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J.S.C.I., e,August, 191s BROWN A N D WHALLEY-FLUORINATION OF ORGANIC COMPOUNDS. 111 331

concentration of 2mg./litre, red uction is complete in 5 min. andthe reduction time is not materially reduced by higher molyb-denum concentrations. T he effect of the residual iron colour onth e calibration graph is shown in F ig. 79 and i t will be observedtha t the effect is more pronounc ed in t he presence of phosphoricacid.

Table VI

Effcctof acidify atid sodirmr tlriocyairate cotrcctrrratioir 01 1 th e colorrr atrdstability of iron-tnolybdcttrrnr thiocyarrare

Molybdenum 0.03 g./l., iron 1.0&/I,, perchloric acid 0'2N., stannouschloride 0.085~.

Water to water = 1.30; I cm.cells; green filters

H,SO, NaCNS,concentration concentration

1 'ON.

2.ON.

4'0%

0.06~0.08

0.1250.140

0.240.28

0.300'370'40

0.040.060.080'10

0'125

0.16

0.260.30

0.37

0.04

0.05

0.08

0'10

0'12

0'20

0'10

0 ' 2 0

0'20

0.15

0.240.30

0'37

Drum reading5 min.

0-6150.4150.2800 .180

0.1350'020

0'010

0

0'0100'100

0.150

0.6200.3600.205

0.1600'120

0'120

0.1300.170

0.250

0 . 525

0 '4500.275

0.1800.1800.2300.2600.3200 '450

0'200

0'210

2 0 min.----

0.420

:::g0

0'0100'100

0.160

--

0.4150 .270

0.170

0.130

0.170

0'275

0'120

0'200

0.6950.5650.280

0'210

0.1800.1800.230

0 '2750'3950.610

Fade per15 min.----

0 . 2 850 '025

0

0

00

0'010

--

0.710

0'110

0

0

0

0

0.050

0 .025

0.1700.1150.005

0

0

0

0

0.015

0'0750.160

Zn terferetices

Copper interferes with the determination of molybdenum dueto the precipitation of cuprous thiocyanate, but with copperconcentrations up to 10 mg./litre, this precipitation ca n beprevented by the addition of gum arabic.

Chromium salts exert a small interference and this must becorrected by a subsidiary correction graph.

Nickel is without influence on the m olybdenum determination.

Acknowledgement <

Our thanks are due to the Ministry of Supply for permissionto publish this paper.

Metallurgy Department,

Farnborough,Royal Aircraft Establishm ent,

Hants.Received July 8, 1946

Hadley, W. H., Anal s t 1941,

Robinson, R. J. and Spoor, H. J., ibid. 1936, 455High, J . H., Analyst 1945, 18Peters,C.A. and French, C. L., Ind. EnR Chem. (Anal.) 1941,604Hnywood, F. W. and Wood, A. A. R., Metallurgical Analysis by

a Schwnrtz, M. C., Ind: Eng. C f k . (Anal.) 1934, 364

Means of the Spekker Absorptiometer," Adam Hilger Ltd. 1 9 4

FLUORINATION OF ORGANIC COM-POUNDS WITH ANHYDROUS HYDROGENFLUORIDE. PART III. UNCATALYSED

FLUORINATIONS

ILCarbon tetrachloride, as-tetrachloroethane, pentachloroethaneand hcxachloropropylenc have been fluorinated by heating with --anhydrous hydrogen fluoride. The reaction mechanism is dis-cussed. -1The work described in this paper is'a continuation of that

reported in Parts 1' an d II.? This section of the research wasconcerned with the use of anhydrous hydrogen fluoride as afluorinating agent, in the absence of a catalyst, and describes apreliminary survey of th e field.

The literature gives little positive information about thistype of reaction, which involves the replacement of the halogen(usually chlorine) by heating the halogen-containing compoundwith anhydrous hydrogen fluoride. R3CC1+ H F -+ R3CFiHCI. Th e production of benzotrifluoridcfrom benzotrichlorideand anhydrous hydrogen fluoride3 and the fluorination of methyl-chloroform and ethylidene chloride' seem to be the onlyrx ord ed cases of this type of reaction. A survey of the literatureindicates the rarity of this reaction by repeated statements to theeffect that the fluorination of benzotrichloride is an excep tionazcribcd to the influence of the phenyl radical. Num erdusreferences to earlier work arc omitted here, since excellentsummaries of work up to 1940are available.& Results embodiedin this paper are the subject of B.P. Nos. 576,189; 576,190.~~'Experimental

The apparatus and method are described in Part I.' T h equantity of hydrogen fluoride added was equivalent to thatrequired theoretically to replace one or more halogen atoms.The product from the autoclave (which was almost invariablyliquid) was usually washed twice with a little aqueous sodiumcarbonate solution and once with water, dried over anhydroussodium sulphate , an d carefully fractionated at a reflux ratio of

about10

toI,

through a well-lagged column, 3 ft. tall, 13 in .in diameter and packed with 8-mm. diameter glass cuts. Anymaterial of boiling point below room temperature, which wascollected from the autoclave off-gases, was fractionated in amodified Podbielniak still. Man y experiments were performedduring this work, Fo r brevity, only one typical batch of eachtype is described; others which are of direct interest aresummarized in the table.

Fhiorinafion of carbon tetrachloride.-Carbon tet rachlo ride(924g.) and anhydrous hydrogen fluoride (250 g.) were heatedto a temperature of 230' during 2 hours ; the pressure attainedwas 1000 lb. per sq. in. Th e temperature and pressure wereheld a t these values while gases were released during 15 minutes.Reaction WBS then comp lete. After cooling to 100' the excesspressure was released via the scrubbing train. Th e condensateconsisted of pure monofluorotrichlorornethane, b.p. 2S0/760mm.T he literature8 records the b.p. as 24-g0/760mm .

Th e residue (680 9.) in the reaction vessel, was a pale brownliquid free from tar. Distillation gave monofluorotrichloro-methane, b.p. 23-28"/76 mm. (355 g.). Th e residue wasunchan ged carbon tetrachloride. Th e total yield of mono-fluorotrichloromethan e was thus 5x3 g., e quivalent to 63%yield.

Fluoriitafion of as-tefractiloroerbite.-As-tetra~hloro~th~~(208g.) and anhydrous hydrogen fluoride (IZO 9.) were heatedin the autoclave to 225O, using a large-sized reflux. condenser,the ratio, volume of autoclave/volume of condenser, being about4 : I. Reaction commenced, and was complete in 20 minutes,without release of gases, the pressure rising to about 750 Ib.

BYJ.

H.BROWN and W. B. WHALLEY

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331 BROWN A N D N'H/ILLEY-FLUORINATION OF ORGANIC COMPOUNDS. III J.S.C.I., e,August, rW8

per sq. in. After cooling to 80" the residual pressure was releasedvia the scrubbers and a pale brown, clear liquid discharged fromthe autoclave. Fractionation gave pure I-fluoro-I :I :2-tri-chlorocthane (600 g.), b.p. 88-89"/753 mm., equ ivalent to a yieldof 80%. The recordeds b.p. is 88.8". The residue wasunchang ed as-tetrachloroethane.

Flrcorinotion of petr~aclrloroerlra~re.-~entachloroethane(1012 g.)and anhydrous hydrogen fluoride (100 9.) reacted during 15minutes at 500 Ib. per sq. in. pressure, when heated to 225',

with an autoclave volume/condcnser volume ratio of 4 : I.

After fractionation the pale b rown liquid produc t (775 g.) gaveI-fluoro-1 : I :2 :2-tetrachloroe thane (710 g.), b.p. 116-118~/742mm., the residue being unchanged pentachloroethane. T h erecorded10b.p. is 116.6"/760 mm.

Fluorination of Ize.~acl~Ioropropylet~e.-Hexachloropropylene(455 g.) and anhydrous hy drogen fluoride (110 9.) were chargedinto the autoclave. Th e temperature of the reaction mixturewas raised to 155" during 2 . 5 hours, the pressure attained a t th esame time being yx-600 lb. per sq. in. Th e reaction was thenstopped by cooling to 30' and releasing the residual pressure.

A clear, dark brown liquid (350 9.) remained in th e reactor.Fractionation of this product gave I :I :2-trifluoro-2 :3 :3-

trichloropropene-2 (120g.),

b.p. 88-92"/757 mm.; I : I-

difluoro-I :2 :3 :3-tetrachloropropene-2 (1 5 g.), b.p. 126-130'/757 mm. j and. I-fluoro-1 :I :2 :3 :3-pentachloropropene-2(15 g.), b.p. 167-168"/750 nun. Hcnne, Whaley and Stevensongive the b.p. of these three substances as 88.3', 128'~and 170.2"respectively," Rep rodu cibilit y of this fluo rinatio n was difficultto obtain, for some unknown reason. Greater or lesser amountsof carbonaceous materials were occasionallyobtained, while morefrequently considerable quantities of a high boiling crystallinesolid of unknown constitution wcte produced. Th is solid wasapparently not homogeneous ; the melting point, which usuallyexceeded 2 2 5 O , rang ed ove r 20-30'. Thi s pro duct was of nod.irect interest to the work described in this paper and was notfurther investigated.

FIuoriiration of trrer~ylchlorofort~r.-Mcthylchloroform (100 g.)and anhydrous hydrogen fluoride (360 g.) were heated to atemperature of 14"during 1.75 hours. After releasing the

pressure and fractionating the product, t he following materialsnere obtained : 1-fluoro-1 :I-dichloroethane (300 g.), b.p.32'/760 mm. j I :I-difluoro-I-chloroethane (195 g.), b.p.-9.5'/760 mm. ; and a little unchanged methylchloroform.T he recorded'? b.p. are 31.7" and -9.6" respectively.

Discussion

The fluorination of methyl chloroform'to a mixture of themono-, di- and trifluorides, and of ethylidene chloride to themono- and difluorides is claimed by I.G. Farben. A.-G?However, despite repeated attempts under varying conditions,it was not possible to fluorinate cthylidene chloride sufficientlyto make the me thod of preparative value. T he best yields offluorinated material never exceeded 2% of mixed r-fluoro-~-chlomthanc and I : I-difluoroethane.

The work described in this paper was initiated using methylchloroform as the experimental material, since this was claimed

to fluorinate readily? No difficulties were encountered, andattention was then diverted to as-tctrachloroethane . Immediatelythe difficulty of non-reproducibility amse-sometimes reactiondid not p roceed under conditions apparently identical with thoseunder which it took place on other occasions. Th is difficultypersisted with experim ents performed using th e sam e reagents,but nevertheless many possible CILUSCS of difficulty, such asvariation in the moisture content of a batch, or the effect oftraces of silicon tetrafluoride and sulphur dioxide (from thehydrogen fluoride) were investigated, all to no result. Therewas one fact only which distinguishe d a "normal " batch froman unsuccessful one, and this was the presence of a very low

pressure until reaction temperature, in the successful experi-ments. During the early stages of the unsuccessful batchesthe rate of increase of pressure with temperature was muchgreater than that in successfkl experime nts. Th e initially lowpressure appears to be the decisive factor which determineswhether fluorination occurs or not. It was shown (see tableand graph), that if the reaction mixture in the autoclave couldattain the requisite reaction temperature (usually in the regionof ZIO~),without the pressure exceeding 50-100 lb. per sq. in.,the reaction proceeded very readily. If the pressure rose aboveIOD Ib. per sq. in. during the heating-up period no reactionoccurred, even at temperatures exceeding 2x0' (e.g., up to250"). Th e total reactant could be recovered unchang ed.Other conditions being constant, the presence or absence ofhigh pressure during the heating-up (no reaction) period depen dspredominantly upon the ratio between the size of the hydrogenfluoride charge and the c ondenser volume, a nd to a very second aryextent upon the temperature of the condenser jackets and theshape ofthe condensers. By suitable adjustmen t of these factorsthe bulk of the hydrogen fluoride can be removed from theautoclave and reta ined in the headgear as a relatively cool liquid,exerting a small vapour pressure, during the heating-up period.

The as-tetrachloroethane, or other highly halogenated hydro-carbon of moderately high boiling point, will remain substan- -tially as a liquid, exerting a vapour pressure of only a fewatmospheres.

Using this combination of suitable conditions the fluorinationproceeded without fail. In order to test this theory, two inter-changeable condensers of different capacities were used withthe autoclave (see table).

Table 1

Reactant CH:Cl.CCI,Press. at

Batch reaction temp. Reactant H F Max. ReactionNo. lb./sq.in. mol. mol. temp. temp. Remarks

6 6 22sa - No reactionSmall reflux6 6 225' ->

6 6 230' - condenser

CC1,F

I7 5

F175* <IW 6 6 232' 210' 6416 of CH:CI.

F177* < l # 6 2 i:z: 198' 70% *I

F179* < I 0 0 6 182" 70% nF181* <IW 6 6 220' 197" 70% s)

F184* 800 6 6 240" - z m l b . N,prcss.Ft85* I00 6 6 220' 207" Batch Fr84

cooled to oo,N, released

Cl.CC1.F

CC1,F

70yb of CHz

F189* I 0 0 5 5 2 5 2 O 225" 8oUbofCHC1:.

* All these batches were performed using a large reflux condenser.

t Vol. of a utoclave/vol. of condenser approx. 13 : I.

Using as-tetrachloroethane, specim ens of all other reagentsfrom com mon stocks, th e sam e apparatus, and an initial pressureof zoo Ib. per sq. in. of nitrogen raised in the autoclave before

heating, no reaction occurred up to 240" (normal reactiontemperatu re 180-2x0'). T he nitrogen retained most of th ehydrogen fluoride in the autoclave, the pressure rose to 800 lb .per sq. in., and no reaction occurred. Th e reagents so treatedwere cooled to oo, the nitrogen released, and reheated in th eusual manner when fluorination commenced about 200' as usual.In a similar manner an experiment which did not operate usinga low capacity headgear would operate when a larger capacityreflux condenser was used . All these facts are compatible withthe fluorination being a heterogene ous gas reaction, taking placeon the walls of the vessels, w ith all reactants and resultants beingweakly absorbed, except the hydrogen fluoride which is strongly

Vol. of autoclave/vol. of conden ser approx. 4: I .

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J.S.C.I., W , A u y e t , 191s VIC'KERY-SEPARATION AN D PURIFICATION OF CERIU M 333

I'resrurelteIirperarirre curves for as-rerracliloroetltarie barclres. CirtwzrF I ~and F25 represent riuo ruccerrfiil e.rperbtctits; reiiiaiirbrg cirmcr wereobtai tledf rom tointccessful experiineirrs

absorbed. In effect the autoclave acts like a hot tube reactor,under pressure, an d fluorination would be exp ected to takeplace when equal molecular proportions of as-tetrachloroethane

and hydrogen fluoride vapours are passed through a hot mildsteel tube. Reaction in fact did occur, at about z~o-~oo",an dalterations of th e as-tetrachloroethanc/hydrogen fluoride ratiofrom I : I to I :2 did not cause an increase in conversion tomonofluoride, but a marked decrease (other work in thelaboratory).

The fact that the effect just described was not encounteredduring the fluorination of methylchloroform, hcxachloropro-pylene and carbon tetrachloride is presumably due to the g reaterease of fluorination of these compounds, by virtue of th eirstructures. Reaction thu s began before th e high pressure ofhydrogen fluoride could be exerted.

(General Chemicals Division),Imperial Chemical Industries Limited,

Widnes Laboratory,Widnes

Received hlnrclr 30 , 1948

1 WhaUey, W. B., J.S.C.I. 1g47,66,427

4 I.G. Fnrben. A,-G., U.S.P. 2,146,354 ;Ch. Abs. 1939~33 ,3396

Ibid., 430Schcrcr, Angew. Chem. 1939,52,457 ;G.P. 575,593

Bockemiiller, W., Angcw. Chcm. 1940,53,41gBrown, J. H. and WhaUey, W. B., and I.C.I., B.P. 576,189Idem., B.P. 576,190Midgley, T. and Henne, A. L., Ind. Eng. Chem 1930, 22,5 42Henne, A. L. and Hubbard, D. M.,J. Amer. Chem. Soc. 1936,

11 Henne, A. L., Whpley, A. M., and Stevenson, J. K. ibid., 1g41,58i04de~e, A. L. and Ladd, E. C., ibid., 402

63,3478Hmej A. L.and Renoll, M. W., ibid. 1 9 3 6 ~ 3 ,889

THE INFLUENCE OF BASICITY UPON THEEFFICIENCY OF OXIDATION/HYDROLYSISPROCEDURES FOR THE SEPARATION AND

PURIFICATION OF CERIUM

Uy R. C. VICKERY

A study of scvcral methods of precipitation of cerium shows thatthe ap arent purity of thc precipitate is depen dent upon the p t~ofthe soktion. An attempt is madc to cvaluatc the efficiency of thcvarying methods and it is found that the classical nitratc/bromatese aration attains the highest efficiency of the procedures examined.TKe probable formation of a basic chloride during hypochloritevcatment of cerium is noted.

Although Moeller and Kremers' very thoroughly surveyedthe basicity characteristics of the rare earth elements, theydid no t s tudy intrinsically any particular element or purificationprocedure ; this was perhaps no t possible or intended in theirpaper, bu t their review served to crystallize the conclusions thathe id ue nc e of basicity on the preparation a n 8 purification ocerium oxide extends into most of the known processes for thispurpose, particularly so in those relying upon oxidation/hydro

1y:is reactions, and consequently has a great influence upon th epurity of the p roduct of any one of them. Th us it is recognizethat the basic nitratc/bromate, or nitrate/sulphate pracedureyield cerium oxide of the highest purity obtainable in oneprecipitation, whilst Prandtl' showed that the sod ium hypochlorite process required several repetitions to obtain a producof 95% purity, and, working with the calcium salt, the writehas obtained a cerium oxide of-only 97% purity after five precipitations when starting with a 37% material. T h c essentiadifference between these oxidation/hydrolysis processes lies inthe p,, of the solution from which the cerium is precipitatedThat p , , in such cases must affcct the purity of the product iobr-ious from the figures compiled by Britton et 0 1 . ~and thefurther study by Moeller and Kremers.' Th us quadrivalencerium is stated to precipitate at a ptlof 2.7 whilst the rem aininlanthanons are grouped around pII7. Obviously the nearer toneutrality the menstruum. of any precipitation becomes, the

greater the possibility of co-precipitation of neo- and pnseody-mium, etc., and conversely the lower the pu rity of th e productIt is further obvious therefore that a process in which the plis regula ted solely by the slow removalof the acid libemfeddu rinhydrolysis of the Cel'ion (nitrate/bromate), or in which hydrolysis is obtained by large dilution (nitrate/sulphate), will give aproduct of higher purity than on e in which an excess of effec tivhydroxyl ions arc present during precipitation (e.g., the N aOCprocess, and to a lesser extent th e conventional permanganatesoda prp'cess).

So far it had not been observed that anyone has attemptedto verify these observations, and in order to do so th e pII.oprecipitation was determined fo r varying methods of p recipitation. T h e procedures examined were :

Basic nitrateBasic nitratelsulphate

Permanganate oxidation/hydrolysisChlorate oxidation/hydrolysisBasic nitnte/bromatePersulphate oxidat iin/hydrolysisHypochlo rite oxidation/hydrolysis.

The starting material was a thorium-free rare earthcontaining 39'2% CeO, with t he approximate contents also oLa,O, 25% Nd,03 25% Pr, OI1 5% Sm,O, I%, SiO,0.5%;Zr and Hf were absent and only very small quantities of thother rare earth elements were present. Th e purity of Ce0obtained in one precipitation was determined, except for the lesefficient hypochlorite separations in which more than one pE