Benzyl chloride via free-radical halogenation

Benzyl chloride, or a-chlorotoluene, is an extremely useful reagent used in organic synthesis. Commercially, it's mainly used to make benzyl esters, which find use in the perfume industry. Unfortunately, benzyl chloride is an extremely dangerous chemical and has been used historically in chemical warfare due being a strong lachrymator (severely burns eyes, like a tear gas) and very toxic. I plan to use benzyl chloride to make benzylamine.

I made some benzyl chloride using a procedure that I modified slightly (link). Toluene is halogenated directly with chlorine in the presence of a halogen lamp to encourage the equillibrium shift of diatomic chlorine molecules to free radical chlorine atoms. Benzal chloride and benzotrichloride are also produced, but the quanitity of these side products can be kept reletivly low by using a large excess of toluene.

To a 500ml round-bottom flask, I added 100ml (0.9442 moles) of technical grade toluene and 2.5ml of 33% hydrochloric acid. I attached a Liebig condenser to the flask and refluxed the mixture on a medium heat for 2 hours with a halogen lamp placed a couple of centimetres from the flask. During reflux, I slowly added in 36.56g (0.1573 moles) of trichloroisocyanuric acid (TCCA) in small portions through the condensor. Complete addition took 1 hour. Sometimes the small amounts of the TCCA become stuck in the condenser so a long rod was used to push it down into the flask. With the first few additions of TCCA, a considerable amount of heat was given off and the formation of yellow-green chlorine gas was observed. For the second hour of reflux, the flask was ocasionally swirled. Anyway, after the reflux, I turned off the heat and left the mixture to stand overnight. The next morning, I filtered off the precipitated white cyanuric acid, transferring the orange filtrate to a 500ml round-bottom flask. I attached a stillhead and condenser to the flask and began distilling, using a thermometer to track the fractions.

The first fraction to come over was excess toluene at 100-124 C. I collected around 35ml of this. The vapour temperature then rose and I began to collect benzyl chloride at 160-186 C. After all the benzyl chloride had come over, there was nothing left in the distilling flask and I ended the distillation. I then redistilled the benzyl chloride, this time collecting the fraction boiling at 160-182. The residue in the boiling flask should consist of mainly benzal chloride and benzotrichloride. Anyway, I dried the benzyl chloride over anhydrous calcium chloride, then transferred it to an amber vial for storage. I got 16ml (0.139 moles) of benzyl chloride which is a 29% yield. The product had a density of 0.921g/cm³ which isn't too far away from the theoretical 1.1 g/cm³. This shows the benzyl chloride I made is probably moderately pure.

The lachrymatory properties of benzyl chloride were actually nowhere near as bad as I was expecting. My eyes were attacked viscously when I was washing the glassware and briefly during the initial reflux but that was about it.

The pour yield could likely be dramatically improved by using a larger excess of toluene. Adding the TCCA more slowly probably would have also helped to increase the yield. I did notice there were a lot of higher chlorination products left over in the distilling flask after the second distillation.

C3N3O3Cl3 + 3 HCl ==> 3 Cl2 + C3N3O3H3

C6H5CH3 + Cl2 ==> C6H5CH2Cl + HCl