Alkylaromatic hydrocarbons, reaction with olefins

As in the case of the reaction of hydroperoxide with the rr-bond of the olefin, the reaction of ROOH with the rr-bond of the aromatic ring occurs more rapidly than the attack of ROOH on the C—H bond of alkylaromatic hydrocarbon. 

In most cases, this is precisely the reaction that limits chain propagation and determines the oxidation rate. Since the strength of the O—bond in hydroperoxide is independent of the structure of the alkyl substituent R and even of the replaconent of R by H, then reaction (2) is exothermic for hydrocarbons with Z)r h < roo— 365 kJ/mol (olefins, alkylaromatic hydrocarbons) and endothermic for hydrocarbons with )r h > 365 kJ/mol (paraffinic and naphthenic hydrocarbons). The activation energy of this reaction is related by a linear correlation to At-n... 

The enthalpy of the R02 + RH reaction is determined by the strengths of disrupted and newly formed bonds AH= Z>R H—Droo—h- For the values of O—H BDEs in hydroperoxides, see the earlier discussion on page 41. The dissociation energies of the C—H bonds of hydrocarbons depend on their structure and vary in the range 300 - 440 kJ mol-1 (see Chapter 7). The approximate linear dependence (Polany-Semenov relationship) between activation energy E and enthalpy of reaction AH was observed with different E0 values for hydrogen atom abstraction from aliphatic (R1 ), olefinic (R2H), and alkylaromatic (R3H) hydrocarbons [119] ... 

The approximate linear dependence (Polany-Semenov relationship) between activation energy E and enthalpy of reaction AH was observed with different E0 values for hydrogen atom abstraction from aliphatic (R1 ), olefinic (R2H), and alkylaromatic (R3H) hydrocarbons [119] ... 

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