Checked by John C. Sheehan and Curt W. Beck.
1. Procedure
In a
1-l. round-bottomed three-necked flask, equipped with a
thermometer, a
reflux condenser, and
two fritted-glass gas dispersion tubes (Note
1), is placed
600 g. (4.54 moles) of pure tetralin (Note
2). The flask is placed in a constant-temperature bath at 70°, and a finely dispersed stream of
oxygen is passed through the
tetralin until the
peroxide content of the reaction mixture is 25–30% as shown by an active
oxygen content of 2.4–2.9% (Note
3). This oxidation requires 24–48 hours. The reaction mixture is then distilled (Note
4) in an all-glass apparatus at 0.2–0.4 mm. through a 60 by
2.5 cm. Vigreux column, until a pot temperature of 70° is reached. About
370–380 g. of unoxidized tetralin, boiling at
32–45°/0.2–0.4 mm., is recovered. The pot residue is a slightly viscous amber-colored oil which weighs
225–235 g. and consists of about
80% tetralin hydroperoxide (Note
5). To obtain the pure
hydroperoxide the residue is dissolved in
450 ml. of toluene and the solution is cooled to −50° with stirring (Note
6). After standing at −50° for 1 hour, the slurry is separated by suction filtration (Note
7) and the precipitate is dried at room temperature at 1–2 mm. There is thus obtained
120–125 g. of moderately pure
tetralin hydroperoxide, m.p.
50.2–52.0°, active
oxygen content 9.20% (Note
8). Recrystallization from
480 ml. of toluene at −30° yields
80–85 g. (
44–57% yield based on the
peroxide content of the oxidized
tetralin) of pure
tetralin hydroperoxide as a colorless solid, m.p.
54.0–54.5°, active
oxygen content, 9.70% (Note
9).
2. Notes
1. Rubber connections must be avoided because rubber is rapidly attacked by
tetralin. Convenient gas dispersion tubes are Pyrex No. 39533.
2. Pure
tetralin was prepared from the practical grade supplied by the Eastman Kodak Company by the procedure of George and Robertson:
2 Three kilograms was fractionally distilled through a packed column, the fraction boiling at 204–207° being retained (2.7 kg.). This was gently shaken with 1 lb. of
mercury, and the upper layer was carefully decanted through
fluted filter paper. The crude
tetralin was next shaken with saturated aqueous
mercuric acetate solution, and the aqueous layer and a small amount of orange precipitate were discarded. The hydrocarbon was then shaken with 5 successive
300-ml. portions of concentrated sulfuric acid, once with
10% sodium hydroxide, and finally with water until the washings were neutral. The
tetralin was dried over anhydrous
calcium chloride and distilled through a packed column in a
nitrogen atmosphere. In this way,
2 kg. of pure
tetralin was obtained, b.p.
206–207°,
nD20 1.5428.
3. Active
oxygen content is determined iodometrically:
3 In an
iodine flask, an accurately weighed sample (0.1–0.3 g.) is dissolved in
20 ml. of an acetic acid-chloroform solution (3:2 by volume), and
2 ml. of saturated aqueous potassium iodide solution is added. The flask is immediately flushed with
nitrogen, stoppered, and allowed to stand at room temperature for 15 minutes. Fifty milliliters of water is then added with good mixing, and the liberated
iodine is titrated with 0.1
N sodium thiosulfate, employing starch as indicator. A blank titration, which usually does not exceed 0.2 ml., is also run. One milliliter of 0.1
N sodium thiosulfate is equivalent to 0.00821 g. of
tetralin hydroperoxide.
4. The distillation should be conducted behind a safety shield.
5.
Peroxide loss up to this point is negligible provided an all-glass apparatus has been used throughout and the distillation temperature has not exceeded 70°.
6. A
Dry Ice-ethanol bath is convenient for cooling the solution.
7. Filtration may be carried out in a
suction funnel surrounded by a Dry Ice-ethanol cooling bath, or using a cold box maintained at −50°.
9.
Tetralin hydroperoxide is a convenient model compound for many studies in
peroxide chemistry. It remains colorless and does not decrease in
peroxide content for months if stored in the dark at or below 0°. Storage under warm summer conditions for several months results in decomposition to a dark, viscous liquid.
3. Discussion
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