The alkaline hydrolysis of substituted phenyltriphenyl phosphonium salts

A thesis presented for the degree of

Master

of

Ucience

in the University of Canterbury,

Ohristchurch, New Zealand.

K

.

Hi ~~

.

by

DAL~:JELL

CHEI<IL"TI\Y PEPt 'l. LIP.R.

OO!lTENT8

hBf\TRACT

I

I !

IHTRODUCTION

General Considerations

llecompasition of

Quaternary

Phosphonium Hydroxides

EXT'EHIMENTAL

A.

Synthesis of Compounds

H. N~easurement of iCinetic Da.ta

O~

Product Analysis

11esul ts

2

2

7

15

15

26

28

32

III DILOtfSgiON

'l1

he Magnitude of the Hho Value

35

'11_{he Jinomalous HatP.}

_for

_{the .£--:'Cyano .Derivative 38}

1_l'he

_Anomalous

_Dates

_for.

_the

_;£-Fluoro,

_{.E.-Methyl and}

E-Methoxy Derivatives

40

Phosphorus has a very high affinity !or oxygen, and

compounds

o£ the type n4r·+ react readily with hydroxide (or

alko:x:ide)

·ions to give phospbina oxides (H

3

1

1₀₎

and

hydro-carbons. The order o£ ease of replacement of R groupe;

c

₆

H

₅

C!~ > C_6H

5

> CH:;, and I?,-No2c6a

4

> c6H

₅

> Q-CH;C6IJ4, indicates

that

the R grour) may be

leaving

as R... Tb.e

reaction with

hydroY~de

ions of a series of substituted

phenyltriphenylphosphonium salts ArP+(Ph)

3

x-

(X "' halogen) in

an

aqueous

1,2•dimethoxyethane solvent system bas been

2

I

INTHODUGTION

G~ueral

Considera.tio..!}!

Although the configuration

of

outer-shell

electrons

about

phosphorus is similar to that of nitrogen, there are

atrik;i.ng

differences

in their

organic chemistry..

'rhere

are

no nitrogen compounds having more

than four covalent bonds to

the nitrogen atom; phosphorus compounds are known with three,

four,

five and six

covalent

bonds to phosphorus. :Phosphorus,

like sulphur and silicon, does not appear to fom stable

unsaturated compounds having p1t-p1t double bonds to

oxygen,

nitrogen

or carbon analogous to nitro, nitroso, azo, diazo,

azido, nitrile

and imino compounds.

On the other.hand, it

does have

the

ability

(as do sulphur and silicon) to form

multiple p1t-d1t bonds; i.e.

Compounds involving p -d

bond.ing

can be .formulated. as

'It 1t

hybrids of electron pairing schemes where the phosphoryl

(triphenylphosphine)

(methylanetriphenylphosphorane)

Consideration of bond energies has shown that the

phosphorus-oxygen single bond is

fairly

strong

(~2?

Koe.l/rnole)

-stronger

in fact than the carbon-oxygen single bo.nd - while

the phosphoryl bond

(P ':l!l

0) is about

45

Kcal/mole

stronger

than the (P - 0) aingle bond. '11

he energy of !orm~;,tion of the

phosphoryl group

provi<les

the

driving force

fo:r

many

reactions

of phosphorus compounds.

F'or example

~

(1) R 2POR

1 ₊

fWl ... R

3

P+-"~-

7

H• Cl- - H:;EO + H1Cl

(2)

These reactions display a type of biphilicity in that a-donor

and n-acceptor stuges are not simultaneous.

Compounds with a

positively

charged phosphorus atom are well characterised. 1

11he successful resolution o£ asymu1etric

quaternary phosphonium salts1-3; of the type

n

₁

H

resemble tetracovalent carbon compounds and quaternary ammonium salts in tr,eir stereochemistry; for example structure (1),

CH~OH

-'"2 3

4

(1) methylethylphenylbenzylphosphonium iodide

[o:}~5

..

~:240

..

Likewise, tertiary phosphine oxides, R

₁

R

₂

R

₃

~ ~ 09 have non-planar configurations. since they can normally be separated into enantiomeric forma4-8 ; .t'or example structure (2)t

(2) metbylethylphenylphosphine oxide Ph

CH 2oH3

~here are interesting differences in the behaviour of quaternary ammonium and quaternary ~boephonium salts towards basic reagents. Whereas tetraalkyl ammonium salts with

hydroxide or alkoxide ions generally form slkenes by a

~-elimination type reaction, e.g.

(Ph)

p+ca

CH + Olt

3

2

3

-Although readily attacked

by

nucleophilea,

the

phosphonium centre is stable to el,;ctrophllic

attack.

:~'or

example, a n-tolyl-phosphoniuxn compound. may be

oxidised

to

the carboxylic aoid·without affecting the phosphonium eentre9;

Phosphoniuf!l compounds may be formed as reaction intermediates,

and in such cases nucleophilic attack on the phosphonium

centre is often a subsequent stage in the reaction. An

example is the following biphilic cyclisation10 , 11 ;

RA

n

-Cl-0

. R . G

.:p

.

_Q

-

- - , ; - ·

...

··Pol .P p

/

2

_/I"~ /

"

/' ...

R _{H Cl Ul} H

Cl

0 H

In relatively rare cases nucleophilic attack does not occur

1?

a.t

the phosphonium centre. :Pyrophosphini tes "", for example,

react with proton supplying nucleOJ)hiles at the

uncharged.

trivalent phosphorus atom, displacing tihe better

ler .... ving

group;

(F

3

c)

2

r-

OH 01- P(CF

6

Go~ phosphorus compounds ce.n undergo nucleophilic attack e.t the atom

f3

to the phosphorus a. tom however,

~

z-

Y

0

p+R:;

and this

reaction

may occur

even

when

the x ... y ~:roup is itself a good leaving u:roup. 1

I1

etraarylo:K.yphosphonium se.l ts may

decompose in thin rc1.anner 1

3.

He!:J.Otions i11volving n.ucleopbilic attack at ~ phosphonium centr(~ can be l'!.t vided :Ln to three

important classes;

(a.)

uirect

,;;:rr2

displacement'

~

Y-

·-

f·:;-+ :;·-

+R R

p+ Y

_+J.

',-X

(b)

(c) add.i tion t

~ X

y- ~;+R

3

~ H:;P ~ y X

Well established exatuples of type (a) reactions are rare but

it is believed to operate in the decomposition of'

tetre.aryl-oxyphosphoniuro. hydroxides and during the oxidation of

phospllonium hydroxides is believed to occur

by

a type (b)

addition-elimination

mechanism

(see below).

Qecomposi tion

oJ.

Quaternary; Phosphonium l(ldroxides

The thermal decomposition of quaternary

phosphonium

hydroxide$ to give phoaph.tne oxides A-nd hydr·ocarbons ha.a been

known for a lonn;

timE~. Oue

of the

earl~r inve:1tigo.tora,

1'. .o·,.tc. h a.e l i s 17 ' 18 . , no t fl . d th· 1 .. d. t b enzy . 1 an p.J.eny groupe cou d } 1 ld b e

eli~ainated (as toluene and benzene respectively)

with

greater

ease than simple alkyl 1:;roups. Meisenheimer and Lichtenstadt1

9

extended this

work

and proposed tbe following

order

for the ease of elimination of various g):'Oups: allyl, benzyl >phenyl

>

methyl, ethyl, n-pro:pyl,

{3-ph':'methyl. JJ'enton

and

!ngold20

later

extended

this

SEhlUence for

the eesa of

elitninr:ttion

of

various

r:roups

~

benzyl

>phenyl >methyl > ~-phenethyl >ethyl >higher alkyls. Even more recently, a series of aryltriphenylphoaphonium salts were decomposed by the

~otion

of

stron~

alkali 21 • The following order of ease o! elimination of aryl !~oups was

observed.:

2-,m-.~·nitropbenyl >

E-chlorophenyl

> ~-oarbethoxyphanyl

> .I?,-biphenyl > a- • ~-,napthyl > phenyl >

12.-

,m ....

methoxyphenyl >

,2-,:s-tolyl

> :£-,!11-aminophenyl > ~-•m-hydroxyphenyl.

In

other publications confirmatory evidence

that hydrocarbon

groups are displaced in order of

their

electronegativity

are

. 22 23

8

24

groups a..re preferred to aryl groups; while among arom:3tic

groups the order was

found

to

be

2

5,

nitro

>

4--chloro

>

4-carboxym.ethylphenyl > 4-biphenyl >

a-,

j3-nnpthol > phenyl > 4 .... amino > 1_{+-methyl > '+-methoxy} > _{l+-hydroxyphenyl.}

1'11 t h i ?G . i . 2_ry ~ h d i ' .1e s ereoc~ em stry- and. l( net~cs ' o..~. t e ecoropos t ... ion o.f meth..-vlethylyhonylbenzylphoephoniuitl bydroxid.e have been

opti.callJr pure levo-rotntory('+) on r6act1on with ::-mdiwn hyd.roxide • nnd t;he

~rn

₂

cH

₃

-

.P CHi'h

I

Ph (3)

+ _{CH CH}

I 2 ;

n

₃

c -

P

=

0

I

J-h (4)

reaction W<:'lO found to be third order, showing

first-order

dependence o:u the ooncentro.tiou of phosphonium c.':ttions and

second-order dependence on

the

concentration

or

hydroxide

ions. The configtwatiou at the phosphorua 3.tom is inverted during the re :ction. 1_{.fhe 'iJi ttig reaction on the other hand}

OR.;z:

:;;""

0 H:; 0 H

2 -.--- .F';

Ph~

(+)

0hOHO

This evidence ·'lms C(,nfirmed by

Horner

et al.. 2<)' 30 Ginoe

oxidation should

proceed with retention and there is

evidence

that

it does do

ao; hydroxide attack presumably proceeds

with

inversion. Dubaequent to the first

kinetic

data to appear,

it

wa.a confirmed

by

Hoff'man31 ,

and

Ankses et

al.

32

t that the d.ecomposi tion of phosphonium hydroxides follow a third order rate law. In recent kinetic st1.1.dies a series of

E.-, •

£!-Y-benzyltribenzylphosphonium

salts

were

subjected to reaction

with sodium hydroxide in 50X, (by

volume)

aqueous

1,2-diwethoxy<-'~thane33.

1

_l'he

cetermination

of rate and product

10

(1) all of the reactions were third· order, with a first ...

order dependence on the concentration o£ phosphonium

c~:-.~tions

and a second-order dependence on hydroxide ions,

(2) the

:t'elative

ease

of

elindnation

of the various

benzyl groups puralleled their stability ae anions•

(3)

the relative ease of

departure

o! a given group was

definitely influenced

by

the nature o£ the non-departing

groups~

(4) the rate data could be correlated in a suitable

ad.a.pta.tion of the Hammett

equation.

Although it is not yet possible to establish

unequivoc-ally a single definitive mechanism the accumulated. evidence

suggests

t

accordi.ng to

~janger

and his co-workers, that the

mechanism consists of the following four steps'4

c

( 1) fa.st reversible

addition

ot

hydroxide

ion

to

the

phosphorus

atom of the

quaternary

p-hosphonium

salt,

(2)

fast reversible

format~on o!

the conjugate

base

of

the intermediate

ill

which the phosphorus is pentacovalent •

(4)

.fa.Bt

oonve:r.sion of the oa.rbanion to the appropriate

hydrocarbon

by

the

action

of wntEJr,

,.,.- lJ 0

Jl. + -'2 ... RH + Ofi.

'Nhen

thi(~ mechanism is applied to

optically

active

methyl-ethylphenylbenzylpbosphoniuru. iodide(?), there is no reason

why

addition of hydroxide ion FJhould not occur at

every

face

of the

tetrahedral cation,

thus giving

four diastereoisomeric

intermediates of the trigonal bipyramidal type, in which

phosphorus

has the sp3d

configuration-

:v;ach

or

the

d.iastereo-isomers would be expected to contribute a

small

equilibrium

concentration of the

oonju~ate

base.

However

in

step

(.3)

o!

the proposed mech~mism, since the benzyl anion is resonance

etabilised

it is formed at a .faster rate t.han the methyl,

ethyl or phenyl anions. Gonoequantl,y ·the

retrction ,,,;i

vee

almost exclusively toluene and methyletbylphenylphoaphine

OXide 8.A prOdUCtS •

{l'he

stereoobemiCr,tl COUrSe Of

the

reaction

cnn be represented tl1us;

cn

3

/ /

OH-1:H20B3

- 0 *" P,

12

There arH tw') conceivable w.u:-iati.onr; t)f this :mech::mism

:.c;hi.ch would 1)('1 conn:Lstont \'Ji th tbe stereochemical and kinetic

data;

( 1) sy:achronoun o.ttaok of the second hydroxide ion and deps.rture of the benzyl anion, and

(2)

rapid i'ormation of an unstable intermedia.t;e

with

two hydroxide groupE'. b(;nc1e.J to phosphorus (a. teti\9;;rorwl

bipjrrrunidal structure) of the correct geometry to cause inversion at the phosphorus atom on rate determining depart-ure of toluene and a hydroxide ion.

Another fundamentally different type of substitution mechanism must also be cc·nsidered. It i.e possible that l>...ydroxide ions could attack un edge of the tetrr:Jhedral

phosphonium C-'ltion (rather than a face) to

tdve

an unstable intermediate in which the <3.tta.cking br?.ee, the hydroxide ion,

the departinf~ bt:lne, i.:;he benzyl union, · oco11py basal posi tiona

of a trigonal bipyramid.i:J,l structure, as shown in a. structure

H

3

OH'"'

H7.C :::--- -, OH

.,1 ' , I

l

~Hif'h

Ph

(10)

OH 2CH

3

+ l:'hOl~

.Ph

. ,~

An atlalyois by Haake nnd 'in~stbeimer .) , showed that collapse

o.f au intermediate ot this type ••:ould cause inversion at the phos·phorus ~ltom.

lu an attempt to study in more detail the :mechanism of these decompositions, an investige.tion bas boon carried out into the reactions of sub;Jti tuted aryl triphenylphoaphonium Baltn

with sodium

hydroxide, i.e.

1_{rhe magni tud.e of}

'14

no .. Jever, r.-~ttempts to ::.,10.:wure ·t;he kiuatics for these J.ecowpos-i i;ionu f aile

a.

.f0:r tocltuical reason:j, Iust~ad the ralati ve rates

ot

ben~M~:ne (<pH), and substituted benzenes (Arl:I), were determined by G.L.C, analysis of the reaction products. It

I I

A. Synthesis

ot

Comoounds

In all synthetic worP.~ reagents were, in thv main, of at least Beagent r:;rade qt.laltty f.l.nd where this wn.s not possible reagents were suitably purified. 'l'hf':1 products of synthesis we:r•c identified by comparison of melting points with

Li tE::r.'ature values, by infrr~red. spectroscopy (Perkin .i~lmer

337

Gr0ting Infrared .'\pec·trophotiomet~er using KBr discs) • :md where appropriate by elementr.tl analysis.

1₁1_{he methods of preparation of various phul::lphoniu:at salta}

are well doeun.:ented36 • In this study two principal met;hodo were employed in the aynthesis of BUbstituted ohenyltriphenyl-phosphonium compound:;;. '11

bese were (a) the dia.'Z.onium salt m8thod"7, and (b) the Grisnard reagent and cob8.lt

~alt

we·thod38• Other methods tried are

r~"tcord.ed

in Appen<li:x I

(see x.:age 43) •

1_{l'he diazoniu111 salt technique relies on the generation of}

ra.dical.EI in n two-ph'i.sG syatem from an acetate buffered solution of e. d.iazoniu!!l nal

t.

A neutra.l a.zo compound is

~xtracted into tho o.rganic phar::.et and decomposes homolytically,

16

1_{.llhia is eho·wn by the fact that the solution will initiate the}

polymerisation of IJCryloni trile. The initially formed phos-J?horanyl r.""uJ..cnl ie oxidised further to the phosphonium salt.

'eV$ral side .react;ion~ of some importance can alF:Io occur and e presumed to be the cause of fairl~r low yields. 'fhe first ·· the production of arylhyd.razylphosphonium salts and/or ] d:razine, and tl .. iphenylphosphine oxide; i.e.

A1\-

11₂ +

+

;"(E'h)

3

1' + H2

o

+ (.l::'h) .,!:' • 0 + N"J T + 21f*"

) ' c.

The SE70ond important side reaction is a reductive dee:mination

process;

i.e.

In the cobalt s.alt method the ar;yl radicals were

initiated. rrhe ini t;ially .formed phospho:r:'R...'lyl radical is oxidined further to the

vhosphonium salt. The postulated

rnechanLsm for the reaction is thU8;

+ CoX ₂ J. l I'' v 'o··· -• ·"·· .A ..,. '-'0.1•..v

2

2i\rUoJ~ '"" Ar-Ar + 2CoX

(Ph)

_-

₃

1' +

Ar"

(l?h) ~p • Ar + CoX,)

..

....

-CoX,.,

_{:!, +

Ar'

(a) 1_{Tctx·aphen;zlphosphot}ium} iodid~

J\niline (9.;s2g, 0,1 mole) wns dissolved in coDcentrated hydrochloric acid ('18.3 ml, 0.25 mole) and we.ter (130 ml).

~i1_{he solution was warmed to dissolve the aniline, cooled to a.}

temperature of

0-5°

and diazotised by slow addition of a

solution

of sodium nitrite

(6.9g, 0.1 mole) in water (50 ml).

After allowing several minutet3 t\H• ree.ction the solution

gave au iilll.O.ediate positive test for exce:3s of nitrous acid with f)(Yt:J.ssium iodide-

starch

paper. 1_{1'he .final,}

highly

soluble diazonium u.al·lJ waf~ up,proxima.tely O.!):Vl in concentro.tion.

1_{fhia had proved ·co be a favourabl'9 ·concentration iu previous}

synthcnes recol'ded

ln the

literature. I·~xcess

acid. maintained

a Pl'Oper oondi tion of acidity required to stabilise the

minimum-18

This solu.tion wee filtered into a three-necked flask ( 1 litre) :.fitted with a droppinf~ .funnel, a bigh speed stirrer with a

mercury seal, and a

.tube

le13.dio.g to a

water

displacement

apparatus-

Uodium acetate was added

in

three molar excess

over acid (approximately 48g). rr\riphen~rlphosphine.

dissolved

in ethyl .ncetate (0.25M) • was auded slowly through the

dropping funnel into the sealed flask and the progress

o:f

the

reaction followed

by

the evolution of nitrogen gas measurAd

via water displacement. The reaction was complete when no

more

nitrogen

was

produced

(~ppro:ximately

5 hours).

~he

aqueous phase was

separated

from

the

organic phase, tbe

organic phase

extracted

once with water (100 ml) a.nd..the

combined aqueous

fractions

extracted twice

with ethel' (100

ml). IJolid sodium iodide was added in excess

and

the product

precipi·tated out of

solution as the iodide

salt.

This crude

product was purified

by dissolving

in

·methanol (

150 ml),

filtering off

any

solid material, and allowing the

methanol to evaporate at

room

tempertJture. 'l:he product was then re-oryet,allised

twice from alcobol/ether mixtures,

m,p.

336-337°

(lit.

;,;?

0) , the yield was 19.6g (4.2%). ~.rhis

workup

(b) n.-G~~gnonhenyl t;:iphen:ylpbosphgnium iodid~ (i)

Cupro~s oyo.nid~39

Cuprous cyanide was prepared using the

following

general

reaction;

Powoered copper sulphate

(250~,

1.0

mole) was

placed in a

banker

(3

litre) and dinsolved

in water

(800 ml) at 40 ...

50°.

Golutions of sodium

m~~tabisulphite

(70g, 0.3? mole)

in W'-·)ter

(200 ml); solution A; and potassium cyanide (708

9

1.08 mole)

in water

(200

ml), solution D;

were

prepared and :filtered to

remove solid impurities. Liolutions A and

:S

were heated

independently to 60°, The copper sulphate solution was

ncidified. with dilute sulphuric acid to give a positive test

to <Jongo

red indicator

paper,

Then solution

A

was added to

the aoppe:r

sulphate solution

\fpbilst stirring over a period o.f

1-2

minutes, .followed immediately

b;( solution B. lifter 10 minutes the

hot solution was

filtered, the product washed

thoroughly with boiling water, and .finally with alcohol. It

was dried

at 100-110° to a powder for 24-'6 hours. Yield was

89.1g (

62!.

5'i~~,).

(ii) Aminooenzonitrile

40

12.-nromoaniline (75.2g,

0.436

mole)

and

cuprous

cyanide ( 46.8g,

0. 52;,

mole)

were placed in a· flask.

Dimethylformoonide

( 64

ml) was added and

the

mixture

re.fluxed

for

4- hours. 1

20

hot solution was poured into a 20% (by weight) solution· of sodium cyanide (436 ml), the mixture shaken vigourou~Jly and the lo\ve:r phase removed and e:x:tr!',oted once with benzene ( 100 ml). 'fhe combined organic .fractions were washed with 10}u (by weight) sodium cyanido solution and

dried over

sodium

sulphate. Aftt3r the removal of solvent the product was

distilled under reduced. pressure to gi 'Ve :Q.-aminobenzon.i tr:Lle, m.p. ?8-'71

) 0 (lit. 85. 5.-86°) after reerystallisation from

carbontetrn.chloricle. 'Yield was 15.1g ( 35>l;) ..

(iii) £-Oxanophenyltriphepylp~osphonium iodide,

F'ollowing th~ procedure

outlined on pages 17-18, ;;:.•

cyanoaniline (

5.90g

t 0.05 mole.) v1aa diazotised with sodiUUl

nitrite (3.45g, 0.05 mole) and

the

solution made up to 100 ml with water. 1₁1_{he product was precipitated as the iodide and}

recrysta.llised twice from alcohol/ether ttti:xtures to give yellow needles of ,2-cyanophenyl triphenylphoephonium iod.ide • m.p_

235---2;37°.

Yield was 2.?8g (11c,:;~).

(e) .u.-Ni,trophep.yl triRhen:ylph2.sphonitll!l iodiQ_e

·~-Nitroaniline

(6.9g, 0.05 mole) was dissolved with

orange-coloured solid

wo.r.;.

reorystalliaed

from alcohol/ether

mixtures

to give .E.-nitrophenyltripbenylphosphonium iodide,

m.p. 225 .... 2~6° (lit. 228° dec.). 1₁1

he yield was

7.38g

(29'1~).

(d)

~-Nit~onhen~ltriRhenxtvhosEhonium

iodide

m-NitJ·oaniline (6.9g, 0.05 mole) wae dissolved. with

gentle hG&ti:ng in concentrated hycrooh.loric. acid (25 ml) plus water (50 ml). 'l1_{he hydrochloride was d.iazotised at room}

temperature with

a.

solution

of sodium nitrite

(:?.45th

0.05

mole) in water

(?5

ml). The

diazon:i,um solution was buffered

with

sodium n.cetate

(82g)

and after

reaction with

triphenyl-phosphine the pro('iuot preoipltated as the iodide. ~~he

yellowish

solid was

reeryetallised

twice

from

alcohol/ether mixtures 'ijo give

m-nitrophenyltriphenylphosphonium iodide,

m.p. 208°

(lit.

215° dec.). The

yield

wa.s

2.97g

(11.6~1,).

41 (e) Anh.:t;drous

cobalt

cb~o:rid~

The

.:f.'ollowing

reaction was used for this preparation;

. 00 T 1:01

... 0 0 + j '· +

.:...

.l!1_inely t~roun~-

aobHlt

_{chloride hexahydrt.l.te} (20g~ _{0.084 mole)}

wo.s

placed

i.n a. flask (250 ml) fitted vd th a r~flux condenser (md drying tu.he ( G9.01

2), together with freshly.

distilled

22

(anhydrous) we.e·~tored .J,Jremnnently in a desiccator over solid potassium byd.roxi,3e to ensure the removal of any residual

thionyl ¢hloride.

(f)

p_-ff.srtihox:x:;phenyl

tripheny:lphgsphoniurq iodide

In

a

two-necked flask (250 ml), fitted with a reflux

condensel'J and d1"yinp; tube ( UHC1

2) • and a dropping fw1nel;

magnesium. turnings (1.215g, 0.05 rucle) and

bromobenzene

(7.85~_~;, 0.05 mole) in anhydrous ether solvent

(75

ml)

were

rEwcted to give uhenylrnagnesium bromide

(approximately

2Ii~;

this has

been

shown

to be an

optimum

concentration).

~rri­

phenylphoaphine (13.11g,

0.05 mol$)

and

anhydrous eobalt chloride (0.6~iOg, 0.005

mole) were

added and

the homogeneous

wixture rflfluxed for 1

hr. ,E-Bromoanisole (18,68g, o.10

mole) was add.ed. d.ropwise whilst

stirring

over ·~ hr,

and the

mixture

then

refluxed

for

3

hrs. 'rhe solution

was then

cooled•

and

poured

into an aqueous 2N hydrochloric acid

solution

(100 ml),

and £11 ta.rad through a Buoh.net· fun·nel under reduced pressure. Most of t~e ~esidue was dissolved and washed into the mother

liquor wi ~h hot water. 'The aqueous phase waa then separated and the p}).oaphonium salt precipitated by r1ddi

tion

of solid sodium io<lide. !rhe solid was rooryatalliaed twice from alcohol/e'Uher mixtures to give :Q ....

mothoxyphenyltriphen;yl-phosphoni\~m iodide, m.p .. 223-~~24° (lit·. 209°)~ IJ~he yield was

6. ?1e; (27 .2;\') • 1

L'his VlOrk-Up procedure was employed for all

compound~':' })roduoed by the GX>ignard reagent plus cobalt salt

(g) m-ft~Jihox;y:pben:l.t:!zip~enz:I;ngq f!}2honi urn iodide ( i) Ja-br·omo@ireoa'+2

!9,-H~omoanisole

was

prf~pared by

methylation

of

!-bromo-phenol with

dimethylsulphate.

A tbree-nocked flask (250 ml) was fitted w-ith a stix·rer,

reflux

cqn<.len.ser. and dropping funnel. A

solution

of

sodium

hydroxi<lEt (?.02f~,

o.1?5

mole)

in water

(70 ml),

and

!!!-bromo-phenol (;:}8.9g,

o.167

mole) were placed in the flask and

stirred,. 'iihE:.n the mixture become homogoneous it was cooled to abont 10° and dimethyloulphate (15.'7 ml) added drop~.vise with st;lnrtng over 1 hr. i1

he

solution

was then

allowed

to

reflux for 2 hrs, and cooled; water was added and the lower

aqueous phase removed. '.Che organic phase wa.s washed

onoe

with

watflr,

twice with dilute sulphuric acid, then repeatedly

with

water until

the washings had a. pH of

7.

'l'he organic

phase wa..'1 then dried over roa.':;nesium sulphate and distilled

under nitrogen to give m-bromoanisole,

b~P·

240°

(lit.

4

~

209-212°/752 tnmHg). 'l'he yield was 19.Gg (6?/••).

( ii) !, .... M~tho?9l:Ehen~l.tri phenxlphosphqnium

iodide

Phentyl magnesium ')romide (2M) was prepared f'rom

magnesium turnings (0.603g, 0.025 mole) and bromobenzene

(;.98g, 0.025 mole) in anhydrous ether solvent (40 ml).

Using the standard method, triphenylphosphine (6.67g, 0.025

mole)• anhydrous cobalt chloride (0.,25g. 0.0025

mole),

and

24

flask. The resulting product

wnr:i,

after reao·tion, t"eorystal-liscd tw:Lce

from

alcohol/ether mixtures to give

m

...

methoxy-phenyltri..phenylphosphonium iodide, m.p. 209-210° (lit. 2QL~0).

~l!he yield was 0.

5g (2>0.

~~he low yield is thought to be due

to the in,stabili ty of the !-methoxyphenyl radical species in this rea¢tion.

(h) ;g-Mat,hylphen;yl triphenylpbospho:gium, iodide

Phenylmagnesium bromide (2M) ·was prepared .from magnesium turnings (1.215g, 0.05 mole) and bromobenzene

(7.85g,

0.05 mole)

in

anhydrous ether solvent

(?5

ml); and reacted with

tripheny~phosphine (13.11g, 0.05 mole),. anhyd_rous cobalt

chloride (0-650g, 0.005 mole), and

.E.-bromotoluene

(17.11~,

o

.1 mole). 1

1'he crude product, preoipi tated as the iodide, was

reocystal,lised

twice

from alcohol/ether mixtures

to give ,2-methylphenyltriphenylphosphonium iodide, m.p.

210° (lit.

207-209°). r.t!he ;yield was 5.60g (23.4')i~) ..

(i)

;g-rnethyl:phen_;zl

triphen:ylphosphon~um iodide :Phen;yl

magnesium bromide

(;~M.) wus

prepared from

mRgnesium. turnings (1.215~, 0.005 mole) and bromobenzene

(7.85g, 0.05 mole) in

anhydrous

ether

solvent

(75

ml); and reacted wtl.tb ·t,riphenylphosphine (13.11g, 0.05 mole),

anhydrous

cobalt chloride (0.650g,

0.005

mole), and

ru.p, 1:K.J···-'198° (lit. 187-190°). 1:he yield wa::J 5.LJ.Qg (22.5~·:')• ( j) J2,-JQ;uorowbenyltrip1}0n~zlphosphonium

ios1,!ge

Pher~yl Wf..i.gneoium bromide (2M) w.::ts prepared i'rom

wagnesiuut turnings ( 1. 24 ~.:,g, 0 .0~) mole) ;:.md. ~;)romobenz.ene (? .85g,

0.05

mole) in anhydrouo ether solvent

(75 ml); and reacted

wit11 triphe.nylpho~3phine (13.11g, 0.05 ti!Ole), auhy<.lrous cobalt chloride ( 0, 650r:;, 0. 00~ mole), and ;p-r1uonoh.t·(~Ji10bemzene

(17,49g, 0.1 mole). '11

he orw10 prod.uct, precipitr.ted as the iot1ide, \tr:u:. rt;~crystallisea. twice from alcohol/ ether mixtures

I i,

to give pale yellow cryE)tals of 12,-fluorophenyl tripbenyl-.

phosphonium

iodide, m.p. 27L~ ...

275°.

(lt'ound:

C •

59.71;

H, 4.09. ''"'' i • t'' ·

r:9

1'::')• IJ' ::t

96.,

1,.,)

u . ..,qu.

ros. ,,

:.> •/"'·) ,(, /• ,tJ •

( k) m-E'l~OfOph~n;zl

tr:iphenylphoaphoniut'l

iodige

Phenyl megnesiu:m l)romide (2ill) ':las prepared from

magnesium turnings

(1.215g, 0.05 mole)

and hromobenzene

(?,85gt 0.05 mole) in anhydroue. ether solvent

(75

ml); and

reacted with

triphenylphosphine (43.11g, 0.05

mole),

onhyd.rous cobalt

chloride (0.6~0g,

0.005

mole), and

m-.fluoro-bromobenzene

('17.1J.9e:,

0.1 mole). 1

J:he crude product,

precipitated ~\8 the iodide, was recrystallised twice

from

alcohol/ether mixture~;;> to give pale yellow cryst;als of

!!!-fluorophenyl tripher!ylphosphonium iodide, m. p.

256-25?

0 (found:

I~ h9 f"i~. I;i· 4 ·")1

B.

1'lea,~~emeut

o:C

K~netip

Data.

f:'or both kinetic

work

and G •

.w.u.

analysis

all

weighings were don~ on a type U6C lVtettler balance. and a.ll

solutions

weru J:ttad~ UJ) using stundi:tr'd H-grade

volm.uetrio

equipment.

l',oltttion[.J of sodium hydroxide (

o ..

?iJl)

were

ruade f1 .. om Ana.laR

~;rB.,de solid sodium hydroxide and. carbon dioxide fx·ee

distilled W<:!l;;er. l(t~agent gr:a.de 1 ,2-diruethoxyethane was distilled before uae. 'i?or all work a oonst~:tnt temperuture

\';tiS :ulaintk\ined, 30.90°

±

0.05°, with a type TU8 IJ.'empunit unit

in

a.

vw.tnrhath of

capaoi

ty 17 li tres. (a) nol~ent /.)yat.§mS

j . ' . . .

-1_{i'he requirements for the}

_{sol vent syster.n were that}

_it

ehould ba (1) oiruilar to those

us~d

in work already reported,

(2) chemically

inert,

(:3) sufficiently polar to be miscible with wa.ter and

a.t

tl:le t:.1a1n~ time dissolve the phosphonium salts.

AqueoUfJ a;cetone and aqueous dioxane systems could not fulfill these

con.di tions..

Al thour:;h aqueous ethanol has been ueed in the past, it mH; rh)t favoured because it is not voesible to

define the

nuoleopl;lilio

:!:!peoies in solution becaUfOe o£ the

equilibrium;

fulfill•3(t the condi tiono outlined and all experimental work wus carried out in 60,;.:~. (by volume) 1 ,2-dimethoxyetha.ne /water udxtures,.

(b) lrLea§uram~nt o.f H. ate Da-y a

It was 'initially r)roposed to measurfl the re.tes of

l~;ydroly~Jis of the substituted phenyltriphenylphosphonium

salts usinc; a U

.v.

~:,p~o)ctro;Jhotometel'

but

this procedure proved tv be unacceptable because of the very small differences in spectra between reaott1nts and products. A.lso tried was a

titration tl3ehnique und1.tr oondi tion1:; 1:>! const.:,mt pH. t<eactions wert3 carried out in a temperature controlled reaction cell

with a ty:pe TTT1c automatic Hadiometer titrn.tor connected to an GBtT1 ;1yringe .Burette unit through an UBB2G

'ri

tigrH.ph. 'fhe electrode e.ssemlilly consisted of . a type J\1+01 c:1lomel

electrodet and H type 020~~0 tslas~s electroo e; thuG the cell

re::,ction can be wri.tten thu:J,

'·" •·,

C~IJ'IO'l'l"' t~

' ,. b IHeaotion

II

.KOl (sat.)

II''

01 rr,.

t·.g '1_{\.g..., · g ,;~.s~ mem rane l3olution salt bridge ·ig("~ 2' -e •}

:1..1 thoueh E:Ood simple pseucL;~ firnt-order kin~3ti~.s were

obtained

for

the

hydrolysis

at

pil

10,00 of the compounds

prepared. these were not rf:l);lroduc.i'ble ~ dl.:te to the failure of the eleotl:'ode system to maintain a constant potential at thit-J high :pH throughout the durB,tion of kinetic runs. 1 t is thought that

the

11

28

41!·

causes

~ however Ht the

time experiments

were carried

out

·tbare wa:.:,1 no re,".'.son to suggest that thio wo.o oo •

.J'Ux·t;:her inventie;ation o.f' the reaction system showed

that

an unknown side reaction v~·CJ.s iuvolved.

C. J~oquct Anal:[ sis

(a) Int~oductorJ:

Analyses wet'e carriedirut on a Variml J~eror~raph 1200-1 Gas Liquid <Jhromatograpli with a •~hima.dzu

type recorder.

Inj octio11.s wero nvJ.de w:l. th a etw.1dord syringe ( ·1. 0 f!l). 1'roduat tia.tios. we~.·e calculated by the triangulation method

e:Kaept in a few c~ses where a Kent Obromolog Integrator was used.

on solid supports (Chromooorbs G and .P) could not adequately sepa.rat.;e 'benzene and 1,2-dimethoxyethane; but a column of

211f, dino:nvlphthalato on a solid r.upport (C:hrO!I!osorb Vi - 80/100

)

~·5

mesh was sucoe~s.ful • ~)ample!:l of benzene, toluene,

1,2-diruetho:x.yeth~:).no mi:xtureB were injected. to check

'.2 ~tbl.e 1

'~""""--he.tio

(benzene/toluene)'"'

r)e.<nple in;j ~;~ction Injection i?rint-out Level

0

•

5'';,

I'·' 1.0):; 2.0;&

..

_.

1(a),(b),(c)

.

7t'j4 ~

.'?65

-790

2( a), (b), (c)

_·790

.?:A

.759

I

*Integrator

r.:;ean benzene/toluene ratio .,

o.

768. idttximum error "'' 2. 9;:6. S\ost cbrome.tocl.~ams were appro:~~imately

25

minutes' duration ~mel to ~;peed up the proceDE the Gbroma.to~·:raph was

tc~t.peratux-e progr·:~mmcd to record the substituted. benzene peak in reasonable time (see J?ig. 1).

Ji'ig.

1

~njegt:J.sm

po!nt

-_.

__~:::I=====-)

IJ.'hc prcr;encr;; of ~'.'ater in tho [3CJllplc8 c:::.uced excessive

'

oolunn1 b).eed and. baBeline drift. 1:a th a.queou::; S;;tmples, at a

colt~Jnn t"~'mpert~.ture ol' 2.0°, ben~en.e i.llid ·1, ~~-di.methoxyethane could be separo.tod but

subsequent elution

of the substituted benzene by tau:qH~rature prop;rannaing was accompa.uied by other mut(;jrial frum the colu:tn.n tm<l this made acoura:lie an~lysis

inwossible. Water wus therefore removed before injection of srunples by C:l.udi·bion of t:ype ~;li rodlBcU.la.r sieves. It was shown by anal;yu:i.. s tl.J.a.t t.uolecula.r sieves <J.id nothins to affect the com.posi ti.on of :rba:nda.rd samples. Four test solutionrs were prepared;

(1) and (ii) containin.t~ benzene (5 parts), toluene (5 parts), 1 ,2-d.imetho:xyet;hane (;~o parts), and (iii) and (iv) containing ideuticel opecics plU:'oi Dwlecu.lar sieves. iJrunples were

injectt,ld onto the colnmn and the benze.t:te 1 toluene ratio established. ..i.eRul ts Rre: shown in t;u_1)le 2 below;

1_{X:able 2}

Latio(benz,ene/tolu.~ne)

*

L.!ample Injection Hh\tio(av.) i~~~ean _J.i:;ttio

~,

2

₃

(i) .99~.

.937

.965

.965

:978

(ii) .98~·

.967

1.020

.991

(iii)

_.953

_.972

_.974

.966

·956

(iv)

.944

.959

.934

.946

(c) ~t~·:J;tiqn of <Jompo'Und ~;am2les

Phoa;phonium nalt (about o.1g) was weighed into an

ampoule (1 rul). To this I.W\S added 1 ,2-dimetho:xyethane (O,f10

m.l) t uquaous 0.'/!·.T sodium hyt1roxi<'te solution )9.40 ml) to give

~J. solven~ mGdium 60~:·,~ (by volume) 1 ,2-dimethoxyethane/water and

containing exoesn byt1roxLle ionn. 'the ampoule v:n:w then aerJ.led and ·placed in the wnterb~1.th (at 30.90°) for 24 hrs.

1

.i1he ampoule wns broken in ice-·wc:~.ter and illolecular sieves

aoded; the mixture allowed to st.md ·for about 1 hr and sample injecteo. onto the column. Peak areas on the Ohroma.tor;raph were metteured as height x width at haLf-height.

('l'riangulat-ion gav~ more conrJistont renul ts tb.a.n those obtained from the Integrator.) hesults are shown on 'table

:?

(page 32).

(d) l:nsttrument Gondi tiona

r.ehe detector tempere:ture ws.s maintained at 290° :for all samples. 'i1_{he injo.~tor tempernturc vm:::~ maintained ut a}

temper-nture some 50° .3bove the component with the highest boiling

point

(1~5-240°).

Nitrogen flow was

maintained

nt

15

ml/

minute. Hydrogen pressure WHS maintained at 10 p.r;.i.

!J:emperatu.re prop;ramme rnte was set at 20° /minu.te from· 20° to 100°. 0ha.rt spe~d ·of the ·:recorder was set A.t

2,5

rom/minute. All injections were of capacity 0.2 j!l except in the ease of

.:e.-cyanophenyl.triphenylJ)honium

salt

where

injections

or

RE~1ITLTS IT!:lbln. .S.<-,..11. ... L :2!:

Comp~ lf!R 1:.rH '~ i:... 5 _{_.,} r .,..,. _.fl

/'-

n.. w _I R _j; ,c rpL ;A,k. r;;k

--., _t";r -~ 1'1--t

7_k

fir

_{(av )}

./:_f.l!,..H •

Ar~. fP' lo·-(A'" :.::. _.,.r:..t .. rE

p-

AtpH ·

)

-·o.7'+7

0.(?70 0 ..

0937

91.43

0.281

!''""\ Mf""\7

\.J. i •j 0.076 0 .. 0954· ... 1 ·::1 ..

29

0.286

J2.-CH

3

0.884 0 .. 085 0.0962 91.23 0.289 0.292 - J • _..l ..

G75

J

0.592

0.060 0.1014 90.80 0.304

0 .. ?19

0.072 0.1001 ';!0.')0 0.?00

0 ..

729

0.107 0 •

"1''7

J; ·-t~ 87.20 0.44'1

0.5?5

0 ..

093

0 .. '162 86.08 0.486

!!-GH

₃

0.497

-0.304

0.658 0.120 0.182 E4.58 0.546

0.935

0.160 0.1?1

85

•...l..,l :40

0.513

0.954- 0 .. 203 0.213 82.45 8.639' 0.820 0.1?2 0 .. 161 86.1 0.483

n-cF

₃

o

0.630 0.0945 0.150

86.95

0.!4-50 C-.550 -t:).26()

0.828 0.168 0.203 .83.1 0.'509

0.653

0 .. 124 0.190 84.0

0.570

H-

-

-

-

{75.0)

-

1.0 0

0.200 0.456

2.28

30.5

6.84

::n-CR 0

-

3

0.210 0.491. 2.34 30.0

7 ..

02

6 .. 56

0.817

0.189 0/366

1.935

32.8 5.81 0.1615 0 ... /98 4.83 15.8 14.ll-9

E-2 ~t4-.

33

1.1;)6

0.0612 0 .. 2890 4.72

17.5

14.16

7:?-?. _{16(;-0* 51.8 1.89}

_{155 ..}

4-

.r-12,-01 165.0 2 .2·18

30* 1?-+4-* 58 .. 2 1.72 '174·. 6 •Ir:tegrated results.

The J.l~I\0

₂

, ~-N0

₂

and !!;-P ~erivatives w0re all shown to proG.uce less than 1 b€:n:z;ene on

reaction ~i th alkali \.)1

Vihere

a

is the stand.t:\rd deviation,

d. "" ~\r

-

t.t. ( t'~N an individuiJl rosul t, 1-l is the statis-tical avero.e;o)

Y .\s t.be 111:.trnber of men.surements.

1

1lnking mw.imUJ<1 e:r.T'Ol"'S into conoideration, with the exception

of the E~c;yruw compound• tho estimated error is of the order

± 10,0. I:t is recor)D.ined that the l)t'o,:.test uncertainty arises vd.th the most r>Jaotive compound., however for the p-c:rl-'lno compound. the observr:H1 result is well outside estimated. e:q>erir:1ent8.1.

error.

1

l'he re(Jponsc of

t;he chroma.

to-graph to standard solutions \i'i'!IS checked and .found to be

34

I I I

.uiUUUUUl ON

_ ; ... ...._..._ ...

A summary of the results is given on page 32. A super-f'idial ex:a.mination shows that the ease of elimintrtion of aryl groups o.:r. anions rele.ti ve to the ease of elimination of the phenyl e;roup rour,hly, pa..re.llels the expected stability of the

anions libcrnted. However~ a cl<HIOl:', quantitative a:xamin,:1t-ion h::t meanr::> of the .ll:tm.cJ.ett equ ·tion reveals sotnA interesting feo.turef.h A e;:r','-:l.'~'lh of log (3k., _{'J/k 1}-r) versus

cP

velues ie

- '.!: .• /1.!' ' 1 1l 1

Hhown on the .followinL~ pag~ (the factor of

3

is simply e..

.Htntistidal correction to allow .for the ff(Ct that; tbree r-·;roups can form henzene anc1 one can form ArH). li'he line i~1 clravm

tlJJ>out_jh the ~ point~3 only.

'l'he Ha:mw.ett plot has three points of interest. 'They are; ( 1) the 1.r1a.p;ni tud.e of the rho vulue,

(2) the apparently abnormally low value for the rate of loss of the ;Q,-cyanophenyl ~roup relative to that of the phenyl group, and

(3)

the apparently high valuf.1 for thG rate of loss of the l2_-tolyl, E.-£1 uorophenyl and ,rr-anisyl e;roups ~

0

.p-C

N

H

-0· 4

o-CH

0

r 3 ,

- 0 · 8 L__-_o_L·

3 _

__j__,L_-

o___l·1 _

__J_-=_l_---L_~o

·3=--_L_--::::o-1:::·

s=---l...---;;-10 · -;;;--7 ___.

12.-cyanophenyl point, a.l thou?;h the fnot that nny benzon.i trile

c.t all w:,;.f3 detocted inr:licateEJ tbat the result is anorrtt:;J.lous

(no fluorObenZmle was detected ft•om t}w res.ction of the ill,-fluoro compound).

~he i!lar"J;ni'1ude of the f1ho

'hlue

rrh~ rho velue wea:.,urt~d. in this work is necesswrily a co.mxwsi te one. J'or the two rencticms below (;p :::· G₆H

5

):

(pH + Ar(()"}'O

'L.

.G'or reaction ( ·1) ·1,:e Cflll write,

PQr reaction (2) similarly,

Co.J.lbini:n,?: tquHtions ( 1) and (2) we obtain,

( 1)

(2)

(1)

(2)

(3) Hut :tor the_ uneubstituted compound (i.e. when. Ar "" q>) the two rN-wtions ~te ar(~ d.ealinr~ v.ith 'lrG identical.

• _-1, 0 ..

1 •. 0

• • ·'"'1

= '-•)

_(,~ (4)

the di:f:C'arc'IlOe in the rho v~tluer:.t of reaction::1 ( 1) and (2).

'I

.\ 1 \~

---c

'P;;,,nl + 1\rH

.~·

(PeJ.i-l.rl'O + q1il

•

•

•

<-.

lol:t' ( l t

/lr ) ·-

't.~

;·1··

" n t~1 .. .., - hi\ T.l· ·'-. J ... , L. .c •. r [ . \f>· I

(I() n 'l i , 'Dl(i)

-.. -.rrp-;(.r-..r-. IJ

::;

rl.··hereforc the :tuU.fiU:L tude of ( p.₁-p

2) refleot8 only the

senr::1itivities of the resp•.:ctive rate-determining steps for th0 two re.cwtions to chl:l.ngef:\ in electron dewdty Ht the reaction . ~i tc:u:1.

(6)

(7)

(8)

The l'1e~:~ .. :-mrecl vn.11.l0 for ( p₁-p

2) is +5.60. In the }!l'oposed w:-cLfmiom, the slow step is ~elieV.;"JCl to he the brl?:ak.in.c; of tho I1

- G bond. 'Phil:: ir: e:~l3ct;t:d to take place nore r~1pidly

Vii'l0n /\r.:.I~J S_s morH stnble than (t~, :l.. r; • . for remction ( 1), p 1 should

be positive.

The

sign

and

magnitude

o£ p

5'7

somowh~1t vnri[1ble r.:>ff'ect of ~::ub:.:>tituents on the r'lt8 o:f' form-rrtion ol' toluene ~d tho:t£7;h there \7Crt~ lni1,i('.:,,tions thnt n vaii.ue of P•) in thirl C1Wn of ::1rountl +1 1.':ould btJ rer..sonable.

'-IGi:wuing the uormal fall-off factoJ.~ along a satura.tad carbon

' ~ 0

ch:nu of

o.

1_{~? , thiu would predict n. fit3UN; of •.. bout}

+a.

-+2.

5

for the tetraph~myl s,vntem. /hen thiB is oombinAd with th.o mea.nurod (p₁-p₂) oi' +),G, it points to a p_{1 value of around}

+'1 ...

+8. ~l.'his fiGure iH high, but not ru=:: high as would be expect•.1<l by applyinfr, th·~ normal fall-off fr:tctlor to the

... ~ Ll-(4

rcnul ts •.)f the work o£ do::: f.man · · on triphenyl ( Bubsti tuteci benzyl) :Jhor'3p.honima hydro:ddes. ~i!he latter obtained ~

V>llue of +-4 .. 62, which would lead to a value of nbout +10

-+'11 in our cnse. 'i1_{hit:: of courne}

assurnes th!;:;t the Axtent of

io HimilB.:t" ;cmd also that the abili t:te8 o£ the two leaving p;roups to stabilise c1 nee;ati ve chare;~ is oompa.rable. Nui tber

or

these is nececBnrily truo.

'1.'he evi(J en en, r:;kGtcby though it :i.s, therefore points to our valuEJ for ( p.₁-p

A l'·•Ossible ext>lan~-1tion for the low p value is elect:ro-_philic JNi:ct1cip:~.tion ·b) the sol vent, which would. result in a lowering ol· tht:? oharge on thr:l lenVillf\ c~roup in the trnn~,;i tion

st dje.. 'i/ld.d phtm.o.vtenon he.s 1Jnr~n suggested ro:r other

r·eac·tiolll!l invol vine; eliwiv.;•tiox.i. of 0<3.rba!lions Lt·9' 50, and will be covered in cuore de·tail l"~ter (page 41).

•J.'he l\nom.a1ous Hute .for the .u.-C;ya:nophcn.rl 'J;~ Vld;~tve

iuc1;i.eoted le::;n than. ·1~. of ben~H.:ne iH the product, any derived voJuo for k,,r,/;·;: 1' _{rt • J. 4) J} \'iOUJ.d be too lnRceurnt;e fol"

it

to bo of

i.lny u.so. I·:xporiment1..1.lly it V'ftlf) found th.::t.t the only cieri

vt;.,t-j VC'::J fnlli!.l.(~ in. to thiG cnter;ory vmre .!£!:-fluorophnnyl,

E-nl tropl•.e:n:Jl cmd }2-ni t;ro,phenyl.· (\urpr.il.d.ngly' the

u ....

cyano-l,•hE·ns 1 COtJtpOun,. (:;avo more thr3.n ·1/ b0nzenc E.U1(l. Cc~lculations

chowe<l that the value of k _II.I' l./k r_r· was about 100 times _{L•' q).£} lower t:hen would he p:r·ndictDd on the bt,_nis of 1 ts (U.pf~ctoc1 elect-ronic effect. 'ssumi.ng th.stt this rflsul t if) not ~m artefact,

and there is no reason to believe it to be one• then this

nbnoro!t:,.~.lly low vo.lue mus·t. bo due to oome f~1.ctor either

increasins the r8te of formation of benzene or decreasing the r:;.te of f\?rmu.tion of ben;:-.oni t:rile. j.'he c;yano nubsti

tuent

~.

<:llentruna in thn

v

n -drc bond forme:c.l.. bet,•:eon phosphorus and

y

rche T)- 0 n-bond in (}Ui te strong and io believed to involve

two ox;n~en lone-p8i.rs of electrons :md two ortho(r,Onal

c-c-,1

orbi tala of the phooph.oruG ntom"" • Of course, only one of tho two p'lt-d.tt bonds coul0 in.ters.ot with the _2-cyanopbenyl

·-')'

of tl.:.e 2 ... G bond h~'l nuclt indiroct. irdiE':;r; .ction 1d th the ox;n:;en

r:,"l

tr.1i::; t;yr~e luJ.ve. lv:nm pro;:cse<l for sul})liOnoz"c.. and i'or phonpho.te

oven r:wre efi\~ct:i_vcly ia tho M:.FIE< of the .12.-n.i trophenyl

oubsti tuent. However, the olec.i;ron-v1i 1)hdra',1.1ing effect of this

nub~.)ti tuHllll, :md oven v1ith tlw t•ate-dBcl·enning -H E.:.ffect being tnh:o.n iHto account, the aruonnt o.f benzene released Ci11.1ld nt.;ill he r1mch too klnl8.ll to me, sure~ on the

G.L.c.

'l'he lUlOUf~lou~{ );a.tcn fm~ the u.-t!et.byl, .u-:>'luoro and u.-h!etbox;r Derivatives

l:Le d.h<>ve the liue through tht:> ~ :pointD, indicntinc:

Bn.<HnalouHly h:l:<h VAlues fo1'l k·'rJ·r/lc . . _1• f'<.c noted. earlier for H 1 (P'

Lh•.::1 CHJ'HJ nf -C;}iJ~ ,£-Ci/~•no t';:cou.o thie c:.m be tlU~:i~ to either of

tv!o f~f.rcnt;s 1 fir8tly, r£>to.r<lr:.tion 0f rr:>let.'.!JG of benz,c~nc, or

:3ecmldly, to a.coe1erntion of role::J.r:so of 1\rH from the

is 11, l~eFm11~ o:f a:n aeec 1.8r:.:J.tiou in the relon.Be of ArH. A

pon:d.blc e:-qfl ;Lnn.tion fnr thi~1 henOliiGllon lios in electro-_phi lie 11..::;si.:;tt:1nce h;v the sol vent in the fisoic1u of the ; ·'- 0 bon0.

H - 0

\

H Ph Ph

\I

y - -- - - - P - - -

o-b + . t t ,_ -," ]' .,

$U S ,.a_ U€H1 f~ SUO!! !-),13 C.!,:)-l

1"-,

inter;:ct• ;:rtrongly b;y ret.;1cnane.;, j

Fh

or -O<JH~ beceuse tl1ey can

)

\'d th the

reaction

site ..

41

r:L1his Jor::n of 8. c:i.ct.·~mce has b.;:-2:n proposed by l':D.born and.

hiE1 co-v/orkers54 us. o.n expl:3na.tion .for enhm1ced reactivity, whan similar E-UhlJti tuents are present, during the base

catnl.yRQd c1euvage of Hryltri:notl,ylsilRnt:~t:: E--tr1d e.ry;t t.ri1nethyl-st.umnneu. In support they l1()te th,xt: incorporation of

p:c·otiuxu in the CG.rbe.nicm relEl:li.ed is f~Jvoured ovor df:mtHrium by a factor o.f four.

In o~r case :Duell electrophilic rttHdstance should be much

G)

rr1n.gnit,ud.Et! observed v;ould. oc: ur 113 diff.'icul t to jud.ge.

1_{.L'r·ippt~tt I'eportod nirailru:· sslecti vi tioa i'or tlu•oe 'Nidely}

dl.i"i:erin1?-: phonphonimn compounds, ond thiu would tend to

:qoto

-'l:\!0 different e:xplan;.ttionB have boon oi'i'(;:.rcd to account

for tlH3 ,2-cyano oompound on the ono hand, :1nd the ].-:Cluoro, .• .1 Q.-methyl and .Q-mctho.:'~J one c. on the other. ln fact ei tber

ex.pla:natiion i:il ono oou.ld concoi Vi':~.bl:t account for both rro,sul ts,

be· duu tu u. (~oc:ccn3ed need fo~' oluct;rophll.Lo <.wc:i otunce, or tho a ceo ler.:, ti1m in r: '.te ::':or the otlw.rs could re:::;ul t from

cleorer:.UJ':!d pn:-d.n ovcr1:D.p d!H1 to elect:t:·on r0p'Ulsion. J!O"JVovcr,

APPENDIX I

(ri) :i·':t~nUf:l.J,\'\tion oi' ~J.£il.tJ~t.J2j1e:~yl:1hospr.tm.\i~. rF'Jl,h'!&.§

't\A.'o :-{rVU ti . .,nal mE~thod.s raported were tried. r;_lhe first

' . ' '36

wn.s tlw:t; reporte~l by 1 Jocwno'" HJtd Niedox· • ~L'he qp·propriate

r~t;her ----+

UH:r

+ other prod.nc.t;-5.

43

bA cont11Jllil1Hted, even after· caretul purJ.fict-:~.tion procedures, and thus not su.i tr;~ble i\)r this work. 'Vhis method was t.ttere-fore ah;i!J.\loned aG ':\ ~~;:tntiJ.t~tic J?oute :t'o:r the production of

:Vhb klecouU. method rovortod involvect the .interaction of

th8 apr>ropriate r.,ryl h.alid.e, trivhenylphospliine, aw'J cobalt

c.b.lorid,;:, in reflt).xinf;: benzoni t.rilA

r1oJveut57.

Heveral

attempts 1;o ini i~:l.ate t:Ois reaction f Riled, therf~fore as a

6

(i)

CN

A

[il]

VNo:- "-(ii)

(j_ii)

,., ( · Sr~~

S9

.

, ,i;~p8 i)- - nnd. ( ii) · wr~re cr~.rri c~d out oucce~sf"ully,

i·tO\Nevor t.ht1 !!!-cynn.oani 1ine hydroch1or:Ldo, du~ to :Ltn Bxtreme

rChe l!!-Cy;l,ll(!phen:yltriphenylr>bonphonium iodide V\'aG therefore

1. ,,:ucJ.i, I~

,1_~ • .'. .. ' V ;).11<~ Cl~ ,; (}I'.f , J • .illU..

c.:t:f, ' I

l j . ·,\,., It

., I I ' ' ' '

, • !.~1. 1.\)tc.tjvie.r'l, -·.1,.

i',WJ~J.i, i'/1 • :;.JtOl}~·;:!_d. UUC~ J' • i ~<U!F.Gl', i> .. bctr: v:~.t.;G uf J'apel'S

t

~ t t1 l .. t h , , t . ]'•' .,_. ' ' ' b . i

j)l:'i'::S:Ol1 ,;;c. :Ct . 1:!.0 ~ '-+() l·JU ~~ona. . >'100 v:U.q:; Q.I 't; .(; fl.mar Call

1' \' . .-1 '')"' t '

' ~ I·") i p ·- ...,.II,; ~· ' ... ':.1•

3.

tf., an.d. L. ;Lichtouctucl"b, Ohom, Her.

_,

Ll4

b. i') .;··

,·~ e ,Lj • f1! c'Gw en , J • .Am.

Cbe¥\• .i·oc. 82, 2.·.'/)C ('10CO) •

.,_ ,.,

----

- .

Ollem •. f_o_g.

f31t

::J80G ( 1C)J9).

10. J_,.D. :,t.uin, c..l • • . n~tero,

c.:u;.

l.!riffin and M. Cordon,

'11_{~Y~re.hcd:ron :Lettero 3GH9 (1964);}

J .. ,D •. :~1.lin an.li J;.i'l •

16. J,~ Horner,

( 1959).

/ pi b l i ..:l -l· \' 1 - 1 '?2q ,'_')9· 5

..• , ~< (~ .ae S Hnv. J • • • i ... OGflt!, ~·, ~t _

L' c.i "'c· n"" ""1' "''"-I'

;.·.~- .... . -l.h,. .• <ll...,. '

.:1.,

e.ud L. l-ichtenstadt,

,li£r.

,!!!±,

356

( 191"1) •

...,,., (' . . t Gl -~ ·1, c: _,, 4:R.8 (1-:_>G·"I).

c.<.!. .. • .':~.ltsnes, ~~_d.~~·. ,' •C"-1?~· ..._ ;.; ., ,

23. G. ::H!.rkl, ,_:;he~n. ~ior. ~' ?)i)05 (1961); ;~;.·J.·.D. ~~·ough and

' • 1

.1'1'ippett' J ft C"hem. c;oc.

2333 (

·1962).

')7

'-

.

"l .,.

'10T.'l:ler, . J • .,

I \teL\ .. e

9!ot:;rtt.hedr·on lJettero, 96;i ('1963).

'+?

J •. :..Ut ...

~ ) ; . '•

~j~· • .L'J. :::ic::wen., .T. f.l.m,.

:\teutrup and P. .Dock,

)1, H- .iiu.fflt.Lmlln, Am.).. S;;S4, 'I (1960).

(1962) •

. ~ ... ! .... ."tm • Gh2liil• ; )LJC. ,

QZ,

39'+8 ( 1965) •

iia.;:t~o, I',G., .J. i\.llt. Ohem.. Goc. 87.,

~--~--- ~

!J. l1o.r>.rHn~ aud

n.

rio C fmnrm,

-

i)or.

n,

L~5 ( 195B).

...

.<{•)r'llt~T- •tncl

n.

1loff'a~Tll), a~r. ()1 r""•""' _{( 195>~)}

,l..J • j l •

-

,.._,

i'h.wnnentheg, H. .\/'osor !:l.nd P. .Beol~. ,

-

.:.ter.

:J.2.,

2'?112 ( 1966).

IVl.

,, •')

t-r_,

l!-6.

W?.

)0.

53.

'' i -l't .~.,.._.f,... '~,~ q 1· c·· ·· c~.~ "L

.I I . ~~6(,.

If

,l I , . : lo j'fl'i ;'-!)ll). '

i!.lli.

§..::d' 1 ( 1 ')(,()) •

'-''. t·roff:.Ltt., ! 'roc.

b

(1950).

· l;. :JI. J'. Cruic:~.:shank, d.

( 3JXl l:Jdi '!i • )

·~d ' ' t )

\., dll •3(1]. ••

28,

-4-09

1002 ( 1952).

( "1~)'?0).

r~,n

.•' (

.

:::oc. 26~ l~6l~ (1904).

·-~