杏耀黑内幕

    四氟化硫是一种选择性有机氟化剂，它的分子结构上S以sp3d杂化轨道形成σ键，分子形状为变形四面体形，在常温常压下为无色带有类似二氧化硫气体的强烈刺激臭气味的气体，有毒，在空气中不燃烧，不爆炸；在600℃时仍很稳定。在空气中强烈水解冒出白烟。遇到有水分的环境会引起类似氢氟酸的。完全水解变成二氧化硫和氢氟酸，部分水解时，生成有毒的亚硫酰氟，但能被强碱溶液全部吸收变成无毒无害的盐类；能溶于苯。

SF4是氟代能力很强的一种试剂，通常和HF一起使用。除了能把转化为单氟代化合物，醛和酮转化为二氟代化合物之外，还能把羧基转化为三氟，是合成三氟甲基化合物的一个重要方法，特别是芳香类三氟甲基化合物。

SF4在氟的发展史上是很重要的一种氟代试剂，随着DAST等新型氟代试剂的发展，SF4在氟化学中的应用逐渐减少，对羟基化合物和醛酮的氟代基本已被DAST等试剂取代。

SF4最重要的应用就是从羧酸合成三氟甲基化合物。脂肪族羧酸为底物反应收率不高，生成的副产物是醚【Dmowski,W; Kolinski, R, A. Pol. J. Chem. 1974, 48, 1697】。

芳香族羧酸底物的产率还可以，不过反应需要加入20－30当量的HF，反应操作不方便。【Zh. Org. Khim. 1974, 10, 886】

反应示例

Twenty-six grams (0.20 mole) of heptanoic is placed in a 145-mL ssure vessel linedwith Hastelloy-C.  The air in thevessel is displaced with nitrogen, and the head ofthe vessel is secured in place.  Thevessel is cooled in a bath of acetone and solid carbon dioxide, and the nitrogenin the vessel is evacuated with a vacuum pump to apressure of 0.5–1.0 mm.  Sixty-five grams (95% pure, 0.57 mole) of sulfur tetrafluoride is transferred to the cold vessel.  This is conveniently done by connecting a cylinder containing 65 g of sulfur tetrafluoride to the pressure vessel by a lengthof copper tubing having a 1/16-in. bore and 1/8-in.outside diameter.

The pressure vessel is heated with agitation at 100° for 4 hoursand at 130° for 6 hours. The vessel is allowed to cool to room temperature andthe volatile by-products [ Caution!Toxic!] are vented.  The crude, fuming, liquid product is pouredinto a stirred suspension of 10 g. of finely divided sodium fluoride in 60 mL of pentane, the mixture is filtered, and the filtrate isfractionated through a 6-in. Vigreux column. 1,1,1-Trifluoroheptane is collected at 100–101°/760 mm., nD251.3449. The yield is .7–24.6 g. (70–80%).

【Hasek, W, R. OrganicSynthese. Coll. Vol. 5, 1082.】

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