Compounds containing the carbonyl group

Syllabus bases revision cards from Unit 4 AQA chemistry.

HideShow resource information

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
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.
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
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
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-
  • Propane -1,2,3-triol
    • 3 O-H bonds
      • forms hydrogen bonds
      • soluble in water
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
  • 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.
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

Comments

No comments have yet been made

Similar Chemistry resources:

See all Chemistry resources »See all Acids, bases and salts resources »