Properties of bases in acetonitrile as solvent—III1Hydrogen bonding between protonated and free nitrogen bases

Coetzee, J. F.; Padmanabhan, G. R.; Cunningham, Glenn P.

doi:10.1016/0039-9140(64)80020-5

Cited by 65 publications

(21 citation statements)

References 6 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Reaction C7 includes the well-known homoconjugation reaction of anions in ACN (10). TMP, TPP, or TMM in ETOH + acid: Similar results are obtained if TFAcH is added to solutions of TPP or TMP in EtOH solvent.…”

Section: Voltammetric Results For Tmm In Acn Solutionssupporting

confidence: 63%

3,4-Disubstituted derivatives of 1,2,5-thiadiazole 1,1-dioxide. Ethanol addition reactions and electroreduction of 3-methyl-4-phenyl and 3,4-dimethyl derivatives in acetonitrile and ethanol solvents

Caram¹,

Mirífico²,

Aimone³

et al. 1996

Can. J. Chem.

View full text Add to dashboard Cite

3-Methyl-4-phenyl-l,2,5-thiadiazole 1,l-dioxide (TMP), as well as 3,4-dimethyl-1,2,5-thiadiazole 1,l-dioxide (TMM), react with ethanol (EtOH), which adds to one of their C=N double bonds. The equilibrium constants for the addition reaction are measured in mixed acetonitrile (ACN) -EtOH solvents by means of UV spectroscopy in the case of TMP, and by I3c NMR spectroscopy in the case of TMM, since TMM presents only terminal UV absorption. Both equilibrium constants are also estimated through cyclic voltammetry (CV) experiments. In the case of TMP, the ethanol molecule adds to the C=N bond located on the methyl-substituted side of the substrate, according to 13c NMR spectroscopy and CV results. The electroreduction characteristics of the substrates and their ethanol addition products are studied using CV techniques in ACN, EtOH, and ACN-EtOH solvent mixtures. The radical anion formed by the first electron transfer to TMM is unstable and decomposes rapidly while that corresponding to T M P undergoes a relatively slow homogeneous second-order reaction with the substrate (k = 3 x lo2 M-' S-I). The equilibrium constant for EtOH addition and the voltammetric properties of the substrates are compared with those of the previously studied 3,4-diphenyl derivative (TPP).Key words: electrochemistry, thiadiazoles, structure-reactivity relations, kinetics.

show abstract

Section: Voltammetric Results For Tmm In Acn Solutionssupporting

confidence: 63%

3,4-Disubstituted derivatives of 1,2,5-thiadiazole 1,1-dioxide. Ethanol addition reactions and electroreduction of 3-methyl-4-phenyl and 3,4-dimethyl derivatives in acetonitrile and ethanol solvents

Caram¹,

Mirífico²,

Aimone³

et al. 1996

Can. J. Chem.

View full text Add to dashboard Cite

show abstract

“…From the set of amines under investigation, piperidine demonstrates the strongest tendency to form homoconjugates. The homoconjugation constant for piperidinium cation, which is 25 M-' (25), indicates that in the range of piperidine concentration (0.0 186-0.623 M, Table 2) used, the equilibrium between piperidinium cation and its homoconjugated form can be observed. Both forms exist in comparable amounts for a concentration of piperidine equal to 1 x lo-* M. With increasing concentration of piperidine above M, the bulk of the piperidinium cation exists as the homoconjugate.…”

Section: Conductometric Measurementsmentioning

confidence: 98%

Study of the dissociation of the products of some proton transfer reactions in acetonitrile solvent

Galezowski¹,

Jarczewski²

1992

Can. J. Chem.

View full text Add to dashboard Cite

WLODZIMIERZ GALEZOWSKI and ARNOLD JARCZEWSKI. Can. J. Chem. 70, 935 (1992) The conductometric study of the products of the proton transfer reactions of C-acids (nitriles, nitroalkanes, and 2,4,6-trinitrotoluene) with the strong amine bases (I ,l,3,3-tetramethylguanidine (TMG), 1,8-diazabicyclo[5.4.O]undec-7-ene (DBU), 1,8-bis(dimethy1amino)naphthalene (DMAN), and piperidine) in acetonitrile shows their large degree of dissociation into free ions. The dissociation constant values have been estimated at 25'C to be larger than I X lo-' M. This weakens the formalism commonly accepted in spectrophotometric kinetic studies of these systems of reactions, based on the assumption that the product is an ion pair. Spectrophotometric equilibrium and kinetic measurements provided evidence that reverse reaction is a second-order process (pseudo-first order because cation concentration is controlled by side reactions). The influence of the common cation (TMGH+) on the equilibria of the proton abstraction from 2-methyl-1-(4-nitropheny1)-1-nitropropane and 4-nitrophenylcyanomethane with TMG base in acetonitrile at 25'C was examined and was found to be compatible with the assumption of large dissociation of the reaction product for free ions. "Equilibrium constants" estimated by the Benesi and Hildebrand method (which assumes an ion-pair product) decreased with increasing concentration of added TMGH+ cation, but these "equilibrium constants" multiplied by [TMGH+] are constant. The observed pseudo-first-order rate constants of the proton transfer reaction, measured at large excess of the base over C-acid, grow with the cation concentration due to the increase of the backward reaction rate. The concentration of added common cation shows a negligible influence on the observed rate constants of deuteron transfer reaction. Thus, as a result of side reactions, in which extra amounts of cation are formed, some second-order rate constants kfH and also kinetic isotope effects (KIEs) (k:'/kF) that have been measured in acetonitrile can be substantially overestimated.Key words: ion-pair dissociation, proton transfer reactions, kinetic isotope effects. .O]undCc-7-t n e (DBU), 1,8-bis(dim6thylamino)naphtaltne (DMAN) et pipkridine) dans I'acCtonitrile montre qu'ils sont fortement dissociCs en ions libres.A 25"C, on a CvaluC que les constantes de dissociation sont plus grandes que 1 x M. Ces rksultats affaiblissent le formalisme gCnCralement accept6 dans les Ctudes cinktiques spectrophotomCtriques de ces systemes de rkactions, qui est bask sur I'hypothtse que le produit est une paire d'ions. L'Cquilibre spectrophotomCtrique et les mesures cinCtiques fournissent des donnCes suggCrant que la reaction inverse est du deuxitme ordre (pseudo-premier ordre parce que la concentration des cations est contr61Ce par des rCactions parasites). OpCrant B 2572, dans 17acCtonitrile, on a examin6 I'influence du cation commun (TMGH+) sur 1'Cquilibre de la rCactions d'enltvement du proton du 2-methyl-I-(4-nitrophCny1)-I-nitropropane et du 4-nitrophCnylcyanom...

show abstract

“…It is the purpose of this communication to draw attention to the sensitive pH-dependence ofhydrogenbonding in (AHA)or (BHB)+ systems, and its possible biochemical significance. Although equilibria involving complexing between acid and conjugate base HA+A--* AHAor base and conjugate acid B + BH+ -BHB+ (la) (lb) have been proposed in the interpretation of conductimetric and potentiometric studies (Muney & Coetzee, 1962;Bruckenstein & Mukherjee, 1962;Kolthoff & Chantooni, 1963;Coetzee et al, 1964;Pawlak, 1973) necessarily implying the equations given here, no explicit discussion appears to have been made along the present lines.…”

mentioning

confidence: 94%

“…Numerous organic bases, including pyridine, quinoline, imidazole, methylimidazole, benzimidazole, thiazole and morpholine, form complexes of this type (Clements et al, 1973a,b,c,d). In only a few cases have the association constants K been measured, and these appear to be very sensitive to the solvent, values ranging from 4.0 for the pyridine complex (Coetzee et al, 1964), in methyl cyanide, to about 3350 for the n-butylamine complex in nitrobenzene (Pawlak, 1973) (the units are not given, but probably are M-1).…”

mentioning

confidence: 99%

pH-controlled hydrogen-bonding (Short Communication)

Wood

1974

Biochemical Journal

View full text Add to dashboard Cite

The pH-dependence of the degree of hydrogen-bonding between a base and its conjugate acid is considered. When only a small proportion of the total base is complexed, the amount complexed is proportional to (1+coshp)(-1) where p=2.303 (pK(a)-pH), pK(a) being the dissociation constant of the conjugate acid. This represents sharp pH-dependence. As the proportion complexed increases, the curve broadens, eventually becoming flat-topped, with more than half the base complexed over the range of pH values pK(a)+/-logKC, approximately. (K is the complex association constant and C is the formal base concentration, including all forms.) There are similarities to the extent of mono-protonation of a dibasic acid.

show abstract

Properties of bases in acetonitrile as solvent—III1Hydrogen bonding between protonated and free nitrogen bases

Cited by 65 publications

References 6 publications

3,4-Disubstituted derivatives of 1,2,5-thiadiazole 1,1-dioxide. Ethanol addition reactions and electroreduction of 3-methyl-4-phenyl and 3,4-dimethyl derivatives in acetonitrile and ethanol solvents

3,4-Disubstituted derivatives of 1,2,5-thiadiazole 1,1-dioxide. Ethanol addition reactions and electroreduction of 3-methyl-4-phenyl and 3,4-dimethyl derivatives in acetonitrile and ethanol solvents

Study of the dissociation of the products of some proton transfer reactions in acetonitrile solvent

pH-controlled hydrogen-bonding (Short Communication)

Contact Info

Product

Resources

About