INHIBITION IN THE G. N.

BY

3,6-DI-TERT-I3UTYLPYROCATECHIN

OXIDATION

OF

I-NONENE

I. Mazaletskaya, L. Komissarova,

G . V. and I.

Karpukhina, S. B e l o s t o t s k a y a

UDC 542.978:547.565o2-542.943:547.313.9

The retardation of oxidation in the olefins is a matter of considerable practical interest. The derivatives of paraphenylenediamine (PPhA) are highly efficient inhibitors for such reactions. In fact these compounds are more effective in this respect than are the monofunctiona! phenols and aromatic amines. It has been suggested [i] that the high antioxidant activity of PPhA is due to the formation of autosynergistic mixtures of the PPhA and quinodiimine, one of its reaction products, which is, in turn, capable of combining with R" radicals in the oxidizing substrate. On this basis it could be anticipated that the high antioxidant activity of bifunctional monomer stabilizers such as the polyolefins, hydroquinone, and ~-tert-butylpyrocatechin [2] could be traced back to the s of synergetic mixtures of the polyphenol and quinone, one of its oxidation products. The present work was a study of the inhibition of the oxidation of 1-nonene by 3,6-di-tert-butylpyrocatechin (PC), one of a new class of spatially hindered pyrocatechins [3]. It has already been demonstrated that PC is an effective h~hibitor for the oxidation of ataxic polypropylene at 160-180~ [4]. EXPERIMENTAL

l-Nonene, which had been purified by the procedure outline in [I], was oxidized in a bubbling-type reactor at 120~ The inhibition period was taken to be the time required for building up a 1.10 -2 moie/li'ler concentration of hydroperoxides in the solution. Hydroperoxide concentrations were deter~rfined iodometrically. 3,6-Di-tert-butyl-o-benzoquinone (DTBQ) concentrations were determined spectrophotometrieally [kma x 406 nm, e 2170 liter/(mole, see)]. PC concentrations were also determined spectrophotometrically, on the basis of the color resulting from the addition of NaNO 2 to the compound in alkaline solution [51. The spectrum of the colored solution corresponded to that of DTBQ. DISCUSSION

OF

RESULTS

In systems containing PC at a concentration of 1.5o10 -r mole/liter, the length of the inhibition period (T) for the autooxidation of l-nonene was 20 h (Fig. i, curve i). For oxidation at these same concentrations, the length of the inhibition period was 10 h or less in systems containing monofunctional aromatic amines and phenols and 13 h in systems containing nitroxyl radicals [6]. Thus PC is a highly effective inhibitor for the lnonene oxidation. Study of the autooxidation of l-nonene in systems containing PC as inhibitor showed DTBQ to be formed (Fig. I, curve 3) as the PC was consumed (curve 2). The form of the kinetic DTBQ buildup curve was that characteristic of an intermediate reaction product. At the end of the inhibition period practically all of the PC and DTBQ had been consumed. The extremal form of the DTBQ vs t curve reflected reaction of the DTBQ with l-nonene alkyl radicals. It has been reported in [7] that DTBQ reacts readily with n-deeane alkyl radicals. DTBQ also reacts effectively with l-nonene alkyl radicals, as can be seen from Fig. 2. At an initial concentration of 1.2.10 -3 mole/liter, the DTBQ reacted with all of the R" radicals formed in the reaction, the rate of consumption being given by W i/f, with f the stoichiometric inhibition coefficient, equal to 2 [8]. Evidence that the DTBQ was completely consumed through reaction with the R" radicals was suggested by the fact that the DTBQ buildup curve (cfo Fig. i, curve 3') for the PC-inhibited autooxidation of benzene (cf. Fig. I) did not pass through a maximum, even though the alkyl radicals formed there reacted more readily w~th oxygen than did the !-nonene aliyl radicals. There the inhibition period came to an end (curve I') when all of the PC had been consumed, despite the fact that the system still contained DTBQ at a relatively high concentration {curve 2'). Institute of Chemical Physics, Academy Akademii Nauk SSSR, Seriya Khimicheskaya, July 13, 1981.

of Sciences of the U SSR, Moscow. No. 3, pp. 505-509, March, 1982.

0568-5230/82/3103-0453S07.50

9 1982 Plenum

Publishing

Translated from Izvestiya Original article submitted

Corporation

453

C" 10 4, m o l e / l i t e r

[ROOH]. 10 2, m o l e / l i t e r

DTBQ" 10 3, m o l e / l i t e r

0 , 5 ~ 0

q

0

12

i6

1]0,5 20

24

28

J2

L o

I to

I 10

~ 30

I- "t #o 50

"i, rain "

Fig. 1 Fig. 2 Fig. i . Kinetic curves for hydroperoxide buildup (I, I'), the consumption of 3,6-ditert-butylpyrocatechin (2, 2'), and the buildup of 3,6-di-tert-butyl-o-benzoquinone (3, 3') in the autoozidation of l-nonene (1-3) and ethylbenzene (1'-3') (120~ [PC]0 = 1.5. 10 -4 mole/liter). Fig. 2. Kinetics of the consumption of 3,6-di-tert-butyl-o-benzoquinone through reaction with l-nonene alkyl radicals (initiator-azoisobutyric acid dinitrile, W i = 5.10 -7 mole/(liter, sec), 70~ Thus, hydrocarbon oxidation in systems containing PC leads to the formation of mixtures of PC, a compound capable of reacting with RO 2" radicals, and DTBQ, an alkyl radical acceptor which appears here as a reaction product. It has been shown in [6] that mixtures of inhibitors capable of reaeting with both RO 2" (InH) and R" radicals (Q) are synergistic. Thus, it was reasonable to assume that the PC-DTBQ mixtures formed during PC-inhibited hydrocarbon oxidation would also show synergism. Most types of mixtures of alkyl radical acceptors with inhibitors capable of reacting with 1202" radicals show maximum synergistic effects at Q : InH = 1 : 2-3 [6]. The mixtures formed in PC-inhibited oxidation would, in general, be rich in DTBQ. Further introduction of DTBQ into such systems could not, therefore, lead to synergism. In fact, PC-DTBQ mixtures are less effective inhibitors for the l-nonene oxidation than PC itself (Fig. 3, curve i). On the other hand, the introduction of an inhibitor capable of reacting with RO 2" radicals into such system should give a more effective inhibition than could be obtained with PC alone. It can be seen from Fig. 3 that the addition of Neozene-D to the oxidizing system led to departure from additivity of the T VS. mixture composition relation (curve 2), while the addition of 4-methoxyphenol gave rise to synergesis effects (curve 3), despite the fact that the ir~hibition periods for Neozone-D and 4-methoxyphenol (9 and i0 h, respectively) were close to the TDT BQ value of 9.5 h. The antioxidant activity of PC in the autooxidation of l-nonene (formation of an alkyl radical acceptor in the course of reaction, effect of the introduction of inhibitors capable of reacting with RO 2" and R" radicals) was reminiscent of the behavior of PPh_A as described in [i]. It should be noted, however, that PC and PPhA differed markedly in their ability to inhibit the l-nonene oxidation. While the value of Tpc at 120~ was 20 h, the length of the inhibition period for the oxidation of l-nonene in systems containing PPhA at a concentration of 1.5.10 -4 mole/liter was 50-52 h, despite the fact that the two inhibitors were comparable in antiradical activity. It is a well-known fact that pyrocatechin is easily oxidized by molecular oxygen. In order to determine whether there was some relation between the relatively low inhibiting action of PC, as compared with PPhA, and its high oxidizability, rate constants for the reaction of each of these compounds with molecular oxygen were measured. Measurements were carried out in chlorobenzene solution, working at 120~ It can be seen from Fig. 4 that the PC + 02 reaction was first order with respect to each of its components. Calculated from the slope of W vs. [PC] 0 (W is the initial rate of consumption, and [PC] 0 the initial concentration, of the PC), the rate constant for this reaction was found to be (9.5 + 0.5)" 10 -4 liter/(mole, see). Here it was assumed that [02] = i-10 -2 mole/liter [9]. Under similar conditions the rate constant for the oxidation of N-phenyl-N'naphthyl-p-phenylenediamine by oxygen was (8 • 2)- 10 -5 liter/(mole, see). In other words, the high oxidizability of PC could account for the fact that this compound is a less effective antioxidant than PPhA. Comparison with the data of the literature showed that PC reacts with 02 more readily than any of the inhibitors studied in [i0, ii]. The value of kpc + r~ at 120~ was 9.5.10 -4 liter /(mole . see), whereas the ~a 2 kin H + O 2 values for various aromatic amines and phenols at 180~ ranged from 5.10 -5 to 2. I0 -3 liter/(mole-

454

%h J0 ~

j

W" 10 s, mole/(liter, sec) 20

/W'10 s, mo le/(liter, sec)

|

~5

','F $

b) /

!

f0

0r # I

PC iO0~

I

z# I

I

i

I

I

I

00 i 20

#0 #0 #0

z40

~/

+,o~ / or ~ J# eo go o ,~

o,5

1,o ~,5 5# C. 10 a, m o l e / l i t e r

/

I/

I/7#%

InH I DTBQ 0

o

Fig. 3 Fig. 4 Fig. 3. Variation of the length of the inhibition period in the 1-nonene oxidation with the composition of the mixture of 3,6-di-tert-buty[pyrocatechin with 3,6-di-tert-butyl-o-benzoquinone (I), with Neozone-D (2), with 4-methoxyphenol (3) (total inhibitor concentration, 1.5" 10 -4 mole/liter, 120~ Fig. 4. The variation of the initial rate of consumption of 3,6-di-tertbutylpyrocatechin (W) in the reaction with O 2 with the initial PC concentration (a) and with the oxygen content of the gaseous phase at a pressure of 760 torr (b) (chlorobenzene, 120~ s ec). The rate of sec), where W 0 is with the rate of PC mole/(liter, see)], of oxidation of PC ted temperatures.

PC consumption in interaction with RO 2" radicals [W 0/f = i-10-9/2 = 0.5.10 -9 mole/(liter. the rate of chain initiation, and f is the stoichiometric inhibition coefficient] is comparable consumption in oxidation [Wn~. ~ = kn~• 9 [PC] 0. [02] = 9.5.10 -4. 1.5- 10 -4. 10 -2 = 1.4.10 -9 .r~ T~.# 2 X-~ ~'J2 even at relatively low initia[ PC concentrations of the order of 10 -4 mole/liter. The ease could limit the use of this compound in systems operating at high concentrations and eleva-

The autosynergistic action of PC-DTBQ mixtures serves to maintain the effectiveness of PC inhibition, despite loss through the reaction with 0 2. Reinforcement of the action of PC in DTBQ mixtures may result from the formation of active radical inhibitors through the reaction OH x

0

]

x

H

x

O" o

x

'~

x

oll

x

X = t-Bu.

ESR

spectra

of the 3,6-di-tert-butyl-2-oxyphenoxyl

radicals

in such systems

have been described

in [12].

CONCLUSIONS i. 3,6-Di-tert-butylpyroeateehin (PC} is a more effective inhibitor for the oxidation of l-nonene than are monofunctional phenols and aromatic amines, or stable 2,2,6, 6-tetramethyl-4-benzoylpiperidin-l-oxyl radicals. 2. The high antioxidant activity of PC is due to synergism 3, 6-di-tert-butyl-o-benzoquinone resulting from PC reaction. 3. Rate constants have been determined diamine with molecular oxygen at 120~

for the reactions

LITERATURE 1~

2.

in the mixtures

of PC

formed

between

PC

and the

and N-phenyl-N'-naphthyl-o-phenylene-

CITED

L. I. Mazaletskaya, G. V. Karpukhina, and Z. K. Maizus, Izv. Akad. (i981). M o n o m e r s , C o l l e c t e d P a p e r s , V. V. K o r s h a k (ed.), I L (1951),

Nauk

SSSR,

Ser. Khim.,

1988

455

3. 4. 5. 6. 7. 8.

!. S. Belostotskaya, N. L. Komissarova, E. V. Dzhuaryan, and V. V. Ershov, Izv. Akad. Nauk SSSR, Ser. Khim., 1594 (1972). E.S. Torsueva, I. S. Belostotskaya, N. L. Komissarova, and Yu. A. Shlyapnikov, Izv. Akad. Nauk SSSR, Set. Khim., 2132 (1976). A.S. Maslennikov and G. N. Poryvaeva, Zh. PriM. Khim., 3_~8, 1327 (1965). L . I . Mazaletskaya, G. V. Karpukhina, and Z. K. Maizus, Neftekhimiya, 1_99, 214 (1979). I . A . Shlyapnikova, V. A. RoginsMi, and V. B. Miller, Izv. Akad. Nauk SSSR, Ser. K h i m . , 2487 (1978). L.I. Mazaletskaya, G. V. Karpukhina, and Z. K. Maizus, Izv. Akad. Nauk SSSR, Ser. Khim., 1988

(1981). 9. i0. ii. 12.

N.M. I~manu~i', E. T. Denisov, and Z. K. Maizus, Chain Reactions in Liquid Phase Hydroei~rbon 9 Oxidations [in Russian], Nauka, Moscow (1965). L.N. Denisova, E. T. Denisov, and D. I. Metelitsa, Zh. Fiz. Khim., 44, 1670 (1970). L.N. Denisova, E. T. Denisov, and D. I. Metelitsa, Izv. Akad. Nauk SSSR, Ser. Khim., 1657 (19,39). E.B. Zavelovich and A. L. Prokof'ev, Chem. Phys. Lett., 29, 212 (1979).

OXYGEN-CONTAINING FOR

THE

AS

ACTIVATORS

WCI G -TETRAALLYLSILANE-CATALYZED

POLYMERIZATION N. A.

COMPOUNDS

OF

CYCLOPENTENE

UDC 541.128.34:541.64:547.514,71

I. P a k u r o , K. L. M a k o v e t s k i i , R. G a n t m a k h e r , and B. A. D o l g o p I o s k

It has been shown [1, 2] that allyl compounds of Si can be combined with tungsten halides to f o r m effective catalysts for the l o w - t e m p e r a t u r e p o l y m e r i z a t i o n of cyclopentene (CP), leading to ring opening with the formation of eis-polypentenylene. The p r e s e n t work was a study of the kinetics of CP p o l y m e r i z a t i o n in toluene solution a t - 3 0 ~ the m e a s u r e m e n t s being c a r r i e d out on s y s t e m s built up f r o m c a r e f u l l y dehydrated m o n o m e r s and solvents and the r e a c t i o n catalyzed by various combinations of t e t r a a l l y l s i l a n e (TAS) and tungsten halides. EXPERIMENTA

L

The kinetics of cyclopentene (CP) polymerization were studied through d i l a t o m e t e r m e a s u r e m e n t s . The reaction components were loaded into a glass s y s t e m which could be h e r m e t i c a l l y sealed and evacuated down to a p r e s s u r e of 10 -4 t o r r . The C P was prepared by dehydration of cyclopentanol and freed of peroxides by t r e a t m e n t with aqueous solutions of FeSO 4 and NaOH. The product obtained was distilled and then dried, f i r s t with a N a - K alloy and then with EtLi. The toluene was of "UV s p e c t r o s c o p y " grade which had also been dehydrated with EtLi. The t e t r a a l l y l s i l a n e (TAS) was vacuum distilled. The WC16 was freed of o z y e h l o r i d e s by vacuum heating at 170~ The WOC14 was prepared by reacting WCI6 with WO3 and distilling the product so obtained. Humidified benzene was p r e p a r e d by extended agitation of a b e n z e n e - w a t e r mizture. The w a t e r content of the benzene was d e t e r m i n e d through NMR s p e c t r o s c o p y , using cyclohexane as an internal standard. The water content of such solutions ranged f r o m 18 to 22 m o l e / l i t e r . In some c a s e s WC1G-TAS-catalyzed polymerization was c a r r i e d out in w a t e r - f r e e solutions; here the WC16 was mixed with CP and held at ~ 20~ until the lilac coloration disappeared and the solution b e c a m e reddish brown (25 min). The d i l a t o m e t e r was put into a bath at -30~ and a thin-walled ampule containing the TAS lying at the bottom of the d i l a t o m e t e r was broken. In the experiments with w a t e r - c o n t a i n i n g solutions, the b e n z e n e - w a t e r mixture and CP w e r e added to the WC16 solution simultaneously at ~ 20~ In the c a s e of the experiments with oxygen-containing solutions the WC16 and CP were held at ~ 20~ for 25 min, cooled to - 3 0 ~ and the TAS and a i r then introduced into the d i l a t o m e t e r under continuous s t i r r i n g . In determining the ionically bound chlorine, the C P and b e n z e n e - w a t e r solution were simultaneously run into the WCI~ solution in toluene. The mixture of solvent and HC1 was condensed into a s e p a r a t e ampule and L. Ya. Karpov P h y s i c o c h e m i c a l Institute, Moscow. Translated f r o m Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 509-513, March, 1982. Original article submitted July 1, 1981.

456

0568-5230/82/3103- 0456307.50 9 1981 Plenum Publishing Corporation