Thermodynamics of protonation of substituted pyridines in aqeous solutions

Chakrabarty, M. R.; Handloser, Carolyn S.; Mosher, Melvyn W.

doi:10.1039/p29730000938

Cited by 21 publications

(12 citation statements)

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“…Since the pyridine nitrogen is more basic than the hydroxy group, it should be protonated first. HMPY is a stronger base ( K a = 3.9 × 10 -6 ) , than 4-pyridinecarboxaldehyde ( K a = 1.8 × 10 -5 ). , Even at pH 7, the pyridine nitrogen is, at least to some degree, protonated. In addition, the protonation of the pyridine N atom should not influence the reduction potential very significantly since this site is removed from the reacting group.…”

Section: Resultsmentioning

confidence: 99%

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A Time-Resolved SERS Study of the Adsorption and Electrochemical Reduction of 4-Pyridinecarboxaldehyde and 4-(Hydroxymethyl)pyridine

et al. 1998

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The electroreduction processes of both 4-pyridinecarboxaldehyde, 4-ALPY, and 4-(hydroxymethyl)pyridine, 4-HMPY, have been studied in aqueous solution on a Ag electrode using surface-enhanced Raman spectroscopy, SERS, and cyclic voltammetry, CV. Each electrode process was investigated at pH 3 and at pH 7 in 0.1M KCl electrolyte. SERS spectra show that both the neutral 4-ALPY and a species which is protonated on the aldehyde group (Py-CHOH + ) adsorb on the roughened Ag electrode surface with an end-on orientation through the pyridine nitrogen, but the species with a protonated ring (H + Py-CHO) prefers adsorption with a face-on orientation through its π-system. The electrochemical reduction of ALPY produces a common product, 1,2-bis(4-pyridyl)ethane (BPE), in both acidic and basic media. The major reaction process was studied by time-resolved SERS, TR-SERS, in the time range of 0.1 to 30 ms. A transient intermediate appears at 3.0 ms and is suggested to be the pinicol Py-CH(OH)CH(OH)-Py on the basis of a Gaussian 94 ab initio frequency calculation. It disappears by 10 ms, at which time the BPE product spectrum is established. The reduction of HMPY also undergoes similar reaction pathways in both acidic and neutral pH conditions, and the major product is the same in either condition. A striking fact is that the reduction of HMPY on Ag produces the same product as that of the ALPY, i.e., 1,2-bis(4-pyridyl)ethane (BPE). The surface species for the reactants and the product on the Ag electrode have been identified by SERS, and vibrational assignments of these species have been made.

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Section: Resultsmentioning

confidence: 99%

“…The protonated forms of the species are related to these unprotonated species by the following reactions: ,− Both H + Py−CHO and Py−CHO are electroactive.…”

Section: Introductionmentioning

confidence: 99%

A Time-Resolved SERS Study of the Adsorption and Electrochemical Reduction of 4-Pyridinecarboxaldehyde and 4-(Hydroxymethyl)pyridine

et al. 1998

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“…In addition to that, we synthesized quinolyl based indenyl ligands and quinolyl based cp-ligands as well. [20][21][22][23][24] [a]: To the best of our knowledge no experimental pK a value is available in literature.…”

Section: Synthesis Of New Ligands and Complexesmentioning

confidence: 99%

“…The donor strength increases from left to right. [ 20 , 21 , 22 , 23 , 24 ] [a]: To the best of our knowledge no experimental pK a value is available in literature.…”

Section: Introductionmentioning

confidence: 99%

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The Stronger the Better: Donor Substituents Push Catalytic Activity of Molecular Chromium Olefin Polymerization Catalysts

Hansen

Wadepohl

Enders

2021

Chemistry A European J

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The donor strength of bifunctional pyridine-cyclopentadienyl ligands was altered systematically by the introduction of donating groups in the para-position of the pyridine. In the resulting chromium complexes an almost linear correlation between donor strength and the nitrogenchromium distance as well as the electronic absorption maximum is experimentally observed. The connection of electron-donating groups in the ligand backbone leads to an efficient transfer of the electronic influences to the catalytically active metal centre without restricting it through steric effects. Therefore, catalytic olefin polymerization activity, which is already very high for the previously studied catalysts, increase considerably by attaching para-amino groups to the chelating pyridine or quinoline, respectively. Combining electron-rich indenyl ligands with para-amino substituted pyridines lead to the highest catalytic activities observed so far for this class of organo chromium olefin polymerisation catalysts. The resulting polymers are of ultra-high molecular weight and the ability of the catalysts to incorporate comonomers is also very high.

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Anhydride Activation by 4‐Dialkylaminopyridines and Analogs (n → π*)

Tandon

Zipse

2016

Lewis Base Catalysis in Organic Synthesis

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Thermodynamics of protonation of substituted pyridines in aqeous solutions

Cited by 21 publications

References 0 publications

A Time-Resolved SERS Study of the Adsorption and Electrochemical Reduction of 4-Pyridinecarboxaldehyde and 4-(Hydroxymethyl)pyridine

A Time-Resolved SERS Study of the Adsorption and Electrochemical Reduction of 4-Pyridinecarboxaldehyde and 4-(Hydroxymethyl)pyridine

The Stronger the Better: Donor Substituents Push Catalytic Activity of Molecular Chromium Olefin Polymerization Catalysts

Anhydride Activation by 4‐Dialkylaminopyridines and Analogs (n → π*)

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