Please help me explain reaction between Isoniazid (isonicotinylhydrazine) and sodium nitroprusside Na2[Fe(CN)5NO] (freshly prepared equal volume: 3 drops mix of sodium nitroprusside and NaOH, addition 2 drops of dilute acetic acid) to give an intense orange colour which fades slowly. If you add 3 drops of HCl, red-orange colour will change to red-brown then yellow.
I've searched for many places on google still can't found anything yet. Thanks so much in advance.