Checked by E. Lewars, P. H. McCabe, and Peter Yates.
1. Procedure
Benzene has been identified as a carcinogen; OSHA has issued emergency standards on its use. All procedures involving
benzene should be carried out in a well-ventilated hood, and glove protection is required.
Sodium-dried diethyl ether (150 ml.) is placed in a
1-l., four-necked flask equipped with a fritted gas-inlet extending to its bottom, a sealed
mechanical stirrer (Note
2), a
100-ml., pressure-equalizing dropping funnel, a
thermometer, and a
dry ice condenser protected with a phosphorus pentoxide drying tube.
Cycloöctene (44.4 g., 53.5 ml., 0.404 mole) (Note
3) is placed in the dropping funnel, and the system is swept with dry
oxygen.
Dinitrogen tetroxide (39.3 g., 27.1 ml. at −9°, 0.427 mole) (Note
4) is condensed (Note
5) in a
graduated, calibrated trap that is protected with a phosphorus pentoxide drying tube and has been swept with dry
oxygen.
The flask is cooled to −10°, and the
dinitrogen tetroxide is distilled with a
warm water bath from the trap into the
ether, with slow stirring; the transfer is aided by a minimal flow of dry
oxygen. The solution is allowed to warm to 0–5°, and the
oxygen flow rate is increased to 10 ml. per minute (Note
6). The
cycloöctene is dropped into the
dinitrogen tetroxide solution, with vigorous stirring, over a 30-minute period. The reaction is exothermic, and the temperature is kept at 9–12° by cooling with a
methanol–dry ice bath at −20°. The dropping funnel is rinsed with
25 ml. of ether, and the yellow solution (Note
7) is stirred for an additional 30 minutes at 10° with continued
oxygen flow.
Triethylamine (121 g., 1.20 moles) (Note
8) is added, with stirring, over a 12-minute period; the temperature of the reaction mixture is kept at 4–12° by maintaining the bath at −4° (Note
9). The mixture is kept at room temperature for an additional 30 minutes, diluted with
150 ml. of ether, and cooled to 0–5°. The excess
triethylamine is neutralized with an ice-cold solution of
72 g. of acetic acid in 200 ml. of water, with stirring. The reaction mixture is transferred to a
2-l. separatory funnel and extracted with three
400-ml. portions of ether. The combined ethereal extracts are washed with two 200-ml. portions of water, three
150-ml. portions of saturated aqueous sodium hydrogen carbonate, and again with water (Note
10).
Most of the
ether is removed at room temperature with a
rotary evaporator. The water that separates is removed with the aid of a small separatory funnel, and the remaining
ether, traces of water, and
cycloöctane (Note
11) are distilled at room temperature (10 mm.) over 3 hours, yielding
59–61 g. of crude
1-nitrocycloöctene as a yellow oil (Note
12) and (Note
13). Chromatography on
silica gel (Note
14) with successive elution with
n-hexane and
benzene gives
39–40 g. (
63–64%) of
1-nitrocycloöctene (Note
15). Distillation (Note
16) gave an analytically pure sample, b.p.
60° (0.2 mm.),
nD20 1.5116 (Note
17).
2. Notes
1. Concentrations of
dinitrogen tetroxide of 100–150 p.p.m. are dangerous for exposures of 30–60 minutes, and concentrations of 200–700 p.p.m. may be fatal after even very short exposures.
2. The checkers found that magnetic stirring could be used in place of mechanical stirring.
3.
Cycloöctene (95% pure) from Columbia Carbon Co., a division of Cities Service, was used without further purification.
4. A slight excess of
dinitrogen tetroxide over olefin is necessary for maximum yields.
5. For good yields all reagents must be absolutely dry. For condensation of dry
dinitrogen tetroxide free of
dinitrogen trioxide, streams of dry
oxygen (run through a flow meter, a
calcium chloride tube, and concentrated
sulfuric acid) and
dinitrogen tetroxide (99.5% pure from the Matheson Company), are combined and run slowly through a phosphorus pentoxide tube before condensation. The freezing point of
dinitrogen tetroxide is −9.3°, and a convenient cooling bath for condensation is methanol–dry ice at −8° to −10°.
6. The use of
oxygen in this reaction prevents formation of undesirable by-products,
e.g., nitro nitroso compounds.
2 For the preparation of
1-nitro-1-octadecene the optimum mole ratio of olefin to
oxygen was found
3 to be 1/50 to 1/150, compared with 1/30 in this procedure.
7. Nitro nitrites are unstable, and it is safe practice to keep them in solution until they are converted to nitro alcohols
2 or nitro olefins.
3
9. At the end of the exothermic elimination reaction the color turns brown with simultaneous precipitation of the triethylammonium salts.
10. The checkers washed the ethereal extracts with saturated brine and dried them over anhydrous
magnesium sulfate before removal of
ether.
11.
Cycloöctane is the major impurity in the starting material.
12. The submitter estimated the crude product to be 95% pure by IR spectroscopy: ε
6.59μ/ε
3.40μ = 3.00 (CCl
4: matched 0.1-mm. cells; analytical absorbances, 0.2–0.7).
13. For further reactions involving reduction,
4 the crude product can be used.
14. The
silica gel column was 14 × 2.5 in. I.D.; a shorter column may suffice.
15. The checkers found for this product:
nD26 1.5106;
1H NMR (CDCl
3), δ 1.6 (m, 8 H), 2.3 (m, 2 H), 2.7 (m, 2 H), and 7.24 (t,
J 
9 Hz., 1 H).
16. It is safe practice to remove the peroxide that may be formed in this free radical reaction by chromatography before distillation. The submitter distilled an aliquot (12.7 g.) of the
hexane eluate, giving
9.9 g. of product, ε
6.59μ/ε
3.40μ = 3.12 (Calcd. for C
8H
13NO
2: C, 61.91; H, 8.44; N, 9.03. Found: C, 61.84; H, 8.27; N, 8.80).
17. Slow decomposition with simultaneous precipitation of a solid occurred on standing for several weeks at 23°. Immediate analysis and use of the product are advised.
3. Discussion
The major advantage of the present method, the only method reported
3 for the preparation of
1-nitrocycloöctene, is the convenience of converting an olefin to a 1-nitro olefin in good yield without isolation of any intermediate. The submitter has also used this method
3 successfully for the preparation of
1-nitro-1-octadecene from
1-octadecene.
In the past the products from the addition of
dinitrogen tetroxide to olefins have been hydrolyzed and converted to 1-nitro olefins by various methods,
e.g., acetylation of the isolated nitro alcohol and elimination of
acetic acid with
potassium carbonate,
5,6 dehydration of the nitro alcohol with
phthalic anhydride7 or
potassium hydrogen sulfate,
8 and base-catalyzed elimination of
nitrous and nitric acid from dinitro compounds and nitro nitrates, respectively.
2 Besides representing longer syntheses, these routes require separation of the nitro alcohol from the dinitro compound and, since these substances occur in approximately equal amounts, 50% of the yield is lost in the first step. Furthermore, in the case of the higher 1-olefins, this separation is difficult
9,10 and tedious.
3 1-Nitro 1-olefins have been employed in the preparation of saturated nitro compounds and oximes.
4
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