Impure benzoic acid Benzoic acid after...
Transcript of Impure benzoic acid Benzoic acid after...
Recrystallization
Impure benzoicacid
Benzoic acid afterrecrystallization
C-OH
O
Benzoic Acid
m.p. = 121 - 122o
Purification of Organic Compounds
Solids: Recrystallization
Liquids: Distillation
Solids and Liquids:
Gas or liquid chromotography
Types of impuritiesSoluble
Insoluble
Partly Soluble
Solubility of benzoic acid in water
Dissolve sample in hot solvent
Compound crystallizes upon cooling
Impure benzoic acid in hot water
Add water and heat until allsoluble material dissolves
Insoluble material is removed by filtration
The hot solution is filtered toremove insoluble impurities
Use fluted filter paper tomaximize surface area.
To avoidcrystallizationin the funnel:
Use GLASS funnel.Put flask on hot plate.
Boil off excess solvent
Boiling Sticks
Hot solutionafter filtration:
Cool Seed Scratch
Crystals form in the warm solution
Next:
Cool, filter, wash, dry, weigh, mp
Buchner funnel..
Filter flask
Heavy-walledtubing
Vacuum
Put filter paper in Buchner funnel..
Filter and wash with cold solvent
Insoluble impurities
Solubleimpurities
Purifiedbenzoic acid
Solubility Example
Compound Solubility g/100 mL
25o 100o
A
I1
I2
1.0
1.5
0.0
80
50
0.0
CompoundSolubility g/100 mL
25o 100o
A
I1
I2
1.0
1.5
0.0
80
50
0.0
A = 10 g I1 = 1.0 g I2 = 1.0 g Total = 12.0 g
100 mL water at 1000
A
I1
I2
dissolves
dissolves
insoluble
CompoundSolubility g/100 mL
25o 100o
A
I1
I2
1.0
1.5
0.0
80
50
0.0
A = 10 g I1 = 1.0 g I2 = 1.0 g Total = 12.0 g
100 mL water at 1000
A dissolves
I1 dissolves
I2 insoluble
Cool to 25o
A
I1
9.0 g crystallize
0 g crystallize
Yield = 100 * 9.0/12.0 = 75%
CompoundSolubility g/100 mL
25o 100o
A
I1
I2
1.0
1.5
0.0
80
50
0.0
A = 10 g I1 = 1.0 g I2 = 1.0 g Total = 12.0 g
50 ml of water at 1000
A
I1
I2
dissolves
dissolves
insoluble
CompoundSolubility g/100 mL
25o 100o
A
I1
I2
1.0
1.5
0.0
80
50
0.0
A = 10 g I1 = 1.0 g I2 = 1.0 g Total = 12.0 g
50 mL water at 1000
A dissolves
I1 dissolves
I2 insoluble
Cool to 25o
A
I1
9.5 g crystallize
0.25 g crystallize
Yield = 100 * 9.75/12.0 = 81%
NOT PURE!
What volume of solvent is needed togive the maximum yield of pure A?
Solubility of I1 = 1.5 g/100 mL
1.5 g100 mL = 1.0 g
x mL
X = (100 mL * 1.0 g)/1.5 g = 67 mL
What is the yield of pure A from 67 mLsolvent?
Solubility of A = 1.0 g/100 mL
1.0 g100 mL = X g
67 mL
X = (67 mL x 1.0 g) / 100 mL = 0.67 g
Yield = 10.0 g - 0.67 g = 9.33 g
% yield = 100 * 9.33 / 12 = 78%