diol (D-galactose) (Avocado, 1 equiv.),
zinc chloride (Avocado, hygroscopic, stored in a desiccator (1.64 equiv.)),
conc. sulfuric acid (98 %, 7 mL/mol),
acetone (analar, 2 L/mol),
sodium carbonate (Avocado (powder), 3.4 equiv.),
water (600 mL/mol),
diethyl ether (GPR, 1.5 L/mol)

Zinc chloride (120 g, 0.88 mol, 1.64 equiv.) was partially dissolved in acetone (1.25 L) and conc. sulfuric acid (4.0 mL) was added at room temperature to give a clear solution (slightly exothermic reaction, cooling in an ice-bath may be necessary on large scale). The diol (D-galactose) (100 g, 0.56 mol) was added in one portion and the resulting white suspension stirred for 6 hours at room temperature. A suspension of sodium carbonate (200 g, 1.89 mol, 3.4 equiv.) in water (300 mL) was added to the yellow reaction mixture at 0 ºC in medium sized portions. The suspension was allowed to stir for 1/2 hour before filtration (discard solid) and solvent removal in vacuo (keep water bath temperature below 30 ºC, otherwise the sugar will decompose; Caution: the acetone-water mixture is likely to bump). This gave the crude product as a yellow oil beneath the aqueous layer. The organic fraction was separated from the aqueous layer, followed by further extraction with diethyl ether (3 x 250 ml). The organics were dried over sodium sulfate, and the solvent removed in vacuo to yield the desired product as a pale yellow oil (143.6 g, >99 %). Purification is generally not necessary, but can be achieved by flash column chromatography (diethyl ether).

This old procedure for the formation of an acetonide was easily applied to large scale and has been carried out on 10 to 100 g of starting material. It allows selective protection of adjacent cis-diols, leaving other hydroxyl groups unprotected. Utilising acetone and a Lewis acid (PTSA or CSA can also be used instead of zinc chloride) is especially useful in carbohydrate chemistry, but it should be noted that for most other diols, other, more suitable methods have been developed. Moreover, the same transformation can be carried out utilising iodine (see other references), but it should be noted that this resulted in only moderate yields at room temperature, and although excellent yields could be achieved at reflux, the crude product was less pure compared with the procedure described above. In the nmr data the anomeric proton is referred to as H-1.

d_H(300 MHz; CDCl₃) 5.50 (1 H, d, J 5.0, H-1), 4.55 (1 H, dd, J 8.0 and 2.5, H-3), 4.24 (1 H, dd, J 5.0 and 2.5, H-2), 4.29 (1 H, dd, J 8.0 and 2.0, H-4), 3.83-3.80 (2 H, m, CH₂), 3.67-3.65 (1 H, m, H-5), 2.40 (1 H, s, OH), 1.48 (3 H, s, CH₃), 1.40 (3 H, s, CH₃), 1.25 (6 H, s, 2 x CH₃)

R. L. Whistler, M. L. Wolfrom, (R. S. Tipson); Methods in Carbohydrate Chemistry II; Academic Press; New York; 1962; 246

K. P. R. Kartha, Tetrahedron Lett., 1986, 27, 3415