Org. Synth. 1965, 45, 96
DOI: 10.15227/orgsyn.045.0096
3-PHENYLSYDNONE
[N-Phenylsydnone]
Submitted by Charles J. Thoman and Denys J. Voaden
1.
Checked by William E. Parham and Edward A. Walters.
1. Procedure
A. N-Nitroso-N-phenylglycine. One hundred grams (0.66 mole) of N-phenylglycine (Note 1) is suspended in 1.2 l. of water contained in a 3-l. beaker placed in an ice-salt bath and stirred until the temperature has dropped below 0°. A solution of 50 g. (0.72 mole) of sodium nitrite in 300 ml. of water is added dropwise over a period of 40 minutes at such a rate that the temperature never exceeds 0°. The red, almost clear solution (Note 2) is filtered as quickly as possible with suction, after which 3 g. of Norit® is added and allowed to stir with the cold solution for several minutes (Note 3). The mixture is again filtered with suction. Addition of 100 ml. of concentrated hydrochloric acid to the well-stirred solution produces, after about 30 seconds, a profusion of light, fluffy crystals. The suspension is stirred for 10 minutes and is then filtered with suction and washed twice with ice-cold water. The precipitate is best dried by leaving it on the suction funnel overnight. The resulting product melts at 103–104°, weighs 96–99 g. (80–83%) (Note 4), and is off-white in color. It can be used without recrystallization.
B. 3-Phenylsydnone. The 99 g. (0.55 mole) of N-nitroso-N-phenylglycine is dissolved in 500 ml. of acetic anhydride in a 1-l. Erlenmeyer flask fitted with a reflux condenser topped by a drying tube. The deep-red solution is heated in a boiling water bath for 1.5 hours with magnetic stirring (Note 5) and is then allowed to cool to room temperature. The cool solution is poured slowly into 3 l. of cold water which is very well stirred (Note 6), white crystals separate almost immediately. After 5 minutes of stirring, the solid is filtered with suction, washed twice with ice-cold water, and dried on the funnel with suction overnight. The dried product is cream-colored, weighs 74–75 g. (83–84%), and melts at 136–137° (Note 7). The overall yield for the two steps is 67–70%.
2. Notes
1.
Eastman Organic Chemicals practical grade material, mud-brown in color, was used without purification.
2.
Often a small amount of insoluble, dark-brown material remains in suspension. Filtration of this product is most difficult, since it tends to clog the filter paper. It seems advisable to change filter papers two or three times during the filtration, if necessary. This step usually requires from 30 minutes to 1.5 hours; however, the time can be shortened appreciably by the use of Hyflo Supercel
®.
3.
This
Norit® treatment, when combined with the preceding filtration, does much to improve the purity of the
N-nitroso-N-phenylglycine; though the yield of nitroso compound thereby is lowered, the yield of the sydnone is increased correspondingly and the sydnone is much purer.
4.
Earl and Mackney
2 report a tan product (
96.8% yield) melting at
102–103°. They did not use the preliminary filtration or
Norit® treatment described above.
5.
The usual method (Earl and Mackney
2) has been to let the solution stand at room temperature for 24 hours. Control experiments proved, however, that the procedure described above gives comparable results.
36.
On rare occasions a small amount of insoluble material may be present in the cool solution; the solution can be poured into the water through a funnel fitted with a plug of glass wool.
7.
Earl and Mackney
2 report a very light tan product, melting at
134–135°, in
73% yield. The product can be recrystallized from boiling water to give cream-colored needles, but this does not improve the purity of the product.
3. Discussion
This procedure is a modification of preparations of
3-phenylsydnone described earlier.
2,3 The dehydration of
N-nitroso-N-phenylglycine has also been effected by the use of
thionyl chloride and
pyridine in
dioxane,
4 thionyl chloride in
ether,
4 trifluoroacetic anhydride in
ether,
4 and
diisopropylcarbodiimide in water;
5 or by reaction of the alkali metal salts of
N-nitroso-N-phenylglycine with
phosgene or
benzenesulfonyl chloride in water
5 or with
acetyl chloride in
benzene.
44. Merits of the Preparation
The present procedure makes possible the preparation of large quantities of very pure
3-phenylsydnone without recrystallization. The earlier procedure
2 produced a tan or brown product which lost its color only after several recrystallizations. Slight variations in this procedure can be used to prepare a variety of 3-substituted and 3,4-disubstituted sydnones.
3-Phenylsydnone is the prototype of that class of mesoionic compounds called sydnones. On acidic hydrolysis it produces
phenylhydrazine, whereas basic hydrolysis regenerates
N-nitroso-N-phenylglycine. This sydnone undergoes a variety of electrophilic substitutions,
3,4,6,7,8,9,10,11,12,13,14,15,16,17,18,19 including mercuration
11,13,16 and formylation,
19 with an ease comparable to
thiophene, and a number of "1,3-dipolar cycloadditions" with numerous alkenes,
15,18 alkynes,
17 and quinones
8 to form, with loss of
carbon dioxide, a variety of pyrazole derivatives.
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
hydrochloric acid (7647-01-0)
Benzene (71-43-2)
ether (60-29-7)
acetic anhydride (108-24-7)
acetyl chloride (75-36-5)
thionyl chloride (7719-09-7)
sodium nitrite (7632-00-0)
Phenylhydrazine (100-63-0)
carbon dioxide (124-38-9)
Norit (7782-42-5)
Benzenesulfonyl chloride (98-09-9)
pyridine (110-86-1)
phosgene (75-44-5)
Thiophene (110-02-1)
dioxane (123-91-1)
N-Nitroso-N-phenylglycine (6415-68-5)
N-phenylglycine (103-01-5)
diisopropylcarbodiimide (693-13-0)
trifluoroacetic anhydride (407-25-0)
3-Phenylsydnone,
N-Phenylsydnone (120-06-9)
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