Reactivity of fluorenylideneketene towards amines. A laser photolysis study with ultraviolet and infrared detection

Lucas, Nanci C. de; Netto‐Ferreira, José Carlos; Andraos, John; Lusztyk, J.; Wagner, Brian D.; Scaiano, J. C.

doi:10.1016/s0040-4039(97)01115-5

Cited by 26 publications

(7 citation statements)

References 18 publications

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“…It was not possible to time resolve the formation of this transient, as it is formed during the laser pulse (≤10 ns). These transients were assigned to the ketenes 4 , 5 , and 6 , respectively, in agreement with earlier reports 3,17,19-21 as well as with previously published results using infrared detection laser flash photolysis 1 Transient absorption spectra measured after 308 nm laser excitation of 1 (76 μs after laser pulse), 2 (30 μs after laser pulse), and 3 (0.4 μs after laser pulse) in ACN solution.…”

Section: Resultssupporting

confidence: 91%

Nucleophilicity toward Ketenes: Rate Constants for Addition of Amines to Aryl Ketenes in Acetonitrile Solution

Lucas

Andraos

et al. 2001

J. Org. Chem.

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Second-order rate constants (k(Nu)) have been measured for the addition of amines to ketenes 4-6 in acetonitrile solution by the laser flash photolysis technique. These ketenes are formed from a photochemical Wolff rearrangement of diazoketones 1-3, respectively. For all diazoketones studied, the presence of amines as nucleophiles in the reaction medium results in the formation of an intermediate that later converts to the amide. The rate of formation of these intermediates is linearly dependent on amine concentration. Various classes of amines, such as primary, secondary, and tertiary, aromatic, and aliphatic, have been used to investigate the ketene reactivity, and rate constants in the range 10(4)-10(9) M(-1) s(-1) have been measured. Reaction rates are dependent upon steric effects in both the ketene and the nucleophile, which is consistent with a reaction mechanism involving nucleophilic attack at Calpha in the molecular plane of the ketene. On the basis of these data, a set of N(+) parameters for the reaction of amines with ketenes was determined.

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Section: Resultssupporting

confidence: 91%

Nucleophilicity toward Ketenes: Rate Constants for Addition of Amines to Aryl Ketenes in Acetonitrile Solution

Lucas

Andraos

et al. 2001

J. Org. Chem.

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“…Further support for this is found when estimates are made of second-order rate constants at ambient temperatures using the thermokinetic parameters obtained in Table and then are compared with known solution phase kinetic determinations. Laser flash photolysis experiments in acetonitrile solution of fulvenones 2 and 3 reacting with pyridine yield second-order quenching rate constants of 2.72 × 10 8 and 1.31 × 10 7 M -1 s -1 , respectively, at room temperature . Results from extrapolations of thermokinetic data obtained here on these systems yield rate constants that are 13 orders of magnitude too slow.…”

Section: Resultsmentioning

confidence: 63%

“…These results are discussed in light of the physical interpretations of rate constant, k , heterogeneity index, α, and thermokinetic parameters and the structure of the matrix. In addition, comparisons are made with solution phase kinetic studies done on the same systems by laser flash photolysis in aqueous and acetonitrile solutions at room temperature. Caveats related to using the technique of matrix isolation spectroscopy at low temperatures as a tool for performing kinetics experiments are also presented.…”

Section: Introductionmentioning

confidence: 99%

Bimolecular Kinetics at Low Temperatures Using FTIR Matrix Isolation Spectroscopy: Some Caveats. Thermokinetic Parameters for the Reaction of Fulvenones with Pyridine in Pyridine Matrixes

Andraos

2000

J. Phys. Chem. A

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The bimolecular kinetics of addition of pyridine to fulvenone (1), benzofulvenone (2), and dibenzofulvenone (3) in pyridine matrixes at 15 to 70 K have been investigated by FTIR matrix isolation spectroscopy. A detailed kinetic analysis reveals a one-to-one correspondence between the disappearance of ketenes and the appearance of the corresponding ketene-pyridine zwitterions ("ketene ylides") formed upon nucleophilic addition. Perturbed second-order kinetics according to the Kohlrausch model were found to describe the data adequately, whereas pseudo-first-order and strict second-order kinetics did not. These results indicate that the bimolecular reaction examined takes place in a heterogeneous medium where distributions of second-order rate constants are obtained. The heterogeneity index, R, obtained from the model varies from 0.35 to 0.56. These findings are consistent with the matrix model proposed by Raff in which the structure of the pyridine matrix is composed of inhomogeneous fast sites where the magnitude of the true reaction rate for chemical reaction exceeds the diffusion rates of both ketene and pyridine molecules. Arrhenius and Eyring thermokinetic parameters obtained from these data reveal that the barrier for reaction under these conditions is very small (less than 1 kcal mol -1 ) with a very large negative entropy of activation (ca. -80 cal K -1 mol -1 ). When compared with analogous solution phase kinetic results from laser flash photolysis experiments, it is concluded that the kinetics observed at these low-temperature conditions are largely that of matrix reorganization. This sets a lower limit for the rates and an upper limit for the activation parameters of the actual chemical reactions. Furthermore, identical magnitudes for E A , ∆H q , and ∆S q are found even when they are calculated from secondorder rate constants based on the incorrect bimolecular model applicable to homogeneous media. It is suggested that the technique of dynamic matrix isolation spectroscopy is not adequate to obtain chemically meaningful activation parameters in bimolecular reactions. Caveats are also pointed out concerning the experimental interpretations of nonlinear Arrhenius plots obtained in cryogenic matrixes, implicit assumptions about the constancy of medium properties in the construction of Arrhenius and Eyring plots, and the calculation of thermokinetic parameters from data fits to linear forms of the Arrhenius and Eyring equations.

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“…87 The addition of amines to ketenes has been widely studied in acetonitrile solutions. 82b,88 The direct addition of an amine to a ketene leads to the formation of a zwitterionics species that tautomerizes to the final amide 71 if a primary or secondary amine is used, or dealkylates by alkene loss 89 strength of several amines toward addition to ketenes has been studied by laser flash photolysis. Secondary amines are stronger nucleophiles than tertiary ones suggesting that the base acts as a nucleophile by direct attack to the ketene carbon atom.…”

Section: Reactions Of Ketenes Derived From the Wolff Rearrangement Wimentioning

confidence: 99%

3.19 The Wolff Rearrangement

Candeias

Trindade

Góis

et al. 2014

Comprehensive Organic Synthesis II

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Reactivity of fluorenylideneketene towards amines. A laser photolysis study with ultraviolet and infrared detection

Cited by 26 publications

References 18 publications

Nucleophilicity toward Ketenes: Rate Constants for Addition of Amines to Aryl Ketenes in Acetonitrile Solution

Nucleophilicity toward Ketenes: Rate Constants for Addition of Amines to Aryl Ketenes in Acetonitrile Solution

Bimolecular Kinetics at Low Temperatures Using FTIR Matrix Isolation Spectroscopy: Some Caveats. Thermokinetic Parameters for the Reaction of Fulvenones with Pyridine in Pyridine Matrixes

3.19 The Wolff Rearrangement

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