J. Org. Chem. 1986, 51, 567-569. DOI: 10.1021/jo00354a037
◆Sodium chlorite (NaClO2) reacts with aldehydes under very mild conditions to give carboxylic acids
◆Hypochlorite ion must be removed in order to avoid side reactions, since the redoxpair HOCl/Cl- is a more powerful oxidant than ClO2-/HOCl. Another drawback is the oxidation of ClO2- to ClO2
◆Consequently, to circumvent the complications described scavengers for hypochlorite were tested such as 2-methyl-2-butene, resorcinol, sulfamic acid, H2O2 and DMSO.
◆Best reaction conditions were achieved by working in a weakly acidic medium, where oxidation was rapid with no competitive reduction of HClO2 to HOCl
◆Best reaction conditions have been achieved in aqueous acetonitrile buffered with NaH2PO4 at pH 4.3, while with very sensitive substrates up to 5 equivalents of hydrogen peroxide at pH 2 are employed in order to accelerate the reduction of HOCl. Reactions are carried out at room temp. or even at 0 °C.
◆Electron rich substrates can be troublesome, giving rise to side products formed by chlorination or oxidation of the aromatic ring. The substitution of H2O2 by DMSO as trapping reagent has been demonstrated to be a viable alternative to circumvent such problems.
◆If isolated double bonds are present in a substrate, chlorination of the double bond cannot be prevented with the reagent combination NaClO2–H2O2. This side reaction might be circumvented if DMSO is used as a scavenger instead, however, oxidations still occur only in moderate yields
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