重氮盐合成氟化合物

Balz-Schiemann 反应

芳香胺类化合物通过重氮盐热解而得到相应的氟化物，是合成氟化合物的一个重要方法，我们称为Balz－Schiemann反应。一般情况下将重氮盐转变为不溶于水的硼氟酸盐ArN2BF4，或直接在硼氟酸存在下重氮化，再加热分解重氮盐，便得到氟化物。

这个反应的另一个改进方法就是直接用HF/NaNO2进行重氮化，或在一些碱如吡啶，2－羟基吡啶，哌啶等存在下重氮化，然后热解生成相应的氟化合物，苯胺类化合物和氨基取代的杂环化合物，如吡啶，嘧啶等都能发生这种反应。

反应示例：

        In a 100-mL PFA made reactorequipped with a reflux condenser, 4-aminopyridine (470 mg, 5mmol) was added to HF/Pyridine (70% HF, 10 mL) at 0^oC. The mixture was allowed to stand at room temperature until 4-aminopyridinewas completely dissolved.  After coolingdown to –78 ^oC, NaNO₂ (380 mg, 5.5 mmol) was added to asolution of 4-aminopyridine in HF, the stirred solution was allowed to stand at0^oC for 30 min and then stand at 60^oC for 15-30 min.  By quenching the resultant solution with icewater, followed by the neutralization with cold saturated NaHCO₃,the resulting mixture was extracted with CH₂C1₂,the combined organic phase was dried over MgSO₄, and evaporatedunder reduced pressure to give the crude product, which was distilled to givethe desired product (460 mg, 95%).

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