Newsgroups: alt.drugs.chemistry
From: [an 263690] at [anon.penet.fi] (DM3)
Date: Sat,  2 Dec 1995 23:46:06 UTC
Subject: Synthesis of Nitroethane


From Kornblum and Ungande, Organic Syntheses, v.38, p.75, 1958 we take the
synthesis of silver nitrite as our initial step.

Under yellow photograhic light prepare a solution of 76 g (1.1 mol) of sodium
nitrite in 250 ml water in a 1 L flask. Prepare a solution of 169.9 g of
silver nitrate (1 mol) in 500 mL water. Slowly add the silver salt solution
to the sodium nitrite solution with vigorous stirring. After addition is
complete, cease stirring and allow the mixture to stand in the dark for 1
hour. A yellow precipitate will form. This is filtered with suction,
collected, suspended in 250 ml fresh water, and filtered again. Repeat this
washing again, collecting the solid after filtering. Dry the product to
constant weight in a vacuum dessicator over KOH pellets. [Note: This means to
place the pellets in the bottom of the dessicator, preferably in a glass
dish. The ceramic stand on which the sample is supported is put in place and
the product, spread thinly on a glass plate, is placed on the support. It
does *not* mean to pour the product over KOH pellets. Vacuum is maintained on
the desiccator during the drying period. Drying to constant weight means that
you weigh the product, dry longer, weigh again, dry longer, weigh again, and
so on until two consecutive weights agree closely; i.e., in the last decimal
place to which your balance will weigh.] The drying may be hastened by
washing the product once with methanol after the two water washings. Should
yield about 134 g (87%). Store in a brown glass bottle and place in a dark
storage area until ready to use.

Kornblum, et al, in J. Amer. Chem. Soc. 78, 1497, 1956 showed that alkali
nitrites, especially sodium nitrite, can be used in the preparation of nitro
compounds if DMF was used as the solvent. Thus, if DMF is available, the
silver nitrite synthesis may be omitted. Use 1-iodoethane dissolved in DMF
and add excess sodium nitrite in DMF with vigorous stirring at 0 C. Stir for
2.5 hours until reaction is complete. If 1-bromoethane is used, stir for 6
hours. Yields 60%.

Using the silver nitrite method, cool 100 g of silver nitrite (0.65 mol) in
150 ml of dry ether to 0 C in a 3 neck 500 ml flask(again in a darkened room
or using yellow light). Drop in 1-iodoethane (or 1-bromoethane) over a 2 hour
period while stirring constantly and maintaining 0 C and dark conditions.
Note that 0.65 mol of the silver salt is used so 0.50 mol of the halo-ethane
should be used.  Stir for 24 hours at 0 C, then 36+/-12 hours at room
temperature. [Note: If the bromo is used, stirring for 48+/-12 hours at room
temperature is necessary] Use the Beilstein test for halogens. The reaction
is complete when no halogen is detected. [Drop a few drops of the reactant
solution into a test tube containing an alcoholic solution of silver nitrate
and note if a precipitate occurs. If so, the reaction is not complete. The
Beilstein test uses a small coil of copper wire in a test tube. A small
portion of the reactant solution is added and it is noted if reaction occurs.
Silver will replace the copper. The first test is quicker and easier to
perform] Silver iodide (or bromide) will precipitate over this time. Filter
off the silver salt, washing with several portions of ether. Evaporate (and
recover if possible) the ether at room temperature. [This may be replaced
with distillation of the ether, using a water bath, at atmospheric pressure.
A 2x45 cm column packed with 4 mm pyrex helices is used. The residue is
distilled at 5 mm. A more efficient column is not used due to the instability
of the nitrite of ethane. Maintain anhydrous conditions since the nitrite
ester will hydrolze to the alcohol and will be difficult to separate.] Then
distill the product at 5 mm. The nitrite of ethane will be the initial
fraction, followed by an intermediate fraction, then the nitroethane will
boil over. Produces about 83%.

An alternate method is to boil ethane with nitric acid, but I have no details
for this and it sounds as if it would be extremely dangerous.

This synthesis (the silver nitrite one) is general for 1-halo-n-alkanes
(straight chain alkanes). Thus nitromethane, nitropropane, etc. may be
produced using this technique. The times required for reaction are also
general to the synthesis so no modifications in reaction times are necessary.
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