Phthalide-based mechanism

In agreement with the phthalide-based mechanism, rufigallol 40, a compound showing interest in both biological and material science, can be synthesized in 80% yield by self-condensation of gallic acid 39 pro-mofed by concenfrated sulfuric acid under 360 W microwave irradiation (Scheme 2.19). ... 

The gas-phase selective oxidation of o-xylene to phthalic anhydride is performed industrially over vanadia-titania-based catalysts ("7-5). The process operates in the temperature range 620-670 K with 60-70 g/Nm of xylene in air and 0.15 to 0.6 sec. contact times. It allows near 80 % yield in phthalic anhydride. The main by-products are maleic anhydride, that is recovered with yields near 4 %, and carbon oxides. Minor by-products are o-tolualdehyde, o-toluic acid, phthalide, benzoic acid, toluene, benzene, citraconic anhydride. The kinetics and the mechanism of this reaction have been theobjectof a number of studies ( 2-7). Reaction schemes have been proposed for the selective pathways, but much less is known about by-product formation. 

The evaluation of the experiments in both reactors was based on the mechanism of the oxidation. The concentration profiles measured in the integral reactor, as well as the finite slope in the origin of the concentration-residence time curves from the loop reactor, reveal that, the xylene is converted by simultaneous reactions to the products phthalicanhydride, phthalide, toluylaldehyde, CO and CO2. The distinct maximum of the phthalide- and tolualdehyde -concentration curve indicates that these are intermediate products which are converted mainly to phthalicanhydride in a consecutive step. From the decrease of the PSA-concentration at high residence times it may be concluded that, this species oxidize to CO, CO2, as well as water and to a lower extend, to MSA. For the evaluation of the ex-... 

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