Carboxylic Acids and Derivatives Flashcards
What is a carboxylic acid?
Functional group?
-COOH (C=O and C-OH)
How do you name carboxylic acids?
-oic acid
Are carboxylic acids soluble in water? Why? What
influences their solubility
Yes. Acid group can form hydrogen bonds with water molecules
What are the intermolecular forces in carboxylic acids?
Hydrogen bonds in solid state - very strong.
What are esters (what are they formed from)?
Functional group, general formula?
Formed from carboxylic acids and alcohols.
RCOOR’ (C=O, C-O-C)
Write an equation for the reaction of ethanoic acid
with propan-1-ol
CH3COOH + CH3CH2CH2OH → CH3COOCH2CH2CH3 + H2O
How do you name esters?
Start with the group that has replaced the hydrogen, then acid part e.g. propyl (from
alcohol) ethanoate (from carboxylic acid).
What characteristic physical properties do esters have?
Volatile, pleasant fruity smells e.g. apple, pear drops
What are some uses of esters?
Flavourings, perfumes (both for longer chains), solvents (short chains), plasticisers.
What are some common natural esters?
Fats and oils
Write an equation for the equilibrium formed by a
ethanoic acid in solution
CH3COOH (aq) ⇌ CH3COO- (aq) + H+ (aq)
What happens to the negative charge on the
ethanoate ion in terms of electrons?
Electrons delocalise so the negative charge is shared across the whole of the carboxylate group
How could you distinguish carboxylic acids from other -OH containing compounds?
Add NaHCO3, acids will produce sodium salt, water and carbon dioxide.
Write an equation for the reaction of ethanoic acid
with NaOH
CH3COOH + NaOH → H2O + CH3COO-Na+
Write an equation for the reaction of ethanoic acid
with Na2CO3.
2CH3COOH + Na2CO3 → 2CH3COO-Na+ + H2O + CO2
What catalyst is needed for the formation of esters from alcohols and carboxylic acids?
Concentrated strong acid e.g. H2SO4
What catalyst is needed for the hydrolysis of esters?
Dilute strong acid e.g. H2SO4
What is an alternative method of hydrolysis?
Base hydrolysis
What are the advantages of base hydrolysis?
Reaction goes to completion due to neutralisation by base - more product in the mixture than acid catalysed hydrolysis.
Which alcohol forms the esters that make up animal
and vegetable oils?
Glycerol / propane-1,2,3-triol
What is the difference between oil and fat?
- Oils are liquid at room temperature, fats are solids
- fats are usually saturated, oils are not
What are the products of hydrolysing fats and oils?
Propane-1,2,3-triol and sodium salts of the acids
that make up the ester (hydrolysed with NaOH)
What are the uses of these products (Propane-1,2,3-triol and sodium salts)?
Soaps and cleaning products
What does the long hydrocarbon chain of the
carboxylate ion do?
Mixes with grease
What does the COO- group do?
Mixes with water
How does the carboxylate ion with a long carbon chain make a good cleaning agent?
Means that grease can be removed from water
What is the IUPAC name of glycerol?
propane-1,2,3-triol
What are some common uses of glycerol?
- Used in pharmaceutical and cosmetic preparations e.g. to
stop creams drying out - Solvent in many medicines, present in toothpaste
- Solvent in food industry e.g. food colourings
- Plasticising various materials like sheets and gaskets, cellophane and paper
How do you make biodiesel (general equation and
conditions)?
NaOH catalyst, 60oC
Lipids (fats/oils - esters) + 3CH3OH → 3 methyl esters + glycerol
What does transesterification mean?
Converting one type of ester to another
What kind of crops is biodiesel made from?
Rapeseed oil or soybean oil
How is the reaction mixture of biodiesel purified and
separated?
Settling tank or centrifuge; remove remainder with water.
Add acid to neutralise excess alkali catalyst.
Solid soap is formed - easy to remove
What is a problem with producing biodiesel?
Crops that could be used to make food are being used to make fuel - are the resources being best used?
What are carboxylic acid derivatives?
Molecules that have the acyl group as part of their structure, formed from carboxylic acids
Name two acid derivatives and give their functional
groups
Acyl chlorides: RCOCl
Acid anhydrides: RCOOCR / (RCO)2O
Which factors determine how readily the acylation of a nucleophile by an acid derivative occurs? (3)
- Magnitude of the delta + charge on the carbonyl carbon, which depends on the electronegativity of the atom/group being substituted.
- How easily the atom/group being substituted is lost
- How readily the nucleophile donates its electrons
What effect do the Cl and O atoms in acyl chlorides/acid anhydrides have on the partial charge of the carbonyl carbon?
Increase the partial + charge by attracting electrons; this means that they react more readily with nucleophiles
Are acyl chlorides or acid anhydrides more reactive?
Acyl chlorides
What is the name of the mechanism by which acyl
chlorides and acid anhydrides acylate nucleophiles?
Addition-elimination
If the nucleophile is ammonia for the acylation of acyl chlorides or acid anhydrides, what are the products of the reaction?
An amide
Write an equation for the reaction of ethanoyl chloride and ammonia
CH3COCl + 2NH3 → CH3CONH2 + NH4Cl
If the nucleophile is a primary amine, what are the
products of the acylation of acyl chlorides or acid anhydrides?
N-substituted amide
Write an equation for the reaction of ethanoyl chloride and methylamine
CH3COCl + CH3NH2 → CH3CONHCH3 + CH3NH3Cl
If the nucleophile is an alcohol, what are the products of the acylation of acyl chlorides or acid
anhydrides?
An ester
Write an equation for the reaction of ethanoyl chloride and ethanol
CH3COCl + CH3CH2OH → CH3COOCH2CH3 + HCl
If the nucleophile is water, what are the products of the acylation of acyl chlorides or acid anhydrides?
Carboxylic acid (hydrolyses ester linkage)
What is the name of this reaction (the acylation of
acyl chlorides/acid anhydrides with water as a
nucleophile)?
hydrolysis
Write an equation for the reaction of ethanoyl chloride and water.
CH3COCl + H2O → CH3COOH + HCl
What is a commercially important acylation reaction?
The manufacture of aspirin
What are the advantages of using ethanoic anhydride as an acylating agent over ethanoyl chloride?
It is cheaper, less corrosive and does not react as readily with water.
It is safer, as ethanoic acid is produced, rather than HCl, which is corrosive.
What would you observe in a melting point determination if the sample was not pure?
Sample melts over a large range (more than 3oC).
Sample’s melting point is below the accepted value due to impurities disrupting structure
Why might the melting point appear different to the true value?
Temperature of the material in the machine might be different to the temperature shown on the thermometer - apparatus error.
When removing flue gases, what are the issues?
Disposal of large amounts of CaSO3 and CO2 is produced.
What conditions are needed to form methyl esters from an acid anhydride or acyl chloride?
React with methanol and heat gently under reflux
When purifying by recrystallisation, why is the
minimum volume of hot solvent used?
So that a saturated solution is created, so that as many crystals will fall out of solution as possible
when it is cooled
Why is the solution filtered hot when purifying by
recrystallisation?
To remove insoluble impurities and ensure that
the crystals do not form in the filter paper
Why is the solution cooled in an ice bath when
purifying by recrystallisation?
To ensure that as many crystals as possible fall out of solution - yield is higher
Why are the crystals washed with cold water when purifying by recrystallisation?
To remove soluble impurities
How would you separate the crystals from the reaction mixture when purifying by recrystallisation?
Filter under reduced pressure using a Buchner
funnel
Why might percentage yield be below 100% (practical reasons)?
- Product is lost during filtration, drying and weighing - spills, not all transferred from one piece of apparatus to the other
- Product is left dissolved in the solution - some does not crystallise.
- Some left on filter paper. Sample still wet
