Compounds containing the carbonyl group

• Carbonyl group --> -C=O
• Aldehydes --> RHC=O
• Ketones --> RR'C=O

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

• 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.

• 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

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

• 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.

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.

• 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

• Sweet smelling
  • Used in:
    • perfumes
    • food flavourings
    • plasticisers
    • solvents

• 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

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

• 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

• 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

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]

• 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.

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

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

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

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!

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)