The halogenation of aromatics: Part I. Gas phase chlorination of chlorobenzene

The gas phase chlorination of chlorobenzene has been investigated at temperatures between 275 and 500° C, using empty glass reactor tubes. Intake ratios of chlorine and aromatics were 1/2 and nitrogen was used as a diluent. Contact times were 1/2‐1 minute. Dichlorobenzenes were obtained in high yields based on chlorobenzene converted. Carbon formation was negligible at temperatures below 465° C; no indications as to formation of by‐products were obtained. Whereas chlorine conversions increased from 2 to 70% over the temperature range studied, isomer compositions of dichlorobenzenes showed little variation, viz. 68‐62% meta, about 24% para and 8‐13% ortho, the first‐mentioned figures applying at the lower reaction temperatures. Meta/para ratios were, therefore, always appreciably higher than 2. A transition of the substitution type, such as has been observed in some cases by Wibaut and his coworkers1), did not occur.