Extraction: Three Small Shakes Beat One Big One

**Check the tap and the stopper before putting anything in.** A funnel with a loose tap empties itself down the front of whoever is holding it. **Never fill more than about two thirds.** There must be room for the layers to move when it is shaken. **Support the stopper with one hand and the tap with the other.** Invert, and **open the tap immediately** to release pressure, pointing the stem away from everyone. Then close, shake gently for a few seconds, and vent again. Repeat with progressively more vigorous shaking. **Pressure is the real hazard.** A volatile solvent warmed by the hand, or a carbonate wash releasing carbon dioxide, builds pressure fast enough to blow the stopper out and spray the contents. Venting every few seconds at the start is not optional. **Stand it in a ring to settle**, and take the stopper OUT before opening the tap — otherwise nothing flows and a partial vacuum forms. **Run the lower layer out through the tap; pour the upper layer out of the top.** Running the upper layer through the tap drags it through the residue of the lower one. Gloves, eye protection, good ventilation, no flames anywhere near.

**Identify the layers before running anything off.** Density decides it: ether, hexane, ethyl acetate and toluene float on water; dichloromethane and chloroform sink. A concentrated salt solution is denser than many solvents that would normally sink in pure water, so adding salt can swap the order. **When in doubt, test.** Add a few drops of water to the layer in question. If they mix in, it is the aqueous layer; if they form a bead, it is not. Five seconds, and it prevents throwing the product away. **Keep every layer until the product is in hand.** This is the rule that saves preparations. A layer that turns out to have been the wrong one is recoverable only if it is still in a flask. **Emulsions** — a cloudy layer that will not separate — come from shaking too violently, from surfactant-like impurities, or from solvents of similar density. The remedies, in order: *Wait.* Many separate on standing. *Add brine.* Saturated salt solution raises the aqueous density and drags dissolved solvent out of it. The standard fix. *Swirl gently rather than shaking.* *Filter through a plug of glass wool or celite.* *Add a little more of one solvent* to change the density difference. Prevention is better: **swirl and invert rather than shaking hard.** Extraction needs contact, not violence.

**An extraction takes the product out; a wash takes impurities away from it.** Same funnel, opposite intent, and the layer you keep is the other one. A standard work-up sequence, and each step has a reason: **Water wash** — removes water-soluble salts and any remaining polar reagent. **Dilute acid wash** — removes basic impurities by ionising them into the water. Only if the product is not itself basic. **Dilute bicarbonate wash** — removes acids. It fizzes, so vent constantly; a stoppered funnel of bicarbonate and acid builds pressure very fast. **Brine wash** — a saturated salt solution pulls dissolved water out of the organic layer, so the drying agent afterwards has much less to do. **Dry over a drying agent**, which is the next rung. **Then remove the solvent.** Two habits worth keeping: **label every flask as it is filled**, because four unlabelled layers on a bench is a preparation lost; and **check the pH of the aqueous layer** after an acid or base wash, to confirm the wash actually did what was intended rather than being neutralised by the product.