Organic compounds -- part of the class 532-570 series – Organic compounds – Azo
Patent
1995-06-01
1998-05-05
Higel, Floyd D.
Organic compounds -- part of the class 532-570 series
Organic compounds
Azo
2524081, 436163, 534800, C09B 2912, C09B 2936, C09B 6742, C09B10900
Patent
active
057476560
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/EP94/03156 filed Sep. 21, 1994.
The invention relates to indicators for determining the proton concentration of strongly alkaline aqueous solutions.
The usual pH range used daily in the laboratory or even in the world around us is from pH 0 to pH 14. The usual pH papers, pH indicator sticks and pH meters are also tailored to this; they only measure in this range. In many cases, however, it is of interest to be able to determine by means of a simple indicator whether a solution present is a 1-, 3-, 5-, 7-, 9- or 11-normal alkali solution. To date, this cannot even be accomplished by a pH meter. On the contrary, a comparatively difficult titration with an acid solution must be carried out in order to determine the content.
The invention is based on the object of making available indicators with which the determination of proton concentrations in the strongly alkaline range is possible in a simple manner.
Surprisingly, it has been found that certain substantive azo dyestuffs can be employed for the purpose according to the invention.
The invention relates to indicators for determining the proton concentration of strongly alkaline aqueous solutions, which are characterized in that they contain at least one compound of the general formula (I) ##STR3## in which ##STR4## and R.sup.1 =H, OH, alkyl having 1-6 C atoms, alkanoyl having 2-7 C atoms,
These compounds are prepared from parent substances known in dyestuff chemistry which, from experience, impart substantive character to the dyestuffs. The parent substances carry at least one amino group, which are (sic) diazotized and coupled with phenols to give the indicators according to the invention (Ullmann, Volume A 3, 5th edition, 1985, pages 279-280). The binding position between the diazotized parent substances and the phenols can be located in all positions of the phenols not occupied by substituents.
2-(4-Aminophenyl)-6-methylbenzothiazole-7-sulfonic acid has proven particularly advantageous as a parent substance. The diazotization and subsequent coupling of the parent substance is carried out with phenol derivatives, preferably with pyrogallol, 3,5-dihydroxytoluene and 2,6-dihydroxyacetophenone.
The substances can be employed in solution like other pH indicators. More advantageously, however, materials made from cellulose, e.g. paper, films or fabric, are dyed with these substances. Because of their substantivity, the substances remain comparatively firmly stuck to these materials and are thus suitable, e.g. in strip form, directly for indicating the alkali concentration. In other embodiments, the dyed material is fixed to a colorless or white plastic film as support and can thus be assessed not only visually, but also photometrically in transmitted light or reflected light.
In order to be able to measure the alkali concentrations, a color comparison scale must be prepared beforehand. For potassium hydroxide solution and in the case of direct use of the indicator the following procedure is used: e.g. 1N, 2N, 4N, . . . 18N or 10%, 20%, 30% . . . 100%. each case. each other. This series is used as a color comparison scale.
1.0 mg of the indicator is dissolved in a 100 ml sample whose potassium hydroxide concentration is to be determined and the solution is filled into a 10 mm cuvette. The alkali concentration is determined by comparing the color of the cuvette containing the unknown sample with the color comparison scale. Since the concentrations of the solutions of the color comparison scale are known, the alkali concentration of the unknown sample is thus also known.
EXAMPLE 1
Preparation of an Indicator
38.4 g (120 mmol) of 2-(4-aminophenyl)-6-methyl-benzothiazole-7-sulfonic acid were dissolved in 75 ml of 2N sodium hydroxide solution and 300 ml of water. A solution of 9.1 g of sodium nitrite in 75 ml of water was added dropwise to this solution at room temperature in the course of 10 minutes and the mixture was stirred for a further 30 minutes. 300 ml of 1N hydrochloric acid were then added dropwise at 0.degree.-5.degr
REFERENCES:
patent: 2795575 (1957-06-01), Sureau et al.
patent: 2843581 (1958-07-01), Riat
patent: 3072585 (1963-01-01), Milionis et al.
patent: 3179650 (1965-04-01), Wehrli et al.
Baum Sylvia
Fischer Wolfgang
Hartig Thorsten
Schleehahn Michael
Higel Floyd D.
Merck Patent Gesellschaft mit beshrankter Haftung
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