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Nanyang Junior College H2 Chemistry (9647) JC2 2015

Tutorial: Carboxylic Acids and Derivatives

Section A: Review Questions

1. Complete the following summary table of reactions of carboxylic acids.

Rxn Reagents and Conditions (Type of reaction)

Rxn Reagents and Conditions (Type of reaction)

1 6

2 7

3 8

4 9

5 10

8 7

6

9 3

4 5

1

2

CH3 C

O

OH

CH3 C

OH

H

H

CH3 C

O

H

CH3

C C

H CH3

H

CH3 C

O

O-Na

+

CH3 C N

10

CH3 C

O

Cl8

2

2. Describe how bromobutane can be converted to the following compounds.

Give the reagents and conditions for each step, as well as indicate the type of reaction. (i) butanoic acid

(ii) pentanoic acid

(iii) propanoic acid

(iv) butanoyl chloride

3. Suggest reagents and conditions, and intermediate if necessary, to convert

(i) OH into

O

OH

(ii) ethanol into phenyl ethanoate

...

Problem Solving Skill Set (PS3) for Q2 & 3 1. Strategy for general synthesis questions: Check the difference between reactants

and products is there a change in carbon length? What functional groups are involved in the reaction? Recall reagents and conditions for the reactions that occur.

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4. Which one of the following is a product of the reaction between phenylmethanol, and ethanoyl chloride, CH3COCl ? A

OCOCH3

B CH2OCOCH3

C COOCH2CH3

D CH2COOCH3

5. In its reaction with sodium, 1 mol of a compound X gives 1 mol of H2 (g). Which compound might X be?

A CH3CH2CH2CH2OH

B (CH3)3OH

C CH3CH2CH2CO2H

D CH3CH( OH)CO2H

6. Ethyl propanoate, CH3CH2OCOCH2CH3 undergoes acidic hydrolysis in the presence of H2

18O. Which of the following products are formed? (18O is an isotope of oxygen) 1 CH3CH2

18OH

2 CH3CH2CO18OH

3 CH3CH2OH

Problem Solving Skill Set (PS3) 1. Strategy for ester synthesis questions: students must be able to draw the structural

formula of the given reactants and hence give the esters required. Note that formula of ester functional group is either written as COO- or OCO-. There is no ester written in the form OOC-.

Problem Solving Skill Set (PS3) 1. Strategy for reaction questions involving arithmetic calculations: students must be

able to recall and balance reactions involving all the functional groups. Recall that each mole of OH and CO2H will react with each mole of Na to give mole of H2.

Problem Solving Skill Set (PS3) 1. Student must note that when an ester undergoes acidic hydrolysis, H atom is added to

the alcohol and the 18OH is added to the acid.

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7. (a) Explain why ethanoic acid is more acidic than ethanol.

(b) Explain why chloroethanoic acid is more acidic than ethanoic acid.

Problem Solving Skill Set (PS3) 1. Student should be familiar with factors affecting stability of conjugate anion and relate

stability of anion to strength of acids. Must recall that comparisons can be between different functional groups and also between different acids.

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Section B: Discussion Questions 8. Hydroxyethanoic acid reacts as shown.

HOCH2CO

2H compound Q compound R

excess PCl5 excess CH3NH2

heat

What are the formulae for compounds Q and R?

Compound Q Compound R

A HOCH2COCl HOCH2CONHCH3

B ClCH2CO2H CH3NHCH2CO2H

C ClCH2COCl CH3NHCH2COCl

D ClCH2COCl CH3NHCH2CONHCH3

9. One industrial preparation of ethanoic acid is the direct carbonylation of methanol using a rhodium catalyst

OHCH3 + COrhodium

catalystCH3 C

OH

O

Which compound could be expected to produce

CH

CO2H

CH2CO2H

CH2CO2H ? A

CH

OH

CO2H

CH2OH

C CH

OH

CH2CO2H

CO2H

B

CH

CH2OH

CH2CO2H

CH2CO2H

D

CH

OH

CH2CO2H

CH2OH

Problem Solving Skill Set (PS3) Strategy for solving reactions not found in syllabus:

1. Observe the patterns in the reaction; what is the type of reaction? 2. What bonds are broken/formed. How is the CO group added to the alcohol?

3. What are the products formed from this reaction?

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10. Which procedure gives the best yield of ethyl ethanoate, CH3CO2CH2CH3, starting from ethanoic acid, CH3CO2H, and ethanol, CH3CH2OH?

A reacting CH3CO2H with SOCl2, then adding CH3CH2OH

B reacting CH3CH2OH with SOCl2, then adding CH3CO2H

C refluxing a mixture of CH3CO2H and CH3CH2OH with NaOH (aq)

D refluxing CH3CH2OH with concentrated H2SO4, then adding CH3CO2H

11. Which compound is most readily hydrolysed by water?

A CH3COCH2Cl

B C6H5CH2COCl

C CH3CHClCO2H

D Cl Cl

Cl

COCH3

Problem Solving Skill Set (PS3) Strategy for solving questions that involve the largest yield of ester:

1. Recall the 2 different sets of reagents and conditions to yield esters 2. Which set gives a compete reaction (e.g. a larger yield)? 3. Recall reactions of functional groups in the above reactions and understand why 3

out of 4 options give a poor or no yield of ester.

Problem Solving Skill Set (PS3) Strategy for solving questions that involve the largest yield of ester:

1. Identify the functional group present.

2. Recall the order of ease of hydrolysis of different functional groups.

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12. 2-hydroxybenzoic acid, A, is a useful intermediate for making aspirin (an analgesic) and oil of wintergreen (used in ointments).

(a) Suggest suitable reagents and conditions for reaction II.

(b) Draw the structural formulae of the organic molecules produced when A reacts with

i. Na

ii. Na2CO3

iii. SOCl2 iv. Br2 (aq)

(c) A student proposes the following synthetic route to get aspirin.

OCOCH3

CN

OCOCH3

CO2Na

OCOCH3

CO2H

NaOH(aq)

reflux

HCl(aq)

Suggest what is wrong with the scheme and propose a correction to the scheme to successfully get aspirin.

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Error in the proposal: ..

..

Correction to the scheme: ..

..

(d) When an aspirin tablet was crushed up in water and titrated with 0.1 mol dm-3 sodium

hydroxide, 13.9 cm3 of alkali was required to neutralise its acidity.

Write a balanced equation for the reaction between aspirin and sodium hydroxide, hence determine the mass of aspirin in the tablet?

Problem Solving Skill Set (PS3) 1. How can we determine mole ratio of aspirin to NaOH? Note that during

neutralisation reaction, all moles of COOH will be reacted away. 2. Consider how the reaction would change if heat was supplied?

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(e) A soluble aspirin contains the calcium salt of aspirin.

(i) What reagent could you use to convert aspirin into its calcium salt? Write an equation to illustrate your answer.

(ii) Suggest why aspirin is insoluble in water whereas its calcium salt is soluble. Draw a suitable diagram to illustrate the solubility of the salt.

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13. Compound L is used medicinally as an anti-spasmodic agent. Hydrolysis of L produces equimolar amounts of phenylmethanol, M, and benzoic acid, N.

Compound P is an isomer of L, and is used in perfumes. Hydrolysis of P produces 4-methylphenol, Q, and benzoic acid, N.

(a) Suggest structures for L and P.

(b) Compound P can be synthesized from compounds Q and N through the

following synthesis process.

L

P

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(i) Suggest reagents and conditions from steps (I) and (II).

Step (I):

Step (II):

(ii) State the type of reaction that has taken place in step (II).

(iii) Hence suggest a possible mechanism for step (II). In your answer,

show any relevant charges, lone pairs of electrons and movement of electrons.

Problem Solving Skill Set (PS3) 1. You may find it helpful to make a comparison to nucleophilic substitution mechanism of RX. 2. Note in the first step, NaOH is used to generate the phenoxide anion, a stronger nucleophile than phenol (to subsequently attack the benzoyl chloride).

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N2009/II/5 modified 14. Values of the acid dissociations, Ka, for some weak acids are given below.

acid formula Ka / mold m-3

Benzoic acid COOH

6.3 x 10-5

Carbonic acid H2CO3 4.5 x 10-7

Ethanoic acid CH3CO2H 1.8 x 10-5

Phenol OH

1.3 x 10-10

(a) An aromatic ester E has the following percentage composition by mass,

C, 70.6; H, 5.9; O, 23.5 (i) Calculate the empirical formula of E.

(ii) Given that Mr of E is 136.0, suggest molecular formula of E.

When the aromatic ester E is hydrolysed with NaOH (aq) and the resulting mixture acidified with a mineral acid such as sulfuric acid, methanoic acid, HCO2H, is not

among the products.

(b) (i) Use this information and your answer to (a)(ii) to suggest two possible structural formulae for the ester E. Draw the displayed formulae of your

compounds in the boxes below.

Structure of E1

Structure of E2

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(ii) For each of your compounds E1 and E2, give the structural formulae of

the organic products that would be formed on heating it under reflux with an excess of NaOH (aq).

E1 produces E2 produces

(c) Suggest what will be formed if CO2 is bubbled through each of the mixtures

formed in (b)(ii). If nothing is formed, write no reaction.

E1 produces E2 produces

Explain your answer:

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15. Describe simple chemical tests which would enable you to distinguish the following compounds. For each test, state the reagents and conditions, and state what would be observed with each compound.

(a) CH3COCl and CH3CH2Cl

(b)

O

O

O

O Compound A and Compound B (Hint: need to break linkage before distinguishing test can be done)

(c) CH3COOH, CH3CH2OH and CH3COOCH3 (Hint: more than 1 test required)

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16. Arrange the following organic compounds in order of increasing pH of solution formed when the same amount of each compound is dissolved separately in water. Explain your answer.

phenol benzoic acid ethyl ethanoate ethanoic acid

....

Problem Solving Skill Set (PS3) for Qn 12 2. Student should be familiar with factors affecting stability of

conjugate anion and relate stability of anion to strength of acids. Must recall that comparisons can be between different functional groups and also between different acids.

3. Students may make reference to the diagram on the below showing electron dispersion of benzoate anion to deduce stability of the benzoate ion.

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17. This question is about compound H, C5H10O2 which is soluble in water and neutral to litmus.

Compound H readily forms compound I, C5H6O4 when refluxed with acidified

potassium dichromate (VI), Compound I forms a diester when warmed with 2 moles of ethanol and concentrated sulphuric acid.

On reaction with aqueous bromine, compound H produced compound J, C5H11O3Br

and decolourized bromine water.

Strong oxidation of H by hot acidified potassium manganate (VII) causes it to form only one organic product M, C3H4O4. M can be synthesized as indicated in the following reaction scheme.

CHOCH2Cl

LiAlH4, ether

refluxK

KCN

ethanolL

i) H+ (aq), heat

ii) Cr2O72-

/H+, reflux

M

Deduce the structures of compounds H to M. Explain the chemistry of the reactions described, with the aid of equations where appropriate. *Please write your explanation in a piece of foolscape paper.

H

I

J K

L

M

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Nanyang Junior College H2 Chemistry (9647) JC2 2015

Carboxylic Acids and Derivatives Assignment

Name: .. Marks:

CT : 14 ..

18. Trichloroethanal (choral), CCl3CHO, was much used up to the middle of this century

as a drug and a stimulant. Choral is easily oxidised to trichloroethanoic acid. (a) Draw a displayed formula of trichloroethanoic acid. [2]

(b) Explain why this acid is a much stronger acid than ethanoic acid.

[2]

19. In 1991, 3-methylhex-2-enoic acid, MHA, was identified as one factor responsible for the offensive odour of human sweat.

CH3CH2CH2C(CH3)=CHCO2H

MHA

(a) Draw the structures of possible organic products when MHA reacts with the reagents in the table below, and state the type of reaction in each case.

(i) SOCl2 Type of reaction:

(ii) HBr Type of reaction:

(iii) LiAlH4, in dry ether Type of reaction:

(iv) Hot acidified KMnO4 Type of reaction:

[8]

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(b) The odour of MHA is removed by reacting it with aqueous sodium carbonate. Draw the structure of the organic product of this reaction, and hence suggest why it has no odour.

[3]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

(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 reaction with alcohols, using ethyl ethanoate as an example

(iii) acyl chlorides, using ethanoyl chloride as an 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 reactions of acyl chlorides with alcohols, phenols and primary amines

(f) describe 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