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Overview

🌳 Concept tree

Lesson 6→Carboxylic Acids, Esters and Organic Polymers

├── The carboxyl group

├── Types

├── Nomenclature

├── Preparation of acetic acid

├── Physical properties

├── Chemical properties

├── Aromatic acids→benzoic acid

├── Important acids and their uses

├── Definition and formation

├── Nomenclature

├── Preparation

├── Physical properties

├── Chemical properties

├── Applications of esters

├── Aspirin

├── Types of organic reactions (summary)

└── Revision key points for Part B

Lesson 6: Carboxylic Acids, Esters and Organic Polymers · 1 / 19

The carboxyl group

Carboxylic acids contain one or more carboxyl groups, –COOH (a carbonyl group C=O and a hydroxyl group –OH on the same carbon).
They are the most acidic of the common organic compounds, but they are weak acids compared with mineral acids (HCl, H₂SO₄, HNO₃).

Comparison aspect	Main idea	Keywords
Aliphatic acids	–COOH attached to an alkyl group (R–COOH). Saturated mono-carboxylic aliphatic acids are called fatty acids because many occur in fats as esters with glycerol	COOHattachedalkylgroup
Aromatic acids	–COOH attached to a benzene ring (benzoic acid)	COOHattachedbenzenering

Lesson 6: Carboxylic Acids, Esters and Organic Polymers · 2 / 19

Types

Mono-carboxylic (monobasic) HCOOH formic acid, CH₃COOH acetic acid, C₆H₅COOH benzoic acid.
Di-carboxylic (dibasic) HOOC–COOH oxalic acid; phthalic acid (benzene-1,2-dicarboxylic acid).
Carboxylic acids are classed as aliphatic and aromatic.
In aromatic acids such as benzoic acid, C₆H₅COOH, the carboxyl group is attached to a benzene ring.

Lesson 6: Carboxylic Acids, Esters and Organic Polymers · 3 / 19

Nomenclature

Common names come from the natural sourceformic (Latin formica, ant), acetic (acetum, vinegar), butyric (butyrum, butter), palmitic (palm oil).

IUPACthe alkane name with -e replaced by -oic acid; the carboxyl carbon is C-1:

Formula	Common	IUPAC
HCOOH	formic acid	methanoic acid
CH₃COOH	acetic acid	ethanoic acid
CH₃CH₂CH₂COOH	butyric acid	butanoic acid
C₁₅H₃₁COOH	palmitic acid	hexadecanoic acid

Substituents are numbered from the carboxyl carbon→2,2-dimethylbutanoic acid; 2,3-dichlorohexadecanoic acid; 2,4-dichlorobenzoic acid.

Lesson 6: Carboxylic Acids, Esters and Organic Polymers · 4 / 19

Preparation of acetic acid

Comparison aspect	Main idea	Keywords
Biological (vinegar) method	dilute alcoholic solutions (wine fermented juice) are oxidised by atmospheric oxygen in the presence of vinegar bacteria (Acetobacter): C₂H₅OH + O₂ → CH₃COOH + H₂O	dilutealcoholicsolutionswine
From acetylene	catalytic hydration of ethyne gives ethanal which is oxidised to the acid: HC≡CH + H₂O —(H₂SO₄/HgSO₄ 60 °C)→ CH₃CHO 2CH₃CHO + O₂ → 2CH₃COOH. (Also: oxidation of ethanol by acidified dichromate hydrolysis of esters.)	catalytichydrationethynegives

Lesson 6: Carboxylic Acids, Esters and Organic Polymers · 5 / 19

Physical properties

The first four members are corrosive liquids with a sharp, irritating smell, completely miscible with water.
The middle members (C₅–C₉) are oily liquids with unpleasant odours and are only sparingly soluble; higher members (above C₁₀) are waxy, odourless solids and insoluble.
Carboxylic acids boil at higher temperatures than alcohols of the same molecular mass because each pair of acid molecules is joined by two hydrogen bonds (a stable dimer):

Acid	M	b.p.	Alcohol	M	b.p.
Methanoic	46	100 °C	Ethanol	46	78 °C
Ethanoic	60	118 °C	1-Propanol	60	97–98 °C

Lesson 6: Carboxylic Acids, Esters and Organic Polymers · 6 / 19

Chemical properties

1. Reactions of the hydrogen ion (acidity and salt formation).→React with:

Comparison aspect	Main idea	Keywords
active metals (above H)	2CH₃COOH + Mg → (CH₃COO)₂Mg + H₂↑	2CH₃COOHCH₃COO
metal oxides and hydroxides	CH₃COOH + NaOH → CH₃COONa + H₂O	CH₃COOHNaOHCH₃COONa
carbonates and bicarbonates (with effervescence of CO₂)	CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂↑ 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂ All carboxylic acids are weak (partially ionised)	CH₃COOHNaHCO₃CH₃COONa2CH₃COOH
2. Reaction attributed to –OH: esterification	(with alcohols conc. H₂SO₄): RCOOH + R′OH ⇌ RCOOR′ + H₂O	alcoholsconcH₂SO₄RCOOH
3. Reaction of the carboxyl group: reduction.	Hydrogen with copper chromite (CuCrO₄/CuCr₂O₄) at 200 °C reduces the acid back to the alcohol (the reverse of oxidation of alcohols): CH₃COOH + 2H₂ → CH₃CH₂OH + H₂O	HydrogencopperchromiteCuCrO₄

Detection of acetic acid:

add sodium carbonate or bicarbonate — effervescence of CO₂ which turns lime water milky; it also gives the fruity ester smell when warmed with ethanol and a little conc.
H₂SO₄.

Lesson 6: Carboxylic Acids, Esters and Organic Polymers · 7 / 19

Aromatic acids: benzoic acid

Preparation oxidation of toluene by air at about 400 °C over vanadium pentoxide (V₂O₅) catalyst: C₆H₅CH₃ + 3[O] → C₆H₅COOH + H₂O (or by KMnO₄).
Aromatic acids are generally stronger, less soluble in water and less volatile than aliphatic acids; they show the same reactions: C₆H₅COOH + NaOH → C₆H₅COONa + H₂O (sodium benzoate); C₆H₅COOH + C₂H₅OH (HCl or H₂SO₄) ⇌ C₆H₅COOC₂H₅ (ethyl benzoate) + H₂O.

Lesson 6: Carboxylic Acids, Esters and Organic Polymers · 8 / 19

Important acids and their uses

Comparison aspect	Main idea	Keywords
Formic acid (methanoic)	secreted by ants for defence (and in nettle stings) used in leather tanning textile dyeing and as a preservative/coagulant of latex	secretedantsdefencenettle
Acetic acid (ethanoic)	colourless corrosive liquid with pungent odour freezes at 16.6 °C into ice-like crystals so pure acid is called glacial acetic acid. A 4–5 % solution is household vinegar. Starting material for synthetic silk (acetate rayon) dyes insecticides food additives and esters	colourlesscorrosiveliquidpungent
Benzoic acid	sparingly soluble in water its sodium (or potassium) salt is soluble and well absorbed. Sodium benzoate (0.1 %) is a food preservative because it prevents the growth of fungi and moulds	sparinglysolublewatersodium
Citric acid	in citrus fruits (5–7 % in lemon about 1 % in orange) prevents the growth of bacteria in food by lowering pH used in drinks and to keep colour and taste of frozen fruit. It has three –COOH groups and one –OH	citrusfruitslemonorange
Lactic acid	CH₃CH(OH)COOH: in sour milk formed from lactose by bacterial enzymes also produced in muscles during hard exercise causing muscle cramps/fatigue	CH₃CHCOOHsourmilk
Ascorbic acid (vitamin C)	needed in small quantities found in citrus fruits vegetables and green pepper destroyed by heat and air. Lack of it causes scurvy (bleeding gums swollen joints)	neededsmallquantitiesfound
Salicylic acid	(2-hydroxybenzoic acid both –COOH and –OH): used in skin-care products (softens skin protects from sun treats warts and acne) and to make aspirin and methyl salicylate	hydroxybenzoicbothCOOHused
Amino acids	amino derivatives of carboxylic acids (an H of the alkyl group is replaced by –NH₂). The simplest is glycine NH₂–CH₂–COOH (aminoethanoic acid). Of the very many amino acids 20 occur in proteins these are α-amino acids R–CH(NH₂)–COOH (the amino group on the carbon next to –COOH). Proteins are polymers of amino acids	derivativescarboxylicalkylgroup

Lesson 6: Carboxylic Acids, Esters and Organic Polymers · 9 / 19

Definition and formation

Esters are produced by the reaction of a carboxylic acid with an alcohol (esterification), with elimination of water:
R–COOH + R′–OH ⇌ R–COO–R′ + H₂O

Esters are widespread in nature and are responsible for the pleasant smell and taste of flowers and fruits.
As the molecular mass of the acid and alcohol increases the odour decreases and the ester changes from a pleasant liquid to a nearly odourless waxy solid.
Waxes (e.g.
beeswax) are high-molecular-mass esters; fats and oils are esters of glycerol with long-chain fatty acids.

Lesson 6: Carboxylic Acids, Esters and Organic Polymers · 10 / 19

Nomenclature

Name = (alkyl group of the alcohol) + (acid name with -ic acid → -ate):

HCOOCH₃ methyl formate (methyl methanoate)

CH₃COOC₂H₅ ethyl acetate (ethyl ethanoate)

C₆H₅COOC₂H₅ ethyl benzoate

CH₃CH₂COOCH₃ methyl propanoate
CH₃CH₂CH₂COOCH₃ methyl butanoate

Lesson 6: Carboxylic Acids, Esters and Organic Polymers · 11 / 19

Preparation

Direct reaction of the acid with the alcohol→CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O. The reaction is reversible and slow, so it is heated with concentrated sulphuric acid (catalyst and dehydrating agent that removes water and shifts the equilibrium toward the ester) or with dry HCl gas.

Lesson 6: Carboxylic Acids, Esters and Organic Polymers · 12 / 19

Physical properties

Most esters are volatile liquids with pleasant odours.
Their boiling points are much lower than those of the acids or alcohols of similar molecular mass, because esters have no –OH group and cannot form hydrogen bonds between their own molecules.
For example (M = 60): ethanoic acid b.p. 118 °C, 1-propanol 97.8 °C, methyl formate 31.8 °C; (M = 74): propanoic acid 141 °C, butanol 118 °C, methyl ethanoate about 57 °C.
For the same reason an ester is less soluble in water than the acid with the same number of carbon atoms.

Lesson 6: Carboxylic Acids, Esters and Organic Polymers · 13 / 19

Chemical properties

1. Hydrolysis→(the reverse of esterification) gives acid and alcohol.

Acid hydrolysis (dilute mineral acid as catalyst, reversible): CH₃COOC₂H₅ + H₂O ⇌ CH₃COOH + C₂H₅OH.
Alkaline hydrolysis — saponification (heating with aqueous NaOH or KOH; goes to completion): CH₃COOC₂H₅ + NaOH → CH₃COONa + C₂H₅OH; C₆H₅COOC₂H₅ + NaOH → C₆H₅COONa + C₂H₅OH. Called saponification because heating fats with alkali gives soap (sodium salts of long-chain fatty acids).
2. Ammonolysis: esters react with ammonia to give an acid amide and an alcohol: CH₃COOC₂H₅ + NH₃ → CH₃CONH₂ + C₂H₅OH.

Lesson 6: Carboxylic Acids, Esters and Organic Polymers · 14 / 19

Applications of esters

Comparison aspect	Main idea	Keywords
Flavours and perfumes	isobutyl formate (cherry) propyl ethanoate (pear) benzyl formate (apricot) methyl butanoate (pineapple) propyl formate (apple) pentyl ethanoate (banana)	isobutylformatecherrypropyl
Fats and oils (triglycerides)	each molecule is formed from one glycerol and three fatty-acid molecules (same or different saturated or unsaturated): glycerol + 3 RCOOH → triglyceride + 3H₂O. Hydrolysis of fat or oil with a strong alkali (NaOH KOH) is saponification the basic reaction in making soap and glycerol: Fat + 3NaOH → glycerol + 3 RCOONa (soap)	moleculeformedglycerolthree
Polyesters	(condensation polymers): from a dibasic acid and a dihydric alcohol. Dacron (polyethylene terephthalate) is made from terephthalic acid HOOC–C₆H₄–COOH and ethylene glycol HOCH₂CH₂OH. The acid end of one molecule reacts with the alcohol end of another repeatedly to give a very long chain. Dacron is chemically inert so it is used for artificial blood vessels (arteries) heart valves and for textile fibres	condensationpolymersdibasicacid
Medicinal esters	aspirin (acetylsalicylic acid) and methyl salicylate (oil of wintergreen used as a rub on rheumatic pains) are esters of salicylic acid. Salicylic acid has both –COOH and –OH so it can behave as an acid (with an alcohol giving methyl salicylate) or as an alcohol (with ethanoic anhydride/acid giving aspirin)	aspirinacetylsalicylicacidmethyl

Lesson 6: Carboxylic Acids, Esters and Organic Polymers · 15 / 19

Aspirin

Aspirin reduces pain, headache and fever, and also reduces blood clotting (helping prevent heart attacks).
Adding the acetyl group to salicylic acid makes it less acidic and tasteless.
In the body aspirin is hydrolysed back into salicylic acid and acetic acid; these acids irritate the stomach wall and can cause ulcers, so doctors advise crushing the tablet or dissolving it in water, and some aspirin tablets are mixed with an antacid such as aluminium hydroxide.

Lesson 6: Carboxylic Acids, Esters and Organic Polymers · 16 / 19

Types of organic reactions (summary)

Type	Typical example
Substitution	CH₄ + Cl₂ → CH₃Cl + HCl; benzene nitration
Addition	ethene + Br₂; ethyne + HBr; benzene + H₂
Elimination (dehydration)	ethanol → ethene + H₂O (180 °C)
Condensation	ester formation; phenol + HCHO → Bakelite
Oxidation / Reduction	ethanol → ethanal → ethanoic acid acid → alcohol with H₂
Hydrolysis	ester + water; R–X + KOH
Polymerisation	ethene → polyethylene (addition) Dacron (condensation)

Relation between families (conversion map):
alkane ⇄ alkene ⇄ alkyne; alkene —(H₂O/H⁺)→ alcohol —[O]→ aldehyde (or ketone) —[O]→ acid; acid + alcohol ⇌ ester; alkyl halide ⇄ alcohol (KOH / HX); ethyne —(H₂O/Hg²⁺)→ ethanal.

Chemistry is a "two-edged sword"→the same knowledge gives medicines, fertilisers, plastics and fuels, but also explosives (TNT, nitroglycerine), CFCs that harm the ozone layer, and poisons; chemists therefore have a responsibility to use it for human benefit, and organic chemistry owes much to the efforts of scientists such as Wöhler, Kekulé and many others.

Lesson 6: Carboxylic Acids, Esters and Organic Polymers · 17 / 19

Revision key points for Part B

Comparison aspect	Main idea	Keywords
Alcohols	classify 1°/2°/3° oxidation products dehydration 180 °C (alkene) vs 140 °C (ether) Na reaction hydrogen bonding explains b.p. and solubility	classifyoxidationproductsdehydration
Phenol	more acidic than alcohols (reacts with NaOH) FeCl₃ violet bromine water white ppt picric acid Bakelite	acidicalcoholsreactsNaOH
Acids	weak H-bonded dimers react with metals/bases/carbonates esterify reduce to alcohols	weakbondeddimersreact
Esters	pleasant smell low b.p hydrolysis/saponification ammonolysis fats polyesters aspirin	pleasantsmellhydrolysissaponification
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Lesson 6: Carboxylic Acids, Esters and Organic Polymers · 18 / 19

Part 19

📖

🔍 In-Depth Explanations, Deductions & Multi-Book Insights:

Chemistry Thanaweya Amma (2026/2027)

Lesson 6 – Carboxylic Acids, Esters and Organic Polymers
Detailed Academic Lesson Overview:
Carboxylic acids contain the carboxyl group (-COOH) representing the highest organic acidity.
Esters (-COO-) are formed by the reversible condensation between carboxylic acids and alcohols, characterized by sweet floral scents and forming fats, polyesters (Dacron), and aspirin.

🌳 Hierarchy Classification & Conceptual Roadmap

Carboxylic Acids and Esters

├── 1. Carboxylic Acids (Aliphatic & Aromatic)

│ ├── Acetic acid (Ethanoic acid CH3COOH)Prepared by bacterial oxidation of ethanol or oxidation of acetaldehyde

│ ├── Benzoic acid (C6H5COOH)Prepared by catalytic oxidation of toluene with V2O5 at 400°C

│ └── Acidity TestReacts with Na2CO3 or NaHCO3 with vigorous effervescence of CO2 gas

├── 2. Esterification and Properties of Esters

Comparison aspect	Main idea	Keywords
•	│ ├── R-COOH + R'-OH ⇌ R-COO-R' + H₂O (conc. H₂SO₄ removes water and prevents reverse reaction)	COOHconcH2SO4removes
│ └── Hydrolysis of Esters	Acidic (reverses to acid + alcohol) Alkaline / Saponification (gives Soap + Glycerol)	Acidicreversesacidalcohol
•	└── 3. Critical Biological & Medical Applications	CriticalBiologicalMedicalApplications
├── Polyesters (Dacron)	Condensation of Terephthalic acid with Ethylene glycol (arterial grafts)	CondensationTerephthalicacidEthylene
├── Aspirin (Acetylsalicylic acid)	Formed by reacting Salicylic acid with Acetic acid (analgesic)	FormedreactingAceticanalgesic
└── Methyl Salicylate (Oil of Wintergreen)	Topical analgesic lotion for rheumatism	Topicalanalgesiclotionrheumatism
•	📋 Master Teacher's Blackboard Rules & Exam Secrets	MasterTeacherBlackboardRules
RULE 1	In esterification isotopic tracer studies (using Oxygen-18) proved that the oxygen atom in the water molecule originates from the CARBOXYLIC ACID (-OH) and NOT from the alcohol (-H)	esterificationisotopictracerstudies
RULE 2	Saponification is the alkaline hydrolysis of fats or oils (esters of glycerol and higher fatty acids) with sodium hydroxide yielding soap and glycerol	Saponificationalkalinehydrolysisfats
RULE 3	Aspirin contains both a carboxyl group (-COOH) and an ester group to prevent stomach irritation it should be taken with antacids or coated tablets	Aspirincontainsbothcarboxyl
📊 Detailed Comparison Matrix	Medical Esters Derived from Salicylic Acid	MedicalEstersDerivedSalicylic

Medical Compound	Reactants Used	Active Functional Roles	Medical Therapeutic Use
Aspirin (Acetylsalicylic acid)	Salicylic acid (acting as phenol) + Acetic acid	Ester of acetic acid + Free -COOH group	Pain relief, fever reduction, anticoagulant
Oil of Wintergreen (Methyl salicylate)	Salicylic acid (acting as acid) + Methanol	Ester of salicylic acid + Free phenolic -OH	Topical skin analgesic for arthritis/muscle pain
Dacron Polyester	Terephthalic acid + Ethylene glycol	Condensation copolymer	Synthetic blood vessels and heart valves

Lesson 6: Carboxylic Acids, Esters and Organic Polymers · 19 / 19

Curriculum

Chemistry

Chapter 1 - Transition Elements and Iron Metallurgy

Chapter 2 - Chemical Analysis

Chapter 3 - Chemical Equilibrium

Chapter 4 - Electrochemistry

Chapter 5 - Organic Chemistry

More lessons

Lesson 6: Carboxylic Acids, Esters and Organic Polymers

🌳 Concept tree

├── The carboxyl group

├── Types

├── Nomenclature

├── Preparation of acetic acid

├── Physical properties

├── Chemical properties

├── Important acids and their uses

├── Definition and formation

├── Nomenclature

├── Preparation

├── Physical properties

├── Chemical properties

├── Applications of esters

├── Aspirin

├── Types of organic reactions (summary)

└── Revision key points for Part B

HCOOCH₃ methyl formate (methyl methanoate)

CH₃COOC₂H₅ ethyl acetate (ethyl ethanoate)

C₆H₅COOC₂H₅ ethyl benzoate

🔍 In-Depth Explanations, Deductions & Multi-Book Insights:

Chemistry Thanaweya Amma (2026/2027)

🌳 Hierarchy Classification & Conceptual Roadmap

Carboxylic Acids and Esters

├── 2. Esterification and Properties of Esters

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