Journal of the Chemical Society. Perkin transactions II p. 243 - 246 (1987)
Update date:2022-08-29
Topics:
Hibbert, Frank
Simpson, Gareth R.
The kinetic and equilibrium acid-base behaviour of four new highly hindered diaminonaphtalenes has been studied in aqueous solution or in Me2SO-H2O mixtures containing hydroxide ion.In concentrated aqueous sodium hydroxide solutions, 1,8-bis(dimethylamino)-2,7-diethoxynaphtalene and 1,8-bis(diethylamino)-2,7-diethoxynaphtalene are almost fully protonated and aqueous pKa values of 16.1 and 15.9, respectively, have been measured from comparative studies with other diaminonaphtalenes in 60percent (v/v) Me2SO-H2O.Studies of the protonation of 1,8-dimorpholino-2,7-dimethoxynaphtalene (pKa 13.0) and 1,8-dimorpholino-2,7-diethoxynaphtalene (pKa 12.5) were made in aqueous sodium hydroxide.The reversible acid-base reactions of the diaminonaphtalenes in the presence of hydroxide ion occur slowly.For example the approach to an equilibrium mixture of the protonated and unprotonated forms of 1,8-bis(diethylamino)-2,7-diethoxynaphtalene in 60percent (v/v) Me2SO-H2O with 0.01 mol dm-3 NaOH occurs with a half-life of 8 s.It is found that 2- and 7-substituents have large effects in increasing the basicity and decreasing the rates of proton transfer and this is due in part to an increase in strain in the amines and in the transition state for proton transfer.
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