Synthesis of Metallo-Deuteroporphyrin Derivatives
and the Study of Their Biomimetic Catalytic Properties
179
5.2.2 Effect of pressure
The reaction pressure, which has great influence on the oxidation of cyclohexane, was
examined at the range of 0.5-1.0 MPa by using Co(II)(DPDME) as catalyst with air in the
absence of additives and solvents, because the oxidation can not occur when the air pressure
is below 0.4 MPa. Fig. 11 shows the effect of pressure on the yield of cyclohexanol and
cyclohexanone. The pressure has slight influence on the yield and the reaction rate at the
beginning of the reaction. The yield increases with the rise of the pressure, and the reaction
time that the maximum yield reached is shortened for 2 h when the pressure changes from
0.5 MPa to 0.8 MPa. This implies that the pressure maintains the amount of oxygen in the
system; as the pressure rises, the concentration of oxygen increases and favors the oxidation.
012345670246810121416Yield (%)time (h)Fig. 11. Effect of pressure on the yield of cyclohexanol and cyclohexanone catalyzed by
M(DPDME). Reaction conditions: cyclohexane 1000 mL, Co(II)(DPDME) 0.02 mmol,
temperature 150 Ԩ, pressure 0.5 MPa (■), pressure 0.6 MPa (●), pressure 0.8 MPa (▲),
pressure 1.0 MPa (▼).
P (MPa) C (%) t (h) S (%) n(Alcohol)/n(Ketone) TON
0.5 20.6 5.5 75.1 0.9 95338
0.6 18.9 4.0 80.7 1.0 87471
0.7 17.8 3.5 82.5 1.1 82380
0.8 18.6 3.5 84.6 1.1 85147Table 2. Effect of pressure on the oxidation of cyclohexane catalyzed by M(DPDME).
As shown in Table 2, the pressure slightly influences the conversion of cyclohexane and the
ratio of alcohol to ketone, but the selectivity varies markedly with the pressure. This result is
basically associated with the reaction time; as the time is prolonged, some of the produced
cyclohexanol and cyclohexanone is over-oxidized to other oxidation products. In this case,
part of the alcohol is also oxidized to ketone, resulting in the decrease of the ratio of alcohol
to ketone. To sum up, 0.8 Mpa is got as the optimum value of the pressure.