1,3-Dioxacycloheptane 1,3-Dioxepan 1,3-Dioxepane 1,3-Dioxepin, tetrahydro- 1,4-Butanediol formal 505-65-7 EINECS 208-015-6 Formaldehyde, cyclic tetramethylene acetal NSC 62077 Tetramethylene formal