Page 254 - Arrow Pushing in Inorganic Chemistry A Logical Approach to the Chemistry of the Main Group Elements

GROUP 16 ELEMENTS: THE CHALCOGENS
234
With that, we have accounted for all the observed products—that was clearly quite a lot of
arrow pushing. It’s important to remember that the mechanism is speculative, but that is all
right. As already emphasized, our goal here is, given a fairly complicated reaction, to come
up with one or more reasonable mechanistic hypotheses.

REVIEW PROBLEM 6.15
Suggest a mechanism for the following isomerization:

F F F
−
KF
S S S S
+
F
Note: KF is a catalyst.

6.12 HIGHER-VALENT SULFUR FLUORIDES

Sulfur tetrafluoride (SF ), a corrosive, moisture-sensitive gas, is commercially available.
4
Industrially, it is most conveniently prepared via the following reaction:

SCl + Cl + 4NaF → SF + 4 NaCl (6.107)
2
4
2
Sulfur tetrafluoride is a powerful fluorinating agent, converting alcohols, carbonyl com-
pounds, and carboxylic acids to the corresponding CF, CF , and CF derivatives, respec-
2 3
tively. Unfortunately, SF is highly toxic, is difficult to handle, and produces HF (which
4
attacks glass) with moisture. As far as laboratory use is concerned, therefore, SF has been
4
largely superseded by a suite of more user-friendly dialkylaminosulfur trifluoride reagents.
Diethylaminosulfur trifluoride (DAST), the first such compound to be introduced (in 1970),
is perhaps the best known among these reagents; others include N-morpholinosulfur triflu-
®
oride (MOST) and Deoxo-Fluor :
O H 3 CO OCH 3

Et Et
F S F N N N
F F SF 3 SF 3 SF 3
Sulfur tetrafluoride DAST MOST Deoxo-Fluor ®

Typical reaction conditions are shown below for an alcohol:

DAST, CH 2 Cl 2
C H OH − 70 °C RT C H F (6.108)
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