Module 6 Chapter 28
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How can organic compounds be extended
By adding C-C bonds from reactions of haloalkanes or carbonyls with cyanide ions, via nucleophilic addition.
When do carbonyls react with cyanide ions
They will react with NaCN/KCN in the presence of an acid. They will react with NACN + sulphuric acid which is safer and increases the rate.
How are haloalkanes reacted with cyanide
When they are heated under reflux with a solution of a haloalkanes and NaCN or KCN in ethanol. In a nucleophilic substitution reaction
DRAW THE mechanism for the nucleophilic substitution of bromomethane with CN-
DRAW IT
What are the reactions of nitriles
They can be reduced to form amines and they can be hydrolysed to form carboxylic acids.
What are the conditions that are required for the reduction of nitriles
They can be reduced to form amines by reacting them with hydrogen at high temperatures with a nickel catalyst.
Draw the equation for the reaction between CH3CH2CN and H2 with a nickel catalyst
DRAW IT
What are the conditions that are required for the hydrolysis of nitriles
Nitriles can be hydrolysed to form carboxylic acids via the formation of an amide under acidic conditions when heating.
What are the two equations for the steps in the hydrolysis of nitriles
R-C(triple bond)N + H2O —(H+)—> RCONH2 RCONH2 + H2O + H+ —> RCOOH + NH4+
What is the net reaction for the hydrolysis of a nitrile
CH3CH2CH2C(triple bond)N + 2H2O + HCl —> CH3CH2COOH + NH4Cl
What are the two ways that the carbon chain can be lengthened in aromatic compounds
Alkylation and acylation
What are the alkylation and acylation reactions respectively
Alkylation: This reaction transfers an alkyl group form a haloalkanes to benzene ring Acylation: Benzene will react with an acyl chloride with AlCl3 catalyst transferring an acyl group from the acyl chloride to the benzene ring.
What is filtration under reduced pressure required for
Separating a solid product from a solvent or liquid in reaction mixture
What are the apparatus that are required for filtration for reduced pressure
Pressure tubing Filter paper Filter/vacuum pump
What are the steps for filtration under reduced pressure (1)
1.One end of the pressure tubing is attached to vacuum/filter pumps, other end to the buccnofunnel. • Fit Büchner funnel to Büchner flask need a good tight fit - use of a Buchner ring or a rubber bung • Switch pump/tap on • Check for good suction by placing hand over funnel
What are the steps for filtration under reduced pressure (2)
• Filter paper in Büchner funnel • Slowly pour mixture in centre of filter paper • Rinse beaker with solvent so all out in funnel • Rinse crystals in Büchner funnel with more solvent and suction so they start to dry.
How are the impurities removed from the solid product
Through recrystallisation
What does recrystallisation depend on
The desired product and the impurities having different solubilities in the chosen solvent.
What is the process of recrystallisation (1)
• Pour solvent into conc flask (if flammable warm over water bath) if water solvent - into flask as tripod/gause/bunsen and warm • Tip impurity into another conical flask/beaker
What is the process of recrystallisation (2)
• Slowly add solvent to impure until it dissolves. Minimal solvent volume. • let solution cool. Crystals will form in conical flask/beaker. When crystals don’t form anymore, filter them under reduced pressure required—> dry crystalline solid.
Mp determination
Tells us whiter a compound is pure - singular mp - very sharp, 1or 2 degree range.
What is the melting range
Melting range = difference between the temp at which the sample starts to melt and the temp when melting is complete.
What happens if the substance is impure
If impure, this happens over a wide range of temperatures Impure has a lower mp than sample.
What are the steps for melting point determination (1)
• Sample needs to be completely dry and free flowing • Glass capillary tube/mp tube. Hold end in the hot flame of BB, rotate in the flame till end is sealed.