4.2.3 Organic synthesis

Question 1

Why is heating under reflux used?

Answer 1

allows a liquid to be continuously boiled without boiling dry

Question 2

Describe the steps of heating under reflux

Why are anti bumping granules used?

Answer 2

1. add reaction mixture and anti bumping granules to a flask
2. set up apparatus - never put a lid on top of condenser
3. reaction mixture is vaporised (bunsen burner allows reaction to be carried out at a fixed temp)
4. condenses when vapor meets the cool outer jacket and then it drips back into the flask

prevent large bubbles forming which could cause vigorous and uneven boiling

Question 3

Why is distillation used?

Answer 3

separates a liquid from a solution

Question 4

Describe the steps of distillation

Answer 4

1. set up apparatus and ensure water is flowing into the cooling jacket at the lowest point
2. flask is heated by a bunsen burner
3. liquid with lowest boiling point is vaporised first
4. vapour condenses and drips back into the collecting flask

Question 5

What piece of equipment is used to remove impurities from an organic product?

Answer 5

separating funnel

Question 6

How is the separating funnel used to remove impurities?

Answer 6

1. put distillate of impure product into the separating funnel
2. add water to identify the aqueous layer (will get larger)
3. open tap and run each layer into a separate container

Question 7

How can acid impurities be removed from an impure product?

Answer 7

• add aqueous**sodium carbonate **
• shake - invert flask and slowly open tap to prevent build up of carbon dioxide gas
• swirl until hydrated salt is finely dispersed (eg not lumpy)
• Decant organic liquid from solid hydrated salt

Question 8

How do you dry an organic product ?
Give examples of three drying agents

Answer 8

use a drying agent - anhydrous calcium chloride, calcium sulfate or magnesium sulfate
- swirl drying agent into liquid
- place stopper on flask and leave for 10 minutes
- continue adding drying agent until solid is dispersed finely (eg not a lump)
- decant liquid into another flask
REDISTILLATION - is boiling points are very similar, distil again

Question 9

Conditions for the alcohol to alkene route

Answer 9

concentrated sulfuric or phosphoric acid catalysts

Question 10

Conditions for the alcohol to aldehyde route
- what type of reaction is this?

Answer 10

Potassium dichromate solution
Heat gently and distil
- partial oxidation

Question 11

Conditions for alcohol to ketone route
- what type of reaction is this?

Answer 11

Potassium dichromate solution
Heat under reflux
- oxidation

Question 12

Conditions for aldehyde to carboxylic acid route

Answer 12

Potassium dichromate solution
Heat under reflux with excess oxidising agent
- oxidation

Question 13

conditions for alcohol to haloalkane
- what type of reaction is this?

Answer 13

concentrated sulfuric acid and sodium halide
heat under reflux
- nucleophillic substitution

Question 14

conditions for haloalkane to alcohol
- what type of reaction is this?

Answer 14

aqueous KOH
Heat under reflux
- nucleophillic substitution

Question 15

Conditions for alkane to haloalkane
- what type of reaction is this?

Answer 15

Br2 or Cl2 and UV light
- free radical substitution

Question 16

conditions for alkene to alkane
- what type of reaction is this?

Answer 16

hydrogen and nickel catalysts
- addition reaction

Question 17

conditions for alkene to haloalkane
- what type of reaction is this?

Answer 17

HBr or Hcl at room temp
- electrophillic addition

Question 18

conditions for alkene to poly(alkane)
- what type of reaction is this?

Answer 18

high pressure
catalyst
- polymerisation

Question 19

conditions for alkene to dihaloalkane
- what type of reaction is this?

Answer 19

Br2 or Cl2 and room temp
- electrophillic addition