Module 6 Chapter 28

Question 1

How can organic compounds be extended

Answer 1

By adding C-C bonds from reactions of haloalkanes or carbonyls with cyanide ions, via nucleophilic addition.

Question 2

When do carbonyls react with cyanide ions

Answer 2

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.

Question 3

How are haloalkanes reacted with cyanide

Answer 3

When they are heated under reflux with a solution of a haloalkanes and NaCN or KCN in ethanol. In a nucleophilic substitution reaction

Question 4

DRAW THE mechanism for the nucleophilic substitution of bromomethane with CN-

Answer 4

DRAW IT

Question 5

What are the reactions of nitriles

Answer 5

They can be reduced to form amines and they can be hydrolysed to form carboxylic acids.

Question 6

What are the conditions that are required for the reduction of nitriles

Answer 6

They can be reduced to form amines by reacting them with hydrogen at high temperatures with a nickel catalyst.

Question 7

Draw the equation for the reaction between CH3CH2CN and H2 with a nickel catalyst

Answer 7

DRAW IT

Question 8

What are the conditions that are required for the hydrolysis of nitriles

Answer 8

Nitriles can be hydrolysed to form carboxylic acids via the formation of an amide under acidic conditions when heating.

Question 9

What are the two equations for the steps in the hydrolysis of nitriles

Answer 9

R-C(triple bond)N + H2O —(H+)—> RCONH2
RCONH2 + H2O + H+ —> RCOOH + NH4+

Question 10

What is the net reaction for the hydrolysis of a nitrile

Answer 10

CH3CH2CH2C(triple bond)N + 2H2O + HCl —> CH3CH2COOH + NH4Cl

Question 11

What are the two ways that the carbon chain can be lengthened in aromatic compounds

Answer 11

Alkylation and acylation

Question 12

What are the alkylation and acylation reactions respectively

Answer 12

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.

Question 13

What is filtration under reduced pressure required for

Answer 13

Separating a solid product from a solvent or liquid in reaction mixture

Question 14

What are the apparatus that are required for filtration for reduced pressure

Answer 14

Pressure tubing
Filter paper
Filter/vacuum pump

Question 15

What are the steps for filtration under reduced pressure (1)

Answer 15

1.One end of the pressure tubing is attached to vacuum/filter pumps, other end to the buccnofunnel.

2. Fit Büchner funnel to Büchner flask need a good tight fit - use of a Buchner ring or a rubber bung
3. Switch pump/tap on
4. Check for good suction by placing hand over funnel

Question 16

What are the steps for filtration under reduced pressure (2)

Answer 16

5. Filter paper in Büchner funnel
6. Slowly pour mixture in centre of filter paper
7. Rinse beaker with solvent so all out in funnel
8. Rinse crystals in Büchner funnel with more solvent and suction so they start to dry.

Question 17

How are the impurities removed from the solid product

Answer 17

Through recrystallisation

Question 18

What does recrystallisation depend on

Answer 18

The desired product and the impurities having different solubilities in the chosen solvent.

Question 19

What is the process of recrystallisation (1)

Answer 19

1. Pour solvent into conc flask (if flammable warm over water bath) if water solvent - into flask as tripod/gause/bunsen and warm
2. Tip impurity into another conical flask/beaker

Question 20

What is the process of recrystallisation (2)

Answer 20

3. Slowly add solvent to impure until it dissolves. Minimal solvent volume.
4. 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.

Question 21

Mp determination

Answer 21

Tells us whiter a compound is pure - singular mp - very sharp, 1or 2 degree range.

Question 22

What is the melting range

Answer 22

Melting range = difference between the temp at which the sample starts to melt and the temp when melting is complete.

Question 23

What happens if the substance is impure

Answer 23

If impure, this happens over a wide range of temperatures

Impure has a lower mp than sample.

Question 24

What are the steps for melting point determination (1)

Answer 24

1. Sample needs to be completely dry and free flowing
2. Glass capillary tube/mp tube. Hold end in the hot flame of BB, rotate in the flame till end is sealed.

Question 25

What are the steps for melting point determination (2)

Answer 25

3. Allow to cool fill with crystals -3mm. Push the unsealed end into solid sample. 4. You can now measure the melting point of which there are two methods to do so.

Question 26

How do you use an electrically heating apparatus to determine the melting point (1)

Answer 26

1. Place capillary into sample tube and a 0-300*C thermometer into the therm hole of melting point apparatus 2. Rapid heating setting, heats up sample whilst observing it through magnifying window. 3. Once it is seen to have melted record, Mp and allow apparatus to cool.

Question 27

How do you use an electrically heating apparatus to determine the melting point (2)

Answer 27

4) Prep second sample and repeat 5) As MP is approached, set to low and raise the temperature slowly whilst observing. A more accurate mp obtained.

Question 28

How do you use an oil bath or thick tube method to determine the melting point (1)

Answer 28

Set up thick tube/oil bath Attach capillary tube with sample to thermometer using a rubber band Insert through hole in cork nor clamp therm.

Question 29

How do you use an oil bath or thick tube method to determine the melting point (2)

Answer 29

End of therm and capillary tube should dip into oil Using micro-burner, slowly heat side arm of Thick tube/oil bath and observe and solid. When starts to melt remove heat and record the temp at which all melted. Slow heating when near mp.

Question 30

What is required when doing the nucleophilic substitution of haloalkanes with CN-

Answer 30

KCN or NaCN with an ethanol solvent (no acid present)