CS217596B1 - A method for the determination of 2-chloroquinoxaline-1,4-dioxide and / or acetals thereof - Google Patents

Abstract

The invention relates to a method for determining 2-formylquinoxaline-1,4-dioxide and/or its acetals, for example dimethyl acetals, starting compounds for the synthesis of 2-substituted derivatives of quinoxaline-1,4-dioxides, used as growth stimulants for livestock. The essence of the method according to the invention consists in adding an excess of semicarbazide hydrochloride to a solution of the sample under investigation in mineral acid, allowing the reaction mixture to react at room temperature or heating it, and after cooling, separating, drying and weighing the semicarbazone that has separated; or determining the excess semicarbazide in the liquid portion after separating the semicarbazone by oxidimetric, preferably bromometric titration.

Description

The invention relates to a method for the determination of 2-formylquinoxaline-1,4-dioxide and / or its acetals, for example dimethylacetals, of the starting compounds for the synthesis of 2-substituted quinoxaline-1,4-dioxide derivatives used in animal growth promoters.

The process according to the invention consists in adding an excess of semicarbazide hydrochloride to a solution of the sample to be examined in mineral acid, allowing the reaction mixture to react at room temperature or warming and, after cooling, the precipitated semicarbazone separated, dried and weighed; or in excess of semicarbazone in the liquid fraction, the excess semicarbazide is determined by oxidimetric, preferably bromometric titration.

217598

The invention relates to a method for the determination of 2-formylchloroxaline-1,4-dioxide and / or its acetals, e.g. dimethylacetal, of formula (I)

CHlOCH ^ 11)

They are a starting material for the preparation of 2-substituted quinoxaline-1,4-dioxide derivatives, many of which exhibit biological activity, for example as growth promoters for livestock. Accurate analytical evaluation of these substances is therefore important for the control of the synthesis. In the search for a suitable method, it has to be taken into account that technical products may contain a significant amount of benzofurazan N-oxide, which is a prior stage of synthesis. Use of the aldehyde group either directly or after hydrolysis of the acetal was contemplated. For the preparation of the process according to the invention, the formation of a very low-soluble and well-filterable semicarbazone was used, the formation of which is not hindered by the strongly acidic environment necessary for the hydrolysis of acetal.

The invention therefore relates to a method for the determination of 2-formylquinoxaline-1,4-dloxide and / or its acetals; it consists in adding an excess of semicarbazide hydrochloride to the sample of the test substance in a solution of a mineral acid such as hydrochloric acid, allowing the reaction mixture to react at room temperature or warming to the initial boiling point, and then precipitating semicarbazone separates, dried and weighs.

Alternatively, the precipitated semicarbazone precipitate is separated and the excess semicarbazide contained in the liquid fraction is determined by oxidimetric, preferably bromometric titration.

Since scmicarbazone 2-formylquinoxaline-1,4-dioxide is only slightly soluble in the medium, the results obtained by the process according to the invention are satisfactory. Excess benzofurazan N-oxide does not interfere with the determination.

Further details of the method according to the invention, including the calculation of results, are apparent from the following exemplary embodiment.

Determination of 2-formylquinoxaline-1,4-dioxide dimethyl acetal (M _r 236,23)

mg (mj of the sample to be examined is mixed with 5 ml of 20% hydrochloric acid and 50 mg (m'2) of semicarbazide hydrochloride (M _r 111,53) in a 50 ml volumetric flask and the reaction mixture is heated to initial boiling, The reaction mixture is cooled with running water and made up to the mark with water, filtered through a dry filter into a dry beaker, 25.00 ml of the clear filtrate are pipetted into a titration vessel, 7.5 ml of 20% hydrochloric acid are added and The excess semicarbazide is titrated by ammonia to a double platinum electrode with a standard potassium bromate solution KBrO3 (c = 0.0166 mol / l) at an applied voltage of 80 mV: consumption a.

The content (%) of semicarbazide hydrochloride used is determined under the same conditions. Dissolve 20 mg of the substance in 20 ml of water and add 10 ml of 20% hydrochloric acid to the solution: consumption b.

M _r υ

b. ——- .100 p. 278.82

4Π --- Calculate the 2-formylquinoxaline-1,4-dioxide dimethylacetal content in% (x) by:

M _r

M _r

100 ALIGN!

m'2

M,

100 ALIGN!

211,808. (mz. y x - mi

100 ALIGN!

5,5765. a) mi

Note: The result is converted to the anhydrous substance; water is determined by K. Fischer method or optionally by drying at room temperature for 24 hours.

Claims (2)

Method for the determination of 2-formylquinoxaline-1,4-dioxide and / or its acetals, characterized in that an excess of semicarbazide hydrochloride is added to a sample of the substance to be examined in a solution of a mineral acid such as hydrochloric acid, and the reaction mixture is allowed to react at The resulting precipitate of semicarbazone is separated, dried and weighed after cooling. 2. A process according to claim 1, wherein the precipitated semicarbazone precipitate is separated and the excess semicarbazide contained in the liquid fraction is determined by oxidimetric, for example, bromometric titration.