1596-25-4Relevant articles and documents
Base strengths of substituted tritylamines, N-alkylanilines, and tribenzylamine in aqueous solution and the gas phase: Steric effects upon solvation and resonance interactions
Canle L., Moises,Demirtas, Ibrahim,Freire, Antonio,Maskill, Howard,Mishima, Masaaki
, p. 5031 - 5039 (2004)
The dissociation constants of the conjugate acids of N-tritylacetamide (1h; pKBH+ = 3.81) and N-benzyl-N-methyl-4,4′, 4″- trimethoxytritylamine (4i; pKBH+ = 9.86) have been measured in aqueous acetonitrile at 25 °C and at other temperatures to determine the enthalpies and entropies of reaction. For 1h, ΔH = 40.7 kJ·mol-1 and ΔS = 64 J·K -1·mol-1, and for 4i ΔH = 9.1 kJ·mol-1 and ΔS = -159 J·K-1·mol-1. In addition, gas-phase base strengths at 25 °C (GB values in kJ·mol-1) of TrNH 2 (1a; 902.1), TrNHPh (1c; 926.3), TrNHAc (1h; 929.7), TrNHC 6H4(o-NO2) (1i; 895.0), DMTrNH2 (3a; 921.3), DMTrNHCH2CO2Me (3b; 879.1), and DMTrNH(p-NO 2Bn) (3d; 886.6) have been determined by ICR measurements. The GB of TrNHAc corresponds to protonation at oxygen and B3LYP/6-31G* calculations indicate that the N-protonated isomer is 46.4 kJ·mol-1 less stable, i.e. the GB value for N-protonation is 883.3 kJ·mol-1. Correspondingly, the literature GB value of 857.6 5 kJ·mol-1 for N-methylacetamide corresponds to protonation at oxygen, and B3LYP/6-31G* calculations indicate that the N-protonated isomer is 58.1 kJ·mol-1 less stable, i.e. the GB value for N-protonation of MeNHAc is 799.5 kJ·mol-1. The GB of PhNH(tBu) (5; 920.1 kJ·mol-1) has been measured and compared with values for other N-alkylanilines, PhNHR, including PhNHTr; the results indicate that the increasing GB values as R increases in size are due solely to the increasing polarisability of R. This indicates that the increasing solution base strength of PhNHR as R increases in size is a solvation effect and is not due to decreasing resonance interactions between the nitrogen lone-pair and the phenyl ring. Similarly, the base-strengthening effect in solution of the (substituted) trityl in TrNHZ, where Z is an alkyl with an electron-withdrawing group, is shown to be due to solvation phenomena as it is absent in the gas phase; for one such compound, TMTrNHCH2CO2Me (4b; pKBH+ = 9-30), ΔH = 17.9 kJ·mol-1 and ΔS = -118 J·K-1·mol -1. In contrast, the difference in solution base strengths between MeNHAc (pKBH+ = -0.56) and TrNHAc (pKBH+ = 3.81) is attributed, at least in part, to a reduced base-weakening resonance interaction between the lone pair on N and the acetyl group in TrNHAc, as the effect is also evident in the gas phase. The GB value for tribenzylamine (6) has also been measured (965.2 kJ·mol-1) and is unexceptional; this indicates that the low base strength of 6 in aqueous solution (pKBH+ = 4.90 at 25 °C) is a solvation effect which is expressed mainly through an abnormally large positive entropy of reaction (ΔS = 76 J·K-1·mol-1), the value of ΔH (50.5 kJ·mol-1) being only slightly larger than normal for tertiary amines. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.
Microwave assisted, Ca(II)-catalyzed Ritter reaction for the green synthesis of amides
Yaragorla, Srinivasarao,Singh, Garima,Lal Saini, Pyare,Reddy, M. Kesava
, p. 4657 - 4660 (2014/12/10)
An efficient solvent-free synthesis of amides by Ca(II) catalyzed Ritter reaction has been reported under microwave irradiation. This green protocol tolerates the substrate diversity and delivers the high yielding amides with minimal loading of inexpensive and more abundant Ca(II) catalyst.
C-S bond cleavage in aromatic sulfide radical cations
Lanzalunga, Osvaldo
, p. 322 - 330 (2013/07/25)
The results of our recent studies of the structural effects on the C-S bond fragmentation process of aromatic sulfur radical cations are reported.
