Sauron - 26-3-2008 at 07:19
Preparation of AIBN Azobis(isobutyronitrile)
The virtues of this preparation are simplicity, absence of the use of NH3 and Cl2, and no need for acetone cyanohydrin.
Dissolve 24 g hydrazine sulfate (0.185 mol) in 175 ml warm water and
place it in a 500 ml Parr shaker bottle. Add 18 g NaCN (0.37 mol) in 50
ml water then 24.5 ml (19.3 g, 0.33 mol) acetone. Stopper the bottle and
mount it in a Parr 3911 or equivalent shaker with a Parr cooling jacket
for cooling water from a recirculating chiller at 20 C as the reaction is
exothermic. (Cooling can be discontinued once reaction subsides as
indicated by thermocouple.)The stopper is fitted with standard Parr T
valve leading to a 100 psi gage, the valve to the onboard gas cylinder is
however closed.
The bottle is shaken intermittently for two days. During that time a
crystalline deposit of Me2(CN)C-NH-NH-C(CN)-Me2 forms.
After 2 days the bottle is vented to hood and the solid separated from
the reaction mixture. It is recrystallized from ether or 95% ethanol.
The yield is 44 g mp 92-93 C.
The product is transferred to a 2 L flask, mixed with 25 ml ethanol and
acidified with dilute hydrochloric acid. The flask is cooled in an ice
bath and stirred vigorously while saturated bromine water (34 g
Br2/liter H2O) is slowly added until a yellow color becomes
permament. Crystalline solid is filtered off and the filtrate again
treated with Br2/water. Product is recrystallized from ether, yield 31.5
g, 71% (56% overall from acetone basis). mp 103-104 C.
Me2-C(CN)-N=N-(CN)C-Me2 (AIBN) 2,2'-azobis(isobutyronitrile)
AIBN is a highly useful free radical initiator for polymerizations and
chlorinations. It is regarded as far safer than dibenzoyl peroxide. It is
however toxic and classified as explosive which makes it difficult and
expensive to ship. Exercise appropriate caution when storing and
handling AIBN.
Dupont sells AIBN under the trademark VAZO and MSDS are
available from them, also Aldrich.
References
Thiele and Heuser, Ann. 290, pp22-23 from larger article pp 1-43.
Dox, JACS 47, 1471 (1925)
Overberger, O'Shaugnessey and Shalit, ibid. 71, 2661 (1949)
These are available in References or from me.
[Edited on 26-3-2008 by Sauron]
garage chemist - 26-3-2008 at 11:14
A very useful synthesis. I did not know how AIBN is made until now.
Is this the way it is done commercially too?
Where I live, we don't use Parr type equipment.
I assume the first step of the synthesis can be done by stirring the reaction mix in a flask in a cold water bath for the time of two days?
vulture - 26-3-2008 at 15:03
I was also puzzled by the Parr aparatus. Why is there a valve on the setup? Is it to keep the thing under its own pressure or something?
Sauron - 27-3-2008 at 06:06
I'll be appending this as time goes by, adding the alternative route from acetone cyanohidrin, and the preps of that material, for comparison and
completeness.
Eventually the AIBN will be employed to polymerize 4-vinylpyridine crosslinked 2% with divinylbenzene and isolated as resin beads. This resin is for
use as solid support for pyridinium chlorochromate - the pyridine being built into the resin.
This resin is fully recyclable and rechargable without loss of activity, it is simple to use, and easy to regenerate, and solves a lot of practical
problems associated with unsupported PCC. PCC is a highly efficient oxidizer for conversion of primary alcohols to aldehydes and secondary alcohols to
ketones.
I will address any questions or comments by PM, or email. Feel free to contact me.
Sauron - 28-3-2008 at 03:10
The following is cortesy of garage chemist. It is the original preparation of hydrazibisisobutyronitrile, the immediate precursor to AIBN, by Thiele
and Heuser. The scale is 1 molar based on hydrazine sulfate, or about 6X that of the preparation described above.
"Translation of the Hydrazoisobutyronitrile synthesis in Saurons article:
130g hydrazine sulfate are dissolved in just the necessary amount of warm water and mixed with a concentrated aqueous solution of 130g KCN (2 mol) and
with 116g acetone (2 mol). The mixture is vigorously shaken.
In order to prevent excessive evaporation of HCN and acetone from the mixture due to the exotherm, the operation is done in a round-bottm flask with
attached reflux condenser.
After some time, the liquid becomes turbid and an oil layer deposits on its surface.
Now the mixture is intensively stirred with a turbine, and during the slow cooling a large amount of white glistening leaflets deposit which
eventually fill the entire liquid.
After standing for 12 hours, the precipitate is filtered with suction and washed with water.
The nitrile thus obtained is already pure.
Because a significant loss of HCN cannot be prevented in the synthesis, the filtrate, which is kept separate from the washing waters, is mixed again
with 1 mol acetone, 1 mol KCN and an amount of acid equivalent to the KCN. Upon standing, a good amount of nitrile again separates and the yield is
now the theoretical one in regard to the used hydrazine sulfate.
For analysis, the nitrile is recrystallized from ether, from which it separates in thick, often centimeter-large, glassy glistening crystals that melt
at 92-93°C.
Apparently monoclinic crystals with fissibility (don't know a better translation for Spaltbarkeit) like gypsum.
Easily soluble in alcohol and ether, less in ligroin, insoluble in water and alkalies, soluble in dilute acids.
Upon warming with water, HCN is given off."
Some comments:
1. Note absence of cooling which likely accounts for the noted loss of HCN through reflux condenser. The subsequent preparations based on this one all
advise cooling the reaction mixture and it is clear from the closely related preps of acetone cyanohydrin that the regulation of the temperature
between 0 and 15 C is not an accident in relation to the boiling point of HCN. This, along with the smaller scale, probably explains why later
workers did not feel obliged to work over the filtrate. Dox, and later Overberger et al, obtained 80% yields without working up the filtrate. On the
scales at which they operated it probably would not have been particularly productive to do so.
A Dewar type condenser would likely also minimize HCN loses. But cooling is IMO still advisible, since the product loses HCN on warming in water.
2. Efficient stirring can probably replace shaking throughout this procedure. In this case no Parr apparatis is required.