Basicity of substituted 2-phenyl-1,1,3,3- tetramethylguanidines and other bases in acetonitrile solvent

Abstract

A series of 30 phenyl substituted derivatives of 2-phenyl-l,l,3,3-tetramethylguanidine was synthesized and the pKa 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, p = 2.18 + 0.16, is significantly lower than p = 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 pKa values in acetonitrile and water. The mean value of Ap~tN-H20 = 8.1 + 0.5 is slightly higher than the value previously observed for ammonia and aliphatic amines, A p~p -H 2 0 = 7.5 * 0. On a synthCtisC une skrie de 30 phtnyl-2 tttramCthyl-1,1,3,3 guanidines substitutes sur le noyau phCnyle et, utilisant une electrode de verre conventionnelle d'usage general, on a mesure les valeurs de leur pK, dans llacCtonitrile. Lapente de la relation de Harnmett, pour les composCs substituks en mPta et en para, p = 2,18 0,16, est beaucoup plus faible que la valeur de p = 2,85 2 0,06 qui a kt6 observee pour les anilines dans l'eau, m&me si le noyau phtnyle est attache directement au centre basique dans chacun des cas. On discute de I'influence des effets sttriques et electroniques sur la basicit6 des composCs. En se basant sur une comparaison des valeurs des pKa dans l'acttonitrile et dans l'eau, on discute aussi de I'effet du solvant sur la basicit&. La

Basicity of substituted 2-pyridyl-1,1,3,3-tetramethylguanidines and aminopyridines in acetonitrile and water solvents

“…of 0.994. This relationship is complementary to the phenylTMG series previously published (1) and gives a range of bases in acetonitrile from a pK,, of 3.0 up to 23.9 (for DBU (1) It is interesting to note that all the bases fall on the same correlation line despite the fact that the aminopyridine bases are protonated on the ring nitrogen atom, while the pyridylTMG bases are protonated on the N-2 atom of the T M G group, although no doubt considerably delocalized onto the N-1 and the N-2 atoms (9). Thus the solvent effect does not depend on the environment of the proton in the conjugate acid of the base, nor does it depend upon specific solvation of the picrate anion, since Coetzee and Padmanabhan (2) …”

“…Hammett plots may be constructed for all of the pyridylTMG compounds in Table 1 (1,5) for the substituents on the pyridine ring, both relative to the position of the TMG group, to give Co in Table 1. These are described by eqs.…”

“…The relationship between the pK, values in acetonitrile and water for the bases in the present study is represented by eq. [1], with a correlation coefficient (c.c.) of 0.994.…”

Synthesis and basicity of 2-N-quinolyl- and 2-N-isoquinolyl-1,1,3,3-tetramethylguanidines

“…This work continues the study of the basicity of 2-N-substituted 1,1,3,3-tetramethylguanidines (TMG) in water and acetonitrile solvents (1,2). A series of 2-N-quinolyl (1) and isoquinolyl (2) derivatives have been prepared from the analogous aminoquinoline compounds and their pK,'s determined, together with those of the starting materials.…”

Study of the properties of pyridine-2-azo-p-phenyltetramethylguanidine as a metal ion complexing agent

“…This was confirmed (21) by a correlation of the pK of the conjugate acids and u for 12 meta-and para-substituted 2-phenyl-l , 1,3,3-tetramethylguanidines, from which it was calculated that up for the TMG group was -0.80.…”