Basicity of substituted 2-phenyl-1,1,3,3- tetramethylguanidines and other bases in acetonitrile solvent
1989; NRC Research Press; Volume: 67; Issue: 4 Linguagem: Inglês
10.1139/v89-089
ISSN1480-3291
AutoresKenneth T. Leffek, Przemysław Pruszyński, Kohila Thanapaalasingham,
Tópico(s)Photochemistry and Electron Transfer Studies
ResumoA series of 30 phenyl substituted derivatives of 2-phenyl-1,1,3,3-tetramethylguanidine was synthesized and the pK a value of each was measured in acetonitrile using a conventional, general purpose glass electrode. The slope of the Hammett relationship, for the para and meta substituted compounds, ρ = 2.18 ± 0.16, is significantly lower than ρ = 2.85 ± 0.06 found for anilines in water, even though the phenyl ring is attached directly to the basic centre in both cases. The influence of electronic and steric effects on the basicity of the compounds is discussed. The solvent effect on the basicity is also discussed, by comparison of the pK a values in acetonitrile and water. The mean value of [Formula: see text] is slightly higher than the value previously observed for ammonia and aliphatic amines, [Formula: see text]. Additionally, the pKa values were measured for seven other cyclic bases, including 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and 1,5-diazabicyclo[4.3.0]non-5-ene (DBN). Keywords: 2-phenyl-1,1,3,3-tetramethylguanidines, pK a measurements.
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