Compounds containing the carbonyl group
Syllabus bases revision cards from Unit 4 AQA chemistry.
3.5 / 5 based on 3 ratings
- Created by: Kirsty Jones
- Created on: 07-06-10 22:02
Aldehydes and Ketones
- Carbonyl group --> -C=O
- Aldehydes --> RHC=O
- Ketones --> RR'C=O
1 of 20
Oxidation
Aldehydes
- aldehydes oxidised to carboxylic acids
- [O] = oxidising agent = acidified potassium dichromate = H2Cr2O2/H+
Ketones
- cannot be oxidised
- C-C bonds stronger to break
- Stronger oxidising agents break the hydrocarbon chain of the ketone molecule resulting in a shorter chain molecule, CO2 & H2O
2 of 20
Fehling's solution
- Made from a mixture of 2 solutions
- Fehlings B containing alkali and a complexing agent
- Fehlings A contains Cu2+ ion and therefore coloured blue.
- When an aldehyde is warmed with Fehlings solution:
- a brick red precipitate is formed --> Copper (i) oxide
- works only with branched and chained molecules
- Ketones give no reaction in this test.
3 of 20
Silver Mirror
- Tollen's reagent
- [Ag(NH3)2]^4
- formed when aq ammonia is added to an aq solution of silver nitrate
- when an aldehyde is warmed with Tollen's reagent, mettalic silver is formed.
- aldehydes are oxidised to carboxylic acids by Tollen's reagent
- The Ag+ is reduced to mettalic silver
- A silver mirror will be formed on the inside of the test tube (which has to be spotlessly clean)
- Reaction:
- aldehyde is oxidised --> RCHO + [O] --> RCOOH
- Silver is reduced --> [Ag(NH3)2]+ +e- -->Ag + 2NH3
- [Ag(NH3)2]^4
4 of 20
Mechanisms you need to know for this part of the t
You'll have to find the detailed mechanisms in txt books because I can't put images in here !
- :CN- with:
- carbonyl
- aldehyde
- Reduction of:
- an aldehyde
- a ketone
- Nucleophilic addition - elimination reactions between acycl chlorides and:
- water
- alcohols
- ammonia
- primary amines
5 of 20
Reduction
- many reducing agents will reduce aldehydes and ketones to alcohols
- e.g. NaBH4
- generates H-
- nucleophile
- Hydride ion
- reduces C=O-
- not C=C as repelled by high density electron bond
- attracted to C.
- generates H-
- e.g. NaBH4
6 of 20
Carboxylic acids are weak acids that liberate CO2
RCOOH
- C = +ve = open to attack from nucleophiles
- O = -ve = may be attacked by +ve charged species
- H = may be lost as H+, when compound is behaving as an acid
Loss of proton
- RCOOH (eqm) --> RCOO- + H+
- CH3COOH + NaHCO3 --> CH3COONa + H2O + CO2
- ethanoic acid + sodium hydrocarbonate --> sodium ethanoate + water + carbon dioxide.
7 of 20
Carboxylic acid + alcohol --> ester + water
- This reaction only occurs in the presence of a strong acid catalyst
- Esters
- acid derivatives
- RCOOR'
- CH3COOH + C2H5OH (eqm)--> CH3COOC2H5 + H2O
- Methanoic acid + ethanol --> ester + water
8 of 20
Uses of Esters
- Sweet smelling
- Used in:
- perfumes
- food flavourings
- plasticisers
- solvents
- Used in:
9 of 20
Mote uses
- used extensively in many pharmaceutical and cosmetic preparations. Because it attracts water, it is used to prevent ointments and creams drying out
- as solvents in medicines (e.g. toothpaste)
- used as solvent in food industry (food colourings)
- Used as plastiser - materials becomes flexible and smooth
10 of 20
Vegatable oils and animal fats are esters of glyce
C3H83O = glycerol
- Only difference between a fat and an oil is the oils are liquid at room temp and fats are solid.
- Carboxylic acids are 'fatty acids'
- triglycerides
- C3H5(ORC=O)3
- triglycerides
11 of 20
Esters can be hydrolised.
- Carbonyl combination of an ester has a +ve charge and is therefore attacked by 2 H2Os acting as a weak nucleophile.
- Equation is:
- RCOOR' + H2O --(H+ catalyst)--> RCOOH + R'OH
- doen't go to completion
- eqm contains:
- ester
- H2O
- acid (catalyst)
- alcohol
- esters can be hydrolised at room temp when a strong acid catalyst is used.
- CH3COOC2H5 + H2O --(H+ catayst)--> CH3COOH + C2H5OH
12 of 20
Oils and Fats can be hydrolysed to give soap, glyc
- Esters can be hydrolised by boiling with sodium hydroxide
- Both products are useful:
- glycerol
- mixture of sodium salts (soaps)
- Equation:
- C3H5(ORC=O)3 + 3NaOH --> C3H5(OH)3 + 3NaOCOR
- Sodium salts are ionic and dissociate to form Na+ and RCOO-
- Both products are useful:
- Propane -1,2,3-triol
- 3 O-H bonds
- forms hydrogen bonds
- soluble in water
- 3 O-H bonds
13 of 20
Bio-diseal
Biodiseal:
- possible solution for our reliance on crude oil
- renewable fuel
- made from oils derived from crops e.g. **** seed
- Oil is a triglyceride ester
- Method:
- oil is reacted with methanol
- strong alkali is a catalyst
- Forms a mixture of methyl esters
- oil is reacted with methanol
- Equation:
- Draw out the molecules - this will make it easier to understand!
- CH2OCO(CH2)14CH3CHOCO(CH2)14CH3CH2OCO(CH2)14CH3 +3CH3OH --> CH2OHCHOHCH2OH + 3(CH3OCO(CH2)14CH3) [biodiseal]
14 of 20
Acylation
- R-C=O
- R =acyl group
- C is attacked by nucleophiles
- acylation is a process by which an acyl group is introduced to another molecule
- produces a group of compounds known as acid derivatives
- derived from carboxylic acids
- general formula --> RZC=O
- R --> if CH3 group then called ethanoyl
- Z = -OR' --> ester , -Cl --> acid chloride, -OCOR' = acid anhydride.
- produces a group of compounds known as acid derivatives
15 of 20
General Reaction
Equation:
- RZC=O + :Nu- --> RNuC=O + :Z-
- :Nu- = nucleophile
How readiliy the reaction occurs depends on 3 things:
- magnitude of +ve charge on C
- How easily Z is lost
- How good the nucleophile is
Acid chlorides (RClC=O) and anhydrides (RCOORCO) are both good acylation agents
16 of 20
Nucleophiles
Have lone pair!
- the best nucleophile is the one that is best at donating the lone pair
:NH3 > :NH2R > :OHR > :OH2
ammonia > primary amine > alcohol > water
- > = better than
17 of 20
Important reactions you need to know!
Ammonia
- With Acid chloride:
- NH3 + RCLO --> RCNH2O [amide] + HCl
- With anhydride:
- NH3 + (RC=O)2O --> RCNH2O [amide] + RCOOH
Amine
- with acid chloride
- R'-NH2 +RClCO --> RCONHR' [N-sub amide] + HCl
- with anhydride
- R'-NH2 + (RCO)2O --> RCONHR' [N-sub amide] + RCOOH
18 of 20
Important reactions you need to know!
Alcohol
- with acid chloride
- R'-OH + RClCO --> RCOOR [ester] + HCl
- with anhydride
- R'-OH + (RCO)2O --> RCOOR' [ester] + RCOOH
Water
- with acid chloride
- H2O + RClCO --> RCOOH [carboxylic acid]
- with anhydride
- H2O + (RCO)2O --> 2RCOOH [carboxylic acid *2]
You need to know the mechanisms for the reactions with ammonia, amine, water and alcohol!
19 of 20
Aspirin!
A working example of the use of acylation in medicine.
Aspirin info:
- used for headaches
- has potential side effect of internal bleeding
- compounds originally extracted from willow bark
Advantages of using ethanoic anhydride over ethanoyl chloride as an acylation agent are:
- It is cheaper
- Less corrosive
- Less reactive with water
- by product is ethanoic acid rather than HCl, so it is safer too.
- More economically variable than ethanoyl chloride (by product ethanoic acid can be sold on)
20 of 20
Similar Chemistry resources:
0.0 / 5
0.0 / 5
0.0 / 5
5.0 / 5 based on 3 ratings
3.0 / 5 based on 1 rating
4.0 / 5 based on 5 ratings
0.0 / 5
Comments
No comments have yet been made