a method for the preparation of 4 - fluoro - α -- y - oxo - n - β - diphenylbenzenebutanamide also known as 2 -- 2 - oxo - 1 - phenylethyl ]- 4 - methyl - 3 - oxo - pentanoic acid phenylamide of the formula i containing about 0 . 1 % or less of α -- γ - oxo - n - p - diphenylbenzene butanamide , about 0 . 05 % or less of difluoro - α -- y - oxo - n - β - diphenylbenzene butanamide and about 0 . 1 % or less of 3 -- 2 - oxo - 1 - phenyl - ethoxy ]- 4 - methyl - pent - 2 - enoic acid phenylamide .