Solid state phase behaviors of dodecyldimethylamine oxide: protonation and counterion effects

Solid phase behaviors of dodecyldimethylamine oxide (C12DAO) studied by differential scanning calorimetry and X-ray scattering have shown clearly the effects of protonation. Besides the protonated (cationic) (C12DAO HCl) and the nonionic (C12DAO) species, 1:1 composition or hemihydrochloride (C12DAO 1/2 HCl) was shown to be a stable complex. The phase behavior of C12DAOHCl was similar to that of dodecylammonium chloride rather than dodecyltrimethylammonium chloride (C12TACl), although similar crystal structure was suggested for C12DAOCl and C12TABr. Solid phase behaviors changed dramatically by changing the counterion from Cl− to NO3− or SO42− for both the cationic and 1:1 species.