Org. Synth. 1961, 41, 67
DOI: 10.15227/orgsyn.041.0067
2-NITROETHANOL
[Ethanol, 2-nitro-]
Submitted by Wayland E. Noland
1
Checked by Melvin S. Newman and Surjan S. Rawalay.
1. Procedure
In a 5-l., three-necked, round-bottomed flask fitted with a 30-ml. dropping funnel, mechanical stirrer, and thermometer extending down into the liquid is placed a suspension of paraformaldehyde (trioxymethylene, 125 g., 4.16 moles) in freshly distilled (Note 1) nitromethane (2.5 l., 46.6 moles). The suspension is stirred vigorously, and 3N methanolic potassium hydroxide solution is added dropwise from the dropping funnel until, at an apparent pH of 6–8, but closer to pH 8 (pH paper), the paraformaldehyde begins to dissolve and the suspension assumes a clearer appearance. About 10 ml. of the alkaline solution is required, and the addition takes about 10 minutes. About 15–20 minutes after addition of the alkaline solution is complete, the paraformaldehyde dissolves completely. Shortly thereafter, the solution temperature reaches a maximum of 13–14 degrees above room temperature and then slowly drops. Stirring is continued 1 hour after addition of the alkaline solution is complete.
Stirring is continued while the added alkali is completely neutralized by adding concentrated (36N) sulfuric acid (1 ml.) dropwise from a medicine dropper over a period of about 3 minutes until an apparent pH of about 4 is reached (Note 2). The solution is then stirred for an hour, during which time the pH should not change (Note 3).
The precipitated potassium sulfate is filtered by passing the solution through a 12-cm. Büchner funnel. The light-yellow or yellowish green filtrate is transferred to a 5-l., one-necked, round-bottomed flask fitted with a Claisen head containing a capillary ebulliator tube and a thermometer, and connected to a water-cooled condenser. The condenser is connected through a vacuum adapter to a 3-l., one-necked, round-bottomed flask, cooled in ice, to act as a receiver. About 2.3 l. of pure, unchanged nitromethane is removed by distillation at aspirator pressure and a water-bath temperature of 40–50°. The distillation takes about 6–7 hours.
The golden-yellow residue (315–365 g.) is transferred to a 1-l., one-necked, round-bottomed flask containing an equal weight of diphenyl ether (Note 4). The flask is fitted with a Claisen head containing a capillary ebulliator tube and a thermometer, and connected to a water-cooled condenser. The condenser is connected to a 3- or 4-port fraction cutter fitted with 100–500 ml., one-necked, round-bottomed flasks, at least one of which is 500 ml. or larger to accommodate the main fraction (Note 5). The mixture is distilled under the vacuum of a good pump. The fore-run, b.p. 29–33° at about 0.10 mm., consisting of nitromethane (about 56 ml.), can be distilled at a water-bath temperature of 32–79° and usually passes directly into the Dry Ice trap protecting the vacuum pump. The temperature then rises as 2-nitroethanol and diphenyl ether codistil. The main fraction, a two-phase distillate initially richer in 2-nitroethanol than diphenyl ether, gradually changes in composition until the proportion of 2-nitroethanol becomes negligible. The main fraction of 410–425 g., b.p. 54–57° at about 0.10 mm. (or 64–66° at about 0.4 mm.), collects at a water-bath temperature of 79–88°. Care should be taken to prevent clogging of the condenser or fraction cutter with solid diphenyl ether (m.p. 27°). The distillation is continued until the proportion of 2-nitroethanol (lower layer) observed in the distillate becomes negligible, and the temperature suddenly starts to rise. At this point heating is stopped, but the residue is cooled to room temperature or below before the vacuum is broken (Note 6).
The two-phase main fraction of the distillate is placed in a 500-ml. separatory funnel and the lower layer of crude 2-nitroethanol (185–200 g., 146–158 ml., n25D 1.4493–1.4513, containing about 92–94 mole % 2-nitroethanol) is drawn off. The 2-nitroethanol is then extracted in a 500-ml. separatory funnel with an equal volume of light petroleum ether (b.p. 60–68°, such as Skellysolve B) or hexane, and the colorless lower layer of 2-nitroethanol (174–188 g., 46–49%, n25D 1.4432–1.4433, containing about 98 mole % 2-nitroethanol) is drawn off (Note 7) and (Note 8). The product turns light yellow after standing for a day or more.
2. Notes
1.
Commercial nitromethane is sometimes quite acidic, and much more methanolic
potassium hydroxide is required to initiate the reaction when such material is used. For safety, the
nitromethane should be distilled at aspirator pressure instead of atmospheric pressure.
2.
Sulfuric acid must be used in an amount slightly
more than enough exactly to neutralize the alkali, and not just sufficient to make the reaction acidic. Otherwise, the metal salts of
nitromethane can form explosive fulminates upon heating.
3.
This is a suitable point at which to interrupt the experiment overnight.
4.
2-Nitroethanol prepared by the formaldehyde-nitromethane method should not be distilled without use of
diphenyl ether as a heat-dispersing agent. The residue, consisting of di- and tri-condensation products of
formaldehyde with
nitromethane, when hot and concentrated, and particularly when the vacuum is broken and air is let in on the hot distillation residue, is very likely to undergo a flash detonation, or at least a fume-off which may proceed with explosive violence. Use of
diphenyl ether is a wise safety precaution in the distillation of
2-nitroethanol made by other methods as well.
5.
If a fraction cutter is not used, the residue should be cooled to room temperature each time before the vacuum is broken.
6.
The large amount of
diphenyl ether (80–125 g.) left as the upper layer in the distilling flask has served the useful purpose, by its mass and volatility, of preventing superheating of the residue and subsequent violent decomposition, as described in
(Note 4).
7.
This procedure has been carried out 30 times by students in the advanced organic laboratory course at the University of Minnesota. The extreme ranges of yields obtained were
32–52%, and the median yield was
46%.
8.
The
2-nitroethanol obtained by this procedure is quite satisfactory for synthetic purposes, such as the preparation of
nitroethylene. The small amount of light
petroleum ether dissolved in the
2-nitroethanol can easily be removed under reduced pressure. Most of the remaining
diphenyl ether can be removed by one redistillation under vacuum, since the fore-run is relatively rich in
diphenyl ether. The main fraction has
n25D 1.4425–1.4431. Although vacuum redistillation of
2-nitroethanol which has been freed by the present procedure from higher condensation products of
formaldehyde with
nitromethane is relatively safe, it is recommended that the procedure be carried out behind a safety shield or a barricade.
3. Discussion
The present procedure is that of Controulis, Rebstock, and Crooks,
2 modified to include the
diphenyl ether purification method of Roy.
3 2-Nitroethanol has been prepared by condensation of
formaldehyde (usually employed in the solid form as
paraformaldehyde) with a large excess of
nitromethane in the presence of an alkali catalyst,
2,4,5,6 as illustrated by the present procedure, or in the presence of a strongly basic ion-exchange resin.
7 Dimethoxymethane has also served as a source of
formaldehyde in a reaction catalyzed by a mixture of acidic and basic ion-exchange resins.
8 2-Nitroethanol has also been prepared by the action of
silver nitrite on
2-iodoethanol (
ethylene iodohydrin);
9,10,11,12 by selective catalytic hydrogenation over
5% palladium on
barium sulfate in
pyridine solution of halogenated derivatives, including
2-chloro-2-nitroethanol,
2,2-dichloro-2-nitroethanol, and
2-bromo-2-nitroethanol;
13 by the action of fuming
nitric acid on
ethylene;
14 and by the action of
dinitrogen tetroxide on
ethylene in the presence of
oxygen15,16,17,18,19 or
nitric oxide,
20 or in
carbon tetrachloride solution.
21 The preparation of
2-nitroethanol from
ethylene oxide by the action of aqueous solutions of
barium,
22 calcium,
22 magnesium,
23 or
zinc22 nitrite, or by the action of
sodium nitrite and
carbon dioxide,
24 has also been reported. The submitter has been unable to prepare
2-nitroethanol from
ethylene oxide using the procedures described for
barium6 or
sodium nitrite; his observation with respect to
barium nitrite has been confirmed in another laboratory.
25 More recently, the preparation of
2-nitroethanol in
50% yield has been reported by adding
ethylene oxide to aqueous
sodium nitrite at 20° under
nitrogen in the presence of a nitrite scavenger, such as
sodium hydrosulfite or
phloroglucinol, at a pH of 7.1–7.3 controlled by the addition of
phosphoric acid.
26 The action of dinitrogen tetroxide on
ethylene oxide in
chloroform solution has been reported to yield
2-nitroethyl nitrate, from which
2-nitroethanol could be obtained by alkaline saponification.
27 This report has since been refuted with the finding that the initial product is the
mononitrite mononitrate ester of ethylene glycol, which saponifies to
ethylene glycol mononitrate and
diethylene glycol mononitrate.
284. Merits of Preparation
The present procedure has the advantage of using inexpensive, commercially available starting materials, combined with an apparently safe method of isolating the product.
2-Nitroethanol is particularly valuable as a synthetic intermediate for the preparation of
nitroethylene.
Nitroethylene is conveniently prepared by heating
2-nitroethanol with
phthalic anhydride and allowing the
nitroethylene to distil under reduced pressure.
29,30
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
petroleum ether
trioxymethylene
dinitrogen tetroxide
methanolic potassium hydroxide
mononitrate ester of ethylene glycol
sulfuric acid (7664-93-9)
formaldehyde (50-00-0)
chloroform (67-66-3)
potassium sulfate (37222-66-5)
magnesium (7439-95-4)
nitric acid (7697-37-2)
oxygen (7782-44-7)
carbon tetrachloride (56-23-5)
nitrogen (7727-37-9)
sodium nitrite (7632-00-0)
mononitrite (14797-65-0)
sodium hydrosulfite (7775-14-6)
carbon dioxide (124-38-9)
phthalic anhydride (85-44-9)
barium sulfate (7727-43-7)
pyridine (110-86-1)
potassium hydroxide (1310-58-3)
zinc (7440-66-6)
calcium (7440-70-2)
phosphoric acid (7664-38-2)
palladium (7440-05-3)
Ethylene oxide (75-21-8)
ethylene (9002-88-4)
nitric oxide
barium (7440-39-3)
Dimethoxymethane (109-87-5)
Nitromethane (75-52-5)
Phloroglucinol (108-73-6)
silver nitrite (7783-99-5)
diphenyl ether (101-84-8)
hexane (110-54-3)
2-Nitroethanol,
Ethanol, 2-nitro- (625-48-9)
nitroethylene (3638-64-0)
2-iodoethanol,
ethylene iodohydrin (624-76-0)
2-chloro-2-nitroethanol
2,2-dichloro-2-nitroethanol
barium nitrite
2-nitroethyl nitrate (4528-34-1)
ethylene glycol mononitrate
diethylene glycol mononitrate
2-bromo-2-nitroethanol
paraformaldehyde (30525-89-4)
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