Effect of Various Alcohols on Lactose

The types of lactose resulting from treatment with various alcohols were studied. Conversion of α-hydrate to the stable anhydrous form of lactose was similar in ethanol, propanol, butanol, and isobutanol; the reaction was slow at room temperature but at refluxing temperature was usually complete in 1h. The reaction was slowed by increasing moisture content in the alcohol, becoming inhibited at 2 to 2.5% moisture, depending on whether the moisture was added or came from the water of crystallization. Converson from α-hydrate to stable-α slowed as the alcohol chain length increased, particularly in the presence of moisture. The product also became more variable. The product of concentrated lactose solution added to methanol contained only anhydrous lactose but at the normal alpha:beta ratio. With moisture content above 10%, some α-hydrate was formed, but at a normal ratio, suggesting either insufficient time and/or insufficient moisture for mutarotation. Above 15% moisture, α-hydrate increased until at 35% moisture α-hydrate became the entire product. Product composition could be controlled by starting with either alpha-or beta-lactose and allowing mutarotation to produce the desired composition before the solution was added to methanol. An explanation is proposed for the transient milldness that sometimes results when lactose solutions and organic solvents are mixed: the milldness is due to the formation of minute α-stable crystals temporarily formed at critical amounts of lactose, moisture, and solvent, with too much moisture preventing formation because of high solubility, and too much solvent resulting in permanent precipitation.