needs to be purified of toxins and ozone depleters such as methylbromide before being released. Additionally, the corrosive nature of bromides at high temperatures requires the reaction be run in expensive titanium reactors. Alternative reaction media The use of carbon dioxide overcomes many of the problems with the original industrial process. Because CO2 is a better flame inhibitor than N2, a CO2 environment allows for the use of pure oxygen directly, instead of air, with reduced flammability hazards. The solubility of molecular oxygen in solution is also enhanced in the CO2 environment. Because more oxygen is available to the system, supercritical carbon dioxide (Tc = 31 °C) has more complete oxidation with fewer byproducts, lower carbon monoxide production, less decarboxylation and higher purity than the commercial process. In supercritical water medium, the oxidation can be effectively catalyzed by MnBr2 with pure O2 in a medium-high temperature. Use of supercritical water instead of acetic acid as a solvent diminishes environmental impact and offers a cost advantage. However, the scope of such reaction systems is limited by the even harsher conditions than the industrial process (300–400 °C, >200 bar). Promotors and additives As with any large-scale process, many additives have been investigated for potential beneficial effects. Promising results have been reported with the following. Ketones act as promoters for formation of the active cobalt(III) catalyst. In particular, ketones with α-methylene groups oxidize to hydroperoxides that are known to oxidize cobalt(II). 2-Butanone is often used. Zirconium salts enhance the activity of Co-Mn-Br catalysts. Selectivity is also improved. N-Hydroxyphthalimide is a potential replacement for bromide, which is highly corrosive. The phthalimide functions by formation of the oxyl radical. Guanidine inhibits the oxidation of the first methyl but enhances the usually slow oxidation of the toluic acid. Alternative routes Terephthalic acid can be prepared in the laboratory by oxidizing many para-disubstituted derivatives of benzene, including caraway oil or a mixture of cymene and cuminol with chromic acid. Although not commercially significant, there is also the so-called "Henkel process" or "Raecke process", named after the company and patent holder, respectively. This process involves the transfer of carboxylate groups. For example potassium benzoate disproportionates to potassium terephthalate, and potassium phthalate rearranges to potassium terephthalate. Lummus (now a subsidiary of McDermott International) has reported a route from the dinitrile, which can be obtained by ammoxidation of p-xylene. Applications Virtually the entire world's supply of terephthalic acid and dimethyl