Organic Syntheses, Coll. Vol. 4, p.828 (1963); Vol. 33, p.79 (1953).
Submitted by Harry S. Mosher, Leslie Turner, and Allan Carlsmith
1.
Checked by N. J. Leonard and E. D. Sutoris.
1. Procedure
Caution! Reactions and subsequent operations involving peracids and peroxy compounds should be run behind a safety shield. For relatively fast reactions, the rate of addition of the peroxy compound should be slow enough so that it reacts rapidly and no significant unreacted excess is allowed to build up. The reaction mixture should be stirred efficiently while the peroxy compound is being added, and cooling should generally be provided since many reactions of peroxy compounds are exothermic. New or unfamiliar reactions, particularly those run at elevated temperatures, should be run first on a small scale. Reaction products should never be recovered from the final reaction mixture by distillation until all residual active oxygen compounds (including unreacted peroxy compounds) have been destroyed. Decomposition of active oxygen compounds may be accomplished by the procedure described in Korach, M.; Nielsen, D. R.; Rideout, W. H. Org. Synth. 1962, 42, 50 (Org. Synth. 1973, Coll. Vol. 5, 414). [Note added January 2011].
In a
1-l. three-necked flask equipped with a
stirrer (Note 1), a
thermometer, and a
dropping funnel is placed
110 g. (1.39 moles) of pyridine. The
pyridine is stirred, and
250 ml. (285 g., 1.50 moles) of 40% peracetic acid (Note 2) is added at such a rate that the temperature reaches 85° and is maintained there. After the addition, which requires 50–60 minutes, the mixture is stirred until the temperature drops to 40°.
B.
Pyridine-N-oxide. The
acetic acid solution is evaporated on the steam bath under the pressure of a
water aspirator, and the residue (180–190 g.) is distilled at a pressure of 1 mm. or less in an apparatus suitable for collecting a solid distillate
(Note 5). The
vacuum pump must be protected with a
Dry Ice trap capable of holding about
60 ml. of acetic acid, which distils as the
pyridine-N-oxide acetate dissociates at low pressure. Heat is provided by an
oil bath, the temperature of which is not allowed to rise above 130°
(Note 6). The product is collected at
100–105°/1mm. (
95–98°/0.5 mm.). The yield is
103–110 g. (
78–83%) of colorless solid, m.p.
65–66° (sealed capillary). The base is deliquescent and must be stoppered immediately.
2. Notes
1.
A convenient seal for stirring under vacuum (see
(Note 3)) is made by running an
8-mm. glass rod, with
propeller or paddle stirrer at the end, through the outside member of an 18/9 spherical joint which is inserted into a suitable
rubber stopper. The inner member of the 18/9 spherical joint is then slipped over the stirrer and held in place with a piece of rubber tubing. This rotating seal may then be lubricated with a drop of oil. Alternatively, one may use a Trubore stirring system.
2.
Becco
peracetic acid (40%) was used. The composition and properties of this commercial preparation are described fully in
Bulletin 4 of the Buffalo Electro-Chemical Company, Buffalo, New York. The manufacturer's recommendations for storing and handling should be followed. Experiments using proportionate amounts of
10% or 20% peracetic acid in acetic acid were equally successful. The strength of the
peracetic acid, as well as the progress of the reaction, can be determined iodimetrically.
23.
The vacuum evaporation proceeds much more smoothly and rapidly if the mixture is stirred mechanically during the process.
4.
The submitters report that the same procedure is successful with four times the amounts given here. With the increased amounts, a
water bath is used for cooling during the initial addition, which then requires about 45 minutes.
5.
Caution! Before distillation, absence of peroxide should be established by test with potassium iodide.The apparatus for distillation of solids in vacuum described in
Organic Syntheses3 is satisfactory, as is a combination of
standard taper flasks, short column, and adaptors.
6.
It is imperative that the pressure be maintained at 1 mm. or lower. Decomposition is usually extensive at higher pressures; however, the removal of the
acetic acid may be initiated at 5–10 mm. pressure. The oil-bath temperature must not exceed 130° if decomposition is to be avoided. A fore-run of
15–20 g., b.p.
90–98°/0.5 mm., can be saved and redistilled in combination with similar cuts from successive runs. About
9–10 g. (
7%) of additional crystalline
pyridine-N-oxide is obtained per run in this manner.
3. Discussion
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