Page 326 - Arrow Pushing in Inorganic Chemistry A Logical Approach to the Chemistry of the Main Group Elements

THE NOBLE GASES
306
HYDROLYSIS OF XeF AND XeF
8.4 2 6

A major reason why main-group reactions have been relatively little studied mechanistically
(compared with organic reactions) is that they tend to be fast, sometimes to the point of
being violent. True to this stereotype, whereas XeF is rapidly decomposed in an alkaline
2
solution, XeF reacts violently with water. Let us consider the XeF reaction first:
6 2
− −
2XeF + 4OH → 2Xe + O + 4F + 2H O (8.17)
2
2
2
Observe that some fairly complex redox chemistry must be involved: Divalent xenon is
−
reduced to the elemental state while OH is oxidized to O . That said, obtaining Xe as the
2
final product is rather easy. Following the examples above, let’s start off with having an
−
OH attack a Xe-bound F:
−
− O
F Xe F + Xe + F (8.18)
HO H F
The product HOF, hypofluorous acid, is not particularly acidic but if we assume it’s depro-
−
tonated by hydroxide, the resulting FO could attack another molecule of HOF as a nucleo-
phile and produce HOOF, an unstable intermediate that we encountered in Section 7.4, as
shown below:
− H 2 O −
O
− O F
HO H F
−
O F − (8.19)
− F O F
O H O
H F

The instability of HOOF is clearly related to its unique structure with three highly elec-
tronegative atoms strung together with single bonds. Shown below is an E2 elimination
with a hydroxide ion as the base that leads to O , a product of the reaction.
2
− H 2 O −
F
− O O O + F (8.20)
HO H O

We have discussed other decomposition pathways for HOOF in Section 7.4.
From an arrow-pushing perspective, the hydrolysis of XeF is rather tame (although
6
that’s not the adjective one would otherwise apply to such a violent reaction); no fancy
redox chemistry is involved. There are two distinct steps, and the reaction can actually be
stopped after the first step by limiting the amount of water:

XeF + H O → XeOF + 2 HF (8.21)
4
2
6
XeOF + 2H O → XeO + 4 HF (8.22)
2
4
3