Esterification joins a carboxylic acid and an alcohol into an ester and water, with a few drops of concentrated sulfuric acid as catalyst. Acetic acid plus ethanol gives ethyl acetate, a fruity-smelling solvent for resins and lacquers. The reaction is reversible and stops at equilibrium, so water in the mixture holds the yield down; ordinary vinegar, which is mostly water, gives only a trace.
Part of Organic Chemistry
Making esters from carboxylic acids and alcohols for use as fragrances and as solvents for resins and lacquers.
The Carrier’s Recipe Works, But It Makes A Smell, Not A Product
The carrier states the reaction as acid plus alcohol giving ester plus water, and the practical version: mix vinegar (acetic acid) with ethanol, add a few drops of concentrated sulfuric acid as a catalyst, and warm gently; the sweet, fruity smell of ethyl acetate appears. It adds that the compound is a useful solvent for resins, for cleaning metal and for making lacquers.
The smell is the proof of reaction; the quantity is the problem. The reaction runs in both directions. Ester and water react back to acid and alcohol, and the mixture settles at a balance. The balance is pushed toward ester by adding more of one reagent and by removing water. Vinegar of household strength is mostly water, so the mixture starts on the wrong side and ends with little ester. Stronger acid, more alcohol, a dry catalyst, and removing the water or the ester as it forms (by distillation) all raise the yield. The corpus does not give a practical yield, so none is quoted here.
What You Need
- Acid: the strongest vinegar you can make; see Vinegar Strength.
- Alcohol: ethanol as dry as you can make it (Dehydration to Fuel Grade).
- Catalyst: concentrated sulfuric acid, a few drops per the carrier (Sulfuric Acid).
- Vessel and condenser: a vented flask with a reflux or distillation arm, never a sealed vessel.
- Heat: a water bath, because ethanol and ethyl acetate both burn.
Method: A Small Test Batch
Step 1: Combine the acid and alcohol in the vessel, with the alcohol in excess.
Step 2: Add the catalyst drop by drop, stirring. Strong acid and water generate heat.
Step 3: Warm gently in a water bath and check for the fruity smell by wafting.
Step 4: Recover the ester by distilling it off, which also removes it from the equilibrium. Ethyl acetate boils at about 77 °C, a recalled value; it distils with some ethanol and water, so the first product is impure.
Worked Example: Theoretical Yield Of Ethyl Acetate
Take 60 g of pure acetic acid (1 mol), the molar mass 60 g from C = 12, H = 1, O = 16: 2 × 12 + 4 × 1 + 2 × 16.
- Ethanol needed for 1 mol: 46 g.
- Ethyl acetate formed if the reaction went to completion: 1 mol × 88 g = 88 g.
- Water formed: 18 g.
- Check: 60 + 46 = 106 = 88 + 18.
That 88 g is the ceiling. Real esterifications at equilibrium, with no water removal, reach only part of it; with equal moles of reagents, a figure of about two thirds is the textbook outcome for simple acid-alcohol pairs. That fraction is from general chemistry, not the corpus, and it is only a guide.
Common Mistakes
- Using weak vinegar and expecting a solvent. You will smell fruit and recover almost nothing.
- Heating over a flame. Ethyl acetate’s flash point is below ordinary room temperature (a recalled property), so use a water bath outdoors.
- Adding water to concentrated sulfuric acid. Add acid to the mixture, never water to the acid; see Safety.
Safety
Concentrated sulfuric acid, flammable vapour and heat in one flask
Concentrated sulfuric acid destroys tissue and releases heat on contact with water; add it a drop at a time into the mixture, and never pour water into the concentrated acid. Ethyl acetate vapour is flammable and heavier than air (molar mass 88 against air’s 29 gives a ratio of 88 ÷ 29 = 3.0), so it sinks to floor level and travels to ignition sources. Work outdoors, vent the vessel, keep flames away, and wear eye protection and gloves. See Spill Response for acid on skin.
What’s Next
- Learn next: Adhesives and Glues — resin solvents and varnishes
- Combine with: Solvent Extraction — esters as selective solvents