3.8/3.9 - Aldehydes and Ketones/Carboxylic acids and derivatives Flashcards
What is the definition of a carbonyl
Caronyls are compounds with a C=O bond, they include aldehydes and ketones
Why are smaller carbonyls soluble in water
They can form hydrogen bonds with the water
What sort of intermolecular forces are present in carbonyls
Pure carbonyls cannot hydrogen bond to themselves but are attracted by permanent dipole forces
Why are carbonyls
O is more electronegative that the C, bond becomes polarised
What are the reagents/conditions for the reaction for aldehyde and ketones to alcohols
Reagents- NaBH4 in aqueous ethanol
Conditions- Room temperature and pressure
Mechanism- Nucleophillic addition, with a H+ from water or weak acid
You can also use LiAH4
What is an alternative way to reduce carbonyls
Cataytic hydrogentation
.Hydrogen and nickel catalyst
. High pressure
What are the reagents/conditions for the reaction of carbonyl > hydroxynitrile
Reagent- Sodium cyanide and dilute sulfuric acid
Conditions - Room temperatures and pressure
Mechanism- Nucleophillic addition
Why is it better to use KCN/NaCN rather than HCN
HCN is a toxic gas that is difficult to contain, there will be a higher concentration of CN- ions with KCN /NaCN as they fully ionise, HCN is a weak acid and only partially ionises
What is the acidity of a carboxylic acid
The carboxylic acids are only weak acids in water, becuase the only slightly dissociate but they are strong enough to displace carbon dioxide from carbonates
How soluble are carboxylic acids in water
The smaller carboxylic acids up to C4, all dissolve in water in alol proportions but after this the solubility rapidly reduces, they dissolve because they can hyrdorgen bond to the water molecules
Why are carboxylic acids salts stable
The pi charge cloud has delocalised and spread out, the delocalisation makes the ion more stable and therfore more likely to form
What does increasing the carbon chain length do for acid strength
Increasing chain length pushes electron density on to the COO- ion making it more negative and less stable, this makes the acid less strong
What does adding an electronegative element to the carbon chain do to acidity
Electronegative atoms withdraw the electron density from the COO- ion, making it less negative and more stable, this makes the acid more strong
What reactions form a salt inolving carboxylic acids
Acid + Metal > Salt + Hydrogen
Acid + Metal > Salt + Water
Acid + Metal > Salt + Water + CO2
Why cannot carboxylic acids be oxidised other than methanoic acid, and give the product of the oxidationh
Carboxulic acids cannot be oxidised by using oxidising agents but methanoic acid is an exception as its structure has effectively an aldehyde group, it would form carbonic acid when reacting
Give the reaction for esterification with water
Carboxylic acid + Alcohol > Ester + Water
Containing a strong acid catalyst
How would you name a carboxylic acid
The bit ending in -yl comes from the alcohol and the bit ending in -anoate comes from the carboxylic acid
Give all the different uses of esters, and why they can be used in this manner
. Esters are sweet smelling and can be used in perfumes and flavourings, for use in these perfumes they need to be non toxic, soluble in solven such as ethanol, volatile and not able to react with water
. Esters can also be used as solvents for polar organic substances, they do not form hydrogen bonds and they are almost insoluble in water
. Esters can be used in plasticisers, pure polymers have limited flexibility , incorporating plasticisers allows the polymer chain to move more easily and become more flexible
What are the reagents/conditions for the hydrolysis of esters via acid
Reagents- Dilute HCL
Conditions- Heat under reflux
This reaction is the reverse reaction of ester formation,and a carboxylic acid and alcohol are formed
What are the reagents/conditions for the hydrolysis of esters via sodium hydroxide
Reagents- Dilute sodium hydroxide
Conditions- Heat under reflux
This reaction goes fully to completion and using excess sodium hydroxide will ensure that the ester if fully hydrolyses the products will be a carboxylic acid salt and an alcohol , addition of a strong acid will convert the salt to the carboxylic acid form
What is the IUPAC name for glycerol
Propane 1-2-3 triol
What are fats and oils
They are esters of glycerol and long chain carboxylic fatty acids, these vegtable oils and fats can be hydrolysed to give soap,glycerol and long chain carboxylic fatty acids
How does soap work
Long chain carboxylic fatty acids that are produced by the hydrolysis of fats act as soaps, the polar CO2- end is hydrophllic and mixes with the water, and the long non polar hydrocarbon chain is hydrophobic and will mix with the grease, this allows the grease and the water to mix and then be washed away
What is biodiesel
Biodiesel is a mixture of methyl esters of long chain carboxylic acids
How can vegtable oils be converted to biodiesel
They can be converted by the reaction with methanol in the prescence of a strong alkali catalyst
What are the 2 derivatives of carboxylic acids
Acyl chlorides and acid anhydrides
Why are the derivatives more reactive than carboxylix acids
The Cl and the OCOCH3 groups are classes as good leaving groups with means they go less effective delocalisation, this makes them more reactive
What are the reagents/conditions for the reaction of acyl chloride/acid anyhydride > Carboxylic acid
Reagent : Water
Conditions: Room temperature
Mechanism:Nucleophillic addition
. When you use acyl chloride HCl is given off
.When you use acid anyhydride you make twice the amuntof acid
What are the reagents/conditions for the reaction of acyl chloride/acid anyhydride > ester
Reagent: Alcohol
Conditions: Room temperature
With acyl chloride HCl is made, with acid anyhydride carboxylic acid is made
Why is it more efficient to make esters using derivatives
Reaction is much quicker and it is not a reversible reaction
What are the reagents/conditions for the reaction of acyl chloride/acid anhydride > primary amide
Reagent: Ammonia
Conditions: Room temperature
With acyl chloride NH4Cl is given off which is white smoke, and with acid anhydride RCO2- NH4 + salt is given off
What are the reagents/conditions for the reaction of acyl chloride/acid anhydirde > secondary amide
Reagent: Primary amine
Conditions: Room temperature
Mechanism: Nucleophillic addition elimination
How do you measure the degree of purity using melting point
.Determine the melting range for the sample
.If the sample is pure melting point will be sharp and the same as the value quoted in the data booklet
.If impurties are present the melting point will be lowered and will melt over a range
. You can use an electronic melting point machine, or byusing a cappilary tube strapped to a themometer that is submeged in heating oil
. You would add a small amount of salt and then heat up slowly near the melting poin t
