GLEKA. RUSSELL A N U ROGERC WILLIAMSON, JR
236-1-
rrsultirig liquid was then flash distilled a t 0.1 iiiiii. This liquid was carefully distilled, giving a pure compound, b.p. 54-55" a t 2' i n i l l . , Z * ' I ~1.5618; lit.41 b.p. 53-54' at 2 mm.,n% 1.5012, 1,5608, and 1.5620. Gas--Liquid Chromatographic Analysis.-Solutioii~ of mixtures ( i f hytlrocarbotis for competitive oxidatiou or chlorination were prepared, theri aliquots niiscd with an aliquot of a standard solution of the iiiterual standard and triplicate g.1.c. aualyses per-
[ C O S T R I B L I T I O N F R O M THE
DEPARTMENT OF
Vol
sc,
formed to provide calibration factors t o convert area ratios into mole ratios. After chlorination or r~sidation,analyses were again performed a t least in triplicate. A number of different coluniti substrates, conditions, and internal standards were empluyed. Pertinent details are summarized elsewhere , 4 2 -
1121 I
+
a n tie shown t h a t when 0 = 1 k t r ~ ' k t k i ) : ' ? . a lineal- ielationship i e i u l t s when t h e l a t c o f r~rirlatiiini - plotted ;iqainsl [.%I 01 in; Sonlineal- relationship+
fing --f
BOOB. (or BOOH BOO.
+ B.)
+ -1(or ?iH) --+
B O O % . (or BOOH
(3) ru = kBrr/kna
kn i
+ A,)
(4)
Termination kt.4.4
2.100. --+
2B00. -400.
ktnn
+
nonradical products
kthn + BOO, --+
This phenomenon has been previously discussed in connection with the cooxidation of mixtures of cumenee tetralin, cumene-indan. and cumene-dibenzyl ether. 3a,h Figure 1 shows the effects of several cooxidants on the rate of oxidation of binary mixtures containing styrene. Curves such as 3 (p-Inethoxystyrene), 4 (p-nitrostyrene), or T (benzyl ethyl ether) indicate t h a t peroxy radicals formed from these substrates have termination rate constants approximately the same as those for termination of styrenylperoxy radicals. This seems reasonable since all the radicals involxTed are ?'-benzylic radicals.6 Apparently, styrenylperoxy radicals tcrniinate more readily than cumylperoxy radicals as i n dicated by the sharp minimum in the rate (curve X, Fig. 1) of oxidation of mixtures of cumene and styrelie. The same effect is observed with cis-decalin (curve 9, Fig. 1) where a mixture of 3 ' and 2'-aliphatic peroxy c a n be observed even when 9 = 1 and k t . i . 4 = ktnn if the valuei of k i t AH, k ~ ~4 H H . and k i i knn a r e quite different Although V d l l l e ' of d or IB] by C U I V fittinC ~ c a n be obtained f r o m pluts oi oxidation l a t e V A [.4] values of k t k . 1 b t n ~cann:it he obtained unless t h e ratio k k i k n H call I,? independently measui ed I b ) w e v e j - , the presence of a sharp minimum i n t h e l a t e curve seems fairly diagnu.;tic r i f la!-ge difference% in the valups of kti.4. k t n n , and O I 6 > > 1 ' , G I C. .4 I? >isell.J ,4177 Cht,iii S o r , 79, 3871 (1!157).
ARALKANESAND ARALKENES WITH
June 20, 1964
radicals are involved.' Presumably the rate minimum would have been more pronounced with cis-decalin if the presence of 2O-aliphatic peroxy radicals could have been excluded in the oxidation. T h e requirements for the sharp minimum, as observed with cumene-styrene mixtures, is that the retarding hydrocarbon should be much more reactive toward peroxy radicals than the hydrocarbon whose oxidation is being retarded and that the peroxy radicals formed from the retarder undergo self or crossed termination reactions much more readily than peroxy radicals derived from the substance being retarded.3a T o obtain reactivity data toward the peroxy radicals the disappearances of cooxidants were measured and the results subjected to kinetic analysis by the "Copolymerization" equation.8 The results entered in the last two columns of Table I indicate considerable spread in the solutions of this equation. In some cases a negative intercept was observed. This must mean that either the analysis for substrate was not accurate or that the reactants are being consumed b y some process in addition to reactions 1-4. Some of the negative solutions occurred when styrene was a cooxidant and would have been positive if less styrene had been consumed. I t would appear that styrene may be consumed by some process in addition to the four propagation reactions, possibly by a reaction between styrene and some oxidation product. Table I1 lists the reactivity data calculated from Table I. Column 2 lists the values of k'p/ktl'Z calculated from the rates of oxidation of the pure substrates, where k', is equal to kp or ka depending on whether hydrogen abstraction or addition is involved. Columns 3-5 of Table I1 list the reactivities observed toward the specific peroxy radicals as calculated by the "Copolymerization" equation.
Discussion The data summarized in Table TI present a reasonably consistent picture. There are no major differences revealed in the reactivity series when the peroxy radical is varied from styrenyl to a-methylstyrenyl, tetralyl, or cumyl. T h e available data for a-ethoxybenzyl and decalyl peroxy radicals are also included in Table 11, but we consider these data less reliable than those for the other four peroxy radicals. The agreement between the present study and a previous oneaa on the relative reactivity of cumene and tetralin is not particularly good (see Table 11). Ii-e conclude from Table I1 that peroxy radicals have about the same reactivity irrespective of the nature of the alkyl substituent. However, termination rate constants for peroxy radicals certainly vary with the nature of the alkyl substituent. In the over-all rate expressions for oxidation this variation appears as an inverse square-root dependence and hence the effect of \-ariation of the termination rate constant on over-all rate is reduced. Severtheless. several examples of variation in kt are obvious in Table I1 in addition to the cumylperoxy-tetralylperoxy radicals discussed previous1y'.8a Styrene is about 10-20 times as reactive as cumene toward peroxy radicals such as tetralyl- or cumylperoxy, but the oxidation rate of styrene is only (7) F R Jaffee T . R Steadman, and R . W. RIcKinney, J . A m C h r m . s o t . , 85. 3,51 rlRH:I) (8) I; R I f a p o and C ll'alling, rheni
R e a , 46, 191 (1950).
PEROXY
2365
RADICALS
140
120
c
5 100
; x
h
N
\
w I
r"
60
40
20
04 0 6 Concentration of styrene, mole:l.
0.2
08
Fig. 1.-Rates of oxidation of binary mixtures of various hydrocarbons and styrene in benzene solution at 6O", 0.10 M A I B N ; total substrate concentration = 1.0 M ; 1, 2-phenyl1,3-dioxolane; 2, 0-methylstyrene; 3 , p-methoxystyrene; 4, p-nitrostyrene; 5 , dibenzyl ether; 6, tetralin; 7, benzyl ethyl ether; 8, cumene; 9, cis-decalin.
five times that of cumene under comparable conditions a t 60". We believe this is due to the fact that styrenylperoxy radicals terminate about ten times as fast as cumylperoxy radicals. Styrene and a-methylstyrene have nearly the same reactivity toward peroxy radicals and the 2-fold difference in rates of oxidation is thus attributed to an enhanced rate of termination of styrenylperoxy radicals. &-Decalin, whose rate of autoxidation is only about one-half t h a t of cumene, is actually more reactive than cumene toward each of the three peroxy radicals studied. Here i t is believed that 2 O-alkylperoxy radicals derived from cis-decalin? lead to a more rapid termination process than t h a t observed for the 3O-peroxy radicals from cumene.Ioa In the present work, cumene was found to be 0.8 as reactive as cis-decalin toward a cumylperoxy radical. Utilizing another experimental approach Xlagy, Clement, and Balaceanu had previously reported t h a t cumene was 0.3 times as reactive as decalin (presumably a mixture of cis and trans isomers.)3b
Experimental Oxidation Procedure .-The apparatus and procedure were identical with those described previously.i (9) The assumption is made that since k B . A i k B B k c . d k c B = 18 t h a t A is s t y r e n e , B is c u m e n e , and C is tetralin T h e best fit with curve 8, Fig 1 , occurs when 8 (ref 3a) = k t . k B ~ ' ( k t . k . k k i B B'12 ) = f
k A A / k B B = 1.5 where
2-3. (10) (a) Suggestions concerning t h e details of t h e termination process consistent with 2'- a n d I0-alkylperoxy radicals terminatinp more readily t h a n 3°-alkylperoxy radicals h a v e been made See also P D BaTtlett a n d T . G Traylor, J . A m Chpm S o t . 86, 2407 (1903) (b) A Kieche, E S c h m i t z . a n d E . Beyer, B P I . .91, , 1938 (19L8)
2366
Substrate A
GLEN-1,KCSSELLANI) ROGERC . \VII,LIZSISOS, JK
Substrate R
Styrene Styrene Styrene Styrene Styrene Styrene Styrene Styrene Styrene Styrene Styrene Styrene Styrene Styrene Styrene Styrene Styrene Styrene Styrene Styrene Styrene Styrene Cumene Curnene Curnene Cuniene Curnene Cumene Cumene Curnene Cumene Cumene Cumene Cumene Cuniene Cu rnene Cumene Cu in en e Curnene Cuniene Cuinene Cumene Cuinene Cumene Cuiiiene Cumene Tetralin Tetralin Tetralin Tetmlin Tetralin Tetrdlin
[Bl
1 000
Styrene Styrene Styrene Styrene Styrene Styrene
[Ala
a-Methylstyrene a-Methylstyrene a-Methylstyrene a-Methylstyrene a-Methylstyrene a-Methylstyrene 2-Phenyl-l,3-dioxolane Z-Phenyl-l,3-diosolane 2-Phenyl-1,3-dioxolane 2-Phenyl-l,3-dioxolane Uibenzyl ether Dibenzyl ether Dibenzyl ether Dibenzyl ether Benzyl ethyl ether Benzyl ethyl ether Benzyl ethyl ether Benzj.1 ethyl ether Benzyl ethyl ether Tetralin Tetralin Tetralin Tetralin cis-Decalin cis-Decalin &-Decalin cis-Decalin cis-Decalin Cumene Cumene Cumene Curnene Cumene Benzyl ethyl ether Benzyl ethyl ether Benzyl ethyl ether Benzyl ethyl ether Benzll ethyl ether Benzyl ethyl ether 2'-Butylbenzene 2'-Butylbenzene 2 '-Butylbenzene 2 "-Butylbenzene 2O-Butylbenzene 2'-Butylbenzene Dibenzyl ether Dibenzyl ether Dibenzyl ether Bibenzq 1 Bibenzyl Bibenzyl Bibenzyl Tetralin Tetralin Tetralin cz r-Decalin czs-Decalin (1s-Decalin Benzyl ethyl ether Benzyl ethyl ether Benz1.l ethyl ether Benzyl ethyl ether Benzyl ethyl ether Benzyl ethyl ether
0 200 500 800 900 950
0 300 500
1 000 0 800 k500 200
100 050
1 000 0 700 500 200
81)O
1 000
0 200 500 800
0 800 500
200 1 000
0 050 200 500 700
0
1 0 200 500 800
0
0 050 200 500 800 700 500 300 100 050 1 000 0 930 800 500 200
0
1
100 030
0 100 200 500 800 900 950 900 500 0 200 500 800 800 500 200 200 500 800 930 800 500 200 100 030
950 800 500 300 000 800 500 200 O(l0 950 800
Benzene
25 4 51 6 39 4 1b 5 24 8 24 4 25 4 7; 4 34 1 26 6 24 0 28 1 25 8 2.3 8 9 11 15 19 13 10 12 21
:3 2 6
500
11
19 18 15 0 10 5 5 7 3 3 5 8 2 9 3 9 5 7 8 1 10 0 10 7 3 7 3 6 3 8 4 2 4 8 5 4 3 7 4 8 12 9 3 0
800 900 970
1 000 0 900 800 500
200 100 0 50 100 500 1 000 0 800
405 608
4 4
11 8 9 10 12 10
0 8 1 2
0 570 3 97 141
0.9 i0 1
1 18 ( J 71,
0 78
0 388 230 16.)
-
0 161
0 i $11
1 b',i f 0 05
417 685
460 183
0 118 3 02 439
0 740 456
0 16; 413 656
0 728
0 594
0 294 190
0
1' rt !I 2 20 56, (J 31)
1 79 1 58, 1 iil
8 74
26;
439 186
*
s 0 :3 5 04 3 iio, ;i 13 3
L ' S 1 0 5 1 07 2 94.4 3
...
424 234
695
6 5 i l 8 1 6 6,4 5
5 70 . . . . . .
0 7-19
0 134
I55
360 680
186
O J i 0 1 41 0 2 , -0 11
3 58 0 163 432 625
0.764
0 147 410 650 730 482 177 192 466 726
0 785
0 600 399 163
0 132 418 710
468 164
1 15 i: 0 05 1 31
1 00,O 96
..
476 168 134 408
662
--a0 I
146 170
I
3
Y.AC
26 1
.. . .
3 8 3 7
[nif
3;; 730
0 186
. .
500 200 200 ;io0 800 800 500 200 070 200 500 800 900 970
0 153
0
7 0 6 4 2 2 5 4 6 3 6 1 6 4 3
[.% 1 f
26 8
14 [ I
200 300 500 700 900 950 0 070 200 500
Chlorobenzene
Vol. h(i
..
2 42 0 89, 0 . 7 8
O f 0 2 0 33 .07, -0 58 58
50
58,0 58 0 $9 f 0 0 2 94 92, n 8.'
June 20, 1964
,%RXLKANES A N D
ARALKEXES
2367
WITH PEROXY R A D I C A L S
TABLE I (Continued) Substrate A
I n i t r a t e of oxid.* ChloroBenzene benzene
Substrate B
[A la [Blo [Alf [B]i r.4' YBC 0.175 1 . 8 9 i 0 01 0.01 0 002 Tetralin cis-Decalin 0.800 0 200 9.5 0.600 Tetralin cis-Decalin ,500 ,500 6.5 ... ,365 ,450 1 88 004 Tetralin cis-Decalin ,200 ,800 4 1 ... 133 750 1 . 8 9 , 1 91 . 0 0 9 , 0 015 Tetralin a-Methylstyrene 200 800 .. 136 458 0 . 8 3 ' 2 ~0 1 1 . 3 XI= 0 . 2 Tetralin a-Methylstyrene 500 .. .. ,354 ,335 500 1 31 1 69 Tetralin a-Methylstyrene 800 ,200 . . 574 123 0.69, 0.59 1 44,0.84 a Cooxidations performed in benzene solution. Subscripts 0 and f refer to initial and final concentration in moles/l. MI. of oxygen (STP) per 100 min. for 10 ml. of a solution containing 0.10 If A I B S , corrected for nitrogen evolution. From solution of the "Copolymerization" equation The first experiment of each set determines a straight h e when Y A is plotted as a function of 7 B ( 7 = ~
+
*
kAa
2100. h --+ XOOA., etc.). The second experiment determines another straight line which intersects the first a t the values listed. The third experiment defines a third line which intersects the first two a t the points shown. The center of gravity of the triangle thus formed is given in italic type. A reasonable experimental uncertainty has been estimated. kAA/kBB;
YB = k B B / k B A ;
TABLE I1 RELATIVE REACTIVITIES OF PEROXV RADICALS TOWARD XRALKASES A N D ARALKEKES, 60", BEXZENE SOLUTION Attacking peroxy radical--------------Substrate
k D ' , kt'/Zn
Styrenyl
a-Methylstyrenyl
Tetralyl
Cumyl
a-Ethoxybenzyl
Decalpl
2-Phenyl-1,3-dioxolane 14 6 2 4 1 a-M ethylstyrene 3.1 1.2 1.2 p-Methoxystyrene 3 2b 4 . Ob Styrene 2 8 1.1 0 8 2 0 -1 -10 1 ib p- Sitrostyrene 2 Ob 0 63 0.75 Benzyl ethyl ether 1.1 1.0 0.48 Dibenzyl ether 2 2 1.7 Tetralin 1 00 1.0 1.0 1.0 1.0 1.0 1 0 0 40 Cumene 0.40, 0 06," O . l O d 0.10, 0.04c 0.48 0 006 2'-Butylbenzene 0 21 0.09 Bibenzyl 0 17 -0 0 19 czs-Decalin 0 53 0.17 0.01 a Relative values; from Table I using the expression, -d[Oz]/dt = k'p[RH](R,)'/2/(2k,)1/z Ri/2 (ref. 6 ) ; R , = 1.31 X 10-6 mole/l.-sec. ( D . G. Hendry and G. A. Russell, J . A m . Chem. Soc., 86, 2368 (1964)). Ref. 4. Ref. 3a, 90". Ref. 3d.
+
Materials.-The solvents, - l I B X , styrene, and cumene employed have been described.l a-Methylstyrene showed a purity of greater than 9 9 5 by g.1.c. It was chromatographically filtered through silica gel before use. Tetralin (Eastman Kodak Co.) was rectified with a spinning band column t o remove a lower boiling component and decalin. The fraction used contained a trace of decalin but had a purity greater than 99.77, by g.1.c. I t was passed through silica gel before use. czs-Decalin was a gift from W. R . Grace Co. Rectification through a Todd column gave a fraction greater than 99C, pure with the major impurity being tetralin. I t was passed through silica gel before use. 2O-Butylbenzene (Eastman Kodak C o . ) was rectified through a spinning band column to give material, n Z o1.4898. ~ Bibenzyl (Eastman Kodak C o . ) was recrystallized from ethanol; m.p. 52.8-53.1 '. 2-Phenyl-1,3-dioxolane mas prepared from equal molecular amounts of benzaldehyde and ethylene glycol in the presence of a trace of p-toluenesulfonic acid. Benzene was employed to azeotrope water which was collected in a Dean-Stark trap. When SOYc of the theoretical water had been collected the reaction was stopped and the product washed with 10yc sodium
bicarbonate solution, dried, and a crude vacuum distillation performed. This was followed by two careful rectifications with a 15-in. spinning band column. The fraction, b . p . 78' a t 2 . 5 mm., n z a1.5270 ~ 1.5269, lit.lob,consisted of 99% 2-phenyl-1,3-dioxolane and lYc benzaldehyde as analyzed by g.1.c. The autoxidation of 2-phenyl-1,3-dioxolane showed a decreasing rate with time, presumably from the ionic decomposition of the hydroperoxide to form phenol. Analytical Procedure.-The oxidates were first chromatographed to remove oxidation products as described previously.* Elution with a 20-fold excess of benzene was proved to elute quantitatively the substrates employed. The concentrations of reactants were determined after oxidation by use of a number of different g.1.c. columns, conditions, and internal standards.I1
Acknowledgment.-Solutions of the "Copolymerization" equation were performed a t the Gulf Research Center utilizing a program written by Mr. ,4. N . Kresge. (11) R . C. Williamson, J r , , P h . D . Dissertation, Iowa S t a t e University 1963.
