ASRJC 2025 H2 Chem Carboxylic Acids and Derivatives Notes

2025 JC2 H2 CARBOXYLIC ACIDS AND DERIVATIVES 2025/ASRJC/Chemistry 1 ANDERSON SERANGOON JUNIOR COLLEGE JC2 H2 CHEMISTRY CARBOXYLIC ACIDS AND DERIVATIVES Content 1. Carboxylic acids (exemplified by ethanoic acid and benzoic acid) (i) Formation from primary alcohols and nitriles (ii) Reactions to form salt, ester and acyl chloride 2. Acyl chlorides (exemplified by ethanoyl chloride) (i) Ease of hydrolysis compared with alkyl and aryl chlorides (ii) Reaction with alcohols, phenols and primary amines 3. Esters (exemplified by ethyl ethanoate and phenyl benzoate) (i) Formation from carboxylic acids and from acyl chlorides (ii) Hydrolysis (under acidic and under basic conditions) Learning Outcomes Candidates should be able to: (a) describe the formation of carboxylic acids from alcohols, aldehydes and nitriles (b) describe the reactions of carboxylic acids in the formation of (i) salts (ii) esters on condensation with alcohols, using ethyl ethanoate as an example (iii) acyl chlorides, using ethanoyl chloride as an example (iv) primary alcohols, via reduction with lithium aluminium hydride, using ethanol as example (c) explain the acidity of carboxylic acids and of chlorine–substituted ethanoic acids in terms of their structures (d) describe the hydrolysis of acyl chlorides (e) describe the condensation reactions of acyl chlorides with alcohols, phenols and primary amines (f) explain the relative ease of hydrolysis of acyl chlorides, alkyl chlorides and aryl chlorides (g) describe the formation of esters from acyl chlorides, using phenyl benzoate as an example (h) describe the acid and base hydrolysis of esters References 1. Chemistry for Advanced Level, Cann and Hughes, Murray 2. Organic Chemistry (5th Edition), McMurry, Brooks/Cole Outline Part I: Carboxylic Acids 1. Introduction 2. Synthesis of carboxylic acids 3. Reaction of carboxylic acids 4. Acidity of carboxylic acids Part II: Carboxylic Acid Derivatives 1. Introduction 2. Esters and its reactions 3. Acid Chlorides and its reactions 4. Amides – (to be discussed in greater details in Nitrogen Compounds)

2025 JC2 H2 CARBOXYLIC ACIDS AND DERIVATIVES 2025/ASRJC/Chemistry 2 PART 1: CARBOXYLIC ACID 1 INTRODUCTION Contain the carboxylic acid functional group General structure: where R may be H, alkyl or aryl group 1.1 Nomenclature The longest carbon chain containing the carboxylic acid functional group is selected as the parent chain and named by replacing the ‘e’ of the corresponding alkane or alkene with ‘oic acid’. The carbon atom in ‘COOH’ is assigned number 1. Examples of monocarboxylic acids C O OHCH3CH2 propanoic acid OHC H CH3 H C H C C O H H H 3–methylbutanoic acid CH3 C C H OH O OH 2–hydroxypropanoic acid C O OH C C C C H H H H H H H pent–3–enoic acid C O OH benzoic acid C O Cl OH 3–chlorobenzoic acid Examples of dicarboxylic acids OH CO C O OH ethanedioic acid C C C C H H H H H H H H C O HO C O OH hexane–1,6–dioic acid C OH C HO OO benzene–1,4–dicarboxylic acid C O O H R C O O H

2025 JC2 H2 CARBOXYLIC ACIDS AND DERIVATIVES 2025/ASRJC/Chemistry 3 2 PREPARATION OF CARBOXYLIC ACIDS How are carboxylic acids synthesised? 2.1 Oxidation from PRIMARY alcohols (Refer to Hydroxy Compounds Lecture Notes for more details) Type of reaction Oxidation Reagents & conditions K2Cr2O7 / KMnO4, dilute H2SO4, heat under reflux General equation primary alcohol carboxylic acid 2 [O] 2.2 Oxidation from aldehyde (Refer to Carbonyl Compounds Lecture Notes for more details) Type of reaction Oxidation Reagents & conditions K2Cr2O7 / KMnO4, dilute H2SO4, heat under reflux General equation aldehyde carboxylic acid [O] 2.3 Oxidation from alkylbenzenes (Refer to Arenes Lecture Notes for more details) Alkyl groups, regardless of the length of the carbon chain, directly bonded to the benzene ring are oxidised by KMnO4 to a –CO2H group (except when the alkyl group is of the –CR3 type). Type of reaction (Side chain) Oxidation Reagents & conditions KMnO4, dilute H2SO4, heat under reflux General equation + 3[O] + H2O methylbenzene benzoic acid KMnO4 , dilute H2SO4 + 6[O] + CO2 + 2H2O ethylbenzene benzoic acid R C O H H H + H 2 O + Heat under reflux + R C O H C O OH C H H H C O OH C C H H H H H R C O OH R C O OH

2025 JC2 H2 CARBOXYLIC ACIDS AND DERIVATIVES 2025/ASRJC/Chemistry 4 2.4 Oxidative cleavage from alkenes (Refer to Alkenes Lecture Notes for more details) Type of reaction Oxidation (or Oxidative cleavage) Reagents & conditions KMnO4, dilute H2SO4, heat under reflux General equation KMnO4 , dilute H2SO4 + 4[O] Heat under reflux 2.5 Hydrolysis from nitriles (Refer to Halogenoalkanes Lecture Notes for more details) Type of reaction (Acid) hydrolysis Reagents & conditions Dilute HCl / H2SO4, heat under reflux General equation nitrile carboxylic acid dilute HCl R–CN + H+ + 2H2O R–CO2H + NH4+ Heat under reflux Type of reaction (Base) hydrolysis Reagents & conditions NaOH(aq) / KOH(aq), heat under reflux followed by acidification by HCl, room temperature General equation R—CN + H2O + OH− RCOO− + NH3 Further acidification RCOO− + H+ RCOOH 2.6 Hydrolysis from esters (Also covered in the section on Esters) Type of reaction (Acid) hydrolysis Reagents & conditions Dilute HCl / H2SO4, heat under reflux General equation ester carboxylic acid alcohol dilute H2SO4 + H2O Heat under reflux acidified KMnO4 C C H R R' H C HO R O C R' OH O C O O R R' C O O R H H O R'+

2025 JC2 H2 CARBOXYLIC ACIDS AND DERIVATIVES 2025/ASRJC/Chemistry 5 Type of reaction (Base) hydrolysis Reagents & conditions NaOH(aq) / KOH(aq), heat under reflux followed by acidification by HCl, room temperature General equation ester salt of carboxylic acid alcohol NaOH(aq) + OH – heat under reflux Further acidification C O O-R + H+ C O OHR 2.7 Hydrolysis from amides (To be covered in Nitrogen Compounds Lecture) Type of reaction (Acid) H