Rate constant ratios in the consecutive chlorination of liquid‐phase p‐xylene with Cl2 and an iron(III) chloride catalyst.

Given that p‐xylene is an important chemical feedstock for many final products in the market from pesticides, pharmaceuticals, peroxides to dyes, its chlorinated derivatives are of interest in the chemical industry. In this paper, the rate constant ratios of the consecutive chlorination of p‐xylene at 70°C in a gas–liquid semibatch reactor using molecular chlorine and iron(III) chloride as a catalyst was investigated up to the fourth successive reaction (tetrachloro‐p‐xylene production). The 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. The 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 = 0.295, k3/k1 = 0.0826, and k4/k1 = 0.00383. The ratio of the dichlo‐isomers produced was also determined as 2.12 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. The existing knowledge found in the literature on the rate constant ratios of consecutive reactions was also extended in this paper with a new mathematical expression for the determination of the third stage product peak concentration. 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. Finally, the propagation of uncertainties for the trichloro‐p‐xylene was estimated using the partial derivatives of this product for each of the rate constants. [ABSTRACT FROM AUTHOR]