Besonderheiten des Pyrolyseverhaltens von Isoalkylaromaten

Abstract

Special Features in Pyrolysis Behaviour of Isoalkylaromatics The pyrolysis of cumene, sec. butyl‐ and tert. butylbenzene proceeds in a laboratory scale quartz vessel in the temperature range 600–750°C. Conversion occurs mainly via a radical‐chain mechanism in the side chain in proportions, determined by the dissociation energies of the CC‐ and CH‐bonds. Dealkylation was observed in greater amounts than for n‐alkylbenzenes. It is interpreted by H‐atom addition to the aromatic nucleus, followed by β‐scission to benzene and isoalkenes. It was be shown, that H‐atoms are formed by unusual reactions such as neophyl rearrangement and homolytic rupture of CC‐bonds in the side chain.

Relative reactivities of some carbon-hydrogen bonds in hydrogen abstraction by methyl radicals at 950 K

“…At 950 K a ratio of 2.1 yields Wnzy, = 6-^^--12.6 (19) ^methylstyrene This value is in reasonable conformity with that from the tracer experiments (rtert,benzyl = 9.0 ± 0.5). Bach et al 16 give the primary products composition of the pyrolysis of some isoalkylbenzenes. At about 950 K (10% conversion) they found 20% «-methylstyrene and 40% styrene from cumene which is in good conformity with our results.…”

“…In case that the hydrogen donor RH does not generate enough methyl radicals by its spontaneous decomposition n-hexane (30-50% of RH) was added as a methyl source. Then eq 15 has to be modified because n-hexane reacts as a hydrogen donor too a ^"RH 4™ ^hexane(^hexane/ vPhT /"rh) «1RH ^ben vbenzene ^PhT (16) £rh/&phT can easily be recalculated from the slope of the regression line if fchexane/kphT is known and the ratio «hexane/«rh is kept constant during variation of «RH/«benzene-…”