VJC 2025 CAD Tutorial

Victoria Junior College JC 2 Chemistry Tutorial: Carboxylic Acids & Derivatives Complete the following tables. 1. Preparation of carboxylic acids Starting compound Reagents and conditions Product K2Cr2O7(aq), H2SO4(aq), heat under reflux OR KMnO4(aq), H2SO4(aq), heat (CH3)2CHCH2CO2H (CH3)2CHCH2CHO (CH3)2CHCH2CH(CN)OH (CH3)2CHCH2CH(CO2H)OH 2. Reactions of carboxylic acids Starting Compound Reaction Type Reagents and Conditions Organic Product [if any] (CH3)2C(OH)CO2H redox NaOH Na2CO3 HBr(g) heat PCl3 or SOCl2, heat OR PCl5 CH3CH(OH)CH3 conc. H2SO4 heat CH3COCl reduction oxidation

Interconversion of Carboxylic Acids and Acid Derivatives Hydrolysis

Preparation and Reactions of Carboxylic Acids 1 Devise syntheses of the following compounds from the given starting material. Identify the reagents and conditions at each step and draw the structural formulae of the intermediates. (a) CH3CH2CHO → CH3CH2CH(OH)CO2H (2-step synthesis) (b) (CH3)2CHOH → (CH3)2CHCO2H (3-step synthesis) (c) CH3CH2CH2OH → CH3CH2OH (3-step synthesis) (d) (2-step synthesis)

2 Citric acid, which causes the sharp taste of lemon juice, has the following formula. What reacts completely with 1 mol of citric acid? A 3 mol of PCl5 C 4 mol of Na B 4 mol of HCl(g) D 4 mol of NaOH(aq) N13/I/27 3 The small hive beetle, which invades colonies of the honeybee, identifies these colonies by detecting the bees’ own alarm signal, the pheromone 3–methylbutyl ethanoate. How may this ester be made in the laboratory? A (CH3)2CHCH2CO2H + CH3CH2OH → ester + H2O B (CH3)2CHCH2CH2CO2H + CH3OH → ester + H2O C CH3CO2H + (CH3)2CHCH2CH2OH → ester + H2O D CH3CO2H + CH3CH2CH(CH3)CH2OH → ester + H2O Modified N10/I/28 Acidity of Carboxylic Acids 4 In which sequence is it correctly stated that the value of pKa decreases continuously? A CH3CO2H > CCl3CO2H > C2H5OH > C6H5OH B CCl3CO2H > CH3CO2H > C2H5OH > C6H5OH C C2H5OH > C6H5OH > CH3CO2H > CCl3CO2H D C6H5OH > C2H5OH > CH3CO2H > CCl3CO2H

Preparation and Reactions of Acyl Chlorides 5(a)(i) Draw a displayed formula of benzoyl chloride, C 6H5COCl. Describe a pathway in which it can be synthesised from benzoic acid. (ii) Describe three reactions of benzoyl chloride with water, ethanol and methylamine, giving a balanced equation in each case. (b) State and explain how the ease of hydrolysis of 1-chloropropane differ from that of propanoyl chloride and chlorobenzene. Adapted J94/I/8, N23/I/22 ………………………………………………………………………………………………….…… ………………………………………………………………………………………………….…… ……………………………………………………………………………………………………… …………………………………………………………………………………………………….… ………………………………………………………………………………………………….…… …………………………………………………………………………………………………….… …………………………………………………………………………………………………….… ………………………………………………………………………………………………….…… …………………………………………………………………………………………………….… ………………………………………………………………………………………………….…… ………………………………………………………………………………………………………..

Preparation and Reactions of Esters 6 Which of the following could be a correct synthesis of aspirin? CO2H OCOCH3 A B C D N90/I/29 Integrated Questions and Structural Elucidation 7(a) Malic acid occurs in green apples and grapes. It is often added to beverages and confectionery to confer a sour taste. Malic acid can be dehydrated to give a mixture of two isomeric alkenedioic acids with the molecular formula C4H4O4.

(i) Draw the structures of the isomers and state the type of isomerism they show. (ii) Suggest the reagents and conditions for the dehydration reaction. …………………………………………………………………………………………………. (iii) The pKa values of the two acidic groups in one isomer J, are 3.0 and 4.4, whereas in the other isomer, K, they are 1.9 and 6.2. Use the pKa values to suggest which isomer, J or K, produces the more stable mono– anion on treatment with 1 mol of NaOH? Explain your answer. ………………………………………………………………………………………….……… …………………………………………………………………………………………….…… …………………………………………………………………………………………….…… …………………………………………………………………………………………….…… ……………………………………………………………………………………………….… ………………………………………………………………………………………..….…….. (iv) Draw the displayed formula of the mono–anion produced in (iii), and use your formula to suggest an explanation for why it is more stable than the mono –anion of the other isomer. ………………………………………………………………………………………….……… …………………………………………………………………………………………….…… ……………………………………………………………………………….………..…….… ……………………………………………………………………………………………….… …………………………………………………………………………………………………. ……………………………………………………………………………………………….…

Gently heating the anhydrous crystals of one of the isomers J or K produces a neutral compound L, C4H2O3, which does not react with sodium metal or give a precipitate with 2,4– dinitrophenylhydrazine. Compound L reacts with ammonia to give a compound M, C4H5NO3, which gives a salt on reaction with NaOH but not with HCl. Compound M decolourises Br2(aq). (b) Suggest structures for compounds L and M, and identify which isomer, J or K, produces L. Write equations for all reactions, and explain the observations. When malic acid is heated with acidified K 2Cr2O7, compound N is formed. Heating N in an inert solvent for several hours produces P, C3H4O3 and a gas Q. Both N and P react with 2,4–dinitrophenylhydrazine. Compound P also gives a yellow precipitate with aqueous alkaline iodine. (c) Suggest structures for N and P, and use the information given to suggest the identity of gas Q. N12/III/5

8 Heating a plant oil under reflux in alkali followed by acidifying the cooled mixture gives an optically active acid A, C18H34O3 and glycerol, HOCH 2CH(OH)CH2OH, in the molar ratio of 3:1. A decolorises an organic solution of bromine. Treatment of A with hot acidified potassium manganate(VII) gives B, which has the formula HO2C(CH2)7CO2H, and a carboxylic acid C, which is optically inactive. Heating C with soda lime causes it to lose its –CO2H group to give an organic compound D, with liberation of carbon dioxide. On warming with alkaline aqueous iodine, C does not give tri –iodomethane. On warming with alkaline aqueous iodine, D does give tri –iodomethane, together with the salt of heptanoic acid, CH3(CH2)5CO2H. On warming with concentrated sulfuric acid, A gives E, C18H32O2. Treatment of E with hot acidified potassium manganate(VII) gives B, heptanoic acid, and other products. Identify compounds A, C, D and E, account for all these observations and suggest a structure for the plant oil. [High marks can be scored for appropriate chemistry without a complete structure for the plant oil.] [12]

Reactions of Alcohols, Aldehydes, Carboxylic acids and its derivatives CH3CH2CH2OH excess conc. H2SO4, heat RCO2H, conc. H2SO4, heat PCl5 NaOH(aq), heat K2Cr2O7(aq), H2SO4(aq), heat with immediate distillation LiAlH4 in dry ether HCN(aq), NaCN or HCN(aq), NaOH(aq) NHH2N NO2 NO2 2,4-DNPH Na LiAlH4 in dry ether r.t. KMnO4(aq), H2SO4(aq), heat Fehling’s solution, heat soda lime, heat H2SO4(aq) PCl5 H2O phenol, NaOH(aq) RNH2 ROH NaOH(aq), heat ROH, conc H2SO4, heat H2SO4(aq), heat NaOH(aq), heat H2SO4(aq), heat NH3 Tollen’s reagent [Ag(NH3)2+], heat