Organic 9: Carboxylic Acids and Derivatives Flashcards
How do you name carboxylic acid compounds?
Suffix is -oic acid
Carboxylic acid is always the root of the name
E.g. benzene carboxylic acid
Describe the solubility of carboxylic acids.
Short chains are completely soluble in water
Because they are able to form hydrogen bonds to water molecules
Long chains are insoluble because the non-polar region predominates
Describe the melting points of carboxylic acids.
Much higher than alkanes of similar molecular mass
Because of much stronger intermolecular forces (hydrogen bonds between molecules)
How can you identify the melting points of carboxylic acids?
Using a Thiele tube
Describe the main physical characteristic of carboxylic acids.
They have very characteristic smells
E.g. ethanoic acid is vinegar, butanoic acid smells like rancid butter
What are esters?
Derived from carboxylic acids
The OH group is replaced with a hydrocarbon group (alkyl or aryl)
How do you name esters?
The first part of the name comes from the alcohol group: methyl, ethyl, propyl, etc
The second part of the name comes from the carboxylic acid: methanoate, ethanoate, propanoate, etc
Describe the physical characteristics of short chain esters.
Fairy volatile
Have fruity, pleasant smells
Often used in flavourings and perfumes
Can be used as solvents and plasticisers
Generally insoluble in water
Describe the physical characteristics of longer chain esters.
Fats and oils
Insoluble in water
How are esters formed?
Carboxylic acid + alcohol –> ester + water
Catalysed by strong acid catalyst (e.g. sulfuric acid)
Reversible reaction
Equilibrium mixture of reactants and products
Write an equation for the esterification reaction of ethanoic acid and ethanol.
CH3COOH + C2H5OH –> CH3COOC2H5 + H2O
Describe acid hydrolysis of esters.
Ester is refluxed with water and a strong, dilute acid catalyst usually hydrochloric acid or sulfuric acid
Reversible reaction
Lots of water must be added to push equilibrium to the right
Ester + water –> carboxylic acid + alcohol
Describe base hydrolysis of esters.
Ester + dilute alkali –> carboxylate ion + alcohol
(reflux)
Produces a negatively charged carboxylate ion which bonds with a positively charged ion from the base used, forming a salt
What is the mechanism for base hydrolysis?
Nucleophilic addition-elimination
What are triglycerides?
Glycerol (propane 1,2,3 triol)
And 3 fatty acids
How are triglycerides hydrolysed?
In acidic conditions to give a mixture of glycerol and fatty acids
By boiling with sodium hydroxide to produce glycerol and a mixture of sodium salts (soaps)
Give a general equation for the hydrolysis of a triglyceride using sodium hydroxide.
What is saponification?
The reaction of sodium hydroxide with triglyceride to produce glycerol and sodium salts
Why is saponification useful?
Produces sodium salts
Useful as cleaning agents because they are ionic and dissociate to form Na+ and RCOO-
RCOO- has two ends: a non-polar hydrocarbon chain and a polar COO- group which is ionic
The hydrocarbon mixes with grease while the COO- mixes with water
What is palmitic acid used for?
Making soaps
What is oleic acid?
A monounsaturated fatty acid
Found in most fats and olive oil
What is linoleic acid?
A polyunsaturated fatty acid
Present in many vegetable oils
Describe the structure and uses of glycerol.
Readily forms hydrogen bonds due to its 3 OH groups
Very soluble in water
Used in pharmacy and cosmetics as it attracts water
Can be used to prevent ointments from drying out
Solvent in many medicines and toothpaste
Food colouring
Plasticiser
What is biodiesel?
A type of fuel made from renewable organic matter
Better for the environment as it produces less pollutants when combusted
How is rapeseed used as a biofuel?
Rapeseed oil is a triglyceride ester
Reacted with methanol to form a mixture of methyl esters which can be used as fuel in diesel vehicles
What makes carbonyl compounds so reactive?
The polar C=O bond is open to attack from nucleophiles
As oxygen is more electronegative than carbon so attracts electrons, making oxygen delta positive and carbon delta negative
The carbon is therefore available to be attacked by nucleophiles
Whereas the oxygen can be attacked by positively charged species like protons
Explain how a carboxylate ion forms.
If the hydrogen on the OH group of a carboxylic acid is lost
The negative charge is shared over the whole carboxylate group (delocalisation) which makes the resulting ion more stable
How do you test for carboxylic acids?
Sodium hydrogencarbonate reacts with carboxylic acids to release carbon dioxide
Helps to distinguish them from other -OH compounds like alcohols
How do carboxylic acids react with sodium hydroxide?
To form ionic salts and water
e.g.
How do carboxylic acids react with sodium hydrogen carbonate?
To form ionic salts, carbon dioxide, and water
E.g.
What is acylation?
The process by which an acyl group is added to another molecule
What are acid derivatives?
Molecules that have the acyl group as part of their structure
E.g. acyl chlorides and acid anhydrides
Give a general equation for the formation of an acid derivative using a nucleophile.
What are the three factors that determine how readily an acylation reaction will occur?
1) Magnitude of positive charge on the carbon (depends on what the variable group is)
2) How easily is the variable group lost
3) How strong the nucleophile is
Why are acyl chlorides and acid anhydrides good acylating agents?
Because the Z groups withdraw electrons easily from the carbonyl carbon to make them more attractive to nucleophiles
Which acid derivative is more reactive?
Acyl chlorides
Chloride ions are stronger leaving groups as they leave behind a more stable ion
Give the main nucleophiles that acid derivatives can react with in the order of their reactivity.
Primary amines
Ammonia
Alcohols
Water
What reaction occurs between acid derivatives and nucleophiles and what is the general mechanism?
Nucleophilic addition-elimination
Why is ethanoic anhydride more useful in industry than ethanoyl chloride?
Cheaper
Less corrosive
Doesn’t react readily with water
Safer as the byproduct is ethanoic acid whereas ethanoyl chloride produces HCl
Important in production of aspirin
What is the systematic name for aspirin?
2-ethanoyloxybenzenecarboxylic acid
What does aspirin do?
Treats moderate pain and fever
Reduces risk of heart attacks and some cancers
Risks:
Intestinal bleeding
