JOURNAL OF THE AMERICAN CHEMICAL SOCIETY (Registered in
U.S. P a t e n t 0 5 4
(0Copyright, 1860, by the American
Chemical Society)
MARCH 31, 1960
VOLUME82
NUMBER 6
PHYSICAL AND INORGANIC CHEMISTRY [CONTRIBUTION FROM THE BARBERTON RESEARCH LABORATORY, COLUMBIA-SOUTHERN
CHEMICAL CORPORATION]
Kinetics and Mechanism of the Epoxidation of Allyl Alcohol with Aqueous Hydrogen Peroxide Catalyzed by Tungstic Acid1 BY ZBIGNIEW RACISZEWSKI RECEIVED OCTOBER14, 1959 T h e kinetics of a novel method of epoxidation of allyl alcohol (AA) to glycidol (G) with aqueous hydrogen peroxide in the presence of tungstic acid catalyst was studied. The changes in the concentration of glycidol were determined analytically and were found to follow the kinetics of two consecutive pseudo-first order reactions. d[G]/dt = kl [AA] - k0 [ G I . The coefficients kl and k2 were calculated by means of the time-ratio method and the effect of several reaction variables on both coefficients was studied. An increase in temperature affects kl to a lesser degree than k 2 ; the respective energies of activation are 15 and 19 kcal. mole-'. Both coefficients are proportional to the concentration of tungstic acid and increase with the decreasing pH of the reaction medium, although not in a uniform fashion. It was concluded that most probably the anion of pertungstic acid, which is produced rapidly from tungstic acid, oxidizes allyl alcohol. The addition of this anion to the double bond appears t o be facilitated by the inductive effect of the hydroxy group, or perhaps the protonated hydroxy group, and possibly by the delocalization of the electron pair, with the accompanying negative charge, via the incipient formation of the oxirane-ring. The analogy between this mechanism and the Sx2' substitutions in the allylic systems is pointed out. An alternative mechanism, specific for allylic alcohols and consisting of a rapid esterification of the hydroxy group prior to the attack on the double bond is also considered, The anion of pertungstic acid was found to participate in the opening of the oxirane-ring.
Introduction During the course of the investigation of the hydroxylation of olefins to the corresponding or& glycols, by the direct addition of hydrogen peroxide in the presence of inorganic catalysts, Mugdan and Young observed that pertungstic acid yields exclusively trans-glycols. In order to explain this stereospecificity the authors suggested, as one possible reaction path, the formation of the intermediate epoxide. The failure to isolate the epoxide was ascribed to its high reactivity under the conditions of hydroxylation. However, recently several reports were published in which the successful epoxidation of olefins by the hydrogen peroxide-tungstic acid system was described. Quite independently a similar method has been developed in this L a b ~ r a t o r y . ~ (1) Presented a t the 136th American Chemical Society Meeting, Atlantic City, September, 1959. ( 2 ) M. Mugdan a n d D. P. Young, J . Chem. Soc., 2988 (1049). (3) (a) P. G. Sergeev and L. M . Bukreeva, Zhur. Obshchei Khiin., 28, 101 (1958), C. A , , 52, l2758j (1958); (b) G. B. Payne and P. H. Williams, J . Org. Chem., 24, 54 (1959); (c) G. B. Payne and C . W. Smith, U. S. P a t e n t 2,776,301 (1957); (d) C . W. Smith and G. B. Payne, U. S. P a t e n t 2,786,854 (1957); (e) G. J. Carlson, J. R. Skinner, C. W. Smith a n d C. H. Wilcoxen, U. S. P a t e n t 2,833,787 (1958); (f) J. R. Skinner, C. H. Wilcoxen and G . J. Carlson, U. S. P a t e n t 2,833,788 (1958).
One phase of the investigation carried out in this Laboratory concerned the kinetics of epoxidation of an aqueous solution of allyl alcohol by the hydrogen peroxide-tungstic acid system. Two groups of experiments were performed. In the experiments of the first group, allyl alcohol, diluted aqueous hydrogen peroxide and a catalytic amount of tungstic acid were brought together, the pH of the mixture was suitably adjusted by the addition of triethylamine, and the reaction was followed by the periodical determination of the concentration of glycidol. From the changes in the concentration of glycidol, the rate equation was derived and the pseudo-first order rate coefficients, kl and kz, for the formation and for the decomposition of glycidol, respectively, were calculated. 0
CHz=CHCHzOH
ki
/ \
+C H z - C H C H z O H
k;.
--+
final products
(1)
In the second group of experiments, the kinetics of decomposition of glycidol under the conditions of epoxidation, but in the absence of allyl alcohol, were studied. In both groups of experiments the
1267
(4) A. Kaman and H. C. Stevens, unpublished d a t a .
Vol. s2
ZUIGNIEWRACISZEWSKI
1268
TABLE I Expt. no.
1
--Initial EtaNd
EPOXIDATION O F ALLYL.4LCOIIOL 7---fiH---Rate cocflicients--composition, mmole/1000 g.After Temp., kl X 106, kz X HzWO, Ha02 CaHeO Init. 2 / k l hr. 'C. set.-' sec. ka/h
ty,
S 57
3 4 5 6 7
7.9 9.8 11.7 13.1 17.7 >l7.7 20.3
8.37 8.57 8.59
5
t7.7
S 57
8
-13.1 R1 5 1ot; . 9
-
0
8.57 8 57
s 61
A. Effect of the PH of the reaction mixture 1910 3.1 2240 3.0 30 19.8 22-10 2240 2110 2250 22.10 2110
1940 19-LO 1930 1940 1.940 1930
3.9
4.9 5.4 6.0 7.0 7.1
30 30 30 30
3.7 47 5 3''
5 C; r i ti"
XJ
(j 9'
30
19.6 18.2 14.7 14.5 4.8 5.8
Max. yield of glycidol'
tms*,"
hr.
0.400 ,163 ,121 ,129 .117
54.5 70.0 75.0 73 5 75.0
.. ..
.. ..
..
21.4 30.6 37.0 44.3 46.4
..
.. ..
1.7 4.1 8.0 9.4 3.9 5.1 10.8 11.5
0.117 .122 ,120 .lo8 ,228 ,151 .294 .178
75.0 75.0 75.0 76.5 G4.5 71.5 60.0 69.0
4G.4 19.9 10.1 7.9 31.1 18.3 13.1 9.0
'73.5 66.0
44.3 70.3
7.9 3.2 2.2 1.9 17
E. Effcct of tuiigstic :tcid concentration 2250 2240 2110 2240 2240 22.10 2210
1940 19-10 1980 1940 19-10 19-40 1940 1940
6.0 5.4 5 1 5.4 5.6 5.4 5.4 5.4
5 (j 6.0 6.3* 7.0 5.lC 5.0" 5.2" 5.5"
30 30 30 30 40 40 50 50
14.5 33.7 66.5 87.3 17.1 33.7 36.7 64.7
12 13 14
9,s'' 13.7" 7.9' 13. iC
25.72 42.86 68 57 -1.29 8 57 4 29 8.57
4 15 16
18.1 19.6' 11.3
C. EBect of the initial Concentration of hydrogen peroxide and allyl alcohol 8.61 2110 1980 5.4 5.3' 30 14.7 1.9 0.129 8.57 6710 1940 5.4 5.lC 30 7.3 1.5 0.205 8.60 2110 3970 5.4 6.sb 30 11.3 ,. ..
9 10
11
224U
..
..
D.
Effect of tcinlxrature 75.0 46.4 5 17.7 8.47 2250 1.7 0.117 1940 6.0 5.6 30 14.5 44.3 4 1.9 .129 13.1 73.5 8.61 2110 1980 5.3' 30 14.7 5.4 12 5.4 18.3 13.7" 71.5 8.57 2240 1940 50" 40 33.7 5.1 .151 5.3 ,154 17.9 71.0 5.3 4.S 40 34.4 13.8 8.61 2120 1980 17 ,178 69.0 50 64.7 11.5 9.0 14 13.7" 5.4 5.5" 8.57 2240 1940 13.8 ,190 68.0 7.5 8.81 2120 1980 50 76.1 14.4 18 5.2 4 6 Calculated from the rate coefficients. * ;ifter l l k , hours it,!. i(Jditioua1 sinill amount of triethylamine was introEstimated error 1 1 . 0 . duced during the course of the reaction.
effect of the pH of the reaction mixture, the concentration of the reactants and the temperature were investigated.
Experimental Epoxidation of Allyl Alcohol.-In a typical experiment 0.540 g. of tungstic acid (Baker Analyzed Reagent), 37.8 g. of 50.7'% solution of hydrogen peroxide ( Columbia-Southern) and 24.0 g. of water were introduced into a four-necked, 300nil. flask equipped with a Teflon Tru-Bore stirrer and immersed in a thertnostated bath, maintained a t a desired temperature (30, 40 or 5Uo) with a tolerance of less than 0.25'. The rnixturc was stirred, and after 30 min. a solution of 29.0 g. of allyl alcohol (Shell, purified by fractional distillation, assay: 99.75%) in 158 g. of water, freshly made and preheated t o the desired temperature, was added. The time of the addition of allyl alcohol was regarded as zero time. Immediately afterwards triethylamine (Eastman Kodak) was introduced in a n amount necessary t o bring the pH of the mixture to the desired level. (The weight of the added amine was roughly determined.) An additional portion of preheated water was added to bring the total weight of the reaction mixture to 252.0 g. The mixture was stirred coiitinuously and at suitable time intervals aliquots wcre taken and analyzed for glycidol and hydrogen peroxide contents. The pH and, in several experiments, the density of the mixture were determined periodically; also the acidity was checked by titration of the aliquots with 0.1 N sodium Itydrositlc. Tlie initial cornpositions o f the reaction mixtures arc listed in Table I . The products of the reaction, glycidol atid glycerol, were isvlitted in two experiments and a representative example is given. After completing the kinetic experiment (No. 3) 161.5 g. of the reaction mixture (containing, by analysis, 14.73 g. of glycidol) was passed through 10 ml. of Ainberlite
IRA-409 (OH-) and washed with water, giving 195.8 g. of the solution free from tungstic w i d . -4 portion of this solution, 192.1 g., was distilled through an 8-cm. Vigreux column. Glycidol was collected in two fractions: b.p. 34" (3.0 mm.) to 45' (1.8 mm.), T Z ~ O D 1.4213, 4.3 g., assay 86.4% and b.p. 45" (1.8 mm.) to 31" (0.7 mm.), n 2 0 ~1.4319, 4.3 g. assay 9C;.3yO; lit.? b.p. 56-56.5' (11 mm.), TZIOD 1.4293. The next fraction constituted glycerol: b.p. 130' (0.65 mm.) to 126' (0.55 mm.), n Z o1.4722, ~ 5.7 g.; lit. b.p. 125.5' ( 1 ni~n.),~ %*OD 1 .4'7399.637 A viscous residue (3.5 g.) remained in the distilling flask. The fraction preceding glycidol (166.0 g.) was analyzed and found to contain 3.45 g. of glycidol. Decomposition of Glycido1.-The equipment and the procedure was the same as in the experiments on the epoxidation of allyl alcohol except that instead of allyl alcohol a n equivalent amount of glycidol (b.p. 65" (13 mm.), n2% 1.4314, assay 99.270) was used. The initial compositions of the reaction mixtures are listed in Table 11. Analytical Methods.-The concentration of glycidol was determined by the pyridiuium chloride-pyridine method described by J. L . Jungnickel, et al. 8 however, instead OF methanolic sodium hydroxide, an aqueous solution was used for titration. Additional tests were pcrformed t o establish if allyl alcohol consumed hydrogen chloride under the conditions of the determination. The coilsumption, if any, was found not to exceed the usual experimental error. The concentration of hydrogen peroxide was determined by titration of the acidified solution of the sample with ceric sulfate, according t o tlie procedure of F. P. Greenspan and D. G. __~._____
( 5 ) D. R. Stiill. />L,L. E t ~ y .Ciicna., 39, 517 (1917). (li) I,. F. Hoyt, i6iti., 26, 329 (1931). ( 7 ) J . C. Snowtlen anrl €I. 0.I.. Fischer, THISJ O U R N A L . 64, 1291
(19LZ). ( 8 ) J . L. Jungnickel, el d..in J . Mitchell, Jr., I. & Kolthoff, I. E. S. Proskauer and A. Weissberger, "Organic Analysis," Vol. I. Interacicncc Publishers, I n c . , N c w l-ork, N \-., 1953, p. 136,
1269
EPOXIDATION OF ALLYLALCOHOL
March 20, 1SGO
TABLE I1 DECOMPOSITION OF GLYCIDOL IN THE ARSRXCEOF ALLYLALCOFIOL rcxpt. mi.
------Initial EtaN 11
composition, mmole,’lOOO g-: IIIWOl fI?O?
Effect of the p H 2050 2050 2050
i\.
19 20 21
2 5 9.7 17 9
8.35 8.31 8.31
20 22 23
9.7 50.9 loo,??
8.3t 41.52 82.74
C311601
---fiIT
---7
After 0 . 2 / k hr.
Temp., OC.
k X IO’;,
Init.
3.9 4.8 6.7“
30 30 30
2.6 1.7 1. 0
4.8
30 30 30
1.7 4.2 8.5
30 30 30
1.7 0.8 1.5
30 40 50
1.7 3.7
of the reaction mixture 3.1 1910 5.3 1900 7.3 1890
sec. -1
E?. Effect of tungstic acid concentration
20 24 25
0
2050 2010 2040
5.3 5.1 5.1
1900 1910 1880
5.3 5.1
C. Effect of the initial concentration of hydrogen peroxide 5.3 4.8 1900 8.34 2050 5.5 5 2” 0 1920 8.35 5.3 5.5 6180 1910 8 32
9.7 0.8 19 0
D. Effect of temperature 8.34 2050 1900 5.3 20 9.7 26 11.4 8.34 2050 1910 5.3 27 11.4 8.34 2050 1890 5.3 Estimated error 2 ~ 1 . 0 . After 0.1/k hours.
M a ~ K e l l a r . ~Additional experiments showed that the presence of tungstic acid, allyl alcohol and a relatively short storage of the acidified solution at room temperature did not affect the results of the hydrogen peroxide determination beyond the limits of experimental error. Johnson and Clark’s modification of Francis’ bromate-bromide method was used for allyl alcohol assays.’O The p H of the reaction mixtures was determined by means of the Beckman Zeromatic pH-Meter, Model 9600, with the General Purpose Glass Electrode, N o . 4990-83, and the fiber-type Reference Electrode, KO. 1170. Rate Equations and Calculation of the Rate Coefficients,The experimental results indicate t h a t the changes in the concentration of glyddol during the course of epoxidation of allyl alcohol follow the kinetics of two consecutive pseudofirst order reactions
ddtm kl[XA] - kg[G] =
(2)
and in the integrated form
k [GI = [:1;\], 2(e--klt ki - kl
e--k,t 2 )
(3)
Here [GI is the concentration of glycidol, [AA] the concentration of allyl alcohol, [AA]o the initial concentration of allyl alcohol and kl and kl the pseudo-first order rate coeficients for the formation and the decomposition of glycidol during the course of epoxidation, respectively. The remaining symbols have their usual meaning. The rate law was established in the following way. From the changes in the concentration of glycidol observed in a given experiment and from the initial concentration of allyl alcohol, the rate coefficients k1 and kn were calculated (vide infra). The coefficients, together with the initial concentration of allyl alcohol, were substituted into eq. 3 and the concentrations of glycidol a t different times t Rere calculated. A factory agreement between the calculated and observed values was found. This agreement is illustrated in Figs. 1, 2 and 3 where the results obtained in several tvDical exoeriments are presented.ll Here the per cent. yielhiof glyGdol, based on the initial concentration of allyl alcohol, are plotted versus the reaction time. The points represent the yields determined analytically and the curves illustrate the calculated values. The coefficients kl and k2 were calculated by means of a suitably modified time-ratio method.’* The useful initial (9) F. P. Greenspan and D G. XncKellar, A n a l . C h m . , 20, 1001 (1948). (10) A. Polyar and J. L. Jungnickel, in J. Mitchell, Jr., I. M. Kolthoff, E. S. Proskauer and A. Weissberger, “Organic Analysis,” Vol. 111, Interscience Publiqhers, Inc., New York, N. Y . , 1956, p. 2.20. (11) Curve 7.0in Fig. 1 (expt G ) was calculated by means of eq. 11.
4.8 5.4 5.1
8.6
information was obtained from the maximum concentration of glycidol and the time at which it occurred.
80 70
“
2
5o
LL
u
2
40
5
30
G
0 W
iz LL Y
2’ I9
IL‘
20
30
40
50
60
73
T I M E , HR
Fig. 1.-Epoxidation of allyl alcohol: dependence of the changes in the concentration of glycido] on the initial p H of the reaction mixtures. The numbers denote the p H values of these experiments: 3.0, expt. 1; 3.9, expt. 2; 4.9, expt. 3 ; 6.0, expt. 5 ; 7.0, expt. 6. For the presentation of both methods it is convenient to transform eq. 3 into eq. 5 by the introduction of the substituents
B = [G]/[AA]n,
7
= kit,
K
= ks/ki
(.1)
(12) T h e time-ratio method was originally used by Swain13 for the treatment of d a t a in the special case of two consecutive first- or pseudofirst order reactions where the rate was measured by the determination of the concentration of a product common t o the first and second step; rf. also ref. 14. (13) C. G.Swain, THISJ O U R N A L , 66, 1696 (1044). (14) A. A. Frost and R. C. Pearson, “Kinetics and Mechanism,” John Wiley and Sons, Inc., New York, N. Y., 1953, p. 153-159.
ZBIGNIEW RACISZEWSRI
1270
I < G L A T I o N I3ETIVEEN VARIOUS
0 92327 0 02 3 9926
0 95455 I:
rmRx
0 01 1 6525
1701.
s2
TABLE I IT RELATIVER A T E CONSTANTS F O R T\f70CONSECUTIVE FIRSTO R D E R REAC'rIONS 0 86413 0 81860 0 46476 0 56819 0 3000 (1 77426 0 66874 0 05 0 07 0 10 0 20 0.35 0 50 0 60 3 1640 2 8599 2 5589 2 0122 1 6154 1 3863 1 2771
.
~ f i ~ / ~7qo/r?o ~ o ,
Eqs. 5 m i d 3 liold for K # 1 ; for K = 1 eq. 6 is valid.
fi = re-7 (6) b?th tlic increasing r , p increases, passes through a maxim u m and decreases. The equations for the maximum value of p and the corresponding r can be derived easily For K # 1: pmnx= K X ' ( ~ - 1.1 (71
. . depend solely on K . Hence, the . . . are also characteristic of a given K .
ratios From the definition of 7 follows that when kl is constant, the ratios of r ' s are equal t o the ratios of the corresponding t ' s . Since the latter are experimentally determinable the calculation of K is possible. 7 6 0 , T ? " , rjo,
From eqs. 7 t o 10 the values of pmnxand 7maxcorresponding to a series of arbitrary selected K ' S were calculated. A portion of these data is presented in Table 111. These data were used for relating, by a graphical interpolation, of the experimentally observed maximum yield of glycidol, pLnSy with the K and T , , , ~ ~ . From T~~~ and the recorded time at which pmsyoccurred, t,, the coefficient kl was calculated. Since K was already known the calculation of k p was a matter of simple arithmetic.
I 1
I
I
IO
20
30
40
50
60
TIME, tiR
Fig. 3.-Epoxiclation of allyl alcohol : depetitlciice of the clianges in the concentration of glycidol on temperature: SO", c r p t . 11; these experiments are represented: 40°, expt. 1 7 ; 30", expt. 4.
I
IO
I
I
20
30 TIME,
Fig, 2.--Epoxidation
, 40
50
60
70
HR
of allyl alcohol:
dependence of
the changes in the concentration of glycidol on the concen-
tration of tungstic acid and hydrogen peroxide. The numbers in the squares denote the relative concentration of tungstic acid; the numbers in the circles denote the relative concentration of hydrogen peroxide and these experiments are represented: 8, expt. 10; 5 , expt. 9 ; 3, expt. 8; I , cxpt. 5 ; 3, espt. 15. Because o f the difficulty in the accurate experimental detcrmination of Pmax and i,, the coefficients kl and ka were associated with a n uncertainty which in some cases was of considerable magnitude. Therefore, i t was necessary to supplement this procedure with the more accurate time-ratio Ineth od . The time-ratio method requires the introduction of the 0 ,rjo . . . and t 3 0 , tao, tso . . . They signify the symbols ~ ~ rqo, values of r , or t , for which /3 is equal t o 0.30, 0.40, 0.50 . . ., rc.\yxtively. Eqs. 5 ant1 (i cleinon~tratethat the valurs of
X series of selected ti's was substituted into eq. 5 and for each K the r i b , 730, rqo . . . were calculated. The results are Since for a given K there are two values listed in Table I V . of rp corresponding t o two identical 8, one on each side of Omax, the 7's (and t ' s ) of the diininishingvalues of /3 are marked with an apostrophe. From the data in Table I V the ratios of 7'5, equal t o the ratios of the corresponding t's, were calculated; a portion of the results is listed in Table V. The experimentally determined p's were plotted z'eyws reaction time and from this graph the t 3 0 , t 4 0 , t j o . . .were read. The ratios t a o / t s o , tso/tro . . . were calculated and used for the determination of the K by a graphical interpolation utilizing the data in Table V. For the determination of the individual rate coefficients a graph was prepared relating the 7 ' s and Ios listed in Table IV. From this graph the 730, 'r'40,730 . . . corresponding t o the already found K were read. Since the Lao, t 4 0 , tho . . .were already known a simple division yielded k, and kt. I n three experiments, Nos. 6, 7 and 16, the time-ratio method could not be applied,15 and the coefficients kl were calculated by the method of least squares from the changes in the concentration of glycidol in the initial stages of the reaction. I:;]
=
[.lAlo(1 -
(11)
(15) I n expts. S and 7 the reactions were very slow, and t h e erperiments were terminated before t h e decomposition of glycidol achieved measurable proportions. I n expt. l G allyl alcohol was in excess, in contrast t o t h e remaining experiments where t h e concentration of hydrogen peroxide a l w a y s exceeded t h a t of allyl alcohol. Hence, there was no siniple, cnmnion w n y of expresiing the per cent. yirld [ i f d y c i -
