Org. Synth. 1970, 50, 6
DOI: 10.15227/orgsyn.050.0006
BIS(TRIFLUOROMETHYL)DIAZOMETHANE
[Propane, 2-diazo-1,1,1,3,3,3-hexafluoro-]
Submitted by W. J. Middleton
1 and D. M. Gale.
Checked by L. Scerbo and W. D. Emmons.
1. Procedure
Caution! This procedure should be carried out in a good hood and behind a shield to avoid exposure to the toxic compounds, hexafluoroacetone imine and hydrazine.
A.
Hexafluoroacetone hydrazone. A
100-ml., three-necked, round-bottomed flask fitted with a
thermometer, a
gas-inlet tube, a
Dewar condenser, and a
magnetic stirring bar is charged with
16 g. (0.50 mole) of anhydrous hydrazine [
Org. Synth., Coll. Vol. 6, 10 (1988)] and cooled in an
ice-methanol bath. The condenser is filled with a cooling mixture of ice and
methanol, the magnetic stirrer is started, and
82.5 g. (0.500 mole) (Note 1) of hexafluoroacetone imine [
Org. Synth., Coll. Vol. 6, 664 (1988)] is slowly distilled into the flask through the gas-inlet tube, while the temperature is maintained below 10°. After the addition, which requires about 1 hour, the cooling bath is removed and the reaction mixture is allowed to warm to room temperature, then poured rapidly into a
500-ml., single-necked, round-bottomed flask containing
150 g. of phosphorus pentoxide. A
spatula is used to partially mix the liquid with the
phosphorus pentoxide (Note 2); the flask is quickly fitted with a simple still head with condenser and heated with a heating mantle until no further distillation occurs
(Note 3). The crude distillate is redistilled through a
45-cm. spinning-band column, giving
48–53 g. (
53–59% conversion) of
hexafluoroacetone hydrazone as a colorless liquid, b.p.
95.5–96°,
n25D 1.3298.
B. Bis(trifluoromethyl)diazomethane. A 1-l., three-necked, round-bottomed flask is equipped with a sealed mechanical stirrer and a 100-ml., pressure-equalizing dropping funnel. The third neck is connected with pressure tubing to a 50-ml. capacity cold trap immersed in an acetone-dry ice cooling bath and protected from the atmosphere with a calcium chloride drying tube. The system is purged with nitrogen, and 375 ml. of benzonitrile and 120 g. (0.271 mole) of lead tetraäcetate (Note 4) are placed in the flask. Stirring is started and the flask is cooled with an ice bath before a solution of 45 g. (0.25 mole) of hexafluoroacetone hydrazone in 50 ml. of benzonitrile is added with the dropping funnel over a period of 1 hour. The ice bath is removed and the reaction mixture is stirred for an additional hour at room temperature. During this time some product collects in the cold trap. The remaining product is distilled into the trap at 10 mm. pressure by removing the drying tube and connecting the trap to a pump or aspirator (a small amount of acetic acid and other impurities can be removed by trap-to-trap distillation), yielding 20–21 ml. or 34–35 g. (76–79%) (Note 5) of bis(trifluoromethyl)diazomethane as a yellow liquid, b.p. 12–13°. The product is neither impact- nor static-sensitive (Note 6) and is stable to long storage at −78°; however, it partly decomposes with loss of nitrogen after several weeks at room temperature.
2. Notes
1.
If it is inconvenient to distill the
hexafluoroacetone imine directly from a cylinder, it may be condensed first in a calibrated cold trap cooled to −10°, then distilled from the trap into the reaction mixture. About 55 ml. of the imine, measured at −10°, corresponds to 0.5 mole.
2.
Caution! A spontaneous reaction may result if mixing is prolonged beyond 1 minute. Rubber gloves should be worn to avoid exposure to hydrazine vapors.3.
About
14 g. (
17%) of
hexafluoroacetone imine can be recovered during the redistillation step if the receivers for both distillations are cooled to −10° or lower. The yield of the hydrazone is about
67% if the recovered imine is taken into account.
4.
Since
acetic acid does not interfere with this reaction, a grade of
lead tetraäcetate that has been stabilized with
acetic acid may be used.
5.
The submitters have obtained yields as high as
90% on runs two times this scale.
6.
Caution! Toxicity data on this material are not available; therefore, it should be assumed to be as toxic as other diazo compounds and handled only in an efficient hood. Although it has been stored in stainless-steel cylinders at autogenous pressure and handled without incident, contact with reagents likely to initiate rapid evolution of nitrogen should be carried out with caution.
3. Discussion
Bis(trifluoromethyl)diazomethane has been prepared by the nitrosation of
1,1,1,3,3,3-hexafluoroisopropylamine2 and by the present procedure,
3 which gives higher yields.
Bis(perfluoroethyl)diazomethane has also been prepared by an extension of this method.
2
Bis(trifluoromethyl)diazomethane is a reactive, electrophilic compound, in that it forms adducts with nucleophiles such as amines and phosphines
3 and adds to olefins, acetylenes,
3 and thiocarbonyl compounds, forming heterocycles. It has been used as a source of
bis(trifluoromethyl)carbene in reactions with
benzene,
3 saturated hydrocarbons,
4 carbon disulfide,
5 and transition metal compounds,
6 and it undergoes a unique radical chain reaction with saturated hydrocarbons, giving hydrazone and azine adducts.
4
This preparation is referenced from:
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
1,1,1,3,3,3-hexafluoroisopropylamine
acetic acid (64-19-7)
Benzene (71-43-2)
methanol (67-56-1)
benzonitrile (100-47-0)
nitrogen (7727-37-9)
carbon disulfide (75-15-0)
hydrazine (302-01-2)
Bis(trifluoromethyl)diazomethane,
Propane, 2-diazo-1,1,1,3,3,3-hexafluoro- (684-23-1)
Hexafluoroacetone imine (1645-75-6)
Hexafluoroacetone hydrazone (1588-41-6)
Bis(perfluoroethyl)diazomethane
bis(trifluoromethyl)carbene
phosphorus pentoxide (1314-56-3)
lead tetraacetate (546-67-8)
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