in a process for producing a tetrabromophthalic diester composition , a liquid reaction mixture is prepared comprising tetrabromophthalic anhydride , a c 2 to c 6 polyhydric aliphatic alcohol and an alkylene oxide selected from the group consisting of ethylene oxide and propylene oxide , said reaction mixture being substantially free of an organic solvent . while agitating the reaction mixture , the temperature of the reaction mixture is raised to at least 50 ° c . to allow the tbpa to react with the paa and ao to produce a diester composition . the reaction is terminated when the diester composition has an acid value equal to or less than 0 . 25 mg koh / gm of the diester composition .