Krapcho

Subsequently Birch and Krapcho and Bothner-By independently postulated the mechanism shown in Eq. (2) and the latter authors presented kinetic data in support of it. Reversible electron addition to the aromatic ring affords a radical-anion (36), the formation of which in other solvents has... 

Krapcho and Bothner-By made additional findings that are valuable ii understanding the Birch reduction. The relative rates of reduction o benzene by lithium, sodium and potassium (ethanol as proton donor) wer found to be approximately 180 1 0.5. In addition, they found that ben zene is reduced fourteen times more rapidly when methanol is the protoi donor than when /-butyl alcohol is used. Finally, the relative rates of reduc tion of various simple aromatic compounds by lithium were deteiTnined these data are given in Table 1-2. Taken together, the above data sho that the rate of a given Birch reduction is strikingly controlled by the meta... 

The relative rate of reduction by lithium with respect to sodium was misquoted by me ii ref. 29 as 62.5 1. Eastham has criticized the accuracy of the original data and Krapchc and Bothner-By have agreed that their rate constants may have been in error. Thi figures cited above include lough corrections made in accord with Krapcho and Bothner-By estimates of the errors. 

Various other observations of Krapcho and Bothner-By are accommodated by the radical-anion reduction mechanism. Thus, the position of the initial equilibrium [Eq. (3g)] would be expected to be determined by the reduction potential of the metal and the oxidation potential of the aromatic compound. In spite of small differences in their reduction potentials, lithium, sodium, potassium and calcium afford sufficiently high concentrations of the radical-anion so that all four metals can effect Birch reductions. The few compounds for which comparative data are available are reduced in nearly identical yields by the four metals. However, lithium ion can coordinate strongly with the radical-anion, unlike sodium and potassium ions, and consequently equilibrium (3g) for lithium is shifted considerably... 

A. P. Krapcho, Burlington, Vermont E. Lukevics, Riga, Latvia A. P. Marchand, Denton, Texas V. I. Minkin, Rostov-on-Don, Russia C. A. Ramsden, Staffordshire, England C. W. Rees, FRS, London, England E. F. V. Sciiven, Indianapolis, Indiana J. Schantl, Innsbruck, Austria... 

Edwin M Kaiser William G Kenyon R A Klein C Konig A Paul Krapcho Stephen J Kuhn William C Kuryla Peter A Leermakers Robert L Letsinger Guy S Lougheed B J Magerlein R J L Martin John G Moefatt D Nasipuri George A Olah D E Pearson R J Petersen G Ploss J Posner A Rieche... 

U.S. Patent 3075968, 1963 Krapcho, J. (Olin Mathieson Chemical Corp.) Chem. Abstr. 1963, 59, 5181. 

For a review of the preparation of spiro compounds by this reaction, see Krapcho, A.P Synthesis, 1978, 77. 

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