A new synthetic route to 4-methoxyisophthalic acid, the key intermediate in the synthesis of Picotamide, is reported. The new protocol starts from commercially available and cheap 4-methylphenol and includes four steps: esterification, Fries rearrangement, methylation, and oxidation; the overall yield is 49%. Unlike the traditional Blanc chloromethylation/oxidation scheme, the proposed procedure avoids using volatile and corrosive hydrochloric acid.
Melt post-polycondensation (MPP) process is one of manufactures industrially that can efficiently increase the molecular weight of polycarbonate (PC). Herein, the MPP experiments of several PC materials using quaternary ammonium hydroxides and alkali metal compounds as the catalyst in the film state are studied. The reaction products are characterized by Ubbelohde viscometer, DSC, 1 H-NMR, ultraviolet spectrophotometry, advanced polymer chromatography and rotational rheometer. It is found that MPP can effectively improve the intrinsic viscosity of PC. After a certain reaction time at a specific temperature, the number average molecular weight ( M n ) of PC is raised from 19,000 to 54,600 g/mol. Furthermore, the 1 H-NMR results reveal that Fries rearrangement products are produced during the MPP process. Based on the functional group model, a reaction kinetic model, combining the effects of the main melt polycondensation reaction and the Fries rearrangement reaction, is established for the first time. The reaction rate constants at different temperatures and the reaction activation energies of the two PC materials are obtained. This work provides a new reaction kinetics model to guide the MPP process of PC, which contains Fries rearrangement reaction.
Tao Liu,Xiaoxue Yuan,Gang Zhang,Yi Zeng,Tong Chen,Gongying Wang
In this paper, the Fries rearrangement of diphenyl carbonate (DPC) catalyzed by organotin compounds with different coordination groups was studied for the first time. The electronic effect and steric hindrance of the coordinating groups were discussed with respect to the reactivity of DPC rearrangement. The results showed that both the electronic effect and steric hindrance of the coordinating groups influenced the acidity of the active tin centers and then affected the catalytic performance of organotin as a Lewis acid for the rearrangement of DPC, and the influence of the electronic effect is greater than that of steric hindrance. The catalytic activity is in the order of BuSnO(OH) > Bu2SnO > Bu2Sn(OCOC11H23)2 > BuSnCl3 > Bu3SnOSnBu3 > Bu3SnCl, and Bu2SnO showed the best catalytic activity due to its strong electron absorption effect, small steric hindrance, and good stability. Under the optimum reaction conditions, the conversion of DPC was up to 93%, and the yields of phenyl salicylate (PS) and xanthone (XA) were 62% and 28%, respectively. In addition, a reaction mechanism of DPC rearrangement catalyzed by the organotin compounds was speculated. This research can provide vigorous theoretical data support to control the byproducts produced by DPC rearrangement in the process of DPC synthesis. It also provides a new route for the preparation of PS and XA.
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