O- Carboxylic acids & derivatives

Question 1

Give the formula for sodium ethanoate.

Answer 1

CH3COONa
Na at end as ethanoate is an organic salt

Question 2

Name C6H5COOH

Answer 2

Benzene-carboxylic acid

C6H5 = phenyl group

Question 3

What are the 2 ways of preparing a carboxylic acid?

Answer 3

1. oxidation of a primary alcohol
- eg. CH3CH2OH + 2[O] –> CH3COOH + H2O
2. oxidation of an aldehyde
- eg. CH3CH2CHO + [O] –> CH3CH2COOH

balancing- 1. count H, 2. balance O

Question 4

What are the conditions when preparing a carboxylic acid?

Answer 4

• acidified K2Cr2O7
• reflux

Question 5

What is the solubility of carboxylic acids in water?

Answer 5

• soluble- form H bonds
• solubility ↓ as chain length ↑
• ∵ carboxyl group is hydrophilic but alkyl chain is hydrophobic
• effect of carboxyl group on phy. properties ↓ as chain length ↑

Question 6

Why does ethanoic acid have a higher bp than propan-1-ol?

Answer 6

• both have H bonds
• stronger in COOH- ∵
  1. O-H is ↑ polarised ∵ e- withdrawing effect of C=O
  2. can be 2 H bonds between pair of ethanoic acid molecules vs 1 in propan-1-ol

Question 7

Why are carboxylic acids better Bronsted-Laury acids than alcohols?

Answer 7

• better proton donor
• carbonyl group is e- withdrawing
• ↑ polarity of O-H bond
• H+ easily lost ∵ bigger δ+

O-H breaks more easily in c. acids than alcohols

Question 8

What type of structure is sodium ethanoate?

Answer 8

ionic
- even though has covalent bonds

Question 9

Uses of esters

Answer 9

1. good solvent for organic molecules- ∵ polar
2. plasticisers- molecular lubricants –> polymer chains slide over each other –> flexible plastics
3. food flavourings
4. perfumes

Question 10

Solubility of esters in water

Answer 10

• low Mr = soluble
• ∵ carbonyl O (=O) ✔ H bond w/ H of H2O
• ↓ soluble as Mr ↑
• hydrophilic functional group forms smaller proportion of molecule
• hydrophobic alkyl group becomes ↑ important

Question 11

Boiling point of esters compared with alcohols and carboxylic acids

Answer 11

• bp of esters is lower
• esters = polar –> dipole-dipole + vdW
• OH + COOH- ✔ H bonds betw molecules vs esters x
• weaker IMF in esters

Question 12

What substances can be used for the hydrolysis of esters?

Answer 12

1. water- slow –> never used
2. dilute acid
3. base (most practical way)

Question 13

Give the equation for hydrolysis of esters with dilute acid and explain why dilute instead of concentrated acid is used.

Answer 13

ester + water ⇌ carboxylic acid + alcohol
- dilute = ↑ water
- eq. shifts to RHS
- ↑ products
- ⇌ H+ (aq)

Question 14

Give the eqaution for hydrolysis of esters with base + an example of a base.

Answer 14

ester + NaOH –reflux–> alcohol + Na salt of carboxylic acid
- –> = reaction goes to completion
- OH- nucleophile attacks C

Question 15

What are oils and fats esters of?

Answer 15

glycerol + fatty acids
- propane-1,2,3-triol
- long chain carboxylic acids

Question 16

Why are oils liquid but fats solid at room temp?

Answer 16

• oils- unsaturated triglyceride molecules x pack as closely tgt
• ∵ Z double bonds cause kinks
• ↓ contact s.a. –> weaker vdW (IMF)
• ↓ mp

Question 17

How is oil converted into fat?

Answer 17

hydrogenation of oils
- changes C=C into C-C
- pass H2 thru heated oil- Ni catalyst
- makes oils ↑ solid

Question 18

What is saponification?

Answer 18

making soap- hydrolysis of fats

Question 19

Equation for saponification

Answer 19

triester + NaOH –> glycerol + Na salt of acid
- soap
- mixture of triesters in natural oils + fats
- split up by hydrolysis, heated w/ conc. NaOH

Question 20

How does soap work?

Answer 20

• hydrophobic tails embed themselves in grease away from water
• hydrophilic heads attract water –> grease (bubble) leaves the surface

Question 21

What is biodiesel?

Answer 21

mixture of methyl esters of long chain carboxylic acids

Question 22

Sources of biodiesel

Answer 22

• soya bean, rapeseed oils
• waste vegetable oils
• discarded animal fats

Question 23

How is biodiesel made?

Answer 23

transesterification
- ester + alcohol ⇌ new ester + new alcohol
- ester bonds broken + reformed

Question 24

Environmental consequences of use of biodiesel + partial solutions

Answer 24

• ➖ habitat loss- ↓ biodiversity
• ➖ loss of land for food crops –> costs of food + hunger
• 🩹 cellulosic material
• 🩹 leftover food (eg. chip oils from maccies)

Question 25

What is acylation?

Answer 25

when an acyl group is added to another molecule

Question 26

2 examples of acid derivatives

Answer 26

1. acid chlorides
2. acid anhydrides

• derived from caboxylic acids

Question 27

General formula for acid anhydrides

Answer 27

RCO-OCOR’
- eg. ethanoic anhydride- CH3COOCOCH3

Question 28

Describe, in words, what happens in acylation

Answer 28

• δ+ C attacked by nucleophile
• nucleophile replaces Z group (Z-RC=O)
• nucleophile = acylated (gains an acyl group)

Question 29

Factors affecting reaction

Answer 29

1. magnitude of δ+ on carbonyl C –> e- releasing/ attracting power of Z
2. how easily Z is lost
3. how good the nucleophile is

Z withdraws e- from C

Question 30

Advantages of using ethanoic anhydride over ethanoyl chloride as an acylation agent in manufacturing.

Answer 30

1. cheaper
2. ↓ corrosive
3. x react w/ water as readily
4. safer- by-product = ethanoic acid x hydrogen chloride