An investigation was made of the cracking reactions of ethyl-, propyl-, isopropyl-, butyl-, sec-butyl-, and tert-butyl-benzenes over a Houdry-type aluminum silicate catalyst.
At space velocities of 0.80–4.00 hour”−1 and temperatures of 330–490° (for ethylbenzene 490–550°) the main reaction of these monoalkylbenzenes consists in the elimination of the alkyl group with formation of benzene and the olefin corresponding to the alkyl group. Reactions of redistribution of hydrogen, isomerization, and polymerization occur only to a slight extent and affect only the products of the breakdown of the carbonium ion of the alkyl group.
Under these conditions the kinetics of the dealkylation of monoalkylbenzenes are in accordance with Frost's equation.
Apparent activation energies for the cracking of the monoalkylbenzenes were determined from the kinetic data: (in cal/mole) ethylbenzene 50,000, propylbenzene 34,000, butylbenzene 33,000, sec-butylbenzene 19,000, isopropylbenzene, 17,500, and tert-butylbenzene 12,700.
The length and structure of the side chain have a definite effect on the extent and rate of cracking of monoalkylbenzenes, and this can be regarded as a confirmation of the ionic character of the dealkylation of benzene homologs over aluminum silicates.
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Georgiev, K.D., Kazanskii, B.A. Dealkylation of alkyl-substituted aromatic hydrocarbons in presence of an aluminum silicate catalyst Communication 1. Kinetics of the dealkylation of monoalkylbenzenes. Russ Chem Bull 8, 463–470 (1959). https://doi.org/10.1007/BF00917702
- Alkyl Group
- Apparent Activation Energy
- Space Velocity