Amine basicities in benzene and in water

Frenna, Vincenzo; Vivona, Nicolò; Consiglio, Giovanni; Spinelli, Domenico

doi:10.1039/p29850001865

Cited by 101 publications

(103 citation statements)

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“…21 The pK a of the conjugate acids of most reactive amines (G, H, and A) is 11.3, while the pK a of the conjugate acids of less reactive amines (I-K) is 10.8. 22,23 Sterics can be used to rationalize the difference in reactivity within these subgroups.…”

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confidence: 99%

Identification of diamine linkers with differing reactivity and their application in the synthesis of melamine dendrimers

Moreno

Simanek

2008

Tetrahedron Letters

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Diamine linkers for the synthesis of dendrimers based on melamine were identified using competition reactions. The relative reactivity of the cyclic monoamines surveyed vary in relative reactivity by 40 times, expanding the previously identified series to an overall relative reactivity range of 320 times. Azetidine is 40 times more reactive than the cyclic, nine-membered ring (C 8 H 17 N), and 320 times more reactive than benzylamine. Reactivity differences are attributed to pKa values and sterics. Incorporating these groups into diamines provides linkers that can be employed in dendrimer synthesis. Specifically, the nucleophilicity of the individual amine groups comprising 3-aminoazetidine, 3-aminopyrrolidine, and 4-aminopiperidine vary by 100 times, 70 times, and 20 times, respectively. These linkers are incorporated into a generation three dendrimer.Our group has invested significant energies in the synthesis of dendrimers based on triazines, also referred to as dendrimers based on melamine deriving from our use of diamine linkers. 1, 2 Our early targets commonly incorporated p-aminobenzylamine because of the significant differences in the reactivity of the amines of this group. That is, during a convergent synthesis, protecting group manipulations and functional group interconversions could be avoided because the benzylic amine would react preferentially (essentially exclusively) with the monochlorotriazine dendron being elaborated. 1,[3][4][5][6][7] The low stability of these aniline derivatives required reasonable, but additional, care on handling. While the use of distilled solvents and inert atmospheres are not uncommon, nor is the requirement for refrigerated storage of intermediates, we recognized that these precautions could impact the broader acceptance of these materials.The low cost and high reactivity of piperazine soon made it a linking diamine of choice for our investigations. However, when using piperazine, dimerization of monochlorotriazines was observed under non-ideal reaction conditions that were usually attributed to concentration, rate of addition, ineffective stirring or lack thereof, temperature of addition and the magnitude of stoichiometric excess. 4,[8][9][10][11][12][13][14][15][16][17][18] Reactions with either p-aminobenzylamine or piperazine could be readily followed by NMR. The shift of the benzylic protons on reaction with the monochlorotriazine dendron or the desymmetrization of methylene groups of the piperazine group were diagnostic. The use of piperazine led to the undesirable formation of dimers, unfortunately. Detecting these dimers by NMR proves difficult due to signal degeneracy between the desired asymmetric monoamine and the symmetric dimer.

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confidence: 99%

Identification of diamine linkers with differing reactivity and their application in the synthesis of melamine dendrimers

Moreno

Simanek

2008

Tetrahedron Letters

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“…Even the value for C1-NS4 is unusual if compared with the protonation of tertiary amines in plain water (triethylamine has a log K value of 10.68 in water [23] ). However, the logarithmic protonation constant for C1-NS4 measured in water is log K = 7.0, a value very similar to that observed in water/TritonX-100.…”

Section: Resultsmentioning

confidence: 99%

Fluorescent Sensors for Hg²⁺ in Micelles: A New Approach that Transforms an ON–OFF into an OFF–ON Response as a Function of the Lipophilicity of the Receptor

Pallavicini

Fernandez

Foti

et al. 2006

Chemistry A European J

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A new approach to the use of micelles in the fluorescent sensing of metal cations is proposed and applied to the case of Hg2+. We demonstrate how it is possible to transform a system from an ON–OFF to an OFF–ON sensor by changing the length of the chain used to lipophilise a ligand that resides inside TritonX‐100 micelles together with pyrene as the fluorophore. Three tetrathia‐monoaza macrocyclic ligands have been synthesised with the same ring but functionalised on the nitrogen atom with a methyl (C1‐NS4), an n‐butyl (C4‐NS4) or an n‐dodecyl (C12‐NS4) chain. The three ligands have been fully characterised in water containing TritonX‐100 micelles by means of potentiometric titrations and their apparent protonation and complexation constants with Hg2+ were determined. On the basis of the distribution diagrams obtained, the more lipophilic C12‐NS4 has been developed as an ON–OFF fluorescent sensor for mercury: working at pH<4, in the absence of Hg2+ the ligand is inside the micelles, protonated and non‐quenching, while on addition of mercury the [C12‐NS4Hg]2+ complex forms which remains inside the micelles and is quenching. On the other hand, the ligand of intermediate chain length, C4‐NS4, can be used to obtain an OFF–ON sensor at 7.07.0 the ligand is unprotonated, it stays inside the micelles and is quenching, while addition of Hg2+ in the 7.0–9.5 pH range results in the formation of [C4‐NS4Hg]2+, which is hydrophilic enough to leave the micelles and to be released into the bulk solution where it is no longer capable of quenching pyrene fluorescence. Additional studies on C1‐NS4, C3‐NS4 and C8‐NS4 indicate that the optimal chain length to observe this OFF–ON behaviour is C3–C4.

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“…In the light of some our previous results on the MRH in benzene in the presence of amines 17 we can suppose that higher orders pathways depend on a catalysis-of-catalysis mechanism. That is, because of the interaction between the N α −H hydrogen of the side chain with the amine a partial positive charge is created on the nitrogen of amine.…”

Section: Comments On the Behavior Of 3d-f In Toluene With Aminesmentioning

confidence: 99%

“…16 The present result, also in the light of the results of a DFT study of the course of the reaction in the uncatalyzed pathway, 7j allows to definitively exclude these two hypotheses and clearly support our previous idea of a catalysis-of-catalysis. 17 As a matter of fact in the presence of BuA 3d-f does react via both a second-and a thirdorder pathway (both paths really contributing to the rearrangement).…”

Section: Comments On the Behavior Of 3d-f In Toluene With Aminesmentioning

confidence: 99%

“…If at this nitrogen atom are linked hydrogen atoms, this fact can cause the interaction with a second molecule of amine determining the occurrence of a catalysis-of-catalysis. In a previous study on MRH 17 to confirm the occurrence of general-base-catalysis in apolar solvents and of a catalysis-of-catalysis pathway we carried out a series of kinetics in the presence of mixtures of amines, eg. of BuA and TEA.…”

Section: Comments On the Behavior Of 3d-f In Toluene With Aminesmentioning

confidence: 99%

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New examples of specific-base catalysis in mononuclear rearrangements of heterocycles found via a designed modification of the side-chain structure

D’Anna¹,

Frenna²,

Guernelli

et al. 2009

Arkivoc

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To select suitable candidates for the occurrence of specific-base-catalysis in MRH of (Z)-hydrazones of 3-benzoyl-5-phenyl-1,2,4-oxadiazole we have designed a modification of the side-chain structure by linking a strong electron-withdrawing system to the hydrazono group. Thus we have synthesized the (Z)-semicarbazone (3d), the (Z)-phenylsemicarbazone (3e), and the (Z)-acetylhydrazone (3f) of the above oxadiazole and examined their kinetic behavior in dioxane/water in a large range of proton concentrations (pS + 4.0−14.5). In all the pS + range examined only a base-catalyzed process has been evidenced (no uncatalysed path occurs). The behavior at the largest pS + values (the reactivity tends to a limiting rate constant) and that at variable concentrations of buffer have furnished clear evidence for the occurrence of a specificbase-catalysed process, thus reaching the target proposed and confirming the prevision.

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Amine basicities in benzene and in water

Cited by 101 publications

References 1 publication

Identification of diamine linkers with differing reactivity and their application in the synthesis of melamine dendrimers

Identification of diamine linkers with differing reactivity and their application in the synthesis of melamine dendrimers

Fluorescent Sensors for Hg²⁺ in Micelles: A New Approach that Transforms an ON–OFF into an OFF–ON Response as a Function of the Lipophilicity of the Receptor

New examples of specific-base catalysis in mononuclear rearrangements of heterocycles found via a designed modification of the side-chain structure

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Amine basicities in benzene and in water

Cited by 101 publications

References 1 publication

Identification of diamine linkers with differing reactivity and their application in the synthesis of melamine dendrimers

Identification of diamine linkers with differing reactivity and their application in the synthesis of melamine dendrimers

Fluorescent Sensors for Hg2+ in Micelles: A New Approach that Transforms an ON–OFF into an OFF–ON Response as a Function of the Lipophilicity of the Receptor

New examples of specific-base catalysis in mononuclear rearrangements of heterocycles found via a designed modification of the side-chain structure

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Fluorescent Sensors for Hg²⁺ in Micelles: A New Approach that Transforms an ON–OFF into an OFF–ON Response as a Function of the Lipophilicity of the Receptor