Union Carbide plans to acquire STP from Beatrice.

The Danbury, Conn.-based company said it will pay $87 million for STP Corp. a leading producer of automotive products. STP, specializing in gasoline and motor oil additives, is based in Boca Raton, Fla., and in 1984 had revenue of about $97 million, according to Beatrice. Chicago-based Beatrice and Union Carbide both said the sale should be completed by the end of May.