Rate constant ratios in the consecutive chlorination of liquid‐phase p‐xylene with Cl2 and antimony pentachloride as a catalyst

• Published in: International journal of chemical kinetics 2022-05, Vol.54 (5), p.317-327
• Main Author: Rigas, Fotis P.
• Format: Article
• Language: English
• Subjects: Antimony; antimony pentachloride; Catalysts; Chlorination; Chlorine; consecutive reactions; Dichloroethane; Graphical methods; Isomers; Mathematical analysis; Maxima; Propagation; propagation of uncertainties; p‐xylene chlorination; rate constant ratios; Ratios; Uncertainty; Xylene
• ISSN: 0538-8066; 1097-4601
• DOI: 10.1002/kin.21561

The rate constant ratios of the consecutive chlorination of p‐xylene at 70oC in a gas–liquid semibatch reactor using molecular chlorine, dichloroethane as a solvent, and antimony pentachloride as a catalyst was investigated up to the fourth successive reaction (tetrachloro‐p‐xylene production). The rate ratios were determined with both mathematical expressions and a graphical method proposed recently in the literature by use of the maxima of the successive products. In addition, to this simple method that concerns only one pair of values of products (single‐point maximum approach), another novel method is proposed and successfully applied concerning many pairs of corresponding values of intermediate products (multiple points maximum approach). This latter method permits the estimation of uncertainties and propagation of uncertainties that proved the usefulness and the possibilities of determining the parameters based on special points of the kinetic dependencies. The rate ratios found for monochloro‐p‐xylene (2‐chloro‐p‐xylene), dichloro‐p‐xylene (the sum of 2,3‐dichloro‐p‐xylene and 2,5‐dichloro‐p‐xylene), trichloro‐p‐xylene (2,3,5‐trichloro‐p‐xylene), and tetrachloro‐p‐xylene (2,3,5,6‐tetrachloro‐p‐xylene) are k2/k1 = 0.09741, k3/k1 = 0.002685, and k4/k1 = 0.000499. The ratio of the dichloro‐isomers produced was also determined in the initial stages as 3.3 in favor of 2,5‐dichloro‐p‐xylene, which is reasonable since 2,3‐dichloro‐p‐xylene is highly hindered by the adjacent groups on the aromatic nucleus. Nevertheless, as the production of trichloro‐p‐xylene increased considerably, the proportion of 2,3‐dichloro‐p‐xylene gradually diminished down to complete disappearance. This is attributed to the ease of this isomer to be further chlorinated to trichloro‐product since its available free sites on the nucleus are less hindered compared to 2,5‐dichloro‐p‐xylene. The standard uncertainties of the rate constant ratios, the standard deviation of the means, as well as the expanded uncertainties of the means were calculated and proved statistically accepted. Finally, the propagation of uncertainties for the trichloro‐p‐xylene was estimated using the partial derivatives of this product for each of the rate constant ratios.