Title Photochemical chlorination of methane

Author(s)

Citation 物理化學の進歩 (1941), 15(3): 86-97

Issue Date 1941-05

URL http://hdl.handle.net/2433/46268

Right

Type Departmental Bulletin Paper

Textversion publisher

Kyoto University

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PHOTOCHEMICAL CHLORINATION OF METHANE.

~ By Mrslo "1'navxn.

The photochemical chlorination of methane proceeds by a chain mechar ~isnt. Ccehn and Cordes'1 found a quantum yield of log. Thin reaction bears a close resemblance to the. hydrogen-chlorine reactioneJ•al, and therefore the reaction mecha-nism is. assumed to follow either of the two alternative schenus:

I.

CI I,+Cl4-+ CI I,CI+CL (3)

II.

Simple considerations make the former seem vtore probable. This point will be refcrred'to later.

Unlike the hyilrogen-chlorine reaction, the methane-chlorine reaction is com-

plex oir account of the variety of the chlorides produced. As the reaction proceeds, methylene chloride, chloroform and carbon tetrtcliloride are Conned besides methyl

chloride. This renders it di(iicult to measure the velocity of the reaction between chlorine and methane alone. Therefore it is desirable to measure the reaction rate at an early st[tge of the reaction, where oily methyl chloride is a little produced and the fa•mation of other chla•ides can he neglected. This ix the very condition satisfied when we use the method of thermal analysis of reaction velocity- which originated with Prof. S. Horiba"I•°~'nr. "this method enables us to measure the rate

rg~i^~rsk~;

i~ •..:

x) Coehn eod Cordes, Z. pkydk. C/rrm., B, 9, x (x9301 z) Jones and Rnles, J..Anr. Ckrm. Soc, 58, zz8z (x9y1). -

3) Peace and Wnlr. J Am. Ckon. Sot., 53, 37z8 (lg3t). q) S Horiba and T. Ichikawa, This Janmal, 1, tq3 (i9z7); "Srzrsgint" (a collection of papers r

dedicated l0 1'rn(. Y. Osnka) 73 (x9z7} T. Ichikawa, This Joarnal, 4, x Q93o); Z. phyrik. C/rrm., B, 10, z99 (x9301

-5) M. Tnmore, 't'his Journal, 11, x (I9;7). 6) M. Tanmrm, ibid., 7, 49 (x9331

1 ~`• ~r-7 ~ r ' . [ ~ ~ - ~ ~ ~ ~ ~ ~ill~lt~ay;~- Vol. 15n-.(.

Na 3 I'IIOTOCIfETIICAI. Cii LORINATION ON MliTIIANE: 87

in the course of the first few seconds of the reaction, in which methyl chloride is

the main jtroduct and the formation of more highly chlorinated prorlitcts is negli-

Bible. In fact, the partial pressure of the methyl chloride formed tbroughout the whole course of our experiments has Ix:en calculated to be less than [attn. 1Ig.

As the initial pressure of methane is fyq mm. Hg and the reaction velocity of

chlorination of methyl chloride, if present in the same amount as methane, is of

the same order of magnitude as that of chlorination. of methane't•"?, the-effect of

successive substitution on the measurement is negligible in the present experiments.

1'he present author has so far IShulied the photochemical chlorination of

hydrogen°1, the phutochentical union u( carbon monoxide and chlorinefit, and the'

chloride-sensitized oxidation of carbon tnonoxidert by this method and measured the

mean lives of reaction chains, concentrations of chain carriers and collision yields

of some partial reactions and so on. Similar :measurements have now been madz

about the photochemical chlorination of methane .and the reaction mechanism

' dISCUSSed.

Experimental Method.

here will be giveti only an outline ol'~the cxpcmnental method. For further informa-

tion, refer to the previous repUrLK'I•"r•''t. 'Phe pressure increase dy of a gts mixture due to

the hctt of reaction was recorded on a photographic film, mica membrane and oplicat lever

being used properly~t. From this record the reaction velocit}• t̀ill rnn lie calculated by the following-equatigt,

being used properly~l,

following-equatiat,

K dz:

where

to the

amt aft

(IE [lt T'9luy

K and k are co h 1

heat of reaction"tar

Ve can thus ctlculat

er shutting off light

nstants, t e va ues b

td k refers to ix

e the reactiou ng 1

Sec, for ex rga

+So (+935} waa a cylindrigl Yymx-gloss tube of about 3.ry em. in diameter and about

aces of which were mode of quartz plnte.+. The vessel Lnd a side htbe with a

msen~ z. p/ry„[, cb.•,,,., A, lit, 343 (rgog) and L. Schjunberg; ibid., A,. 172, scion of CI LOCI is about qry ktaL Using this vnluc and other thermal data,

CL=C1rsCl} HCIts3g ktnly

and Rossini s ° Thmmodumirfry of CJvmira! Subrtmtter" (rg36), the reac-the present paper weuse 23.3,kcr1. (or the calndalien. i

the reaction velocit}• ~dt

~,

of which an he easily o

the cooling of the•gas m

velocity at any time duri

am plc, .r' -. ,and z.

ry) T(. Tamura, .ibid., 9, S) The rrsdinn vessel

r3.6-cm. in lenglL, both b thin mica membrane.

9)' According In Tho +97 (+935), the heat of combo we obtain

CH~t

According to Bichowsky tion-hmt.ls s3.8 kcal, IIut in

P~~.

rnn he calculated by the

fit)

rained. K is proportional

tore. ,

the letiod of illumination

(T94Y1! -..•~

5

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:~ .~

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~~

Y

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5

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s8 bL'TATIUKA Vol. XV

Preparationof~Reactt;nts. "

Chlorine was prepared h}• electrol}sing a solution of potassium chloride acidified x•ith

h}drochlodc acid. The ~ s. was purifier) hy~ washing with water and then with sulphuric acid, ~hothin darkened vessels, and was paned througfi a tuhe filled with gl.tss lwtlls and heated at

35o C., and then was collected with solid nrhon rlioside. 'T'his chlorine wasihen subjected

to repeated fractional distillation, in vacuum.

Methane was. prepared frt?m aluminium uarhide.and purified b}' the. procedure clue to R.

Sehenck'D'. Just before the experiment, the methane thus obtained was wbjected to repeated

fmcticnal distillationin vacuum. +

In •all ptnce+lures much pre was taken as In the exclusion of oxygen.

• Experiments .

r

The reaction "vessel was e•ashed severd tinfes with chlorine, and dtr: grease

used was that treated with chlorine and heat@d in vacuum. The initial partial

pressures of gases were read by a mercury manometer, a spring manometer of P}•rcx glass being used as the zero point instrument to avoid the rlirecY contact q(

mercury with chlorine.

In.'general, the sensitivity of the gas.:-mixture to ligl+t variedduring the period

of illumination, probably due to the destruction of impurities. This chance of

sensitivity became very small when ntethanc a•as very carefully purified. The

methane used in the present experiments was of such a high purity as no notice-

able change of sensitivity n•as obsen•ed when illuminated for 3 minutes. Through-

out the whole course of the present experiments, the total time of illuminatiot was

only about 3o seconds. The reproducibility a•as, therefore, satisfactory. Nohvith-

standing'our careful purific"ation," a small amount of impurities must have been

present in the gas mixture. But it must be emphasized here that the results of

calculation gi~~en later on arc entirely uninfluenced by the presence of the small

amount•of impurities. -

The reaction vessel, light source, filters and others were the same as used in

the esixrhnents previously.carricd out by the author°>•'D•r'. The light source was

a tooo C.Y. Pbintolitc lamp, operated from a battery suppl}•. ']'he-light e•as passed

Through a y3mm. layer of a solution rCuS0r+2t6o NHa Molar) filters- of various tr \a

xo) R. Schenck,.2. tr) The absorption

length of the light and

e~-aSiY

180

nsparene}''°. The light beam u~as rendered

nnarg. Clam., 164, rq5 (x9s7). of chlorine taken info consideration, g4oo A can he regSrde

Deed for the caltulalion of quantum gield.

and ncutnd tint

approximately

d~as the'mean wavt

~la%I~

Li~4~D

i.

`~ S 40

T

C N 7 20

u e v N_

O

1

1~,

photostationary state.

velocities in photosta[

we. notice that therea

power of light intensi

dx dt

As is seen in Table 1

quantum yields were

statiatary state was, f

Fig. 3. ,

'f

~ill~lt~at;1>=~ Vo 1, 15n

No. 3 PIIOTOCIIEi.IICAi. CIILORINATION ON MF.1'IIANF.. 89

parallel ,and slightly smaller in diameter thmt that of the cylindrical reaction vessel.

The initial partial pressure of methane was t 79 mnt. Hg and that of chlorine t [ [

mm. / Ig. The initial pressure of mMhyl chldridr teas o.o mm. Hg and the final

pressure less than t mm. Hg. The esper.mcnts were carried out at room tunpera-

t

A) Change of the Reaction Velocity during Exposure. Effect of Light Intensity and Quantum Yield.

"1'he reaction velocities durin~* the period of illumination calculated by equation '

([) using experimental records are given in Fig. t. LI this fw~ure J's represent light intensities in arbitrary unit. The numbers under the curves indicate the ex-

lxrimental numbers. As is seen from. the figure, upon illumination the reaction ~- velocity increases rapidly to reach a constant value, which is the velocity in

~;

J =0.d

,~, ̀ ~

dN

2.6.

J. J. J =O.l

0 62 O.Q o.6 O.$ 1.0 3.2 ' Time (sec) ~ ,

OO, 1. O Experimental. t Thmrelicnl. Fig. I. Change of Reaction Velocity during Iixpnure.

ry state. In this figure, (or the reactions by ]t taker lights, only the

photostatianary state are given. From the above eslxrimenta] data, tt the reaction velocity in the stationary state is propurtional Co o.6-th

It intensity, namely,

dx =kJ°~°• ~Z) dt

I Table I, k is constant enough to justify the above expression. .The

ds were also measured"/. The smaller the velocity in the photo-

te was, the larger the quantum }rield was as shwvn in Table l and

ti_R :d_

.~ '!V

.~-

ao

F.x

~' ',

'~? a~

~~_

~~ ./

..

1,

M. TAMURA

Table ].

(Cl~=ut mm. IIg, (CRS)=r79 mm. Hg. Temperature: i9°L

n1= ~

Vol. XV

F.xpl. No. Light Intensify J inArbilrnoy Unil.

Iteaztion Velocity inPholn

/slnlinnary Slnle

\r~6nMl~SCe.

k Qnn alum field

4J117

4J1t

J5

r.~

o{x

o.r3

57.3

3q.o

r 7.8

57

57

6r

.

_700

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6q;c

Ga

qo

ao

~~

Elr .

~

e

o_

`r.

Fig,

.^

ran

Esc

it

in

/,, ~~

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R ~•

rT-

i i ~S

K

A

prefersG:

i

ti, i

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u i E

e

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Ifi000

]2Onn

5000

/000

O 0.2 O.(j 0.6 O8

Time (sec.) . Rc

~., Q, ~ lizperimcntal. } 'I'heorelicaL

Fig, z Chnnge of Reaction Veloci[q otter ` Fig, $ 'the Shutting off Light. in Yholns[

(nr 2

After shutting oCf light, the reaction velocity di

it ran as shottm in Fig. a. The curve indicates the

in Expts. A`o. I, 4 and y after shutting off light.

Discussion.

A) Collision .Yield of Partial

CI+CH, -+HC1+CH,.

As will be explained later, the reaction mechar

prefers is neiNter I nor II given above. Rut ten

i.

ff~avr2i/a.fabw.... _ _ .. ~ ....

/~ o zo qo (»

Reaction Velocity Y([o-s mol\ sec f.

OO EaperimentaL + Theoretical.

Pig. $ 'fhe Relation Irc[ween the Reaction Velatity in Yholns[ationary State and the Qmntum Yield

(nr 2X the Mean Length of Chain).

t velocity did not immediately vanish, but

indicates the change u( the reaction velocity

.~~'~~1;

'artist Reaction ,

+CH,.

mechmtism which the present author

tut temporarily u•e ttse the scheme I

1

~ . b - _ -. ~i11~1t~a?itt~ ~Vol: ~15n ~.

No. 3 PfIO'I OCHIshfICAL CFILORINATION OF METTIANE. 91

for simplicity. This does not affect the results of calcu]ation given below.

Now ]et the time taken for a chain link be r sec., then one molecule of hydrogen chloride are forrried by a chlorine atom in r sec. "I'he life of a chain is

given by T=cv, v.bcing the chain length or the number of chain links in thu chain.

Just as in the case of hydrogen-chlorine reaction°j, we c:m easily evaluate T and v and hence r from our experimental results. The mean life of chain, T ,

after shutting off light is obtained from the velocity curve in Pig, 2. Let Va repre-

sent t1le reaction velocity at the moment of shutting off light, then T is given by

T" Y~ ~ I~dt. (3) 0 Thus, from Fig. ^_. u•e have T =0.962 x ~o 'sec.. As the chain length is one half

of the quantum yield, tfie moan chain length v,,, which 'corresponds to T , is

obtained from Fig. 3. in the following way. Since the exlxrimentd results show

that the velocity is proportional to o.Gth power of the light intensity, it is possible

to conclude that the reaction chains arc terminated principally by the combination ,

of chain carriers-bchveen themselves rather than by such an inhibitor as oxygen.

The chain becomes, therefore, longer, as the concentration of chain carriers beconus

smaller or the reaction velocity becomes smaller, for the reaction velocity is pro-

portional to the caxcntmtion of chain carriers. vm is, therefore, obtained from Fig. 3. by the following relation :

I ro v,.. = V (quantum yield) d V. (q) 2

a

Thus we get v„,=2800. Flence r is calculated to be 3.¢¢x io'asec. r is the

time taken by a chain ]ink, but the partial reaction (g) in I may be considerred to .

be faster than the-partial reaction (2) and the latter can be reasonably considered to take r sec r depends, of course, upon the partial pressures of component gases

and tenlpcrah~m, and can be considered as reciprocally proportional to the concen-tration of methane.

Now let us evaluate the collision yield of the reaction (2). The number of

collisions of a chlorine atom with methane molecules in one second is given by

L=x+/ err

tt,e atomic or m

Ac, ~' ~cu,

)-JMc~-F n1cu.

r

where d is

12~

. '.:::IUC .~!•.~

L.oebr " Krru[is

\ z / N d/~, ~9~,

c or molecular diameter, M th

Thrary of Cat" p. 5~7 (t9=7D

• h' T • ~ Crto

c atomic or

~ 5)

weightI110~CC4id7

~~~.L '~i ., ..~

) `~S~+ 11J'~ } . P

~~

`• ~ .~

,~~

?:

.~

~~ ~~, '~ h

V

~}~ .~

•I~

.~ ' ~N

.: 2

i

. ~~ ~N

.• ~ i

>~

:,

y

~ T

y

~` 1

~i ~..

..~

~~

.:

..'

'r ~

1

5 , •~ ~,r_

a ~ >^ v, a J _~.--- i ~ill~Tt~O)i~~ doll 95n

92 M. TAMURA Vol. XV

and Ate, the number of metl[ane molecules in I cm°.

Assuming that the clilorine atom is spherical and has the same dcusity as that

of chlorine molecules, we have dot=z.6 x Io ° col.'=' Whentlic pressure of methane'"' is [ atm. and the temperature I~°C., Z is o.5zx 1010. The collision yield of the

partial reaction (z) is, therefore,

I "1 =z.4x l0'6 o.5zxld°x I~x3.44x1o~

7

' Let & represent the activation energy of m~action (z) and p the stcric factor, then

Since p is equal to or less than unity, from equation (6) GL 6.z kcal. The reaction mechanism I[ given above contains a partial reaction, CI-I-CfLt

--~ CH°Cl-1-N. Rut this reaction is enduthem»e by about z[ kcal1Ol and obviously

incompetent as the partial reaction of a rapid chain reaction at room temperature.

D4oreover, according to our results the heat of activation of the me determining

partial reaction must be at most about 6.z kcal, so the above reaction cannot be considered as a partial reaction. 1'htts the w[sttitableness of the reaction mecha-

nism II is evident.

B) Concentration of Chain Carriers. Mechanism of Chain Breaking..

~Ve can estimate the concentration ~of chain carriers in the following way. Let

ar° represent the number-of chlorine atoms produced by light in one c.c. in one

second and T°,,, the mean life of chain in photosbltionary state, then the product 7r°Tao represents the number of chain carriers in I c.c. in photostationary state.

Trr.~ is given by ~ :r, r being the quantum yield. Thus in our exlx:riments t, 4 and 7, ehere w°=t4.6x [o", -=3.44x to-6 sec. and T=zyoo, »°T,r, is G.8x [010. in

other words the partial pressure of chain catriers is L9 x low nun. 1-Ig. Now it is

reasonable to assume that this partial prgssurc gives that of CI (or possibly the

t;) 71e diameter oC methane molecule was assumed to be 3•t4 x 10=° cm. t4) This value is of the same order of magnitude. as the collision yield nC the reaction, CI}1L+

IICI+f L, oMained by the present author, the latter being t.9 x t~°. (Sce foot-note 5). t t5) CI[,t+CL=CI[°Cl}ftCl+z3 kcal.

p-FCI:CL+57 knl.

- IICI=IC+Ci-rot knl. -

CI [c+c1=C7I°Cl+x-zt kral.

~. vrt~ir_,.-

r

(19411)

.-~.. :1tYl.'R

t ~ :.~~ -. -va r - ,~ ~_ ~i1C~1t~0)itt~ Vol

~: e-,15n

No. 3 PHOTOCIIEhCICAI. CICI,O[iINA1'ION OP \fE'I7CANE. 93

sum of I><~rtial pressures of CI and CI;, as will be explained hater), for in the reac-

tion mechanism I the partial reaction (3) will be fast in comparison with the

reaction (a), and hence the mean life of the chlorine atom will be longer Ulan

- that of Cf la.

As the reaction velocity is pro)xxtiona] to a power of the intensity of light

approaching to 0.5, it is concluded that the reaction chains arc terminated princi-

pally by the combination of chain carnets behveen themselves, ether than by such

an inhibitor as oxygen or by the wall of the vessel. Note first Ict us assume that

1_gx to amm. IIg obtained above gives the lutrtial pressure oEchlorine atoms., Then

we can easily calculate the number of ternary collisions, CI+CI+M's', which a

chlorine atom suffers in one second in our experiments t, 4 and 7. The result of

calculation shows that the number of sudt ternary collisions is about z.6x fo '. It

takes, therefore, about 4o sccondi before a chlorine atom recombines in this manner.

But as shown above, the mean life of chain in expenmcnts t,q and y is only

3.44x Io~k2yoox ~ =4.65x lo"='sec., so that the chain breaking reactiat can- not be CI+CI+\lyCl.+1•'f. Similar insult teas also obtained in our expcnment

on the photochemical union of hydrogen and chlonneat and so we considered the

possibility that the chain might be 'broken by the reaction CIa+CIa-. 3C1_.

I:ollefson and ]iyring'r' put forward on quantum mechanical grounds the following

mechanism for the recombination of chlorine atoms,

According to them, quasimolecule CI;< has a very long life as compared with the

dutltion of an ortlinaty collision atnl hence ternary collision is unnccesslry fur the

former reaction. -

But recently Ritchic and Smith'at mcasurcd the photoexpansion of chlorine

under various conditions :md their results agreed with the mechanism

CI+Ch+I11-CIa+Rt CI,+CI,-.3CI,.

Notv let us examine whether this aucchanism is available for our experiment i or not, Let us assume that t.g x to-0 mm.Ilg given above represents the conecn-

tration of CIa in the photostationary state in expcnments I, 4 and, y : then the time

taken for a CIa to disappear in the reaction CIa+CIa-+3CI, is calculated's) to be

[6) ri represeols a third hady. I7) RolleCson and Eyring, J..1nr. Chrm. Sa:., 54, [70 (t93z).

[S) Ritchic and Smith, J. Client: .Sat., 3qq ([9qo).- Ig)- Assuming shat Cly is spherical and hat the same density

3.SX [~scm. for the diameter of Cly.

~~i '

as that of dtlorine molecules, we gel

i

, i

~_ .~~

c'sga~

`~ 4

~~

•~

,a

,~

.!

•A~

s

J~

~~

~~

:' L

•.~

.~

~S .;

. _~

:. ~~~

~.

t

F::~•

?'~ .

4 ;, r"

r

.z

^.

~~. {.

1~

}~

I

~

'`I , b.

f•

1

~~ ~.

1~ 4: 1 3 :: i ~-~

.

~..~~ kf,•,

... •~"t '~' •- - - ~ .- _ .~'41~1Ct~~i11~11Vo1?y

94 M. TAMUI2A VoL XV

9~5 x to-"-sec. 6y taking the collision yield as'unity, and it agrees well with the mean life of chain in order of magnitude, the latter being q.q x to- sec. as is given

above. This indicates that the chain terminating reaction may be either

and that the concentration of CI, must be either of the same order of magnitude as, or higher than, that of CI. Craggs, Squire and Allmand~' introduced the

following equilibrium to explain their experimental results on the photochemical anion of hydrogen and chlorine.

CI+CI, ~ CI, (iii)

~Or Cl+Clo}1~IFC~,+li4. (IV)

And according to them, reaction chains are ended by the disappearance of chlorine

atoms and of Cl, radicals, both on the walls and, without Yernary collisions, in the

gas phase. As will be explained later on, in our experimcnhl condition equi-

librium (iii) or (iv) can be considered to exist. Taking the experimental results

of Ritchie and Smith19j into account, we prefer here (iv) to (iii). The equilibriilm constant K„ given by Craggs, Squire alid Allmand°01 is o.oogg mm. ~ and that .

calculated from the data given by Rollefson and Eyring"' o.o76mm.'' at t8°C. Hence in our experimental COn(ht1o115, the concentration of Cl, is estinslted to be .

o[ the same order of magnitude as that of CI in agreement with our conclusion

_ stated above.

. Though Cl, is introduced, such reaction chains as

. CI,±CH, --• CH,+IICI+CI= (vi)

are . to be neglected. According to Rollelsat and liyring'" or to Craggs, Squire

and Allmand"-0', the beat of activation, of reaction (v) is ¢5-5 kcal. hence the time taken for a CI atom to make a CI, radical in accordance with the reaction

(v) is, in our conditions, about to 'sec.=o and is very long as compared with the time taken for a chain link, 3.4q x toy sec, According to. Kimball and Eyring_1 the collision yield of the. reaction Cl,} Ho--~ Cl_+hlCl+fi is tom-to-' times the

yield of CI-IL_ collisions. There .arc some colisidcrations, which are unfavorable

zo) zt) 22~

Craggs, Squire

The third lad

KimLall and E

f/1`w_ 6.

1 atom to make a CI, radical in accordance with the react

ons, about to 'sec.=D and is very long as compared with

in link, 3.4q x toy sec, According to. Kimball and Eyrie,

the. reaction Cl,} Ho--~ Cl_+IICI+fi is tom-to-' times

sions. There .arc some cotisidcrations, which are unfavon

i and Allmand, J. Clam. Sot., 1878 (1937)• y.M was asdumal aot to ay cataly[ically nud reduce W< heat of activation. Y^"C, ./• 1Ln. Clam. Sar., 51, 3$76-f=93z)-

nY Ci! D

•i , _ ~

r

' Na 3 1'IIOTOCIIEAI~CAL C(IL(1IiINA'1'ION Up METRANE. 95 -

to their .views', but let us assume in our reaction which is similar to the hydrogen- ,

chlorine reaction, that the yield of CI,-CII, collision is to;' times that of CI-CH,

collision. Por these reasons the neglect reaction chains consisting of (v), (vi) and

(vii). In short, our c~periment:d insults accord with the following rcactiat mecha- '

raisin. 'III.

Cl}Cl_+ItI-.CIa+NI _ O m equilibrium ~ ~"

CI}Clf.-+CIIa+11C1 (n)

CI }'Cla-+ aCly rchain-breaking"t (~) CliICh OIIS. CI or Cl,+impurities or wall -+ (tl) = \ .

Under our eslterintental condition the can, as stated abgve, assume the con-

centration of CI to be nearly equal to that of Cla• If so, it is calculated that, in

the phokost.-ttionap• state of. thr: esperinlents I, q and y, Io"-to" chlorine atoms t^ and Cla radicals per c.c, and per sec., are formed and lost by the reactions( and

(r)st, and that io" chlorine atoms arc produced by (a) and lost by ({) and (r/) alter conversiot into Cla radicals; lo" CI;, radicals are lost by ({) while to16 ,.

chlorine atoms react with methane in accordance with (8) and are immediately ~~ regatented by- (_). The disappearance of CI and Cla by (Il) is evidently negligible.

Thus the conditions sufficient fur the c~uilibriuin between (t4) and (r) arc nearly h satisfied. ~°

There is still a point to be referred to. As the assumed that the yield of ~

Cla-CH, collision is Io a times as much as that of CI-CH, collision, e•e arc led 4 to the result that lo'" Cla radicals per c.c, and per sec., are lost by the reaction / '

(vi) and the same amount of CI atoms are immediately produced by (vii). This does not remarkably disturb the equilibrium. If the yield of CI,-CH, collision is

larger than that assumed and hence the rate of conversion of CI; tildicals through ~~i

23) Rolle(snn, f..AUt. C/ren~. Soa,.55, 579 (x934)• 24) The breaking. of the chain by the disappenrnnce of CI[a may he neglected, owing to its low

concentration. (B)is of importance,as compared with (~) and (y) only when the concentration of chain rsrriers is-]aw.

25) TLe. heat of actiVelion n( the reaction (r) was asspmed In be 7.5 kcal., acoordioty to Crnggs, Sgnirc. and Allmand, :See loot-note 20)- ,

./ - •=i 'Y

-

~__. '~

..

S+

_~r

~~.,

~A~ ~l f;

k" -

ct

~•

~1,, ~'

~':.. ~,~

Y •

_~

~E~ ~

_

~'

R

~/

4 8

F '-:

t•

.; . ., - ~

96 ~ - DL TATSURA VoL XV •

1

(vi). and (vii) into'CI is high, equilibrium will be dishirbcd and the ratio (Cl)/(CI,) will become la ~c.. Rut_this is contrary to our conclusion that the. concentration of GI, radicals must be nearly equal to, or higher than, that of CI atoms.

~ The move scheme IlT has been obtained under some .assumptions, and. it can not, of ~oursc, 6c. considered to be perfect. But the results. of the present cspcri-

ments can be e~p]ained by it and not by I or TT.

C) Equations Representing the F.aperimental Curces.

Theoretical egnsiderations ]cad to the following equations representing the

relation-behvccn the reaction velocity and time, and thah behveen the quantum

yield and [hc reaction velocity in photostationarystates'. Fur the reaction vchicily during the cslwsure we get

O

And the reaction velocity after shutting off light is given

the quantum }Meld sad the reaction velocity in photostationary

y

=1, (7)

ty after shutting off light is given

(~)

reaction velocity in photostationary

~9)

reaction velocity in the unit of

ary state, r the yuantum yield, t -

tt'hose VHIUCS are 3.6i, 0.34 and

onstants and chc derivation of the.

ogcn-chlorine reaction'1. "I he point ed by the above equations. "[hey•

thane and chlorine has Ix:en in-

Using this method we can avoid nation. e time taken for a chainlink have

the concentration of Chain can•iers

l

tYhere Q= ~rl"-by

The rol state is

ht the . nto

~ log -

anon between the c,

expressed by

A+ RY=

•tbove thre

~, 1/o the

e in sec., . spectively.

quations, + in Figt

t .to fall n

`The phot

ed by the lusion bro

The' mea

Iculated,

~R...1~i-_.

+ 4,~?S.

30

t0 x sec

the tim

t 33o re

.above `c

marked

are seep

~7

vcstigat the con

y~.

been is

x.. '. '

rY

c equations,

reaction vel

and A, P a

As to th

refer to the

ves i, 2 and

car the esli

ochcmical r

meClrod of

ught about

m li(e of rea 'fh

e results

=r r

f~ represents the

Deity in photostation

nd N are constants

e details of these e

refwrt on the bydr

3 arc those gb[ain

erimental curves.

Summary.

eaction betmr:en me

thermal analysis.

by successive chlori

coon chains and th

of the estimation of

1

-.. -..y-~~_

1

tly CJ:.

?g*~"y_ Y _-•a - r - - - ° •~ t ~ ~ ~I~1t~Ot ~f.~Jdl. ~15,t~ .9

.. ~ ,~

1~

No. S I'1[OTOC _t[EhIICAL CI[LORTNATION OF TfETHANE. 97 ~ "~

:ndicatc that the chin-terminating reaction is not of the ternary collision -type, / $ such as CI+CI-I-ni-+C1~+:1f, but of ;binary collision tylx, such as CI,~-CI,-+

3Clo or CI+CIa-+zCl._. The reaction mechanism is discussed aad a plausible one given. ~ - ~

3) The collision yield of the reaction CI}CFI,-. CH,}flCl is calculated to r be 2.qx low; in other teords, the. heat of activation of this partial reaction is at

most 6.z kcal.

4) In the ntcthanechlorine reaction at room temperature, a mechanism cdn- taining.almrtial reaction, CI}CIIa-.CI-[,Cl}H, must be discarded.

J In conclusion, the author wishes to express his hearty (hanks to Professor S. ,

n Horiba (or 'his kind guidance throughout this investigation.

27ie Lrebmntory of Physinzl Cherniebry, ]tjalo Imperdxl Unireraitg

oral - The Inbomlory of Phyaiml Chenri~ry, - -

TokyoUnacr~ity o,(Engineeriuy. - - (Re¢ived April x5, rgge)

1 .1

/,

_ ~ .~

~ N

4• ~Y