Four reactions account for most practical organic chemistry: saponification (fat plus alkali gives soap and glycerol), esterification (acid plus alcohol gives an ester and water), transesterification (oil plus methanol gives biodiesel and glycerol) and polymerisation (small molecules joined into long ones). Each is a particular functional group meeting another, so once you can name the groups you can predict the reaction. Start with soap, which is the simplest and the most useful.
Part of Organic Chemistry
The short list of organic transformations a rebuilding community can actually perform, and how they relate to each other.
Each Reaction Is Two Groups Meeting
The carrier’s “Key Reactions You Can Perform” section gives the pattern in word equations. They are worth reading side by side.
| Reaction | In words | Groups meeting | Product use |
|---|---|---|---|
| Saponification | Fat + strong alkali → soap + glycerol | Ester and hydroxide | Soap, glycerol |
| Esterification | Acid + alcohol → ester + water | Carboxyl and hydroxyl | Solvents, fragrances |
| Transesterification | Vegetable oil + methanol → biodiesel + glycerol | Ester and alcohol | Engine fuel |
| Polymerisation | Many small molecules → one long molecule | Reactive groups or double bonds | Plastics, adhesives |
Saponification and esterification are mirror images: esterification builds an ester from an acid and an alcohol, and saponification breaks one apart with alkali. That is why the carrier calls fats and oils “esters”. Transesterification swaps the alcohol part of an ester for a different alcohol, which is how thick oil becomes a thin fuel.
Where Each Reaction Is Taught
- Saponification and Soap Quality Control
- Esterification
- Biodiesel, with the full procedure in Biodiesel Production
- Polymerization
What You Need
- Clean reaction vessels of glass, glazed ceramic or enamel (not aluminium for alkalis).
- Accurate scales. Every reaction here depends on weighing reagents, not guessing.
- An indicator for pH (red cabbage juice) and a thermometer.
- Eye protection and gloves: three of the four use corrosive or toxic reagents.
Worked Example: Mass Balance In An Esterification
Reactions conserve mass, so you can check any recipe on paper. Take acetic acid (60 g per mole) and ethanol (46 g per mole), which join to form ethyl acetate (88 g per mole) and water (18 g per mole). Reagents: 60 + 46 = 106 g. Products: 88 + 18 = 106 g. The books balance. If a recipe’s quantities cannot be reconciled this way, one of its numbers is wrong. Molar masses use rounded atomic masses C = 12, H = 1, O = 16.
Common Mistakes
- Assuming a reaction goes to completion. Esterification stops at an equilibrium and needs a push; see its article.
- Skipping the weighing. Too much alkali leaves caustic soap; too little leaves soft, greasy soap.
- Treating the by-product as waste. Glycerol from soap and biodiesel is useful, but the biodiesel version carries lye and methanol; see Glycerin Byproduct.
Safety
Three of the four reactions use a hazardous reagent
Lye burns skin and eyes; concentrated sulfuric acid, used as the esterification catalyst, burns and generates heat on dilution; methanol, used for biodiesel, blinds and poisons through skin and lungs. Wear eye protection and gloves, work outdoors or in strong ventilation, and add reagents slowly. Never heat a sealed container.
What’s Next
- Learn next: Esterification — the reaction behind solvents and fragrances
- Combine with: Functional Groups — the groups each reaction joins