Handbook of Solvents - George Wypych - ChemTech - Ventech!

13.3 Effects of organic solvents on phase-transfer catalysis 837
Figure 13.3.12. The apparent rate constants vs. the molar ratios of NaOH/HOCH 2CF 3; 0.059 mol of (NPCl 2) 3,
9.6×10 -5 mol of TBAB catalyst, 50 mL of chlorobenzene, 20 mL of H 2O, 20 o C; and (Δ) 0.07 mol of HOCH 2CF 3, (*)
0.058 mol of HOCH 2CF 3, (O) 0.075 mol of NaOH, (�) 0.063 mol of NaOH (Adapted from Ref. [138], by permission.)
The other experiments, in which the concentrations of the components in the aqueous
phase are fixed, were carried out by Wu 157 . The volume of organic phase is also fixed at 50
mL, in which the amount of catalyst and phosphazene are also fixed. A generalized apparent
rate constant (pseudo-first-order rate law) k� i,app is defined as
[ ]
k′ = k / Resin / V ; i = r, f
[13.3.21]
i, app i, app ( s ) a
where Resin (s) and V a indicate the total molar equivalent active sites and the volume of water.
The results are given in Table 13.3.30. 157 The apparent rate constants k� r,app and k� f,app are
increased with the increase in the volume of aqueous phase. These results are explained by
low concentration of sodium 2,2,2-trifluoroethanoxide in the organic phase because
HOCH 2CF 3 and NaOCH 2CF 3 are all insoluble in chlorobenzene. After 4 hours of reaction,
only 8% of hexacyclotriphosphasene is reacted. The increase in reaction rate by increasing
the volume of aqueous solution is not due to the increase in the concentration of
NaOCH 2CF 3 in the organic phase. However, the mass transfer rate within the particles is obviously
affected by increasing the concentration of NaOCH 2CF 3 in the aqueous phase.
Table 13.3.30. Apparent rate constants in various NaOCH 2CF 3 concentration under
constant amount of water or constant amount of NaOCH 2CF 3
NaOCH2
CF3 (M)
NaOCH 2CF 3
(mole)
Variation of NaOCH2CF3
k r,app a
kf,app a k�f,app b Volume of
water (mL)
Variation of water
k r,app a
k f,app a
k� f,app b
1.3 50 0.033 0.0031 8.61
1.6 0.035 0.025 0.005 5.56 40 0.038 0.0033 7.33
2.2 0.0525 0.041 0.005 5.56 30 0.044 0.0041 6.83
2.8 0.07 0.055 0.005 5.56 20 0.055 0.0050 5.56
Data obtained from Wang and Wu;157 a min -1 , b Lmin -1 meq×10 -4 ; Reaction conditions: 50 mL of chlorobenzene,
0.0059 moles of (NPCl 2) 3, 0.175 meq of catalyst, 20 o C