Kinetic Studies of the Reaction of Picryl Chloride with Sodium Methoxide in Methanol

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The kinetics of the reactions between sulfite ion and picramide, N-methylpicramide, and N,N-dimethylpicramide, to form 1 : 1 a-complexes in aqueous solutions of constant ionic strength 0.14 M , have been investigated using a stopped-flow spectrophotometer. Specific rate constants for the formation and decomposition of these three complexes a t 25.0 "C are 5.7 + 0.2 x lo4 M-' s-' and 7 f 1 s-', 1.4 t 0.1 x lo4 M-' s-' and 0.20 + 0.02 s-', and 4.1 t 0.2 x lo3 M -' s -' and 0.14 t 0.04 s-', respectively. Enthalpies and entropies of activation characterizing the formation of the 1 : 1 a-complexes have been determined. Equilibrium constants, determined spectrophotometrically at a number of temperatures, have been used to calculate the enthalpy ( A H 0 ) and entropy (AS0) changes associated with 1 : 1 and 2: 1 a-complex formation. These values are compared with corresponding ones for complex formation of sulfite ion with 1,3,5-trinitrobenzene and 2,4,6-trinitrobenzaldehyde. The extent of solvation of the o-complexes is considered to play a primary role in determining the observed trends in the enthalpies and entropies of reaction.On a Ctudie a I'aide d'un spectrophotomttre a debit interrompu la cinitique des reactions entre I'ion sulfite et la picramide, la N-methylpicramide et la N,N-dimithylpicramide; ces reactions conduisent a des complexes-o 1 :1 dans des solutions aqueuses de force ionique constante 0.14 M . Les constantes spicifiques de vitesse pour la formation et la dCcomposition de ces troix complexes a 25.0 "C sont respectivement egales a 5.7 + 0.2 x

Section: Introductionmentioning

confidence: 99%

Kinetic and Thermodynamic Studies of the Reactions of Sulfite Ion with Picramide, N-Methylpicramide, and N,N-Dimethylpicramide in Aqueous Solution

Buncel¹,

Norris²,

Russell³

et al. 1974

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“…A variety of o-complexes which are For personal use only. closely analogous to 3 and 4 have been characterized by nmr as well as uv-vis spectroscopy (1)(2)(3)(4)(5)(6)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22). However, there is as yet no unambiguous uv-vis or nmr evidence for the carbanions 5 and 6.…”

mentioning

confidence: 99%

Hydrogen exchange studies. XIV. Kinetics and mechanism of base-catalyzed hydrogen exchange in 1,3-dinitrobenzene in aqueous dimethylformamide and relationship with σ-complex formation

Buncel¹,

Zabel²

1981

ERWIN BUNCEL and ALLEN W. ZABEL. Can. J . Chem. 59, 3177 (1981). Kinetic data have been evaluated for hydrogen exchange in 1,3-dinitrobenzene (DNB), occurring at the 2-position, in dimethylformamide (DMF) -D,O mixtures containing deuteroxide ion. The pseudo first order rate constants for exchange, k,,,. show inverse dependence on the initial DNB concentration, which can be quantitatively related to the extent of o-complex formation in these systems. The profile fork,,,, as function of medium compositio~l exhibits a maximum at ca. 70 mol% DMF, and E ,~, for o-complex formation reaches a plateau at about the same medium composition. The equilibrium constants for o-complex formation, K,, are used to calculate the free. or uncomplexed, deuteroxide ion concentrations, which then allow one to calculate k 2 . the second order rate constants for exchange. The k, values show a uniformly increasing tendency with increased DMF content. Correlations with medium basicity are examined, and the nature of the log k, and log K, vs. H-plots afford insight into the origin of the medium dependence of proton exchange. The results of the present study are consistent with the cr-complex being an unreactive form of the substrate towards exchange, which occurs via uncomplexed DNB present in small concentration. The study also rules out the possibility that the colored species present in these systems is the carbanion formed on deprotonation of DNB.ERWIN BUNCEL et ALLEN W . ZABEL. Can. J. Chem. 59. 3177 (1981). O n a evalue les donnees cinetiques de l'echange d'hydrogene se produisant en position 2 du dinitro-1,3 benzene (DNB) dans des melanges de dimethylformamide (DMF) -D,O contenant I'ion deuteroxyde. L a constante de vitesse d e pseudo ordre un de l'echange k,,,, revele un effet inverse de la concentration initiale de DNB qui peut etre relie quantitativement aux taux deformation du complexe o dans ces systemes. 1.e profil de k,,, en fonction de la composition du milieu montre un maximum pour environ 70 molR de DMF et le E, , , de la formation du complexeo atteint un plateau pour environ la meme composition du milieu. On a utilise la constante d'equilibre d e la formation du complexe o K,, pour calculer les concentrations de I'ion deuteroxyde libre. ou non complexe qui permettent de calculer k, la constante d e vitesse d'ordre deux de I'echange. Les valeurs de k2 montrent une tendance d'augmentation uniforme avec la teneur en DMF. On a examine les correlations avec la basicite du milieu; la nature des courbes de log k, et log K, en fonction de H-fournit des renseignements sur I'origine de l'effet du milieu lors de I'echange de proton. Les resultats de la presente etude sont en accord avec un complexe o qui ne donnerait pas de reaction d'echange celui-ci se produisant par I'intermediaire du DNB non complexe present a une concentration faible. L'etude ecarte egalement la possibilite que l'espece coloree presente dans ces systemes soit le carbanion forme par la protonation du DNB.[Traduit par le journal]

“…Thus the value of K3 for picryl chloride is ca. six times smaller than the value for TNB (the corresponding ratios for reaction with methoxide ions (21) and with hydroxide ions (18,22) are 6.5 and 5. respectively) and this change is due largely to a decrease in the value of k3 while values of k-3 are similar. The value of kl for attack at the 1-position of picryl chloride is ca.…”

Section: Reaction Of Malononitrile Anion With Picry1 Chloridementioning

confidence: 70%

“…[3] for reaction of TNB. However, since here methoxide attack at the 3-position may be neglected (the equilibrium constant is known (21) to have the low value of 2.6 L mol-' ) we obtain eq. [6].…”

Section: Reaction Of Malononitrile Anion With Picry1 Chloridementioning

confidence: 99%

Kinetic and equilibrium studies of the σ-adduct forming reactions of 1,3,5-trinitrobenzene and picryl chloride with some carbon bases

Crampton¹,

Kee²,

Wilcock³

1986

. Can. J. Chem. 64, 1714Chem. 64, (1986. Reaction of 1,3,5-trinitrobenzene (TNB) with the malononitrile anion in methanol yields a carbon-bonded cr-adduct, (3). Ionisation of the remaining exocyclic hydrogen is favourable and yields the dianion (4). The initial reaction of 1-chloro-2,4,6-trinitrobenzene similarly occurs at an unsubstituted rlng position, but is followed by slower nucleophilic attack at the 1-position yielding the substituted product. A major difference In the reaction of the ethyl malononitrile anion with TNB is that the adduct formed (11) has no readily dissociable proton. Hence, here, conversion to the carbon-bonded adduct is less favourable. Kinet~c and equilibrium data are reported for these reactions and are compared with data for adduct formation involving methoxide ions. MICHAEL R. CRAMPTON, TERENCE P. KEE et JENNIFER R. WILCOCK. Can. J. Chem. 64, 1714Chem. 64, (1986.La rCaction du trinitro-1,3,5 benzkne (TNB) avec I'anion malononitrile, dans le mCthanol, conduit A un produit conduisant a la formation d'un adduit-a liC a un carbone (3). L'ionisation de l'hydrogkne exocyclique residue1 est favorable et conduit au dianion 4. La rCaction initiale du chloro-l trinitro-2,4,6 benzene se produit de la m8me manikre a la position non-substituCe du cycle; toutefois, elle est suivie d'une attaque nuclCophile plus lente au niveau de la position 1 qui conduit au produit substituC. Une diffkrence importante dans la reaction de l'anion Cthylmalononitrile avec le TNB est que l'adduit qui se forme, 11, ne porte pas de proton dissociable. Alors, sa conversion en un adduit liC par le carbone est moins favorable. On rapporte les donnCes cinetiques et dlCquilibre de ces rCactions et on les compare avec les donnCes obtenues pour la formation d'adduits impliquant les ions mCthylates.[Traduit par la revue]Many carbon-bonded a-adducts have been characterised from the reactions of activated aromatic molecules with carbon bases (1, 2). However, relatively few kinetic studies of these systems have been reported, due in part to the difficulty of generating the nucleophiles under conditions suitable for such :tudies. A notable exception here is the work of Kavhlek, StCrba, and co-workers which showed that carbanions generated from malonic acid derivatives were suitable nucleophiles (3-5).In this paper w e report kinetic and equilibrium data for the reactions of malononitrile anion with 1,3,5-trinitrobenzene and with picryl chloride (1-chloro-2,4,6-trinitrobenzene) in methanol, and equilibrium data for reaction of the ethyl malononitrile anion with 1,3,5-trinitrobenzene. The results are important in that the equilibrium constants give a measure of the carbon basicities of the nucleophiles (thermodynamic affinity for carbon) while the rate constants measure their nucleophilicity and nucleofugality. There is current interest in the comparison of these quantities for different types of nucleophile, and in different types of reaction (6, 7). Results and discussion Acidities of malononitrile and ethjl malononitrile in m...