Oxidation of Metaxylene to Isophthalic Acid and Its Application

Abstract

Isophthalic acid (IPA) has been found wide application in organic synthesis. Its physical properties and applications of have been over reviewed. IPA is commercially produced by oxidizing metaxylene (MX) with air accelerated by the homogeneous Co–Mn–Br catalytic system. Such commercial process and the catalytic mechanism of the Co–Mn–Br catalytic system have also been discussed, as well as the combustion of the acetic acid, IPA, and MX caused by the Co – Mn – Br catalysts . However, bromide corrodes the expensive reactors and forms methyl bromide that depletes the ozone layer. It is necessary to develop a bromine-free catalyst system to meet the needs of environmental protection and anticorrosion. A homogeneous catalyst system composed of H 3 PW 12 O 40 (HPW)/Co(II)/Mn(II) can oxidize MX to IPA. Compared with the H 3 PW 12 O 40 /Co(II)/Mn(II) system, the heterogeneous catalytic system consisting of H 3 PW 12 O 40 @C and Co(II) is able to get a higher MX conversion and IPA yield, lower oxidation of acetic acid and IPA, and smaller H 3 PW 12 O 40 consumption. Some measures have been tried to transform the physical structure and chemical properties of the carbon surface to improve their performance as catalyst supporters. The H 3 PW 12 O 40 @C catalysts loaded on the activated carbon oxidized by HNO 3 and H 2 O 2 can get higher MX oxidation and IPA yield than that obtained by the H 3 PW 12 O 40 @C loaded on the original carbon. The MX conversions and IPA yields obtained by the H 3 PW 12 O 40 @C catalysts prepared by the carbons modified with oxalic acid, acetic acid, tartaric acid, and ZnCl 2 solution are much greater than that obtained by the H 3 PW 12 O 40 @C catalysts prepared from the original carbon. The increase of acidic groups and the amplification of surface area on the carbon surface are the reason for the improvement of the catalytic capability of the H 3 PW 12 O 40 @C catalyst. The surface chemistry plays a more important role than the physical property in determining the activity of H 3 PW 12 O 40 @C catalyst.