With Replacement of Hydrogen

Generally speaking, the 1,3-azoles do not show the pyridine-type reactions in which hydrogen is displaced on reaction with a strong nucleophile. 

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With Replacement of Hydrogen Atoms in the Tellurophene Ring... 

Intnductton of COCl (Chlorocarbonylation). Kharasch and Brown found that some saturated hydrocarbons react with oxalyl chloride in the presence of light or a peroxide with replacement of hydrogen by COCl. Thus a mixture of 0.3 mole of cyclohexane, 0.2 mole of oxalyl chloride, and 1.2 g. of dibenzoyl peroxide when... 

Various substituted 2-pyrazolin-5-ones react with metal salts with replacement of hydrogen and formation of semipolar bonds with electron donating atoms. The most important of these compounds are the metal complexes of 4-arylazo-2-pyrazolin-5-ones. These complexes are widely used in the dye industry to give desired properties to 4-arylazo-2-pyrazolin-5-one dyes. Although a large number of metal-dye complexes have been used in dyeing, only a few such compounds have been characterized and reported in the literature. Usually a solution of the azo compound and an appropriate salt such as cupric chloride or nickel sulfate are mixed in solution and heated.326 The reaction is... 

The reaction of nucleophilic radicals, under acidic conditions, with heterocycies containing an imine unit is by far the most important and synthetically useful radical substitution of heterocyclic compounds. Pyri-dines, quinolines, diazines, imidazoles, benzothiazoles and purines are amongst the systems that have been shown to react with a wide range of nucleophilic radicals, selectively at positions a and y to the nitrogen, with replacement of hydrogen. Acidic conditions are essential because A-protonation of the heterocycle... 

Mercuration takes place very readily with replacement of hydrogen, or carbon dioxide from an acid." ... 

The 1,2-azoles do not generally react with nucleophiles with replacement of hydrogen. In favourable situations, an A-nitro group in 1-nitro-pyrazoles can act as a leaving group to allow substitution of hydrogen. ... 

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