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Preparation of acetic anhydride and acetyl chloride 
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Acetyl Chloride
===============

Connect a dry 250 ml three neck flask with a distillation adapter,
condenser and addition funnel.  Use a 250 ml rb flask for the receiver
connected to the condenser with a vacuum adapter.  Use the vacuum adapter
to make a gas trap with rubber tubing to an anhydrous CaCl2 drying tube
exiting to an inverted funnel suspended over a beaker of water.  This
important stage is to protect the distillate from water while absorbing HCl
evolved in the reaction.

Place 54 g. (52 ml.) of glacial acetic acid in the three neck flask, close
with a stopper  and add slowly through the addition funnel 46 g. (29 ml.)
of phosphorus trichloride. Cool the flask by immersion in a water bath. Mix
the reactants thorougly and, after allowing the mixture to stand for ten
minutes, heat the water bath to 40-50? and maintain it at this temperature
for thirty minutes, with occasional swirling of the flask. During the
heating the liquid usually separates into two layers. Acetyl chloride forms
the upper layer.

Distill the acetyl chloride by heating the water bath to boiling and
maintaining it at that temperature as long as any liquid passes over. Cool
the receiver in an ice bath during the distillation. The syrupy residue in
the distilling flask is phosphorous acid, which is discarded.

--> CAUTION: The reaction mixture must not be overheated since this will
lead to formation of phosphine, which is spontaneously flammable in contact
with air.

To the distillate add two drops of glacial acetic acid, to destroy mixed
phosphorous-acetic anhydrides that would cause turbidity to develop on
standing. Redistill the acetyl chloride from a distillation apparatus
arranged as before  except without the addition funnel and with a
thermometer. Collect separately in a dry receiver the portion boiling at
50-56? and transfer it to a dry weighed glass-stoppered bottle. Acetyl
chloride attacks corks and rubber stoppers. The yield is 44-56 g.

Acetic Anhydride
================

The apparatus for this process is similar to that used for the preparation
of acetyl chloride. The same precautions for exclusion of moisture must be
observed but it is unnecessary to provide the inverted funnel arrangement,
since hydrogen chloride is not evolved.

In a 250ml. rb flask fitted as for making acetyl chloride, place 60 g. of
finely pulverized anhydrous sodium acetate.*  Arrange in place the
condenser, dry receiving flask and drying tube; the receiver need not be
cooled. Check to insure that all connections are tight. Cool the reaction
flask in a bath of cold water and add dropwise, through the addition
funnel, 40 g. (36 ml.) of acetyl chloride.

After the addition has been completed, remove the water bath and shake the
flask to obtain good mixing of the reactants. Recheck the connections for
tightness.

Dry the outside of the flask with a towel and heat it with a mantle or oil
bath. Continue the heating until no more distillate comes over but do not
overheat the solid residue.

To the distillate add 4-6 g. of finely powdered anhydrous sodium acetate,
to react with a small amount of acetyl chloride that may be present.  Add a
boiling chip and redistill the crude acetic anhydride.  Collect the product
distilling at 132-138? in a dry flask.  The yield is 30-40 g.

* NB: Commercial anhydrous sodium acetate usually contains some moisture.
      To remove moisture fuse 70-80 g. in a casserole and stir until no
      more water is evolved.  Do not overheat!  Cool and quickly pulverize.
      Store in a tightly sealed container before use.


Acetic Anhydride and Propionic Anhydride
========================================

Here's what everyone's looking for. Some things are a little wierd about
it, like the fact in the acetic anhydride synth they use a small quantity
of acetic anhydride as a solvent. However, as one sees in propionic
anhydride, such a solvent may not be necessary.

From "Chemistry & Industry", 1945, p. 382; "LABORATORY METHOD FOR THE
PREPARATION OF ORGANIC ACID ANHYDRIDES" by Jehuda Orshansky and Eliahu
Bograchov.

"...(1) Acetic anhydride. To 50 g. acetic anhydride in a round-bottomed
flask of 1500 cc. capacity, placed in cold water, 440 g. of powdered sodium
acetate (dried by fusion at 320 C) and at the same time a solution of 22. g
of sulfur in 320 g. bromine is added while stirring. The operation takes
about 30 minutes. 

"The mixture is then stirred for a further 5 minutes, after which period
the initially dark brownish-red colour has changed into pale yellow, and
the anhydride is distilled off from a water bath under reduced pressure.
The crude anhydrie (310 g) is redistilled under normal pressure, and the
fractionboiling between 134-138 C is collected. Yield, 295 g. of 98%
pureity = 87.5%. The so purified anhydride contains neither bromine nor
sulphur compounds and leaves no residue on evaporation..." 

"(2) Propionic anhydride. To 40 g. fused and powdered sodium propionate in
a flask of 250 cc. capacity a solution of 2 g. sulphur in 22 g. bromine was
added while stirring. The temperature was kept at about 50 C. When the
operation was completed, the anhydride was distilled off in vacuo. The
crude product (25g.) was fractioned under normal pressure, and the fraction
155-156 C was collected. Yield, 23 g. propionic anhdride of 90% purity =
85%..." 

The paper mentions that other alkali metals and alkali earth metals work
just fine. Calcium propionate is a food preservative added to cheap white
bread to keep it from molding. With these nuggets of information, the most
closely watched reagent on the DEA's watched list, propionic anhydride,
just turned OTC. I can almost see the fentanyl analogs clogging the opioid
market already. 

The one reason, and justafiably so, they poo-poo using chlorine (which
does indeed work nicely) is that its a hassle to work with, especially
considering the fact that they'd be adding a gas to a solid to make a
liquid. I propose that perhaps with the use of chloroform as a solvent,
chlorine could be bubbled in readily, and the reaction would go as
previously stated. I assume they tried to avoid using extra solvents in
hopes of staying away from azeotropes messing up their products' purity,
so this may or may not work, depending on what you're trying to do.

- drone #342

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Iudexk:
    
To 66.5g fused AcONa (made from AcOH + NaOH) was added a soln. of 3.3g S in 
48.4g Br2 over 5mins, under manual stirring. Brown colour disappears rapidly on 
stirring to give slightly off-white mixture. Stirring continued for another 15mins. 
Mixture has v. strange consistancy; becomes almost liquid while stirring but as 
soon as one stops stirring it becomes solid again. Thus formed sludge was scooped 
up and dumped in a distillation flask (spilling much in the process - do this rxn 
in the same flask you're gonna distil from), and distilled. 

Yield of Ac2O=29.2g as a clear pungent liquid.

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