Halogenations of Anthracenes and Dibenz[a,c]anthracene with N-Bromosuccinimide and N-Chlorosuccinimide

Article abstract of DOI:10.1021/jo991495h

Halogenation of dibenz[a,c]anthracene (1) by NBS in CCl₄ affords the products of 9- and 10-monobromination in the ratio of 9:1. The reaction is accelerated by iodine, and HBr effects rearrangement of 9-bromo product to the sterically less crowded 10-bromo isomer. The mechanism is proposed to involve reversible addition of Br₂, followed by elimination of HBr. Reaction of NCS with 1 in CCl₄ requires addition of HCl and affords exclusively 9-chlorination. The different reactivities of NBS and NCS are ascribed to the relative amounts of free halogen produced (due to differences in N-X bond strengths involving Br and Cl), and the different sizes of the halogens. Under similar conditions, NCS chlorinates 9-bromoanthracene (2a) to afford 9,10-dichloroanthracene and 9-bromo-10-chloroanthracene in the ratio of 65:35. This reaction ostensibly occurs by addition of Cl₂ to 2a, followed by preferential loss of HBr rather than HCl. 9-Methylanthracene (3) affords exclusively 9-(bromomethyl)anthracene with NBS in the absence of iodine, but mainly (67%) 9-bromo-10-methylanthracene in the presence of iodine. Chlorination of 3 with NCS in the presence of HCl also affords mostly (65%) nuclear halogenation. Nuclear bromination of anthracene, 9-methylanthracene, and dibenz[a,c]anthracene by NBS in the absence of added HBr is accelerated by iodine. This effect is probably due to an increase in the amount of bromine produced from NBS in the presence of iodine.

Full text of DOI:10.1021/jo991495h

J . Org. Chem. 2000, 65, 3005-3009
3005
Ha logen a tion s of An th r a cen es a n d Diben z[a ,c]a n th r a cen e w ith
N-Br om osu ccin im id e a n d N-Ch lor osu ccin im id e1
Shaoming Duan, J eff Turk, J oseph Speigle, J ean Corbin, J ohn Masnovi,* and
Ronald J . Baker
Department of Chemistry, Cleveland State University, Cleveland, Ohio 44115
Received September 22, 1999
Halogenation of dibenz[a,c]anthracene (1) by NBS in CCl4 affords the products of 9- and
10-monobromination in the ratio of 9:1. The reaction is accelerated by iodine, and HBr effects
rearrangement of 9-bromo product to the sterically less crowded 10-bromo isomer. The mechanism
is proposed to involve reversible addition of Br2, followed by elimination of HBr. Reaction of NCS
with 1 in CCl4 requires addition of HCl and affords exclusively 9-chlorination. The different
reactivities of NBS and NCS are ascribed to the relative amounts of free halogen produced (due to
differences in N-X bond strengths involving Br and Cl), and the different sizes of the halogens.
Under similar conditions, NCS chlorinates 9-bromoanthracene (2a ) to afford 9,10-dichloroanthracene
and 9-bromo-10-chloroanthracene in the ratio of 65:35. This reaction ostensibly occurs by addition
of Cl2 to 2a , followed by preferential loss of HBr rather than HCl. 9-Methylanthracene (3) affords
exclusively 9-(bromomethyl)anthracene with NBS in the absence of iodine, but mainly (67%)
9-bromo-10-methylanthracene in the presence of iodine. Chlorination of 3 with NCS in the presence
of HCl also affords mostly (65%) nuclear halogenation. Nuclear bromination of anthracene,
9-methylanthracene, and dibenz[a,c]anthracene by NBS in the absence of added HBr is accelerated
by iodine. This effect is probably due to an increase in the amount of bromine produced from NBS
in the presence of iodine.
In tr od u ction
in CCl4 has been proposed to occur by electrophilic
aromatic substitution,9 whereas bromination of an-
thracene was proposed to involve a radical chain with
bromine atom carriers.10
N-bromosuccinimide (NBS) and N-chlorosuccinimide
(NCS) commonly are used to effect allylic and aromatic
halogenations.2 Despite the wide usage of these haloge-
nating agents, many aspects of the mechanism of halo-
genation remain controversial. Allylic bromination by
NBS generally is described as a free radical chain
reaction. This process originally was proposed to involve
succinimidyl radicals,3,4 but more recently studies have
implicated bromine atoms,5 or an equilibrium between
both radicals,6 as chain carriers. A similar mechanism
for allylic chlorination by NCS may be presumed.
Nuclear halogenations of aromatic compounds with
NBS and NCS to form haloarenes also are known. In
polar solvents, the mechanisms probably are electrophilic
aromatic substitutions7 and involve molecular halogen.8
The mechanism for nuclear halogenation of aromatic
compounds in nonpolar solvents is less clear. For ex-
ample, nuclear bromination of methylanisoles with NBS
Recently, we desired the regiospecifically defined nitrile
of dibenz[a,c]anthracene (1), 9-cyanodibenz[a,c]anthracene
(1g), for which no synthesis has been reported. Chloro-
sulfonyl isocyanate has been used effectively for cyana-
tions of related aromatic hydrocarbons.11 However, chlo-
rosulfonyl isocyanate failed to react with 1 under a
variety of conditions. Steric effects likely are responsible
for the unreactivity of 1 toward CSI. An alternative
convenient, efficient, and general synthetic route for
cyanation of arenes involves halogenation followed by
reaction of the aryl halide with cuprous cyanide.12,13 Use
of NBS to halogenate 114 (the Wohl-Ziegler reaction15
)
was reported to afford 9-bromodibenz[a,c]anthracene
(1a ),16a the desired precursor to 1g. We found that the
nature of the products obtained from this reaction is
sensitive to the reaction conditions.1 This result led us
to pursue the present study concerning the effects of
(1) Taken in part from the Ph.D. Dissertation of S. Duan, Depart-
ment of Chemistry, Cleveland State University, 1996.
(2) Horner, L.; Winkelmann, E. H. Angew. Chem. 1959, 71, 349.
Thaler, W. A. Methods Free-Radical Chem. 1969, 2, 121. Bovonsombat,
P.; McNelis, E. Synthesis 1993, 237.
(3) Bloomfield, G. F. J . Chem. Soc. 1944, 114.
(4) Dauben, J r., H. J .; McCoy, L. L. J . Am. Chem. Soc. 1959, 81,
4863.
(5) Incremona, J . H.; Martin, J . C. J . Am. Chem. Soc. 1970, 92, 627.
Kim, S. S.; Lee, C. S.; Kim, C. C.; Kim, H. J . J . Phys. Org. Chem. 1990,
3, 803. Day, J . C.; Katsaros, M. G.; Kocher, W. D.; Scott, A. E.; Skell,
P. S. J . Am. Chem. Soc. 1978, 100, 1950.
(6) Chow, Y. L.; Zhao, D. C. J . Org. Chem. 1987, 52, 1931.
(7) Braeuniger, H.; Kleinschmidt, E. G. Pharmazie 1969, 24, 140.
(8) (a) Eberson, L.; Finkelstein, M.; Folkesson, B.; Hutchins, G. A.;
J onsson, L.; Larsson, R.; Moore, W. M.; Ross, S. D. J . Org. Chem. 1986,
51, 4400. (b) An electron-transfer mechanism recently was proposed:
Eberson, L.; Hartshorn, M. P.; Radner, F.; Persson, O. J . Chem. Soc.,
Perkin Trans. 2 1998, 59.
(9) Gruter, G.-J . M.; Akkerman, O. S.; Bickelhaupt, F. J . Org. Chem.
1994, 59, 4473.
(10) Mayo, D. W.; Pike, R. M.; Trumper, P. K. Microscale Organic
Laboratory, 3rd ed.; Wiley: New York, 1994; pp 392-396.
(11) Dhar, D. N.; Murthy, K. S. K. Synthesis 1986, 437.
(12) Friedman, L.; Shechter, H. J . Org. Chem. 1961, 26, 2522.
(13) Newman, M. S.; Boden, H. J . Org. Chem. 1961, 26, 2525.
(14) Weinshenker, N. M. Org. Prep. Proc. 1969, 1, 33.
(15) Buu-Hoi, N. P. Ann. Der Chem. 1943, 556, 1. Barnett, E. D.;
Cook, J . W. J . Chem. Soc. 1925, 125, 1086. Bartlett, P. D.; Cohen, S.
G.; Cotman, J . D., J r.; Kornblum, N.; Landry, J . R.; Lewis, E. S. J .
Am. Chem. Soc. 1950, 72, 1003.
(16) (a) Harvey, R. G.; Aboshkara, E.; Pataki, J . Tetrahedron 1997,
53, 15947. (b) The chemical shifts of 1a appear at a higher field in the
crude reaction mixture than in the isolated product and shift to a lower
field as the reaction progresses, indicative of some dynamic process
involving 1a , such as shown in Scheme 1.
10.1021/jo991495h CCC: $19.00 © 2000 American Chemical Society
Published on Web 04/26/2000

3006 J . Org. Chem., Vol. 65, No. 10, 2000
Duan et al.
Sch em e 1
Sch em e 2
reaction conditions on the products obtained in halogena-
tions of anthracene and its derivatives with NBS and
NCS.
Discu ssion
Bromination of anthracene (2) with NBS in CCl4
affords 9-bromoanthracene (together with a small amount
of 9,10-dibromoanthracene) in good yield. The reaction
is accelerated markedly by the presence of iodine, a
known retarder of free radical brominations.4 Like an-
thracene, the meso (e.g., 9-) positions of dibenz[a,c]-
anthracene are the most reactive. Bromination of 1 with
NBS in CCl4 proceeds very slowly in the absence of iodine
and affords a mixture of about 90% 9-bromodibenz[a,c]-
anthracene (1a ) and 10% 10-bromodibenz[a,c]anthracene
(1b) whether or not iodine is present (Scheme 1). Bro-
mination at the less reactive 10-position of 1 likely is due
to steric hindrance about the meso positions.4 Over time,
1a rearranges to afford 1b. This rearrangement is
promoted by additives that produce HBr, such as Br2,4
excess NBS, or HBr itself. These results are best ex-
plained by a mechanism involving reversible electrophilic
addition of halogen to the arene,17 followed by the
elimination of hydrogen halide (Scheme 1).16b The effect
of I2 to accelerate, rather than retard, the reactions of 1
and 2 indicates that a free-radical process is not directly
involved.
Under the same conditions, recrystallized NCS did not
react with 1 unless a catalytic amount of HCl was added.
In the presence of HCl, excess NCS and 1 afforded
exclusively 9-chlorodibenz[a,c]anthracene, 1c (Scheme 1),
and 9,10-dichlorodibenz[a,c]anthracene from the subse-
quent reaction of 1c with excess NCS. The regiochemistry
of the reaction was verified by cyanation12 of both 1a and
1c to the same 1g.18 The requirement for HCl presumably
arises from the need to generate sufficient Cl2 for the
reaction to proceed. We attribute the lower reactivity of
NCS compared to NBS to the greater strength of a N-Cl
bond compared to a N-Br bond.19 Thus, the amount of
chlorine produced from NCS (in the absence of added
HCl) will be much less than the amount of bromine
produced from NBS under similar conditions. Further-
more, chlorine is smaller and more reactive than bro-
mine, so that steric effects are less important.20 Chlori-
nation then occurs exclusively at the most reactive (meso)
positions of 1.
To test this mechanism, halogenations of several
substituted anthracenes were examined. First, chlorina-
tion of 9-bromoanthracene (2a ) by NCS in CCl4 was
examined. If halogenation of anthracenes with NBS and
NCS generally proceeds by addition of halogen, then 2a
will afford 9,10-dichloroanthracene (2d ) by elimination
of HBr (Scheme 2). In fact, 2d was the principal (65%)
primary product from this reaction. A lesser amount of
9-bromo-10-chloroanthracene (35%), produced by elimi-
nation of HCl, also formed. The preferential elimination
of HBr rather than HCl reflects the better leaving group
ability of bromide compared to chloride.
Competition studies in reactions of anthracene, 2a , and
9-chloroanthracene (2c) revealed that the reactivity of
the haloanthracenes toward NCS in CCl4 is comparable,
and anthracene is about 20 times more reactive than
either. This result may be explained by a combination of
inductive and steric effects. The steric effect of a bromine
substituent will be larger than that for chlorine, which
would compensate for the greater deactivating inductive
effect of a chlorine substituent. Importantly, 2c was found
not to be a significant product from chlorination of 2a .
Since 2a and 2c react at similar rates, substantial 2c (if
formed) should be observed at early times in the reaction
of 2a with NCS. This result rules out the intermediacy
of 2c in the formation of 2d from chlorination of 2a , and
it is consistent with the observation of formation of 2d
as a primary product.
Halogenation of 9-methylanthracene (3) was investi-
gated to address the effect of iodine on the reaction.
Reaction of 3 with NBS in CCl4 occurs slowly in the
absence of iodine to afford solely 9-(bromomethyl)an-
thracene, 3b (Schemes 3). 3b reacts even more slowly
(17) (a) Halogenations of anthracenes proceed, at least in part, by
addition intermediates: de la Mare, P. B. D.; Ridd, J . H. Aromatic
Substitution; Academic Press: New York, 1959; p 174. (b) Although
ionic mechanisms cannot be ruled out, nonionic reactions should be
preferred in solvents of low polarity (such as CCl4): Hubig, S. M.; J ung,
W.; Kochi, J . K. J . Org. Chem. 1994, 59, 6233.
(18) Single-crystal X-ray analysis of 1g demonstrated the presence
of steric crowding near the cyano group, which is slightly bent (the
C-CtN bond angle is 174.3(7)°), and the aromatic system is highly
nonplanar.
(19) The homolytic dissociation energy of N-Cl bonds is about 0.7
eV larger than that of the corresponding N-Br bonds: Andrieux, C.
P.; Differding, E. D.; Robert, M.; Save´ant, J .-M. J . Am. Chem. Soc.
1993, 115, 6592.
(20) Kaeding, W. J . Org. Chem. 1961, 26, 4851.

Halogenations of Anthracenes with Succinimides
J . Org. Chem., Vol. 65, No. 10, 2000 3007
Sch em e 3
methylanthracene, 3c, 65%) and radical-derived (9-
(chloromethyl)anthracene, 3d , 35%) products. However,
iodine did not affect the yield for nuclear chlorination;
the main effect of iodine was to divert formation of 3d to
lepidopterene. The 9-(halomethyl)anthracenes were shown
independently to react slowly in the presence of iodine
to form lepidopterene (Scheme 3).21 Preferred nuclear
substitution by chlorine, and the absence of an effect of
iodine on this process, may be due to the presence of a
relatively high concentration of Cl2 formed by the addi-
tion of HCl to the reaction medium.25
Con clu sion
Dibenz[a,c]anthracene halogenates with NBS in CCl4
to afford 9- and 10-monobromination products 1a and 1b
in the ratio 90:10. The reaction is accelerated by iodine,
and HBr effects rearrangement of 1a to the sterically less
crowded 1b. The mechanism is proposed to involve
reversible addition of Br2, followed by elimination of HBr.
Reaction of NCS with 1 requires addition of HCl and
affords exclusively meso chlorination. The difference in
reactivities of NBS and NCS is ascribed to the relative
amounts of free halogen produced (due to differences in
bond strengths involving Br and Cl), and the different
sizes of the halogens. The 9- and 10-halodibenzan-
thracenes can be cyanated with CuCN to afford the
respective cyano derivatives without rearrangement.
Consistent with the proposed mechanism, NCS chlo-
rinates 9-bromoanthracene to afford mostly 9,10-dichlo-
roanthracene. 9-Methylanthracene affords exclusively
9-(bromomethyl)anthracene with NBS in the absence of
iodine, but mainly 9-bromo-10-methylanthracene in the
presence of iodine. Iodine also accelerates the nuclear
bromination of 3, as well as that of anthracene itself,
when the reaction is performed with NBS in the absence
of added HBr. Acceleration of nuclear bromination by
iodine probably is due to an increase in the amount of
bromine produced in the presence of iodine.
with NBS to afford 9-bromo-10-(bromomethyl)anthracene.
Addition of iodine not only accelerates the rate of reaction
of NBS with 3 but also affords a new product, 9-bromo-
10-methylanthracene (3a ), in 67% yield, together with a
lesser amount (31%) of 3b. These products do not
interconvert under the reaction conditions.21 Benzylic
bromination of 3 in CCl4 in the absence of iodine occurs
by a free radical mechanism. The sluggish reaction of the
3b product by a subsequent nuclear bromination, rather
than by a second benzylic halogenation to form 9-(dibro-
momethyl)anthracene, probably is due to the conforma-
tion of the bromomethyl substituent, which precludes
alignment of the methylene hydrogens with the an-
thracene π system, as observed for 9-alkylanthracenes.23
Comparison of relative reaction rates indicates that
iodine promotes nuclear bromination by accelerating the
aromatic substitution. This may happen by generation
of hydrogen halide (HI or HBr), which increases the
amount of free Br2 present. The observation that 1a and
1b form in essentially the same ratio from 1 in the
presence and absence of iodine, even though reaction is
accelerated in the presence of iodine, suggests that the
same halogenating agent is responsible for the nuclear
brominations whether iodine is present or not.24 This
mechanism is in agreement with studies of methylben-
zenes and NBS, which indicate that nuclear halogenation
occurs by electrophilic aromatic substitution.7,9 Similar
product ratios in reactions of anthracene using NBS and
molecular bromine also are consistent with this proposal.
Chlorination of 3 with NCS in the presence of a catalytic
amount of HCl afforded analogous nuclear (9-chloro-10-
Exp er im en ta l Section
Ma ter ia ls. Anthracene (MCB), dibenz[a,c]anthracene (Al-
drich), 9-chloroanthracene (Aldrich), 9,10-dichloroanthracene
(Aldrich), 9-methylanthracene (Aldrich), 9-(chloromethyl)an-
thracene (Aldrich, N-bromosuccinimide (Aldrich), iodine (Fisher),
and anhydrous carbon tetrachloride (Aldrich) were used as
received. N-Chlorosuccinimide (Aldrich) was recrystallized
from benzene. 9-Bromoanthracene was prepared by bromina-
tion of anthracene with NBS.10 9-Bromodibenz[a,c]anthracene
and 10-bromodibenz[a,c]anthracene were prepared by a lit-
erature procedure.16a
Products were identified by mixed mp (mmp) and by 1H and
13C NMR spectra (spiking the samples with small amounts of
authentic materials), and volatile products (haloanthracenes)
were identified by GC/MS. Crude products were quantified by
1H NMR, as well as by GC/MS where indicated for the
halogenated anthracenes.
Br om in a tion of Diben z[a ,c]a n th r a cen e. To dibenz[a,c]-
anthracene, 1, (84 mg, 0.30 mmol) and N-bromosuccinimide
(53 mg, 0.30 mmol) in carbon tetrachloride (5 mL) was added
a catalytic amount of iodine (one drop of a solution containing
0.2 g of iodine in 10 mL of CCl410). The reaction mixture was
heated at reflux for 24 h under a nitrogen atmosphere. The
warm mixture was filtered through a Hirsch funnel and the
effluent concentrated under reduced pressure. Analysis of the
(21) In the presence of iodine, 9-(bromomethyl)anthracene slowly
is transformed into lepidopterene,22 a process characteristic of the
formation of the 9-anthrylmethyl radical. The failure to observe 1,2-
di(9-anthryl)ethane can be ascribed to the low concentration of alkyl
radicals, which discourages dimerization. For example, a low concen-
tration of 9-anthrylmethyl radicals may add to the 10- position of
9-(bromomethyl)anthracene as the first step in formation of lepidop-
terene, Scheme 4.
(22) Becker, H.-D.; Andersson, K.; Sandros, K. J . Org. Chem. 1980,
45, 4549.
(23) Thus, an “inverted” reactivity order was reported for hydrogen
atom abstraction by bromine from 9-alkylanthracenes, with reactivity
decreasing for methyl (1.00) > ethyl (0.063) . isopropyl (<0.0001):
Tanko, J . M.; Mas, R. H. J . Org. Chem. 1990, 55, 5145.
(24) Other halogenating agents, such as IBr, also may be expected
to afford nuclear bromination. For example, chlorination is reportedly
the sole reaction of ICl with anthracene: Turner, D. E.; O’Malley, R.
F.; Sardella, D. J .; Barinelli, L. S.; Kaul, P. J . Org. Chem. 1994, 59,
7335.
(25) It also is possible that chlorine has a greater propensity toward
addition to methylanthracene, or the addition may be less reversible,
than bromine.

3008 J . Org. Chem., Vol. 65, No. 10, 2000
Duan et al.
Sch em e 4
1
crude reaction mixture by H NMR revealed 70% conversion
to a 90:10 mixture of 1a :1b. Reactions under otherwise
identical conditions but containing no iodine afforded after 7
days 10% conversion to an 85:15 mixture of 1a :1b.
9,14-Dich lor od iben z[a ,c]a n th r a cen e (1f): mp 200-201
1
°C; H NMR 9.08 (2H, dd, 8.3, 1.3 Hz), 8.60 (2H, dd, 6.6, 3.2
Hz), 8.35 (2H, dd, 8.0, 1.2 Hz), 7.73 (2H, dd, 6.5, 3.3 Hz), 7.60
(2H, td, 7.6, 1.3 Hz), 7.50 (2H, td, 7.7, 1.4 Hz); 13C NMR 131.56,
130.78, 129.35, 129.12, 129.03, 128.71, 127.84, 126.51, 126.19,
125.50, 123.62. Anal. Calcd for C22H12Cl2: C, 76.10; H, 3.48.
Found: C, 76.78; H, 3.41.
The structure of 1c was verified by chemical conversion to
9-cyanodibenz[a,c]anthracene (1g), which was identical to 1g
prepared from 1a (see below).
Prolonged reflux of the crude product mixture led to a
gradual change in the isomer distribution. For example, after
7 days, this ratio was 60:40 for the reaction performed in the
presence of iodine. The rate of isomerization was accelerated
by HBr. When the reaction was performed (without iodine) in
the presence of a catalytic amount of bromine (a drop of a
dilute solution in CCl4) or a small excess (0.06 mmol) of NBS,
the initial product (by 1H NMR) was predominantly the
9-bromo isomer. However, continued reflux for 18 h afforded
conversion to mostly 10-bromodibenz[a,c]anthracene. Thus,
repeated column chromatography of this product using Woelm
(activity I) alumina eluting fractionally with petroleum ether
and dichloromethane eventually afforded 16 mg (15%) of pure
9-bromodibenz[a,c]anthracene (1a ), 81 mg (76%) of 10-bro-
modibenz[a,c]anthracene (1b), and 4 mg (5%) of recovered 1,
identified by comparison with authentic samples.16a A trace
amount (about 1 mg) of a compound tentatively identified as
9,14-dibromodibenz[a,c]anthracene (1e) [with 1H NMR: 8.99
(2H, dd, 8.3,1.3 Hz), 8.60 (2H, dd, 6.6,3.2 Hz), 8.31 (2H, dd,
7.9,1.3 Hz), 7.71 (2H, dd, 6.6,3.2 Hz), 7.59 (2H, m), 7.48 (2H,
m)] also was isolated.
Ch lor in a tion of Diben z[a ,c]a n th r a cen e. A stirred mix-
ture of 1 (477 mg, 1.71 mmol) and N-chlorosuccinimide (457
mg, 3.42 mmol) and a catalytic amount (5-10 µL) of concen-
trated hydrochloric acid in carbon tetrachloride was heated
to reflux under a nitrogen atmosphere. The progress of the
reaction was routinely checked by TLC (Whatman silica gel
60 Å plates) and NMR. (Reactions under the same conditions
but containing no added HCl afforded no product.) After 2
days, the warm mixture was filtered and the filtrate concen-
trated under reduced pressure. Purification of the residue by
repeated chromatography (Woelm activity I alumina) eluting
fractionally with petroleum ether-dichloromethane afforded
342 mg (64%) of 1c, 150 mg (25%) of 1f, and 48 mg (10%) of
recovered 1.
9-Cya n od iben z[a ,c]a n th r a cen e (1g). A stirred mixture
of 1a (5.0 mg, 0.014 mmol), cuprous cyanide (2.5 mg, 0.028
mmol), and dimethylformamide (1 mL) was heated at reflux
overnight. The resulting brown complex of nitrile and cuprous
halide was poured into a solution of ferric chloride and
concentrated hydrochloric acid in water. The reaction mixture
was maintained at 60-70 °C for 30 min to decompose the
complex, after which the layers were separated. Extraction
with dichloromethane afforded a dark brown organic layer that
was filtered through a short column of silica gel, dried over
anhydrous sodium sulfate, and concentrated under reduced
pressure. The residue was recrystallized from benzene-
ethanol to give 3.8 mg (90%) of 1g as pale yellow needles: mp
1
210-211 °C; H NMR 9.64 (1H, td, 8.1, 2.4 Hz), 9.25 (1H, s),
8.66 (1H, dd, 6.3, 3.4 Hz), 8.58 (2H, m), 8.52 (1H, m), 8.13 (1H,
d, 8.2 Hz), 7.74 (4H, m), 7.68 (2H, m); 13C NMR 133.82, 132.95,
131.66, 131.04, 130.03, 129.71, 129.14, 128.93, 128.78, 128.73,
128.53, 128.06, 127.90, 127.63, 127.36, 127.30, 127.26, 125.65,
123.56, 123.54, 123.49, 119.99, 104.17; EI-MS (20 eV), 303 m/z
(100% RA). X-ray (from dichloromethane-toluene): space group
Pna21, a ) 7.5703(5) Å, b ) 9.5106(12) Å, c ) 20.2404(14) Å.
Anal. Calcd for C23H13N: C, 91.06; H, 4.32; N, 4.62. Found:
C, 91.19; H, 4.36; N, 4.45.
Alternatively, 350 mg (1.1 mmol) of 1c, 200 mg (2.2 mmol)
cuprous cyanide in 10 mL of N-methylpyrrolidone could be
used. (No reaction was observed in the lower boiling DMF
solvent.) The yield of 1g was 310 mg (93%) after flash
chromatography on silica gel (Baker, 43 µm), eluting fraction-
ally with petroleum ether and dichloromethane. This product
had mmp and NMR spectra identical to those of 1g prepared
from 1a .
10-Cya n od iben z[a ,c]a n th r a cen e (1h ). A stirred mixture
of 10-bromodibenz[a,c]anthracene (32 mg, 0.090 mmol), cu-
prous cyanide (16 mg, 0.18 mmol), and dimethylformamide (2
mL) was heated at reflux overnight. The resulting brown
complex of nitrile and cuprous halide was poured into a
solution of ferric chloride and concentrated hydrochloric acid
9-Ch lor od iben z[a ,c]a n th r a cen e (1c): mp 155-156 °C; 1H
NMR 9.40 (1H, dd, 8.1,1.5 Hz), 8.98 (1H, s), 8.63 (2H, m), 8.50
(2H, m), 8.08 (1H, dt, 8.8, 0.6 Hz), 7.64 (6H, m); 13C NMR
132.24, 131.75, 131.10, 130.35, 130.09, 130.02, 129.74, 128.93,
128.79, 128.31, 128.12, 128.01, 127.74, 127.33, 126.89, 126.57,
125.64, 125.36, 123.69, 123.25 (broad, possibly two peaks
overlapping), 120.71. Anal. Calcd for C22H13Cl: C, 84.48; H,
4.20. Found: C, 84.02; H, 4.15.

Halogenations of Anthracenes with Succinimides
J . Org. Chem., Vol. 65, No. 10, 2000 3009
in water. The reaction mixture was maintained at 60-70 °C
for 30 min to decompose the complex, after which the layers
were separated. Extraction with dichloromethane afforded a
dark brown organic layer that was filtered through a short
column of silica gel, dried over anhydrous sodium sulfate, and
concentrated under reduced pressure. The residue was recrys-
tallized from benzene-ethanol to give 26 mg (95%) of 10-
cyanodibenz[a,c]anthracene as a pale yellow powder: mp 206-
Ch lor in a tion of 9-Br om oa n th r a cen e a n d 9-Ch lor oa n -
th r a cen e. A stirred mixture of 2a (9.3 mg, 0.036 mmol), 2c
(6.3 mg, 0.030 mmol), N-chlorosuccinimide (2.9 mg, 0.022
mmol), and a catalytic amount (5-10 µL) of concentrated
hydrochloric acid in carbon tetrachloride (1 mL) was heated
to reflux under a nitrogen atmosphere. The progress of the
reaction was monitored by 1H NMR, and aliquots were
sampled after about 5%, 10%, and 30% conversion. The initial
rates of disappearance of the haloanthracenes were nearly the
same, and proportional amounts (ratio 1.1:1) remained after
about 30% of the NCS was consumed.
Br om in a tion of 9-Meth yla n th r a cen e in th e P r esen ce
of Iod in e. To a suspension of 54 mg (0.28 mmol) of 9-methyl-
anthracene (3) and 50 mg (0.28 mmol) of NBS in 0.4 mL of
carbon tetrachloride was added a catalytic amount of iodine
(one drop of a solution containing 0.2 g of iodine in 10 mL of
CCl410). The mixture was heated at reflux for 1 h. Analysis by
1H NMR revealed 97% conversion to 9-bromo-10-methylan-
thracene,27,28 3a (67%), 9-(bromomethyl)anthracene,27,29 3b
(31%), and 9-bromo-10-(bromomethyl)anthracene,30 3e (2%).
Purification by column chromatography (activity III Woelm
alumina eluting fractionally with hexanes and dichloromethane,
and then methanol) afforded 40 mg (53%) of 3a and 10 mg of
(13%) 3b, along with 10 mg (17%) of its hydrolysis product
9-(hydroxymethyl)anthracene.
1
207 °C; H NMR 9.09 (1H, s), 8.79 (1H, s), 8.63 (1H, m), 8.50
(1H, m), 8.42 (2H, m), 8.11 (1H, d, 8.4 Hz), 7.89 (1H, dd, 7.0,
1.0 Hz), 7.61 (4H, m), 7.48 (1H, dd, 8.4, 7.1 Hz); 13C NMR
133.31, 132.93, 131.00, 130.32, 130.15, 130.09, 129.53, 128.95,
128.90, 128.42, 128.20, 127.67, 127.48, 124.48, 123.99, 123.53,
123.33, 123.27, 123.23, 122.61, 119.00, 117.99, 109.91. Anal.
Calcd for C23H13N: C, 91.06; H, 4.32; N, 4.62. Found: C, 91.10;
H, 4.30; N, 4.59.
Br om in a tion of An th r a cen e w ith NBS. The effect of
iodine on the bromination of anthracene (2) was studied by
following the literature procedure10 in the presence as well as
the absence of iodine. Although 9-bromoanthracene (2a ) was
the major product (75% yield) in both cases (together with
about 10% 9,10-dibromoanthracene, 2b, and 5% anthraqui-
none, 10% unreacted 1 was recovered), the reaction was slower
by at least severalfold in the absence of iodine. This was
indicated by complete consumption of NBS within 1 h in the
presence of iodine, but only about 30% in the absence of iodine;
several additional hours were required for the NBS to be
consumed in the latter reaction. The isolated yield of 9-bro-
moanthracene from the literature procedure was 60% (al-
though anthracene and dibromoanthracene were not removed
by the workup described).
Br om in a tion of 9-Meth yla n th r a cen e in th e Absen ce
of Iod in e. A suspension of 54 mg (0.28 mmol) of 3 and 50 mg
(0.28 mmol) of NBS in 0.4 mL of carbon tetrachloride was
1
heated at reflux for 1 h, after which H NMR analysis revealed
8% conversion to 3b.27 Reflux for an additional 23 h followed
by analysis by 1H NMR revealed clean conversion to 3b in 98%
yield, together with 2% of 3e.30
Br om in a tion of An th r a cen e w ith Br om in e. Bromina-
tion of 2 with 1 equiv of molecular bromine at 0 °C afforded
essentially the same product mixture as reaction with NBS.
Recrystallization from ethanol failed to separate the an-
thracene and dibromoanthracene from bromoanthracene. Care-
ful column chromatography (activity I Woelm alumina, eluting
fractionally with petroleum ether and dichloromethane) af-
forded 6.5 g (45%) of relatively pure (g95%) 2a from a
preparative scale reaction starting with 10 g (56 mmol) of 2.
Ch lor in a tion of 9-Br om oa n th r a cen e. A stirred mixture
of 2a (50 mg, 0.19 mmol), N-chlorosuccinimide (5.2 mg, 0.039
mmol), and a catalytic amount (5-10 µL) of concentrated
hydrochloric acid in carbon tetrachloride (1 mL) was heated
to reflux under a nitrogen atmosphere. The progress of the
reaction was monitored by removal of a small aliquot and
analysis by 1H NMR. The crude reaction mixture was subjected
to NMR and GC/MS analysis to determine the identities of
the products and their ratio, which was invariant with reaction
time at low conversions of 2a . The products 9,10-dichloroan-
thracene (2d ) and 9-bromo-10-chloroanthracene26 (2e) were
identified by comparison with authentic compounds, and their
ratio was found to be 65:35. 9-Chloroanthracene (2c) was ruled
out as a potential product by comparison of the 1H NMR
spectrum of the crude reaction mixture with that of authentic
2c.
At this point, addition of a catalytic amount of iodine (one
10
drop of a solution containing 0.2 g of iodine in 10 mL of CCl4
)
followed by reflux for 24 h resulted in no isomerization.
However, prolonged reflux in the presence of iodine resulted
in the gradual conversion of to lepidopterene, 4.22 The residue
was taken up in hot cyclohexane and filtered and the filtrate
concentrated to afford 61 mg (80%) of 3b.
Use of 2 equiv of NBS in the absence of iodine accelerated
the initial formation of 3b, which was followed by a very slow
reaction to form 3e.30
Ch lor in a tion of 9-Meth yla n th r a cen e. A suspension of
54 mg (0.28 mmol) of 3, 37 mg (0.28 mmol) of NCS in 0.4 mL
of CCl4, and a catalytic amount (5-10 µL) of concentrated
1
hydrochloric acid was heated at reflux for 1 h. Analysis by H
NMR revealed conversion of 66% to form mostly (70%)
9-chloro-10-methylanthracene,28,31 3c, and 30% of either 9-(chlo-
romethyl)anthracene,29 3d , in the absence of iodine or 422 in
the presence of iodine. Column chromatography (activity III
Woelm alumina, eluting fractionally with petroleum ether and
dichloromethane) of the reaction performed in the absence of
iodine afforded 20 mg (32%) of 3c and 6 mg (9%) of 3d .
Ack n ow led gm en t. The authors thank Professor
Thomas W. Flechtner for helpful comments and the
Cleveland State University College of Graduate Studies
for support of this work.
No reaction between HCl and 1a occurred under these
conditions.
Ch lor in a tion of 9-Br om oa n th r a cen e a n d An th r a cen e.
A stirred mixture of 2a (18.2 mg, 0.071 mmol), 2 (6.4 mg,
0.036), N-chlorosuccinimide (5.7 mg, 0.043 mmol), and a
catalytic amount (5-10 µL) of concentrated hydrochloric acid
in carbon tetrachloride (1 mL) was heated to reflux under a
nitrogen atmosphere. The progress of the reaction was moni-
Su p p or tin g In for m a tion Ava ila ble: Instrumentation
and tables of crystallographic data, atomic coordinates, and
bond distances and angles for 9-cyanodibenz[a,c]anthracene.
This material is available free of charge via the Internet at
http://pubs.acs.org.
1
tored by H NMR, and aliquots were sampled after about 5%,
J O991495H
10%, 15%, and 20% conversion. The disappearance of bro-
moanthracene initially was much slower than that of an-
thracene, and after about 20% of the NCS was consumed, most
(27) Hartmann, M.; Raethe, M. Z. Chem. 1979, 19, 373.
(28) Mosnaim, D.; Nonhebel, D. C.; Russell, J . A. Tetrahedron 1969,
25, 3485; Gibson, S.; Mosnaim, D.; Nonhebel, D. C.; Russell, J . A.
Tetrahedron 1969, 25, 5047.
(29) Bentley, M. D.; Dewar, M. J . S. J . Org. Chem. 1970, 35, 2707.
(30) Rigaudy, D.; Seuleiman, A. M.; Nguyen, K. C. Tetrahedron
1982, 38, 3151. Masnaim, D.; Nonhebel, D. C. J . Chem. Soc. C 1970,
942.
1
of the original bromoanthracene remained. H NMR analysis
of the products revealed formation of 2c (92% based on NCS
consumed), 2d (4%), and 9-bromo-10-chloroanthracene, 2e
(2%).
(26) Nonhebel, D. C. J . Chem. Soc. 1963, 1216. Mosnaim, D. C.;
Nonhebel, D. C. Tetrahedron 1969, 25, 1591.
(31) House, H. O.; Ghali, N. I.; Haack, J . L.; Van Derveer, D. J . Org.
Chem. 1980, 45, 1807.