Kinetics anti-Arrhenius

The thermoregulated phase-transfer function of nonionic phosphines has been proved by means of the aqueous-phase hydrogenation of sodium cinnamate in the presence of Rh/6 (N =32, R = n-CsHu) complex as the catalyst [16]. As outlined in Figure 2, an unusual inversely temperature-dependent catalytic behavior has been observed. Such an anti-Arrhenius kinetic behavior could only be attributed to the loss of catalytic activity of the rhodium complex when it precipitates from the aqueous phase on heating to its cloud point. Moreover, the reactivity of the catalyst could be restored since the phase separation process is reversible on cooling to a temperature lower than the cloud point. 

Fig. 2 Atmospheric-pressure hydrogenation of sodium cinnamate using Rh/6 (N = 32, R = n-CsH,) as the catalyst in water at different temperatures. The cloud point of the catalyst is 64 °C. Anti-Arrhenius kinetic behavior results due to the inversely temperature-dependent water-solubility of the nonionic phosphine [16].

Figure 2 Anti-Arrhenius behavior of the kinetics of a host-guest complex during enclathration.

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