Arsinic acids are organoarsenic compounds with the formula R2AsO2H. They are formally, but not actually, related to arsinic acid, a hypothetical compound of the formula H2AsO2H. Arsinic acids are monoprotic, weak acids. They react with sodium sulfide to give the dithioarinates R2AsS2Na. Arsinic acids are related to phosphinic acids (R2PO2H.).