Chevron Chemical, a Chevron subsidiary, said it will close the the alkylbenzene manufacturing plant in Richmond, Calif., later this year and reassign its 18 workers to other jobs at the refinery . . . Singer Co. reported that it has completed the acquisition of Textron's Belmont, Calif.-based Dalmo Victor division for $174 million . . . Todd-AO, 85%-owned by United Artists Communications, said it purchased the Glen Glenn Sound division of Republic Corp., excluding real estate, for about $8.9 million.