Phthalocyanine Derivatives as Catalysts for Soft Peroxidative Oxidation

L.I. Simandi (Editor), Dioxygen Activation and Homogeneous Catalytic Oxidation 0 1991 Elsevier Science Publishers B.V., Amsterdam

461

PHTHALOCYANINE DERIVATIVES AS CATALYSIS FOR SOFT PEROXIDATIVE OXIDATION

V.M. Derkacheva, S .V.Berkanova, 0. L.Kaliya, E.A.Luk'yanets Organic Intermediates and Dyes Institute, B.Sadovaya 1/4 103787 Moscow. USSR

Abstract The influence of peripheral substituents and axial ligands nature in a series of highly soluble in benzene cobaltous phthalocyanine derivatives on velocities and mechanisms of cumene hydroperoxide catalytic decomposition, of cyclohexane oxidation and catalyst destruction in the presence of cumene

hydroperoxide was studied. The structural factors increasing the stability of catalyst with comparatively little decrease of its activity were interesting phenomenon of

determined. The

catalyst stabilization by

cyclohexyl radicals due to their axial coordination was detected. The routes of efficient catalysts design were proposed.

The interest

in hydroperoxidative catalytic liquid-phase oxidation

of hydrocarbons increased markedly after discovery of new effective oxidative systems

comprising partially reduced dioxygen: hydroperoxides,

peracids, iodosobenzene etc.[ 11. On the other hand, these catalytic systems can be used as models of enzymatic hydroxylating systems such as cytochrome P-450. That is why

the synthetic analogs of their active centres

-

me-

talloporphyrins and their stable azaanalogs [ 21 pththalocyanines (PcM) and tetrazaporphines (TAPM) - attract the attention of many

investiga-

tors. The hydroperoxide decomposition in the presence of PcM is well known

since 1938 [ 3 ]

and was intensively investigated up

to now [ 4 ] ,

though

462

mechanism

of this process

isn't yet clear

in many details. That makes it

difficult to construct soft hydroxylating catalytic systems on the basis

of PcM and TAF'M. In the present and following (P-09)reports the kinetics and mechanism of cumene hydroperoxide ( C H P ) decomposition in benzene solutions of PcM and

TAPM as well a5 of cyclohexane oxidation by CHP catalyzed by these complexes have been described. The first report is devoted to the establishment of the relationships between catalyst structure and parameters

of investigated

processes, in the second one the main features of these processes are des-cribed in detail. We have investigated the kinetics of CHP decomposition in the presence

1 2

of subs ituted cobaltous Pc's ( R R PcCO):

R 1=H, R 2=t-Bu (%cCo) 1

2

R =PhS, R =t-Bu

1

R =NO

2

R =t-Bu

1 2' 2 R =PhO, R =H

1

2

R =H, R =PhO 1

2

R =Rr, R =t-Bu

The tions

reaction under investigation was

(benzene

2OoC), its

main products

(DMPC), acetophenone (AF') and oxygen. For rate of

carried out

are dimethylphenylcarbinol

all

1 2

R R PcCo the initial

CKP decomposition is described by equation ( 1 ) :

The values of k&s

are represented in table.

in mild condi-

463

It is to be mentioned are undergoing We

that during

1

2

CHP deoomposition all R R PcCo

oxidative destruction in the beginning of the reaction.

investigated the kinetics of PcCo destruction using highly solub-

le 'PcCo

as an example at the following concentrations of reagents: t -5 -4 [ PcCoI = 0 . 2 5 - 1 1 . 3 ~ 1 0 M, [CHP] = 0 . 6 5 - 6 . 5 ~ 1 0 M. No change in electronic 0 0 t absorbtion spectrum of PcCo was observed ( h =668nm), indicating that the max reaction proceeds with retaining Co-ion valency. A characteristic feature of t kinetic curves of PcCo destruction is the occurence of so-called "induction" period (fig.1). Introduction into reaction mixture bitor

-

of radical inhi-

N-phenyl-2-naphthylaine ( I d ) up to certain concentration only

prolongates "induction" period without changing the rate of the reaction. Further addition of InH results in its decrease. The observed kinetic effects can be explained by multifunctional

properties of InH and are in a

good agreement with the hypothesis of real catalyst formation during

the

"induction" period (see P-09).The real catalyst of suggested structure "A" t is formed by molecular interaction of PcCo with CHP:

cok$&

OOR

Structure "A"

Complex "A" is very active in CHP decomposition with formation of two types of radicals: RO' and RO' the latter ones lead to rapid 2'

tPcCo destruction

(maximal rate on kinetic curve). The direct comparison of RO 'and RO ' 2 t reactivity towards PcCo was carried out in the model reactions of d i c w l peroxide

thermolysis in deaerated benzene

solutions

of

$cCo

(RO '

generation) and of azoisobutyronitrile thermolysis in aerated benzene solutions of tPcCo (RO' generation). A s was shown by these experiments, RO; 2 t are at least an order of magnitude more effective in PcCo destruction than

RO..

464

-.)

0.8

E S a3

$

2

0.6

L

2

2

kcr

0.4

4

0

v)

m

*

0.2

I

0

2 4 T IME ,mi n

8

6 + -

t Figure 1. Effect of increasing [ I d ] on the reaction PcCo with CHP. [ tP~Co]~=2xlO -5M, [cHp]o=2.5x10-3M. [ I d ] x104,M: 1 - 0, 2 - 0.65, 3 - 1.3,

4

- 5.0, 5 - 10.0,

0

6 - 167.

t Decrease of the initial rate of PcCo destruction at high InH concen-

tration is caused by its regeneration from oxidized forms. The degradation rate during "induction" period is described by equation (3):

w"ind-- kind [tPcColo[cmPlo (kind= 2.6 M and maximal rate

woIWlX=

-

-1 -1 s

(3) )

by equation ( 4 ) :

kpc[tPcColo~cHPlo

(kp

5 -2 -1' = 6 . 4 ~ 1 M0 s )

(4)

465

Analysis of evolved part of kinetic curves leads to following equation (5):

0[tPcCol

t t When [ PcCo] =[ PcCo]

.r.

0

(5)

z

womaX=kJPcColo[CHP1

equation (5) transforms into equation ( 4 ) . Equation

(5) shows the functional relationship between processes of $cCo and CHP degradation: the formation of a real catalyst of CHP degradation is a re*

sult of molecular

interaction

[tPcCo]o[CHF']o)

h C o destruction occurs

and

of

LPcCo

with

CHP

(product

in the evolved process

with participance of RO' radicals formed. The kinetic equations of inte2 1 2 raction with CHP are similar for all R R PcCo. The values of their maximal rate constants (

%C)

are presented in the table. With the exception

of tetra-3-nitro-tetra-5-tert-butyl-PcCo

the

'bC

values are almost indepen-

dent of Pc structure. The absence of their correlation with 6 Haamett constants is not surprising because

Scis a complex constant

constants of three processes at least: formation of real

including rate catalyst, CHP

decomposition and PcCo destruction. The introduction of four nitro group in Pc molecule results in essential stabilization of catalyst

(430 times as compared to "PcCo) while

catalytic activity decreases only about

7 times.

The axial ligands

-

pyridine (b), quinoline (Q) - not only diminish, as was established, the rate of CHP decomposition but also strongly increase PcCo stability; in this case central ion Co(I1) transforms into Co(II1). Kinetic curves of t PcCo destruction do not have induction period here. When 4. was added in value decreased in 200 times (fig.2) while CHP demolar ratio 2:l the k Pc composition rate diminished only 10 times.

466

2

4

M

[PY]0XiO4,

6

t Figure 2 . Plots of PcCo degradation rate constant versus Py concentration. t [ P ~ C =~ I~IO-*M, I [ C H P I ~ = 0.05 M. 0

t We have investigated the kinetics of PcCo destruction in the presence of Q as axial ligand.

The initial reaction rate

is described by equation

(6):

n

Such substantial strong decrease

of RO' 2

t PcCo

stabilization could

rate formation. But

difficult to explain the relatively tion

rate

in the presence

of

small

be

the result

in this case

it would be

decrease of CHP

axial ligand. Another reason

stabilization of tPcCo by axial ligands

may be

of

the formation

decomposiof high of more

stable to RO' complex. To solve this dilemma we have investigated the kine2 t t tics of PcH discolouration in the four-component system: PcCo t CHP t 2

467

t

Q + PcH2. tPcH2 was used in this case as a trap of Ro’ 2 The tPcH discolouration rate in the absence of Q 2 by equation (7):

is described

and in the presence of Q - by equation ( 8 ) :

t The absence of [ PcCo] in the denominator of equation ( 8 ) is the ki0

netic proof of the inertness of tPcCo coordination forms towards RO’ 2’ t In the presence of Q the rates of PcH discolouration and CHP decom2

position

(see P-09)

decreased

not more

than an order

of magnitude.

Supposedly, decrease of Ro’ concentration is negligible in comparison with 2 tPcCo stabilization effect (200 times). It is possible to conclude that t PcCo stabilization by axial ligands is a result of the formation of more t stable towards RO‘ adducts with Q having high (but less than PcCo) cataly2 tic activity in CHP decomposition. Bathochromic shift in electronic spectra and kinetic data suggest the structure of this adduct to be t [ PcCo(III)L]X-. In accordance with this structure radical destruction of t PcCo occurs only with preliminary coordination of RO * type radicals by 2 central metal ion. Using these data it is possible to design systems.

effective hydroxylating

It was shorn that in above-mentioned system (PcCo + CHP

in

benzene, 2OoC) cyclohexane (SH ) was easily oxidized to mixture of 2 cyclohexanol ( 01 ) and cyclohexanon ( OpZ ) in ratio 1.5:l (for detailed

468

mechanism see P-09). The kinetics of 01 and

on

formation was investigated. As shown in

fig.3, 02 and o?l.are forming in parallel reactions that was comfirmed by independent experiment - 07. when added to reaction mixture does not yield

[qj,* The initial rates of 07, and

formation for all PcCo under investiga-

tion are described by equation (9):

The values of k and k are outlined in the table. 01 mnl

1

r 0.01

9.

0

n

a

I

I 3

TIME, m i n

on

Figure 3. Typical kinetic curves of 01 and formation and CHP decomposit -4 tion. [ PcCo] ~ 1 x 1 0 M. [SH ] ~ 2 . 3 M, 2 inert atmosphere. 0 2 0

469 Table, 1 2 Values of rate constants of CHP decomposition, R R PcCo degradation and 01 and

@I. formation as a function of catalyst structure.

1 2 R R PcCo

1 2 R =H, R =tert-Bu 2 R ~ R ~ = P ~R s=tert-h , 1 2 R =Br, R =tert-Bu 1 2 R =NO2,R =tert-Bu 1 2 R =PhO, R =H 1 2 R =H, R =PhO

kobs

%c

k

k .-

&-1

M-2s-1

fls-l

M-ls-l

3.1

1.85

3.9

2.0

4.4

2.5

0.7

0.4

1.9

1.1

4.5

2.4

16

19 13 2.3 14.7 21.1

5 6.4~10 5 0.83~10 5 0.5~10

0.015~10 5 0.72~10 5 2.5~10

01

Lk

Spectral data suggest that SH oxidation in anaerobic conditions 2 is accompanied by oxidation of Co(I1) to Co(II1). The enhanced stabi-

lity of catalyst seems to be caused by its partial transformation in reaction conditions into inactive form - PcCo(1II)R' (R'=C H ) . The values of 6 11 rate constants allows us to conclude that introduction of electronwithdrawing substituents such as NO

groups in PcCo molecule increases 2 strongly its stability without essential decrease of catalytic activity in

cyclohexane oxidation. Thus, in case of tetra-3-nitro-tetra-5-tert-butylPcCo the latter decreases about four times by more than 400-fold increase of stability.

So, the most effective catalysts of hydroperoxidative oxidation can be found among derivatives of PcM and especially TAPM with high values of oxidation potentials.

470

REFERENCES 1

P.Battioni, J.P.Renaud,J.F.Bartoli, M.Reino-Artiles, M.Fort, D.Mansuy. J.Am.Chem.Soc. v.110 No. 25 (1988) 8462-8470 and references herein.

2 S.V.Vulfson,O.L.Kaliya, O.L.Lebedev, E.A.Luk’yanets, J.Obshch.Khirn., v.46 NO. 1 (1976) 179-184. 3 A.H.Cook. J.Chern.Soc.,(1938) 1774-1780. 4 H.Kropf, J.Spangenberg, A.Gunst, J.Hinrichsen, Lieb.Ann.Chem., No. 12 (1980) 1923-1938.