Action of Dry Hydrogen Halides

General Synthetic Methods for Thia20le and Thiazolium Salts 

This method has been applied to the synthesis of 4-methyl (659), 4-aryl (416, 519, 659), 4,5-dimethyl (137, 220, 221), 4,5-dialkyl (229, 681), 4-methyl-5-O-acetoxyethyl) (229), 4-methyl-5-(j3-carbethoxyethyl) (229), 4-ary 1-5-bromo (579), and 2-chlorothiazoles from the corresponding a-thiocyanatoketones (Table 11-28). 

2-CHLOROTHlAZOLE DERIVATIVES FROM a-THIOCYANATO-KETONES AND DRY HYDROCHLORIC ACID IN ETHEREAL SOLUTION 

These compounds can also be obtained from the corresponding 2-hydroxythiazoles and phosphorylchloride (68, 109, 137, 221, 229, 428, 519), but the method is restricted by the availability of the hydroxy compounds, which are discussed in another section (Chapter VII), 

The same general procedure was applied satisfactorily to the synthesis of 2-bromothiazoles using hydrogen bromide below 0°C (465, 507) (Table 11-29). 

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The pentavalent halides and oxyhalides, as in the case of other niobium compounds, are the most stable. It is remarkable that the pentavalency is maintained with increase in the atomic weight of the halogen. All the halogen compounds are characterised by their ready tendency to undergo hydrolysis on the addition of water or even in damp air with precipitation of niobie acid and formation of the hydrogen halide. Their preparation can, therefore, be effected only in the dry way (a) synthetically, or (b) by the action of chlorine, carbon tetrachloride, or sulphur monochloride on the oxide or sulphide. They do not possess saline properties, and cannot be prepared by the action of the halogen acids on the oxide. 

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