2,4-Diamino-1,3-thiazole Hydrotribromide1

[75117-14-5]  · C3H6Br3N3S  · 2,4-Diamino-1,3-thiazole Hydrotribromide  · (MW 355.87)

(solid brominating agent1)

Physical Data: mp 198-200 °C (dec).

Solubility: sol methanol, ethanol; slightly sol acetic acid; insol H2O, ether, chloroform; sol but reacts with DMSO, acetone.

Preparative Methods: to a solution of 11.7 g of 2,4-diamino-1,3-thiazole [67355-26-4] in acetic acid or in water, 12 mL of 48% hydrobromic acid is added. Slightly less than 1 equiv of bromine is then slowly added at 0 °C. After 1-2 h, the solid hydrotribromide precipitates and is collected by filtration and washed with ether or chloroform. The solid is recrystallized from methanol (without heating) to yield 13 g (60%) of the desired reagent.2 4-Amino-2-dimethylamino-1,3-thiazole hydrotribromide (mp 150-153 °C) is prepared in the same way from 4-amino-2-dimethylamino-1,3-thiazole and is slightly more stable than the corresponding 2,4-diamino derivative.

Analysis of Reagent Purity: usual KJ titration indicates the amount of free bromine.

Handling, Storage, and Precautions: the dry solid is stable in the dark for several weeks.

Bromination of Aryl Ketones.1

a-Bromo ketones are obtained by reaction of the reagent (1) with aryl ketones in acetic acid at 25 °C (eq 1).

Bromination of Phenols.1

Bromination of phenol with this reagent produces the para and ortho monobromides in a 4:1 ratio (eq 2).

Both a- and b-naphthols are monobrominated to bromonaphthols (eq 3). b-Naphthol affords 1-bromo-2-naphthol in 82% yield.

2,4-Diaminothiazole (and 4-amino-2-dimethylaminothiazole) are slightly soluble in acetic acid and may be recovered and collected by simple filtration after each bromination run.

1. Forlani, L. S 1980, 487.
2. Davies, W.; Maclaren, J. A.; Wilkinson, L. R. JCS 1950, 3491.

Luciano Forlani

Universitá di Bologna, Italy

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