Article

Mechanism of the Kolbe-Schmitt reaction with lithium and sodium phenoxides

Russian Journal of Physical Chemistry (Impact Factor: 0.56). 08/2007; 81(9):1392-1397. DOI: 10.1134/S0036024407090087

ABSTRACT

The mechanisms of the carboxylation reactions of lithium and sodium phenoxides are investigated by means of the DFT method
with a CEP-31 + G(d) basis set. The introduction of diffusion functions does not affect the outcome of the calculations. As a consequence, the
results of this investigation are in good agreement with the findings obtained by means of the LANL2DZ basis set. Lithium
phenoxide yields only salicylic acid in the Kolbe-Schmitt reaction. The reaction of sodium phenoxide can proceed in the ortho and para positions, but the para-substituted product can be expected at a very low concentration in the reaction mixture. The deviation of lithium and sodium
phenoxides from the mechanisms of carboxylations of other alkali metals is a consequence of the small ionic radii of lithium
and sodium.

Download full-text

Full-text

Available from: Zoran Marković, May 17, 2014
  • Source
    • "Konačno, mehanizam karboksilacije NaONaph u položajima 3 [18] i 6 [19] koji se ne zasniva na elektrofilnom napadu ugljenika na C3 i C6, danas više nije ubedljiv. Važno je istaći da su svi teorijski radovi o Kolbe-Schmitt-ovoj reakciji izvedeni pomoću metode B3LYP [12] [13] [14] [15] [16] [17] [18] [19] [20]. Danas postoje mnogo sofisticiniraniji funkcionali, kao što su metahibridni funkcionali, koji su tako parametrizovani da se uspešno primenjuju u ispitivanju termohemije i kinetike hemijskih reakcija [21] [22]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Aromatic hydroxy acids, the compounds of large industrial importance, can be prepared in the Kolbe-Schmitt reaction, i.e., a carboxylation reaction of alkali metal phenoxides (MOPh) and naphthoxides (MONaph). On the basis of the experimental results the two contradictory reaction mechanisms have been proposed: the one of direct carboxylation, and the other involving initial formation of the MOPh-CO2 or MONaph-CO2 complex. Previous theoretical investigations of the carboxylation reaction of sodium 2-naphthoxide, performed by means of the B3LYP method, confirmed the initial formation of the NaONaph-CO2 complex, and showed that the carbon of the CO2 moiety performs an electrophilic attack at Cl of the ring, leading to the formation of sodium 2-hydroxy-1-naphthoate (E1). Surprisingly, transition states for possible electrophilic attacks at C3 and C6 were not revealed, and the formation of other two products (E3 and E6) was explained by a number of consecutive rearrangements. In addition, this mechanism includes a reaction step with rather high activation energy. Since more sophisticated functionals are today available, the aim of this work is to reinvestigate the mechanism of the Kolbe-Schmitt reaction of NaONaph in all three positions (1,3 and 6). Our investigations with the M062X method demonstrated that CO2 and NaONaph can spontaneously build two complexes: B (the one previously reported) and C. While B cannot be further transformed to yield the reaction products, the CO2 moiety in C takes perfect position for electrophilic attacks at all three sites of the ring. These attacks are realized via the transition states TS1, which lead to the formation of the new C-C bonds, and corresponding intermediates D. In the next, bimolecular reaction step two D intermediates exchange the protons adjacent to the CO2 groups. These intermolecular reaction steps require significantly lower activation energies in comparison to the intramolecular proton shift from C to O. The carboxylation reaction in the position 6 is both kinetically and thermodynamically unfavourable, whereas the pathways in the positions 1 and 3 are competitive. Pathway 1 requires the lowest activation energies, but E3 is significantly more stable than other two products. In accordance with these findings are the experimental results which show that, at very low temperature (293 K) only E1 is formed at low yield, whereas the yields of E3 and E6 increase with the increasing temperature. Since the Kolbe-Schmitt reaction is experimentally performed at relatively high temperatures (around 500 K), the main product is thermodynamically most stable E6.
    Preview · Article · Sep 2015 · Hemijska industrija
  • Source

    Full-text · Article · Jan 2002
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Our investigation elucidates the structure of the intermediate in the first stage of the carboxylation reaction of potassium phenoxide. Under the reduced pressure of carbon dioxide the complex is not solvated with the CO(2) molecules. Under the conditions of the carboxylation reaction the potassium phenoxide-carbon dioxide complex is solvated with one or two CO(2) molecules. One of the added CO(2) moieties performs an electrophilic attack on the benzene ring, whereas the old CO(2) moiety becomes a molecule of solvent. Our findings are in good accord with the experimental results obtained by the NMR and IR measurements.
    Full-text · Article · Jul 2007 · Journal of Chemical Information and Modeling
Show more