1、 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。
对一些热稳定性差的化合物，也可以通过光解或超声波分解得到相应的氟化物。用六氟磷酸代替氟硼酸，得到的重氮盐ArN2PF6 溶解性更小，因此提高了反应产率。
另外，其他重氮盐如ArN 2 SbF 6 ，ArN 2 AsF 6 ，ArN 2 SiF 6 也有报道。
这个方法的缺点是有时候硼氟酸盐ArN 2 BF 4 不太稳定，容易分解，其制备和分离比较困难，反应的重复性较差。
反应示例
A. o-Bromobenzenediazonium hexafluorophosphate. A solution of 95 mL of 12N hydrochloric acid in 650 ml. of water is added with stirring to 60 g. of o-bromoaniline (0.35 mole; in a 2-L. three-necked flask equipped with stirrer and thermometer. Solution is effected by heating the mixture on a steam bath. A solution of 29 g. (0.42 mole) of sodium nitrite in 75 ml. of water is added with stirring while the mixture is maintained at −5° to −10° by means of a bath of ice and salt or of dry ice and acetone. At the end of the addition there is an excess of nitrous acid, which can be detected with starch iodide paper. Seventy-four milliliters (134 g., 0.60 mole) of 65% hexafluorophosphoric acid is added in one portion, with vigorous stirring, to the cold solution of the diazonium salt. Cooling and slow stirring are continued for an additional 30 minutes, and the precipitated diazonium hexafluorophosphate is then collected on a Büchner funnel. The diazonium salt is washed on the funnel with 300 ml. of cold water and with a solution of 80 ml. of methanol in 320 ml. of ether. The salt is partly dried by drawing air through the funnel for 2 hours. It is then transferred to a pile of several filter papers, powdered
with a spatula, and dried at about 25°/1 mm. for at least 12 hours. The dried o-bromobenzenediazonium hexafluorophosphate is cream-colored; weight 108–111 g. (94–97%); m.p. 151–156° (dec.).
B. 1-Bromo-2-fluorobenzene. Caution! This step should be carried out in a hood because the PF 5 evolved on thermal decomposition of the diazonium salt is poisonous. The apparatus consists of a 1-L, three-necked, round-bottomed flask equipped with a thermometer, a condenser, a magnetic stirrer (optional), and a 250-mL Erlenmeyer flask that is attached by means of a short rubber Gooch connecting tube. The dry powdered hexafluorophosphate salt is placed in the Erlenmeyer flask, and 300 mL of heavy mineral oil is placed in the round-bottomed flask. The mineral oil is heated to 165–170° by means of an oil bath or electric heating mantle and maintained at this temperature while the salt is added rapidly in portions over a period of 30 minutes. The flask is cooled rapidly to room temperature, the side flask is removed, and 400 mL of 10% aqueous sodium carbonate is added slowly through the condenser. The mixture is steam-distilled until no more oil is visible in the distillate.
The oil, which is heavier than water, is separated, and the aqueous layer is extracted with three 50-mL portions of methylene chloride. The oil and extracts are combined, dried over anhydrous sodium sulfate, and distilled from a Claisen flask with an indented neck. Colorless 1-bromo-2-fluorobenzene is collected at 58–59°/17 mm. or 156–157°/760 mm.; weight 45–47g. (73–75% based on o-bromoaniline); n D 25 1.5320–1.5325.
这个反应的另一个改进方法就是直接用HF/NaNO 2 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 14 ，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 reactor equipped with a reflux condenser, 4-aminopyridine (470 mg,5mmol) was added to HF/Pyridine (70% HF, 10 mL) at 0 ℃. The mixture was allowed to stand at room temperature until 4-aminopyridine was completely dissolved. After cooling down to –78 ℃, NaNO2 (380 mg, 5.5 mmol) was added to a solution of 4-aminopyridine in HF, the stirred solution was allowed to stand at 0℃ for 30 min and then stand at 60℃ for 15-30 min. By quenching the resultant solution with ice water, followed by the neutralization with cold saturated NaHCO3 , the resulting mixture was extracted with CH2C12 , the combined organic phase was dried over MgSO4 , and evaporated under reduced pressure to give the crude product, which was distilled to give the desired product (460 mg, 95%).
2、从α-氨基酸合成α-氟代羧酸
在 Olah 试剂（HF/pyridine）存在下，α-氨基酸的氨基在重氮化后被氟取代，生成α-氟代羧酸。高 HF/pyridine 比例(70/30)可能导致重排生成β-氟代羧酸，通常情况下使用的 HF/pyridine 比例为 48/52。α-氨基酸酯也能发生同样的反应。
反应示例
To the alanine (1.74 g, 20 mmol) in pyridinium polyhydrogen fluoride (50 mL) in polyolefin bottle with good stirring at 0 o C was added NaNO 2 (2.1 g, 30 mmol) in three prortions over aperiod of 30 min. Stirring was continued at room temperature for 5 h, then quenched with 100 mL of ice water and extracted with ether. The organic layer was washed with brine and dried over Na 2 SO 4 . The solvent was removed under reduced pressure, the residue was recrystallized to give the desired product (1.39 g, 76%)。
