[3486-35-9] · CO3Zn · Zinc Carbonate · (MW 125.40)
Physical Data: dec with evolution of CO2 at 300 °C; d 4.42-4.45 g cm-3.
Solubility: insol H2O, organic solvents.
Form Supplied in: white crystalline powder; commercially available.
Preparative Method: addition of 0.1M Na2CO3 to 0.1M ZnSO4 gives a precipitate of zinc carbonate, which is filtered off, and dried in vacuo.1
Handling, Storage, and Precautions: reputed to be nontoxic.
The specific chelating properties of zinc (or magnesium) carbonate were required in the formation of coumarin (2) from phenol (1) (eq 1). The nonchelating sodium or potassium carbonates do not effect this transformation. Although yields are only moderate, (1) is
exceptionally sensitive to acidic reagents1, rendering some other procedures for coumarin synthesis under acidic conditions6 impractical in this case. Moreover, this cyclization step to the aflatoxin system had proved difficult in a previous synthesis.7
Phenolic2 and enolic3 alkynes are cyclized to furans or pyrans (eqs 2-4) with, in some cases, very small catalytic quantities of ZnCO3.
Various dienals4 and dienones5 can be prepared by Claisen rearrangement of enol sulfoxides (3), followed by PhSOH elimination (eq 5). The rearrangement occurs on distillation from small amounts of ZnCO3. These fairly vigorous conditions, however, suggest that alternative catalysts8 would often be preferred with less robust molecules.
ZnCO3 reacts with carboxylic acids to form the zinc salts, which can be used to effect solvolysis of tertiary halides (see Zinc Oxide).
SmithKline Beecham Pharmaceuticals, Harlow, UK