Arsinic acids are organoarsenic compounds with the formula R<sub>2</sub>AsO<sub>2</sub>H. They are formally, but not actually, related to arsinic acid, a hypothetical compound of the formula H<sub>2</sub>AsO<sub>2</sub>H. Arsinic acids are monoprotic, weak acids. They react with sodium sulfide to give the dithioarinates R<sub>2</sub>AsS<sub>2</sub>Na. Arsinic acids are related to phosphinic acids (R<sub>2</sub>PO<sub>2</sub>H.).
Well known arsinic acids include diphenylarsinic acid and cacodylic acid, R<sub>2</sub>AsO<sub>2</sub>H (R = Ph, Me, respectively).