AbstractThe carbon monoxide uptake in the reaction of allylbenzene with CoH(CO)4 in n‐octane leading to acylcobalt tetracarbonyls and aldehydes is catalyzed by Co2(CO)8. The rate is half order in Co2(CO)8, first order in allylbenzene and shows a complex dependence in CoH(CO)4 and CO. From kinetic experiments between 15 and 45° C the temperature dependence of the observed rate constant was determined. The complete analogy of this kinetics with that obtained for heptene‐1 shows that the main aldehydic product 2‐phenylbutyraldehyde is formed by a mechanism characteristic for aliphatic olefins and not by one operative for styrenes.