My PhD dissertation - Institut Fresnel

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the reacting phosphonium salt (R 2 ), occurs in an irreversible process from the common
pentavalent phosphorus intermediate (Figure 2). From the ratio measured experimentally, it
was assumed that one can deduce the relative kinetic constant:
n
k 1/
2 =
n
where n1 and n2 are the amount of phosphine oxides 1 and 2 respectively formed.
Finally, the use of the Eyring equation allows the determination of the activation free enthalpy
difference which was thought to be representative of the relative ease of the alkyl substituents
to accommodate a carbanionic character according to the Bell-Evans-Polanyi Theory [126 - 128] :
G
R 1
P
R 2
R 1 R 2
+ KOH
X
1
R 1
R 1
R 2
P
R2 OH
2
∆∆ 12
≠
R 1
R 1
G = −RT
ln k = α ∆∆G
R 2
P
R2 O
∆G 1
3'
3
∆G 2
1
2
1/
2
∆∆G 12
o
12
R 1 R 2
P
R O 1
0
∆∆G12 R
P
O
2 R 2
R1 + R 2 H
+ R 1 H
Reaction Coordinates
Figure 2. Energetic profile of the alkaline decomposition of phosphonium
salts in case of a non concerted mechanism.