| Popis: |
A detailed kinetic study has been made of the rate of chloride exchange between liquid phosgene and solute aluminium chloride. At low concentrations the rate is first order in aluminium chloride, but it changes over to a rate intermediate between 1 and 2 at higher concentrations. The cross-over point occurs at high concentration when the temperature is low and low concentration when the temperature is high. The energy of activation is 14·1 kilocalories in the first order region and 18·3 kilocalories in the region of higher order. It is suggested that phosgene and aluminium chloride undergo a weak acid-base interaction leading to chloride exchange. It is also suggested that the cross-over to higher order is due to the appearance of ions in the solution, rather than to a specific chemical effect. In conformity to this picture, it is found that chloro-aluminate ions, for example, AlCl4−, undergo much slower exchange of chloride with solvent phosgene than does aluminium chloride. It is also found that the presence of ions in this solution can have a drastic effect toward raising the rate of exchange between phosgene and solute aluminium chloride. Hydrogen chloride suppresses the rate of exchange of chloride between phosgene and solute aluminium chloride, possibly by means of such a reaction as AlCl 3 + HCl+COCl 3 ⇆ HCOCl 3 + + AlCl 4 − It appears that while there is no compound formation between hydrogen chloride and aluminium chloride by themselves, yet aluminium chloride can force hydrogen chloride to donate a proton to a proton acceptor, even one as weak as phosgene. |
