Experiment #7
Esterification,
Grignard synthesis
The GRlGNARD Reactiop
Victor Grignard
born 1871
Reaction discovered
1898
Nobel Prize awarded
1912
Grignard Reaction
d
8
Real challenge is to prepare the reagent;
to get the reaction started!
Tricks that may start a reluctant Grignard:
1.
"Purest" trick is to crush some Mg;
this pxposes fresh surface
reactive Mg
.
2.
Most common trick: add a few crystals of
Mgi2 is ether soluble
.
cleans off the metal surface
Added bonus with 12 :
Mg12
+
H20
+
Mg12 .H20
-
Mg12 H20- is ether insoluble
water "precipitates" out
12
Other tricks:
3.
Add CH3l
verv reactive halide
* (alkyl
>> aryl
cleans surface, exposes fresh Mg
ether soluble
4.
and I >> Br >> CI)
Add BrCH2CH2Br
also a very reactive halide
BrCH2CH2Br
+
Mg
-t
and CH2=CH2 is a gas!
CH2=CH2
+
MgBr2
Is the reaction really startea ???
How do you tell ??
1. Reaction,mixture turns cloudy
2. Iodine color disappears
Exothermic reaction
spontaneous and sustained reflux
without external heating
add a few additional drops of the halide:
boiling/reflux should become
more vigorous
If you pdd all the bromobenzene
before the reaction has started
What will happen ??
1. a possible violent reaction
2. low (or NO) yield of product
3. 0120 technique grade
-----
Mondayrruesday Next Week
Make-up Labs
all experiments through #7 (Grignard)
must be completed
Hour Exam II
Tuesday at 12 noon
Carbonyl Chemistry (#5)
Diels-AlderIHydrogenation (#6)
NO SPECTROSCOPY