LEY CIVIL DEL MATRIMONIO CONSTITUIDO ENTRE

ctiou of the form:

2’h.CH.*—> Pb.CiU*CH.,*Th

«; d <2

io unquestionably preheat* Moreovert since the plot

(rate of formation of toluene)/(po: ti«l nreaoure of fluorene) at centant temperature and partial pressure of diheo.jri

(see

figure 1' «

,,;e 8^ } shoes a straight • ine

dependency on fluorene concentration* the concentration of benny1 radical© is not levered by the rate of their re oval as. toluene in these experiment©*

iwo procedures have been proposed to account for thi •

(X) Thu decomposition to oen&yl radicals is very high,

and recombination and further reaction do net occur in the furnace area but take pin co In the cooler outlet*

(2) "he rate of <©composition and the rate of recombina­ tion ere both

very

high, an the result la a

small

equilibrium concentration of radicals. Tn affect thin la equivalent to a reaction of the fores

PheCH^.CFKs h «—•> 2Fh.C>U.

c tl &

Of these suggestions care (1) la unsatisfactory« aa it io unlikely that the presence of ouch a large con­

centration of radicals would reult in so small an Increase

in toluene production when fluorene io introduced* Ihe addition of an equlmolecular proportion of fluorene causeo the rate of formation to increase by a factor <*f *1 only* Cn the other hand, if case (2) is operative this snail increase would seem more plausible as dibonayl and

fluorene would be competing for benzyl radicals on equal terms, and a factor of 3*1 is reasonable for two hydrogen donors where the energies of abstraction may differ by

two or three k*cal*/mole*

t has been demonstrated that caee (?) would lead to a 1*5 order lar with respect to toluene formation, yet the plot ^/partial pleasure of dibenayl at constant

Figure 54.

7.0

8.5 *

Slope = 'n' = 1.57.

S.O

Logw (Dibenzyl) (fcle,/u) 8.0

1>5.

shoes that the calculated 1*5 order rate constant la not

Independent of partial pressure. The

apparent

order of reaction la in fact eeeeehat lower than 1**>*

Ince •a’* the order of reaction*

is defined by

the equation:

dx a k.a 1 dt

tn.« Xog.g " l0«** * na°«’a

«hea a plot of the log* of the rate of formation of toluene 0,1 alnot the logarithm of the artial nren^ure of dibeasyl injected nhould glee a straight line whose slope Is

This has been done in Figure 5*' ana a

value

of ‘a* » 1* >? was obtained*

owevor* I rem the evidence o<" the

ror* alone*

i in dear Uiet the proposition is basically soun< * and that the re ctlon runt proceed through o steady &tate con* castration of honey 1 radicals caused by the ra, id decon* position of di bona;/ 1 an,; an almost equally rapid recon*

bias ticn*

Any doubts on this ecore or removed on con i ering

the results of the sms ©poctronetric etudes of the

diMMiayl • denteredibenayi air

teres* slag temperatures

tell below the ran^e for an red able toluene formation

the © x~ evidence of a ran ionisation of th< eemreaento* ■one idea of the relative ra idity of

thio reaction

con

.r->~ - J

u*

’’equilibration” occur© » i*e* ^hcre randomisation is

com lots* iablo 6 shoes that thia situation is reaohed at ap roxidately 6>o < « a temperature correoponding to

<'•>9$ decomposition

to toluene* Honco, the rates of formation and recombination

of

be

nay

1 radical© are many

txmeo greater than the rate

of

their reaction with

dib nzyi

to

form toluene*

'row thia ovidence, the princl al reaction of the mechanism can bo established as

h*CH~*CH~* h <?’—»•> d ii* 3(»\_« <2 <2 £

Deopite thin Confirmation of the Initial processes, the failure to conform acre accurately to a 1*> order law remains unexplained* The hooua.tion was made that the

steady otatc concentration of benzyl radicals nan snail,

but even if thin eaa not ao, it coul4 not account for the ap meat 1*57 or ^ei dependence* or, if at any moment

x • the amount of dibonsyl decomposed to toluene etc* y n the iibeasyl dla&oclnted to benzyl radicals*

a a the dibonayl injected*

then (a~x-y) » the uadieaeeiated dibenryl*

.*• the r e of .-in tion C" <.olueae » Jt *^y*(a»x*^ ) 1* now *C a '

(5^7) •

•*. 2y a VUa-M-y)^ >.

•% dx w J* it a Vs

The experimental data h<ve boon applied to the

quatt on

dt obo«

(a-x)

5/2 £>•

thua k .

U-a>v,« k .itfya-x-yP'2

6.

ooo» a

or *CbO.S *V* ,(1 - -^-?/2 7*

• tt~x)

Ja»t froa equation 2, tne concentration of radlcala

depends on the equate root of the oibenayl concentration*

an hence at low prssauroa oi dlbenzyl the fraction dlo- aociated would be higher than at nigh preanuren*

!• • y would decrease with rnoreaelag preeaure of

a-x

dibenzyl*

we

Cl * > *©uXd xner a«e with increasing ;te ;ure

a~x

of dib>nzyl* and reaoa a limit of unltj at higher orosonrs®*

Thus* if the concentration si benzyl rauioalo tsaa

ap reciablo* tus oboeivod rate constants* calculated fron equation >• would be lover than the true rate constant at the low preomureo and tend to approach the true* or higher* value at high preo&urea* Tnio la the raveroe of the

oboorvoa behaviour for Ulbenzyl (Figure 2C)«

An explanation can be fount ii the nuggett^on* mode in

th«

first o ctlon of this chapter* ia adopted* viz •

that phen. i radical® are involved In the neshanlaa* A

otudy of the graphs of product ration indicate® that the production of toluene la too coa lex to have a simple order

156.

ascribed to it*

If paenyl radloaU do decompose on the

wall, the

tCvUeno

formation has no

loagor

a si«; 1©

kinetic

dependence on the concentration of Ib^nsyl* but io altered ap; reolably by the reaction of hydroen atone

produced in thio aide reaction* At lor pressures the

. oportjon of tolu no to the ottur reouXtaata is increased*

and hence the rate of production

is nlgber

than would be c leui tod assuring a 1*> order depen once* t higher

peeourea

tne secondary effect xs

coaslder bly

reduced*

;xvin>; a closer a

roximation

to the expected order* tn coin&yj-nce of this complex bcaaviour* it is obvious that a study of the r<ue oi iormation of toluene

In document Vida y Ética Año 19, Nº 1, 2018 (número completo) (página 118-121)