PURPOSE: To obtain a high-purity alkenyl aromatic compound which is a starting substance for naphthalenedicarboxylic acid used as a starting substance for polymers by reaction of an alkylbenzene with butadiene in the presence of metallic sodium, a rubidium salt and specific aromatic compound.

CONSTITUTION: In the presence of (A) metallic sodium, (B) a rubidium salt (preferably rubidium hydroxide or carbonate) and (C) an aromatic compound which forms a charge transfer complex with a component (A) such as naphthalene or anthracene, an alkylbenzene and 1,3-butadiene are allowed to react with each other, preferably in the absence of moisture and oxygen to give the objective compound. The reaction is preferably carried out at 80-180°C for 0.3-5 hours. The component A is preferably supported on the component B which is sufficiently dried by firing at 200-600°C and has 10-50μm average particle size through the inert solvent dispersion process. The inert solvent is preferably the alkyl benzene as a starting substance from an industrial point of view.