Definition
Ethanol can be oxidized to acetic (ethanoic) acid using an oxidizing agent such as acidified (or acidified potassium dichromate) — in this reaction, manganese in is reduced (from to a lower oxidation state) as it oxidizes the alcohol.
On a commercial scale, acetic acid is made by fermenting ethanol in the presence of acetic acid bacteria, which requires a sufficient supply of oxygen: . Oxygen's role here is as the actual oxidizing agent, directly reacting with ethanol (via the bacteria's enzymes) to convert it into acetic acid — without enough oxygen, this oxidation can't proceed.
Definition
Esterification is the reaction of a carboxylic acid with an alcohol (usually with an acid catalyst) to form an ester and water: acid alcohol ester water.
Ethanol reacts with propanoic acid by esterification: .
Example 1 — identifying reactants that give a specific ester
Which substances react to produce ?
- The acid part, , comes from butanoic acid ().
- The alcohol part, , comes from ethanol ().
Answer: Butanoic acid and ethanol
Example 2 — ester formula from named reactants
Find the formula of the ester formed from methanol and propanoic acid.
- Propanoic acid gives the acid part: .
- Methanol gives the alcohol part: .
Answer: (methyl propanoate)
Definition
Carboxylic acids react with reactive metals (like magnesium) to give a salt and hydrogen gas: .
Carboxylic acids react with carbonates (like magnesium carbonate) to give a salt, water, and carbon dioxide: .
Ethanoic acid reacts with sodium hydroxide (an acid–base neutralization) to give sodium ethanoate and water: .
Definition
Carboxylic acids and esters act as flavouring agents in food and drinks — many fruit flavours and aromas are actually specific esters (e.g. the ester responsible for apple flavour is a form of amyl/pentyl acetate-type ester), and various carboxylic acids (like citric acid) are common flavour enhancers, adding a tart/sour taste.
Carboxylic acids play a role in preparing beverages by contributing tartness/acidity (e.g. citric acid in soft drinks) and acting as natural preservatives that inhibit microbial growth.
Acetic acid's acidity (and its ability to lower pH enough to inhibit bacterial and fungal growth) makes it suitable as a preservative in pickles — the acidic environment it creates prevents spoilage organisms from thriving.
Carboxylic acids are used as solvents in industry, since many of them (and their esters) can dissolve a range of organic substances that water cannot, useful in manufacturing paints, coatings, and other products.
Carboxylic acid derivatives help improve medicines like aspirin and ibuprofen: aspirin is itself an ester (of salicylic acid), and modifying carboxylic acid-based structures allows chemists to fine-tune a drug's solubility, absorption, and how long it stays active in the body.
Definition
A dicarboxylic acid reacting with a diol (a molecule with two groups) forms a polyester through repeated esterification at both ends of each molecule, linking many units together into a long chain polymer — this is used to make synthetic fibres (e.g. polyester fibre, used widely in clothing and fabric).
Polymethyl methacrylate (PMMA), commonly known as Perspex (or acrylic glass), is a transparent polymer made from methyl methacrylate monomers and is commonly used as a substitute for glass, since it's lighter, more shatter-resistant, and easier to shape than ordinary glass.
Definition
Malic acid is present in apples; citric acid is present in lemons (and other citrus fruits); vinegar's characteristic acid is acetic (ethanoic) acid.
Vitamin C is chemically known as ascorbic acid — itself a carboxylic-acid-related compound important as an antioxidant and for immune function.
Pure acetic acid — a corrosive, colourless solid (or liquid, depending on temperature) completely miscible with water — is called glacial acetic acid, named for the ice-like crystals it forms when it solidifies at temperatures just below room temperature.
Quick Recap
- ●Ethanol acetic acid; commercially via fermentation with acetic acid bacteria sufficient O
- ●Esterification: acid alcohol ester water (name the ester from its acid and alcohol parts)
- ●Carboxylic acid reactive metal salt H; carbonate salt HO CO; base salt HO
- ●Uses: flavouring (esters/acids), beverage tartness/preservation, pickle preservative (acetic acid), solvents, drug design (aspirin, ibuprofen)
- ●Dicarboxylic acid diol polyester (synthetic fibre); PMMA (Perspex) glass substitute polymer
- ●Malic acid (apples), citric acid (lemons), acetic acid (vinegar, glacial form pure), ascorbic acid Vitamin C
