Essential Essence Production

THEORY

    Last semester, we had used acetic anhydride to acetylate various alcohols, and, if our imaginations were strong enough, we could smell various fruity fragrances, "essential essences" as botanists say. Today we shall elaborate upon that activity to attempt to manufacture, isolate and purify those very essences in perhaps gram quantities by using methods such as refluxing (boiling without losing the vapors), extracting by partitioning the product between immiscible solvents (see the end-box on this), and distillation of either the product or its solvent away from each other. All this, we hope, without overwhelming our senses with too much perfume!

    As before we shall use acetic anhydride, Ac₂O ( (CH₃CO)₂O as shown at the right). But instead of a multitude of different alcohols, we shall focus our attentions on only two of them - butyl alcohol (normal butanol), and iso-amyl alcohol (iso-amylol or 3-methyl-butanol). Unlike before, this time we shall measure out molar quantities in order to optimize the "organic syntheses" involved.

    The reactions being performed are

Ac₂O + n-butanol → AcOH + n-butyl acetate
Ac₂O + iso-amylol → AcOH + iso-amyl acetate

    In order to maximize the yield, we will add more moles of the cheaper alcohols to the more expensive, and noxious acetic anhydride. Hopefully, in doing so we won't have much if any of the anhydride left over to deal with.

WHAT TO DO

    You should fill your 100-mL reaction flask no more than half-full to give it room to boil. So we are limited with putting no more than 50 mL of liquids into it. Suppose we use 20 mL of Ac₂O, which is 0.2 mole. To have an excess, we want more than 0.2 mole of our specified alcohol. 0.3 mole of n-butanol is about 25 mL, and of iso-amylol it is about 30 mL. (What is our limiting reagent? Ac₂O, which we want to use completely.) (How much acetic acid will we be producing? 0.2 mole = 12 gms.

    On the following table, cross out the lines that another group will be using so you don't inadvertantly add them to your flask.

TABLE OF BOILING POINTS
Reagent	Molec. Wt.	b.p. °C	mL to use
Ac2O	102	140	20
n-butanol	74	117	25
butyl acetate	116	126	n.a.
iso-amylol	88	128	30
iso-amyl acetate	130	142	n.a.
water	18	100	5

    Both of these require some heating, and thus we will boil our ingredients for about 20 minutes. We do not want them to boil away and so we "reflux" them by placing a cold-water condenser on top of the boiling flask. The boiling vapors rise into the condenser and condense to drip back into the boiling brew.

    Hooking up the condenser:

1. Place a non-flammable support under a heating mantle.
2. Insert the reaction flask in the mantle
3. Affix the neck of the flask to the ring stand with a clamp
4. Add your fluid component (Ac₂O and your specified alcohol) to the flask
5. Drop in three or four boiling beads
6. Insert the condenser into the top of the flask. Use two clamps to hold it vertically in place. Make sure that one clamp supports the condenser right below one of the water taps so that the condenser cannot slide down through the clamps.
7. Affix two rubber tubes to the two condenser taps. Attach the lower tube to the water faucet, direct the second tube to the drain in the sink.
8. Gently turn on the water. Watch the level rise in the condenser and spill out the exit tube. The water need not flow fast. A slow dribble is okay.
9. Dry off the desk.
10. Obtain a variac (a variable "autotransformer"). Place it on the desk so that water will not spill onto it in event a water-tube comes loose. Turn its switch to "off," and the dial down to zero
11. Plug the mantle into the variac.
12. Plug the variac into the "house" outlet.
13. Turn the variac "on" and move the dial up to about 50 (vac). In a few minutes you should feel warmth where the mantle touches the flask. If you don't, the variac's fuse is probably blown.
14. Adjust the heat by turning the dial up or down.
15. The vapors should not rise more than halfway up the condenser. If they do, turn down the variac.
16. Boil for 20 minutes.
17. Put about 5 mL of distilled water in a beaker. Using a plastic dropper, add dropwise the water to the top of the condenser. Fast addition results in a steam explosion because the boiling reagents are hotter than 100°c. Slow addition of the water allows the water to cool the reaction mixture down to 100°c.
18. Boil for another 5 minutes to hydrolyze the unused Ac₂O.
19. Turn off the variac.
20. Remove the support under the mantle and drop the mantle to the desk to facilitate more rapid cooling.
21. You may wish to raise a container of warm water up under the hot flask to help it cool faster.
22. While this is cooling, remove the condenser and lay carefully on the desk. You will soon be using it in another configuration.
23. If you sniff the flask do so only by wafting fumes with your hand to your nose. Do NOT put your snoot into the flask unless you want to clean your sinuses out! Most of what you will smell is the strong scent of acetic acid (vinegar). You might also smell some of your unreacted alcohol; perhaps you can smell your product as a sweet, fruity smell. Usually, however, the acetic acid overwhelms your product.

    We must now rid the system of the acrid smell of the acetic acid by converting it from a volatile organic compound to a non-volatile salt.

24. Add another 10 ml of distilled water and a couple of drops of methyl red. MR turns red in acid. Is it acid? How much acid should have been produced if all the 0.3 moles of Ac₂O were used? (Approx. 0.3 moles: half went to make your ester product and half to acetic acid.)
25. Pour your reaction mixture into a 500 mL flask.
26. Using a 50 mL graduated cylinder filled to the 50 mL line with 5 M NaOH, add some to the beaker until the red just disappears. Keep track of how much NaOH you add. Then add two more drops. Shake the reaction flask furiously to make sure all the acetic acid moves from the immiscible organic phase and into the water to react with the base. If redness reappears, add more NaOH.
27. Record how much NaOH you used. (molar x mL = millimoles; is your amount reasonable?)
28. Rinse your hands and clean up any stray drops and dribbles of NaOH. It will cause skin rashes as it dries on you. You may rinse your hands with 0.1 M HCl to neutralize the base. (When HCl dries, it all evaporates unlike NaOH which doesn't and gets more and more concentrated.)
29. Pour the contents of your flask into a separatory funnel ("sep funnel"), and set it in a metal ring to allow the two layers to separate.
30. After the layers have resolved, you wonder which one is the aqueous layer, and which is the organic layer? Test the top and bottom layers as to which can dissolve in water: Let out a drop from the bottom of the "sep funnel" and let if fall into a beaker of tap water. If it is the organic layer, it should not mix but rather settle as a droplet to the bottom of the water; if it is the aqueous layer, it will then instantly mix with the beaker's water.
31. Throw away the aqueous layer with its NaOAc salt.
32. Use your sniffer now. What do you smell? What you have are two major components: excess alcohol and your product.

    Now to separate the excess alcohol from your desired product. You will want a distillation set-up. But before you start the distillation, you should have an idea of what properties your various remaining components have. So visit the preceding table again and look at the relevant boiling points. When the boiling starts, which one should begin boiling first? That is the one that will start dripping from the condenser first. You should see that the thermometer reads approximately at the bp of the liquid that boils at the lower temperature.

33. Add boiling beads to the flask if you have lost the previous ones.
34. Again use the support stand under the mantle. Rest the reaction flask in the mantle and clamp it to the ring stand.
35. Insert the distillation connector, and clamp it to the ring stand.
36. Insert the the condenser to the side-arm of the connector, and clamp it again in two places to the bars. Jiggle it a bit to make sure it won't slide, fall and break. Workers who allow their expensive glass condensers break are sent down to the basement to feed the dragons.
37. Line up a few very small receiving beakers or test tubes (better) near the exit end of the condenser. Place one under it to collect the first drippings. Your whole setup should look like the silhouette next to the title.
38. Start the water flowing. Clean up spills.
39. Cut off about 1/8 inch of the rubber tubing to make a tiny rubber band and run that up the special distillation thermometer (reads to higher temperatures than the thermometers you have used so far). Set the thermometer down into the connector such that the bulb is even with the bottom of the hole leading into the side-arm. Adjust the rubber band as needed.
40. Connect the variac to the mantle and turn up the heat.
41. Collect 5 ml of drippings and label each container with the temperature it "came off at".
42. When only about 5 mL of boiling fluid remains, turn off the heat, lower the mantle.
43. Perform some sniff tests. Results? Conclusions?
44. If you wish, you may determine the quality of your products by using the refractometer and comparing your results with those available in the tables.

    Carefully disassemble your set-up, drain out the water from the condenser, remove the tubing, and clean out your reaction flask. Remove the band from the thermometer.

    Now go back to the appropriate equation for your alcohol, and place the amount of moles in front of each of the reactants and products. Show the instructor.

    Yes, you may take the product home with you. Just remember that the method you has gone much further toward completion than the much less expensive commercial method. In the real world outside with the chemical industry, it's all about cost/benefit ratios. What they do is boil their alcohol with acetic acid for hours and hours, and then do the distillation with water. The vapors that come off are collected and cooled. The desired "essence" separates from the water phase. But it took hours and hours, which we don't have in a 3-hr lab schedule.