117-34-0Relevant articles and documents
Kinetics and Mechanisms of the Reactions of Ketenes with Water and Alcohols in Dioxane Solutions
Poon, Nai L.,Satchell, Derek P.N.
, p. 1485 - 1490 (1986)
The spontaneous addition of water to diphenyl- and to dimethyl-ketene in dioxane-H2O and dioxane-D2O mixtures is third order in the stoicheiometric water concentration, s, when s H2O/kD2O = 1.7-2.3 for all the systems studied.The addition of ethanol to diphenylketene in dioxane-ethanol mixtures has a kinetic pattern very similar to that for addition of water to this ketene, except that the change to a lower order occurs when s = 5M.The variation of the activation parameters with medium composition is also very similar for all these spontaneous additions: at low water or ethanol concentrations Ea = 1+/- 1 kcal mol-1, and ΔS++ = -60 +/- 8 cal K-1 mol-1; at higher concentrations Ea rises somewhat, and ΔS++ becomes less negative.The results are considered in the light of previous work.It is concluded that water and alcohol add to ketenes by a common mechanism in non-hydroxylic solvents of low dielectric constant, and that this involves a cyclic, hydrogen-bonded transition state such as (1).Hydroxide ions (ca. 5*1E-3M) have no effect on the rate of water addition in dioxane, but hydrogen ions have powerful effects: the addition to diphenylketene is inhibited, that to dimethylketene is catalysed.These observations are explained.The isotope effect kH3O+/kD3O+ = 1.9 for the catalysis.We propose a catalytic mechanism with a cyclic transition state (3) involving a dominant slow proton transfer to the ketene β-carbon atom.
A Comparison of the Mechanism of Hydrolysis of Diphenylketene and Dimethylketene in Diethyl Ether Solution
Poon, Nai L.,Satchell, Derek P. L.
, p. 1381 - 1383 (1983)
The spontaneous hydrolysis of diphenylketene in diethyl ether solution at 25 deg C is first order in the ketene concentration and third order in the stoicheiometric water concentration; unlike the hydrolysis of dimethylketene, it is not-auto-catalytic and hydrolysis is negligibly catalised by added carboxylic acids.Added boron trifluoride strongly inhibits the hydrolysis of diphenylketene in ether but powefully catalyses that of dimethylketene; the formation of the strong Broensted acid H2OBF3 (association constant K = 120 +/- 20 l mol-1 at 25 deg C) underlines these effects.A pKa value of ca. 0.5 is deduced for this acid and the results as a whole point to the marked inability of diphenylketene , compared with dimethylketene, to accept protons from Broensted acids.Predominantly nucleophilic attack on the ketene is, however, easier for the diphenyl-derivative whose spontaneous hydrolysis varies between ca. 5- and ca. 40-fold faster over the range of stoicheoimetric water concentrations used.
The mechanism of the reaction of diphenylketene with bases in aqueous solution: Nucleophilic attack versus general base catalysis of ketene hydration
Andraos,Kresge
, p. 5643 - 5646 (1992)
Diphenylketene was generated in aqueous solution by flash photolysis, and rates of its decay accelerated by 30 bases of various structure were determined. The rate constants so obtained did not show the regular dependence on basic strength expected if the bases were serving as general base catalysts assisting the attack of water on the ketene, but they did vary with polarizability and steric bulk of the base in the way expected for direct nucleophilic attack of the base on the carbonyl carbon atom of the ketene. Assignment of a direct nucleophilic role to the bases is supported by the formation of amide products in addition to diphenylacetic acid in the reaction of diphenylketene accelerated by ammonia and morpholine, and quantitative analysis of the product ratios shows that these two bases serve only as nucleophiles and that the diphenylacetic acid is formed by uncatalyzed reaction of diphenylketene with solvent water.
COBALT-CATALYZED SYNTHESIS OF α-ARYLPROPIONIC AND DIARYLACETIC ACIDS
Francalanci, F.,Gardano, A.,Foa, M.
, p. 277 - 282 (1985)
The cobalt-catalyzed carbonylation of ArCH(R)X (R=CH3, C6H5; X=Cl, Br) in alcoholic solvents under atmospheric pressure of CO is reported.Selective, high yield synthesis of the corresponding acids ArCH(R)COOH can be achieved within a very narrow range of experimental conditions by controlling kinetically the reversible interconversion of intermediate aryl and alkylcobalt complexes.The important roles of the base and of the alcoholic medium are briefly discussed.
Electrosynthesis of 2-benzhydrylidene-4,4-diphenyl-[1,3]oxathiolan-5-one: The reaction pathway
Lozano, Jose I.,Barba, Fructuoso
, p. 1259 - 1266 (1996)
The pathway for the electrochemical formation of 2-benzhydrylidene-4,4-diphenyl-[1,3]oxathiolan-5-one (2), in dichloromethane tetraethylammonium bromide on graphite cathode is proposed. It involves reaction between electrogenerated diphenylketene (3), 2-bromo-2,2-diphenylacetyl bromide (1) and sulfide anion. The latter is formed from H2S generated in the anodic compartment and electrogenerated bases.
Anodic oxidation of benzil hydrazones in the presence of halide ions
Okimoto, Mitsuhiro,Takahashi, Yukio
, p. 2059 - 2060 (2002)
Benzil hydrazones were subjected to electrolytic oxidation in MeOH containing halide ion source, such as KI and KBr. The results show that the reaction products were dependent on both the electrolytes and the substituents. In the presence of KI, benzoylphenyldiazomethanes were obtained, whereas in the presence of KBr, benzil dimethyl acetals were obtained.
Synthesis of l -octaarginine through microencapsulated palladium-catalyzed allyl ester deprotection
Pérez-López, Ana M.,González-Calderón, Dávir,Occorso, Antonio,Galindo-ángel, Javier,Domínguez-Seglar, José F.,Tamayo, Juan A.,Díaz-Gavilán, Mónica,Gómez-Vidal, José A.
, p. 2319 - 2322 (2014)
Octaarginine has been described as a molecular transporter. We report a useful synthesis of orthogonally protected l-octaarginine by using a method based on a microencapsulated palladium catalyst. Known palladium-based methods for allyl ester deprotection have been modified to facilitate purification of the unprotected intermediates. This improvement in the purification step has also been tested with a variety of allyl α-amino esters and allyl α,β-unsaturated esters.
X-ray crystallographic studies and comparative reactivity studies of a sodium diisopropylamide (NDA) complex and related hindered amides
Andrews, Philip C.,Barnett, Nicholas D.R.,Mulvey, Robert E.,Clegg, William,O'Neil, Paul A.,Barr, Donald,Cowton, Lucy,Dawson, Andrea J.,Wakefield, Basil J.
, p. 85 - 95 (1996)
Two related sodium amide complexes derived from secondary amines with bulky organic substituents have been synthesised and crystallographically characterised. Both [(iPr)2NNa(TMEDA)]2 and [Cy(iPr)NNa(TMEDA)]2 adopt dimeric crystal structures with a central, planar (nitrogen-metal)2 azametallocycle, a now familiar feature in both lithium amide and sodium amide chemistry. TMEDA ligands chelate in their usual bidentate manner making the Na+ cations four-coordinate with a distorted tetrahedral geometry. In the latter complex, the amido substituents are disposed in a trans conformation with respect to the (NNa)2 ring plane. The deprotonating ability of the former complex has been tested against that of the parent amide [(iPr)2NNa]∞ and the lithium congener [(iPr)2NLi]∞ (LDA) in a series of simple organic reactions: selective enolate formation from 2-octanone and 2-methylcyclohexanone; synthesis of diphenylacetic acid via diphenylmethane. In general, the performance of the sodium reagents compares favourably with that of the lithium reagent.
Bis-Rhodamines Bridged with a Diazoketone Linker: Synthesis, Structure, and Photolysis
Belov, Vladimir N.,Bossi, Mariano L.,Hell, Stefan W.,Shojaei, Heydar
, p. 56 - 65 (2022/01/03)
Two fluorophores bound with a short photoreactive bridge are fascinating structures and remained unexplored. To investigate the synthesis and photolysis of such dyes, we linked two rhodamine dyes via a diazoketone bridge (?COCN2?) attached to p
Relative activity of metal cathodes towards electroorganic coupling of CO2 with benzylic halides
Engelhardt, Helen,Klinkova, Anna,Medvedev, Jury J.,Medvedeva, Xenia V.
, (2021/05/26)
Electrochemical reduction of benzylic halides represents a convenient route to generating carbanions for their subsequent coupling with CO2 to obtain various carboxylic acids. Despite the industrial prospects of this synthetic process, it still lacks systematic studies of the efficient catalysts and reaction media design. In this work, we performed a detailed analysis of the catalytic activity of a series of different metal electrodes towards electroreduction of benzylic halides to corresponding radicals and carbanions using cyclic voltammetry. Specifically, we screened and summarized the performance of 12 bulk metal cathodes (Ag, Au, Cu, Pd, Pt, Ni, Ti, Zn, Fe, Al, Sn, and Pb) and 3 carbon-based materials (glassy carbon, carbon cloth, and carbon paper) towards electrocarboxylation of eight different benzylic halides and compare it to direct CO2 reduction in acetonitrile. Extensive experimental studies along with a detailed analysis of the results allowed us to map specific electrochemical properties of different metal electrodes, i.e., the potential zones related to the one- and two-electron reduction of organic halides as well as the potential windows where the electrochemical activation of CO2 does not occur. The reported systematic analysis should facilitate the development of nanostructured electrodes based on group 10 and 11 transition metals to further optimize the efficiency of electrocarboxylation of halides bearing specific substituents and make this technology competitive to current synthetic methods for the synthesis of carboxylic acids.
