- Base strengths of substituted tritylamines, N-alkylanilines, and tribenzylamine in aqueous solution and the gas phase: Steric effects upon solvation and resonance interactions
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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.
- Canle L., Moises,Demirtas, Ibrahim,Freire, Antonio,Maskill, Howard,Mishima, Masaaki
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- Magnetic CoFe2O4 nanoparticle immobilized N-propyl diethylenetriamine sulfamic acid as an efficient and recyclable catalyst for the synthesis of amides via the Ritter reaction
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A magnetic CoFe2O4 nanoparticle immobilized diamine-N-sulfamic acid (CoFe2O4@SiO2-DASA) was synthesized and used as efficient heterogeneous catalyst for the synthesis of amides via the Ritter reaction under solvent-free conditions. The magnetic nanocatalyst could be readily recovered by applying an external magnet and recycled several times without considerable loss of its catalytic activity.
- Zhao, Xiao-Na,Hu, Hai-Chuan,Zhang, Fu-Jun,Zhang, Zhan-Hui
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p. 258 - 265
(2014/07/08)
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- Microwave assisted, Ca(II)-catalyzed Ritter reaction for the green synthesis of amides
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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.
- Yaragorla, Srinivasarao,Singh, Garima,Lal Saini, Pyare,Reddy, M. Kesava
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p. 4657 - 4660
(2014/12/10)
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- Ritter reactions between alcohols and acetonitrile mediated by the conducting polymer poly-(3,4-ethylenedioxy thiophene) (Pedot)
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Herein, we report new reactivity of the conducting polymer, poly-(3,4-ethylenedioxy thiophene) (PEDOT), where PEDOT mediates a Ritter reaction between alcohols and acetonitrile. The yields were variable and in most cases competitive with results obtained using sulfuric acid. Attempts at a stoichiometric reaction between benzonitrile and diphenylmethanol are also reported herein. Finally, described here are preliminary mechanistic studies that suggest PEDOT is behaving as an alcohol-selective or specific Lewis acid. Taylor & Francis Group, LLC.
- D-Angelo, John G.,Cody, Jeremy A.,Larrabee, Christian,Ostrander, Danica J.,Rugg, Kyle W.,Mamangun, Donna
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supporting information
p. 3224 - 3232
(2014/01/06)
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- C-S bond cleavage in aromatic sulfide radical cations
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The results of our recent studies of the structural effects on the C-S bond fragmentation process of aromatic sulfur radical cations are reported.
- Lanzalunga, Osvaldo
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p. 322 - 330
(2013/07/25)
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- Preparation of different amides via Ritter reaction from alcohols and nitriles in the presence of silica-bonded N-propyl sulphamic acid (SBNPSA) under solvent-free conditions
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A number of methods have been proposed for the modification of the Ritter reaction. However, many of these methods involve the use of strongly acidic conditions, stoichiometric amounts of reagents, harsh reaction conditions and extended reaction times. Th
- Shakeri, Maryam-Sadat,Tajik, Hassan,Niknam, Khodabakhsh
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p. 1025 - 1032
(2013/03/14)
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- Amberlyst-15 as a recyclable heterogeneous catalyst for synthesis of N-tert-butylamides via Ritter-type reaction
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Highly efficient method for the preparation of N-tert-butylamides by reaction of nitriles with tert-butylacetate is described using Amberlyst-15 as a recyclable heterogeneous catalyst. Selective amidation of benzonitrile in the presence of acetonitrile was also achieved.
- Mokhtary, Masoud,Goodarzi, Gholamreza
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experimental part
p. 293 - 296
(2012/05/07)
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- Zinc chloride homogeneous catalysis in the tritylation of hydroxyl- and amide-bearing molecules
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A tritylation protocol based on the transfer of the triphenylmethylcarbenium ion from trityl acetate to substrates having hydroxyls, in the presence of catalytic amounts of ZnCl2, is described. The advantages of this method are broad scope, mild conditions, and easy handling. The comparison with the procedure based on the use of equimolar mixture of TrCl and ZnCl2 in the presence of TEA shows that comparable results are obtained. However, only this method allows reactions of secondary or benzylic alcohols such as oxidation or formation of symmetric ethers to be suppressed. Both procedures are successfully extended to simple and substituted amides. Irrespective of its low solubility in acetonitrile, even asparagine can be directly tritylated on its amide group.
- Maltese, Maurizio,Vergari, Maria Cecilia,Donzello, Maria Pia
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supporting information; experimental part
p. 483 - 487
(2011/03/18)
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- A simple synthetic protocol for the protection of amides, lactams, ureas, and carbamates
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A new procedure for protecting the amide, lactam, urea, and carbamate NH group with a triphenylmethyl (Tr) group is described. The utility of this method is illustrated with molecules that contain other functional groups. A mild deprotection using trifluoroacetic acid makes this a useful method for attaching amide groups on resin for combinatorial synthesis.
- Reddy, Dandu R,Iqbal, Mohamed A,Hudkins, Robert L,Messina-McLaughlin, Patricia A,Mallamo, John P
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p. 8063 - 8066
(2007/10/03)
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- Facile conversion of alcohols into N-substituted amides by magnesium hydrogensulfate under heterogeneous conditions
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Different classes of alcohols react efficiently with nitriles in the presence of magnesium hydrogensulfate, Mg(HSO4)2, to produce amides in high yields.
- Salehi,Khodaei,Zolfigol,Keyvan
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p. 1947 - 1951
(2007/10/03)
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