#1: Experiment Grignard Synthesis of 2Methyl2Hexanol
ObjecAves:
To synthesize a 3o alcohol from an alkyl halide and a ketone
using a Grignard reacAon.
To purify product using a liquid extracAon method and a
disAllaAon method
Before coming to lab
Review the following techniques:
ExtracAon
Drying organic solvents with K2CO3
DisAllaAon
You will be expected to perform these will
liPle review, as you learned these techniques
in the rst semester lab.
CHEMICAL EQUATION
MAKING THE GRIGNARD REAGENT
Organic halides react with magnesium metal in ether to yield an
organomagnesium halide: RMgX
ETHER
RX + Mg > RMgX
Where R= 1o, 2o, or 3o alkyl, aryl or alkenyl
X= Cl, Br, I
The CMg bond is a highly polar covalent bond. The carbon atom
is both nucleophilic and basic making it very reacAve with a wide
variety of E+.
WHEN THE GRIGNARD REAGENT MEETS
WATER
Since the carbon atom of a Grignard reagent is so nucleophilic
and basic, it reacts with proton donors (Brnsted acids) such as
H2O, ROH, RCOOH, RNH2 to yield hydrocarbons.
This makes it extremely important to keep the reacAon ask and
solvent completely dry of water.
MECHANISM
EXPERIMENTAL PROCEDURE
(Synthesis of Grignard reagent)
Place Mg turnings and iodine in 100mL ask
Clamp ask to ring stand and set up remainder of
reux with addiAon apparatus.
Start reacAon with a small amount of n
butylbromide
Once the reacAon starts, add ether to dilute
Add remaining nbutylbromide and ether to sep
funnel.
Add to reacAon mixture dropwise once reacAon
starts
EXPERIMENTAL PROCEDURE
(Synthesis of alcohol product)
Add acetone/ether to sep funnel.
Add to reacAon mixture dropwise.
Cool reacAon ask in ice water bath.
Add ice and NH4Cl 1:1 to a beaker
Transfer reacAon mixture, warmed to
room temperature to beaker.
EXPERIMENTAL PROCEDURE
(PuricaRon)
Set up an extracAon apparatus.
Transfer the liquid from the beaker to the funnel.
Extract aqueous layer with ether
Wash with water, NaHCO3, and then water.
Transfer organic layer to a 50 mL ask and dry over
K2CO3.
Transfer dried organic liquid to a beaker.
Setup disAllaAon apparatus and collect product at
132C145C
Notes on ExtracAon
Which phase is H2O?
It depends on the
organic solvent.
If you know the organic
solvent, how do you know
which phase is H2O?
The denser solvent is on
the bottom.
DistribuAon Coecient (K)
When a compound is distributed an between organic
solvent and water, the raAo of the solute concentraAon in
both phases can be expressed as:
Any compound with K > 1.5 can be separated from water
by extracAon with an insoluble organic solvent.
If the compound is impure:
inorganic impuriAes remain in the water layer;
organic impurites will also migrate to the organic layer.
Phase Interface
Emulsions
Occasionally an emulsion
forms between the two
layers.
It appears as a 3rd milky layer
between organic and aqueous
phases.
Emulsions dont appear
during diethyl ether
extracAons but are common
for chlorinated solvents.
VenAng
Work in a hood while performing an extracAon
VenAng releases gases that may otherwise build up and
pop out the stopper.
Shake the two phases, invert the separatory funnel, point
the funnel toward the back of the hood and open the
stopcock.
Aqueous SoluAons
These aqueous soluAons are someAmes used instead of
pure H2O during extracAon
1. Aqueous acid (HCl, NH4+) removes organic bases;
2. Aqueous base (NaOH, NaHCO3, Na2CO3) removes organic
acids;
3. Saturated NaCl (aq) (or brine) is used when the solute is
slightly watersoluble. K generally increases going from
water to brine.
Removing Bases
SeparaAng these two
compounds is simple
because one is neutral and
the other basic.
Ionic compounds always go
to the aqueous layer.
Removing Acids
SeparaAng these two
compounds is simple
because one is neutral
and the other acidic.
Removing Acids
Be very careful venAng
extracAons in which NaHCO3
(aq) or Na2CO3 (aq) are used
to remove acids.
Both form CO2 (g) with acids
that can pop o the stopper.
Amer adding NaHCO3 (aq),
swirl once, then vent.
SalAng Out
For extracAons using brine and an organic solvent:
Organic solutes become less soluble in the aqueous phase.
Water becomes less soluble in the organic layer.
Both of these are good from a chemists perspecAve.
Some Advice
Clearly label all beakers or asks that hold your extracAon layers.
Never throw any extracAon layer away unAl you are certain it
doesnt have your product!
Amer you open the stopcock, liquid wont drain from the
separatory funnel unless the stopper is removed.
DisAllaAon
process of heaAng a liquid unAl it
boils, capturing and cooling the
resultant hot vapors, and
collecAng the condensed vapors
idenAcaAon and the puricaAon
of organic compounds
The amount of each liquid in the
disAllaAon ask is unimportant.
DisAllaAon Setup
Thermometer Setup
Too high
Too low