Ethanoic Acid & Esterification Reactions
Section: 11. Organic Chemistry | Syllabus: Cambridge AS Level Physics 9702
Ethanoic Acid & Esterification Reactions Ethanoic Acid (Acetic Acid) Ethanoic acid is the most important and commonly encountered carboxylic acid in everyday life. Molecular Formula: CH₃COOH or C₂H₄O₂ Structural Formula: CH₃-COOH Structure H O | ‖ H - C - C - OH | H Physical Properties Appearance: Colorless liquid Smell: Sharp, pungent, vinegary odor Boiling point: 118°C Melting point: 17°C (can freeze in cold weather - "glacial" acetic acid when pure) Solubility: Completely miscible with water (mixes in all proportions) Acidity: Weak acid with pH around 2.4-3.4 in dilute solution Chemical Properties As a carboxylic acid, ethanoic acid shows all typical acid reactions: Reacts with metals to produce hydrogen Reacts with bases and metal oxides to form salts Reacts with carbonates to produce CO₂ Can be neutralized by alkalis Undergoes esterification with alcohols Production of Ethanoic Acid 1.
Oxidation of Ethanol Ethanol can be oxidized to ethanoic acid using oxidizing agents or bacteria: CH₃CH₂OH + 2[O] → CH₃COOH + H₂O Chemical oxidation: Use potassium dichromate(VI) in acid Biological oxidation: Acetobacter bacteria in the presence of air This is how wine/beer turns to vinegar when exposed to air 2.
Industrial Production Methanol reacts with carbon monoxide in the presence of a catalyst: CH₃OH + CO → CH₃COOH Uses of Ethanoic Acid Vinegar - 3-5% solution used in cooking and food preservation Food industry - flavoring, preservative (E260) Manufacturing esters - for fragrances, flavors, solvents Making plastics - cellulose acetate, polyvinyl acetate (PVA) Pharmaceuticals - making aspirin and other medicines Textile industry - dyeing and printing fabrics Descaling - removing limescale from kettles and appliances Esters What are Esters?
Esters are organic compounds formed when a carboxylic acid reacts with an alcohol. They contain the ester functional group: O ‖ -C-O- Ester An organic compound formed from the reaction between a carboxylic acid and an alcohol, containing the -COO- functional group.
General Formula: R-COO-R' (where R and R' are alkyl groups) Characteristics of Esters Sweet, fruity smells - often smell like fruits or flowers Volatile - evaporate easily at room temperature Insoluble in water - but soluble in organic solvents Less dense than water - float on water Neutral - not acidic or basic Lower boiling points than corresponding acids (no hydrogen bonding between ester molecules) Esterification Reaction Esterification The reaction between a carboxylic acid and an alcohol to form an ester and water.
General Equation: Carboxylic acid + Alcohol ⇌ Ester + Water R-COOH + R'-OH ⇌ R-COO-R' + H₂O Conditions Catalyst: Concentrated sulfuric acid (H₂SO₄) - acts as a dehydrating agent and acid catalyst Heat: Warm/heat the mixture (usually under reflux at 60-70°C) Reversible reaction: The ⇌ symbol shows the reaction can go both ways Key Features Reversible/Equilibrium reaction - doesn't go to completion Condensation reaction - water is produced as a by-product Slow reaction - needs heating and catalyst To increase yield: use excess alcohol or acid, remove water as it forms Example Reactions 1.
Ethanoic Acid + Ethanol → Ethyl Ethanoate CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O (ethanoic acid + ethanol ⇌ ethyl ethanoate + water) Ethyl ethanoate smells like pear drops/nail polish remover 2. Ethanoic Acid + Methanol → Methyl Ethanoate CH₃COOH + CH₃OH ⇌ CH₃COOCH₃ + H₂O (ethanoic acid + methanol ⇌ methyl ethanoate + water) 3.
Propanoic Acid + Ethanol → Ethyl Propanoate C₂H₅COOH + C₂H₅OH ⇌ C₂H₅COOC₂H₅ + H₂O (propanoic acid + ethanol ⇌ ethyl propanoate + water) 4. Methanoic Acid + Propanol → Propyl Methanoate HCOOH + C₃H₇OH ⇌ HCOOC₃H₇ + H₂O (methanoic acid + propanol ⇌ propyl methanoate + water) Naming Esters Esters are named in two parts: First part: From the alcohol - name the alkyl group from the alcohol and add "yl" Second part: From the acid - change the ending from "-oic acid" to "-oate" Naming Pattern [Alkyl group from alcohol] + [acid name with -oate ending] Examples Acid Alcohol Ester Name Formula Ethanoic acid Ethanol Ethyl ethanoate CH₃COOC₂H₅ Ethanoic acid Methanol Methyl ethanoate CH₃COOCH₃ Propanoic acid Ethanol Ethyl propanoate C₂H₅COOC₂H₅ Methanoic acid Propanol Propyl methanoate HCOOC₃H₇ Butanoic acid Methanol Methyl butanoate C₃H₇COOCH₃ Memory Aid "Alcohol first, acid second" - Ethanol + Ethanoic acid = Ethyl ethanoate Hydrolysis of Esters Hydrolysis The reverse of esterification - breaking down an ester using water to reform the acid and alcohol.
Acid Hydrolysis Conditions Dilute acid (HCl or H₂SO₄) and heat under reflux Ester + Water ⇌ Carboxylic acid + Alcohol CH₃COOC₂H₅ + H₂O ⇌ CH₃COOH + C₂H₅OH Reversible reaction Slow process Alkaline Hydrolysis (Saponification) Conditions Sodium hydroxide (NaOH) or potassium hydroxide (KOH) and heat Ester + Sodium hydroxide → Sodium salt of acid + Alcohol CH₃COOC₂H₅ + NaOH → CH₃COONa + C₂H₅OH Not reversible (goes to completion) Faster than acid hydrolysis Produce…
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