Org. Synth. 1973, 53, 38
DOI: 10.15227/orgsyn.053.0038
DIDEUTERIODIAZOMETHANE
[Methane-d2, diazo-]
Submitted by P. G. Gassman
1 and W. J. Greenlee.
Checked by David G. Melillo and Herbert O. House.
1. Procedure
Caution! Diazomethane is toxic and explosive. The operations described in this procedure must be carried out in a good hood with an adequate shield (Note 1).
A distilled,
ethereal solution (300 ml.) containing approximately 0.06 mole of diazomethane (Note 1) is prepared from
22.5 g. of a 70% dispersion (15.8 g., 0.063 mole) of bis-(N-methyl-N-nitroso)terephthalamide (Note 2),
75 ml. of aqueous 30% sodium hydroxide,
55 ml. of diethylene glycol monoethyl ether, and
375 ml. of diethyl ether by the procedure described in
Org. Synth., Coll. Vol. 5, 351 (1973). The receiving flask containing the ethereal
diazomethane is capped with a
rubber stopper fitted with a
drying tube containing potassium hydroxide pellets to protect the solution from atmospheric moisture. The concentration of
diazomethane may be determined either by titration with ethereal
benzoic acid (Note 3) or spectrophotometrically
(Note 4).
A dry, 250-ml. Erlenmeyer flask equipped with a Teflon-coated magnetic stirring bar is charged with 11 ml. of a solution (Note 5) containing 0.01 mole of sodium deuteroxide in 10 ml. of deuterium oxide and 1 ml. of anhydrous tetrahydrofuran. After the solution has been cooled in an ice bath, 120 ml. of the ethereal solution containing 0.039 mole of diazomethane is added, the flask is stoppered loosely with a cork, and the reaction mixture is stirred vigorously at 0° for one hour. The lower deuterium oxide layer is removed with a pipette and a fresh 11-ml. portion of the sodium deuteroxide solution is added. This mixture is then stirred for one hour at 0°, and the process is repeated until a total of four exchanges have been performed. The ethereal diazomethane solution is then decanted into a clean, dry, 250-ml. Erlenmeyer flask and dried over 10 g. of anhydrous sodium carbonate. The resulting solution (approximately 110 ml.) contains (spectrophotometric analysis, (Note 4), or titration with benzoic acid, (Note 3)) 0.020–0.022 mole (51–56%) of dideuteriodiazomethane, which is 98–99% deuterated (Note 6).
2. Notes
1.
Diazomethane is not only toxic, but also potentially explosive. Hence, one should wear heavy gloves and goggles and work behind a safety screen or a hood door with safety glass, as is recommended in the preparation of
diazomethane described in
Org. Synth., Coll. Vol. 4, 250 (1963). As is also recommended, ground joints and sharp surfaces should be avoided; thus, all glass tubes should be carefully fire-polished, connections should be made with rubber stoppers, and
separatory funnels should be avoided, as should etched or scratched flasks. Explosion of
diazomethane has been observed at the moment crystals (sharp edges!) suddenly separated from a supersaturated solution. Stirring with a Teflon-coated magnetic stirrer is much preferred to swirling the reaction mixture by hand (there has been at least one case of a chemist whose hand was injured by an explosion during the preparation of
diazomethane in a hand-swirled reaction vessel). It is imperative that
diazomethane solutions not be exposed to direct sunlight or placed near a strong artificial light because light is thought to have been responsible for some of the explosions encountered with
diazomethane. Particular caution should be exercised when an organic solvent boiling higher than
ether is used. Because such a solvent has a vapor pressure lower than
ether, the concentration of
diazomethane in the vapor above the reaction mixture is greater and an explosion is more apt to occur. Since most
diazomethane explosions occur during distillation, procedures that avoid distillation offer certain advantages. An
ether solution of
diazomethane satisfactory for many uses can be prepared as described in
Org. Synth., Coll. Vol. 2, 165 (1943), where
nitrosomethylurea is added to a mixture of
ether and
50% aqueous potassium hydroxide, and the
ether solution of
diazomethane is subsequently decanted from the aqueous layer and dried over
potassium hydroxide pellets (not sharp-edged sticks!). However, the reported potent carcinogenicity
2 of
nitrosomethylurea mitigates other advantages of this procedure. Two procedures involving distillation of
diazomethane, those in
Org. Synth., Coll. Vol. 4, 250 (1963) and
Coll. Vol. 5, 351 (1973), may be recommended. In neither case is there much
diazomethane present in the distilling flask. The hazards associated with
diazomethane are discussed by Gutsche.
33.
The concentration of
diazomethane may be determined by reaction of an aliquot of the ethereal solution with a weighed excess of
benzoic acid in cold (0°) ether solution, as described in
Org. Synth., Coll. Vol. 2, 165 (1943). The unchanged
benzoic acid is then determined by titration with standard aqueous
0.1 M potassium hydroxide.
4.
Caution! The following spectrophotometric analysis should be performed in a hood. To determine the concentration of
diazomethane obtained in this preparation, a 5-ml. aliquot of the distilled solution is diluted to 25 ml. with
ether, and a portion of this solution is placed in a cylindrical Pyrex cell with an internal diameter of 1.0 cm. The optical density of the solution is determined at 410 nm with a suitable colorimeter such as a Bausch and Lomb Spectronic 20. From the molecular extinction coefficient, ε 7.2, at 410 nm for
diazomethane in ether solution, the concentration of
diazomethane can be calculated. In a typical preparation the optical density of the diluted solution at 410 nm was 0.46 corresponding to a
diazomethane concentration of 0.064
M; thus, the concentration of the undiluted solution was 0.32
M, corresponding to a 77% yield of
diazomethane.
5.
It is convenient to prepare 110 ml. of this solution at a time. Since
hydrogen is evolved, the solution should be prepared in a hood. A dry,
250-ml. three-necked flask is fitted with a magnetic stirrer, a
rubber septum, a
glass stopper, and a
125-ml. Erlenmeyer flask attached to the third neck of the reaction flask with a 10-cm. length of Gooch rubber tubing or nylon tubing. The apparatus is flushed with
nitrogen from a hypodermic needle inserted through the rubber septum. Small, freshly cut chips of metallic
sodium (2.3 g., 0.10 g.-atom) are placed in the Erlenmeyer flask and
100 ml. of deuterium oxide (99.7% pure grade obtained from Columbia Organic Chemicals Company, Inc.,) is placed in the reaction flask. With a hypodermic needle inserted through the rubber septum to permit the escape of
hydrogen, the
sodium chips are added, slowly and with stirring, to the reaction vessel. When reaction with the
sodium is complete, the solution is diluted with
10 ml. of anhydrous tetrahydrofuran and stored under a
nitrogen atmosphere.
6.
The
deuterium content can be determined by reaction of the deuterated
diazomethane with
benzoic acid- -d in anhydrous
ether followed by analysis of
methyl benzoate for
deuterium content either by
1H NMR spectroscopy or by mass spectroscopy.
Benzoic acid- -d is prepared by heating a mixture of
48.6 g. (0.216 mole) of benzoic anhydride (obtained from Aldrich Chemical Company, Inc.),
0.10 g. (0.00090 mole) of anhydrous sodium carbonate, and
7.0 g. (0.35 mole) of deuterium oxide to 90° for 2 hours. The resulting mixture is distilled at atmospheric pressure in a short-path still fitted with a
receiver protected from atmospheric moisture by a drying tube. After removal of a forerun, b.p. 100–101°, the
benzoic acid-O-d is collected at
245–247°. During the distillation it is necessary to warm the distillation apparatus with a heat gun or an IR lamp to prevent solidification of the
benzoic acid-O-d before it reaches the receiver.
Caution! The following reaction should be performed in a good hood (Note 1). A cold (0°) solution of 1.43 g. (0.0116 mole) of benzoic acid-O-d in 10 ml. of anhydrous ether is placed in a dry, 100-ml., round-bottomed flask fitted with a rubber stopper and a Teflon-coated magnetic stirring bar. The flask is cooled in an ice bath, and a sufficient amount of the ethereal dideuteriodiazomethane solution is added from a pipette, providing excess dideuteriodiazomethane in the reaction mixture. The reaction flask is stoppered loosely, and the resulting yellow solution is stirred at 0° for 10 minutes and concentrated by first warming the solution on a steam bath in the hood, then removing the last traces of solvent under reduced pressure. The residual liquid methyl benzoate (1.4–1.5 g., 90–95% yield) is analyzed for deuterium content. For a 1H NMR analysis, the spectrum of the pure liquid is taken and the extent of deuteration is determined by integration of the areas under the multiplet in the region δ 7.1–8.3 (aromatic CH) and the peak at δ 3.82 (OCH3). For mass spectroscopic analysis, the mass spectra of the deuterated sample and a sample of undeuterated methyl benzoate each are measured at an ionizing potential sufficiently low (approximately 12 eV.) to minimize the formation of an M-1 fragment at m/e 135 in the spectrum of the deuterated sample. The relative abundances of the m/e 136 and 137 peaks in the spectrum of the undeuterated sample are then used to correct the peaks at m/e 137, 138, and 139 in the deuterated sample for contributions from the 13C isotope. From the relative abundances of the m/e 136 peak and the corrected m/e 137, 138, and 139 peaks in the spectrum of the undeuterated sample the relative proportions of d0, d1, d2, and d3 species in the deuterated methyl benzoate can be calculated. Both 1H NMR and mass spectral analysis indicated the methyl benzoate to be 98% deuterated (6–7% d2 species and 93–94% d3 species). When the dideuteriodiazomethane solution was allowed to react with undeuterated benzoic acid, hydrogen–deuterium exchange occurred more rapidly than esterification. The methyl benzoate produced was 70% deuterated (1H NMR analysis) and contained 4% d0, 37% d1, 30% d2 and 29% d3 species (mass spectral analysis).
3. Discussion
The exchange procedure described was developed for the preparation of
dideuteriodiazomethane, for use in labeling studies. It is basically a modification of a procedure that has been used extensively;
5 however, the literature procedures give relatively little detail. This modified procedure permits the synthesis of fairly large amounts of high-purity
dideuteriodiazomethane.
Dideuteriodiazomethane has also been prepared from
N-nitrosomethyl-d3-urea and related trideuterated
diazomethane precursors.
6 Deuterated
chloroform and
hydrazine hydrate have also been used to prepare
dideuteriodiazomethane.
3,7The procedure described provides a general method for the hydrogen–deuterium exchange of simple diazoalkanes.
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
Methane-d2, diazo-
N-nitrosomethyl-d3-urea
ether,
diethyl ether (60-29-7)
hydrogen (1333-74-0)
sodium hydroxide (1310-73-2)
chloroform (67-66-3)
sodium carbonate (497-19-8)
nitrogen (7727-37-9)
Benzoic acid (65-85-0)
Benzoic anhydride (93-97-0)
potassium hydroxide,
potassium hydroxide pellets (1310-58-3)
sodium (13966-32-0)
hydrazine hydrate (7803-57-8)
methyl benzoate (93-58-3)
Diazomethane (334-88-3)
Nitrosomethylurea
Tetrahydrofuran (109-99-9)
bis-(N-methyl-N-nitroso)terephthalamide
diethylene glycol monoethyl ether (111-90-0)
Dideuteriodiazomethane (14621-84-2)
sodium deuteroxide (14014-06-3)
deuterium oxide (7789-20-0)
deuterium (7782-39-0)
Benzoic acid- -d,
benzoic acid-O-d (1005-01-2)
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