I n a similar way di-p-phenoxyphenyl ketone was made irom duryl P-phenoxyphenyl ketone and phenyl ether. A mixture of 1.0 g. of t h e duryl ketone, 20 nil. of phenyl ether atid 20 nil. of polyphosphoric acid was brought t o 150' over
[COSTRIBCTION FROM THE POLYXER
a 1-hr. period and maintained at t h a t temperature for (ihr. The yield of di-p-phenoxyphenyl ketone was -11%. I;KRASA.
RESEARCH ISSTITCTE,
ILL.
POLPTECHSIC ISSTITUTE O F R R O O K t Y S ]
Reactions of Polymers with Reagents Carrying Two Interacting Groups. 11. Bromine Displacement from cu-Bromoacetamide and the Bromoacetate Ion by Foly(methacrylic Acid) and Poly-(vinylpyridine Betaine) IZYHARRY LADENI-IEIM AND HERBERT LIORAXXTZ RECEIVED MARCH16, 1959 T h e second-order rate c m s t a n t s for bromine displacement from a-brornoacetaniide by carboxylate groups of singly a i i c l doubly ionized dicarboxylic acids show a very slight increase of reactivity with increasing basicity of t h e carboxylate. The carboxylates in pirtially ionized poly-(methacrylic acid) are 4-10 times as reactive as those in the dicarboxylic acids and their reactivity decreases sharply with rising degree of ionization of the polymer. A similar effect was observed with poly-(vinylpyridine betaine) which displaces bromine From both bromoacetamide a n d bromoacetate, although the reaction rate of its monofunctional analog 4-methylpyridine betaine is not experimentally observable. XI1 these observations may be accounted for by a concentration of the low molecular weight reagent in t h e region of the macromolecular coil. The dependence of the reaction rate of poly-(methacrylic acid) with bromoacetamide on the degree of ionization of the polymer suggests t h a t the amide is bound t o the carboxyl groups and t h a t t h e bond is stronger when the carboxyls are un-ionized.
Introduction In a previous report3 we described the result of the first of a series of studies concerned with the reaction rates of polymers with bifunctional reagents. The main purpose of this program is t o define conditions leading to cooperative effects as represented below diagrammatically. Here the functional group -4 carried by the polymer is engaged i n a displacement reaction on AT, while the 21--S
(y x A' x I
1
:
A
-4'
I
1
(1)
energetic interaction between ,1'and ?: serves to accelerate the reaction by stabilizing the transition state. The groups -1and X' may be ideiitical or may represent different states of ionization of the groups attached to the polymer chain.4 In the present investigation we measured the rates of bromine displacement from a-bronioacetamide and bromoacetate ion by partially ionized poly-(methacrylic acid) and by isoelectric poly-(+ vinylpyridine betaine), which were compared with the analogous reaction of singly or doubly ionized dicarboxylic acids and 4-rnethylpyridine betaine. Experimental Materials.--Broiiioacetic aci(l and a-brotnoacctniiiitle were obt:iined :is in the previous itivestigation . 3 Glutaric acid was recr\-stallizeci from henzetie (111.p. 96.5", neutralizatiou equirslent weight 66.8). Maleic anhydride recryst:illizcd from chloroform (1n.p. 5 2 " , neutralization equivnlcrit weight 49.7) was used to prepare solutions o f maleic acid. Fumnric :icid ( i n . p . 282") 1i:itl :I neutr:ilization cqui\alent weight 58.7, (1) Taken in l i x t from a thesis submitted by H. 1,adenheim i n pnrtiiil fulfillment of the requirements fur ii P h D. deqree. June, l Y S . '2) Financial assistance of this study by the Office of Ordnance Rcsearch, U. S . &my. and by a #r;int of t h e Slonsauto Chernicdl Co.
are gratefully acknowledged. ( 3 ) H. 1,adenheim Ti. M. Loehl and H. SIorawetz, THIS JOURNAL, 81, 20 (1959). (i)A study of M. L. Bender and Y-I,. Chow (ibid.,81,3929 (1959)) is concerned with a similar problem involving the reaction of t w r , iiifrinctional small molecules, o-nitriiphenyl hydrofyn o x a l n t e : ~ n d2 aminopyridinium i o n .
The preparation of 4-methylpyridine betaine vl-hich lias not been reported previously was carried out as tiescrihetl for pyridine b e t a i i ~ . The ~ product lost one mole of water of crystallization wlicn heated at atmospheric pressure :it 100" and decomposed at 180". T h e ultraviolet spcctruiii had maxima a t 232 n i p ( e 6710) and 257 mp ( E 4630). d n u l . Calcd. for C8H9SOa.H20:C , 56.79; I € , (i.53; S, 8.28. Found: C, 56.64; H, 6.72; X, 8.38. ~olj--(inetliacrylicacid) was prepared from nietliacry,lic acid diluted with a sixfold volunie of methanol :tiid containiiig 1.6 X 10-3 inole of azo-bis-isobutyroiiitrile initiatur per mole of monomer by heating for 20 hours :it 63". The polyiiier solutioii was diluted with water, exhaustively tlinlyzed and freeze-dried. T h e drj-ing of the polyrricr was completed under reduced pressure a t 50". T h e carboxyl cutitelit determined by poteiitiometric titratioti \v:i~ iii esact agreement with theory; the light scattering molecular weight was 187,000. The preparation of the poly-(-1-viri)-lpyridiite betaine) used in this work liiis lieen tlescrihetl ill :L previous report.6 Kinetic Runs and Interpretation of Data.-Initial rates a t 30' were followed by bromide evolution as descrilictl pre\-iouily, making the :il;propriate correction for the hytlrolysis of the C ~ - B rbond3 in the interpretation ( i f tlic tlat:i. The results \yere expressed in terms of ii second-ortlcr rate constant k2 (l.-equiv.-' inin-'). For tlie reartimi of a1)rf)moncetainide with Doly-(methacrylic acid) ( P h I . l ) , ici w i s tlcfiiied by RT - Rn = KZ!BAc)C,a' (2) where RT is the total ohservecl rate of bromide evoltitiim, K H t h e rate due t o h?-drolysis, (B.ic) the ol-l)roiiio;icetaiiiirie coiicentration, C, the normality of tlie PMA and a' its tlegree of ionization, which ~ r - a sobtained from the degree of neutralization a and the hydrogen ion concentration by a' = cz $- (H+)/C,. \\.it11 the dicxboxylic acids kinetic ruiis were carried out in solutions in which the fractioii i j f neutralized carboxyls was 1/4 or a / 4 , so t1i:it the reageiit .;er\-ctl ;ilso t o buffer the solution. T h e results thc tn-ri ruiis wcrc iiiterpreted by r j f
X.r - Rrr = (R.h)[k>'(HA-) 12k:" (.A=]] ( 3 ) where (H.1-J and (.A=) itre tlie concentrations of tlie singly ant1 doubly ionized acid, while k?' auti k?" are set( incl-order rate constants characterizing ionized carboxyl groups iti these two species. \Vith brumoacetic ncitl, second-order rate constants were calculated for reactions of the bromoacetate ion from the difference of the tutal oliserveti rate of 1x"iirle evolutiriri IIT ( 5 ) E Y . Gerichten, Be?., 15, 12:l (1882). ((;I IT. 1-adenhein1 a n d H . bli,ran.etz. J . Po:;viri. (I!rli).
.Cfi ,
26, 2 , j l
and a blank R A which contained in addition to the hydrolytic rate the reaction of un-ionized hromoacetic acid, assumed to have the same rate constant as e-hromoacetamide.
Results and Discussion The reaction of carboxylic acid anions with bromoacetate and chloroacetate was first investigated by Dawson and his collaborator^,^ who showed that i t proceeds by the pathway RCOO- f XCHcCOO-
+
+ X-
(4a)
+ HOCH2COO-
(4b)
RCOOCHzCOO-
RCOOCH2C00-
4861
POLYMERS AND REAGENTS WITH Two INTER.\CTING GROUPS
Sept. 20, 1959
+ H?O +
RCOOH
We restricted our study to the initial reaction rate so as to avoid the kinetic complications resulting from the attack of the glycolate ion formed in (4b) on the C-Br bond. In principle, the action of carboxylate groups of a polycarboxylic acid could differ from the behavior of monofunctional reagents for two reasons : ( I ) Since the effective acidity of the carboxyl groups attached to a polymer decreases sharply with an increasing degree of ionization,8 the nucleophilic power of the carboxylate groups could increase if the reaction obeys the Br@nsted relatione9 ( 2 ) The reactivity of the carboxylate groups of the polymer may differ from that of monocarboxylic acid anions if there is an energetic interaction between the polymer and the second reagent.I0 Such reactions may involve not only long-range coulombic forces acting on charged reagents3 but also hydrogen-bonding or the “hydrophobic bond.’“l All these effects should be subject to variation with the degree of ionization of the polymer. Although the reaction rates of various carboxylic acid anions with bromoacetate and chloroacetate were correlated by Smith12with the use of the Br@nsted relation, the suggested proportionality of the rate constants on the inverse 0.2 power of the acid dissociation constants suggests t h a t the reactions are rather insensitive to the base strength of the carboxylate. In addition, the correlation is not very reliable, e . g . , acetate and formate are equally reactive, although they differ by a factor of ten in basicity. Reaction with Dicarboxylic Acids.-Before considering the results obtained with a polymeric acid, i t will be appropriate to consider the reaction rate constants observed with singly and doubly ionized dicarboxylic acids listed in Table I. It will be noted that with glutaric and fumaric acid, carboxylate groups act almost independently of one another in their reaction with a-bromoacetamide, so that the doubly ionized acid is very nearly twice as reactive as the singly charged anion. The ratios of the first and second ionization constant of these (7) H . H. Dawson and N. B. Dyson, J. Chem. Soc., 49, 1133 (1933); H. H. D a m o n , E. R. Pycock and G. F.Smith, ibid., 517 (1943). (8) J . T . Overbeek, Bull. soc. chim. Belgrs, 57, 252 (1948); A. Katchalskg and J Gillis. Rec. tyalr. chim., 68, 879 (1949). 19) J. N. Brdnsted, Chem. Rets., 6, 322 (1928); J. N. Br@nstedand K . Pedersen, Z . p h y s i k . C h e m . , 108, 188 (1924). (10) H. LIorawetz and E. W. Westhead, J r . , J. Polymer Sci., 16, 273 (1955). (11) W. Kauzmann, “The Mechanism of Enzyme Action,” ed. W. D. McElroy and B. Glass, Johns Hopkins Press, Baltimore, hid,, 19.54. p. 71. (12) G. F. Smith, J . Chem S o c . , 521 (1913).
TABLE I REACTIONOF CPBROMOACETAMIDE ( B h c ) AND RROMOACETATE (sa-) WITH DICARBOXYLIC A C I D S AT Acidb
103. (HA-)
103. (A?
Glutaric Glutaric Fumaric Fumaric Maleic Maleic Maleic
50 36.7 25.1 26.8 50.2 37.0 11.4
2 . 3 2 4.83 0 . 8 7 3 . 4 1 .. 36.7 2.38 10.7 .80 3 . 4 1 3 . 9 .. 2.38 2.34 .89 2.43 .. 27.3 2.42 5.66 .90 2 . 4 3 2 . 4 . . 2 . 4 2 2 . 2 1 .OO 1 . 0 8 . . 2 . 4 8 9.10 .94 1 . 0 8 3 . 9 4 5 . 6 2 . 6 3 11 2 .98 1 . 0 8 4 1
103.
(SAC)
IO’Rr
10’Rir
1Oliir’
108/1;2”
, ,
102.(BA -) C
24.0 36.6 51.4 40.0
..
2.40 3.19 2.62 0 . 4 7 3 6 . 7 2 . 5 7 3.88 2 . 9 7 0.25 . . 1.30 2 . 4 8 2.49 0 3 2 . 7 2 57 2 . 5 0 2 . 4 6 0 The pk’ values of the acids “ I o n i c strength 0.148. (ref. 13) are: glutaric, pK1 4.32, pK2 5.42; fumaric, pK1 3.02, pK? 4.46; maleic, pK1 1.91, pk-? 6.27. e The concentration of the ionized species was calculated from the stoichiometric concn. and the PH assuming 3. pK of 2.95 for bromoacetic acid. Glutaric Glutaric Maleic Maleic
two acids are 12 and 28, respectively,I3 so t h a t after making allowance for the statistical factor of 414 we obtain a rather small difference in the basicities of the carboxylates in the singly and doubly ionized species. Only with maleic acid, in which the first ionization constant is 23,000 times as large as the second would Smith’s correlation12 predict an increase in the reactivity of the carboxylates in the doubly ionized acid by the appreciable factor of 5.6 in reasonable agreement with our observed ratio of 3.7. I t is also not unexpected that the reaction of the carboxylates with bromoacetate, involving an interaction of two negatively charged species, is considerably slower than the a-bromoacetamide reaction. The singly ionized glutaric acid reacts one-eighth as rapidly with bromoacetate as with bromoacetamide, which is similar to results obtained by Dawson and Dyson7 who found the rate of the attack of a carboxylate on broinoacetate to be one-eighth as fast as the rate of attack on the un-ionized acid. Addition of singly and doubly ionized maleate produced no significant increase of bromide liberation from bromoacetate. This may be accounted for by the low basicity of the singly ionized species and by the strong repulsion of bromoacetate from the two closely spaced carbosylates of the doubly ionized maleic acid. Reaction with Partially Ionized Poly-(methacrylic Acid) .-The second-order reaction rate constants obtained with partially ionized poly(methacrylic acid) as the nucleophile are listed in Table 11. With the exception of one run, the ionic strength was kept a t the relatively high value of 0.148, so t h a t long-range electrostatic effects were largely swamped by the high counter-ion concentration.I5 The effective dissociation constant of the carboxyl groups defined by K a = U H + a ’ / ( l - a’) deto 1.5 X clined, as a result, only from 8.0 X as a’was increased from 0.12 to 0.65. (13) Birger Adell. Z. p h y s i k . Chem.. 8 1 8 6 , 101 (1989). (14) B. Bjerrum, i b i d . , 106, 210 (1923). (15) J. J . Hermans and J. T. G. Overbeek, Rec. Wau. chim., 67, 761 (1948): A. Katchalsky and S. Lifson, J . P o l y m e r Sci., 11, 409 (1953).
TABLE I1 R EACTIOY
OF
a-BRORIOACETAMIDE ACRYLIC
r! 148
,148 ,148 .148 .I48
,002 ,143
,148
9 07 9.07 9.07 9.07 9 07 9 07
1s 1 9.07
2 4 4 5 3 G 5 6
TVITH
POLY-(IvfETII-
ACID) AT 50'
78 2 48 21 8 0 2 4 4 83 3 9 2 3 8 2.5 3 0 2 44 21 4 s 2 4 2 2.1 0 6 2 3 0 52 3 I) 2 32 08 1 5 2 4 2
i)
1 2 2 2 2 4 2
96 n . 9 4 .. 93 .91 3 . 9 25 89 3 . o 47 .91 2 . 0 60 90 1 . 5 39 .84 1 . 5 os .87 1.5 01 .90 1 . 2
solvation of the chain during the initial stages of its ionization.17 Reaction with 4-Methylpyridine Betaine and Poly-(4-vinylpyridine Betaine) .-The rcsults obtained in the reaction of a-bromoacetamide and bromoacetate ion with 4-methylpyridine betaine and poly-(4-vinylpyridine betaine) are listed iri Table 111. Although the carboxyl in pyridine REACTION OF AMIDE (BAc) ASD
TABLE 111 (BA-)
BRO?,IOACETATE
(hZilliequiv. per l i t e r )
Three aspects of the results should be emphasized: ( I ) The rate constants are generally higher, by a factor ranging from 4 to 10, than the corresponding rate constants involving carboxylate groups of the dibasic acids. ( 2 ) The reactivity of the carboxylate groups attached to the polymeric chain decreases sharply with increasing degree of ionization. ( 3 ) There is no change in the reactivity of half-ionized poly- (methacrylic acid) on reducing the ionic strength from 0.143 to 0.002, although the dilution of the counter-ions results in an eightfold reduction of K,. This shows, in agreement with previous results, that changes in the basicity of the carboxylate groups have a ncgligible effect on their reactivity with a-bromoacctamide. The relatively high reactivity of the polymer indicates that portions of the macromolecule other than the carbosylate attacking the C-Br bond participate in stabilizing the transition state by interaction, e.g., with the amide group of abroinoacetainide, while no such cooperative effects play a significant role with the dicarboxylic acid anions, This difference in behavior is not difficult to account for: If one carboxylate of, e.g., doubly ionized glutaric acid attacked the C-Rr bond of a-bromoacetamide while the other was engaged in hydrogen-bonding with the amide function, a 10-membered ring would result which is known to have a very low probability. On the other hand, if the C-Br bond is attacked by a carboxylate group of PhlX, the amide function will find itself within the smollen polymer coil in a region of very high local carboxylate concentration and although the probability of chelate formation with any given carboxylate will be small, the aggregate probability of chelation with a n y one of them will be quite high. This effect has been demonstrated previously in a case where chelate rings formed easily with a polymeric reagent, although the smallest possible ring size contained 20 The decrease in the reaction rate constant with increasing ionization of the polymer may be taken as an indication that brornoacetamide associates more strongly with the un-ionized polymer, but the physical situation is too complex to expect a simple relation between ks and a ' , I n this context we may draw attention t o anomalies in the titration curve of poly- (methacrylic acid) mhich have been interpreted as clue to drastic changes in the (16) 11. h l o r a w e t z
(1967).
a n d E. S;tnm:rk, J . l'hys. Ch!!!., 6 1 , 1357
p
0 0.148 ,003 ,148
ANI,
pH
( B e t a i n e ) (SAC) (B.A-)a
5.75 17.5 5 . 4 8 17.3 4.80
20.0
5.70 1 6 . 1
M PB 8.19 ..
(Molcs-l.-min.-l)
RT X 107
XI X
10'
1031~~
1.40 1.22
.. ..
3.36
1.25 1.25 3.23
3.30
,
3.40
3.2:i
*'3.3
3.21
..
.. ..
P\TB 6.36 2.22 .. 2.49 4.18 G 35 2 2s .. 2.11 .ooz 3 . m ~ i . 3 5 . . 2 . o ~ 3 so 1'48 3 . 6 9 (i.35 . . 2.24 3 . 2 2 Sce footiiotc c of Table I .
0 0.148
WBROMOACET-
~METHYLPYRIDINE BETAINE (MPJ3) P O L Y - ( 4 - v I s ~ ' L r Y R I D I N EBETAITE)(P'v'PB AT 50") WITH
3.99
0.81 0.8;; 2 3s 2.41
. ..
11.9
s.7
ii).x 67
betaine is very acidic (betaines having generally
PK values below 2ls), it was expected that the reaction with bromoacetate would be fairly rapid due to the electrostatic interaction of the quaternary nitrogen with the carboxylate of the bromoacetate as represented i n I
c=o
H3C0/"li.-
Q--C--H2C--- 0 - S
!I
0
~
r
Hr -li
On the other hand, with a large number of the betaine units held in close proximity to each other by the backbone of a polymer chain, the high local concentration of dipolar ions should lead to a high effective dielectric constantIg and thus slow down the bromine displacement reaction which leads to a dispersal of charge in the transition state.?O I t was found, however, that 4-methylpyridine betaine failed to produce with either bromoacetate or a-bromoacetamide a significant increase in the rate of bromide formation above that due t o hydrolysis, while an appreciable reaction rate was observed in both cases with poly-(3-vinylpyridine betaine). The relatively high values of K A preclude an exact comparison of the relativc reactivity of the polymer and its low molecular weight analog, but it is clear from the data that the betaine groups of the polymer must be more reactive by a t least a factor of about 30. Since very similar results were obtained with the charged bron.ioacc(17) A . L l . Kotliar and €1 hlorawetz, Tins S U I ' R N A L . 77, :3G'j? (1'133, CIS) 0 . Weidcr, Ber., 68, 263 (1933): C . C.ustafsr,n, : b i t ) . , 77B, f i r ; (l!l.M). (19) J. 'A'ymiin, Cheiiz. R w s , 1'3, 213 ( 1 9 3 0 ) . ( 2 0 ) D . Stmup and E. J. Colin, Tars J U U R N A L , 57, 179-1 (l!l%j.
Sept. 20, 1959
ALLYLICBROMINATION BY N-BROMOSUCCINIMIDE
tate and the uncharged bromoacetamide, no longrange electrostatic forces can be involved. It must be concluded that both reagents are being concentrated in the region occupied by the polymer since they are better solvating agents than water. This effect apparently more than compensates for t h a t to be expected due to the concentration of dipolar groups. Conclusions.-The results of this investigation show that uncharged reagents may react with functional groups of polyelectrolytes a t rates differing substantially from those characterizing monofunctional or bifunctional analogs. This phenomenon is probably the result of a concentration of the low molecular weight reagent in the region occupied by the swollen polymer coil. I n
[CONTRIBUTION FROM
N-Bromosuccinimide.
THE
4563
the poly-(vinylpyridine betaine) reaction this seems to be due to mutual attraction of the hydrophobic residues, while the high reaction rates with poly-(methacrylic acid) appear to be a consequence of a cooperative effect involving interaction of several groups of the polymer with the second reagent. Although this is formally analogous to the presumed principle of enzyme action, it must be emphasized t h a t the enhancement of the reaction rate reported in the present study represents a relatively minor effect. Acknowledgment.-A constructive criticism of the manuscript by Professor M. L. Bender is gratefully acknowledged. BROOKLYN 1, N. Y.
DEPARTMENT O F CHEMISTRY, UNIVERSITY O F
\vASHISGTOS]
I. Allylic Bromination, a General Survey of Reaction Variable~l-~
BY HYP J. DAUBEN, JR.,
AXD
LAYTON L. McCou4
RECEIVED DECEMBER 31, 1958 The effect of environmental factors (oxygen, light), reactant impurities (water, hydrogen bromide, bromine, hydroperoxides) and added substances of potential catalytic or inhibitory activity on the course and the relative reaction times of the reaction of N-bromosuccinimide (NBS) with cyclohexene in refluxing carbon tetrachloride has been investigated, Successive removal of reactant impurities and of environmental factors leads t o increasingly longer reaction times and ultimately t o very slow allylic bromination and increased bromine addition, presumably due t o bromine formed by the reaction of NBS with hydrogen bromide eliminated thermally from the allyl bromide product. Initiation of the usual preparative allylic brominations is attributable t o allyl hydroperoxides, inadvertently present in the alkene due to prior autoxidation. Comparative reaction times, using cyclohexene with or without its hydroperoxide, for runs with and without added substances have shown t h a t bromanil, picric acid, s-trinitrobenzene and iodine function as inhibitors or retarders and t h a t three classes of compounds a c t as accelerators: ( a ) known radical generators (azo-bis-isobutyronitrile, benzoyl peroxide, tetralyl and cyclohexenyl hydroperoxides); ( b ) bromine generators with NBS (bromine, hydrogen bromide, water, ethanol, thiophenol); (c) t-amines (triethylamine, pyridine). From effectivity and reactivity orders i t is evident t h a t ( i ) retarders-inhibitors act on t h e chain-carrying succinimidyl radicals, (ii) known radical sources initiate the reaction by thermal primary dissociation, except for hydroperoxides, which probably also show radical-induced decomposition and oxidation-reduction decomposition with NBS, (iii) bromine, alone or from its congeners, thermally or photochemically yields bromine radicals t o catalyze the reaction, and (iv) t-amines accelerate the reaction in the absence of peroxides by a n oxidation-reduction decomposition reaction with NBS aiid in the presence of peroxides additionally by a n oxidation-reduction decomposition reaction with the hydroperoxide. Definition of the mechanism of action of t-amines with NBS provides rational explanation of the earlier antagonistic report (Braude and Waight) of predominant bromine addition t o alkenes. I n light of new evidence, the mechanism of the allylic bromination reaction must involve different initiation and termination reactions from those proposed by Bloomfield. I n its simplest form, initiation results from thermal or photochemical dissociation of initiators to radicals t h a t react with NBS or alkene to produce the propagation radicals, propagation involves a chain reaction of succinimidyl radicals with alkene and of allyl radicals with NBS, the former probably being rate-determining, and termination presumably occurs by the interaction of two succinimidyl radicals to produce not the coupling product, bis-N-succinimidyl, but instead other stable products, possibly succinimide and acryl isocyanate.
Since 1942, when Ziegler and co-workers5 first reported t h a t N-bromosuccinimide (NBS) could be used to effect allylic brominations of alkenes, many papers concerned with NBS, N-chlorosuccinimide (NCS) and related compounds have been published, and several review articles summarizing these findings have appearede6 Most of these publications (1) Presented in part before the 118th Meeting of the American Chemical Society, Chicago, Ill., Sept., 19.50 (Abstracts, p. 11-N). (2) Taken from the Ph.D. Thesis of Layton L. McCoy, University of Washington, 1951. (3) Supported in part by research contract No. N8-onr-52007 with the Office of Naval Research, U. S. Navy. (4) Predoctoral Fellow, Atomic Energy Commission, 1950-1951. ( 5 ) K. Ziegler, A. Spath, E. Schaaf, W. Schumann and E . Winklemann, A n n . , 551, 80 (1942). (6) (a) C. Djerassi. Chem. Reus., 43, 271 (1948): (b) W. Ringli, “Rromierungen mit Bromsiiccinimid,” Leeman, Zurich, 1948; (c) T. D. Waugh, “NBS, I t s Reactions and Uses,” Boulder, Colo., Arapahoe Chemicals, Inc., 1951; (d) N. P. Buu-Hoi, Record Chem. Prop., 13,
have dealt with synthetic applications of these reagents. Some have involved studies of certain aspects of the mechanism of side-chain (benzylic) chlorination or bromination,’ and others have obtained certain results, usually incidental to other objectives,s bearing on the mechanism of allylic bromi30 (1952); (e) R. Oda and M. Nomura, K a g a k u , 8 , 428 (1033); (f) T. Kubota, ibid., 10, 5 5 5 (1935). :7) (a) J. Adam. R. A. Gosselain and P. Goldfinger, Bull. soc. chim. Belges, 6 5 , 523 (1950); P. Goldfinger, P. A. Gosselain and R. H. Martin, Nature, 168, 30 (1931); 51.F. Hebbelynck and R . H. Martin, B d l . SOL. chim. Belges, 69, 193 (1950) : (b) E. C. Kooyman, R. Van Helden and A. F. Bickel, Koninkl. h’ed. A k a d . Welenschappen Proc., B56, 75 (1953); (c) 0. 0. Orazi, R. A. Corral and E. Colloccia, Anales asoc. quim. Argentina. 43, 55 (195.5); 0. 0. Orazi, N. M. I. hlercere, R. A. Corral and J. hleseri, ibid., 40, 91 (1952); H. J. Schumacher, 0. 0. O r a d and R. A. Corral, ibid., 40, 19 (1952); (d) F. D. Greene, W. A. Remers and J. W. Wilson, THISJOURNAL, 7 9 , 1416 (1957); (e) K . B. Wiberg and L. H. Slaugh, ibid., 80, 3033 (1958). (8) (a) M. G. Ettlinger, Ph.D. Thesis, Harvard University, 1945; cf. rel. Ga; (b) G. F. Bloomfield, J . Chem. Soc., 114 (1944); (c) H.
