Carboxylic acids and derivatives 3.3.9 Flashcards
What type of acids are carboxylic acids and what does this mean
Weak acids - dissociate partially to form a H+ ion and a carboxylate ion
what functional group does a carboxylic acid have
- COOH
( carbonyl group C=O)
( Hydroxyl group O-H)
What products does a carboxylic acid and a carbonate produce
a salt , carbon dioxide gas and water
What is the chemical test for a carboxylic acid
Add sodium carbonate
result : gentle fizzing / effervescence
What functional group does an ester have
- COO -
How can an ester be produced from carboxylic acids
React carboxylic acids with an alcohol and a sulfuric acid catalyst
What kind of catalyst is sulfuric acid
homogenous catalyst
How is an ester produced when reacting with an acid anhydride
React acid anhydride with an alcohol
How do we name esters when formed from a carboxylic acid
The alkyl group is formed from the alcohol and is named first . e.g. ethyl , methyl etc
The rest of the molecule is former from the carboxylic acid
Remove “-oic acid” and replace it with “-oate”
Named second when naming an ester
When we name esters with alkyl branches e.g. ch3 , we number from the carbons in the C-O-C part
What type of things are esters used in , in the commercially and industrial processes
- Perfumes and food savouring
- Solvents
- Plasticisers
How are esters used in perfumes and food savouring
Some esters have sweet smells such as pear drops
This makes them ideal in fragrances and food products
How are esters used in solvents
- Esters are polar so other compounds will dissolve in esters.
- Rhey also have low boiling points and evaporate easily .
This makes them valuable in making glues
How are esters used in plasticisers
Esters are used to make plastics more flexible during the polymerisation process
How do plastics that are made from esters become more brittle
The esters can leach out of the plastic over time . This could happen if plastic is left out in the sun for too long ( UV causes plastic to become brittle )
How can ester hydrolysis be sped up
- Using an acid ( acid hydrolysis )
- Using a base ( base hydrolysis)
What is the process acid hydrolysis
Use a dilute acid to split an ester into a carboxylic acid and an alcohol
What condition and reagent is used in acid hydrolysis
Sulfuric / hydrochloric acid
Conducted under reflux
What is the reaction for a acid hydrolysis reaction
Ester + water => carboxylic acid + alcohol
What’s the process of base hydrolysis
Use a dilute base to split an ester into a carboxylate ion and an alcohol
What condition and reagent is base hydrolysis in
Reagent : Sodium hydroxide
Condition : distillate , aqueous
What’s the reaction of a base hydrolysis reaction
Ester + Hydroxide ( -OH) => carboxylate + alcohol
How do we produce an ester which makes fats and oils
React glycerol ( alcohol) and fatty acids ( carboxylic acids)
What is the chemical name for glycerol
Propane-1,2,3-triol
What is glycerol reacted with
Long chain fatty acids which can be saturated ( no double bonds) or unsaturated (contains at least 1 double bond )
What is a polysaturated fatty acid
Contains more than 1 double bond
What is an oil
an ester
What are some properties of vegetable oil
- Unsaturated hydrocarbon chains that aren’t straight
- This means that chains can’t pack closely together
- This means that they have lower Van der Waals forces
- Lower melting points and are liquid at room temperature
What are fats?
An ester
What are some properties of animal fats ?
- They have saturated hydrocarbon chains that are straight and more uniform than oils
- This means the chains can pack together closely
- This means higher Van der Waals forces
- This means higher melting points
- Therefore solids at room temperature
How can we make soap
Animal fats and vegetable oils can be hydrolysed by heating them with sodium hydroxide
what reaction is used when using animal fat to make a soap
animal fat + sodium hydroxide => glycerol + sodium salt (soap)
How can biodiesel be formed
Vegetable oils can be converted into biodiesel by reacting oils with methanol and a potassium hydroxide as a catalyst
What is biodiesel
A mixture of fatty acids made from methyl esters and can be made from rapeseed oil
What is the reaction to form biodiesel
Oil + methanol => ^(KOH as catalyst) Glycerol + methyl ester
What are some physical properties of carboxylic acids
- Can form hydrogen bonds with water molecules
- This means that carboxylic acids up to , and including , four carbons are completely soluble in water
- Also forms hydrogen bonds with one another in solid state
- Therefore have higher melting points than alkanes
what is the equation for a carboxylic acid reacting with a metal
Acid + metal (Na) => salt + hydrogen
What is the reaction between carboxylic acid and an alkali
Acid + Alkali ( NaOH) => salt + water
What is the reaction of a carboxylic acid and a carbonate
acid + carbonate (Na2CO3) => salt + water + carbon dioxide
what is biodiesel used for
Source of fuel for motor vehicles
it’s a renewable fuel
What is the acyl chloride functional group
-COCl
How is an acyl chloride named
By finding the longest carbon chain and then adding “-oyl chloride “ on the end
What is the reaction of acyl chloride and water
Acyl chloride + water -> carboxylic acid + hydrogen chloride gas
What are the observations produced and what kind of reactions are with acyl chlorides
Vigorous reaction
White misty fumes of hydrogen chloride gas produced
(HCl) gas produced
What is the reaction with acyl chloride and ammonia
Acyl chloride + ammonia -> amide + hydrogen chloride gas
What is the functional group of an amide
CONH2
What’s the reaction between acyl chloride and an alcohol
Acyl chloride + alcohol => ester + hydrogen chloride gas
What is the reaction between an acyl chloride and a primary amine
Acyl chloride + primary amine => N- substituted amide + hydrogen chloride gas
What is an N- substituted amide
Usually an amide would contain NH2
But one of the hydrogens is replaced by an alkyl group
How would you name an N- substituted amide
Put an N - ( alkyl group that replaced the hydrogen ) and then the amide
Example : N- methyl ethanamide
In acyl chloride reactions what is cl substituted for
Either an oxygen or nitrogen
What do acyl chlorides react with
Water
Ammonia
Alcohol
Primary amines
What is an acid anhydride
A molecule made from 2 carboxylic acids that are the same
How are acid anhydrides named
By naming the known carboxylic acid it’s made from and removing the “-acid” and adding “-anhydride” on the end
How are the reactions of acyl chlorides and acid anhydrides different
Acid anhydrides are less vigorous because they produce carboxylic acids , whilst acyl chlorides produce hydrogen chloride gas
What do acid anhydrides react with
Water
Ammonia
Alcohol
Primary amine
What’s the reaction between an acid anhydrides and water
Acid anhydride + water => carboxylic acid + carboxylic acid
What’s the reaction between acid anhydrides and ammonia
Acid anhydrides + ammonia => amide + carboxylic acid
What’s the reaction between acid anhydrides and an alcohol
Acid anhydrides + alcohol => esters + carboxylic acids
What’s the reaction between acid anhydrides and a primary amine
Acid anhydrides + primary amine => N- substituted amine + carboxylic acid
What happens in acyl chloride reactions
Acyl chlorides have a strong delta positive on the carbon which is susceptible to attack from nucleophiles.
They have a strong delta positive as the oxygen and chlorine atoms are electronegative and draw electrons to themselves
What is the mechanism called for acyl chloride mechanisms
Nucleophilic Addition - elimination
What is aspirin
An ester
How is aspirin made
Reacting ethanoic anhydrides or ethanoyl chloride and salicylic acid
What’s the reaction to make aspirin
Ethanoic anhydride or ethanoyl chloride + salicylic acid => aspirin + ethanoic acid
Why is ethanoic anhydride used instead of ethanoyl chloride in making aspirin in industry
- safer as it’s less corrosive
- safer as it doesn’t produce HCl gas
- Cheaper
- safer as it does not react vigorously with water
What is reflux
A technique that allows strong heating without losing volatile reactants and products
Volatile compounds evaporate and condense and fall back into the flask
Why is heating in reflux not done using a naked flame
Heating flammable liquids
So we use a water bath or a mantle
It’s safer than using a naked flame
When is distillation used
When we want to separate substances with different boiling points
What if your compound has a lower boiling point than the starting mixture in distillation
Heat to the temperature of the boiling point of compound you want to separate .
Collect product in the separate vessel
What if your compound has a higher boiling point than the starting mixture in distillation
You heat to the temperature of the boiling point of your compound you want to separate . Your compound will remain in the round bottomed flask
When’s using distillation useful
When you want to extract a chemical before it reacts any further
When is redistillation used
When we want to purify volatile substances which can be purified further using separation
What’s the method of redistillation
Collect different substances by monitoring the temperature they boil at and collecting the different liquids as they come out of the condenser
What is a separation technique
Used to remove impurities that are dissolves in water
What’s the method for using separation
- add products from distillation into a separating funnel
- add water to dissolve soluble impurities and create an aqueous solution
- after allowing the solution to settle , 2 layers will form
Top layer = impure product
Bottom layer = aqueous layer containing water soluble impurities - drain aqueous layer off
- remember to remove the stopper
- take the impure product from the separating funnel and add to a round bottom flask (purification )
- add anhydrous Cacl2 (calcium chloride ) .
This is a dehydrating agent and removes aqueous substances still remaining - invert flask and leave for 20-30 minutes
- filter the solid drying agent to remove
What’s the dehydrating agent used in separation and purification
CaCl2 calcium chloride
What technique is it when you take impure product from separating funnel and add to a roundbottomed flask
Purification
What is filtration
A technique use to separate solids from liquids
Why is a vacuum used in filtration
Used to help separate the liquid and the solid components thoroughly
What’s the method for filtration
- place a filter paper disc in the Büchner funnel and dampen slightly
to make a seal - pour the reaction mixture into the Büchner funnel with the vaccine line on
- vacuum creates a reduced pressure in the flask and pulls the liquid through .
- the solid will be left in the Büchner funnel
What is recrystallisation
A method to purify solids and the solvent chosen is very important
What’s the method of recrystallisation
1) add just enough hot solvent to allow impure solid to dissolve. This will mean you have a saturated solution of your impure product
2) allow the solution to cool down slowly , crystals will start to form
3) your impurities will remain dissolved in the solution as there is a smaller quantity of them , it takes a lot longer for them to crystallize
4) filter to get your solid purified crystals . Wash with very cold solvent and dry them off
What’s choosing a solvent very important in recrystallisation
You want your impure solids to dissolve fully in hot solvent but virtually insoluble when it’s cold .
If your substance won’t dissolve in hot solvent and you can’t filter the purified solid if it is soluble in cold solvent
Why is measuring the boiling point important
Can help to detect impurities
How can we find out impurities using boiling points in distillation
If we gently heat the sample we can measure the temperature at which it distill at using a thermometer. This is the boiling point
Compare boiling point against data book value
If your boiling point is higher than what is recorded in the data book value it contains impurities
How do you know if your sample contains impurities
If the boiling point is higher than what is recorded in the data book
Your sample boils over a range of temperature
Why may you need to use other analytic techniques to spot impurities of various organic compounds
Various compounds have the same boiling points . Need to use other analytic techniques such as mass spectrometry to spot impurities
How can the purity of a compound be determined
By measuring the melting point
What’s the method to determining the purity of a compound
1) add a sample of the solid product into a capillary tube and place into the heating element of the melting point apparatus
2) slowly increase temperature until substance starts to melt
3) there is a temperature range from when the solid just starts to melt to when it fully melts
4) compare melting point against data book values
5) if your substance contains impurities the melting point will be lower and the temperature range the substance melts at will be larger
EQ : suggest why aqueous ethanol is a suitable solvent when heating the coconut oil with KOH.
Give a safety precaution used when heating the mixture and justify . (3)
- Allow to dissolve both oil and KOH
- Use a water bath for heating mixture
- Ethanol is flammable
EQ: The crude aspirin can be purified by recrystallisation using hot ethanol ( bp = 78) as the solvent . Describe two important precautions when heating the mixture of ethanol and crude aspirin (2)
Precaution 1 :
Use a water bath
Precaution 2:
Heat to temperature below bp
EQ : The pure aspirin is filtered under reduced pressure . A small amount of cold ethanol is then poured through the Büchner funnel. Explain the purpose of adding a small amount of cold ethanol. (1)
To remove any soluble impurities
what reagent and observations is it if we test for acyl chlorides
Reagent : water / aq silver nitrate
Observation : white misty fumes / sweet smell / white precipitation
