1288 R~DIIAL AND HAWKINS CATALYSIS 1" THE: CXXX1X.-Catalysis in the Hydyolysis of Esters by Infra-red Radiation. By ERIC KEIGHTLEY RIDEAL and JAMES ARTHUR HAWKINS. ACCORDING tlol the quantum ra8diamtion hypothesis of chemical and physicad actions as deweloped by Trautz Lewis and Perrin (com-pare Ann. Physique 1919 [ix] 11 5) molecules only become reactive after absosptnioln ojf al definite! amount of energy the oritical energy inoremelntl although it appelars probable that fa HYDROLYSIS OF ESTERS BY INB'RA-RED RADIATION 1289 different readdons the degree olf activa'tion necessa,ry may diff sr, yet tnhw va,rious &ages of a,ctlivaltion corresponding with various ariticad elnergy incremelnts a,re rehtetd t'o olne atnother in a simple manner. This e.nelrgy acquired by t'hei moIle.de is poltentlia81 and is assumed to be supplield by radiahioa; thus all re'a8ctjions in the brolad sense of the1 te,rm are1 phot,ochemica,l o'r pholtophysical.The chaicad and physical eIffec8ts proiduced by a-particles. and edectlroins may be includeld sinc,el the chasact.e,ristics olf photsohmioal relac-tiona may be quaatit,a,tiveIly interpreted with tlhe grea.test f acilitiy on a aolrpwaular tlheory of ra,diatdoa. Up ta the praent timel with tthe exceptlion of the photaahemical reamatlions taking pla,ce in the actlinio part of the spect'rum there hae bean no direr& prmf of bhe vadidity of t~he extensioln od this hypolthesisl into the &her pasts of tlhe spectrum especially the infracred tlhe arguments in favour od such a,n hypothesis being indireut based an expelrimeintla81 datla such as the tempera'ture-mlefficient of uhetmioa,l aad physicall retaotiolns the he8a.ts of form-a,tion of chemical compounds or the lamteat' heat of evapration of t'he element@.The tempwature-ooe~fficie;nt oaf methyl acetate has beeln studied in detail by Lamble and Lewis (T. 1914 105 2330) who1 found tthamt the critiaal energy increme~nt was ab3oat 17,000 ca'lories per gram-moleoule whiah on t,he quaatturn thelolry would be provided by light of frequency of v=1'6 x lo1* or wave-length h=1*9 p in the infrwxd portioln of the spectrum. I n a constant temperatlure enclolsure such as a t,helrmosmtla,tl the density of the activahing ra,diatio<n u, is cmstant and t'he m a t convenient method of causing a.n altelratfion in a, and the4re:fore of the remtion-veloloity is by a,ltelra4tlioin of the telmpelra,tarel.u, mn holwever be alt elreld bmy elither decre'a.sing or increasing the absor bab,la r a,di ati on density wit.hou t a.lter ing the meIan temper a,-turei. Thus plants which a.re photosensitive tlo the a,ctinia part of the spestrum practioally cease growing in t,he dark alt,holugh main-tained aii the same tempera8ture aad otlher t,ypioal phot,ochemical a,nd photwatadytdu rea8ct~ioiis behave in like manner. I n the case, of infra-red ra8dia8tion however itl is difficultl to shield a,ny pa,rtl olf the reciding system from radiaibon of any pa.rticulas absorbable! frequenay since the system itsellf ca>n emitl t*his ra,dia,tio>n either as a reault of intramolleculas vibra(tion or even intermo~lwula,r oollisions (s,ee Nernst " Die Theoretischen und Exp.Grundlagen des neuen Warmesatzes," Halle 1918 p. 63). Alteration of the medium in which t.hs rela8cting molecules a.rel disperse<d doea how-ever prduoe an a.lt8e.ra.tion in the! reactlion velocity but as pointed out above it is atl preisent unmrt,ain whethelr this is t.he relsult of 3B" 1290 RIDEAL AND HAWKINS1 CATALYSIS IN THE an altsrattlio~n in u, t'he activating radia,tbon density or due t,o an alteration in v equivalent to an alteration in the activating ra(diatio1n ,f relquencies and ths mechaaism of the re,action or to both f ad'ors. It is holwever quite. possible t'ol inorebasel the1 density of the activating radiation v by illumination with radiation of the colrrect wa-vet-length A = 1.9 p.In the1 course of t.ime this radiation will be1 absorbeld and thei elnelrgy will be1 equally distributed over t,he whollel spectrum reeulting in a,n etlelva4tioln of tempeIrat.ure but 'if t,he relaotion is t,ruly photochemical and seIlelotivdy absorbs ra,dia,tion of this f rsque,noy a marked accmletratioa in the re.a&ion-vellocity shoiuld result withoat a.n appreciable1 rise in ttemperaturel. To1 teat this point a selries of pre3imina.ry elxperimente was con-dudmd oln the1 ratel of hydro'lysis of methyl a,mtate dissolved in dilutei hydrochlorio a.cid and etxposeld tlo inf racreld ra'diation ; the1 velocity-coelfficietnts obtained in this way wetre compareid with t4he norma,l va1ues o;bmt'aineld from idelntJcal solutions madained in the dark.EX P E R I M EN T A L. As a soiUrce 04 inf ra,-reid ra4diahioln pretlimina,ry e,xpelrimenla indioa'tsld tha,tt a'n a,ro lamp was unsuitlablel sincw although the cmrboln .speotsum lines could be maintaineid ah fairly unif olrm intensity the inf ra,-reld polrtion olf the spedcum (pmduced by the hot vapours) fludua,teld in intmsit,y. A uniform a,lthough rda-tbvely feeble infra-red belam was obtained from a sma,ll bundle of the oxide filaments mmmoinly emplolyeld in the Nernst glow-lamp. A number olf experiments wetre likewise oo.nduchd with a niohrome spiral raised to 600O; t'hha mlahively large quantity of noa-ra.diant heat prowed holwever to be1 a serious disadva.ntage. The1 sun was fo,und ta be the1 rnoetl convenielntl solurcet of suitab'le radiafiotn.I n all casea tlhei spelctirum wa's obt,ained by dispersion throlugh a simple1 opt'ioal syst'em of leinsea aslid quastz prism a d t prism not being a~vailalble. No1 a,ttemptl was made select any narrolw spectiral beam but thatl part of the spect.rum was employed come'ncing wit'h the portioln od the red just beyond the visible and stretching to an indefinite elxt.entl into the infra-red. To e81iminaate as far as polssible t,he material a,bsoirption od the1 ra,dia-tJon and thus minimise the dissipation of t,hel eiielrgy as heat,, the1 methyl acetate was illuminateld directly wit$ the radiation wit,hsut tihe int8emrvelntion of any glass. The solution undergoing hychlysis was. cont,aine;d in a 100 C.O. betake,r covereld on the out-side with tinfolil a similar beaker containing the1 cont'rd mlutio'n HYDROLYSIS OF ESTERS BY INFRA-RED RADIATION.1291 Both belakers were) maint,ained atl uniform tempe~ra,ture by immeasicm in a tmhermost.amtl or in broke'n icel a.nd water. The tempera.tnrel otf elach solution wa's cmtdnually o'bserveid and samples f o'r aaa,lysis wit.hdra,wn a t simultane.ous intervals for t,it,ratJoii wit,h 0'054A7-ba,ryt~a. I n all respe~cts elxce,ptl for illumina.tioa both soluticms wemret maint,ained undelr i den t i cagl condi t'ions and tse alted in the same ma.nner. I n the foillotwing t.ab,les a,rel givelii the) datmaL of a' number of elxpelriments aad the velocitly-c~elfficielnt~ t,he,red rom. Ill~rninant~ Nernst Filame,nts. Acid 0.1987N-HC1. I; calculated as a unimolecular coastant.(1.) Time. + Min-Hrs. utes. 1 55 2 9 2 39 3 4 4 15 5 25 U 12 46 12 58 1 14 1 31 1 46 2 14 3 10 4 45 oc (111.) Time. + Min-Hrs. utes. 9 35 9 49 10 7 10 49 11 49 1 0 a Control. - Tempera- Titre. ture. C.C. 21.75" 7-36 - 7.50 21-75 8.22 - 8.34 21.75 8.80 - 9.48 - 15.19 20.9" 22.3 23.4 23.7 24.9 24.5 18-35 18-35 -7.30 7.34 7-37 7.45 8.01 8.16 8.51 9.84 (?) 11.40 Illuminated. - Tempera- Titre. k x lo4. ture. c.C. 7cx 104. 21.75" 7.36 - -12.71 - 7.76 36.79 23-16 21.80 8.54 36.81 22.46 - 8-64 25-77 14.10 21.80 8.83 14.39 15.07 - 9-50 15.24 - - 15.19 -- 21.1" 7.20 (?) 26.00 7-39 22.3 7.45 31-67 6.00 23.7 7.65 41-35 9.26 23.85 8.00 42.09 25.22 24.7 8.38 41.69 (Time 2 hrs.4 mins.) 26.54 24.2 8.57 -24.27 18-2 9-10 40.15 41.94 17.9 9.55 41-94 - 11.40 - -Titre. C.C. +-\ Illum-Control. inated. 6-09 6.09 6.26 6.25 6.50 6.57 7.08 7.38 7-31 7.67 8-46 8.79 12-21 12.21 Temper at ure . & Illum-Control. inated. 21-70" 21.70" 21.70 21.70 21.30 21.30 21.20 21.25 20.75 20.75 20.75 20-80 20.75 20.75 7c x 104. -7 Illum-Control. inated. - Dark. 19.66 19.66 20-04 26.22 22.99 30.83 16-42 18.21 23.39 27.78 - 1292 RIDEAL AND HAWKINS CATALYSIS IN THE Illuminant : Time. - Min-Hrs. utes. 1 28 1 39 1 51 2 3 2 13 2 29 2 51 3 52 00 Sunlight. Illuminant: Time. - Min-Hrs. utes. Temper at ure . & Con- Illum-trol. inated. 1.0" 1-0" 0.5 0.5 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1-0 1.0 4.0 4.0 - -1 50 2 3 2 12 9 23 2 53 3 14 6 9 Time.+-Min-Rrs. utes. 1 50 2 3 2 12 2 23 2 53 3 14 6 9 00 Titre. C.C. - Con- Illum-trol. inated. 7-20 7-20 7-22 7-23 7.23 7.25 7.26 7.30 7.28 7-31 7-30 7.35 7.34 7.38 7.48 7.54 11.06 11.06 k x lo4. - Con- Illum-trol. inated. Remarks. 4.99 8.47 -4.46 5-82 -4-39 6-85 -4.34 6.28 Sun clouded. 4-23 6.26 -4-34 5.75 Sun clouded. 4.39 5-47 -- - I - - -Sunlight' and Niahrolma Coil. Temperature. , Control. 4.0" 2.0 1.5 1.5 1.5 1-5 1-5 -Sun. 4.0" 4.0 2.5 2.5 2.5 2-5 2.6 --I Nichrome. 14.0" 11.0 11.5 11.0 11.0 11.0 11.0 -Titre. C.C. c Control. Sun.Nichrome. 7-10 7.10 7.10 7.13 7-15 7.17 7-18 7.28 7.35 7.23 7.28 7.37 7-25 7.30 7.62 7-25 7.30 7.67 7-70 7-81 8.49 13.29 13.29 13-29 k x lo4. Nichrome calculated A > Control. Sun. Nichrome. 3-84 4.89 12-21 18-97 4.93 12.29 18.49 3.80 7-41 13.48 2.37 5.34 13.82 4.05 3.34 9.61 - 4.85 10.12 - -on temperature basis. 9.02 12-23 11-90 9-19 5.73 5.27 -It is elvidelnt thati the illuminateld methyl -tab is hydrolysed much more rapidly than that maintaineld at the1 same temperature in the dark. That the1 variability in the1 velocity-copefficient of the illuminated reactants is chiefly due( ts an altelratlion in the intensity of the infraxed radiation was evident from the obvious alteratlion i n the intensity olf tlhe sunlight by the1 passage od crloluds.To1 control this factor elxpelriments were conductled in which the rate of liberation of iodine by catalytia atmosphelriu olxidatioln from acidifield potassium ioldidei was simultanelously measured. This reaation is a typical pholtochemical one. It is ewidelnt from the follolwing figures thatl the same1 fador namely the1 radiation intensity affects both reactions an alteration in the velocity-coefficient of one! relaction coinciding approximately with a similar alteration in thei &her Illuminant Sun. Time. Hrj-ins. 1 38 1 53 2 9 2 23 2 40 3 1 3 22 3 41 00 1 12 1 26 1 46 2 2 2 17 2 31 2 46 m Titre. C.C. - Control. Illuminated. 5.90 5.90 5.93 5.93 5.96 6-03 6-00 6.08 6.03 6.10 6.06 6.16 6-11 6-20 6.13 6-23 9.73 10.90 5-88 5.90 5.93 5.95 6.02 6.02 6.05 11.60 5.82 5.85 6.05 6.08 6.11 6.10 6.17 11.14 Temperature.& Control. Illuminated, 9.0 3.0 0.5 0-5 0-5 2.0 1.0 1.0 -9.0 3.5 0.5 0.5 0-5 2.0 1.0 0.5 -6.0 9.0 1.0 3.0 1.0 1.0 1.0 0.5 1.0 1.0 1.0 1.0 1.0 1.0 -& Control. 3.32 3-33 3.66 3.66 3.36 -3.47 3.21 -2.78 2.69 2.48 3.68 3.05 2.94 1294 RIDEAL AND HAWKINS CATALYSIS IN THE Illurninant' Sun. Tempesature Oo. Time. Control. Illuminated. Milligram of A - iodine liberated Hrs. Mins. Titre. C.C. k x 10'. Titre. C.C. k x lo4. per minute. 2 35 5.75 1.87 5.75 -2 51 5.77 2.06 5-85 9.92 0.0043 3 8 5.81 3-70 5.86 4.11 0.0025 3 33 5-88 4-36 5-90 * 4.39 0.0025 3 51 5.95 - 5-97 5.99 0.0030 CC 11.85 - 11-85 - --It seemed possible] that t,he radiation falling omn the1 surface of the methyl amaelt,attei solution would proldum a looal rise of tempera-tlure aad t,hat~ the1 he.a,t would be carrie'd by conduction to the walls of the vessel beforel t*hel who3e.boldy o!f tihe so,lution ac.quired it highelr telmpelratnrel; thus locad rapid hydro'lysis might be1 pro-duced. This possibilitly was in relalitly relmote8 since the1 solut,ioa was f requelntlly agitated and no1 difference) in telmpesa8turei was olbserved. Nelverthelees it' was thought derjirablel to test this point, eIxperimentlarlly. A small vetssell conhining oil which could be ma.intaineld ah any det3ire.d t'elmperaturel by me'ans od an e'lectrio rwist,anm hnmelrsed in it was lowered just undelr the1 surface omf t'he rneit8hyl amlt'atel d u t i o n and sufficient elnergy was supplield to the oil t'ol maintsain the methyl acelt,a,tel a,bout.0 . 5 O higher than tshe coatroll elxpariment. The velocity-mefficielnts olbtaineld in t'his way agreed veiry closely with thoee calculated from the1 cont.ro1 eixpelriments after corretcltio8n for a rise1 in tetmpesattnrel of 0.6O as is elvide'nceld from the] following values : k x lo4 observed ............... 2.13 3.98 3-73 3.92 3-96 k x lo4 calculated ............... 2.13 3.99 3.73 3.86 3.96 From these elxpe.riment,s i t would seem tha,t t'he hydrolysis of me.thyl acetlat.e is in reality a.c*ellera.ted by irradiation in t,hel infra-reld portJoln of the speotrum an intelresting example of infra-reld photochemicad actioln ; furthesmore tha.t this speldral region is the1 region o'f adivity a,nhicipa.ted by t'he app1ica;tdon of t,hei activat,ion and quantum themies t'o chemical change.It is hopeld to continuel and extmd t8he8w e,xpelrirnelnts in the, near future in order if possible to e'lucida.te tlhe melchanism o f the cahalytic activity olf the acid e,mployed. There1 amre] two t,ena,ble theoriw to1 explain this cata,lyticl activit'y either bry an inorelasel in the a&va.t.ing radiation de,nsity or by an aclte8ration in the meoha.nism of the re:action. Although the1 above expesiment,al dab limit,e'd to1 olnel acid con-ceatsatioln a,rel tool limited to draw any definite condusio~n it would appear probable t.ha,t the1 second hypothesis, na.medy an alteIrahio HYDROLYSIS OF ESTERS BY INFRA-RED RADIATION.1295 in t4he meloha,nism of the relarotion t,hat is the intelrmediab compound thelory of catla,lysts is the correct one. It will be noted t.ha.t during the first period of illurninahion there is a very remarkable inmelase in the1 velocity-ooelfficient and that sub,sequently the1 ratel od refa,ction diminishes t'o a fairly aonstant valuel which is howelver still greaker than tha,t~ of the unillwnina,td sample. This phenomenon is not readily intelligible on the assumption of the action od t,he acid as afiecting a simple inoreass in the ra,diat,ioln delnsity sinw a f urthelr inorease in t,he ra.diatbm density should increase the1 reaction vellotoit~y pro1 ra.ta.On the inter-meldia3te-compolund theory hotwelver t,hs observed result is to be antioipa,bd. Briefly if the twa reactions be1 reprewnted by tnha follocwing purely hypothetical ecptionns : (i) CH,*CO,Me + H20 (ii) CH,*CO,Me + HCl + H20 MeOH + CH,*CO,H CH,*CO,Me,HCI,H1O CH,*CO,Me,HCl,H,O IT MeOH + CH,*C02H + HCI. t'he rate olf decompositioln in sach case beling unimolecular in exoeas of wa4telr t,hen the1 first reta,ctlion-velocity is gove'rned by the rate of a.otiva,tdon od the1 methyl aoatat'e to! re,aotl with t'he a,ctive wa,ter, a,nd t,he swond by two relatct8ioiis namely the1 ratel ojf activa8tioa of the1 melthyl acetatel to react with active1 hydrochlo'ria acid and by the rate of adiva,tion of the complelx t o bre,ah down into the pro-ducts of the reaction.The rate of any sequent reaction is always governed by the slowat od the1 inklrme.diatet relacotions ; thus i f we assume the slowest one in hhis case1 t.o be the decomposition of the1 mrnples theln illumina,tion with a' pa,rticula.r frequenay of light will acce;leIra.tel the decompo'sition of the compla so tha,t the re:action-velocity will t'heln be1 govermd by the next sloweat rwa tIon which we have assumed to ba t'hel co!mbination of the methyl amtlate and hydra,ted hydrochloric a'oid. This relaation however, t a k a p1a.m) morel rapidly tlhan the1 combinatioa of methyl acetate and waf,er. On this hypothesis of selries reactions t<he prima4ry acceleration on illumination is to be aikributed to the rapid decom-pwition of the ampletx which is premnt in redactively large quaati-ties since it bre.aks down but slowly; the primary acmlelrates then fadls off until the! normal rate of the1 next slowest rsaotion sets in. Summary. Preliminary experiments have1 indicated that! the hydrolysis of methyl amtatel is ca,taJytically awe;lerated by infra-red radiation. 3 B* 1296 HINKEL THE ACTION OF CHLORINE ON The speotral region of photoachivity is in agrtxmeint with that ca,lcrulalhd o n the aativation and quantum tbwria of chemical &lion. The experimental data obtained asa most readily interpreted on the1 intermediate-mmpounds hypothesis in the caw of thel hydrolysis of esters by dilute acids. It is propoaed to1 extend thew experirneat's in order ta obtain further information as to the number and nature of these intmediatel colmpaunds and t o examine the spectral region o f their a4ctivation in more detail. UNTVE~SITY OF ILLINOIS U.S.A. AND TRINITY HALL CAMBRIDGE. [Received July 15th 1920.