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Benzenediazonium Tetrafluoroborate is much higher stability than the corresponding chlorides; shock-insensitive; often used when pure, isolated arenediazonium salts are needed; reagent for introducing aryl, arylazo, arylhydrazono, or amino groups; forms fluoroarenes upon heating; building block for heterocycles.

Preparative Methods of Benzenediazonium Tetrafluoroborate:  The most commonly used procedures consist in diazotization of an aromatic amine (ArNH2) with NaNO2 in aqueous HCl or H2SO4 followed by precipitation of the salt with added NaBF4 or fluoroboric acid. Alternatively, the diazotization can be carried out directly in 40-50% aqueous HBF4. Aromatic amines that do not dissolve in aqueous mineral acids can be reacted with NO+BF4 - in an anhydrous organic solvent or in liquid SO2. This method can also be applied to N-(trimethylsilyl)anilines and for the preparation of those salts that are not easily isolated from water. An improved, high-yielding one-pot procedure employs ArNH2, t-BuONO, and BF3. Et2O in an anhydrous organic solvent, typically CH2Cl2.

Poison by ingestion andsubcutaneous routes. Questionable carcinogen withexperimental tumorigenic data. Mutation data reported.When heated to decomposition it emits toxic fumes ofNOx and F^-.

the dry parent salt of Benzenediazonium Tetrafluoroborate can be stored for more than a month at rt or for a few years at -20 °C under N2 in the dark, but decomposes when exposed to direct sunlight. Rapid recrystallization from warm water or from acetonitrile-Et2O is possible without decomposition. Although arenediazonium tetrafluoroborates, in contrast to the chloride salts, are renowned in general for their enhanced thermal stability and shock-insensitivity, some care should nevertheless be taken. Some salts are known to decompose while drying, e.g. 3-methoxybenzenediazonium, 2-methylbenzenediazonium, and certain heteroarenediazonium tetrafluoroborates. Avoid contact with metals.