March 1947
INDUSTRIAL AND ENGINEERING CHEMISTRY
liuoroethenes. Again, dehalogenation experiments invariably yielded only dehydrofluorinati.on products. This ease of dehydrofluorination could hardly be expected if the fluorine atoms involved were not activated by being on one of the carbon atoms of the ether linkage. The action of ethanolic caustic solution on the phenoxychlorodifluoroethane to yield a product containing chlorine but devoid of fluorine further indicates the 1,l-difluoroether structure. Thus the aryloxychlorodifluoroethanes are assumed to be aryloxy-2-chloro-l, 1-difluoroethanes. PROOF OF STRUCTURE OF .%RYLOXY-2-CHLORO-l,1,3,3,3-PENTAFI.LOROPROP.ASES. Starting with 2-chloro-1,1,1,3,3,3-hexafluoropropane and metallic aryloxidee, the only probable ether-retahing chlorine is a 1,l-difluoroet,her. The ease of dehydrofluorination of the ethers substantiates this structure, since it must involve :I reactive fluorine atom, one of which is attached to the aliphatic carbon of the ether linkage. In its behavior with sodiuin aryloxides, 2-chloro-1,1,1,3,3,3hexafluoropropane resemble both 1,2-dichloro- and 1,2,2-trichloro-1,l-difluoroethane. T h e halogen replaced is in all cases attached to a carbon substituted with fluorine atoms.
+ CFaCHClCF3 -+ N a F + CsH50CFKHClCF3 + CF*ClCHKl+ S a C l + C6HsOCF?CH?Cl + CF&lCHCll+ S a C l + C6HbOCF2CHCL
( '6H50Xa
( '8H:OSa
C&Oi\'a
(4) (5) (6)
General concepts of the chemistry of the organic chlorofluorides indicate that the chlorine atom on carbon atoms holding no
415
fluorine atom5 should be replaceable. However, this group apparently resists attack and, in fact, seems to have an activating effect on the adjacent fluorinated grouping. 4CKNOW LEDGMEhT
Acknowledgment is gratefully made t o the Ethyl Corporation for sponsoring the research fellowship which supported this work. LITERATURE CITED
Gowland, T. B. (to Imperial Chern. Industries). B r i t . Patent 523,449 (July 15, 1940). Henne, A. L., and Hubbard, D. X I . , J . A m . Chem. Soc., 58, 404-6 (1936).
Henne, A. L., and Ladd, E. C., Ibid., 58,402-3 (1936). Henne, A. L.. Whaley, A. M.,and Stevenson, J. K., Ibid., 63, 3478-9 (1941).
Henne, .4.L., and Wiest, E. G . , Ibid., 62, 2051-2 (1940). Locke, E. G., Brode, W. R., and Henne, A. L., I bid., 56, 1726-8 (1934).
McBee, E. T., et al., unpublished data. Miller, W. T., J . Am. C h m , Soc., 62, 993-5 (1940). Swarts, F., Bull. a d . r o y . BJg., [3] 37, 357-83(1SR9),
[71
1901, 383-414. Zbid., 131 35, 3 7 5 4 2 0 (1898); 1913, 241-78. Ibid., 1911, 663-89. Swarts, F., Bull. aoc. chim., [ l l ] 25, 103-7 (1919). Swarts, F., Mem. Couronas acad. roy. Bele., 61 (1901). ABSTRACTBD i n part from
a doctoral thesia aubmitted b y R. 0. Bolt t o the faculty of Purdue University.
PERFLUORO DIBASIC ACIDS AND DfRlVATlVES E. T. McBee, Park A. Wiseman', and G. B. Baehrnan PURDUE UNIVERSlTY AND PURDUE RESEARCH FOUNDATION, LAFAYE'ITE, IND.
PERCHLOROBENZENE and perchlorocyclopentadiene have been fluorinated with antimony pentafluoride to produce 1,2-dichloroperfluorocycloallrenes. The latter have been oxidized to perfluoroadipic and perfluoroglutaric acids with aqueous permanganate. These perfluorodibasic acids have been converted to esters, diamides, dinitriles, and diamines. Physical constants of new compounds are reported. 2,2,3,3,4,4,5,5-Octafluoropentanoicacid has been produced from perfluoroadipic acid dihydrate.
T
HIS paper describes the synthesis and properties of certain perfluoro dibasic acids and their derivatives which were desirable as intermediates in the preparation of synthetic resins and fibers. Until recently no fluorinated aliphatic dibasic acids had iwixn reported. Perfluoroglutaric acid has been synthesized from ~,erehloroc~-elopentene(octachlorocyclopentene) by fluorination Lvith antimony trifluoride and antimony dichlorotrifluoride and oxidation of the resultantl, 2-dichloroperfluorocyclopentene (2). l'erfluorosuccinic acid has been prepared by oxidation of 1,2(lichloroperfluorocyclobutene(4). Reported data on perfluoroglutaric acid substantiate results obtained in this laboratory, following the preparation of perfluoroglutaric acid by the procedure described here. Perfluoroadipic acid and derivatives, as \vel1 as some derivatives of perfluoroglutaric acid, are new compounds. Antimony pentafluoride, used in the fluorination st,ep of the present syntheses, has been known for some time. Ruff ( 3 ) prepared it from antimony pentachloride and hydrogen fluoride. and used this liquid to convert carbon tetrachloride to trichloroIluoromethane. Antimony pentafluoride may also be prepared 1
Present address, Firestone Tire & Rubber Company. Akron, Ohio.
from antimony trifluoride and elemental fluorine, but the firstmentioned method is more desirable; the use of elemental fluorine, when it is not an absolute necessity, is economically impractical. FLUORINATION
I n the fluorination of perchlorocyclopentadiene (hexachlorocyclopentadiene) and perohlorobenzene (hexachlorobenaene), antimony pentafluoride waa found to add fluorine to double bonds as well as to replace chlorine with fluorine. Reaction temperatures were maintained between room temperature and about 125' C. during themajor part of thereaction, the final temperatures being elevated t o distill reaction products. Less volatile products were recovered from solid antimony salts by steam distillation. Thc desired 1,2-dich~oroperfluorocyc~oa~kenes were obtained by rectifying the mixture of reaction products in yields up to 60%. The following equations are representative of the fluorination with antimony pentafluoride:
c1 Cl/'.JC!
+ SbFb
C1C ,l
c1 Clz C
c1c
CCl II c1c-CC1
I/
+
SbF'
+
-
$:: Fz
F,&l F G1 A C I 1
(a,
Perchlorobenzene and perchlorocyclopentadiene were fluorinated with antimony pentafluoride in a 2-liter three-neck &k providc.d with a mercury-seal stirrer, thermometer, and reflux
-
INDUSTRIAL AND ENGINEERING CHEMISTRY
416
condenser. The reflux condenser was conneated in scries ir-ith air-cooled and dry ice-cooled receivers. Perchlorobenzene (300 grams) and antimony pentafluoride (1.0 kg.) were mixed in the reaction flasli a t room temperature and heated a t loo1 C. for 2 liours. The reflux condenser was then arranged for cii.gillation. and the temperature vas raised slowly to 200" C. and maintained at, this level as long as product distilled. Further purifiication was effected by steam distillation, followed by n-ashing thoroughly with aqueous hydrochloric acid (17%) and water to removc antimony salts, drying, and rectifying in a 4-foot hclix-p:wketi column. The fraction boiling a t 111-113° C. Tvas essentially 1,2dicliloroperfluorocyclohexene, yield 44y0,. 1,2-Dichloroperfluorocyclopentene was prepared in a similar manner from perchlorocyclopentadiene and antimony pentafluoride. The fraction boiling a t 88-89" C. was essent,ially 1,2dichloroperfluorocyclopentene,yield 50 %. OXIDATION
After isolation of the 1,2-dichloroperfluorocycloalkene,oxidation of the double bond with aqueous potassium perman,canate was productive of the desired perfluorodicarboxylic acid in yields up to 90%:
\CF,-COOH
c
CFz-COOE t
(6)
Ah1.MONOLYSIS
Amnionolysis of diesters a t ice temperature was productive of diamides in quantitative yields, and subsequent, dehydration of the diamides with phosphorus pentoxide resulted in yields of dinitriles up to 70%. This reaction is illustrated tiy equations for the preparation of perfluoroadipic acid derivatives and by the examples Tvhich folloiv.
Fz
P 2 n
E ~ O E ~CFz-CFy-C"SIII +
CFz--CF,-COOEt
I
CFz-CFz-COOEt
+"I-
CF2-CF,-COKHz
i
As an example of procedure employed for oxidation, 1,2-dichloroperfluorocyclohexene (295 grams) and water (300 ml.) were poured into a 3-liter three-neck flask provided Tvith a refluv condenser. The mixture was heated with stirring to reflux, and potassium permanganate (320 grams) was added gradually. As oxidation proceeded, chlorine was evolved from the top of the condenser and manganese dioxide precipitated. After 24 hours of heating, the oxidation mixture was steam-distilled to recover unreacted 1,3-dichloroperfluorocyclohexene(148 grams). The distillation residue was filtered by suction to remove insoluble manganese dioxide, decolorized with sodium bisulfite, and evaporated under reduced pressure to 200 ml. This solution was acidified by adding concentrated sulfuric acid (100 ml.) slowly, and the resultant mixture was extracted exhaustively with diethyl ether. Removal of the ether left 134 grams (83% yield) of vhite, solid, nonhygroscopic perfluoroadipic acid dihydrate. The neutralization equivalent was found to be 161.6 as compared with the theoretical value of 163. Perfluoroglutaric acid was prepared in a similar manner from 1,2-dichloroperfluorocyclopentene, yield 90%. Hoivever, no unreacted organic starting material was recovered from the reaction mixture. ESTERIFICATION
Esterification was accomplished by refluxing the acid and ethanol in the presence of a catalytic amount of hydrochloric acid. CFz-CF2-COOH CFz-CFS-COOH
CF2,
These reactions were conducted in a 1-liter round-lIotto[n flask provided with a reflux condenser. Ethanol (500 ml.), perfluoroadipic acid dihydrate (100 grams), and concentrated hydrochloric acid (1 ml.) were mixed and refluxed for about 16 hour.?. Excess ethanol \\-'as removed by distillation, and a second 500-1111, portion of ethanol as added and distilled slowly from the reaction flask. Distillation \vas continued a t atmosphcric pressure, 90 granii of a colorless liquid boiling betn-een 215' and 219' C;, being collected. This product lvas dried and rectified under v:tcuum in a 3-foot helis-packed Column. Seventy-six grams (0.22 Inole) of diethyl perfluoroadipate was collected: boiling point a t 2.5 mm., 70-71" C.; n2j 1.3541; dig 1.4026. The yield of purified ester n-as 72y0,. This ester was found to contain 46.7w0 fluorine and to have a saponification equivalent of 169 as compared with theoretical values of 44.0 and 173. Perfluoroglutaric acid was converted to the diethyl ester in a manner similar to that described for the esterification of perfluoioadipic acid. The yield of diethyl ester (boiling point a t 3 mm., 76" C.; n2: 1.3646; d i g 1.3444) was 81%. This ester was found to contain 38.75, fluorine (theory, 38.57,).
Fz
~
/CFz-COOEt
+ EtOH HCl
CFz-COOH
CF,
Vol. 39, No. 3
HC1 +EtOH
-+
CFz-CFZ-COOEt
1
CF2-CFz-COOEt
(5)
CFZ-CFz-COXHz
~
CF,--CF,-COSIIz
(7)
CF2--CFy--CS
+ pzos + CFy-CFl-CS
(8)
Diethyl perfluoroadipate (107 grams, 0.67 mole) was added to anhydrous diethyl ether (900 grams) in a 2-liter three-neck flask provided with a reflux condenser, thermometer, and gas inlet tube. The mixture was cooled, and anhydrous ammonia bubbled into the solution a t 0-10" C. until ammonia was no longer absorbed. The reaction mixture was then narmed slowly to room temperature, and the precipitated diamide removed by filtration. The filtrate mas distilled to dryness and the residue combined Lvith the precipitate. After washing with diethyl ether and drying, the diamide weighed 161 grams (0.56 mole), yield 98%. The diamide of perfluoroadipic acid, after recrystallization from benzene, is a white solid melting a t 237" C. (uncorrected). Perfluoroglutaramide was prepared similarly in 96% yield from the diethyl ester of perfluoroglutaric acid. DEHYDRATION
Perfluoroadipamide (60 grams, 0.17 mole) was mixed intimately with phosphorus pentoxide (225 grams, 1.58 moles), and the resulting mixture was heated v,-ith a Bunsen burner in a I-liter distilling flask as long as product distilled. The distillate was collected in an ice-cooled receiver. The products obtained from two dehydrations were combined and redistilled. Perfluoroadiponitrile (56 grams, 0.22 mole), boiling a t 61-63' C. (n2: 1.2770, d:' 1.4304), mas obtained in a yield of 64%. This material contained 61.2% fluorine and had a molecular weight of 249 as compared with theoretical values of 60.5 and 252. Perfluoroglutaronitrile, boiling a t 37-38' C., was prepared similarly from perfluoroglutaramide. I n addition t o the perfluoroglutaronitrile, a second compound, boiling at 155-159' C.,
INDUSTRIAL AND ENGINEERING CHEMISTRY
March 1947
417
Upon heating.perfluoroadipic acid hydrate in the presence of catalytic amounts of crystalline barium hydroxide, 2,2,3,3,4,4,5,5-octafluoropentanoic acid was unexpectedly obtained. Following the usual procedure for cyclization of a dibasic acid to a cyclic ketone containing one less carbon atom, decarboxylation but no cycliziLtion uccurrcd. This strong organic acid is a colorless hygroscopic liquid, boiling a t 155-160" C. and having an odor resembling that of pentanoic acid. I t readily forms an ethyl ester (boiling a t 140-142' C.) which possesses a pleasant fruity odor. Perfiuoroadipic acid dihydrate (40 gramsj was mixed with crystalline barium hydroxide (4 grams) in a 125-m1.distilling flask. The resultant mixture mas heated slowly to about 280" C., and this temperature maintained as long as material distilled. The product byas poured into distilled water (100 ml.); the soluHYDROGENATION tion was neutralized with dilute sodium hydroxide and extracted Reductive acetylation of the dinitriles produced diacetylwith ethyl ether. The ether extract gave no test for a ketone. amines, vihich were then converted to diamines, usually through The aqueous solution was, then evaporated t'o dryness, concenthe hydrochloride or sulfate salts. trated sulfuric acid (100ml.) was added to the saltlike residue, and the mixture was distilled. About 13 grams of a compound boiling between 155' and 160" C. \vas CF*-CF?-CS ptO CF,-CFL-CHzNHCOCH, HZ (CH3CO'I:O -+ , (9) collected. This material, believed to be 2,2,3,3,4,1 CF*-CF,-CHzSHCOCH3 4.5,5-octafluoropentanoic acid, was a strong waterCFz-CF*-CX soluble acid. CF?-CF?-CH?THCOCH, E t O E t CF>-CF,-CH2SHz 2,2,3,3,4,4,5,5-0ctafluoropentanoic acid (15 +SaOHI (lo) grams, 0.061 mole), absolute ethanol (100 ml.), CF,-CF?-CH,SHCOCH3 CFp-CF,-CHzNHZ and concentrated hvdrochloric acid (1 ml.) were refluxed overnight. T h e resultant solution was disThe production of diamines through acetyl derivatives is illustilled, and 10 grams (0.036mole) of an ethyl ester boiling between trated as follons: Perfluoroadiponitrile (50 grams), platinum 140"and 142" C. was collected. This ester was a stable, colorless oxide catalyst 12 grams), acetic anhydride (41 grams), and anhyliquid with a pleasant, sweet odor (n2: 1.3261, dig 1.4528,yield drous ethyl ether (100 ml.) viere mixed in a 500-ml. Parr bomb. 60%) and contained 57.0% fluorine as compared with a calcuHydrogen was introduced until a pressure of 1000 pounds per lated value of 5 5 . 5 . square inch was attained. The autoclave was sealed and heated ACKNOWLEDGMENT slowly with shaking. \Then the temperature reached 40-50° C., the pressure dropped to approximately 100 pounds per square The authors wish to acknowledge the financial assistance of the inch in a few minutes, an indication that hydrogenation had ocAmerican Viscose Corporation, which made this work possible. curred. Hydrogen \\-as added until the pressure reached 1000 They also wish to acknowledge the assistance of G. Hueschen pounds per square inch, and the reaction mixture was allowed t o in the preparation of the manuscript. cool overnight during which time there was no appreciable clecrease in pressure. The reaction product was poured into aceLITERATURE CITED tone, and the resulting mixture filtered t o remove the catalyst. (1) Gilman. H., and Jones, R. G., J . Am. Chem. SOC.,65, 1458-60 The filtrate vias distilled on a steam cone, leaving a yellow-white (19431. solid which was essentially the diacetyl derivative of 2>2,3,3,4,4,5)-(2) Henne, A. L., and Zimmershied, W. J., Zbid., 67, 1235-7 (1945). 5-octafluoro-1,6-hexanediamine.This material contained 45.3% (3) Ruff, O., Ber., 39, 4310-27 (1906). (4) Scherer, Microfilms of I. G. Farbenindustrie 8.-G., Frankfort fluorine (theory, 44.27,). a. M. Hochst, "Fluor0 Derivatives of Propane and Butane", The diacetyl derivative of 2,2,3,3,4,4,5,5-octafluoro-1,6-hexane1943 (available in this country, 1945); Henne et al., J . Am. diamine was rcfluxed overnight with 200 ml. of 25y0 sulfuric acid, Chem. Soc., 69, 281 (1947). and the resulting solution filtered while hot. On cooling, a gelatinous solid, believed to be the monosulfate of the diamine, sepaPREBEKTED before t h e Symposium on Fluorine Chemistry as paper 76, Division of Industrial and Engineering Chemistry, 110th Meeting of rated from the filtrate. A small portion of the product mas reAM~RICA CHEMICAL N SOCIETY, Chicago, Ill. crystallized from water; this material contained 41.5yofluorine (theory, 42.4%). The crude sulfate was mixed with 100 ml. of mater, and a sufficient quantity of sodium hydroxide solution was added to give Fluorine Articles in Analytical Chemistry a slightly basic solution. This solution was extracted exhaustively with diethyl ether, and the ether extract distilled to give a The March issue of Analytical Chemistry will include t h e followresidue (36 grams) of a dark brown oil. This product,, upon ing six papers on fluorine or its compounds : vacuum distillation, yielded 20.5 grams of \\-bite, crystalline Determination of Hydrogen in Fluorine-Containing Halohydrocar2,2,3,3,4,4,5,5-octafluoro-1,6-hexanediamine (melting point, 44bons. Miller, Hunt, Hass, and McBee (page 146) 45" C.; boiling point a t 5.5 mm., 65-66' C.) which contained Decomposition and Analysis of Organic Compounds Containing 59.2y0 fluorine (theory 58.5%). The yield of distilled product Fluorine and Other Halogens. Miller, Hunt, and McBee (page 148) was 39.87,. Determination of Fluorine and Chlorine in Organic Compounds. The 2,2,3,3,4,4,5,5-octafluoro-1,6-hexanediamine was converted Kimball and Tufts (page 150) to the white crystalline dihydrochloride by mixing an ether soluConstant Temperature Steam Distillation Apparatus for Isolation of tion of the diamine wit,h ethyl ether saturated with hydrogen Fluorine. Huckabay, Welch, and Metler (page 154) Spectrophotometric Determination of Fluorine in Glass. Parrish, chloride. This material contained 21.OwO chlorine and 45,9y0 Widmyer, Brunner. and Matson (page 156) fluorine as compared with theoretical values of 21.3 and 45.6, Semimicro Method for Simultaneous Determination of Carbon, respectively. 2,2,3,3,4,4,5,5-0ctafluoro-1,6-hexanediamine apFluorine, and Chlorine in Halocarbons. Teston and McKenna pears to possess unusual stability to both air and light. (page 193) was obtained. This compound has been tentatively identified as perfluoroglutarimide. The perfluoroglutaronitrile contained 55.4% fluorine (theory 55.99). The dinitriles were found to produce physiological effects. For example, perfluoroadiponitrile is-toxic to white rats in small dosages and appears to have vasoconstrictor activity; it causes noticeable shortness of breath and flushing of the face after any considerable exposure period. The boiling point of perfluoroadiponitrile (63" C.), compared with the boiling point of adiponitrile (295"C.),illustrates strikingly the effect of hydrogen bonding on boiling point. Similar observations ( 1 ) have been noted with trifluoroacetonitrile (boiling a t -63.9" C.) and acetonitrile (boiling a t 82" C.).
+ +
