Chapter 28 - Organic Synthesis

Question 1

What is the functional group of a nitrile

Answer 1

C=-N.

Question 2

How to make nitriles from haloalkanes

Answer 2

Haloalkanes + NaCN or KCN –> Nitrile + KCl or NaCl.

Mixture must but in ethanol.

Question 3

Making nitriles from haloalkanes is what type of reaction

Answer 3

A nucleophilic substitution reaction

Question 4

How to make nitriles from aldehydes and ketones

Answer 4

Aldehydes or ketone + HCN –> hydroxynitrile (or cyanohydrin)

With H2SO4 / NaCN above the arrow.

Question 5

Why can’t you use HCN directly on the aldehydes/ ketones to make nitriles?

Answer 5

Because HCN is too poisonous.

Also, this is a nucleophilic addition mechanism.

Question 6

Reduction of nitriles

Answer 6

Nitriles + hydrogen –> amines

Nickel catalyst above the arrow.

Question 7

Hydrolysis of nitriles

Answer 7

Nitriles + water + aq. acid –> Carboxylic acid + Ammonium Cl.

Heat above the arrow.

Question 8

Alkylation.

Formation C-C bonds to benzene rings

Answer 8

This is a reaction that transfers an alkyl group from a haloalkane to a benzene in the reaction of a catalyst, AlCl3.

Question 9

Acylation.

Formation C-C bonds to benzene rings

Answer 9

This is when a benzene reacts with an acyl chloride in the presence of AlCl3, and a ketone is formed.

Question 10

Define an organometallic compounds

Answer 10

Compounds that contain a carbon-metal bond.

Question 11

Define grignard reagents

Answer 11

These are organometallic compounds that are made by reacting Mg with an alkyl or aryl haloalkane dissolved in an ether solvent.

Question 12

Preparation of an organic solid.

Answer 12

Filtration under reduced pressure 
Apparatus: 
Buchner flask 
Buchner funnel 
Pressure tubing 
Filter paper 
Access to filer/ vacuum pump

Method:

1. Connect one end of the pressure tubing to the vacuum outlet or the filter pump whilst attaching the other end of the rubber tubing to the Buchner flask.
2. Fit the Buchner funnel to the flask ensuring that there is a good tight fit. This is usually obtained using a Buchner ring or a rubber bung.
3. Switch on the vacuum pump, or tap to which the filter is attached.
4. Check for good suction by placing your hand across the top of the funnel.
5. Place a piece of filter paper inside the Buchner funnel and wet this with the same solvent used in preparing your solid. You should see the paper being sucked down against the hole in the funnerl.
6. To filter the sample, slowly pour the reaction mixture from a beaker into the centre of the filter paper.
7. Rinse out the beaker with the solvent so that all of the solid crystals collect in the Buchner funnel.
8. Rinse the crystals in the Buchner funnel with more solvent and leave them under suction for a few minutes so that the crystals start to dry.

Question 13

Define recrystallisation

Answer 13

Used to remove impurities from the solid product.

Question 14

Method for recrystallisaiton

Answer 14

1. Pour a quantity of the chosen solvent in o the cnical flask. (Flammable = place the falsk in a water bath. If the solvent is water = place on a tripod and heat.)
2. Tip the impure sample into the second conical flask.
3. Slowly, add the solvent to the impure sample until it dissolves in the solvent.
4. Once the solid is dissolved, allow the solution to cool. Crystals will form, and when this stops, filter the crystals under reduced pressures (to gain a dry crystalline solid)

Question 15

Define Melting point determination

Answer 15

Is used to identify if a solid compound is pure.

The impure sample melts over a wide range of temperatures and has a lower melting point that a pure samples.

Question 16

Method of the melting point determination.

Answer 16

1. Before taking the m.p, you should ensure that the sample is dry.
2. Take a glass capillary tube or melting point tube. Hold one end in the hot flame. Rotate the tube in the flame until the end is sealed.
3. Allow the tube to cool, then fill it with crystals to about 3mm depth.
4. Then, take the m.p

Question 17

Methods to determine the melting points

Answer 17

Electrically heated m.p apparatus.

Using an oil bath or theile tube method.

Question 18

Method for Electrically heated m.p apparatus.

Answer 18

1. Place capillary tube into a sample hole and 0-300 degrees celsius in the thermometer hole of the m.p apparatus.
2. Use the rapid heating setting to heat the sample.
3. Once the solid is seen to melt, record the m.p
4. Prepare the 2nd sample and start heating it up again.
5. As the m.p is approached, set the heat to low and gain a more accurate m.p

Question 19

Method for oil bath or theile tube

Answer 19

1. Set up an oil bath or theile tube
2. Attach the capillary tube with the sample to a thermometer.
3. Insert the thermometer through the hole in the cork or clamp the thermometer. The end of the thermometer and capillary tube should dip into the oil.
4. Using a microburner, heat the side arm of the Thiele tube or the oil tube whilst observing the solid. As the solid starts to melt, remove the heat and record the temperature when the solid has melted. Heat the oil slowly when approaching the m.p and repeat.

Question 20

Alkene to an alcohol

Answer 20

Add water. 300 degrees Celsius.

At 60-70 atm and phosphoric (v) acid catalyst.