On Biomimetics by Lilyana Pramatarova

On Biomimetics
178

10. No products were found when the temperature was below 110 Ԩ. Fig. 10 shows how the
    yield of cyclohexanol and Cyclohexanone changes with the reaction time in the presence of
    Co(II)(DPDME) at different reaction temperatures. The reaction rate is evidently influenced
    by the temperature and the yield increases notably as the temperature rises at the beginning.
    The higher the temperature is, the shorter is the reaction time that the maximum yield
    reached. Fig. 10 also indicates that the yield decreases rapidly after reaching the maximum
    value, especially when the reaction temperature is 170 Ԩ. This implies that part of the
    catalyst may be destroyed at high temperature. The group of Chang (Chang & Kuo, 1979)
    reported the similar result that the meso-unsubstituted metallo-porphyrins are prone to
    attack at the meso-carbon during oxidation, leading to the degradation of porphyrins.
    Although the decomposition of catalyst is a problem at somewhat elevated temperatures,
    well over 11.4% yield has been observed in the oxidation of neat cyclohexane at 170 Ԩ
    catalyzed by Co(II)(DPDME).

T (°C) C (%) t (h) S (%) n(Alcohol)/n(Ketone) TON

130 15.9 5.5 88.1 1.2 73587

150 18.6 3.5 84.6 1.1 85147

170 18.8 3.0 60.6 1.0 87008

Table 1. Effect of temperature on the oxidation of cyclohexane catalyzed by M(DPDME).
Reaction conditions: cyclohexane 1000 mL, Co(II)(DPDME) 0.02 mmol, pressure 0.8 MPa.

From Table 1, it can be found that the selectivity of cyclohexanol and cyclohexanone
decreases as the temperature increases. The selectivity is 88.1% at 130 Ԩ, but rapidly falls to
60.6% at 170 Ԩ. This suggests that the high temperature might be beneficial to the
convertion of alcohols and ketones to acids and esters.

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Yield (%)

time (h)

Fig. 10. Effect of temperature on the yield of cyclohexanol and cyclohexanone catalyzed by
M(DPDME). temperature 130 Ԩ (■), temperature 150 Ԩ (●), temperature 170 Ԩ (▲).