.beta.,.beta.'-Dithiodipropionic acid 1119-62-6 3,3'-Dithiobis(dipropionic acid) 3,3'-Dithiodipropionic acid Dithiodipropionic acid NSC18841 Propanoic acid, 3,3'-dithiobis- Propionic acid, 3,3'-dithiodi-