromotropic acid R-acid 2-Hydroxy-Jnaphthotc acid
0002
0002
03
01
0001 0001
04IO5 0 01
o-3 03
01 0 06
Chromotropic actd R-acid 2-Hydroxy-3naphthotc acid
0001
0 03
0 05
01
0002 0001
0 05 0 03
05 01
03 01
Chromotropic acid R-acid 2-Hydroxy-3naphthoic acid
0.001
0 05
1
08
0002 0401
0 08 0.05
1 02
1 01
Chromotropic acid R-actd 2-Hydroxy-3naphthotc acid
0001
01
2
0.5
0001 00003
01 0 05
05 1
05 03
0 001
0 03
01
01
0001
0 05
1
05
Chromotroptc actd R-acid 2-Hydroxy-3naphthoic acid
Cresolphthalem
Plasmocorinth
Mg’+
B
Note
pH = 13 5, acetone
pH = 12.5, acetone
pH = 12.5, acetone
pH=125
pH=125
Short commumcatrons
609
Four ml of a solutton of surtable pH were taken m a test-tube, and a small amount of the reagent solution was added to develop the colour. If the colour was already red, due to the presence of alkahne earths as impurities m the buffer solution, the colour change was reversed by the addition of just sufficient 2 x 10-4MEDTA solutron to mask the Impurttres, The solution was divided between two test-tubes, and a few drops of the alkalme earth solution were added to one, and the colour was compared with the origmal. At the most favourable pH (at which the colour-change from blue to red 1smost dtstmct) a suitably diluted solutton of the metal ion was added drop by drop and the mmmum number of drops (at least onedrop) after wluch the colourchange waslust nottceable, was determmed. From the number of drops the hmitmg concentration was calculated. The results are summarized in Table I, along with those for Enochrome Black T and Plasmocorinth B, because they are sard to be very sensitive reagents for magnesium and calcmm. DISCUSSION From Table I, the order of decreasmg sensmvrty of the cations 1s seen to be magnesium, calcmm, strontmm, barmm, and the sensmvtty is about the same as or better than that with Plasmocorinth B and Eriochrome Black T. The substrtuents of the phthalein or sulphonphthalem have little effect on the hmiting concentration for the detection of the metals, but the nature of the couplmg component is much more Important. As a coupling component, m o-hydroxyazo compounds, chromotroptc acid, R-acid and 2-hydroxy-3naphthoic acid are superior to the other components used.4-8 The hmttmg concentrations for these reagents are not very different from each other. Sulphonphthalem derivatives are very soluble m water, but the syntheses are dtfficult, and the pure compounds are not obtainable. From a consideration of the sharp-colour change and ease of synthesis, bn (chromotropeazo)phenolphthalein 1s the best one. 2-Hydroxy-3-naphthotc acid derivatives differ from chromotroptc acid and R-acid derivatives. The latter are blue at pH 10-13, but the former are red at pH 95-10 4 and blue at pH 11.3-13 5, but the chelates are blue at pH 9 5-10 4 and red at pH 11.3-13 5. At pH 10 4, the hmmng concentration IS 0 002 ,ug/ml for magnesmm, 0 1 rg/ml for calcmm, and 0 5 ,ug/ml for strontium and for barmm, and these values are somewhat higher than those m Table I The addttton of acetone improves the senstttvtty of these reagents Bis(chromotropeazo)phenolphthalem was found to react with thonum at pH 2, and the hmmng concentratton was 10 ,ug/ml. This compound 1s the most sensitive reagent for alkaline earths yet found, Its htghersensmvrty probably being due to rtsbemgano,o’-dthydroxyazo compound, and having a larger conlugated system than a monoazo compound, and also due to the ease with which the human eye differentiates red from blue. Department of Chemrstry Faculty of Science, Okayama Unrversity Tsushzma, Okayama-shl Japan
TOSHIKOKOBATAKE TADASHIIWACHIDO KYOJI T~EI
Summary-Some new phthaleinazo compounds+,o’-drhydroxyazo compounds-have been prepared by couplmg chromotroprc acid, R-acid, and 2-hydroxy-3-naphthorc acid with bis-dtazotized dmminophthalems. These compounds have been found to be very sensmve colour reagents for alkaline earths m alkaline media, and m particular, bts(chromotropeazo)phenolphthalem is the most sensrttve yet found. Zusammenfassung-Eimge neue Phthalemazoverbmdungen-o,o’-Dthydroxyazoverbmdtmgen-wurden durch Kupplung von Chromotrop saure, R-Saure und 2-Hydroxy-3-naphthoesaure mit tetrazotierten Diese Verbmdungen stellen sehr Drammophthalemen dargestellt. empfindhche Farbreagentten auf Erdalkahen m alkahschen Medten dar; msbesondere 1st Bis(chromotropazo)phenolphthalem das empfindlichste unter den blsher bekannten Reagentten. R&nG--On a prepare quelques nouveaux composes phtalemazo-o,o’dthydroxyazo composes-par copulatron de l’acrde chromotroptque, de l’actde R et de l’acrde 2-hydroxy 3-naphtotque avec des dtammophtalemes bls-drazot&es. On a trouve que ces composes sont des reactifs color& tres senstbles des alcahno-terreux en mtheu alcalm et, en partsuher, la bts (chromotropeazo) phenolphtaleme est le plus sensible trouve JUSqU’~ present.
610
Short commumcatlons REFERENCES
1. 2. 3. 4. 5. 6.
L. Gattermann, Ber., 1899,32, 1131. A. Bayer and G. Fraude, Ann., 1880,202,163. Beilsteins Handbuch der Orgumschen Chemie, Vol. XIX, p. 111. Sprmger, Berlm, 1934. K. Em], K. T&i and H. Mlyata, Nippon Kagaku Zasshz, 1957,78,736. K. Eml, K. T8el and T. Wada, ibid., 1957, 78,974. K. Emi, K. T8ei and K. Harada, fbzd, 1957,78,1299.
14. pp 607 to 610
Pergamon Press Ltd
Synthetic and analytical
607
Printed m Northern Ireland
studies on colour reagents--IX
The reactions of phthaleinazo compounds with the alkaline earths (Received 21 October 1966. Accepted 10 January 1967) IT 1swell known that o,o’-dmydroxyazo compounds react with the alkalme earths to form stable coloured chelates m alkaline media. To find more sensitive reagents for these elements, a series of phthaleinazo compounds was synthesmed, and the linntmg concentrations for the detection of magnesium, calcium, strontium and barium were determmed. EXPERIMENTAL Synthesis of reagents Phenolphthalein, Cresolphthalem, Thymolphthalem, Phenol Red, Cresol Red and Thymol Blue were used as starting materials and the syntheses were carried out as follows:
R’
\R
Sulphonphthalein derivatives were also synthesized in the same manner, except for nitration. Nztrutzon. Phthalems were nitrated by Gatterman’s method’ (Cresolphthalem can also be nitrated by Bayer’s method*). As sulphonphthaleins cannot be nitrated by Demont’s methods the following procedure was used. The sulphonphthalem was dissolved in concentrated sulphunc acid, cooled to O”, and the calculated amount of potassmm nitrate, dissolved 111concentrated sulphurrc acid, was added dropwtse Reductzon. The theoretical amount of sodmm hydrosulphite was added httle by little to the dmttro compound m alkaline solution. The colour of the solution turned from orange through green to blue. 6
Short commumcattons
608
The blue colour mdlcated the completion of the reaction. The blue solutton was acidified wtth hydrochloric actd and filtered to remove unreacted dmttro compound. The filtrate was neutrahzed with ammonia solution to precipitate the dtammo compound. Dlazotzzation and couplmg. The dtammo compound was dtssolved in concentrated hydrochloric acid below 0”, and concentrated sodium nitrite solution was added dropwtse. Diazotmation of the two ammo groups was Judged to be complete from the amount of mtrtte consumed. As the dtammo derrvattves of sulphonphthalems are unstable, the compounds could not be prepared m the pure solid state, and the solutton obtained by the reduction was dtrectly diazottzed without any puriticatton The dtazotmed solutton was added dropwtse mto a strongly alkaline solutton contammg chromotropic acid, R-acid, or 2-hydroxy-3-naphthotc acid, below 0”. After standmg overnight at room temperature, the solution was acidtiied wtth concentrated hydrochloric acid to precipitate the phthaleinazo compound. (If the product IS not precipitated, it may be salted out, or used directly in the solution as it is ) Determrnatzon of lrmrtrng concentrations Magnesium, calcium, strontmm and barmm soluttons were prepared from magnesium nitrate, calcium chloride, strontium nitrate and barium chloride, respecttvely. The concentrations were 0 1 pg/ml for magnesmm and calcmm and 1.0 ,ng/ml for strontmm and barmm. Various pH buffer solutions were prepared from ammonia solutton, ammonium chloride and sodmm hydroxtde, m the range pH 8 5-13 5. TABLEI.-DETECTION LIMITSFOR ALKALINEEARTHS@g/ml) AT pH 11 3 Bis-dtazo component
Coupling component
-
Phenolphthalem
Phenol Red
Cresol Red
Thymol Blue
Ertochrome Black T
Cal+
Srs+
Ba”+
0*0003
0001
0.05
0 05
0001 0001
0 005 0 05
0 05 0 05
0 05 0 08
Chromotropic acid R-acid 2-Hydroxy-Jnaphthotc acid
0002
0002
03
01
0001 0001
04IO5 0 01
o-3 03
01 0 06
Chromotropic actd R-acid 2-Hydroxy-3naphthotc acid
0001
0 03
0 05
01
0002 0001
0 05 0 03
05 01
03 01
Chromotropic acid R-acid 2-Hydroxy-3naphthoic acid
0.001
0 05
1
08
0002 0401
0 08 0.05
1 02
1 01
Chromotropic acid R-actd 2-Hydroxy-3naphthotc acid
0001
01
2
0.5
0001 00003
01 0 05
05 1
05 03
0 001
0 03
01
01
0001
0 05
1
05
Chromotroptc actd R-acid 2-Hydroxy-3naphthoic acid
Cresolphthalem
Plasmocorinth
Mg’+
B
Note
pH = 13 5, acetone
pH = 12.5, acetone
pH = 12.5, acetone
pH=125
pH=125
Short commumcatrons
609
Four ml of a solutton of surtable pH were taken m a test-tube, and a small amount of the reagent solution was added to develop the colour. If the colour was already red, due to the presence of alkahne earths as impurities m the buffer solution, the colour change was reversed by the addition of just sufficient 2 x 10-4MEDTA solutron to mask the Impurttres, The solution was divided between two test-tubes, and a few drops of the alkalme earth solution were added to one, and the colour was compared with the origmal. At the most favourable pH (at which the colour-change from blue to red 1smost dtstmct) a suitably diluted solutton of the metal ion was added drop by drop and the mmmum number of drops (at least onedrop) after wluch the colourchange waslust nottceable, was determmed. From the number of drops the hmitmg concentration was calculated. The results are summarized in Table I, along with those for Enochrome Black T and Plasmocorinth B, because they are sard to be very sensitive reagents for magnesium and calcmm. DISCUSSION From Table I, the order of decreasmg sensmvrty of the cations 1s seen to be magnesium, calcmm, strontmm, barmm, and the sensmvtty is about the same as or better than that with Plasmocorinth B and Eriochrome Black T. The substrtuents of the phthalein or sulphonphthalem have little effect on the hmiting concentration for the detection of the metals, but the nature of the couplmg component is much more Important. As a coupling component, m o-hydroxyazo compounds, chromotroptc acid, R-acid and 2-hydroxy-3naphthoic acid are superior to the other components used.4-8 The hmttmg concentrations for these reagents are not very different from each other. Sulphonphthalem derivatives are very soluble m water, but the syntheses are dtfficult, and the pure compounds are not obtainable. From a consideration of the sharp-colour change and ease of synthesis, bn (chromotropeazo)phenolphthalein 1s the best one. 2-Hydroxy-3-naphthotc acid derivatives differ from chromotroptc acid and R-acid derivatives. The latter are blue at pH 10-13, but the former are red at pH 95-10 4 and blue at pH 11.3-13 5, but the chelates are blue at pH 9 5-10 4 and red at pH 11.3-13 5. At pH 10 4, the hmmng concentration IS 0 002 ,ug/ml for magnesmm, 0 1 rg/ml for calcmm, and 0 5 ,ug/ml for strontium and for barmm, and these values are somewhat higher than those m Table I The addttton of acetone improves the senstttvtty of these reagents Bis(chromotropeazo)phenolphthalem was found to react with thonum at pH 2, and the hmmng concentratton was 10 ,ug/ml. This compound 1s the most sensitive reagent for alkaline earths yet found, Its htghersensmvrty probably being due to rtsbemgano,o’-dthydroxyazo compound, and having a larger conlugated system than a monoazo compound, and also due to the ease with which the human eye differentiates red from blue. Department of Chemrstry Faculty of Science, Okayama Unrversity Tsushzma, Okayama-shl Japan
TOSHIKOKOBATAKE TADASHIIWACHIDO KYOJI T~EI
Summary-Some new phthaleinazo compounds+,o’-drhydroxyazo compounds-have been prepared by couplmg chromotroprc acid, R-acid, and 2-hydroxy-3-naphthorc acid with bis-dtazotized dmminophthalems. These compounds have been found to be very sensmve colour reagents for alkaline earths m alkaline media, and m particular, bts(chromotropeazo)phenolphthalem is the most sensrttve yet found. Zusammenfassung-Eimge neue Phthalemazoverbmdungen-o,o’-Dthydroxyazoverbmdtmgen-wurden durch Kupplung von Chromotrop saure, R-Saure und 2-Hydroxy-3-naphthoesaure mit tetrazotierten Diese Verbmdungen stellen sehr Drammophthalemen dargestellt. empfindhche Farbreagentten auf Erdalkahen m alkahschen Medten dar; msbesondere 1st Bis(chromotropazo)phenolphthalem das empfindlichste unter den blsher bekannten Reagentten. R&nG--On a prepare quelques nouveaux composes phtalemazo-o,o’dthydroxyazo composes-par copulatron de l’acrde chromotroptque, de l’actde R et de l’acrde 2-hydroxy 3-naphtotque avec des dtammophtalemes bls-drazot&es. On a trouve que ces composes sont des reactifs color& tres senstbles des alcahno-terreux en mtheu alcalm et, en partsuher, la bts (chromotropeazo) phenolphtaleme est le plus sensible trouve JUSqU’~ present.
610
Short commumcatlons REFERENCES
1. 2. 3. 4. 5. 6.
L. Gattermann, Ber., 1899,32, 1131. A. Bayer and G. Fraude, Ann., 1880,202,163. Beilsteins Handbuch der Orgumschen Chemie, Vol. XIX, p. 111. Sprmger, Berlm, 1934. K. Em], K. T&i and H. Mlyata, Nippon Kagaku Zasshz, 1957,78,736. K. Eml, K. T8el and T. Wada, ibid., 1957, 78,974. K. Emi, K. T8ei and K. Harada, fbzd, 1957,78,1299.