Subj: Cinnamic acid & beta-bromo-styrene FAQ
From: ncoffey@teleport.com (Nick Coffey)


Cinnamic Acid (The Perkin Reaction)
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In a dry 500 ml flask place 12g of freshly fused and pulverized potassium 
acetate.  This is prepared by melting ordinary potassium acetate in a 
porcelain dish and heating gently, with occasional stirring, until no 
more water vapor is evolved and the salt is completely fluid.  After 
cooling, the solid mass is ground quickly in a mortar and transferred to 
a tightly corked bottle until needed.  To the potassium acetate add 30 g. 
(28 ml.) of acetic anhydride and 21 g. (20 ml.) of freshly distilled 
benzaldehyde (obtained from extraction of bear claws or oxidation of 
toluene).  Mix the materials thoroughly and provide the flask with an 
air-cooled reflux condenser about 60 cm. in length and 10 mm. in 
diameter.  Heat the reaction mixture in an oil bath at 155-160 degrees 
for one hour and then increase the temperature of the bath to 160-170 
degrees for three to three and one-half hours.

If the heating is interrupted the reaction mixture should be protected 
from atmospheric moisture by means of a calcium chloride tube.

While the reaction mixture is still hot, pour the contents of the flask 
into a 5L round-bottom flask and rinse the reaction flask with two 
200-ml. portions of boiling water.  Add 600-700 ml of water and steam 
distill the mixture until all the unchanged benzaldehyde has been 
removed.  The distillate may be discarded.

Add enough water to the contents of the flask to bring the volume to 
about 1.2 L and heat to boiling.  Cool slightly, add 4 g. of decolorizing 
charcoal (Norit), and boil the solution gently for five to ten minutes.  
Filter the hot solution rapidly through a fluted filter.   Heat the 
filtrate to the boiling point, add 12-14 ml. of concentrated hydrochloric 
acid and cool the solution with stirring.  After the cinnamic acid has 
crystallized completely, filter with suction and wash the crystals with 
several small portions of cold water.  Allow the acid to dry completely 
before taking the melting-point. If the cinnamic acid is not sufficiently 
pure it should be recrystallized from hot water.  The yield is 12-15 g.

Beta-Bromostyrene
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Dissolve 30 g. of dry cinnamic acid in 200 ml of hot carbon tetrachloride 
in a 1 L round-bottom flask and cool rapidly to obtain a fine suspension 
of crystals.  Provide the flask with a calcium chloride tube and a small 
separatory funnel (with a good stopcock).  In the separatory funnel place 
a solution of 38 g. (12 ml) of bromine  in 50 ml. of carbon tetrachloride 
and allow this to drop in slowly, at room temperature, while flask is 
being vigorously shaken.  It is advisable to carry out the addition of 
bromine in the presence of sunlight, or in the vicinity of a powerful 
electric light.  After all the bromine has been added, allow the mixture 
to stand for fifteen minutes.  Cool in an ice bath and filter the 
phenyl-a,b-dibromopropionic acid with suction.  Wash the precipitate with 
50-60 ml. of cold carbon tetrachloride.  This crude product, weighing 
50-60 g., is used directly for the next step.

Place the crude dibromo acid in a 2 L round-bottom flask and add 240 ml. 
of 95% ethanol (Everclear will do nicely) and a solution of 60 g of 
potassium acetate in 150 ml. of water.  Shake the mixture thoroughly, 
adjust a reflux condenser, and heat to gentle boiling (preferably on a 
steam bath).  Shake the mixture occasionally, and continue to reflux 
gently for four hours.  The product, bromostyrene, separates as a heavy 
oil upon cooling.  Dilute with water to about 1 L total volume, separate 
the heavy oil, and extract the upper aqueous liquid with two 50-ml. 
portions of carbon tetrachloride.  Combine the oily layer and the carbon 
tetrachloride extracts and wash with saturated sodium bicarbonate 
solution until all acid has been removed.  Wash once with water, dry over 
8-9 g. of anhydrous calcium chloride, and distill off the carbon 
tetrachloride.  Distill the residual bromostyrene under reduced pressure, 
bp 108°C at 20 mmHg, 116-117°C at 35 mmHg. The yield is 22-24 g.