Checked by Marjorie C. Caserio and John D. Roberts.
1. Procedure
A finely divided suspension (Note
1) and (Note
2) of
10.0 g. (0.056 mole) of phenanthrene (Note
3) in
200 ml. of dry methanol (Note
4) is placed in a
standard ozonolysis vessel (Note
5). The reaction mixture is cooled in a
Dewar flask by an acetone-Dry Ice mixture to about −30° (Note
6) and (Note
7), and
ozone (Note
8) is passed through at a rate of about 20 l. per hour (Note
9) until all the
phenanthrene has reacted (Note
10).
To the cooled reaction mixture are added
25–30 g. (roughly 1.5 times the theoretical 0.112 mole) of sodium or potassium iodide and
30 ml. of glacial acetic acid (Note
11). After the addition, the reaction mixture is allowed to stand at room temperature for 30 minutes to 1 hour. The released
iodine is reduced with
10% sodium thiosulfate solution, after which the reaction mixture is placed immediately under an air blast (Note
12). As the
methanol evaporates, the product begins to crystallize (Note
13). The crystallization should be well advanced by the time most of the
methanol has evaporated. Water is then added, and the solid is removed by filtration and dried. The yield of crude product, softening at about 54° and melting at
59–62°, is
9.2–11.4 g. (
78–96%). The crude product may be recrystallized by dissolving it in the minimal amount
(40–50 ml.) of dry ether and slowly adding about
150 ml. of ligroin (Note
14). Small crystals separate halfway through the addition, and crystallization is completed by cooling the mixture in an
acetone-Dry Ice bath. An
80–90% recovery of pale yellow crystals melting at
62–63° is obtained. A second recrystallization from
70% aqueous ethanol gives nearly colorless crystals melting at
62.5–63.5° (Note
15).
2. Notes
1. This is produced by dissolving the
phenanthrene in the refluxing solvent and cooling rapidly.
2. The finely divided suspension is necessary in order for the
phenanthrene to go into solution and react readily during the ozonolysis.
3. Eastman white label 599, m.p.
99–100°, was used.
4. Commercial
methanol reagent containing 0.1% or less of water is satisfactory.
5. The usual
long, cylindrical, gas-absorption-type vessel with an inlet tube extending to near the bottom is satisfactory.
2 The total volume of the vessel should be at least twice that of the reaction solution. More elaborate reaction vessels equipped with a
stirrer3 are very useful in reactions such as this in which the reactant is suspended in the solvent. However, the commercially available vessels of this type are not large enough for the reaction mixture described here.
6. The temperature of the reaction mixture should not be allowed to rise above −20°, because at higher temperatures
ozone tends to react with the solvent and the reactions shown below also occur. Compound III is not readily reduced to the dialdehyde.
7. Compound II may precipitate during ozonolysis at −30° or below. This is in no way detrimental.
8. A Welsbach T23 ozonator was used by the submitters.
Oxygen dried by a Pittsburg Laboratory-Lectrodryer to a dew point of −60° was passed through the ozonator, which was set to produce a
5–6% by weight concentration of ozone.
4 Following the ozonation flask were a
potassium iodide trap and a wet-test meter.
4 The checkers used a simple ozonator capable of producing
3.8% by weight of ozone at a flow rate of 20 l. per hour from
oxygen dried by passage through a
30-cm. column of silica gel.
9. The rate should be sufficiently great to cause considerable agitation of the suspended
phenanthrene. As the reaction proceeds, the reaction vessel should be shaken frequently in order to maintain good contact between the
phenanthrene and
ozone. For smaller runs a reaction vessel that includes a stirrer is advantageous (Note
5).
The checkers found it convenient to use leads of Tygon tubing of sufficient length to allow the reaction flask to be withdrawn at intervals from the Dewar flask and shaken manually.
10. Unreacted
ozone starts passing through to the potassium iodide trap toward the end of the reaction. However, it is best to continue the reaction until all the suspended
phenanthrene has disappeared. This usually requires a total of 1.1–1.3 mole-equivalents of
ozone. Unless all the
phenanthrene has reacted, difficulty is encountered in the crystallization and/or recrystallization of the dialdehyde.
11. The reduction may be carried out in the ozonolysis flask, or the reaction mixture may be transferred first to an
Erlenmeyer flask or
beaker. The iodide and
acetic acid should be added simultaneously. The reaction of peroxides with
iodide ion is exothermic. The temperature of the reaction mixture should be kept below −20° while the
sodium iodide and
acetic acid are added, after which it may be allowed to rise slowly to room temperature.
12. It seems to be detrimental to the crystallization and recrystallization of the product to postpone the evaporation of the reaction mixture, probably because the product becomes contaminated with
sulfur if the reduced reaction mixture is allowed to stand.
13. Sometimes difficulty is encountered in starting the crystallization, since the product may separate as a yellow oil. It is helpful to induce crystallization by rubbing the sides of the vessel with a
stirring rod and seeding the solution with any crystals that form on the sides of the vessel during the evaporation.
14. The
ligroin used was Skellysolve B.
15. About
30 ml. of warm absolute ethanol readily dissolves
8–9 g. of product. Addition of 15 ml. of water and cooling effect crystallization with about
90% recovery of product.
3. Discussion
The present method is based on the earlier described ozonolysis of
phenanthrene in
methanol.
9 The reduction of the peroxidic reaction mixture with
trimethyl phosphite to give
diphenaldehyde, isolated as the
di-p-nitrophenylhydrazone, in quantitative yield has been described recently.
10 The disadvantage of this method is that the dialdehyde cannot be isolated in the free state in high yield.
Diphenaldehyde has also been obtained by
sodium iodide reduction of peroxidic products from ozonolysis of
phenanthrene in solvents that do not react
2 with the zwitterion intermediate.
11,12 The yields are inferior to those obtained by the present method. The aldehyde has been obtained in
91% yield using
dimethyl sulfide as the reducing agent.
13 An
81% yield of
diphenaldehyde has been obtained from the ozonolsis in acqueous
t-butyl alcohol followed by distillation of the solvent at pH 7.5.
14 Hydrogen peroxide is a by-product.
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