What is the purpose of decolorizing carbon?
-to remove colored impurities from the sample
careful: too much would remove starting material
Steps for recrystallization
1) Dissolve crude crystals in minimum amount of hot solvent
2) Cool to room temperature
3) Ice bath to cool solution (15-20min)
4) Filter the crystals
How do you set up a reflux condenser?
Water in at bottom, water out at top (see drawing)
It allows the reaction to be carried out at the boiling point of the solvent.
Prevents loss of reagents
Why do we use a weak base for extraction?
Weak base is used bc carboxylic acid is a much stronger acid than phenol, the weak base selectively deprotonates carboxylic acid and leaves phenol
What does aqueous and organic layer mean?
Aqueous layer is water and the carboxylic acid
Organic layer has diethylether
What can you use to help dry the organic layer?
anhydrous magnesium sulfate
Why is brine used in extraction?
Brine is used to rinse the organic layer and pull out water
Why do you extract multiple times?
It is efficient
Why do you soak the cloves in water before beginning distillation?
This will allow the water to penetrate the cloves and should allow more eugenol to be isolated
What is iodine used for in the Grignard Rxn
Iodine catalyzes the reaction by cleaning Magnesium oxide?
What do you observe during the synthesis of a grignard?
1) Start with magnesium and bromophenol, yellow-orange
2) benzophenone – orange-> deep red -> pink
Why do you use a double equivalent of grignard in ester?
It can attack twice in an ester
Explain the purpose of hot gravity filtration. Why is it good to use the stemless funnel for this technique?
Hot gravity filtration is used to separate insoluble impurities from a hot solution
A stemless funnel is used because products could recrystallize in a long stem
what is lirgroin?
Ligroin is a flammable, nonpolar mixture of hydrocarbons that boils from 20C to 135C, obtained from petroleum by distillation and used as a solvent.
What are some important factors in choosing a solvent for recrystallization?
1) Solvent must completely dissolve both the desired compound and any other organic impurities when the solvent is hot (usually at BP)
2) The desired compound must be insoluble in chosen solvent at cold temperatures and the organic impurities must remain soluble when solution is cooled. If not, no purification will be achieved.
Why should you not stir crystals during recrystallization?
It makes the filtration less efficient and does not adequately remove the solvent from the crystals
Why are boiling chips used during distillation?
They prevent superheating of the liquid being distilled and they will cause a more controlled boil, eliminating the possibility that the liquid in the distillation flask will bump into the condenser
What solvent was selected for the recrystallization of acetophenetidin?
H2O with drops of 95% ethanol
How do you calculate percent yield?
(actual yield/theoretical yield) x100
Devise a simple experiment you could use to determine if the samples in the acetophenetidin experiment are identical.
Mix the cruse products and find the melting point. If the mp is low and the range is large, the two samples are different
How many moles of acetic anhydride are used in the acetophenetidin experiment if 1.8mL is used?
molecular weight: 102.09 g/mol
density: 1.08 g/mL
Consider the following solvent pairs when mixed: Which are immiscible/miscible? If the solvents are immiscible, which solvent would be in the top layer?
a) hexane and water
b) methylene chloride and water
c) ethanol and water
d) ether and water
a) Immiscible, hexane
b) Immiscible, water
d) Immiscible, water
In a good reflux, where should the vapor line be?
the vapor line should be between 1/4 and 1/2 of the way up the condenser
What do you do if you have cooled your solution completely to room temperature, but there are no crystals?
You will need to “scratch the flask”
-rub the end of your stirring rod on the inside wall of the beaker or flask at the air/solvent interface. This process scratches the glass and makes a sharp edge where crystal nucleation can occur
How do you calculate percent recovery?
(mass of recovered recrytallized product/mass of crude prodcut used in recrystallization) x100
How do you calculate atom economy?
(mass of desired product/mass of reagents) x100
What are the criteria for a successful liquid-liquid extraction?
1) The two solvents that are chosen for the extraction must be immiscible (for most extractions, one solvent is usually a nonpolar organic liquid and the other is polar-typically water or aqueous soltuion)
2) The compounds to be extracted must have different affinities for the two solvents (remember like dissolves like)
T/F: Weak bases will extract strong acids, and strong bases are needed to extract weak acids
What is something that you may observe while extracting oils from orange rind?
You may hear a hissing sound coming from the tube because CO2 vapor is escaping
What are the steps of extraction (flow chart)
1) Dissolve carboxylic acid and phenol in ether solvent
2) Use sodium bicarbonate (weak base) to create 2 layers (organic + aqueous), shake
3) Separate the aqueous solution from organic
1) Add 10% HCl to neutralize the aqueous solution until in proper range (pH ~2)
note: Add slowly or will foam over.
2) If precipitates: vacuum filtration
If no precipitation: back extract the compound into ether
1) rinse with brine, this will remove water
2) add anhydrous magnesium sulfate (drying agent)
3) gravity filter solution from the drying agent
Why is phenol much more acidic than cyclohexanol?
Phenol is aromatic and has 4 resonating structures, therefore it can easily release it’s H+
Cyclohexane is not aromatic and therefore is not stabilized by resonance structures
What mixture of carboxylic acid and phenol did we discover in our extraction lab?
A 50/50 mixture of p-toluic acid and ?-naphthol
What is used to extract the eugenol from water in the distillation experiment?
It will be in the lower layer
Describe the practical reasons behind the direction of the flow of water through the condenser
The direction of flow of water enters at the lower end of the condenser jacket. This is more efficient because the difference in temperature between cooling water and the substance being distilled is what drives heat exchange
Can IR spectroscopy be used to distinguish 2-pentanone from 2-hexanone
No, because IR is used to distinguish between functional groups. Both of these structures have the same functional group, so you will need to distinguish their hydrogens in HNMR
An unknown compound was determined to be 74.97% carbon, 8.39% hydrogen, and no nitrogen. Calculate the empirical formula
note: assume there is 100g in the entire compound and that the remaining percent is oxygen
T/F: Make sure to wash your glassware before performing the Grignard experiment.
False, any water in the reaction apparatus will cause the reaction to fail