The Heller’s color test for indican in urine is interesting because besides detecting this important biomarker it reveals the dual function of nitric acid since it can accomplish the synthesis of indigo blue and indigo red, as well as it can degrade them to isatin, depending upon the reaction conditions. Moreover, the Heller’s test inspired other tests for indican detection, using other oxidizing reagents. Actually, indican in urine is detected by a colour chart with different tones of blue indicating the concentration of indican via indigo blue formation. In this paper we provide the series of reactions that occur during the test, there are nitrations followed by redox reactions. The organic intermediates are oxidized and the inorganic reagent is reduced to nitrous acid. However, indigo blue and indigo red can be degraded by nitric acid on .heating. The electron flow is given in each step.
The study of what is going on in a chemical test is important, the more if the involved substance is glucose in urine. In the Crismer’s test the blood-red colour of safranin solution in alkaline medium is discharged if the glucose concentration is higher than 100 mg/dl. The reagent is not affected by uric acid or creatinine as is the case with the Fehling solution. The safranin test detects sugar in saliva when other reagents failed. Since the reaction mechanism of this test has not been advanced, we provide the electron flow, step by step.
The Froehde reaction for morphine employs a solution of sodium molybdate in concentrated sulphuric acid. This test has been extended to other alkaloids giving different colours. In this communication we present an insight into the reaction with morphine. It has the particularity that it does not invoke the concept of electron back donation since this known point of view reverses the normal polarization of a functional group. This route is based on a novel theoretical finding: the activation of a mixed ester (organic-inorganic) by means of protonation and water loosening. This causes Umpolung (polarity inversion) at ortho position, favouring a nucleophilic attack instead of the electrophilic one due to the original phenol group in morphine. The final part of the route to morphine ortho-quinone goes smooth via a six member concerted mechanism.
Being morphine a restricted drug, a rapid colour test for its detection is very useful. Tattersall employed as reagent trisodium ortho-arsenate in sulphuric acid. However, the more common disodiumhydrogen ortho-arsenate heptahydrate can be used also because both salts yield the same reactive species, that is, protonated arsenic acid and a cation with arsenic(IV). An arsenate is formed with the phenolic group in morphine. Dehydration of this organometallic ester yields a cationic intermediate that induces reaction with arsenic acid at ortho-position (electromeric effect), and a concerted mechanism takes place. A dienone is formed and there is elimination of meta-arsenous acid. Aromatization followed by acidolysis of the new arsenate gives water, meta-arsenous acid, and morphine ortho-quinone, via a six-member concerted mechanism. The colours observed in the test are due to halochromism.
Glucose is an analyte and has drawn the attention of researchers for a long time. Baeyer accomplished several synthesis for indigo. The one under study was adapted by Hoppe-Seyler for detection of glucose in urine. The blue colour observed in the test is due to the formation of indigo. The reagent used in the test is o-nitrophenylpropiolic acid. However the route from the starting compound to indoxyl has not been cleared out. There are missing intermediates or inadequate ones have been proposed. In this communication we provide the route and the reaction mechanism involved in each step. This is in accordance with experimental data and the chemical deportment of the involved compounds.
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