4-allyl catechol

4-allyl catechol really only serves one purpose - as an intermediate to synthetic safrole. It is a white to tan powder with a characteristic smell of diesel/smoke. Quick or easy are two words that should never describe the synthesis of 4-allyl catechol. While it's not particularly hard, the reagents needed have to be made or bought from a special supplier. It is produced by reacting with an aluminum halide to form the phenol adduct, which is then hydrolyzed.

Aluminum Iodide demethylation

This route is perhaps the easiest, because I find it significantly easier to purchase iodine crystals than anything else. It is made by reacting aluminum with iodine in a solvent, then introducing the eugenol to this. I can't stress this enough: everything must be DRY! The only downside to this reaction is it takes an assload of iodine (which is expensive) to do any sizeable amounts.

2Al + 3I2 ----> 2AlI3

C10H12O2 + AlI3 ----> AlI2C9H9O2 + CH3I

AlI2C9H9O2 + 3H2O ----> C9H10O2 + 2HI + Al(OH)3

Eugenol 3 neck 1000ml RBF w/ 24/40 joints
Aluminum metal (foil, powder, chips) Reflux Column w/ 24/40 joints
Iodine Vacuum filtration equipment
Benzene or cyclohexane (NOTE A) addition funnel (24/40 joints)
Inert Atmosphere (NOTE B) Magnetic stirrer recomended
Your favorite fabric softener Separatory funnel

Prelab: After all of the glassware is washed, it should be dried in an oven to remove all traces of water. Set up the three neck flask with one stopper, one reflux column and the addition funnel. Once put together, attach a calcium chloride drying tube to the top of the condensor. Water elimination is extremely important as even 1ml of water can reduce the yeild to 0.

Into the 1000ml RBF, pour 150ml of benzene or cyclohexane (NOTE A). To this, add 60g of iodine crystals, followed by 4.5g of aluminum (foil, chips, powder). Reflux this until the red/violet iodine color disappears and a grey-tan color is introduced. Once this is done, set up your inert atmosphere (NOTE B) by hooking it to the previously stoppered joint on the flask. Displace any air in the system with the inert atmosphere as you cool it in an ice bath to below 30C. Once below 30C (or roughly). Charge the addition funnel with 30g of eugenol, 3-5ml of your favorite fabric softener (I used snuggle), and a little (~20ml) benzene or cyclohexane to wash it all down. Begin slowly adding this to the mixture while maintaining the cool water through the condenser. If you do not have a 3-neck flask, or an addition funnel, you may drip it through the reflux column.

At this point, methyl iodide is being formed. It boils at 42C, so you can see why reducing the temp below 30C is important. Methyl iodide is quite poisonous and adequate ventilation is necessary. Continue slowly adding, while maintaining the inert atmosphere. It is recommended to include magnetic stirring at this point, but I did without it. Once it has all been added, reflux it for 1-2 hours with the inert atmosphere still running. After this time, you'll have a flask full of anything from dark brown to light tan solids. Let it cool to room temp and add 100-200ml of water. Continue the inert atmosphere the entire time. If there are clumps in there, you will have to break them up in some fashion to fully hydrolyze it. Once it is a fine suspension, transfer it to a beaker of adequate size. Use a wash bottle to get out any of the remaining solid. You may discontinue the inert atmosphere at this time. Let the precipitate settle to the bottom for a couple hours. Once settled, decant the water into a filter, and follow it by the precipiate. Use vacuum and get off as much liquid as possible in the filter. You must let it settle first, otherwise you will be waiting forever for it to filter, and atmospheric exposure to wet 4-allylcatechol can decompose it.

Place 100-150ml of diethyl ether in the 1000ml flask from before to get any residue, then pour it into a 600ml beaker. Add the solid material on the filter to the beaker of ether and stir it well. This will extract the 4-allyl catechol from the aluminum hydroxide and other salts. Cover the beaker and let it settle for a few hours again. Once again, decant the ether into a filter, followed by the solid. Run a small portion of ether through the solid before it clogs up the filter completely. You must let it settle and decant first, otherwise the superfine aluminum salts will clog up the filter and your ether will evaporate faster than it can go through the filter. If there is water in your ether, separate it with a separatory funnel, then just evaporate the ether off with a water bath or with vacuum. You should be left with a white to tan colored solid. This can be recrystallized from petroleum ether. Theoretical yeild is 23.67g but you should obtain about 20g.

NOTE A: Substitute the solvent as you like with a non-polar solvent. Do not use diethyl ether or ethyl acetate. Useable solvents include benzene, cyclohexane, toluene, xylene, chloroform (reduced yeild), nitrobenzene (poor yeild), chlorobenzene, etc.

NOTE B: For the inert atmosphere, nitrogen is recommended, but this requires a cylinder of nitrogen. Propane can be used without any problem. Use a torch and connect a rubber tube to it. Run it through a calcium chloride dryer first, then run it into the flask. At the top of the reflux condenser, place a stopper with a small peice of glass tubing extending from it. Since propane is very flammable and also contributes to global warming, it is best to burn it as it is used. Let propane flow through the flask/condenser for 30 seconds, then light the little glass tube. You only want a very small flame - similar to a cigarette lighter - to come from the tube. You can increase the size if it wont stay lit. A benefit of this, is it will burn off any methyl iodide that leaves the condenser, producing CO2, H2O and I2 in the gas phase. Iodine is toxic, so ventilation is required, but it's less dangerous than methyl iodide and gives an interesting purple smoke as it burns.