46835-92-1Relevant academic research and scientific papers
Solvolytic Behavior of Aryl and Alkyl Carbonates. Impact of the Intrinsic Barrier on Relative Reactivities of Leaving Groups
Mati?, Mirela,Kati?, Matija,Denegri, Bernard,Kronja, Olga
supporting information, p. 7820 - 7831 (2017/08/14)
The effect of negative hyperconjugation on the solvolytic behavior of carbonate diesters has been investigated kinetically by applying the LFER equation log k = sf(Ef + Nf). The observation that carbonate diesters solvolyze faster than the corresponding carboxylates and that the enhancement of aromatic carbonates is more pronounced indicates that the negative hyperconjugation and π-resonance within the carboxylate moiety is operative in TS. The plots of ΔG? vs approximated ΔrG° for solvolysis of benzhydryl aryl/alkyl carbonates and benzhydryl carboxylates reveal that a given carbonate solvolyzes over the higher Marcus intrinsic barrier and over the earlier transition state than carboxylate that produces an anion of similar stability. Due to the lag in development of the electronic effects along the reaction coordinate, the impact of the intrinsic barrier on solvolytic behavior of carbonates is more important than in the case of carboxylates and phenolates. Consequently, the solvolytic reaction constants (sf) are generally lower for carbonates than for carboxylates. Because of considerable lower reaction constants of carbonates, an inversion of relative reactivities between aryl/alkyl carbonate and another leaving group of similar nucleofugality (Nf) may occur if the electrofuge moiety of a substrate is switched.
Solvolytic Behavior of Aliphatic Carboxylates
Matic, Mirela,Denegri, Bernard,Kronja, Olga
supporting information, p. 1477 - 1486 (2015/10/05)
The leaving group abilities (nucleofugalities) of a series of aliphatic carboxylates have been obtained by determining the nucleofuge-specific parameters (Nf and sf) from solvolysis rate constants of X,Y-substituted benzhydryl carboxylates in a series of aqueous ethanol mixtures by applyication of the linear free energy relationship (LFER) equation: log k = sf (Ef + Nf). These values can be employed to compare reactivities of carboxylates with those of other leaving groups previously included in the nucleofugality scale, and also to estimate the solvolysis rates of various carboxylates. It is confirmed that the inductive effect is the most important variable governing the reactivities of halogenated carboxylates in solution. Moreover, both the Hammett correlation and the solvolytic activation parameters have revealed a strong influence of the inductive effect on the nucleofugality of alkyl-substituted carboxylates. The reaction constants (sf) indicate that carboxylate substrates with weaker leaving groups solvolyze via later, more carbocation-like, transition states, which is in accord with the Hammond postulate. In addition, due to the weaker demand for solvation of transition states that produce more strongly stabilized benzhydrylium ions, in which more efficient charge delocalization occurs, the reaction constants (sf) obtained with most of the leaving groups investigated here increase as the polarity of the solvent decreases.
Fe2(SO4)3·xH2O on silica: An efficient and low-cost catalyst for the direct nucleophilic substitution of alcohols in solvent-free conditions
Li, Lingjun,Zhu, Anlian,Zhang, Yuqin,Fan, Xincui,Zhang, Guisheng
, p. 4286 - 4291 (2014/01/17)
Fe2(SO4)3·xH2O on silica has been found to be a novel efficient catalyst for the direct nucleophilic substitution of alcohols in solvent-free conditions. In this reaction system, the alcohols can react with various nucleophilic reagents for the convenient construction of C-C bonds and C-N bonds with the benefits of high conversion, no requirement to use excessive amounts of the nucleophile, only a catalytic amount of iron catalyst required, solvent-free and benign reaction conditions, and the feasible reusability of the catalyst.
Ambident reactivities of formaldehyde n,n-dialkylhydrazones
Maji, Biplab,Troshin, Konstantin,Mayr, Herbert
, p. 11900 - 11904 (2013/11/19)
What can attack at carbon? With a nucleophilicity N≈7 for attack at the azomethine carbon, formaldehyde hydrazones can undergo noncatalyzed reactions at room temperature with electrophiles that have a reactivity parameter E that is greater than -12. Copyright
Nucleofugality and nucleophilicity of fluoride in protic solvents
Nolte, Christoph,Ammer, Johannes,Mayr, Herbert
supporting information; experimental part, p. 3325 - 3335 (2012/06/17)
A series of p-substituted benzhydryl fluorides (diarylfluoromethanes) were prepared and subjected to solvolysis reactions, which were followed conductometrically. The observed first-order rate constants k1(25 °C) were found to follow the correlation equation log k1(25 °C) = sf(Nf + Ef), which allowed us to determine the nucleofuge-specific parameters Nf and sf for fluoride in different aqueous and alcoholic solvents. The rates of the reverse reactions were measured by generating benzhydrylium ions (diarylcarbenium ions) laser flash photolytically in various alcoholic and aqueous solvents in the presence of fluoride ions and monitoring the rate of consumption of the benzhydrylium ions by UV-vis spectroscopy. The resulting second-order rate constants k-1(20 °C) were substituted into the correlation equation log k-1 = sN(N + E) to derive the nucleophilicity parameters N and sN for fluoride in various protic solvents. Complete Gibbs energy profiles for the solvolysis reactions of benzhydryl fluorides are constructed.
Nucleophilic reactivities of tertiary alkylamines
Ammer, Johannes,Baidya, Mahiuddin,Kobayashi, Shinjiro,Mayr, Herbert
supporting information; experimental part, p. 1029 - 1035 (2011/07/09)
The kinetics of the reactions of tertiary amines, triethylamine (1a), N-methylpyrrolidine (1b), N-methylpiperidine (1c), and N-methylmorpholine (1d) with benzhydrylium ions (Ar2CH+) have been studied in acetonitrile and dichlorometha
Nucleophilicity and nucleofugality of phenylsulfinate (PhSO 2-): A key to understanding its ambident reactivity
Baidya, Mahiuddin,Kobayashi, Shinjiro,Mayr, Herbert
supporting information; experimental part, p. 4796 - 4805 (2010/06/17)
Second-order rate constants for the reactions of the phenylsulfinate ion PhSO2- with benzhydrylium ions Ar2CH + have been determined in DMSO, acetonitrile, and aqueous acetonitrile solution using laser-flash and stopped-flow techniques. The rate constants follow the correlation equation log k (20 °C) = s(N + E), which allows the determination of the nucleophile-specific parameters N and s for PhSO2- in different solvents. With N = 19.60, PhSO 2- is a slightly weaker nucleophile than malonate and azide ions in DMSO. While PhSO2- reacts with highly stabilized benzhydrylium ions to give benzhydryl phenyl sulfones exclusively, highly reactive benzhydrylium ions give mixtures of sulfones Ar 2CH-SO2Ph and sulfinates Ar2CH-OS(O)Ph; the latter rearrange to the thermodynamically more stable sulfones through an ionization recombination sequence. Sulfones generated from PhSO2 - and stabilized amino-substituted benzhydrylium ions undergo heterolysis in aqueous acetonitrile and the rate of formation of the colored benzhydrylium ions was followed spectrophotometrically by stopped-flow techniques. The ranking of the electrofugalities of the benzhydrylium ions (i.e., the relative ionization rates of Ar2CH-SO2Ph) was not the inverse of the ranking of their electrophilicities (i.e., the relative reactivities of Ar2CH+ with nucleophiles), which was explained by differences in Marcus intrinsic barriers. While sulfones are thermodynamically more stable than the isomeric sulfinates, the intrinsic barriers for the attack of benzhydrylium ions at the oxygen of PhSO 2- are significantly lower than the intrinsic barriers for S-attack, and the activation energies for the attack of carbocations at sulfur are only slightly smaller than those for attack at oxygen. Because reactions of PhSO2- with carbocations of an electrophilicity E > -2 (i.e., carbocations which are more reactive than Ph3C+) are diffusion-controlled, the regioselectivities of the reactions of PhSO 2- with ordinary carbocations do not reflect relative activation energies.
Generation of diarylcarbenium ion poolsviaelectrochemical C-H bond dissociation
Okajima, Masayuki,Soga, Kazuya,Watanabe, Takashi,Terao, Kimitada,Nokami, Toshiki,Suga, Seiji,Yoshida, Jun-Ichi
experimental part, p. 594 - 599 (2009/11/30)
The "cation pools" of diarylcarbenium ions have been generated by the low-temperature electrochemical oxidation of diphenylmethane derivatives. In addition to diphenylmethanes having various substituents, 9,10-dihydroanthracene, dibenzosuberane, and xanth
Dynamics of the transient species generated upon photolysis of diarylmethanes within zeolites - Deprotonation and oxidation reactions
Shea, Suzanne,Schepp, Norman P.,Keirstead, Amy E.,Cozens, Frances L.
, p. 1637 - 1648 (2007/10/03)
The oxidation of diarylmethanes is a multistep process involving initial formation of a radical cation, deprotonation of the radical cation to the radical, and oxidation of the radical to the carbocation. The dynamics and efficiency of the last two steps in this process, namely deprotonation and oxidation, in acidic zeolites and non-acid zeolites are examined in the present work as a function of the acidity of the diarylmethane radical cations and the oxidation potential of the diarylmethyl radicals. Our results indicate that rate constants for deprotonation strongly depend on the acidity of the radical cations, but not on the composition of the zeolites. In addition, oxidation of the radicals to the diarylmethyl cations is strongly dependent on both the oxidation potential of the radicals and the oxidizing ability of the zeolite. This dependence allows oxidation potentials of the zeolites to be estimated.
The role of aromatic radical cations and benzylic cations in the 2,4,6-triphenylpyrylium tetrafluoroborate photosensitized oxidation of ring-methoxylated benzyl alcohols in CH2Cl2 solution
Branchi, Barbara,Bietti, Massimo,Ercolani, Gianfranco,Angeles Izquierdo,Miranda, Miguel A.,Stella, Lorenzo
, p. 8874 - 8885 (2007/10/03)
A steady-state and laser flash photolysis (LFP) study of the TPPBF 4-photosensitized oxidation of ring-methoxylated benzyl alcohols has been carried out. Direct evidence on the involvement of intermediate benzyl alcohol radical cations and benzylic cations in these reactions has been provided through LFP experiments. The reactions lead to the formation of products (benzaldehydes, dibenzyl ethers, and diphenylmethanes) whose amounts and distributions are influenced by the number and relative position of the methoxy substituents. This behavior has been rationalized in terms of the interplay between the stabilities of benzyl alcohol radical cations and benzyl cations involved in these processes. A general mechanism for the TPPBF 4-photosensitized reactions of ring-methoxylated benzyl alcohols has been proposed, where the a-OH group of the parent substrate acts as the deprotonating base promoting α-C-H deprotonation of the benzyl alcohol radical cation (formed after electron transfer from the benzyl alcohol to TPP*) to give a benzyl radical and a protonated benzyl alcohol, precursor of the benzylic cation. This hypothesis is in contrast with previous studies, where formation of the benzyl cation was suggested to occur from the neutral benzyl alcohol through the Lewis acid action of excited TPP+ (TPP*).
