Author Topic: Benzyl Chloride Synthesis - Douchermann  (Read 195 times)


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Benzyl Chloride Synthesis - Douchermann
« on: August 14, 2009, 07:58:38 PM »
Benzyl chloride is the monochloride of the three possible side chain chlorinated toluenes. This means, it's toluene, but instead of C6H5CH3 it's C6H5CH2Cl, where as benzal chloride and benzotrichloride are C6H5CHCl2 and C6H5CCl3 respectively. It is quite useful, and is moderately easy to produce, however cleanup is not fun at all. Clean-up isn't exactly difficult, until you get to the point where you can no longer see. That’s right, benzyl chloride is a lachrymator, and a powerful one at that. In the presence of water, it hydrolyzes to benzyl alcohol and hydrochloric acid, so it's clear why it burns your water saturated eye so bad. The burn is quite disorienting too, so during cleanup, or anytime you are exposed to the vapors, wear the proper protection (full face mask or sealed goggles. It is also very unhealthy to breathe in the vapors, as your lungs are mostly water as well. Fortunately, the lachrymatory effects are only temporary and cause no permanent damage. I cannot say the same for inhalation however. It is generated by the photocatalyzed free-radical chlorination of toluene, with a slight change. Instead of involving anhydrous chlorine gas, I nixed the chlorine gas all together and went for a much more friendly alternative.

3C6H5CH3 + C3Cl3N3O3 ----> 3C6H5CH2Cl + C3H3N3O3

Into a 1000ml flask, pour 600ml of toluene followed by a few drips of concentrated hydrochloric acid. This will impregnate some toluene with a small amount of hydrogen chloride, which is necessary to initially kick off the reaction. Set the flask up for reflux with a thermometer in the second neck, and a plain stopper in the third, and begin heating on an oil bath. Remove the glass UV filter from your halogen lamp, and get it as close as possible to the flask. Set up a fan to blow air across the flask, at a moderate to high rate. This is because you will be opening the flask fairly often, and when you have a 600watt halogen lamp next to a flask spewing boiling toluene vapors, there WILL be a fire. I started a fire my first time doing this. However, a fan will completely negate the chance of a fire.

Once the toluene has started warming up, measure out 90g of trichloroisocyanuric acid (TCCA). Add a small amount of the TCCA to the hot toluene and close the flask back up. Note, you can not add the TCCA through the condenser. The coils will form condensation and the TCCA will stick to this. Not only will you lose TCCA, but it's also a pain in the ass to clean. It must be added through the only unused neck. Repeat the small additions until all 90g has been used up. This should take 30 min to 1hr to complete and the boiling toluene should be milky white, due to precipitated cyanuric acid. Remove heat and let it cool down

As soon as the mixture is decently cool, it should be a clear liquid (varying from water white to yellow) above a white precipitate. Filter off the precipitate, which is cyanuric acid. It is almost necessary to use vacuum filtration here, otherwise it will take the rise and fall of three successive galaxies to complete filtration. Rinse 3 portions of toluene through this. Read the notes at the bottom for suggested uses of the cyanuric acid on the filter paper. Add your filtered solution to a distillation apparatus and begin simple distillation. At first you will collect a very large amount of toluene which can be reused. approximately 500ml, read notes below for purification. Then, switch flasks and collect the portion coming over at 175-185C. This is relatively pure benzyl chloride. Redistill with a fractioning column, collection the portion between 178-182C for pure benzyl chloride. Theoretical yield = 147g (134ml). Mine was 106g (72%) but I spilled a lot of TCCA.


All flasks that came in contact with benzyl chloride should be treated with a hot 5% sodium hydroxide solution. This will hydrolyze all benzyl chloride into benzyl alcohol and sodium chloride. After which, soap and water will clean the equipment completely. Cyanuric acid can be removed by treating with dilute sodium hydroxide solutions, and excess TCCA treated with dilute hydrochloric acid.


The cyanuric acid can be used to prepare sodium cyanide. Reacting sodium cyanide and benzyl chloride will give benzyl cyanide, a useful reagent.

The toluene distilled off should be well shaken with sodium bicarbonate until it registers neutral. It is then dried using magnesium sulfate or calcium chloride. It can be filtered and used directly from this to produce more benzyl chloride. However for anything else it should be redistilled, collecting fractions between 108-112C.
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