Abstract: A method for preparing .alpha.-(4-isobutylphenyl)propionic acid or its precursor is here disclosed which comprises the following steps (I), (II) and (III):step (I): subjecting isobutylbenzene and a polyalkylbenzene to disproportionation reaction in order to form p-isobutylethylbenzenestep (II): dehydrogenating p-isobutylethylbenzene obtained in the step (I) to form p-isobutylstyrene, andstep (III): the following step (IIIa) or (IIIb):step (IIIa): reacting p-isobutylstyrene obtained in the step (II) with carbon monoxide and hydrogen to prepare .alpha.-(4-isobutylphenyl)propionaldehyde, orstep (IIIb): reacting p-isobutylstyrene obtained in the preceding step (II) with carbon monoxide and water or a lower alcohol to prepare .alpha.-(4-isobutylphenyl)propionic acid or its alkyl ester.

Abstract: A method for preparing .alpha.-(4-isobutylphenyl)propionic acid or its precursor is here disclosed which comprises a step A of forming p-isobutylstyrene from p-isobutylethylbenzene and a step B of forming .alpha.-(4-isobutylphenyl)propionaldehyde from p-isobutylstyrene or a step C of forming .alpha.-(4-isobutylphenyl)propionic acid or its alkyl ester from p-isobutylstyrene.Furthermore, a method for preparing said p-isobutylethylbenzene is also disclosed which comprises alkylating isobutylbenzene or 4-ethyltoluene with ethylene or propylene.

Abstract: A method for producing p-alkylstyrene which is characterized in that side reaction scarcely occurs, catalyst and unreacted material are easily recovered for the reuse, the p-position selectivity is excellent and yield of aimed product is high. In the method, monoalkylbenzene having an alkyl group with 3 or more carbon atoms is reacted with acetaldehyde in the presence of hydrogen fluoride catalyst under the conditions of a temperature of 0.degree. C. or lower, a molar ratio of 2 to 100 in "alkylbenzene/acetaldehyde", the other molar ratio of 1.7 to 300 in "hydrogen fluoride/acetaldehyde", the proportion of hydrogen fluoride to the sum of hydrogen fluoride and water in the reaction system of 65% by weight or higher, and the concentration of acetaldehyde in the reaction system of 1.0% by weight or lower to obtain 1,1-bis(p-alkylphenyl)ethane, and then subjecting it to catalytic cracking at a temperature in the range of 200.degree. to 650.degree. C. in the presence of an acid catalyst.

Abstract: A method for producing arylethylene comprising four steps of: (I) bringing 1,1-diarylethane into contact with an acid catalyst in the presence of an inert gas to crack said compound into arylethylenes and alkylbenzenes; (II) separating the reaction mixture obtained in the above cracking step (I) into at least a fraction mainly containing 1,1-diarylethane; (III) bringing said fraction mainly containing 1,1-diarylethane into contact with hydrogen gas in the presence of a hydrogenation catalyst; and (IV) re-cracking hydrogenated fraction obtained in the preceding hydrogenation step (III) by bringing it into said cracking step (I).Particularly, this method is useful for producing p-isobutylstyrene which is a starting material for preparing a valuable medicine of ibuprofen.