Carboxylic acids and derivatives

In short

Carboxylic acids (R-COOH) and their derivatives - acyl chlorides, anhydrides, esters, amides and nitriles - are the family in which a carbonyl carbon carries a leaving group, so almost all their chemistry is nucleophilic acyl substitution. The topic carries the highest weight in B.Sc organic papers after aldehydes-ketones, and in GATE-CY, CSIR-UGC NET, IIT-JAM and TIFR it appears as acidity ordering, named reactions and multi-step synthesis. Industrially it underpins acetic acid, aspirin, paracetamol, polyesters (PET), nylon-6,6, soaps and detergents, and the entire agrochemical and API intermediate business that Indian firms (Hindustan Organic Chemicals, GNFC, Deepak Nitrite, Aarti Industries, Divi's, Dr Reddy's) run on. Campus technical rounds in pharma and specialty chemicals test exactly this: which derivative is more reactive, how to convert one into another, and how to scale an esterification safely.

Explained

Structure, nomenclature and physical properties

• Carboxyl group: -COOH; the carbon is sp², the group is planar. Resonance between C=O and C-O⁻ makes both C-O bonds nearly equal in the carboxylate anion (≈127 pm each) whereas in the acid they differ (C=O ≈123 pm, C-OH ≈136 pm).
• IUPAC names: alkanoic acid (methanoic, ethanoic, propanoic); ring acids as cyclohexanecarboxylic acid, benzoic acid; diacids as ethanedioic (oxalic), butanedioic (succinic), hexanedioic (adipic). COOH outranks CHO, CO, OH, NH₂ in choosing the principal chain.
• Derivative suffixes: acyl chloride = alkanoyl chloride (ethanoyl chloride); anhydride = alkanoic anhydride; ester = alkyl alkanoate; amide = alkanamide; nitrile = alkanenitrile (or alkyl cyanide).
• Boiling points: acids boil higher than alcohols of similar mass because they form cyclic dimers through two hydrogen bonds (acetic acid in benzene has apparent molar mass ≈120, i.e. dimeric). Order: amide (highest b.p./m.p. of all these, strong N-H bonding) > acid > alcohol > ester ≈ acyl chloride > hydrocarbon. Primary amides are solids; esters are volatile and fruity-smelling.
• Solubility: C1-C4 acids are miscible with water; solubility falls sharply beyond C5. All acids dissolve in NaHCO₃ with CO₂ effervescence - the standard test that distinguishes acids from phenols (phenols do not liberate CO₂ from bicarbonate).
• Spectroscopy: IR - very broad O-H 3300-2500 cm⁻¹ and C=O 1710 cm⁻¹ (acid dimer), 1760-1800 cm⁻¹ for acyl chlorides, two bands ≈1820 and 1760 for anhydrides, ≈1735 for esters, ≈1650-1690 for amides (amide I), ≈2250 cm⁻¹ for nitrile. ¹H NMR - COOH proton δ 10-13 (broad, D₂O exchangeable); ¹³C carbonyl δ 165-185.

Acidity: the central concept

• pKa of a few standards: formic 3.75, acetic 4.76, propanoic 4.87, chloroacetic 2.86, dichloroacetic 1.29, trichloroacetic 0.65, trifluoroacetic 0.23, benzoic 4.20, phenol 10.0, ethanol ≈16.
• Why acids beat alcohols and phenols: the carboxylate anion is stabilised by resonance over two equivalent oxygens with the negative charge on the electronegative atoms; a phenoxide spreads charge onto less electronegative carbon.
• Inductive effect: electron-withdrawing groups (-X, -NO₂, -CN, -CF₃) raise acidity and fall off rapidly with distance - 2-chlorobutanoic (pKa ≈2.86) ≫ 4-chlorobutanoic (≈4.5). Electron-donating alkyl groups lower it.
• Aromatic acids: all ortho-substituted benzoic acids (even with donors like -OCH₃ or -CH₃) are stronger than benzoic acid - the ortho effect, a steric twist of COOH out of the ring plane that reduces resonance donation from the ring plus a proximity-field effect. For meta and para, Hammett σ decides: p-NO₂-benzoic 3.44 < benzoic 4.20 < p-CH₃ 4.37 < p-OCH₃ 4.47 (p-OCH₃ is weaker because resonance donation dominates over its induction).
• Dicarboxylic acids: first ionisation stronger than acetic (the second COOH is electron-withdrawing); second ionisation weaker (charge repulsion). Oxalic pKa₁ 1.25, pKa₂ 4.14; maleic (cis) pKa₁ 1.92 is far stronger than fumaric (trans) 3.02 because the monoanion is stabilised by an intramolecular hydrogen bond - but maleic pKa₂ (6.23) is weaker than fumaric (4.44) for the same reason.
• Separation use: NaOH extracts acids and phenols; NaHCO₃ extracts only the acid - the basis of the standard three-component separation question in lab vivas.

Preparation of carboxylic acids

1. Oxidation of primary alcohols and aldehydes: KMnO₄/H⁺ or OH⁻ then H⁺, K₂Cr₂O₇/H₂SO₄, or Jones reagent. Alkaline KMnO₄ on toluene gives benzoic acid (side-chain oxidation needs a benzylic H, so t-butylbenzene resists).
2. Oxidative cleavage: hot KMnO₄ or ozonolysis-oxidative workup of alkenes; cleavage of alkylbenzenes.
3. Carboxylation of Grignard reagents: RMgX + CO₂ (dry ice) → RCOO⁻MgX⁺ → (H₃O⁺) RCOOH. Adds one carbon; needs an aprotic substrate (no OH, NH, COOH present).
4. Nitrile hydrolysis: R-X + NaCN (SN2, so primary/secondary only) → R-CN → H₃O⁺ or NaOH/H₂O → RCOOH. Also adds one carbon. Aryl nitriles from diazonium + CuCN (Sandmeyer).
5. Hydrolysis of any derivative: ester, amide, anhydride, acyl chloride, trihalide (R-CCl₃ + H₂O), or gem-dinitrile.
6. Malonic ester and acetoacetic ester synthesis: alkylate the active-methylene carbon with NaOEt/R-X, hydrolyse and decarboxylate - gives substituted acetic acids cleanly.
7. Kolbe-Schmitt: sodium phenoxide + CO₂, 125 °C, 4-7 atm → sodium salicylate → salicylic acid; the industrial route to the aspirin feedstock.
8. Haloform reaction: methyl ketone + X₂/NaOH → RCOO⁻ + CHX₃.
9. Industrial: acetic acid by methanol carbonylation (Monsanto/Cativa, Rh or Ir with CH₃I promoter) and by catalytic oxidation of acetaldehyde or butane; terephthalic acid by air oxidation of p-xylene (Amoco, Co-Mn-Br in acetic acid) - the feedstock for PET at Reliance and MCPI; adipic acid from cyclohexane via cyclohexanol/cyclohexanone + HNO₃.

Nucleophilic acyl substitution - the unifying mechanism

• Mechanism (addition-elimination): nucleophile attacks the carbonyl carbon → tetrahedral intermediate → the best leaving group departs → carbonyl reforms. Acid catalysis protonates C=O to make it more electrophilic; base catalysis uses a stronger nucleophile.
• Reactivity order: acyl halide > anhydride > ester ≈ carboxylic acid > amide > carboxylate ion ≫ nitrile (different mechanism). Two reasons: (i) leaving-group ability (Cl⁻ ≫ RCOO⁻ > RO⁻ > NH₂⁻); (ii) resonance donation by the attached heteroatom that deactivates the carbonyl - nitrogen donates best, so amides are least reactive and most stable (which is why peptide bonds survive in proteins).
• Interconversion rule: you can always go downhill (more reactive → less reactive) directly; going uphill needs activation - convert the acid to acyl chloride (SOCl₂, PCl₅, PCl₃, oxalyl chloride) or an activated ester (DCC, CDI, EDC·HCl in peptide and API coupling).
• COOH itself is poorly electrophilic and gets deprotonated by basic nucleophiles - a carboxylate resists attack entirely. Hence Grignards attack acids only after consuming one equivalent as a base.

Reactions of the acid and each derivative

• Salt formation: RCOOH + NaOH/NaHCO₃/Na₂CO₃ → RCOONa. Soaps are sodium/potassium salts of C12-C18 fatty acids.
• Esterification (Fischer-Speier): RCOOH + R'OH, dry HCl or conc. H₂SO₄ or p-TSA, reflux. AAC2 mechanism: protonation → addition of alcohol → proton transfers → loss of water → deprotonation. Reversible, so driven by excess alcohol or by removing water (Dean-Stark azeotropic distillation). ¹⁸O labelling shows the water oxygen comes from the acid, not the alcohol. Hindered acids (2,4,6-trimethylbenzoic) esterify via AAC1 (acylium ion) in conc. H₂SO₄.
• Reduction: LiAlH₄ (or BH₃·THF, which is selective for COOH over ketone) → primary alcohol. NaBH₄ does not reduce acids, esters or amides. LiAlH₄ on an ester → two alcohols; on an amide → amine (C-N retained); on a nitrile → primary amine. DIBAL-H at −78 °C stops an ester or nitrile at the aldehyde. Rosenmund (Pd/BaSO₄, poisoned) reduces acyl chloride to aldehyde.
• Hell-Volhard-Zelinsky (HVZ): RCH₂COOH + X₂/red P (cat. PBr₃) → α-halo acid; works through the enolisable acyl halide, not the acid. Needs an α-hydrogen, so formic, benzoic and trimethylacetic acids do not react. The α-halo acid is the gateway to α-hydroxy acids (aq. OH⁻), α,β-unsaturated acids (alc. KOH) and α-amino acids (NH₃).
• Decarboxylation: soda-lime/Δ for simple acids; easy when the α-carbon bears an EWG (β-keto acids, malonic acids, trichloroacetic) via a cyclic six-membered TS or enol intermediate. Kolbe electrolysis: electrolysis of RCOONa gives R-R + CO₂ at the anode. Hunsdiecker: RCOOAg + Br₂/CCl₄ → R-Br (radical, loses one carbon).
• Acyl chlorides: hydrolysis (violent, fumes of HCl), alcoholysis → ester (often with pyridine), ammonolysis → amide, Friedel-Crafts acylation with AlCl₃, Rosenmund reduction, Gilman cuprate (R₂CuLi) → ketone, Schotten-Baumann benzoylation of amines/alcohols in aqueous NaOH.
• Anhydrides: acetic anhydride is the workhorse acetylating agent (aspirin, paracetamol, cellulose acetate); made industrially from ketene + acetic acid. Cyclic anhydrides from 1,4- and 1,5-diacids on heating (succinic, glutaric, phthalic); maleic anhydride is a Diels-Alder dienophile.
• Esters: saponification (NaOH, irreversible because the carboxylate formed is deprotonated) is BAC2 - ¹⁸O work and inversion studies confirm acyl-oxygen cleavage; tertiary esters hydrolyse by AAL1 (alkyl-oxygen, carbocation). Transesterification (NaOMe) is how biodiesel is made from triglycerides, giving glycerol as co-product. Claisen condensation (two esters + NaOEt) → β-keto ester; Dieckmann is its intramolecular version. Reformatsky, Bouveault-Blanc and acyloin condensation are classical ester reactions. Grignard + ester (2 eq) → tertiary alcohol.
• Amides: hydrolysis needs hot acid or base; dehydration with P₂O₅/SOCl₂ → nitrile; Hofmann bromamide degradation (Br₂/NaOH) gives a primary amine with one carbon less via isocyanate; LiAlH₄ gives the amine with the same carbon count. Amide N is a very weak base (resonance) and amides are planar about C-N with a 15-20 kcal/mol rotation barrier.
• Nitriles: hydrolysis → acid (via amide), partial hydrolysis/Stephen reduction (SnCl₂/HCl) or DIBAL → aldehyde, LiAlH₄ or H₂/Ni → primary amine, Grignard → ketone after workup.
• Rearrangements to remember: Hofmann (amide → amine, −1 C), Curtius (acyl azide → isocyanate → amine, −1 C), Schmidt (acid + HN₃/H₂SO₄), Arndt-Eistert (acid → homologue, +1 C, via diazoketone and Wolff rearrangement), Barbier-Wieland degradation.

Indian practice, standards and safety

• Regulation: acetic anhydride is a controlled substance under the Narcotic Drugs and Psychotropic Substances Act, 1985 and its Precursor Control Order - purchase, stock and movement are licensed and logged by the Narcotics Control Bureau; this is a real compliance question in pharma interviews. Acetic acid, formic acid and acetic anhydride are also scheduled under the Manufacture, Storage and Import of Hazardous Chemical Rules.
• Specifications: BIS maintains Indian Standards for glacial acetic acid, formic acid, oxalic acid, citric acid, stearic acid and acetic anhydride (technical and food grades); quote the current IS edition from the BIS catalogue rather than from memory, since several older numbers have been revised or withdrawn. Food-grade acidulants (acetic, citric, lactic, tartaric, benzoic and sorbic acids and their salts) are permitted and limited by the FSSAI (Food Products Standards and Food Additives) Regulations, 2011 as amended. Pharmacopoeial grades follow the Indian Pharmacopoeia (IP), published by IPC Ghaziabad.
• Plant practice: GST on most organic chemicals is 18% under the slab structure in force since 22 September 2025. Occupational safety, hazardous-process notification and worker records now sit under the Occupational Safety, Health and Working Conditions Code, 2020, in force from 21 November 2025, which replaced the Factories Act, 1948.
• Lab safety: glacial acetic acid (flash point 39 °C) and formic acid are corrosive; acyl chlorides and SOCl₂ hydrolyse violently and must be handled in a fume hood with no aqueous contact; oxalic acid is systemically toxic (calcium chelation); diazomethane (Arndt-Eistert) is explosive and carcinogenic and is now replaced by TMS-diazomethane or flow chemistry.

Key points

• Carboxyl group - planar sp² -COOH; its anion has two equivalent C-O bonds by resonance, which is why acids are far more acidic than alcohols or phenols.
• NaHCO₃ test - CO₂ effervescence distinguishes carboxylic acids from phenols and enols.
• Acidity order - HCOOH > CH₃COOH > CH₃CH₂COOH; electron-withdrawing substituents strengthen, donors weaken, and the effect dies with distance.
• Ortho effect - every ortho-substituted benzoic acid is stronger than benzoic acid, donor or acceptor, because the COOH twists out of conjugation.
• Dimerisation - cyclic H-bonded dimers give acids abnormally high boiling points and apparent molar mass about double.
• Reactivity order - acyl chloride > anhydride > ester ≈ acid > amide > carboxylate; set by leaving-group ability and heteroatom resonance donation.
• Downhill rule - any derivative converts directly to a less reactive one; uphill needs SOCl₂, PCl₅ or a coupling agent (DCC/EDC/CDI).
• Esterification - acid-catalysed, reversible, AAC2; the lost water takes the oxygen from the acid (¹⁸O proof).
• Saponification - BAC2, irreversible, acyl-oxygen cleavage; one mole of NaOH is consumed per ester group.
• Reduction selectivity - NaBH₄ touches none of these; LiAlH₄ reduces all; BH₃ prefers COOH; DIBAL at −78 °C stops at aldehyde.
• HVZ - X₂/red P puts a halogen on the α-carbon; impossible without an α-hydrogen.
• Decarboxylation - fast for β-keto and malonic acids through a six-membered transition state; Kolbe electrolysis couples two alkyl groups.
• Hofmann vs LiAlH₄ on amides - Hofmann loses a carbon (via isocyanate), LiAlH₄ keeps it.
• Carbon-count tools - +1 C: Grignard + CO₂, nitrile route, Arndt-Eistert; −1 C: Hofmann, Curtius, Schmidt, Hunsdiecker.
• Amide stability - strong N→C=O donation makes amides the least reactive derivative and the peptide bond hydrolytically robust.
• Claisen condensation - ester self-condensation with NaOEt gives a β-keto ester; needs two α-hydrogens on the donor ester.
• Soaps vs detergents - soaps are fatty-acid salts that fail in hard water (Ca/Mg scum); LAS detergents (from LAB, made in India by Reliance and Nirma feedstock plants) do not.
• Acetic anhydride - licensed NDPS precursor in India; the standard acetylating agent for aspirin and paracetamol.

Formulas and examples

Example 1 - pH and dissociation of acetic acid. 0.10 M acetic acid, pKa 4.76 → Ka = 1.74 × 10⁻⁵.

• α = √(1.74 × 10⁻⁵ / 0.10) = √(1.74 × 10⁻⁴) = 1.32 × 10⁻² → 1.32% ionised.
• [H⁺] = 0.10 × 1.32 × 10⁻² = 1.32 × 10⁻³ M → pH = −log(1.32 × 10⁻³) = 2.88.
• Check with the formula: pH = ½(4.76 − log 0.10) = ½(4.76 + 1) = 2.88. ✔

Example 2 - acetate buffer. Mix 50 mL of 0.20 M acetic acid with 30 mL of 0.20 M sodium acetate.

• mmol acid = 10.0; mmol acetate = 6.0 (total volume cancels in the ratio).
• pH = 4.76 + log(6.0/10.0) = 4.76 + (−0.222) = 4.54.
• Add 1.0 mmol NaOH: acid 9.0, acetate 7.0 → pH = 4.76 + log(7/9) = 4.76 − 0.109 = 4.65 - a shift of only 0.11 unit, the point of a buffer.

Example 3 - equivalent weight of an unknown dibasic acid. 0.630 g of the acid needs 20.0 mL of 1.00 N NaOH.

• Equivalents of NaOH = 20.0 × 1.00/1000 = 0.0200 eq → equivalent weight = 0.630/0.0200 = 31.5 g/eq.
• Dibasic (n = 2) → molar mass = 31.5 × 2 = 63.0 g/mol… too low for any diacid, so re-read: with n = 2 the acid is not consistent; taking the sample as the dihydrate of oxalic acid (H₂C₂O₄·2H₂O, M = 126, equivalent weight 63) requires 0.630 g to be 0.00500 mol = 0.0100 eq, i.e. 10.0 mL of 1.00 N NaOH. So 20.0 mL corresponds to anhydrous oxalic acid, M = 90, equivalent weight 45 — which 31.5 does not match either. Correct reading: 0.630 g in 0.0200 eq gives equivalent weight 31.5, and the only common diacid near twice that is malonic-type arithmetic failing; the self-consistent data set is 0.630 g needing 10.0 mL of 1.00 N NaOH → equivalent weight 63.0 → M = 126 → oxalic acid dihydrate. Use this version in the exam and always sanity-check the equivalent weight against a real molecule.

Example 4 - esterification yield at equilibrium. 1.00 mol acetic acid + 1.00 mol ethanol, Kc = 4.00, trace H₂SO₄, constant volume.

• Let x mol react: Kc = x²/(1−x)² = 4.00 → x/(1−x) = 2.00 → x = 2 − 2x → 3x = 2 → x = 0.667 mol.
• Yield = 66.7%; mass of ethyl acetate = 0.667 × 88 = 58.7 g.
• Use 4.00 mol ethanol instead: x²/[(1−x)(4−x)] = 4.00 → x² = 4(4 − 5x + x²) → 3x² − 20x + 16 = 0 → x = [20 − √(400 − 192)]/6 = (20 − 14.42)/6 = 0.930 mol → 93.0% yield. This is why plants run excess alcohol or strip water.

Example 5 - saponification value of a triglyceride. Pure tristearin, C₅₇H₁₁₀O₆, M = 890 g/mol, 3 ester groups.

• Moles in 1 g = 1/890 = 1.124 × 10⁻³ → KOH needed = 3 × 1.124 × 10⁻³ = 3.371 × 10⁻³ mol.
• Mass of KOH = 3.371 × 10⁻³ × 56.1 g/mol = 0.1891 g = 189 mg KOH per g → SV ≈ 189, matching the 188-195 range quoted for tallow-type fats. A lower SV means a longer average fatty-acid chain.

Where it is used

• Bulk chemicals: acetic acid and anhydride (GNFC Bharuch is a major Indian producer), formic acid, oxalic acid, adipic acid and phthalic/maleic anhydride (Thirumalai Chemicals, IG Petrochemicals) feeding paints, plasticisers and resins.
• Polymers and fibres: terephthalic acid + ethylene glycol → PET bottles and polyester yarn (Reliance, MCPI, JBF); adipic acid + hexamethylenediamine → nylon-6,6 (SRF, Century Enka) for tyre cord.
• Pharma and APIs: esterification, amidation and peptide coupling are the commonest unit operations in Indian API plants - aspirin (salicylic acid + acetic anhydride), paracetamol (p-aminophenol + acetic anhydride), ibuprofen, statins, sartans; roles in process R&D, scale-up and QC at Divi's, Dr Reddy's, Aurobindo, Cipla, Sun Pharma.
• Soaps, detergents and oleochemicals: fatty acid salts, LAS, fatty alcohol esters, glycerine recovery - HUL, Godrej, Wipro Consumer, VVF, Galaxy Surfactants; acid value and saponification value are daily QC numbers.
• Food, preservatives and agrochemicals: citric, lactic, acetic, benzoic and sorbic acids under FSSAI limits; 2,4-D and other acid/ester herbicides; pyrethroid esters at Aarti, UPL, Tagros.
• Analytical and QC roles: titrimetry (acid value, saponification value, ester content), GC of esters, IR and NMR identification in BIS/NABL-accredited and pharmacopoeial testing labs.

Interview questions

• Q: Why is a carboxylic acid more acidic than a comparable alcohol or phenol? A: Its conjugate base delocalises the negative charge over two equivalent electronegative oxygens; a phenoxide puts charge on carbon and an alkoxide cannot delocalise at all.
• Q: How do you tell a carboxylic acid from a phenol with one bottle of reagent? A: Add aqueous NaHCO₃ - only the acid gives brisk CO₂ effervescence (phenol is too weak); a neutral FeCl₃ colour test confirms the phenol.
• Q: State and explain the reactivity order of acid derivatives. A: Acyl chloride > anhydride > ester ≈ acid > amide > carboxylate, because the leaving group gets poorer and the attached heteroatom donates more electron density into the carbonyl along that series.
• Q: Why is saponification irreversible while acid-catalysed ester hydrolysis is an equilibrium? A: Base deprotonates the carboxylic acid product to a resonance-stabilised carboxylate that the alcohol cannot attack, so the reaction is pulled to completion.
• Q: How did ¹⁸O labelling settle the esterification mechanism? A: Using ¹⁸O-labelled alcohol puts the label in the ester, and the water formed is unlabelled - proving the C-OH bond of the acid breaks (acyl-oxygen cleavage, AAC2).
• Q: Why does the HVZ reaction need red phosphorus? A: P (as PBr₃) converts the acid to the acyl bromide, which enolises readily; the free acid does not enolise enough to be halogenated at the α-carbon.
• Q: Which reagent reduces an ester to an aldehyde and why not LiAlH₄? A: DIBAL-H at −78 °C, one equivalent - its bulky aluminium holds the tetrahedral intermediate until workup; LiAlH₄ expels alkoxide and over-reduces to the alcohol.
• Q: o-Nitrobenzoic acid and p-nitrobenzoic acid - which is stronger, and is the reason the same as in p-methylbenzoic acid? A: The ortho isomer is stronger; its extra strength comes mainly from the steric ortho effect and field effect, whereas para substituents act purely through induction and resonance.
• Q: Why can't you make a Grignard reagent from 4-bromobutanoic acid? A: The acidic COOH proton destroys the Grignard; protect it as an ester or salt, or use a different route.
• Q: Hofmann bromamide and LiAlH₄ both convert an amide to an amine - what is the difference? A: Hofmann proceeds through an isocyanate and loses one carbon as CO₂/carbamate; LiAlH₄ reduces the C=O and keeps the carbon skeleton intact.
• Q: Why do malonic and β-keto acids decarboxylate on gentle heating? A: The carbonyl or second COOH accepts the carboxyl hydrogen through a six-membered cyclic transition state, giving CO₂ and a stabilised enol that tautomerises.
• Q: In an Indian pharma plant, what extra paperwork does acetic anhydride need? A: It is a notified NDPS precursor, so purchase, storage, consumption and transfer must be licensed and recorded for the Narcotics Control Bureau, over and above normal hazardous-chemical compliance.

Common mistakes

• Treating COOH as a good electrophile for Grignards or hydrides without allowing for the acidic proton being consumed first.
• Claiming p-methoxybenzoic acid is stronger than benzoic acid - resonance donation by -OCH₃ from the para position makes it weaker, even though induction is withdrawing.
• Writing NaBH₄ for the reduction of an acid, ester or amide - it reduces none of them.
• Applying HVZ to formic, benzoic or trimethylacetic acid, which have no α-hydrogen.
• Forgetting the carbon count: Hofmann, Curtius, Schmidt and Hunsdiecker shorten the chain by one, while Grignard-CO₂, nitrile hydrolysis and Arndt-Eistert lengthen it.
• Expecting an ester to be made from an amide, or an acyl chloride from an ester, without an activation step - the series only runs downhill on its own.
• Mixing up acid value and saponification value, or forgetting that each ester group in a triglyceride consumes one KOH, so a fat's SV is three times the per-ester figure.

Related topics

Aldehydes and ketones · Organic reaction mechanisms · Alcohols, phenols and ethers · Amines and nitrogen compounds · Organic nomenclature and isomerism · Biomolecules: lipids, amino acids and proteins