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Bis- and oligo(trifluoromethyl)benzenes: hydrogen/metal exchange rates and gas-phase acidities

The proton mobilities (kinetic acidities) of bis- and tris(trifluoromethyl)benzene are dictated to a large extent by steric factors; the trifluoromethyl group is a fairly bulky substituent that can seriously impede the approach of the metalating reagent. Most satisfactory results in terms of yields and selectivities have been achieved with lithium 2,2,6,6-tetramethylpiperidide or with methyllithium in the presence of potassium tert-butoxide, a slim version of the std. superbase. The rates of deprotonation under irreversible conditions do not parallel the thermodn. (equil.) acidities. Substituent effects on the deprotonation energies in the gas phase appear to be additive: each trifluoromethyl group lowers it by 13 kcal mol-1 when located ortho with respect to the carbanion, and by 10 kcal mol-1 when located in a meta or para position. [on SciFinder (R)]

    Keywords: Trifluoromethyl group (charge-stabilizing effect; hydrogen/metal exchange rates and gas-phase acidities of bis- and oligo(trifluoromethyl)benzenes); Free energy; Protonation enthalpy (deprotonation; hydrogen/metal exchange rates and gas-phase acidities ; fluoromethylbenzene lithiation gas phase acidity; steric effect lithiation trifluoromethylbenzene; deprotonation fluoromethylbenzene gas substituent effect; kinetic thermodn acidity trifluoromethylbenzene

    Note:

    CAN 129:189002 22-12 Physical Organic Chemistry Institut de Chimie organique de l'Universite,Lausanne-Dorigny,Switz. Journal 0947-6539 written in English. 40315-44-4 (Lithium azetidide) Role: CAT (Catalyst use), USES (Uses) (acid-base equil. catalyst; hydrogen/metal exchange rates and gas-phase acidities of bis- and oligo(trifluoromethyl)benzenes); 42175-48-4 (1,2,3-Tris(trifluoromethyl)benzene) Role: RCT (Reactant), RACT (Reactant or reagent) (attempted lithiation; hydrogen/metal exchange rates and gas-phase acidities of bis- and oligo(trifluoromethyl)benzenes); 454-92-2P (3-(Trifluoromethyl)benzoic acid); 455-24-3P (4-(Trifluoromethyl)benzoic acid); 211742-40-4P (2,3,5-Tris(trifluoromethyl)benzoic acid) Role: BYP (Byproduct), PREP (Preparation) (hydrogen/metal exchange rates and gas-phase acidities of bis- and oligo(trifluoromethyl)benzenes); 98-08-8 ((Trifluoromethyl)benzene); 320-23-0 (1,2,4,5-Tetrakis(trifluoromethyl)benzene); 393-05-5 (1,2,4-Tris(trifluoromethyl)benzene); 402-31-3 (1,3-Bis(trifluoromethyl)benzene); 433-19-2 (1,4-Bis(trifluoromethyl)benzene); 433-95-4 (1,2-Bis(trifluoromethyl)benzene); 598-30-1 (sec-Butyllithium); 729-81-7 (1,3,5-Tris(trifluoromethyl)benzene); 917-54-4 (Methyllithium); 38227-87-1 (Lithium 2,2,6,6-tetramethylpiperidide) Role: PRP (Properties), RCT (Reactant), RACT (Reactant or reagent) (hydrogen/metal exchange rates and gas-phase acidities of bis- and oligo(trifluoromethyl)benzenes); 109-72-8 (Butyllithium) Role: RCT (Reactant), RACT (Reactant or reagent) (hydrogen/metal exchange rates and gas-phase acidities of bis- and oligo(trifluoromethyl)benzenes); 433-97-6P (2-(Trifluoromethyl)benzoic acid); 725-89-3P (3,5-Bis(trifluoromethyl)benzoic acid); 24821-22-5P (2,6-Bis(trifluoromethyl)benzoic acid); 25753-26-8P (2,4,6-Tris(trifluoromethyl)benzoic acid); 32890-87-2P (2,4-Bis(trifluoromethyl)benzoic acid); 42175-55-3P (2,3-Bis(trifluoromethyl)benzoic acid); 42580-42-7P (2,5-Bis(trifluoromethyl)benzoic acid); 133804-66-7P (3,4-Bis(trifluoromethyl)benzoic acid); 149836-48-6P (2-Iodo-1,3-bis(trifluoromethyl)benzene); 202465-22-3P (2,4,5-Tris(trifluoromethyl)benzoic acid) Role: SPN (Synthetic preparation), PREP (Preparation) (hydrogen/metal exchange rates and gas-phase acidities of bis- and oligo(trifluoromethyl)benzenes); 865-47-4 Role: PRP (Properties), RCT (Reactant), RACT (Reactant or reagent) (lithiation agent activator; hydrogen/metal exchange rates and gas-phase acidities of bis- and oligo(trifluoromethyl)benzenes); 3030-47-5 (PMDTA) Role: RCT (Reactant), RACT (Reactant or reagent) (lithiation agent activator; hydrogen/metal exchange rates and gas-phase acidities of bis- and oligo(trifluoromethyl)benzenes)

    Reference

    • LSCO-ARTICLE-1998-008

    Record created on 2006-03-03, modified on 2016-08-08

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