四氟硼酸硝硝化反应

NO2BF4 是一种很强的硝化试剂，但是其制备不方便，其是由硝酸，氢氟酸和三氟化硼反应制得。当苯环被吸电子基团钝化，用一般的方法难以硝化，而此类试剂则能顺利实现硝化，这种方法对合成多硝基取代的化合物比较有效。

反应实例

A 500-ml. four-necked flask is equipped with a mechanical stirrer, a dropping funnel, a thermometer and an inlet for dry nitrogen. It is baked thoroughly by means of a Bunsen flame and allowed to cool to room temperature with a slow stream of dry nitrogen passing through it. The flask is charge, preferably in a dry box, with 335 g of tetramethylene sulfone and 73.1 g (0.55 mol) of nitronium tetrafluoroborate. The thermometer is adjusted so that the bulb is immersed in the liquid. The reaction mixture is stirred well and kept at 10–20° by means of an

ice bath while 58.5 g (0.50 mol) of freshly distilled o-tolunitrile is added dropwise. The nitronium tetrafluoroborate only partially dissolves in the tetramethylene sulfone, but through good stirring a homogeneous suspension can be obtained. As the dissolved nitronium salt reacts with the nitrile, more and more salt dissolves until all of it is in solution. The addition of o-tolunitrile requires 25–35 minutes. After the addition is complete, the cooling bath is removed and stirring is continued for 15 minutes at 35°. The dropping funnel is removed, 74.5 g (0.56 mol) of nitronium tetrafluoroborate is added, and the opening of the flask is closed with a glass stopper. The well-stirred reaction mixture is heated by an electric heating mantle to 100° in 15 minutes and kept at 100–115° for 1 hour. The reaction mixture is allowed to cool to room temperature with continued stirring and is then poured into 800 g of ice water. Crude 3,5-dinitro-o-tolunitrile

separates on top of the aqueous mixture as a dark oil that solidifies after standing a few minutes. The solid is collected on a Buchner funnel. It is triturated on the funnel with five 50-mL. portions of cold water and with 40 mL of ice-cold ethanol. After being dried in a vacuum desiccator, the crude nitrile weighs 75–84 g., mp 60–65°. Recrystallization from about 110 mL of hot methanol gives 50–55 g (48–53%) of 3,5-dinitro-o-tolunitrile, mp 82–84°C。

【Organic Syntheses, Coll. Vol. 5, p.480; Vol. 47, p.56】

四氟硼酸硝的制备

Synthesis of Nitronium tetrafluoroborate: Caution! Hydrogen fluoride is very hazardous. All operations must be carried out in a hood, and the precautions outlined in should be followed. A 1-L three-necked polyolefin flask is provided with a short inlet tube for nitrogen, a long inlet tube for gaseous boron trifluoride, a drying tube, and a magnetic stirring bar. The flask is immersed in an ice-salt bath and flushed with dry nitrogen. Under a gentle stream of nitrogen and with stirring, the flask is charged with 400 ml. of methylene chloride, 41 mL

(65.5 g, 1.00 mole) of red fuming nitric acid (95%), and 22 mL (22 g., 1.10 moles) of cold, liquid, anhydrous hydrogen fluoride.

Gaseous boron trifluoride (136 g, 2.00 moles) from a cylinder mounted on a scale is bubbled into the stirred, cooled reaction mixture. The first mole is passed in rather quickly (in about 10 minutes). When approximately 1 mole has been absorbed, copious white fumes begin to appear at the exit, and the rate of flow is diminished so that it takes about 1 hour to pass in the second mole; even at this slow rate, there is considerable fuming at the exit. After all the boron trifluoride has been introduced, the mixture is allowed to stand in the cooling

bath under a slow stream of nitrogen for 1.5 hours. The mixture is swirled, and the suspended product is separated from the supernatant liquid by means of a medium-porosity, sintered-glass Buchner funnel. The gooey solid remaining in the flask is transferred to the funnel with the aid of two 50-ml. portions of nitromethane. The solid on the funnel, nitronium tetrafluoroborate, is washed successively with two 100-mL portions of nitromethane and two 100-mL portions of methylene chloride. In order to protect the salt from atmospheric moisture

during the washing procedure, suction is always stopped while the salt is still moist. The moist salt is transferred to a round-bottomed flask and dried by evaporating the solvent. At the end of the procedure the flask can be gently heated to 40–50°. The yield of colorless nitronium tetrafluoroborate is 85–106 g (64–80%). It is stored in a wide-mouthed polyolefin bottle with a screw cap. The edge of the cap is sealed with paraffin wax.

【Organic Syntheses, Coll. Vol. 5, p.480; Vol. 47, p.56】

商业化社会，能买还是买吧，自己做太危险，CAS: 13826-86-3。