Note: Super Dry Alcohol Alcohol (ethanol) of the required dryness can be made using methylated spirits as the starting point (95.6% alcohol). Absolute ethanol (>99.5%) is obtained by heating this under reflux with dry (recently fired) calcium oxide. To significantly improve the yield in the synthesis of barbiturates, even dryer alcohol is required. To remove more of the water, thereby converting the 99.5% ethanol to ‘super dry’ alcohol (>99.8%), use 5gm of magnesium turnings with 0.5gm of iodine in a boiling vessel. Let the magnesium react with ~50ml of the 99.5% ethanol producing hydrogen and magnesium ethanolate. When all of the magnesium has been consumed, the remainder of the absolute alcohol is added, refluxed for 30 minutes, and distilled directly into the planned storage vessel. The resulting ethanol should be better than 99.95%. See the Video ‘Making super dry alcohol’.
Step 2 Sodium ethoxide catalyst is again needed in the reaction vessel, and this time 47g of the monosubstituted ester from Step 1 is converted to a di-substituted ester by reflux (or reaction in an autoclave) with the second side chain. For the synthesis of Amytal, this second sidechain is 1-bromo-3 methylbutane. In the case of Nembutal, it is 2-bromopentane, in each case 38g is required.
At the end of this stage the di-substituted malonate is removed again by vacuum distillation. This is 3-methyl-butyl-ethyl malonic ester in the case of Amytal synthesis; 1-methyl butyl- ethyl malonic ester if Nembutal is being manufactured.