June 20, 1959
COMMUNICATIONS TO THE EDITOR
3165
pletion of the reduction of azobenzene to hydrazobenzene takes thirty minutes a t room temperature. Similar to azobenzene itself, substituted derivatives such as 4-fluoroazobenzene, 4,4’-difluoroazobenzene, 4,4‘-dichloroazobenzene, 3-trifluoromethylazobenzene and 4-fluoro-3’-trifluoromethylazobenzene were reduced by the catalytic LAH reduction to the corresponding hydrazobenzenes with 90% yields or better. It is possible to use instead of the metal halides other metal salts (such as nitrates, carbonates, sulfates, acetates) or metal oxides. However, metal oxides as Moos, V206, WOa, TiO2, Cr03, CuO and NiO are considerably less active catalysts than the corresponding metal halides and the completion of the reduction of 0.1 FRICK LABORATORY mole of azobenzene in ethereal solution a t room PRIXCETON UNIVERSITY PAULv o s R. SCHLEYERtemperature takes from 2-6 hr. PRIXCETON, XEW JERSEY DEPARTMEST OF CHEMISTRY Nitrobenzenes are reduced by the catalytic ROBERT WEST UNIVERSITYOF WISCOXSIX LAH reduction in ether solution directly and with MADISOS,WISCONSIS 90% yield or better to hydrazobenzenes. AS the RECEIVEDMAY1, 1969 reduction of nitrobenzenes by LAH to the corresponding azobenzenes in itself is quite vigorous, CATALYTIC EFFECT OF METAL HALIDES AND it is advantageous to add the ethereal solution of OXIDES ON T H E LITHIUM ALUMINUM HYDRIDE the azobenzene first to the ethereal LAH solution REDUCTION O F AZOBENZENES AND NITROBENand then the catalyst. ZENES T O HYDRAZOBENZENES On addition of an ethereal solution or suspension Sir : of the catalytic halide to the ethereal LAH s o h The interaction of metal halides and oxides tion generally a dark colour and some precipitate with lithium aluminum hydride (LAH) is known.’ is formed. The color of the solution is due to the A reduction method based on the use of mixed formed intermediate, unstable but highly active hydrides prepared from equimolar quantities of mixed metal hydride. The precipitate is finely LAH and aluminum halides also was developed.2 dispersed metal from the decomposition of the metal Different metal halides were used as additives in hydride. Similarly using metal oxides as catalyst ether cleavage reactions with LAH.a a marked change of color is observed. The presLAH alone can reduce azobenzenes to hydrazo- ence of metal-hydrogen bonds in the intermediate benzenes only with considerable d i f f i c ~ l t y . ~Large metal compounds has been proved. excess of the hydride, higher temperatures and proIt is interesting to note that aluminum halides longed reaction times (some days) are needed. are quite inactive as catalysts in the above menNitrobenzenes were known to be reduced by LAH tioned reduction. only to the corresponding azobenzenes, a reaction CONTRIBUTIOX KO.18 which also is used for the qualitative analytical EXPLORATORY RESEARCH LABORATORY G. A. OLAH Dovv CHEMICAL OF CANADA, LIMITED determination of nitro group^.^ It has now been observed that the addition of SARNIA,ONTARIO,CANADA RECEIVEDAPRIL3, 1959 catalytic amounts of certain metal halides such as MoC15, TiC14, TiC13, TiC12, vc13, WC16, CrCI3, FeCl3, Cu2C12, CoBr2, SnC14, CdI2, CbC15, BiC13, FLUORINATION REACTIONS O F SbC16 PbC12 has a very marked effect on the SULFUR TETRAFLUORIDE reduction of azobenzenes with LAH to hydrazo- Sir: benzenes. In ethereal solution and a t room temIn an investigation of the little-known chemistry perature 0.1 mole of azobenzene was reduced of sulfur tetrafluoride (SF4),1 we have found this quantitatively in the presence of less than 0.001 compound to be an unusual fluorinating agent, mole of the above mentioned metal halide catalysts especially for the unique replacement of carbonyl to hydrazobenzene by LAH. The reductions are oxygen with fluorine, The reaction is effective very fast and generally are completed in less than ten /C=O \ + SFI +>CF2 + SOFz minutes. Some less active metal halide catalysts are ZrC4, TaC15 and PtC12. With them the com-
prevent optimum interaction with the adjacent hydroxyl group. The same objections hold for the results with p-haloethanols (Table I). Completely unambiguous data confirming the same order, I > Br > C1 > F, is provided by intermolecular studies (Table 11). Data for analogous oxygen and nitrogen compounds have been included for comparison. Clearly, electronegativity does not play a dominant role. I n addition, results for similar derivatives of the second and third row elements, sulfur, phosphorus and arsenic, have been added to the tables where available. It is particularly noteworthy that, as proton acceptors, they rival their first row congeners despite their larger covalent radii.
(1) N. G. Gaylord, “Reduction with Complex Metal Hydrides,” Interscience Publishers, Inc., New York, N. Y.,1956, pp. 41-60. 77,2644 (1955); R. F.Nystrom ( 2 ) R. F.Nystrom, THISJOURNAL, and C. R. Berger, ibid., 80,2898 (1958); R. F.Nystrom, ibid., 81, 610 (1959). (3) P. Karrer and 0. Rutter, Helv. Chim. Acta, 38, 812 (1950); V. L. Tweede and M. Cuscurida, THISJOURNAL, 79, 5463 (1957). (4) R. F. Nystrom and W .G. Brown. ibid., 70,3738 (1948); F. Bohlmann, Chem. Ber., 85, 390 (1952); G.A. Olah, paper presented a t the Organic Chemistry Symposium of the Chemical Institute of Canada, December 8, 1958, Ottawa (Ontario). ( 5 ) H. Gilman and T. N. Goreau. THISJOURNAL, 73, 2939 (1951).
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