Notes - Quinoxaline-2-Thiols

Abstract

The only representative of the class of quinoxaline-2-thiols was recently reported by Wolf, Wilson, Jr., and Tishler.3 This paper presents the preparation of quinoxaline-2,3-dithiol, an unusually sensitive reagent for nickel. The dithiol was prepared by treating 2,3dichloroquinoxaline with thiourea and hydrolyzing the isothiouronium salt. This compound was also made by refluxing a mixture of 2,3-dihydroxyquinoxaline and phosphorus pentasulfide in dry pyridine.Also described is the preparation of 3-alkylquinoxaline-2-thiols. These compounds were prepared directly by treating the corresponding chloroquinoxalines with thiourea in absolute alcohol. The intermediate isothiouronium salts did not precipitate, and the desired thiols crystallized on cooling.All of these thiols were characterized by converting them to mercapto ethers. EXPERIMENTAL4Quinoxaline-2,8-dithiol. (a) From 2,3-dichloroquinoxaline. A solution of 4 g. (0.02 mole) of 2,3-dichloroquinoxaline5 and 8 g. (0.105 mole) of thiourea in 100 ml. of absolute alcohol was refluxed for two hours. The solution was concentrated to a small volume, diluted with 250 ml. of water, made alkaline by the addition of 25 g. sodium hydroxide, and then refluxed for one-half hour. On acidifying with acetic acid, a brownish-orange product formed which was separated by filtration, washed with water and dried. The yield -was 3.76 g. or 96.4%.The dithiol could not be recrystallized from any solvent tried, but was purified for analysis by repeated dissolving in alkali and reprecipitation by acetic acid. Prolonged heating in alkaline solution appeared to cause some oxidation and lightening of color. A characteristic behavior was shown on heating. Between 230-250°the color of the compound started to change to chrome yellow; the change wras completed by 280°. Decomposition began at 290-295°, with partial fusion, at which point the substance turned greenish-gray.

Control of Oxo-Molybdenum Reduction and Ionization Potentials by Dithiolate Donors

“…Purification of solvents was accomplished using the following methodologies: triethylamine from potassium hydroxide; toluene from sodium/benzophenone. Quinoxaline, quinoxaline dichloride, and toluene-3,4-dithiol were purchased from Aldrich, and (L-N3)MoOCl2, 36 (L-N3)MoO(tdt), 36 and H2qdt 8, 37 were prepared as previously described.…”

A novel method for heterocyclic amide–thioamide transformations

“…Transforming heterocyclic amides into thioamides is an important task in organic synthesis. Earlier reports for this type of O/S conversions were achieved by several thiating reagents; for instance, Lawesson's reagent (2,4-bis(4-methoxyphenyl)-1,3-dithia-2,4-diphosphetane 2,4-disulfide) [ 1 – 3 ], Berzelius reagent [ 4 – 6 ] (P 4 S 10 ), and phosphorus pentasulfide [ 7 ] in dry toluene, xylene or pyridine under reflux conditions. A two-step approach for the purpose of thiation of heterocyclic amides attracted our attention: as a first step, we applied a chlorination of heterocyclic amides, followed by thiation via reaction with thiourea on the basis of reagent-promoted desulfurylation of isothiourea under strong basic conditions [ 8 – 9 ].…”

Efficient diverse approach for quinoxaline‐derived glycosylated and morphinylated analogs

“…The 2,3‐dimercaptoquinoxalinedithiol [12] ( 1 ) has served as a key starting material. It was prepared from the condensation of oxalic acid and o ‐phenylenediamine and the product was converted to 2,3‐dichloroquinoxaline whose reaction with thiourea gave the isothiouronium salt whose treatment with alka1i gave 1 .…”

“…The product was filtered off and dried to give 1 in 93% yield, mp 298–300°C, lit. mp 295–298°C [12].…”