title: Deprotonation equilibrium of 5-tropolonediazonium salt strongly favors 1,2,5-tropoquinone-5-diazide structure in certain solvents.
abstract: 5-Tropolonediazonium salt 1 is a well-known intermediate for the preparation of 5-substituted tropolone derivatives, but 1,2,5-tropoquinone-5-diazide 2, which is expected to be formed by deprotonation of 1, has not been reported. We synthesized 2, and the structures of 1 and 2 were investigated and compared. NMR and UV spectral data indicated that 1 is easily deprotonated in water, methanol, DMSO, and DMF and exists in the form of 2 in these solvents (but not in acetone or acetonitrile) because of its strong acidity (estimated pKa -2.07). Thus, the acid-base equilibrium shows strong solvent-dependence. Compound 2 may be synthetically available as a carbene precursor.
authors.affiliation: Research Foundation Itsuu Laboratory, 2-28-10 Tamagawa, Setagaya-ku, Tokyo 158-0094, Japan. aito@ac.shoyaku.ac.jp
authors.forename: Ai
authors.initials: A
authors.lastname: Ito
authors.forename: Hideaki
authors.initials: H
authors.lastname: Muratake
authors.forename: Koichi
authors.initials: K
authors.lastname: Shudo
mesh_terms: D001386:Azides / Q000138:chemical synthesis / Q000737:chemistry*; D004121:Dimethyl Sulfoxide / Q000737:chemistry*; D004126:Dimethylformamide / Q000737:chemistry*; D000432:Methanol / Q000737:chemistry*; D015394:Molecular Structure; D011522:Protons; D012492:Salts / Q000138:chemical synthesis / Q000737:chemistry; D012997:Solvents / Q000737:chemistry; D014334:Tropolone / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: C584627:1,2,5-tropoquinone-5-diazide; D001386:Azides; D011522:Protons; D012492:Salts; D012997:Solvents; D014867:Water; D014334:Tropolone; D004126:Dimethylformamide; D000432:Methanol; D004121:Dimethyl Sulfoxide