The mechanism of Mecke’s test for opioids

The mechanism of the interaction of uric acid with sodium tungstate in phosphoric acid (Folin test) is described. This insight involves the following steps: addition of tungstic acid to the carbon-carbon double bond in uric acid. Protolysis of the organometallic ester gives rise to dihydroxyoxotungsten and an epoxide, via a concerted mechanism. Acid catalyzed ring opening of the oxirane produces a vicinal diol via reaction of the intermediate carbocation with water. Isomerization of the resulting carbinolamide groups is enhanced by the resonance of the ureido group. Breaking of the second carbinolamide gives urea and alloxan, 5-ketobarbituric acid hydrate. Uric acid oxidation in strong acidic medium like phosphoric acid produces alloxan, whereas oxidation in alkaline, neutral, or slightly acidic medium, gives allantoin.

Section: Introductionmentioning

confidence: 91%

On the mechanism of the Folin test for uric aci

Sánchez-Viesca¹,

Gómez²

2023

“…In this communication the electron flow is given in each step of the series of reactions that take place during this colour test. This paper is a follow up of our studies on reaction mechanism, [3][4][5][6][7].…”

Section: Introductionmentioning

confidence: 91%

On the chemistry of the Archetti test for caffeine and uric acid

Sánchez-Viesca¹,

Gómez²

2023

The Archetti colour test is based on the reduction of ferricyanide ions to ferrocyanide, giving Prussian blue. However, the oxidation sequence of reactions that take in the organic molecule has not been described. Some electroanalytical experiments on the oxidation of caffeine have been done but the results have not been adequately interpreted. Besides, they are incomplete since only the redox reactions can be detected, but not the isomerization and degradation path. In the present communication the complete oxidation route of caffeine is given, as well as the electron flow in each step. It involves hydration of the imino group and oxidation to 1,3,7-trimethyl-uric acid, formation of radical ion at C-9, interaction with the C─C double bond, aziridinone formation, carbon monoxide extrusion, carbonium ion neutralization, imine acidolysis, isomerization of carbinolamine and hydrolysis to the end products.

“…This compound is p-phenetolcarbamide, Figure 1. This paper is a follow up of our studies on reaction mechanism, [2][3][4][5][6].…”

Section: Introductionmentioning

confidence: 91%

On Dulcin detection by electron transfer

Viesca¹,

Gómez²

2023

The artificial sweetener Dulcin has been detected by reaction with mercury nitrate (Jorissen test), with silver nitrate or with mercury chloride (Ruggeri test). With these reagents a violet colour is developed. Since there are few violet organic compounds, and these exhibit structures more complex than the expected one from Dulcin, it was pertinent direct the attention in order to clear up the chemistry involved in these assays. The reagents employed have reducible cations; thus, there must be oxidations via electron transfer. However, the Dulcin molecule does not show an adequate site for this type of reaction. Nevertheless, hydrolysis of the ureido chain in Dulcin gives 1,4-phenetidine which is suitable for electron transfer. This way organic radical cations similar to the violet Wurster’s salts can be formed. These compounds are in resonance with quinonoid structures. The sui generis hydrolysis of the ureido chain is commented. This reaction and the degradation of the companion isocyanic acid occur via zwitterions.