Benzoin is a white crystaline compound made from benzaldehyde. It is mainly used as a precursor for benzil. In this process, thiamine (vitamin B1) will be used as a catalyst.
2C6H5CHO --thiamine--> (C6H5)2C2H2O2
|Benzaldehyde (Synthesis/OTC)||500ml Round bottomed flask|
|Thiamin Hydrochloride||Reflux Column|
|3M Sodium Hydroxide Solution|
Into a 500ml flask, place 9.2 grams of thiamine hydrochloride. Add to this 32mls of water and swirl to dissolved all the thiamine hydrochloride. Now, measure out 120mls of 96% ethanol and pour this into the flask. Cool this in an ice bath for a short period of time and measure out 20ml of 3M sodium hydroxide solution. Add this to the previous solution in small ammounts at a time, making sure the temperature doesn't go above 20C. Once it is all added, pour in 60mls of benzaldehyde. Set this flask up for reflux in a water bath. Reflux it at 60C (the mixture at 60C, not the water bath). Never should the temperature go above 65C or even get close. Let this reflux for 1.5 hours at this temperature. If you do not want to risk it, you can store the mixture at room temp for 48hours and the reaction should be completed by then. The reaction rate doubles after every 10degree increment.
After it is done reacting, cool the solution in a salt/ice bath. If crystalization does not start, dip a stirring stick into the solution and pull it out. The drop of solution will evaporate leaving crystals. Dip the stirring stick back into the solution and scrape the sides a little bit. This should start crystalization. Filter the solution out while still cold (vacuum filtration helps). Rinse the flask out with a 1:1 mixture of water and 96% ethanol then pour this through the filter also. Last, run some more of the 1:1 ethanol:water mixture through the crystals in the filter. These should be white to off-white crystals; yeild is typically around 45-48 grams. If you want the product purer, you can recrystalize from ethanol, 8ml ethanol to 1 gram of benzoin.