Proton bonding to 1,8‐bis(dialkylamino)naphthalenes

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Abstract
Proton NMR spectra of 1,8‐bis(dimethylamino)naphthalene and 1,8‐bis(diethylamino)‐naphthalene (MPS and EPS) solutions to which acetic acid or trifluoroacetic acid (TFA) has been added exhibit several characteristic features caused by proton exchange phenomena. In the presence of less than one mole of TFA per mole of diamine the protonated and unprotonated forms can be observed separately. The proton in the protonated amine resonates at unusually low field (∼20 ppm). When more TFA is added another proton signal at low field, between 18 and 12 ppm down field from TMS, is observed. The nature of the latter proton resonance is discussed. The proton in the amine is probably in a bridge between the two nitrogen atoms, since no magnetic inequivalence is observed for the four methyl or ethyl groups attached to the nitrogen. In the presence of acetic acid instead of TFA the proton in the amine molecule changes places with the other protons in the solution. From the temperature‐dependence of the spectra the activation energy for the exchange of D+ between amine molecules has been estimated. The possible use of MPS as a probe for the investigation of hydrogen bonding phenomena in carboxylic acid solutions in non‐aqueous solvents is indicated.
Funding Information
  • Central Laboratory TNO