Offers natural yellow food color. defination: presenting riboflavin-5-phosphate, a natural yellow, perfect substitute for tartrazine, e 102. e 101 (ii) riboflavin-5-phosphate synonyms: riboflavin-5-phosphate sodium class: isoalloxazine einecs: 204-988-6 chemical name: monosodium (2r, 3r, 4s)-5-(3)10-dihydro-7, 8-dimethyl-2, 4-dioxo-10-benzo[]pteridinyl)-2, 3, 4-trihydroxypentyl phosphate chemical formula: for the dihydrate form: c17h20n4nao9p2h2o & for the anhydrous form: c17h20n4nao9p molecular weight: 541, 36.