Mechanism of hydroquinone-inhibited oxidation of acrylic acid and methyl methacrylate |
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Authors: | N N Pozdeeva E T Denisov |
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Institution: | (1) Institute of Physical Chemistry, Peking University, Beijing, 100 871, Peoples Republic of China; |
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Abstract: | The kinetics of hydroquinone-inhibited oxidation of acrylic acid and methyl methacrylate was studied volumetrically by measuring
the oxygen uptake in the presence of an initiator (azobisisobutyronitrile) at T = 333 K and P
O
2 = 1 and 0.21 atm. The oxidation of acrylic acid inhibited by 4-methoxyphenol was studied under the same conditions for comparison.
The rate constants of the reactions of the peroxyl radicals of acrylic acid (∼CH2CH(COOH)O2·) and methyl methacrylate (∼CH2CMe(COOMe)O2·) with hydroquinone (HOC6H4OH) (1.20 × 105 and 7.16 × 104 l mol−1 s−1, respectively) and of the reaction of peroxyl radicals of acrylic acid with 4-methoxyphenol (p-CH3OC6H4OH) (3.25 × 104 l mol−1 s−1) were measured. The stoichiometric inhibition factors f were determined. The reaction between the semiquinone radical and oxygen, O2 + HOC6H4O·, plays an important role, decreasing the factor f and the efficiency of the inhibition effect of hydroquinone. The rate constants of this reaction were calculated from kinetic
data: k = 5.72 × 102 (in acrylic acid) and 4.60 × 102 l mol−1 s−1 (in methyl methacrylate). |
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