The Preparation Method of Bronopol

Bronopol can be obtained by two reactions of alkanes hydroxylation and bromination with nitromethane and formaldehyde as raw materials and under alkaline conditions. 

The reaction equations are as follows:

CH₃NO₂ + 2HCHO→HOCH₂C(NO₂)HCH₂OH

HOCH₂C(NO₂)HCH₂OH + NaOH→[HOCH₂C(=NO₂)CH₂OH]Na + H₂O

[HOCH₂C(=NO₂)CH₂OH]Na + Br₂→HOCH₂C(Br)(NO₂)CH₂OH + NaBr

Two preparation processes of bronopol:

1. Add nitromethane, 30% formaldehyde, calcium chloride and sodium hydroxide into the reaction equipment at a molar ratio of 1:2:2:2 and stir it, then add bromine and dichloroethane into the solution below 0℃. The addition of bromine and dichloroethane should be finished within 1 hour, and the molar of bromine should be equal to that of nitromethane. Vaporize the dichloroethane after the dichloroethane layer is separated, then the white solid (coarse product) will be obtained. Extract the water layer of the reactants with ether, then vaporize the ether in the ether extract, and another part of the coarse product is obtained. Finally, combine the coarse products and recrystallize them with ether to obtain the pure product.

2. First, prepare 2-nitro-1,3-propandiol. Add nitromethane and 30% formaldehyde solution into the reflux reaction equipment at a molar ratio of 1:2, followed by the addition of 2% potassium carbonate. After 1 hour of heating reflux, cool the solution and separate out the crystal. Extract the water layer of the reactants with ether, then dry it and vaporize the ether to obtain  2-nitro-1,3-propandiol. Next, dissolve the 2-nitro-1,3-propandiol in methanol, add methanol solution containing 20% sodium methylate and stir the solution at 20℃ to separate out 2-nitro-1,3-propandiol sodium. After that, filter out the sodium salt and make it suspend in the dry ether for bromination: add bromine to the ether suspension liquid of 2-nitro-1,3-propandiol sodium below 0℃, and then stir the solution for 10 minutes. Finally, evaporate the ether after filtration, and bronopol can be obtained.