Abstract: Process for the production of at least one compound that is selected from among monoalkyl aromatic compounds, dialkyl aromatic compounds and trialkyl aromatic compounds by alkylation or transalkylation of an aromatic compound by at least one alkylating agent that is selected from among the olefins, whereby the process is characterized in that it is carried out in one or two stages, involving two reaction zones in series, whereby one of these two zones can be switched off so as to be able, depending on whether or not one of the zones is switched off, to meet the demand either of the three types of mono, di- and trialkyl aromatic compounds, or two of these types or a single one of the types of mono- or di- or trialkyl aromatic compounds.

Abstract: Synthetic oil that contains wholly or partly of dialkylbenzenes and/or partially or totally hydrogenated dialkylbenzenes. The synthetic oil according to the invention can also be used as an oil base or oil base additive and comprises at least one dialkylbenzene and/or at least one partially or totally hydrogenated dialkylbenzene and meets the general chemical formula: R1—A—R2 in which R1 and R2 represent alkyl groups and A is a benzene core and/or a cyclohexane core and/or a cyclohexene core and/or a cyclohexadiene core and is characterized in that it contains between 1 and 20% by weight or ortho isomers and in that at least one of the alkyl groups is attached for the most part to group A by carbon 2 of the aliphatic chain. The two alkyl groups are preferably attached for the most part to group A by carbon 2 of the aliphatic chain.