TECHNICAL REVIEW
Autoxidation of Aldehydes in Acetic Acid Solution Ch. F. Hendriks, H. C. A. van Beek;
and P. M. Heertjes
Laboratory of Chemical Technoiogy, University of Technology, 136 Juliaoaiaan, Delft, The Netherlands
Charles F. Hendriks is a research associate in t h e Chemical Technology Department of t h e University o f Technology, Delft. H e obtained the degree in chemical engineering at the same University in 1969. Since that time he worked primarily i n the field o f catalytic oxidations in t h e liquid phase and the chemistry of photographic dyestuffs. H e is a member of t h e Royal Dutch Chemical Society.
Hendrik C. A. van Beek is a lecturer at the Uniuersity of Technology, D e l f t , i n chemical engineering since Decem.ber 1969. He studied at the same Uniuersity and obtained t h e degree in chemical engineering i n of, doctor of tech1955: in 1960 he receiued theZ demee ,, nical sciences on the subject: fading by light of anthraquinoid mordant dyes. He authored several p a pers, for example, in the fields ofphotoreduction of azo dyes and fading by light of organic dyes o f textiles. He is a member of the Royal Dutch Chemical Society.
270
Ind. Eng. Chem.. Prod. Res. De"., VoI. 16,No. 4, 1977
Pieter M. Heertjes studied at t h e Uniuersity of Technology, Delft, obtained the degree in chemical engineering in 1932 and t h e degree of doctor of technical sciences in 1938. I n 1973 h e became Doctor H.C. o f Loughborough Uniuersity of Technology. After a short period as a lecturer he took the chair o f ordinary Professor in chemical engineering at t h e Uniuersity of Technology, Delft, i n 1946. He was President of t h e Roval Dutch Chemical Societv and is a member of several societies including T h e Institution of Chemical Engineers and the Chemical Society. His scientific field.? of interest are chemical engineering and dyestuffs.
The initiation of aldehyde autoxidations in acetic acid has been investigated under circumstances where the radical chain processes were inhibited. Phenol, 4-methylphenol, and 2,6-di-feff-butyl-4-methylphenol were used as inhibitors. It was found that the initiation reactions were combinations of a photochemical and, particularly at higher temperatures, a bimolecular thermal process. The thermal reaction is responsible for the influence of oxygen on the overall autoxidation rates. Oxidation of benzaldehyde in the presence of 2,6-di-tert-butyl-4-methylphenol led to the conversion of the latter into its hydroperoxy- and benzoylperoxy derivatives, thus confirming its activity as scavenger of peroxy chain radicals. Uninhibited autoxidations were second order in the aldehyde concentrations for cyclohexanecarboxaldehyde and halogen substituted aldehydes. Other aldehydes gave firstorder reactions. These results, together with those obtained for the initiation reaction, give information regarding the nature of the chain termination reactions.
Introduction Several investigations dealing with the autoxidation of aldehydes have been published ( 2 , 4 , 5 ,7,11,14). Scattered information on different intermediate steps in the conversion of the aldehydes to the corresponding peracids, the BaeyerVilliger (BV) reaction of the peracids with the aldehydes, the initiation of the radical chain oxidation and its inhibition by phenolic substances is available. Cocivera and Trozzolo (6) studied the photolysis of benzaldehyde under anaerobic conditions with the aid of NMR spectra. The occurrence of CIDNP signals could be explained by the formation of the phenylcarbonyl/a-hydroxybenzyl radical pair. While the N hydroxybenzyl radical will be reoxidized under aerobic conditions to benzaldehyde ( 3 ) ,the radical chain will be initiated by the phenylcarbonyl radical in the presence of oxygen (reaction IV; see below). Based on these results photochemical initiation, as has been observed by Zaikov et al. (151,can be explained by hydrogen abstraction from the aldehyde by a photo-exited aldehyde molecule (reaction I). Some authors describe the thermal initiation, based on the kinetics found in the presence of a phenolic inhibitor for the propagation steps, as a hydrogen abstraction from the aldehyde by oxygen (13, 1 4 ) (reaction 11). Emanuel et al. (9) propose, as thermal initiation, the termolecular reaction 111, which has a much higher exothermal effect than the bimolecular reaction 11.This initiation reaction was also suggested by Boga and M6rta ( 4 ) for the autoxidation of benzaldehyde in acetic acid solutions. The propagation reactions IV and V are generally accepted. However, the kinetics found for the overall autoxidations in different solvents are very diverse. Reaction orders found for the aldehyde and oxygen concentration vary respectively from 0-2 and 0-1 ( 2 , 4 ,5, 7, 11, 14). Evidently these kinetics are determined by the combined effects of the initiation, propagation, and termination reactions. From kinetic data, obtained in chlorobenzene, Zaikov et al. (15)concluded that both a second-order and a first-order termination of peroxy radicals must occur (reactions VI and VII). The termination reaction VIII, suggested by us, will be discussed below. Reactions X-XI11 are generally accepted as hydrogen abstractions from phenols and radical recombinations, which may play a role in autoxidation processes, inhibited by phenols. It appears that unequivocal interpretation of the data given above is hindered by the use of different solvents in different investigations and by the fact that effects of initiation, propagation, and termination reactions have not been separated. The present knowledge is summarized in the general reaction scheme included here as Scheme I. We now have measured separately the kinetic and stoichiometric parameters of the initiation reaction in the presence of phenolic inhibitors for the propagation steps and of the overall autoxidation of a number of aldehydes in acetic acid (see Tables I and 11). With the data obtained, a more detailed reaction scheme for these autoxidations has been constructed.
Experimental Section Materials. Acetic acid was purified by distillation (bp 118-120 "C a t 1 atm, water content 0.1 M). The aldehydes were distilled or crystallized and stored under nitrogen in the dark. Phenol, 4-methylphenol and 2,6-di-tert-butyl-4methylphenol were of A.R. quality. Analysis. Oxygen consumption was measured volumetrically. Peracids and hydrogen peroxide were determined by iodometric titration. Because of the low reduction rate, hydrogen peroxide could be determined separately from the peracids. Aldehydes, phenols, carboxylic acids (after methylation with diazo methane) and other oxidation products were determined quantitatively by GLC (3-m 10% SE-30 on chromosorb-W column) using chlorobenzene as internal standard. Identifications were based on retention times, mass spectra, and IR and NMR spectra. Equilibrium oxygen concentrations in acetic acid were determined polarographically a t 25 "C: 8.3 X M; 36.2 "C: 6.3 X lo-" M; and 49.1 "C: 5.1 X 10-3 M. Within experimental error Henry's law was obeyed. Preparation and Analysis of Oxidation Products of 2,6-Di-tert-butyl-4-methylphenol. Acetic acid solutions of 0.05 M aldehyde were oxidized at 25 "C with oxygen in the presence of 0.1 M 2,6-di-tert-buty1-4-methylphenol in the dark and under irradiation with a 100-W tungsten lamp (glass filter, X of light transmitted >300 nm, light absorbed -lo4 lumen). By chromatographic separation on a silica column (10) followed by evaporation of the solvent (trichloroethylene)
Scheme I Initiation:
-
photochemical: RCHO'
RCHO* RCO + RCHOH
RCHO
'
1%
(1)
RCH'O + HOO. thermal:
RCHO + 0,
+
ZRCHO + 0,
RCO + HOO.
+
(11)
ZRCO + H,O,
(111)
Propagation: RCO + 0, + RCO,. RCO,. + RCHO Termination:
:
+
RCO
+
non-radical products
RCO,.
+
non-radical products
RCO,. + RCHO
Baeyer-Villiger
RC0,H
+
ZRCO,.
--*
R C 0 , H + RCHO
Phenol inhibition RCO,, + ROH HOO. + ROH
+ +
RC0,H + RO. + CO
+
ZRC0,H
RC0,H + RO. H,O, + RO.
RO. + RCO,.
+
non-radical product
RO. + HOO,
+
non-radical product
Ind. Eng. Chem., Prod. Res. Dev., Vol. 16, No. 4 , 1977
271
Table I. The Autoxidation of Benzaldehyde at Different Temperatures and Oxygen Pressures Temp, "C 16.0 20.0 25.0 36.2 41.0 49.1 56.5 61.1
103 k , min-1 a b
Irradiated klkl a b
lo6 k 1, min-I a b
lo3 ha, M-' min-I
1.1
1.1
1.3 1.6 4.2
1.3 1.5 2.0
0.8 0.8 0.9 1.7
0.8 0.8 0.9 1.o
2.5
1.4 1.6 1.7 2.0
8.3
2.8
2.9
1.1
2.9
2.5
5.5
4.8
1.2
4.4
4.6
21
1.4 1.6 1.8
Not irradiated lo6 k l , min-1 a b
11.4 23 31 52 75
0.09 0.60
0.02 0.11
1.1
0.2
p O I(atm) was 0.98 (16.0 "C), 0.98 (20.0 "C), 0.97 (25.0 "C), 0.94 (36.2 "C),0.88 (49.1 "C),0.79 (61.1 "C). po2 (atm)was 0.21 (16.0 "C), 0.21 (20.0 "C), 0.20 (25 "C), 0.19 (36.2 "C),0.18 (49.1 "C), and0.17 (61.1"C).
Table 11. The Autoxidation of Substituted Aldehydes Irradiated lo3 k2, 25.0
Aldehyde
OC, M-lmin-'
Not irradiated
25.0 "C
49.1 "C
PO,,
lo3 k , M-'
lo6 h i ,
lo3 k , M-'
lo6 h i ,
atm
min-'
min-1
min-1
min-1
klhi, M-1
25.0 "C IO6 hi, min-1
49.1 "C IO6 h l ,
min-1
4-Bromobenzaldehyde
11.4
a
9.4
3.6
23.0
11.0
2.1
0.10
4.0
b a
3.6 2.0
16.0 19.0
7.6 6.4
3.0
0.02 0.15
0.7
32.2
8.9 3.3
2.1
4-Chlorobenzaldehyde 2-Chlorobenzaldehyde
12.8
b a
3.2 2.7
2.0 2.5
6.9 25.0
2.4 8.4
2.9 3.0
0.02 0.11
0.6 5.9
2.7 47
2.5 3.4
6.8 190
2.4 16
0.02
1.1
19.0
b a
2.8
2,6-Dichlorobenzaldehyde 3,4-Dichlorobenzaldehyde
37.7
b a
44 1.9
3.4 1.7
53 23
3.5 4.0
15 5.7
2,4-Dichlorobenzaldehyde
15.3
b a
1.9 16
1.7 3.5
19 50
1.8 9.0
5.2 --
b
Cyclohexane Carboxaldehyde
96.7
a
16 8.7
3.5 2.6
19 26.
3.4 5.8
5.6 4.5
b
8.6
2.6
24
5.4
4.4
lofik . rnin-'
4-Methylbenzaldehyde
12
106 h , min-1
3.0
3.3
klk 1
11.4
a
160
3.3
320
4.0
80.0
0.20
0.9
b
160 2
85.7 13.1
0.2
a
3.5 1.6
0.05
-
3.3 0.6
300
4-Methoxybenzaldehyde
-
1.6 4.5 2.4 1.6
b
4
13.1 2.4 2.5 8.1 9.3
4-Formylbenzaldehyde
-
a
760
0.6 2.4 2.4 0.7 0.7 4.3
21 11
2-Naphthaldehyde
b a b a
2
1-Naphthaldehyde
b -
a
740 150
4.3
4-Carboxybenzaldehyde
23.9
b a
150 960 770
0.9 0.8
Hexanal-1
b
5 5 5
2.2 2.2
21
6 13 13
1.4
800
4.5
187
770 200
4.5 2.3
168
200 4500 2000
2.3 4.1 2.5
87 1097 800
87
See Table I. four reaction products derived from the phenolic inhibitor could be isolated. The infrared spectrum and elemental analysis of one of the products were in accordance with those of 2,6-di-tert-butyl4-methyl-4-hydroperoxy-2,5-cyclohexadienone, prepared according to Coppinger (8) by the catalyzed decomposition 272
Ind. Eng. Chem., Prod. Res. Dev., Vol. 16, No. 4, 1977
of hydrogen peroxide in solutions of this inhibitor. Found: C, 71.0; H, 9.8. Calcd C, 71.4; H, 9.5. The infrared spectrum of a second product obtained in approximately the same yield in mol %, based on converted starting material, as the hydroperoxy derivative showed a twin absorption band a t 6.0 wm, characteristic for quinoid compounds, bands a t 11.4 wm (pe-
roxy group), 5.8 pm (carbonyl group), 6.3 and 6.9 pm (phenyl group). The compound oxidizes iodide directly, which also indicates a peroxy structure. NMR spectra gave a ratio for aromatic:vinyl:methyl:tert-butylprotons of 5:2:3:19, which fits almost exactly with the ratio in 2,6-di-tert-butyl-4-benzoylperoxy-2,5-cyclohexadienone(theoretical proton ratio 5:2:3:18). The results of elemental analysis agree with this structure. Found: C, 73.9; H, 8.2. Calcd C, 74.2; H, 7.9. The other two isolated products gave mass spectra which indicated structures as 1,2-bis-(3,5-di-tert-butyl-4-hydroxypheny1)ethane and 3,3’,5,5’-tetra-tert-butylstilbene-4,4’quinone and were formed in quantities less than 1%of the total amount of product.
Results and Discussion The Initiation Reaction. The aldehydes (0.05-0.2 M, see Tables I and 11) were oxidized in acetic acid at different temperatures and oxygen pressures in the presence of an inhibitor (0.1 M). The inhibitors used were 2,6-di-tert-butyl4-methylphenol, 4-methylphenol, and phenol. The experiments were carried out in the dark and in visible light. In separate experiments it was ascertained that the inhibitors did not react with oxygen in acetic acid solution. When 2,6-di-tert-buty1-4-methylphenol (A) was used as inhibitor for the aerobic oxidation of benzaldehyde, it was converted mainly into 2,6-di-tert -butyl-4-methyl-4-hydroperoxy-2,5-cyclohexadienone (B)and 2,6-di-tert-butyl-4methyl-4-benzoylperoxy-2,5-cyclohexadienone (C). Analysis of the reaction mixture also gave indications for the formation of traces of 1,2-bis-(3,5-di-tert-butyl-4-hydroxyphenyl) ethane and 3,3’,5,5’-tetra-tert-butylstilbene-4,4’-quinone.Based on these results it is very probable that in this process the phenol is converted into phenoxy radicals, which then combine with benzoylperoxy and/or hydroperoxy radicals. Inhibition is then caused by reactions X and XII. The formation of the hydroperoxy derivative confirms reaction XIII. For the autoxidation of benzaldehyde in the presence of A the relative conversions of reactants and products were measured at different reaction times. The average values obtained were
-
0
104
2.104
3.104
t (min)
Figure 1. The kinetics of the autoxidation of benzaldehyde in acetic acid in the presence of 2,6-di-tert-butyl-4-methylphenol as inhibitor during irradiation with a 100-W tungsten lamp (A >320 nm, light absorbed by the solutions -IO4 lumen): 0 ,various oxygen pressures higher than 0.1,16 “C; t,20 “C; A ,25 “C; 0,pop = 0.19,36.2 “c; A , ~~s=0.94,36.2oC;O,p~,~0.18,49.1oC;~,p~,~0.88,49.1oC;X, Po2 = 0.17,61.1 “C; 0 ,pop = 0.79,61.1 “C (Po, in atm).
-d[C6HsCHO]/dt:-d[Oz]/dt:-d[A]/dt:d[B]/dt:d[C]/ dt:d[H202]/dt:d[C6HsCOOH]/dt = 1:1.34:0.66:0.31:0.31:0.29:0.68.
It follows from these data that the overall conversions concerned can be written as: 3C6HsCHO
+ 402 f 2A
B
-+
+ c + Hz02 -I-2C6HsCOOH
The experimental stoichiometry of the overall conversion also follows directly from the reactions I or 11, IV, and X-XIII, but cannot be explained if the termolecular initiation reaction I11 would occur. The absence of perbenzoic acid in the reaction products of the phenol-inhibited autoxidation of benzaldehyde is probably caused by the fact that its consumption by the Baeyer-Villiger reaction IX is much faster than its formation. The kinetics of the autoxidation of the investigated aldehydes in the presence of the inhibitors were measured by determining the rates of consumption of oxygen, the aldehyde, and the inhibitor. The rates were found to be equal for all inhibitors used and remained constant if the inhibitor concentrations used were >0.1 M. The conclusion must be drawn that a t these inhibitor concentrations the chain propagation is completely suppressed. In all cases the reaction rates were linear with the aldehyde concentrations. In irradiated solutions the rates were independent of the oxygen pressures at low temperatures (see Figure 1).At higher temperatures these rates increased with the oxygen pressures. In Figure 1 the
kinetic data, obtained by measuring the consumption of benzaldehyde in irradiated solutions containing 2,6-di-tert butyl-4-methylphenol are given as an example. From the measurements, pseudo-first-order rate constants k 1 (which at higher temperatures or absence of light depend upon the oxygen pressures) were calculated and are given in Tables I and 11. Observations and Conclusions about Autoxidation. In the experiments concerned, no inhibitor was added to the solutions, and in all experiments the solutions were irradiated. The rates of oxygen and aldehyde consumption were measured at different temperatures and oxygen pressures during the initial stage (1-30 min) of the reaction. During this initial stage the peracids derived from the aldehydes were the main reaction products, while phenols and oxidation products of phenols were only formed in minor quantities (0.1-0.5% of the amount of peracids formed). The influence of the BaeyerVilliger reaction on the reaction rates was also negligible in this period. For halogen-substituted benzaldehydes and cyclohexane carboxaldehyde the reaction was found to be second order in the aldehyde concentration. For the other aldehydes a firstorder reaction was found. The kinetic data, obtained by measuring the oxygen consumption at 25 “C, are given as an example in Figures 2 and 3. Similar data were obtained for the aldehyde consumption and peracid production. From these Ind. Eng. Chem., Prod. Res. Dev., Vol. 16,No. 4, 1977 273
-" t
/
r
F i g u r e 4. Formation of phenol during the autoxidation of benzaldehyde; 25 O C , poZ = 0.1-1 atm: 0 , [PhCHOIo = 0.25 M; X, [PhCHOlo = 0.46 M.
-
-1
0
-0.5 log
0.5
[RCHO]o
Figure 2. Rates of uninhibited autoxidation of aldehydes, 25 "C, pol = 0.98 atm: 0 , benzaldehyde; A , 3,4-dichlorobenzaldehyde;A, 2chlorobenzaldehyde; 0,4-chlorobenzaldehyde; +, cyclohexanecarboxaldehyde; 0 , 4-bromobenzaldehyde; X, 2,4-dichlorobenzaldehyde:
m, 2,6-dichlorobenzaldehyde.
x/
,
-
-1
0.5
0
0.5
log [RCHO]o
Figure 3. Rates of uninhibited autoxidation of aldehydes, 25 OC,po2 = 0.98 atm: 0,4-methylbenzaIdehyde; A,4-methoxybenzaldehyde; A, 1-naphthaldehyde; 0 ,2-naphthaldehyde; +, 4-formylbenzaldehyde; 0,4-~arboxybenzaldehyde; X , hexanal-1.
data rate constants k (which a t higher temperatures depend upon the oxygen pressures) were calculated and are given in Tables I and 11. The k values of the autoxidation of benzaldehyde in the temperature range, where the influence of the oxygen pressure is negligible, gave a linear Arrhenius plot, 274
Ind. Eng. Chem., Prod. Res. Dev., Vol. 16, No. 4, 1977
from which an activation energy of 5.8 f 0.2 kcal/mol was calculated. In Tables I and I1 the chain lengths, represented by the ratio of the rate constants of the overall autoxidation and the initiation reaction ( k l h l ) ,are also given. It can be seen that within experimental error these ratios are in all cases independent of the oxygen pressure. This indicates that the oxygen influence on the overall autoxidation rates can be ascribed to the thermal (nonphotochemical) initiation reaction. In order to obtain a complete set of rate constants for the autoxidations, the Baeyer-Villiger reaction (1) was also studied. Solutions containing the aldehydes and the corresponding peracids were prepared by partial aerobic autoxidation of the aldehydes. The solutions were then flushed with nitrogen to avoid continued autoxidation. The kinetics of the Baeyer-Villiger reaction were obtained by measuring the rates of aldehyde and peracid consumption. In all cases the reactions were first order in the aldehyde and peracid concentrations. The rate constants kz are also given in Tables I and 11. The lzz values of the Baeyer-Villiger reaction between benzaldehyde and perbenzoic acid gave a linear Arrhenius plot, indicating an activation energy of 12.0 f 0.5 kcal/mol. The formation of phenolic or hydroxylic by-products during the overall autoxidation of the different aldehydes has been investigated using gas chromatographic analysis. In all cases these by-products were indeed found, together with carbon monoxide and carbon dioxide. For benzaldehyde the phenol production is given in Figure 4 as an example. It can be observed that in this case the phenol production can already be detected at the beginning of the reaction when the BaeyerVilliger reaction still can be neglected. Prolonged autoxidation leads to increased formation of phenol as a by-product of the Baeyer-Villiger reaction (1). It therefore follows that phenol is also produced in the overall autoxidation, possibly by a reaction as represented by reaction VIII. The amounts of phenol produced do not lead to appreciable inhibition in the initial period of the autoxidation of benzaldehyde. Autoxidation of 4-methyl-benzaldehyde gives as a by-product 4-methylphenol. The chain radical scavenging activity of this compound is so high that, even though formation has been found a t a rate which is approximately equal to the rate of production of phenol from benzaldehyde, the autoxidation of 4-methylbenzaldehyde is completely inhibited after 20-3096 conversion. Other minor by-products of the autoxidations were benzene, mono-, and dihalogen benzenes and methyl acetate from mono- and dihalogenbenzaldehydes; methyl acetate, cyclohexanol, and cyclohexanone from cyclohexane carboxaldehyde.
Conclusions From the results, useful conclusions can be drawn regarding the autoxidation of the aldehydes in acetic acid solutions (see Scheme I). At room temperature (-25 O C ) the initiation is
caused by photo-excitation of the aldehydes (I). At the wavelengths of the radiation used (A >300 nm) the light absorption is caused by the long-wavelength tails of the n-n* bands of the aldehydes. As the extinctions are small, the amounts of light, absorbed by the dilute solutions, and therefore also the reaction rates are approximately linear with the aldehyde concentrations. The initiation is independent of the oxygen pressures. These observations can be explained if it is assumed that in acetic acid the photo-excitation results in an H abstraction, followed by a rapid reaction of the radicals formed with oxygen (I and 11). At higher temperatures also a thermal reaction takes place, which is first order in the aldehyde concentration and the oxygen pressure (11). It follows that a t higher temperatures under irradiation the initiation invariably is first order in the aldehyde concentrations and an order 0-1 in the oxygen pressure depending upon the irradiation intensity. No support has been obtained for the trimolecular initiation (111) proposed by Emanuel et al. (9). An interesting observation was made upon comparison of the rate constants of the initiation reaction and the overall autoxidation, determined a t temperatures at which the rate constants were a function of the oxygen pressures. It was found that the ratios of these rate constants were independent of the oxygen pressures, which proves that the influence of oxygen is only determined by the thermal initiation reaction (11). The overall autoxidation was found to be second order in the aldehyde concentrations for halogen-substituted aldehydes and cyclohexane carboxaldehyde, and first order for the other aldehydes. For the second-order reaction the simplest reaction scheme consists of reaction I, 11, IV, V, and a termination reaction, which competes with the propagation step (V), and which is zero order in the aldehyde concentration. Possible are, for example, the monomolecular decompositon of the aroyl (or acyl) peroxy radicals (VII), yielding carbon dioxide and aroxyor alkoxy radicals, or the hydrogen abstraction from the sol-
vent giving initially carboxymethyl and methyl radicals, which can subsequently combine to form methyl acetate. The reactions suggested are supported to some extent by the observed formation of phenols and methyl acetate as products of the chain oxidation. For the first-order kinetics of the overall autoxidation, the simplest scheme contains the reactions I, 11, IV, V, and a termination reaction, which is first order in the aldehyde concentration and which competes with reaction V. For this reaction we suggest reaction VIII, which can proceed in a similar fashion as the Baeyer-Villiger reaction, yielding a radical addition product, which decomposes to form the aroxy or alkoxy radicals, the carboxylic acids derived from the aldehydes and carbon monoxide. Finally, it can be concluded that the analysis of the reaction products of oxidations carried out in the presence of 2,6-ditert-butyl-4-methylphenolconfirm that reactions such as X, XI, XI1 and XI11 can indeed occur.
Literature Cited (1) Baeyer, A., Villiger, V., Ber., 32, 3625 (1899). c l m C. E. H., Jolley, J. E., Proc. Roy. SOC.London, Ser. A, 237, 297 (2)mBawn,
,.- --,.
(3) van Beek, H.C. A.. Heertjes, P. M.. Schaafsma, K.,Red. Trav. Chim. Pays Bas, 92, 1189 (1973). (4) Boga, E., Marta, F., Acta Chim. Acad. Scient. Hung., 78, 105, 193 119731. -, (5) Bolland, G.,Gee, G., Trans. Faraday Soc., 42, 236 (1946). (6) Cocivera, M., Trozzolo, A. M., J. Am. Chem. SOC.,92, 1772 (1970). (7) Cooper, H. R., Melville, H. W., J. Chern. Soc., 1984, 1994 (1951). (8) Coppinger, G. M., J. Am. Chem. SOC.,79, 2758 (1957). (9) Emanuel, N. M., Maizus, Z. K., Skibida, I. P., Angew. Chern., 81, 91 (1989). (10) Horswill, E. C., Ingold, K. U., Can. J. Chem., 44, 269 (1966). (11) Mulcahy, M. E., Watt, I. C., Proc. Roy. SOC.London, Ser. A, 216, 10, 30 (1953). (12) Ogata, J., Tabushi, I., Akimoto, H.. J. Org. Chem., 26, 4803 (1961). (13) Sheldon, R. A., Kochi, J. K., Oxid. Combust. Rev., 5 , 135 (1973). (14) Waters, W. A., Wickam-Jones, C., J. Chem. SOC.812 (1951). (15) Zaikov, G. E., Howard, J. A,, Ingold, K. U., Can. J. Chem., 47, 3108 (1969).
.
~
Received for review March 4, 1977 Accepted July 1,1977
Ind. Eng. Chem., Prod. Res. Dev., Vol. 16, No. 4, 1977
275
