O- Carboxylic acids & derivatives Flashcards
Give the formula for sodium ethanoate.
CH3COONa
Na at end as ethanoate is an organic salt
Name C6H5COOH
Benzene-carboxylic acid
C6H5 = phenyl group
What are the 2 ways of preparing a carboxylic acid?
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
What are the conditions when preparing a carboxylic acid?
- acidified K2Cr2O7
- reflux
What is the solubility of carboxylic acids in water?
- 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 ↑
Why does ethanoic acid have a higher bp than propan-1-ol?
- 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
Why are carboxylic acids better Bronsted-Laury acids than alcohols?
- 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
What type of structure is sodium ethanoate?
ionic
- even though has covalent bonds
Uses of esters
- good solvent for organic molecules- ∵ polar
- plasticisers- molecular lubricants –> polymer chains slide over each other –> flexible plastics
- food flavourings
- perfumes
Solubility of esters in water
- 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
Boiling point of esters compared with alcohols and carboxylic acids
- bp of esters is lower
- esters = polar –> dipole-dipole + vdW
- OH + COOH- ✔ H bonds betw molecules vs esters x
- weaker IMF in esters
What substances can be used for the hydrolysis of esters?
- water- slow –> never used
- dilute acid
- base (most practical way)
Give the equation for hydrolysis of esters with dilute acid and explain why dilute instead of concentrated acid is used.
ester + water ⇌ carboxylic acid + alcohol
- dilute = ↑ water
- eq. shifts to RHS
- ↑ products
- ⇌ H+ (aq)
Give the eqaution for hydrolysis of esters with base + an example of a base.
ester + NaOH –reflux–> alcohol + Na salt of carboxylic acid
- –> = reaction goes to completion
- OH- nucleophile attacks C
What are oils and fats esters of?
glycerol + fatty acids
- propane-1,2,3-triol
- long chain carboxylic acids
Why are oils liquid but fats solid at room temp?
- oils- unsaturated triglyceride molecules x pack as closely tgt
- ∵ Z double bonds cause kinks
- ↓ contact s.a. –> weaker vdW (IMF)
- ↓ mp
How is oil converted into fat?
hydrogenation of oils
- changes C=C into C-C
- pass H2 thru heated oil- Ni catalyst
- makes oils ↑ solid
What is saponification?
making soap- hydrolysis of fats
Equation for saponification
triester + NaOH –> glycerol + Na salt of acid
- soap
- mixture of triesters in natural oils + fats
- split up by hydrolysis, heated w/ conc. NaOH
How does soap work?
- hydrophobic tails embed themselves in grease away from water
- hydrophilic heads attract water –> grease (bubble) leaves the surface
What is biodiesel?
mixture of methyl esters of long chain carboxylic acids
Sources of biodiesel
- soya bean, rapeseed oils
- waste vegetable oils
- discarded animal fats
How is biodiesel made?
transesterification
- ester + alcohol ⇌ new ester + new alcohol
- ester bonds broken + reformed
Environmental consequences of use of biodiesel + partial solutions
- ➖ habitat loss- ↓ biodiversity
- ➖ loss of land for food crops –> costs of food + hunger
- 🩹 cellulosic material
- 🩹 leftover food (eg. chip oils from maccies)
What is acylation?
when an acyl group is added to another molecule
2 examples of acid derivatives
- acid chlorides
- acid anhydrides
- derived from caboxylic acids
General formula for acid anhydrides
RCO-OCOR’
- eg. ethanoic anhydride- CH3COOCOCH3
Describe, in words, what happens in acylation
- δ+ C attacked by nucleophile
- nucleophile replaces Z group (Z-RC=O)
- nucleophile = acylated (gains an acyl group)
Factors affecting reaction
- magnitude of δ+ on carbonyl C –> e- releasing/ attracting power of Z
- how easily Z is lost
- how good the nucleophile is
Z withdraws e- from C
Advantages of using ethanoic anhydride over ethanoyl chloride as an acylation agent in manufacturing.
- cheaper
- ↓ corrosive
- x react w/ water as readily
- safer- by-product = ethanoic acid x hydrogen chloride
