The reaction of an aromatic heterocycle with a proton is called a protonation. One of articles about this theory is 《The Walden rearrangement in the succinic acid group》. Authors are Holmberg, Bror.The article about the compound:(S)-2-Bromosuccinic acidcas:20859-23-8,SMILESS:O=C(O)[C@@H](Br)CC(O)=O).COA of Formula: C4H5BrO4. Through the article, more information about this compound (cas:20859-23-8) is conveyed.
Opinions on the frequency of the Walden inversion (C.A. 5, 2820) have varied all the way from that of Walden himself, who considered the rearrangement as the exception and result of “”abnormal”” reaction, to that of Olson (C.A. 27, 3874), who proposed the theory that rearrangement always accompanies substitution on the asym. C atom. The results of Fredga (C.A. 39, 1392.8), as well as many of the author’s own, support Olson’s thesis in that reactions such as L(-)-HO2CCH2CH(OH)CO2H → PCl5 D(+)-HO2CCH2CHClCO2H, involving only a simple substitution, always cause inversion. Fredga’s “”quasi-racemate”” method was used to establish configurations. Reactions such as esterification of malic acid do not change the optical configuration since they do not effect the asym. C atom. Hydrolysis of L(-)-bromosuccinic acid to either D(+)- or L(-)-malic acids, depending on the means, is explained by the fact that this hydrolysis always proceeds via the D(+)-malic acid β-lactone, which is saponified by either alkali or acid to D(+)-malic acid, leading to the conclusion that the bond broken in saponification is that between the CO2H group and the lactone O. Hydrolysis with H2O alone yields L(-)-malic acid, since the bond from the asym. C atom to the lactone O is in this case broken by addition of the elements of H2O. Thus the pH of the solution is the factor determining which optical antipode of malic acid is formed in the hydrolysis of bromosuccinic acid. Walden’s Ag2O here serves only to further the formation of lactone. Walden’s observation that the presence of Cu++ ions in the hydrolysis causes formation of D(+)-malic acid is explained on the grounds that the Cu complex formed with HO acids has the same catalytic action on hydrolysis as H+ ions. This has been proven for the hydrolysis of acetylated HO acids. However, L(+)-HO2CCH2CH(NH2)CO2H + HONO → L(-)-HO2CCH2CH(OH)CO2H and L(+)-HO2CCH2CH(NH2)CO2H + NOCl → L(-)-HO2CCH2CHClCO2H. Asparagine reacts in analogous fashion, whereas the di-Et L(-)-aspartate yields the D(+)-derivative The diazotization reaction of aspartic acid is therefore the only exception to Olson’s rule. So far it has been impossible to find any intermediate in this reaction that might cause a 2nd optical inversion as in the hydrolysis of bromosuccinic acid. Thus even 1-step reactions on the asym. C atom may not lead to Walden rearrangement, but this must be considered the exception rather than the rule.
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Reference:
Copper catalysis in organic synthesis – NCBI,
Special Issue “Fundamentals and Applications of Copper-Based Catalysts”