Ring-chain tautomerism in 1,3-disubstituted diazolidines has been proved an acidic catalyzed ring opening process. Chain form of 2-aryl-substituted 1,3-diazolidines can be stabilized by the resonance of positive charge on the aryl ring, leading to the removal of benzaldehyde due to the nucleophilic attack of water on the double bond of chain imines under the flux of trifluoroacetic acid. These previous studies shed light on possible reaction mechanisms of different reaction pathways in microdroplets and bulk phase in this work.