Organic Syntheses, CV 5, 191
Submitted by W. D. Emmons and A. S. Pagano
1.
Checked by G. Ryan and Ronald Breslow.
1. Procedure
Caution! The preparation and distillation of the oxazirane, like that of any active oxygen compound, should be carried out behind a safety screen.
A.
N-t-butylbenzaldimine. A
1-l. three-necked flask equipped with stirrer, thermometer, and condenser for downward distillation is charged with
109.5 g. (1.5 moles) of t-butylamine (Note
1).
Benzaldehyde (106 g., 1.0 mole) is then added in four increments to the stirred solution over a 20-minute period. A mild exotherm is noted which raises the temperature to 40–50°.
Benzene (150 ml.) is then added and the solution is heated until distillation commences. Solvent (a mixture of amine, water, and
benzene) is removed by distillation until a pot temperature of 110° is reached. The product mixture is then cooled to room temperature, dried over
magnesium sulfate, and stripped free of solvent at aspirator pressure. Distillation of the yellow liquid so obtained yields
120–151 g. (
78–94%) of colorless
N-t-butylbenzaldimine, b.p.
59–63° (1 mm.),
n26D 1.5174,
n20D (Note
2).
B.
2-t-Butyl-3-phenyloxazirane. A
1-l. three-necked flask equipped with an addition funnel, stirrer, and condenser is charged with
68.0 g. (0.422 mole) of N-t-buylbenzaldimine (Note
3) and
50 ml. of benzene. The stirred solution is cooled in an
ice bath and a solution of
61 g. (0.445 mole) of perbenzoic acid in
315 ml. of benzene is added dropwise over a 40-minute period. After one additional hour the stirrer is stopped, and the reaction mixture is allowed to stand overnight with the concurrent melting of the ice bath. The light blue
benzene solution is then filtered to remove the precipitated
benzoic acid and is washed sequentially with three
100-ml. portions of sodium carbonate,
100 ml. of 5% hydrochloric acid,
100 ml. of saturated sodium bisulfite solution, and finally with 100 ml. of water. The solution is dried over
magnesium sulfate, and the solvent is evaporated at room temperature (Note
4) at aspirator pressure. There is obtained
46–60 g. (
60–78%) of crude oxazirane,
n26D 1.5065. This product assays 96–98% purity by iodimetric titration (Note
5) and is sufficiently pure for many purposes. Distillation of the crude product through a
short Vigreux column yields, after a few drops of forerun,
42–55 g. (
56–74%) of pure oxazirane,
n26D 1.5062,
n20D 1.5144, b.p.
55–58° (0.05 mm.),
74–76° (0.2 mm.). Iodimetric assay of this product indicates a purity of 99–100%.
2. Notes
1. Eastman Kodak white label reactants are satisfactory. The
benzaldehyde should be freshly distilled before use.
2. The checkers handled and stored this material under
nitrogen.
4. A
rotary evaporator is very convenient for this operation.
5. A 0.200–0.300 g. sample of the oxazirane is weighed into a stoppered flask to which is added
15 ml. of glacial acetic acid and
2 ml. of saturated aqueous sodium iodide solution. After 5–10 minutes 25 ml. of deionized water is added, and the liberated
iodine is titrated with
0.1N sodium thiosulfate with freshly prepared starch as indicator. Each milliliter of thiosulfate solution is equivalent to 0.00885 g. of
2-t-butyl-3-phenyloxazirane.
3. Discussion
Oxaziranes are in a real sense active oxygen compounds and exhibit many reactions grossly analogous to those of organic peroxides. Thus they undergo one electron transfer reaction with ferrous salts and on pyrolysis they are converted to amides. Oxaziranes are also useful synthetic intermediates since in appropriate cases they may be isomerized to aromatic nitrones which are a convenient source of N-alkylhydroxylamines.
3 The reaction of oxaziranes with peracids also provides a source of nitrosoalkanes and is in many instances the method of choice for preparation of these compounds.
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