PREPARATION OF AROMATIC FLUORINE COMPOUNDS
Dec. 5, 1930
The melting point was not depressed when mixed with an authentic sample recently prepared in this Laboratory by a Sandmeyer reaction upon 3-fluor0-4-nitroaniline.~~ 2,3,5,6-Tetrachloro-4-fluoronitrobenzene(XV).-A mixture of 2,3,5,6-tetrachloro-1 ,Cdinitrobenzene (3.1 g.), desiccated K F (5.8 g.) and D M F (18 ml.) a t 100-140" for 30 minutes by procedure B-1 gave from ethanol 1 g, or 35% yield of XV, m.p. 80-81'. Anal. Calcd. for C&&FNOZ: c , 25.82; c1, 50.88; N, 5.02. Found: C,25.53; C1,51.10; N,4.89. Alkali Fluoride Comparisons.-The effectiveness of the alkali fluorides in D M F was tested qualitatively. A mixture of 0.04 mole of alkali fluoride and 2 g. (0.01 mole) of 2,4-dinitrochlorobenzenein 4 ml. of D M F was stirred a t 140-150" for 15-30 minutes when a reaction was apparent and for 1 hr. when halogen interchange was questionable. After dilution of the reaction mixtures in water, the extent of exchange was judged by an aqueous chloride ion test with silver nitrate. The lithium and sodium fluoride experiments gave only traces of chloride, whereas rubidium and cesium fluorides gave heavy silver chlorid: precipitates. The exchange properties of the latter two are comparable to those of potassium fluoride. A mixture of NaF (10.5 g.), KCl (9.3 g.) and 2,4-dinitrochlorobenzene (25 9.) in nitrobenzene (30 ml.) was heated a t 18,5205O for 18 hr. The aryl chloride "as recovered, thus indicating no KC1 influence upon NaF reactivity. A mixture of K F (7.25 g.), NaF (5.25 9.) and 2,4-dinitrochlorobenzene (25 9.) in nitrobenzene (30 ml.) was heated at 200-205' for 2 hr. Estimated yield of fluor0 analog was 17.9 g., or 77%. Sodium and potassium fluoride mixtures containing less than one mole of potassium flc.oride per mole of aryl chloride gave conversions to the extent expected by the reaction of the potassium fluoride alone. Inasmuch as lithium and sodium fluorides fail to give the aryl chloride-metallic fluoride exchange, the reverse ex(28) H. H . Hodgson and D . E. Nicholson, J . Chem. Soc.,7G6 (1941). reported erroneously the melting points of the amire and acetyl derivative as 153 and 13S0, respectively. The data obtained in this Laboratory are m.p. 161° (amine) and 173-174' (acel.ylamino).
6037
change, aryl fluoridemetallic chloride, was examined. A mixture of 2,4-dinitrofluorobenzene (17.2 g . ) , LiCl (10.6 8.) in nitrobenzene (30 ml.) at 200-210" for 30 minutes showed no reaction; 97% of the aryl fluoride was recovered. Sodium chloride gave a similar result. Miscellaneous Compounds. 2,2 '-Di-( trifluoromethyld4,4'-dmitrodiphenyl Ether.-This ether, m.p. 115-116 , was obtained by recrystallization from ethanol of the distillation residue from 11. Anal. Calcd. for Cl4H6FsNzO~:C, 42.44; H, 1.53; N, 7.07. Found: C, 42.70; H , 1.47; N, 7.16. Stannous chloride reduction of the preceding ether gave 2,2 '-di-( trifluoromethyl)-4,4'-diaminodiphenyl ether, m .p. 123-124'. Anal. Calcd. for c14HloFeNzO: C, 50.00; H, 3.00; N, 8.33. Found: C, 50.03; H,3.00; N,8.31. 2,2 '-Dinitro-4,4'-di-( trifluoromethy1)-diphenyl Ether .This ether, m.p. 107-108', was obtained by recrystallization from ethanol of the distillation residue from 111. I t melts a t 114-115" when recrystallized rapidly. Anal. Calcd. for C14Hd?~Nz05:c, 42.44; €1, 1.53; N, 7.07. Found: C, 42.48; H, 1.50; N, 7.21. Stannous chloride reduction gave the corresponding 2,2'diamino-4,4'-di-( trifluoromethy1)-diphenyl ether, m .p. 79.580". Anal. Calcd. for ClaHloFeNzO: C, 50.00; H , 3.00; N, 8.33. Found: C, 50.06; H , 3.26; N, 8.29. 2-Fluor0-5-trifluorornethylaniline.~~-Aniron reduction of I11 gave an 86% yield of the corresponding aniline, 2fluoro-5-trifluoromethylaniline, b.p. 81' (20 mm.), n z o D 1.4608. Anal. Calcd. for C T H ~ F ~ N C,: 46.94; H, 2.81; N, 7.82. Found: C, 46.86; H, 2.59; N, 7.96. The acetyl derivative, m.p. 121.5-122", did not depress the melting point of material prepared via the nitration of 4fluorobenzotrifluoride Anal. Calcd. for C ~ H I F ~ N ON,: 6.33. Found: N, 6.35. ILLINOIS URBANA,
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[CONTRIBUTION FROM SCIENTIFIC DEPART ME^ T, ISRAEL MINISTRYOF DEFENCE, AND DEPARTMENT OF ORGANIC CHEMISTRY, HEBREWUNIVERSITY]
A New Method for the Preparation of Aromatic Fluorine Compounds BY ERNEST If. BERGMANN, S. BERKOVIC AND R. IKAN RECEIVED JUNE 29, 1956 Aryl fluorides have been prepared by the reaction of diazonium fluoroborates with copper powder or cuprous chloride i n dry or aqueous acetone. This method avoids the difficulties of thermal decomposition of diazonium fluoroborates.
In a recent communication' it has been reported that certain acylamino-substituted diazonium fluoroborates are soluble in water, everi in the presence of an excess of the fluoroborate ion, but can nevertheless be converted into the corresponding aryl fluorides by the addition of copper powder to their aqueous solution. This observation suggested that a radical mechanism may be operative in the synthesis of aryl fluorides from diazonium fluoroborates, of the type assumed by IVaters in the Gattermann reaction. One should, then, ex293
(1) E. D. Bergmann and M. Bentov, J . Org. Chem., 19, 1594 (1954). (2) W. A. Waters, J . Chem. Soc., 26fi (1942). (3) For a survey of the theories of the Schiemann reaction. see A. Roe, "Organic Reactions," Vol. V, John Wiley and Sons, Inc., New York, N. Y.,1949, p. 193; see also H . A. Hodgson, S t . Birtwell and J. Walker, J . Chem. Soc., 770 (1941). I t is significant that the application of the Schiemann reaction to optically active 6,6'-diamino2,2'-dimethylbiphenyl is accompanied by racemization, whilst the transformation of the amino-groups into iodine atoms gives an optically active product.
pect that the conditions favorable for radical decomposition of diazonium salts4 would permit the preparation of aryl fluorides. This would mean the circumvention of the experimental difficulties attending the thermal decomposition of diazonium fluoroborates, especially in the case of the nitrosubstituted compound^.^ It has, indeed, been found that diazonium fluoroborates decompose to give aryl fluorides when their solutions in acetone or aqueous acetone are stirred with small amounts of copper powder or-preferably-cuprous chloride a t room temperature. It is possible by this method to decompose batches (4) Cf.,e.g., the Meerwein reaction, in which diazonium salts react with Q,P-unsaturated acids in arpeous acetone and in the presence of cupric ions. See F. Bergmann and J. Weizmann, 1. Org. Chem., 9 , 415 (1944); D . H . Hey and W. A. Waters, Chem. Revs., 21, 169 (1937); J. K. Kochi, THIS JOURNAL, 77, 5090, V, 5374 (1955); 78, 1226 (1956): S. C. Dickerman, K. Heiss and A. K . Ingberman, J . Org. Chcm., 21, 380 (1956). (5) See A . Roe, ref. 3.
'r.4uL.E I ---Diazonium liuoroborates----. Dec. iwint, Yield, Lit. yield,
I
Amine
l-I'lie~i y leiiediaiiii~ie'' m-PlienylenediaIIiirie" 0-Xitraiiiline nt- S i t r d l i n c /)-Nitratiiliiic o-Aminobenzoic acid p-Aminobenzoic acid p- Amiiioacetophciione 13ciizidinc /~-Arriii~opl~ciiylaeetie acid p-Ainiiiociiiiiaiiiic acid o-h-aplitli ylaiiiiiie $-ZJnpli thylainiiie
'ro
%
95-98 96 06 97 98 51 50 88-90 90
78-82 88 63-92 79-99 80-100 0-3; 31; 80'
oc. 180 "00 135 165 156 126 1-10 135-135 140 ... 100"' 110 115 1'35-2cro ltiO--liO 120
Yield, %5
38 28 52
21-23 31 63-78 34-54 32-58 7 0 ; 401
8!J
(TBO)
8 2 . 2 (760)' 115 (26)" 34 ( 2 ) , 2O.j (7W)' 47 26 61 lli--l1(1 (froin 1LOj 48 180-181 (froin 11.0) 43 no 21 7u-8 (10)D 0 64-92 17% HO (purified by ste,iiii distil, i 80 (1 0 1 6 %( 2 ) ; 9 k 0 h s7 iti 8Y'V' 4x -I 1 209 (fruiii 1 3 ~ ) '32 CiS--!J 1 -1- u 21%( i 6 0 j k 77--'3O fj2-.97 93 (10-97 4 59 (puriiicd by s t c m i di5tii. ! l-Aiiiiiic3aiitliraqtiiilrJiie SY ... 7% 1 Pi-128 (purified b y subl.) ... ~ - ~ ~ i i i i i i ~ ~ ~ ~ i ~ I i r ~ t9~ ~ ~ ~ i e 5 ~ t i i ~ i (iX 41 8(j 202 (purified by subl.) > 2-Aiiiinofluorciic 77 76 98 (from bz) 60 p - Aiiiiiiupheiiul . . 71 ... 189 ( 7 6 0 ) ; 36" o.-Aiiiiiiopliciiol 40 154 (760 IUIII.) ... ... ... 8%1 /~-Aiiiii~oacetanilidc ti 5 Y-l llG-11S 148 (from 40% alcohol) 55 Yield, calculated 011 :uiiiiie, b Tctrazoiiiuiii dcrivative. c dig 1.16X). d diE 1.3B73, ~ 1 8 u1.5188, X I < caled. 31.S5, fouud 53.50. e 1.3250, zi8u 1.5562; MI? calcd. 31.85, fouiid 33.40. J It is intcrestiiig t o note that according to J. 1'. J. Dippy atid 1'. K. Williams ( J . Chcnt. SOC.,1466 (1934)) p-fluorobenzoic acid eaiiiiot be made by the Schiemanii reaction. J. C. Gruritori and H. Suschitzky ( J . Chenz. Soc., 1035 (1955)), however, succeeded with this preparation. From o-aminobenzoic acid, the diazoiiiuni fluoroborate was obtained in 37L;d yield, the fluoroacid in 77, yield (calcd. on the amine). 111the case of tlic nz-isoiner, tlie yields werc 31 and 557,, respectively. 0 dzg 1.1385, xZ5u1.5080; M R calcd. 35.50,found 36.10. '' Dippy aiid n'illiains (ref.f) obtained in the diazotizatiori of p-uiiiiiiopliciiylacetic acid a brown, amorphous product. They prci)arcd the p-fluorol)heiiylacetic acid by an indirect route and gave m.p.86". Ethyl ester. ! S e e cxperirnental. d:: Not isolatcd. 1.1340, n% 1.5938; X I
