Process for the preparation of liquid mixtures of alkylated 2-(2-hydroxyphenyl)benzotriazoles

An improved process for the preparation of a mixture of 2-(2-hydroxyphenyl)-benzotriazoles which is liquid at room temperature by alkylating 2-(2-hydroxy-5-methylphenyl)-benzotriazole with a C.sub.8 -C.sub.14 -alpha-olefin in the melt at elevated temperature, in the presence of a sulfonic acid catalyst, wherein the improvement consists essentially of

• (i) employing not less than 0.5 mol of acid catalyst and only 1.5 to 3 moles of alpha-olefin per each mole of 2-(2-hydroxy-5-methylphenyl)-benzotriazole,
• (ii) carrying out the alkylation reaction in the temperature range from 165.degree. to 190.degree. C.,
• (iii) separating the upper crude product phase from the lower sulfonic acid phase, and
• (iv) isolating the final product mixture by working up said crude product phase by distillation using a thin-film evaporator, a thin-film evaporator fitted with a distillation column or a short-path distillation apparatus.