Combine 45 mL of conc. sulfuric acid and 30 mL conc. nitric acid in an ice bath. The reaction temperatures must be kept below 10°C. Start slowly adding 7.5 g of erythritol, with magnetic stirring, keep the solution below 10°C. Leave the solution to stir for 20 minutes, pour the solution into 150 mL ice cold water with ice, start adding some sodium carbonate solution until bubbling stops, filter, dry and recrystallize the ETN in ethanol.
Stirring the solution in an ice bath
ETN precipitated in ice-cold water