R B P O l t 0 1 A NEW ENG OCIATION

0 RECENT ADVANCES IN FLUORINE CHEMISTRY'

amm C. FIWER= Illinois State Geological Survey, Urbana, Illinois

TAT: phenomenal ndvnnees in fluorinr chemistry during the past t rn yearn rnnbled the rhemicnl indurtry to announce some of the most unusrrnl p r d u r t s known to thr inclustrinl \\-nrld. With grateful npprerintion to the press, populnr nttrntion \m cnllecl to the hnndi\vork of the fluorine npwinliatssuch nsnr\\.plnstics, lubricnnts, clielectrics nnd mnny other prmluct? with auprrh and unique propertirs. Evrn the nvcrnpr studrnt of chemistry nns caught hy surpri.se with these nnnounce- ments on the king $11 thr lunlogrn fnmily. This unn\vnrenerrs is ensily understml. 'hthorn of rollege textbooks hnrr hrrn most pnrnimonious on the ~ u l ~ j r c t , nnd thrir nbbrevintd discusions gnve n tlinholicnl undertone t o fluorine rhrmirtry, ns judged by the re- activity and corrosivenrsq of the fm element nnd its ncid. Little thought \vns given to the h n m r s d energy of this element, capable of producing some of the most stnhlr compounds known to mnnkind. Since the avcr- ngr render is interrsterl in genernl informntion rather thnn complex tl~eorirs nnd rcnctions the writer hns chasm to touch hriefly on the occurrpnre of fluorine, its position in thr Periodic Tnhlc, fluorine's historic milrvtonm, nnd the rommercinl implimtiona of the I9-l!Kdl ern.

1:luorine wrura to the extent of 0.03 per cent in the mrth's rrust, nnd in spite of this low concentrntion it is ninetwnth in nbun~lnnce among the elements. Its nhuntlnnrr is twrrthirds thnt of chlorine, three timrs thnt c$ ropper, nnrl 15 times thnt of lend. l'hc chief fluorine minrrnls nre rnrk phosphnte, fluorrrpnr, and c.ryolite, with fluorine contents of 3.5, 48.5, nnd 51 per eent, rrspectivrly. Cryolite, SmhlFa, is ine0n.x- quentinl Iwrnusc of its smrrity nncl thc s t m n ~ com- petitive position of synthetic cryolite from fluornpnr. Outside of fluosiliric neitl nnd its snlts, which arc hy-

I'reaented at the Twelfth Summer Conference, New Endnnd .\mintion of Chemistry Teachers, Univenity of Conncrtirut, Smrm, Conneetirut, Aufgst 24,1050.

'Chemist nnd ]lead of tho Fluompar Divkion and ita fluorine m w r h i:hlarntorics.

products of the phosphnte frrtilimr ncidulntion industry, rock phosphntr, Cnl.'(~i4(1'0,)~. is not n convenient. source of fluorine. Ilo\vrvrr, i t is potentially the world's grmtrst fluorinr rr.wn-e (I). Flunrnpnr, CnF3, is the chief source of fluorinr for the chemienl industry. The Illinois-I<entucky fluonpnr distrirt nrcounts for over 80 per rent of the pr~luc t ion of the ITnited States. Ikpcnding upon rronomic conditions and the drpletion of fluonpnr rr.wwrr, the nnturnl minernl mny hnvr competition from a synthrtic rnlrium fluoride ohtninerl hy n rnrk phosphate clrfluorinntion prorrss now under investigntion hy thr Trnnesre f i l ley Authority (2, 3. .$). I:?isentinlly, the prnrrss invol\-ca the renction of water \vit,l~ molten rrxk phosphntr, causing the fluorine to he evolvwl ns nn impure h y h - fluoric acid stack gns and recovered in n limestone filled tower as cnlcium fluoride.

The development of syntl~ctic opticnl cnleium fluoride crystals for usc in infrared instn~ments should be men- tioned. nernu.w of the srnrcity of natural opticnl mntcrinl the IInrnhnw ('hemicnl (:ompnny is pmluring Inrgc single crystnls by its special cooling prowss frnm thc molten stnte. Lithium fluoride crystnls nrr pro- tl~med in the same wny.

1Iydrofluoric ncid, especially the anhydrous acid, is rapidly becoming u common rhemicnl of commercr, end is pr~xlued by the reartion of sulfuric ncid on fluors;)nr in n hentcil rotnry kiln. The proll~~ction of this :wid hns progrcswl in the laqt dccndc to cnrlond lots, s t~ rh ns 27,000 tons for IW9 (Z). A new plnnt (6) completwl in 19-I!) 1m.q n produrtion cnpnrity of ti00 tons per month and ran he opera td wfrly with two opernt.on on n shift. This is a far cry from IInrggrnf's discovery of the mid in 17W nnd the unfortunate expcricnces of Hrrzelius, Dnvy, Gny-I.~i~~nc, Thennrd, the Knox brothers, Ifoisvm, nntl othcn of chemistry's IInll of Fnmr. The corrasive nncl toxic propertirs of hydrogen fluoride cnnnot he mitignted, but with modem tech- niques in the Inborntory nntl plnnt it can be handled wfrly and with simpliriby. Sinrr the acid is fluorine

49

50 JOURNAL OF CHEMICAL EDUCATION

chemistry's key chrmicnl, its growth in tonnnge p m durtion is nn rxrrllrnt index of the hrondening impnet of n nrw firld of rhrmistry.

'I'o thr uninilintwl, fluorine nppmrs to h n~rroundecl with n shroud of mystery, hut n glnnce a t the pcriwlic tnhlr will rrrenl some fundnmentnl fnrts nhout the 1)r. Jrkyll nncl I Ilycle proprrtirs of fluorine nnd its compor~ncls. I.lunrinc orrupies the upper right-hand rornrr, i~nd is the first mrmher of Grnup VII, the hnln- pen fnmily. It is the most electronegntive nncl most rrnrtivr rlement known. Sinre i t is the first elrment in thr hnlogrn fnmily it has n dunl prnonnlity, in thnt it not only hrm fnmily nttrihutrs hut nlsn properties quite forrign to thr other hnlogrns. If the s~~hje't is n p pron~~hnl from this point of view thr nrtunl pirture is murh less c-onfusinp, nntl spcrulntion hy nnnlogy is trmpcml ~ 4 t h rnution.

'l'hr two most hrillinnt scientists of nll time in fluorine rhemistry nrr \Ioissnn of Frnnre nnd Swnrts of Relginm. They were contrmpornrit*~ nncl thrir studies lnid the foundntion stones of mnny of our mndrrn clrvelop ments. Moiswn (7) isnlnted fluorine in thr frrr stnte in 1886 11y thr electrolysis of potns3inm nricl Ruoridr nnd then studinl mnny of its mrt ions. Ncdern rrIIs oprnting on the Rnmr principle nrr prnduring fluorinc on n tonnngr hnsis. l fnny of thr highrr mrtnllic* fluoridm suprrficinlly t l r s r r i ld hy this snvnnt nrr now nruilnhlr in qunntitirs. ?'hr expl~~sive rmctivit.y of fluorine with organic molecules, oh.wwcul hy Noisqnn, indurnl S\rnrts to lnnk for nn rntirrly dilTerrnt methwl for the synthesis of orgnnir fluorinr rompounds. In I892 Swnrts nnnounrnl the nynthmis of ('('Ll: nncl ('11('1,1~ hy the rmrtion of nnhydrous nntimony tri- fl~wridr on cnrhon tetrnrhloride nnrl rhloroform, rrsprr- tively. This rrnrtion of nn orgnnic rhloride with n mrtnllir fluoride nnd its rxpnndnl rrnion is now known as the S~rnrts rrnrtion. Its in~lustrinl signifirnnre is exprrwud in the prnduction of fl~torinntnl rlrrivntirrs of mrthnnr nnd rthnne for usr ns rrfrigrrnnts, propel- lnnts in nrrosol homhs, etc. As enrly :IS I!144 the prn- jrrtrd prcxlurtion rnpnrity of cli(~I~lorwliflr~orornrthnne ~ r u s 2400 tons per month (8). In I!M9 the prcxh~rtion of nerosnl 11omhs nlonr rrns 25.000.(nWI units (9). 'l%e stuclirs of Swnrts nt the turn nf thr century on the fluorinntrd ethylmes lnid the foundntion for the new fluorinntnl polymers thnt nrr now I>minning to npprnr on the mnrkrt. In rrtrmprrt, it is quite diffirult to tlirorre prrsmt-rlnv ndrnnrrs from thr inflnrnw of the studirs of Moiwtn nncl S\rnrts. ('ollrrtirrly they p u b lishnl over 100 papers.

'I'he 1930-10 clrcnrle is especinlly significnnt in the industrinl ntrnkminp and ilrrrlopmrnt of fluorine compounds. I'rior to this prricxl the only compounds nrnilnblc in commrrrinl qunntities 1rere nqueous hycln~fluoric nrid nnd some of its mom common snlts. h o t . 1930, two very importnnt industrinl devrlop- mrnts took plnce, the commrrrinl prnduction of nn- hydrous hydrofluorir ncid (10) nnd the new Freon refrigerants (11). Thew industrinl chcmirnls hroke

the hottlrnerk of the nvnilnhility of rnv mntcrinls. ('low on the hwls of thew clrvrlopmenh, new fluorine- rontnining dyes of unusunl stnhility nppt'nml on the ~\mrrirnn mnrkct from (;ermnny. Thr I. G . Fnrhenin- clustrir in 193.7 ohtninnl n pntent on the 11sc of IITZ in the synthesis of nromntic fl~~orine compounds (I?), nncl in 193!l \r:w cmlitrd with thr first pntmt on f l ~ ~ n - rinntrrl polyethylme polymers (19).

\Vith the prccnling hnrkground mnterinl, the writer hnq c h w n the 191%50 drrnde ns the perind of recent nclvnnres. 'I'his p r r i d is rhnrncteriznl hy the fnbulous eqwncliture of mnnry on fl~~orine rrsenrch, the v:~qt amount of experimrntnl dntn rollectnl, nncl the unfor- tunntr slnnting of rrsrnrrh fh~ring n wnr eNort.

In 1941 the (111 Pont Company ohtnincd :r pntcnt on a tetrnfl~~ororthylmc polymrr i c l is rommerrinlly nvnilnhlr nndrr the trndr name of Teflon. ;\t the l rhrst of the XInnhnttan Atomic 1Sncrgy projrrt, the drvelopmrnt of thr former I. G. chlorotrifluomthyl- rne polymrr w\.ns expnlitnl nnd is knownns Fluorwthc.ne nnd IGW. Thew plnstirs hnve unique properties (14, 1;). nrr w r y rrsistnnt 111 solrrnts and rnrrosivc rhemirnl ngrnts, noninflnmmnhlr, stnhlc over n wida trmprrntum rnnge up to 2TW, nnrl poxwss exrrllent dielrrtrir prop- erties. For csxtrrmr conditions, thry nrr Iwing fnllri- cntnl into gnskrts, dinphragms, rlrrtrirnl insulntom, nnrl other itrms. As s~~sprnsoitls they arc Iwrirming nvnilnl~lr for conting purpns~s.

Thr synthesis of highly fl~~orinnted hydrncnrhons is one of the most remnrkablr nrhirrements in orgnnic fluorine rhemistry. Ilrsults of thin rrsenrrh (16, 17) nrr mnnifrstecl in the nrw noncorrosive nncl chemicnlly inert liquids, grrasps, and trnxrs which nrr now Iwcom- ing nvnilnl~le ns clirlectrirs, fire extinguishers, luhricnnts, pump oils, hydrnulic fluids, mngnntir clutrh liquids, ctr. Essrntinlly they nrr complt.tely fluorinnhl rom- pounds with very little unsnturntion nncl hyflrogrn content. 1)uring the war thc term "perRuorwnrho~~s" !ra. coined for tl~ese compounds ns nsimple:~ppellntir~n. The methods of s.ynth~sis \rhirh hnve hwn dr\-rl~)ped cnn l r cl:wsifi~l :IS: (I) polynerizntion, (2) clirwt fluorinntion with gn.wus fluorine or higher mrtnllic fl~~ori(les. nncl (3) elrrtrnrhrmirnl floorinntion. The first mrthnd depend3 upon the cr~ntrollnl polymerizn- tion of fluorinntnl ethylenrs to the physicnl stnte (lesiml; the nforrmentionnl plastics rcprrsmt the npprr limit of polymrriz:ltion. Iligher molccnlnr weight rompounds with n ((T& constitution rnn he ohtnind nlxo by n thrrmnl crnrking prncess of CIICIF2; trtrnfluorwthylmc nnd ortnfluor~wyclohr~tanc nre among the prnducts of rmrtion. A rrcrnt discovrry (18) thnt CIZtI nnd GFsl will renct with olefins in the prrwncc of ultrnviolet light to form long-chnin com- pounds merits wntching. These proeesws hnve the ndvnntnge of using ximplc compounds procluced by the S~rnrts rrnction.

The direct fluorinntion of hydrocnrbons (19) with fluorine gas is nccomplished in n copper reactor pncknl with copper shot or gnuze. Ordinnrily the fluorine

strenm is dilutnl with an inert gns mch as nitrogen. h mcilificul and somewhat more ronvrnient method is the pnssage of n hydrwnrhon over rrrtnin higher metallic fluoriclrs mr11 ns CoF3 and hgF2 nt n m~it:~hle trmprrnt~~re. The net rcsult is thnt the metnllic fluorirk gnrs to n lower vnlenre stnte hy giving up part of its fluorine under more eontmllnhlc contlitions. After reprnrrnting the spent mntcrinl with fluorinc or chlorinr trifluoricle the rycle cnn Lr repent~l . This prrwrss is known ns the Fowlrr mrthcil. lloth fluorinn- tinn procexsrs give ruther romplrx mixtorrs remlting from the nlptrlrr of cnrhon-rnrhon linkages, rmrrnngr- ments, etr. These fl~~orinntion st~xlirn on organic rompounds nre sprctncdnr when it is ronsidrred that thr hent m e w relcawl in fluorine substitution nnd nddition is grrntrr than the hond strength energy of nny incliviclunl linkngc in the orgnnir molreulr.

l lost oniqur of nll prorrsws for nrhicving the "per- fluoro" stutr is the rlertrorhrmirnl fl~~orinntion methnrl nnnouncrcl hy Simons in 1948 (20). It inrolvrs the pnsyngr of nn rlertric rurrrnt ( 5 4 volts) through nn r lrr t r~~lyt ic cell r h n r g ~ l with nnhydrnus hydrofluoric acid nncl the orgnnic romportnd to IF fluorinntnl. The iron rrll ensc is the cnthnrlr, nntl :I wrirs of nirkcl sheets fnirly rlosc together mnkr up the nncile "pack." S o fluorinr is lil~rrntnl, l ~ u t complete fluorinntion of the orgnnic rompound tnkrs plnrr. The prorrss is cnpnhle of prciluring not only "prrfl~~omnrl~ons" hut nlso com- plrtely fluorinntd nrirls, nminm, nlrohols, etr. (21).

Some fluorinntcd nliphntic nrirls such as mono- and trifl~~oroncctir (22,?S) nntl heptnfluorobutyric (Zt) neids nrc lryoncl the I:~horntnry stngr. In penernl, the acids arc quitc stnhlr, w r y nridir. nnd in scme cnsrs vrry toxir. 111c first reportrcl rxistrnce of an orgnnic fluo- rine rompound in nnture wns nnnouncerl in 19-11 by the isolntion nf nwnofl~~oronretic nrid ns the toxir principle in n South Afrirnn plnnt (2:;). This nrid nncl its drrivn- tivm if tnkrn intrrnnlly nre dendly poisons for \vhirh thcrc is no kno\vn nnticlotc. ;I cwnmerrinl rnrlenticirlr ( i r i ) known ns "1080" is the mlium snlt of the toxic nrid. l'hrnoyl trifl~~omnrrtonr (27) is n\.nilnhle for the sepnrntion of mrt:ds through chrlnte complex formn- tion. I<thyl trifluoroncrtntr (27, 2.9) is n pilot. plnnt item nnil is useful in opq~nir s.vnthrsis. l i l~~orinc in plwe of rhlorinr in the hrnzmr rings of I)IY1' is thr I~:~sis of 1)FI)T (20) which \Yes p r n r l ~ ~ c d in eommrrcinl tonnngrs in Grrmany during the rrcrnt wnr. For the nllrvintion of rrrtnin gnitrous conditions two nromntic f l~~or inr rompounrl* ~~nc l r r the trndr nnmrs of Pnrclinnn ( I ) nncl Cnpncin (S'O) nrr nvnilnhlr in the German drug trnclr. 14rforr Irnving the suhjrrt of organic fluorinr compouncls, mrntion should hc mndc of tl~r Amrrienn prnrl~~rtion of lwnmtrifluoridc and relntcrl compo~~ncls (10) nntl thr pos4hle use of hromofluoromethnnrs n s fire rxt inguishing ngrnts.

Tr rmrnhus strklex \vem made in the inorganic field. As entnlysts, hornn trifluoride and HF were r r r o g n i d ns po\vrrful tools in the uynthetic orgnnic industry. 'I'hr tonnngr rquircmrnt for 111: nu n rntnlyst in the

prduct,ion of "alkylnte" for 100-oetnne nvintion gas(+ line (R) k a m e rnormous after the estnhlishmmt of the first plnnt in 1942. I t has k n rcportd t11nt some "nlkylntc" renetors mere built for n cnpncity of 50 tons of 111'. Lnrgr qunntities of I IF were usnl nlno in tho prcil~tction of fluorinr for atomic enrwy ptrrpows. Fl~~~~rinrgmrrntorsoprrntingnt 20Wnmprrrswith nrur- rent rRrirncy of 95 prr crnt and rnpnhlr of prdur ing 2000 pounds of fluorine prr month were drvelopnl (I). A monthly prnrlr~rt ion of 50 tons of fluorinr \\.IT- rrportnl in Grrmany hrforc it.? enpitulntion. ITor lahorntory pur- pows n smnll grnrrntnr (31) is uvnilnhlr nnd is recom- mended over that of thr purchhse of fluorine in cylindrm. Chlorine trifluoride is on t,hr mnrkrt in .mall steel rylindrn, nnrl its futun: a. :r convcwient fl~mrinnting agrnt is promising. No one has k n nhlr to unclmtnnd ~vhy the Germnns had contcmplatrcl p r d ~ c t i o n of this compound in tonsexrcpt for n pox~ii~lo IISC in inrendinry homhs. The hig push in fl~torinr prnrltrction enme Imnu?u! of its csrrntird u.se in the prciluction of the ntom homh. ITrnnium in th?: form of its h~xnfluoricle hns n sul~limntion point of 5ti0 nnd as such is nmrnnl~le to the wpnrntion and concentrntion of its iuntoprs n m l d for nwlrnr energy (I). 1'11rr srtlfw hrxnfl~~oridc is rxlrrmrly stnhlr, nontoxic, noninflnmmnl~lc~. nnd l w n ~ ~ w of its high clielcctrir vnlue it. is ~~ru r l in X - r q rquipment as a g m u s insulat,or (I). Pn tawi~~m fl~~osilirnta is k i n g usrd in n process for mnking SF-

t t i i n ( ) Elrrtroplnting in solutions of mrtnllic flrtnl~orntrs cnme into prominrncr.

Among the commrrrinl infnnts nrc the fluorophnn- phoric nrids (HJ'OJ?, lllW?l~?l:l, nncl HPIJ8) and s imr of thrir salts. They hnvc hccn lalwlrd F P ecicls nno snltn hy thrir fimt prciluccr (39). 'I'hr nrirls rxhihit cnta- lytic properties in olrfin pnlymrrizntirm, nod the anlts mny 111. u w l ILS fluxing agrnts. l'hr I T - inn is quite stnhlr, nncl the III'F6 arid with certnin orgnnir h n . ~ forms insolul)lr snlts quitr nnalopo~~s to 11('104 and IlRF, rtndrr thr snmr eonclitions. Crrtnin orgnnic rstrrs of the monofl~~oronrid \vrw idcntifinl :in t l ~ r very toxir n rwr gnvs ( S j ) prnpowl hy the Grrmnns; it hns I w n repnrtrcl that one of thr compouncls, di-isopropyl f l~~~~rophosphatc (DIV), in w r y low concentrntions is I I S ~ ~ I I in r n l i i n . While on the suhjrrt of "prc~dinr" nricls nnd snlts, mrnt,ion should he mnclr of the work of EmrI611s nt ('nmhridgr (Ihglnnd) (3:;). H r has prc- pnml 11 lnrgr numhrr of complrx rompnuntls of hromine triflwride (IlrF.,), cxnmplrs of whirh are KllrFt, g r 4 lln(IlrF4)l, r r r . Evirlrnrr points to the fnct thnt llrFa is nn ionizing solvrnt, proclueing llrFl+ and HrF,- ions. This work oprns nn rntirrly new field of flwrinr rewnreh.

LITERIITURE CITED

(1) VOUKUIL, IIAURICK. FINOER, AND REED. "Fluonpar and Fluorina Chrrnicnh,'' llepnrt of Invmtigationa No. 141, Illinois Stnte (;mlogienl Surwy, Urbnnn, Illinois, 1WP. fir dm Chcm. Idrrrlrir.~, 63, 012 (lW3) nnd M, 5 1 (l!l49).

(2) I ~ I ~ N E T T AND Hussum, 11d. En#. Chem., 38, 1208 (1946).

&r JOURNAL OF CHEMICAL EDUCATION

(3) H r o m A N U RIEOXL, ibiA., 41.2493 (1949). (4) KREMEW, ihid.. 32, 1478 (I!t40); Ckm. IdwfnGx, 64. 732

(l!t40). (6) "FnrL* lor Industry," Runnu of thc Census, C . R. Dcparl-

ment of Commerce, \\ 'mhinmn, I). C., 194% (6) Z~nar., Chem. Indrufrica, 66,508(19%). (7) MO~SSAN. "Lo Fluor d S e Compm&." G. St<*inhcil, Paria, . .

1900. (8) h K m : ~ C b m . 6 >Id. Enq.,51, I01 (June, 1944). (9) G o ~ u n e n a , Chem. Idtcalnw, 65,374 (1049).

(10) I h a e o ~ , iW., 36,120 (1035). (11) Xllnar.m AND IIEss):, Inrl. Eng. Chem., 22,542(1930). (12) I. G . I~wl~.nind. , Ccrmnn pntnnta 5i5,593 (1933) nud 000,-

iOG (10341; Chrm. rllulmrl~, 27, 4513 (I!IBB) nnd 28, i2CO (I!t:i.t), n?apw:tivcly.

(13) I. U. Fnrlwnind., Oermnn p a k n t 071,071 (1939); Chrm. Abfraeln, 33.33124 (1!1:1!1).

(14) R E N F ~ E W AND I.EWR, Illrl. Eng. Ch~m.. 38,870 (10%). (15) Chon. c t Eng. A'nrr,26.2721(1048). (16) Chm. Indrralrirr, 67, 25, 245 (1050).

(17) Sc*ncc A'm Wfcr, 55,4 (January 1,1049). (18) IIARZELDINE, N a f u n , 165, IS2 (1950). (10) A serics of papem on fluorine chemistry, id. Eng. Chem.,

39,24M34(1047). (20) Chrm. Idtwlrie.~, 63.785 !194R). (21) S ~ w s x , ('hem. Eag., 57, IZ!t(Jaly, 19.50). (22) Oil, I'ninl rind 1)rtq Rrp., 156, 4 (.*up14 29, 1040). (23) Chon. & En!;. Snm, 27, 1:1!1!1 (1!140). (24) iltid., 27,3061 (1949). (2%) ~<LINOENR\IITH, SrirmX, 102 ,6n (19451. (26) JENKISS ASU KOKIILER, Chem. Ind~11~11r;ra. 62.Xi2 (1049). (27) Avnil:il,lc from tIw D o r Chcmienl (h.. X1icll:mcl. Michigan. (28) Chem. In r la~ l r i r~ . 65, iCB (19411). (2!l) Scinuc.Ynrs Ldlcr, 55, !)(January I. 1949). (30) MAY, Deal. nd. Il'ochxhr., 74,374 (1!l4!1) (31) Ilnrshnw Ch~nlicnl Co., Clevrlnnrl, Ohio. (32) Chrm. Eng., 57. Sa.30, IGO(I!)T,O). (Xi) Cbrm. X. Eng. .\'em, 26,2570 (I!l4R). (:(-I) Ihirl., 26. :is20 (ll4Rl. (35) Ibirl., 28,51 (19.50).