1 H NMR ( 300 MHz , DMSO - d 6 ) δ ppm 3 . 25 ( s , 3 H ) 3 . 69 ( s , 3 H ) 7 . 73 ( d , J = 8 . 69 Hz , 1 H ) 8 . 16 ( dd , J = 1 . 00 Hz , 1 H ) 8 . 42 ( s , 1 H ) 8 . 83 ( d , J = 2 . 27 Hz , 1 H )