111 F. Bentz and G.-E. Nischk, DAS 1235300 (1967), Farben- fabriken Bayer AG. 121 F. Bentz and G.-E. Nischk, DAS 1235302 (1967), Farben- fabriken Bayer AG. 131 Cf. P. A . Petjunin and V. P. Cernyek, 2. org. Chim. 1966,285. [4] F. Bentz, R . Braden, and G.-E. Nischk, DAS 1293741 (1969), Farbenfabriken Bayer AG.

H H H H NO2 NO2 CI H H H H H H

m.p. 144 "C). A further 28 g can be recovered by concentra- tion of the mother liquor, m.p. 142"C, total yield 91 %. If recrystallized starting material is used, yields of more than 93 of the ether can be obtained.

Received: September 5, 1969 [Z 86 1El German version: Angew. Chem. 82, 19 (1970)

Publication delayed at authors' request

NO2 NO2 c1

A New Synthesis of Substituted Diphenyl Ethers

By H . Wit t , H. Holtschmidt, and E. Miiller[*]

Dedicaied to Professor K . Hansen on the occasion of his 60 th birthday

It has already been reported 111 that phenyl o-phenoxy- benzoate can be prepared in high yields by heating a melt of diphenyl carbonate in the presence of small amounts of KzC03 a t 23&270 "C. We have now found that the diphenyl ethers (2) can be prepared from 0- and/or p-substituted di- phenyl carbonates ( I ) when subjected to similar reaction conditions.

'R3 (1)

[*I Dr. H. Witt, Prof. Dr. H. Holtschmidt, and Dr. E. Miiller Wissenschaftliches Hauptlaboratorium der Farbenfabriken Bayer AG 509 Leverkusen-Bayerwerk (Germany)

[l] P . W. Bachmann and B. W. Hammarin, US-Pat. 2319197 (May 18, 1943) General Chemical Co.; Chem. Abstr. 37, 62807 (1943); A . Davis and 1. H . Golden, J. chem. Soc. (London) B 1968, 40. 121 H. Witt, H . Holtschmidt, and E. Miiller, DAS 1290148 (May 13, 1967), Farbenfabriken Bayer AG. 13) Cf. Th. K. Brotherton and J. W. Lynn, US-Pat. 3256220 (June 14,1966) Union Carbide Corp.; Chem. Abstr. 65,18498 G (1966); J . M . A. Hoeflake, Recueil Trav. chim. Pays-Bas 36, 62 (1916); 40, 510, 513 (1921).

Mesoionic 2-Benzoyl-1-benzoylimino- 4,5-dime thyl-l,2,3-triazole

By S. Petersen and H . Heitzer [*I

Dedicated to Professor K, Hunsen on the occasion of his 60th birthday

The oxidation product first prepared by H . v. Pechmann and W. Bauer by reaction of 2,3-butanedione bis(benzoy1hydra- zone) ( I ) [11 with potassium hexacyanoferratefrrr) wasformulat- ed [21 as 2,3-dibenzoyl-5,6-dimethyl-2,3-diliydrotetraazine (2).

Catalyst wt.- % calc. w. r. t. ( I )

1 K2CO3 0.5 KOCOCH, 1 KOCOCH, 1 KOCOCHi 1 K2C03 1 KzCO, 1 K2CO3 1 K2C03

Temp. f "C)

210-250 180-205 190-220 156-1 86 186-226 200-242 240-260 200-2 14

17 > 90 41 89 31 65 66 22

[a ] Not optimized.

A prerequisite for this reaction is that a t least one of the groups R1-R" is a second order substituent; preparatively useful yields, however, are obtainable only from symmetri- cally substituted, particularly p,p'-disubstituted, diphenyl carbonates. Numerous other alkali metal compounds may be used as catalysts (in amounts of 0.5-2 wt.-%) instead of potassium carbonate.

4,4'-Dinitrodiphenyl ether (2), Rl=R2=N02, R3=R4=H [21

4,4'-Dinitrodiphenyl carbonate (1 000 g) (crude phosgenation product, m.p. 140 "C) [3J is melted (silicone oil bath) in a 2 1 three-necked flask fitted with stirrer, internal thermometer, and a delivery tube connected via a bubble counter. Potas- sium acetate (5 g) is added slowly, with stirring, to the melt a t a temperature of 150 'C. Decarboxylation (18@-205 'C, bath temperature 190-215 "C) is complete after 4-5 hours. The temperature of the mixture is then allowed to drop to 150 'C, and, after the apparatus has been fitted with a reflux condenser, toluene (580 g) is added slowly. The solution is filtered hot from insoluble residue (ca. 8 g). The filtrate is then cooled and the 4,4'-dinitrodiphenyl ether which crys- tallizes out is recovered by filtration, washed with a little methanol, and finally dried in a vacuum (yield 749 g (88 %),

H3C ,N-NH-CO-C,H,

H3C x N-NH-CO-CBH, H3C

The 1H-NMR spectra (in CDC13) of the oxidation product at 60 and 220 MHz 131 show that the compound does not have a symmetrical structure. Two methyl-group signals appear in the 60 MHz spectrum at 2.23 ppm and 2.36 ppm in addition to a multiplet (signal width ca. 20 Hz) centered at 8.1 ppm which is due to the protons of both aromatic rings that are ortho to the carbonyl groups. i n the 220 MHz spectrum the multiplet is resolved into two pseudo doublets at 8.116 ppm and 8.236 ppm ( J = 7.8 to 8.0 Hz). The remaining six aro- matic protons absorb between 7.4 and 7.8 ppm. On the basis of these findings, therefore, we suggest that the oxidation product has the structure of a mesoionic triazole (3),

(3), R = CO-C6H5

which is in agreement with the chemical properties of this compound. The ready hydrolytic and thermal loss of a benzoyl group is now understandable since the compound is being considered as an azolider41. As is already known, com- pound (3) affords l-(dibenzoylamin0)-4,5-dimethyl-1,2,3- triazole (4 ) 151 when heated and l-benzoylamino-1,2,3-tri- azole ( 5 ) when treated with hydrochloric acid. Hydrolysis of (3) with concentrated hydrochloric acid at higher tempera- tures leads to formation of the free 1-amino-4,s-dimethyl- 1,2,3-triazole ( 6 ) [21. We have obtained 4-chlorobenzoic an- hydride as reaction product by recrystallizing compound (7)

Angew. Chem. internat. Edit. 1 Vol. 9 (1970) 1 No. I 67