CHEVESWALLINGAND ANNEL. RIEGER
3134
averaging 93y0of NBS reacted with t h e toluene experiments and 86y0 in the other systems. Considering t h a t some polybromination and KBS decomposition t o p-bromopropionyl isocyanate must be occurring, the agreement is very satisfactory. Bromine Reactions.-The data of Table 11' were obtained by direct competition reactions, essentially as in the case of NBS; relative reactivities (per molecule), ethylbenzene: toluene, 8.70, 8.27. The competitive bromination of ethylbenzene and toluene by S B S in the presence of 6 mole c/1 added bromine was also carried out directly: relative reactivity per molecule, ethylbenzene:toluene 7.74, 7.79, 10.21, 8.24. Detection of p-Bromopropionyl Isocyanate.--Decomposition of 0.1 mole of S R S in dry refluxing chloroform in the presence of 2 mole 5; benzoyl peroxide and 10 mole 5; allyl chloride gave a reaction mixture with a n infrared spectra showing the peaks reported for p-bromopropionyl isocyanate. 30 Removal of solvent and treatment of the residue with methanol gave 11.3 g. of p-
[CONTRIBUTION F R O M
THE
Vol. 85
bromopropionyl carbamate after recrystallization from methanol; m . p . 132-134.5 (lit.31 137-138'). The isocyanate was also detected by infrared spectra ( b u t not determined quantitatively) in decompositions run in methylene chloride with and without allyl chloride, and its characteristic odor noted in other systems containing relatively unreactive substrates. NBS Reactions in Presence of Olefins.-Typically 380 mg. of NBS and 0.320 ml. each of toluene, o-xylene, and ethylbenzene were allowed t o react in the presence of 0.1 mg. of AIBN, 0.320 ml. of olefin, 2.60 ml. of CCI,, and 0.320 ml. of chlorobenzene a s a n internal standard. Reactions took 90 min. for complete reaction as compared with 45 min. in the absence of olefin. Products were analyzed as before. Little olefin (O-lOC,i) was consumed, but trans-dichloroethylene underwent 70-74(;i isomerization t o cis. Similar experiments in the presence of either 0.320 or 0.032 nil. of styrene showed no significant reaction in 6 hr. a t 80" a t which time t h e initiator was essentially exhausted.
DEPARTMEST O F CHEMISTRY, COLUMBIA UNIVERSITY, KEW YORK 27, h-.Y.]
Positive Halogen Compounds.
IX. Structure and Reactivity in Halogenation with Some Further N-Haloamides
BY CHEVES WALLINGA N D ANNEL. RIEGER* RECEIVEDMARCH23, 1963 Relative reactivities of a series of hydrocarbons toward bromination with three S-bromohydantoins and Sbromoacetamide have been determined and compared with results from S-bromosuccinimide bromination. Relative reactivities for ethylbenzene:toluene are quite similar (6-15) and p-values for substituted toluenes appear within experimental error (-1.10 t o -1.36). I t is concluded t h a t all reactions occur most probably through bromine atom chains. Relative reactivity of cyclohexane :toluene toward Xchlorosuccinimide is 3.9 f 0.3, indicating a chlorine atom chain in this case.
Although they have attracted much less attention and received less use than N-bromosuccinimide (NBS),a number of other N-haloamides are known to act as effective halogenating agents for the replacement of allylic and benzylic hydrogen by what are quite evidently free radical chain processes. In particular, the series of N-bromohydantoins have been studied in some detail by Orazi,3and an allylic bromination by N-bromoacetamide ( N B A I )was reported as early as 1919 by Wohl.? I t accordingly seemed worthwhile to extend our studies with NBS5 to a series of other such N-haloamides, both t o see whether differences in selectivity exist which would be of synthetic interest, and to identify if possible the chain carriers in the radical reactions involved. This paper reports an investigation of the reactions of 1 -bromo-5-isobutyl-%methylhydantoin (I), l-bromo-3,5,5-trirnethylhydantoin (11), 3-bromo1,j,%trimethylhydantoin (I1I ) , N -bromoacetamide (NBA), and N-chlorosuccinimide. CH 3
CH,
(CH,)!CH CHUC-CO
,
BrX
"eo; I
CH3
CH;J!-CO
\
NH
CH3C-C0
I
\
BrN
'cod I1
NCH,
I
C&N
\
NBr
\ /
co
111
Results and Discussion Substituted Toluenes.-Relative reactivities of substituted toluenes toward the four N-bromoamides mentioned above were determined in CCl4 solution a t SO", using azobisisobutyronitrile as initiator, essentially as in our work with NBS, employing stepwise comparisons when compounds differed markedly in ! l i T a k e n f r o m t h e P h D Dissertation of Anne I. Rieger. C o l u m b i a U n i v e r s i t y , 1962 S u p p o r t o t this w o r k h y a g r a n t from t h e S a t i o n a l Science F o u n d a t i o n is gratefully acknowledged ( 2 ) Socnny RI,,hil Oil C o Fellow 1960-1961 (:9 0 0 Orazi a n d J Lleseri, A n a i r s u s o c q i i i m a v g r i i l i i t a . 37, 142 (1449). a n d s u b s e q u e n t papers f 4 ) A WcBhl, B U Y 62B, , 5 1 (1919). ( 5 ) C \Valling, A I, Kieger, a n d D D . T a n n e r , . I . A m Chein S o c , 8 5 , .1129 (1963)
reactivity. Results are summarized in Table I together with our NBS results.; Experimental errors are average deviation of the mean for duplicate experiments unless a larger number is indicated in parentheses. The Hammett p-u relation was investigated for each N-brornoamide, and i t was found in every case (as with NBS) that u+-constants6gave a better correlation with the data than did u-constants. Values of p and Y (the correlation coefficient) and s (standard deviation from the regression line) are included in the table. The close similarity of p ' s for the different brominating agents strongly suggest a common radical chain carrier. In fact, treating all of the data as applying to a single reaction yields p = - 1.27 with 7 = 0.945, s = 0.15. A similar comparison has recently been carried out for several substituted S-bromosuccinimides by Martin,' and, since NBS and Br2 also show parallel r e a ~ t i v i t i e s , ~he , ' . ~concludes that a bromine atom chain is involved in all his systems. The good fit of all of our data (including that on NBS) to a single p-value points to a similar conclusion here, further supported by the results described in the next section. Other Hydrocarbons.-Relative reactivities of some other hydrocarbons are listed in Table 11. The most critical reactivity is that of ethylbenzene, and values are again seen to be very close in all systems. Data for saturated hydrocarbons are subject to considerable uncertainty and may represent merely orders of magnitude. In any case, the results again support the hypothesis of a common bromine atom chain as the major reaction path, and suggest that as far as selectivity is concerned, all of the S-haloaniides are equivalent for synthetic purposes. N-Ch1orosuccinimide.-The participation of chlorine atom chains in chlorinations involving N-chlorosuccinimide was first proposed by Goldfingergand has been supported by deuterium isotope effect measurements by ( 6 ) H C. Brown a n d Y . Okarnotn, ibid., 8 0 , 4Y7Y ( 1 0 3 8 ) ( 7 ) R E Pearson a n d J C . R l a r t i n , ibid , 86, B A A 11969) ( 8 ) G A Russell, C D e Buer. a n d K A I D e s m o n d . ibid , 86, 365 (1963). (9) J A d a m , P A Gosselain, a n d P. Goldfinger, .Yattcrr. 171. 704 (19JH).
HALOGENATION WITH N-HALOAMIDES
Oct. 20, 1963
3135
TABLE I RELATIVEREACTIVITIESOF SUBSTITUTED TOLUENES TOWARD ri-BROMOAMIDES IN CCl, I
NBSa
Toluene
Relative reactivitiesI1
11.7 2.56 1.52 1.00 0.75 .80 .58 .54
AT
XO",
PER
BENZYLHYDROGEN >
NBA
I11
6.75 5.7 f 0.2 8.2 f0.4 1.59 1 . 3 4 f .02 1.21 f 0.01 1.18 1 . 0 6 f .02 ... 1.00 1 .oo 1.00 0 . 8 8 f 0.05(4) ... ... .68 f . 1 0.46 i0.01 0.72 f 0.01 p-c1 .46 f . 1 .38 f .02 .49 f .02 p-Br . 7 7 f .01 .62 f . 0 1 .64 f . 0 1 P-F ... .24 f . 0 1 .22 f . 0 1 ... m-C1 0.24 ... . 1 5 i ,002 . 1 9 f .01 0.38 f 0.01 m-Br -1.21 -1.10 -1.28 -1.36 -1.35 P 0,980 0.967 0.955 0.967 0.955 r 0.10 0.12 0.16 0.12 0.15 S a From preceding papers; p , r , and s here calculated for only points listed for better comparison with the other d a t a ( p for all points = - 1.38). p-OCHa P-CHa m-CH3 H (std.) m-OCHa
12.6 f 0 . 5 2.33 f .03 1.80 f .08 1 .oo ... 0.77 f 0.01 .69 f . 0 1 . 5 5 i .02 .28 f .01
'
TABLE I1 RELATIVE REACTIVITIES OF OTHER HYDROCARBOVS TOWARD NBS PER MOLECULE IN CC1, AT 80" Substrate
NBS
1 Octene
Ethylbenzene o Xylene Toluene (std 1 2 , 3 Ihmethylbutane Methylcyclohexane n Octane Cyclohexane
I
I11
h-BA
844
10*14
1 00
1 00
I1
25 =k 10 1 1 + 4 5 6 2 + 0 3 3 8 7 3 ~ 0 8 1 00 1 00 0 10
26 4 15 8 428 1 00 0 07 027
OF
022 012
017 017
Wiberg and Slaugh lo We find further confirmation in competitive measurements on toluene-cyclohexane Relative reactivity measurements (per H) gave cyclohexane toluene 3 9 f 0 3 per molecule, very close to the I 1-octene
-
3.60
f
* 0.08
2
3.20
4
15
f o
4.66
p-fluorotoluene
*
J 10'02' .61
I
* 0.06
f 0.01
\
10.645
+ 0.01 0.59 2
n-hexane
1.09 i 0.02,
O.l 0.01 0.173
0.424
ethylbenzene 4.5
L
n-octane
p-methoxytoluene 2 86
'*
068t
002
Toluene
-
* o 01,
0 683 f/ 0003 -
I * 0.01 0.19
J
2 37
/
t
f 001
m-xylene 0 384
A . 1 3 (I)
p-chlorotoluene 0.22
3:r:-
1.07 i 0.01
+I =
0 005
p-fluorotoluene m-Gethoxytoluene /
0.01 0.305
I i 0.01
=*%
\
0.35
t*
0.06
m-xylene
* 0 01
p-bromotoluene
NBA $-xylene 4-~pp-methoxytoluene
0.285 i ( 1 )
J J m-chlorotoluene
m-bromotoluene Fig. 1.-Competitive experiments using hydantoins I and 11. Sumbers are relative reactivities of compound a t head of arrow t o t h a t a t tail. All experiments in duplicate unless another number is shown in parentheses. (IO) K B Wiberg and L H Slaugh, J A m Chem S O L 80, , 3033 (1958)
I
IO *+.43
0.002
1.01 f 0.0%
ethylbenzene 6 2 i\3
0.314
ethylbenzene
11
p-bromotoluene
1
2.68
f 0.1
\ m-chlorotoluene
0.171
f 0002
f
m - b r o m o t o l u e n e m 2 p-fluorotoluene-m-chlorotoluene /
\
J \cyclohexane
\
p-methox ytoluene
0.04
* 0.021 0.74 i 0 03
p-xylene
0.49 & 0.01
I
2.68
p-methoxytoluene
m e t h y l c y c l o h e x a n e d 2,3-dimethylbutane
\*
p-xylene
p - ~ h l o r o t o l u e n eToluene ~ ? ~
2.7
0.11 f 0 . 0 0 5 0 . 1 8
I
q
-
1
0.90 f 0.01 0.77 f 0 . 6
$-chlorotoluene-
* 0 09
\
Toluene
p-bromotoluene
111 ethylbenzene
\
O $T(A **
o-xylene
\3.87/
Experimental Materials.-The 1-bromo-5-isobutyl-5-me thylhydantoin (I)] was a gift from t h e Arapahoe Chemical Co.; purity ( 2 lots) 96.6 and 102.870 by titration. Attempts to purify it further by crystallization gave product with too high titration values, so it was used as received. The l-bromo-3,5,5-trimethylhydanto~ (11) was prepared as described b y Orazi,I4 m.p. 161-164 ,
8.44 (1)
2 25
1.58 f 0.01
m-xylene
C1. value ( 2 . 9 ) " and entirely different from that obtained with NBS (0.012).5 Furthermore, reactions of N-chlorosuccinimide carried out in the presence of bromobenzene (intended as an inert internal standard) yielded detectable quantities of chlorobenzene. Such a displacement is also a known reaction of chlorine atoms.12
-
0.68 f 0.02
p-bromotoluene
& 0.01
Toluene 2.01 0 . 7 2 .t 0.02
* 0.08,
-
(4)
0.625
p-chlorotoluene
m-xylene
* 0.015 m-bromotoluene
p-fluorotoluene Fig. 2.-Competitive experiments with hydantoin I11 and N-bromoacetamide. Numbers have the same meaning as in Fig. 1. purity 100.2% by titration after recrystallization from water and CCl,. The 3-bromo-l,5,5-trimethylhydantoin(111) was prepared by variations of the method of Biltz and Slotta" and 0 r a ~ i . l ~I t was obtained from t h e hydantoin in 327; yield, (11) G. A. Russell, i b i d . , 80, 4997 (1958). Relative reactivities for the chlorine reaction vary somewhat with reaction media. (12) B . Miller and C . Walling, ibid , 79, 4187 (19.57) (13) Actually the position of the bromine in this molecule is not unequivocally established. Our hope that relative reactivity data might help to establish its position was thwarted by the similarity in reactivity of all the hydantoins studied (14) 0. 0. Orazi, R . A Corral, and J . D. Bonafede, Anales O S O L quim argentina, 4S, 139 (1957). (15) H . Biltz and K . Slotta, J. prakt Chem., 118, 233 (1926).
GLENA. RUSSELLAND CHARLES DEBOER
3136
m.p. 169-170" dec., purity 100.17Gb y titration. N-Bromoacetamide was prepared b y t h e method of Oliveto a n d GeraldI6; m.p. 104-107", purity 99.8%. N-Chlorosuccinimide was commercial material rapidly recrystallized from benzene; m.p. 149-150", purity 98.65%. Competitive experiments were carried out and products analyzed by gas chromatography essentially as in our NBS work.6 Relative reactivities were calculated from direct competitive experiments whenever possible, although a number of
THE
cross checks were carried out as well. The actual competitions carried out are shown in Fig. 1 and 2.'' Reactions with Nchlorosuccinimide were very slow a n d required 24 hr. heating a t 80' in the presence of benzoyl peroxide for complete reaction. Three experiments yielded relative reactivities for cyclohexane : toluene of 3.0, 3.3, and 5.7, and (using bromobenzene as a n internal standard) chlorobenzene was detected among the products. -
(17) Direct comparisons f o r toluene with o-xylene, +xylene, a n d e t h y l benzene using h y d a n t o i n (I) were carried o u t b y D r . D. D . T a n n e r .
(16) E P Oliveto a n d C Gerold, Org S y n , 31, 17 (1551)
[CONTRIBUTION FROM
VOl. 85
DEPARTMENT OF CHEMISTRY, IOWA STATEUNIVERSITY, AMES,IOWA]
Substitutions at Saturated Carbon-Hydrogen Bonds Utilizing Molecular Bromine or Bromotr ichloromethane' * B Y GLENA.
KCSSELL3a AND
CHARLES DEBOER3b
RECEIVED MARCH 27, 1963 competitive photobrominations of aralkyl hydrocarbons utilizing molecular bromine or bromotrichloromethane have been performed. The results establish reactivity scales of benzyl-type hydrogen atoms toward the bromine atom and the trichloromethvl radical.
Results Table I summarizes a number of competitive brominations using molecular bromine in carbon tetrachloride a t 40". The last column of this table lists the relative reactivities calculated by the equation
where k.4 and k g are defined as
+ RAH--+ I
