- Ambident Reactivity of Phenolate Anions Revisited: A Quantitative Approach to Phenolate Reactivities
-
Prompted by the observation that the regioselectivities of phenolate reactions (C versus O attack) are opposite to the predictions by the principle of hard and soft acids and bases, we performed a comprehensive experimental and computational investigation of phenolate reactivities. Rate and equilibrium constants for the reactions of various phenolate ions with benzhydrylium ions (Aryl2CH+) and structurally related quinone methides have been determined photometrically in polar aprotic solvents. Quantum chemical calculations at the SMD(MeCN)/M06-2X/6-31+G(d,p) level confirmed that O attack is generally favored under kinetically controlled conditions, whereas C attack is favored under thermodynamically controlled conditions. Exceptions are diffusion-limited reactions with strong electrophiles, which give mixtures of products arising from O and C attack, as well as reactions with metal alkoxides in nonpolar solvents, where oxygen attack is blocked by strong ion pairing. The Lewis basicity (LB) and nucleophilicity (N, sN) parameters of phenolates determined in this work can be used to predict whether their reactions with electrophiles are kinetically or thermodynamically controlled and whether the rates are activation- or diffusion-limited. Comparison of the measured rate constants for the reactions of phenolates with carbocations with the Gibbs energies for single-electron transfer manifests that these reactions proceed via polar mechanisms.
- Mayer, Robert J.,Breugst, Martin,Hampel, Nathalie,Ofial, Armin R.,Mayr, Herbert
-
p. 8837 - 8858
(2019/07/08)
-
- Impact of aryloxy initiators on the living and immortal polymerization of lactide
-
This report describes two different methodologies for the synthesis of aryl end-functionalized poly(lactide)s (PLAs) catalyzed by indium complexes. In the first method, a series of para-functionalized phenoxy-bridged dinuclear indium complexes [(NNO)InCl]2(μ-Cl)(μ-OPhR) (R = OMe (1), Me (2), H (3), Br (4), NO2 (5)) were synthesized and fully characterized. The solution and solid state structures of these complexes reflect the electronic differences between these initiators. The polymerization rates correlate with the electron donating ability of the phenoxy initiators: the para-nitro substituted complex 5 is essentially inactive. However, the para-methoxy variant, while less active than the ethoxy-bridged complex [(NNO)InCl]2(μ-Cl)(μ-OEt) (A), shows sufficient activity. Alternatively, aryl-capped PLAs were synthesized via immortal polymerization of PLA with A in the presence of a range of arylated chain transfer agents. Certain aromatic diols shut down polymerization by chelating one indium centre to form a stable metal complex. Immortal ROP was successful when using phenol, and 1,5-naphthalenediol. These polymers were analysed and chain end fidelity was confirmed using 1H NMR spectroscopy, MALDI-TOF mass spectrometry, and UV-Vis spectroscopy. This study shed light on possible speciation when attempting to generate PLA-lignin copolymers.
- Chile,Ebrahimi,Wong,Aluthge,Hatzikiriakos,Mehrkhodavandi
-
p. 6723 - 6733
(2017/07/10)
-
- 5-halo-6-nitro-2-substituted benzoxazole compounds
-
Novel benzoxazole compound having, at the 2 position, a group bonding through a carbon atom having no or one hydrogen atom and introduced with a chlorine or bromine atom at the 5 position. The compounds are key intermediates useful for preparing 2-amino-5-nitrophenol derivatives which are useful as intermediates for synthesis of industrial materials, reducing agents, antioxidants, cyan-image-forming couplers and the like.
- -
-
-
- Process for preparing 2-amino-5-nitrophenol derivatives
-
A process for efficiently preparing 2-amino-5-nitrophenol derivatives in which benzoxazole derivatives are subjected to nucleophilic substitution reaction at the 5 position thereof to obtain corresponding benzoxazole derivatives, and the oxazole ring of the benzoxazole derivatives is then subjected to ring-opening to obtain 2-amino-5-nitrophenol derivatives. The 2-amino-5-nitrophenol derivatives are useful as industrial starting materials, reducing agents or antioxidants and intermediates for cyan-image-forming couplers.
- -
-
-
- Mechanism of the Base-Catalyzed Elimination of Para-Substituted Phenoxides from 4-(Aryloxy)azetidin-2-ones
-
4-(Aryloxy)azetidin-2-ones 4-7 react in dilute aqueous alkali to give 3-hydroxyacrylamide oxyanion and para-substituted phenolate ions.Similarly, 4-(aryloxy)-3,3-dimethylazetidin-2-ones 8-11 give 2,2-dimethylcarboxaldoacetamide and para-substituted phenolate ions.Reactivity is proportional to the fraction of (aryloxy)azetidin-2-one anions, Ka/(Ka + ).Kinetic pKa's of 4-11 and first-order k2's for (suggested) reversible E1cB elimination of para-substituted phenoxide ions from N-1 anions are reported.Reactions are further characterized kinetically by solvent deuterium isotope effects: kOH/kOD = ca. 0.5, ρ(k2) = 2.2 for 4-7 and ρ(k2) = 2.7 for 8-11, and βlg = -0.65 for 4-7 and βlg = -0.75 for 8-11.
- Fedor, Leo R.
-
p. 5094 - 5097
(2007/10/02)
-