Acidity and N-methylation of N-aryl-N ′-cyanoguanidines †

Cunningham, Ian D.; Cox, Brian G.; Wan, Nan Chi; Povey, David C.; Smith, G. W.

doi:10.1039/a900953a

Cited by 3 publications

(3 citation statements)

References 13 publications

(7 reference statements)

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“…Similar principles have been used by other authors. [13][14][15][16] The formal replacement of sp 2 bonded oxygen atom by another superstrong double-bonded substituent, dC(CN) 2 , in derivatives of formic, cyanoformic, or similar carboxylic acids leads to various cyano-substituted vinyl alcohols. For example, the pK a of tricyanovinyl alcohol, (NC) 2 CdC(CN)OH, in aqueous solution has been estimated by Boyd 14 to be around -5, thus definitely exceeding the acidity of H 2 SO 4 , HNO 3 , etc.…”

Section: Introductionmentioning

confidence: 99%

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Generalized Principle of Designing Neutral Superstrong Brønsted Acids

et al. 2002

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A generalized principle of designing superstrong Brønsted acids is suggested according to the following scheme: M=O --> M=Z(X)(n). It consists of the formal replacement of =O fragment in carbonyl, sulfonyl, etc. groups in various acidic systems (e.g., CH(3)CHO, FSO(3)H, where M is the CH(3)CH= or FSO(2)H=fragment, respectively) by =NSO(2)F, =NCN, =C(CN)(2), =P(SO(2)F)(3), =S(CN)(4), or any other formally bivalent group =Z(X)(n) (where the formal valency of the central atom Z is n + 2), leading to highly acidic systems (e.g., HC(=P(CN)(3))NH(2), FS(=C(CN)(2))(2)OH, etc.). It is demonstrated that in several cases the introduction of the double-bonded substituent at the central atom (e.g., N, C, P, S, Cl) that carries the potentially acidic proton or the acidity site (e.g., OH, NH(2), CH(3), etc. groups) will lead to the enormous (up to ca. 120 kcal/mol or 88 pK(a) units!) increase of the intrinsic acidity of the respective parent acid. The acidity of the resulting acids and the scope and limitations of the principle are explored using density functional theory calculations at B3LYP 6-311+G level. Some of the resulting acids (or their anions) were found to undergo fragmentation in the course of the geometry optimization. The general trend that follows from the results of the calculations is that the stability of the resulting compounds is influenced by both the M and the Z. If M is a first row element (carbon or nitrogen), then stable species are produced with almost any Z. If M is a second row element (sulfur or phosphorus), then the species with first row Z are mostly predicted to be stable, but most of the species with second row Z are expected to undergo fragmentation during the geometry optimization. The Z = N and Z = C derivatives (e.g., =NSO(2)CF(3), =C(CN)(2), =C(SO(2)CF(3))(2), etc.) are predicted to be the most stable. However, they have relatively modest electron-accepting power as compared to their penta-, hexa-, and heptavalent counterparts. The acidifying effects of the =Z(X)(n)() groups with the same X increase with increasing n: =NCN < =C(CN)(2) < =P(CN)(3) < =S(CN)(4) and =NSO(2)F < =C(SO(2)F)(2) < =P(SO(2)F)(3). Also, the acidifying effect of a fluorosulfonyl-substituted substituent is higher than that of the corresponding cyano-substituted substituent.

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Section: Introductionmentioning

confidence: 99%

“…In the case of trivalent Z − nitrogen atom − and X as SO 2 F or SO 2 CF 3 , we obtain the Yagupolskii substituents. For X = NO 2 and X = CN, one obtains the substituents described in ref and references therein. For n = 2, Z = C, and X = CN, one obtains the above-mentioned C(CN) 2 substituent. , …”

Section: Introductionmentioning

confidence: 99%

Generalized Principle of Designing Neutral Superstrong Brønsted Acids

et al. 2002

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“…The compound N-(4-chlorophenyl)-NA-cyanoguanidine 1, prepared from 4-chloroaniline and dicyanamide, 9 is weakly acidic. 10 Treatment of 1 with BuLi and excess MeI yielded N-(4-chlorophenyl)-NA-cyano-N,NB,NB-trimethylguanidine 2 (Scheme 1) as a mass of small microcystals (56 mg, 17% yield). 11 Preliminary X-ray crystallographic analysis of one of these crystals indicated a chiral space group P2 1 2 1 2 1 .…”

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confidence: 99%

Total spontaneous resolution of a cyanoguanidine showing only conformational chirality

2000

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Kinetic study of nitrosation of guanidines

Fernández

Hervés

Parajó

2008

J of Physical Organic Chem

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The kinetics of the nitrosation reaction of three guanidines, dicyandiamide, N,N(-dimethyl-N 00 -cyanoguanidine and guanidine have been studied. The nitrosation rate is first order with respect to both the guanidine and acid concentration. The absence of catalysis by nucleophilic anions, the observed general acid-base catalysis and the observed deuterium isotope effect lead us to propose mechanism for the nitrosation of guanidines similar to that which operates in the case of the amides and ureas, in which a slow proton transfer is the rate determining step. From this mechanism we were able to obtain the values of the rate constants for the nitrosation and denitrosation processes. The catalytic constants in presence of buffers were also obtained and the analysis of the Brö nsted slopes suggests a process with a transition state more similar to reactants than products.

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Acidity and N-methylation of N-aryl-N ′-cyanoguanidines †

Cited by 3 publications

References 13 publications

Generalized Principle of Designing Neutral Superstrong Brønsted Acids

Generalized Principle of Designing Neutral Superstrong Brønsted Acids

Total spontaneous resolution of a cyanoguanidine showing only conformational chirality

Kinetic study of nitrosation of guanidines

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