| 摘要 |
<p>Polychlorinated phenols (e.g., pentachlorophenol) of improved color are made by vacuum distilling polychlorinated phenols containing dark color-forming impurities in the presence of a color inhibitor such as zinc dust or free radical-acting substances (e.g., free radical-acting compounds of the phenol, hydroquinone, organic sulfur derivative, organic phosphite, amine and aldehyde type). Ethylene thiourea or zinc dust appear to offer an optimum combination of improved color, cost and process efficiency and are therefore the preferred color inhibitors. In addition, the chlorodioxin content of the impure pentachlorophenol (generally about) 2,000 p.p.m.) is reduced to a residual chlorodioxin content of less than 25 p.p.m. during distillation.</p> |
