K-10 montmorillonite-catalyzed solid phase diazotizations: Environmentally benign coupling of diazonium salts with aromatic hydrocarbons to biaryls

Article abstract of DOI:10.1039/c7gc02804k

A new heterogeneous catalytic diazotization and subsequent coupling of diazonium salts with aromatics for the synthesis of biaryls is described. The method involves the solid phase diazotization of anilines and the successive C-C bond formation of the diazonium salt with alkylbenzenes. Excellent yields were obtained for a broad range of anilines and aromatic nucleophiles. The reaction was carried out using K-10 montmorillonite as an acid catalyst and medium as well. The high selectivity, metal-free, recyclable catalyst, easy work up, and absence of harmful waste make the process a sustainable alternative to available methods.

Full text of DOI:10.1039/c7gc02804k

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K-10 montmorillonite-catalyzed solid phase diazotizations:
environmentally benign coupling of diazonium salts with aromatic
hydrocarbons to biaryls
zReceived 00th January 20xx,
Accepted 00th January 20xx
Garima Pandey and Béla Török*
DOI: 10.1039/x0xx00000x
www.rsc.org/
A new heterogeneous catalytic diazotization and subsequent catalyzed cross coupling reactions between organometallic reagents
coupling of the diazonium salts with aromatics for the synthesis of (ArM, M =MgX, ZnX, SnR3, B(OH)2, SiFnR3-n) and aryl halides,
biaryls is described. The method involves the solid phase including the Suzuki-, the Negishi-, the Stille-, the Kumada- and the
diazotization of anilines and the successive C-C bond formation of Hiyama-couplings.22 Furthermore some other cross coupling
the diazonium salt with alkylbenzenes. Excellent yields were reactions, addressing the limitation of scope of the electrophile
obtained for a broad range of anilines and aromatic nucleophiles. component (Ar’X) by using O-aryl carbamates23 and sulfamates,24
The reaction was carried out using K-10 montmorillonite as an aryl sulfones,25 and aryl mesylates26 have been explored. Recently,
acid catalyst and medium as well. The high selectivity, metal-free, the oxidative- or dehydrogenative cross coupling has gained much
recyclable catalyst, easy work up, and absence of harmful waste attention for the construction of these scaffolds. Although these
make the process a sustainable alternative to available methods.
reactions are known as excellent, they use transition metals,
moisture sensitive organometalic compounds and suffer from a
variety of limitations for e.g. homocoupling, overoxidation, and
polymerization.27 The first metal-free direct oxidative aryl coupling
of anilides with aromatics using a stoichiometric hypervalent iodine
reagent has recently been reported.28 A similar organocatalytic
C−H/C−H' cross-biaryl coupling of unfunctionalized heteroaromatics
with aromatic compounds by using iodine(III) compound as oxidants
has extended the scope.29 Despite the advantages of these
reactions, they use stochiometric hypervalent iodine reagents thus
generating nonrecyclable iodine product (e.g. PhI) as waste.
Extending our efforts on developing heterogeneous catalytic
green processes,30 herein, we report a metal free solid acid-
catalyzed synthesis of biaryls by the coupling of anilines with
aromatic hydrocarbons as nucleophiles. This reaction involves an in
situ K-10 montmorillonite-catalyzed diazotization and subsequent
C-C bond formation by the nucleophile. This approach provides an
environmental benign, simple, convenient and low cost synthetic
route to the target compounds with excellent yields.
Introduction
Aryl-diazonium salts are extensively used as one of the most
1
promising substrates for organic synthesis, and their reactions in
aquous medium have been considered as an important tool for
green synthetic approaches.2-4 These salts are excellent
electrophilic agents in various transition metal-catalyzed cross
coupling reactions of C-C bond formation.5,6 They are synthesized by
the diazotization of inexpensive primary amines.1 The conventional
diazotization methods are limited to the use of sodium nitrite and
suffer from the harsh reaction condition of strong, corrosive acids
such as hydrochloric acid,6 sulfuric acid7 or p-toluenesulphonic
acid.8 A potential alternative, the commercially available acidic clay
catalyst, K-10 montmorillonite is an efficient, transition metal-free
catalyst for C-C bond formation reactions.9-12 It offers mild,
heterogeneous catalytic reaction conditions and is considered as an
environmentally benign substitute for harmful mineral acids. Its low
price, ease of use, recyclablility and the temperature-controlled
acidity make it a frequent choice for heterogenous solid acid
catalysis.13-16
Results and discussion
Based on our earlier success with K-10 montmorillonite it has
been selected as a catalyst for the target transformation.17 It is an
easily accessible and environmentally benign solid acid with acid
strength similar to that of ccHNO3.9 Its high surface area (250-300
m2/g), and stability under high temperature conditions makes it a
frequently used catalyst. In a recent work we have reported that in
the presence of NaNO2 K-10 catalyzed the partial diazotization of o-
Biaryls are an important class of organic compounds due to
their diverse presence in natural products, pharmaceuticals,
agrochemicals, ligands, polymers and organic materials.17 Their
classical syntheses include the Gomberg-Bachmann-Hey reaction,18
Pschorr cyclization,19 the Ullmann reaction20 and the Kharasch
coupling.21 The contemporary methods are based on Pd or Ni
phenylenediamines which concluded with
a ring closure to
benzotriazoles.31 Building upon this observation it was hypothesized
a.Department of Chemistry, University of Massachusetts Boston, 100 Morrissey
Blvd. Boston, MA 02125, USA; email: bela.torok@umb.edu
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J. Name., 2013, 00, 1-3 | 1
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that the solid phase diazotization followed by a nucleophilic attack
Journal Name
While pursuing the optimization the formatioVniewoAfrtiacle sOmnlianlel
may provide suitable conditions for C-C bond formation as well. amount of aniline self-coupling product waDsOreI:g1u0l.a10rl3y9o/Cb7sGeCrv0e2d8.0T4oK
Using aromatic hydrocarbons, such as mesytilene the reaction could avoid the self-coupling of aniline it was decided to study the effect
lead to biaryls. To achieve a suitable chemical process a broad range of the aniline/nucleophile ratio (Table 2). The gradual increase in
of reaction conditions were examined using aniline as a diazonium the amount of mesitylene appeared to further enhance the already
salt precursor and mesitylene as a nucleophile (Table 1).
high yields to an effectively quantitative reaction (Table 2, entry 3).
This optimization led to the establishment of a suitable protocol
for the reaction and these conditions (aniline (1 mmol), mesitylene
(2 mmol) K-10 (2 g), NaNO2 (2 eq), 110 °C for 15 h) were applied for
the extension of the scope of the process. In order to establish a
generally applicable methodology, a variety of substituted anilines
as well as alkylbenzenes were selected (Table 3).
Table 1. Optimization of reaction conditions for the synthesis of
biaryls by K-10 montmorillonite mediated solid phase diazotization
using the test reaction of aniline and mesitylene.a
Entry
K-10
(g)
NaNO2
(mmol)
0.5
1.0
1.5
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
T
(°C)
Time
(h)
1
1
1
1
1
1
1
1
3
6
10
15
Yield
(%)
12
15
25
35
37
39
20
29
65
79
85
95
Table 3. Synthesis of biaryl derivatives via the diazotization and
subsequent C-C bond formation of aniline with aromatic
nucleophiles by K-10 montmorillonite catalysis.a
1
2
3
4
5
6
7
8
9
0.5
0.5
0.5
0.5
1.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
110MW
110MW
110MW
110MW
110MW
110MW
90MW
100MW
110CH
110CH
110CH
110CH
entry
R1
R2
Time
(h)
Product
Yield
(%)b
1
H
H
H
15
15
15
90
98
98
2
1,3,5-
trimethyl
1,3,5-
trimethyl
3
3-Cl
2-F
10
11
12
4
5
1,3,5-
trimethyl
2.0
15
15
97
94
a1.0 mmol of aniline, 1.0 mmol of mesitylene and 1.5 mL water;
MWmicrowave irradiation; CH conventional heating
3-CF3
1,3,5-
trimethyl
6
7
8
9
4-Br
4-Et
3-Pr
3-Cl
1,3,5-
trimethyl
As the data show, the reaction occurred, however, with low
yield when aniline (1mmol), mesitylene (1mmol) and NaNO2 (0.5
eq) were reacted under microwave irradiation for 1h (Table 1 entry
1). While the increase in the amount of the NaNO2 and K-10
appeared to improve the yields up to 39% it has been clear that the
microwave heating was not ideal for the reaction (Table 1, entries
1-8). Selecting the best microwave-assisted conditions (Table 1
entry 6), the reaction was further optimized by conventional
heating. Surprisingly, conventional heating used under the same
parameters resulted in 65% yield in a short 3h reaction without any
byproduct formation (Table 1 entry 9). Additional increase in the
time of the conventionally heated reaction resulted in a gradual
increase in the yields (Table 1 entries 10-11). Finally, a 15h reaction
led to an excellent, 95% yield (Table 1 entry 12).
15
15
15
15
97
93
91
95
1,3,5-
trimethyl
1,3,5-
trimethyl
1,4-
dimethyl
10
11
12
2-F
4-Et
3-Cl
1,4-
dimethyl
15
15
99
1,4-
dimethyl
96
92
1,3-
dimethyl
24
24
13
14
15
4-Et
4-Br
H
Me
Me
94
88
24
24
Table 2. Optimization of the nucleophile amount for the synthesis
of biaryls by K-10 montmorillonite mediated solid phase
diazotization using the test reaction of aniline and mesitylene.a
1,2-diCl
85c
91
58d
16
17
H
H
Br
15
24
NO2
aReaction conditions: 1.0 mmol of aniline, 2.0 mmol of NuH, 2.0 g of K-10,
1.5 mL of water and 2.0 mmol of NaNO2; b GC-yields; c major product shown,
2,3-diCl-biphenyl:3,4-diCl-biphenyl=30:70; dat 150 °C, 3-NO2/4-NO2 = 75:25.
Entry
NuH
(mmol)
1
A
(Yield %)
95
B
(Yield %)
1
2
3
5
3
2
1.5
2.0
97
98
As illustrated the reaction showed only negligible substituent
effect; excellent yields were obtained for every aniline derivative
whether it possessed electron-withdrawing or electron-donating
a2 g of K-10, 2.0 mmol of NaNO2, 1.0 mmol of aniline, 1.5 mL water, 110 °C,
conventional heating, 15h
2 | J. Name., 2012, 00, 1-3
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substitutents. Even the strongly electron withdrawing CF3 group did becomes a partial C-electrophile and upon the nucleophilic attack
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DOI: 10.1039/C7GC02804K
not affect the yield negatively, although the reaction of 4-Et-aniline by mesitylene an N2 molecule leaves the system and a C-C bond is
with toluene and with m-xylene (Table 3, entry 12 and 13), the formed. Thus the reaction is proposed to be of Friedel-Crafts nature
reaction of 4-bromo-aniline with toluene (Table 3, entry 14) from the nucleophile’s point of view. This is supported by the
required longer reaction time. Considering the nucleophile, reactivity difference observed with different nucleophiles. The
benzene and substituted benzenes with electron donating respective initial reaction rates have been determined in a 3h long
substituents reacted smoothly and provided excellent yields. While reaction using identical conditions. The obtained yields and product
the presence of electron withdrawing substituents somewhat formation rates are: yieldmesitylene= 65%, rmesitylene= 2.17.10-1 mmol h-
decreased the reaction rates the reactions still proceeded with 1, yieldbenzene= 9%, rbenzene= 3.0.10-2 mmol h-1; yield1,2-diCl-benzene= 2%,
good to excellent yields using aniline with 1,2-dichlorobenzene r1,2-diCl-benzene= 6.67.10-3 mmol h-1. The reaction rates appear to
(Table 3, entry 15) or aniline and bromobenzene (Table 3, entry 16) gradually decrease parallel with the decrease in the nucleophilic
Interestingly, even the notoriously unreactive nitrobenzene strength of the aromatic hydrocarbon. Applying mesitylene resulted
provided acceptable yields (58%, Table 3, entry 17) indicating, that in one order of magnitude higher rate than that obtained with
this is a benign yet powerful system for the aryl coupling, although benzene and about two order of magnitude higher rates than that
this reaction required harsher conditions (150 °C, 24 h).
with 1,2-dichlorobenzene. These rate differences are in agreement
with the expectations based on the reactivity of these aromatic
compounds, using benzene as a standard of scale. Due to the
presence of the three methyl groups mesitylene is a highly active,
while the deactivating presence of the two chloro substituents
explain the lower reactivity of 1,2-dichlorobenzene. We have also
carried out an independent reaction by using a well-known radical
scavenger, Trolox,32 to observe whether its addition to the system
would modify the coupling reaction of aniline with mesitylene. The
presence of Trolox should block the reaction if it occurred via a
radical mechanism. As no change in reaction rate or yield was
observed compared to the control reaction (carried out in the same
time under identical conditions) it is concluded that the reaction
likely proceeds via electrophilic mechanism.
After establishing the scope of the reaction the recyclability of
the catalyst has been tested in several successive experiments. The
reaction of aniline and mesitylene was selected as
a test
transformation for this process. Based on earlier recycling
experiments the catalyst was washed with a small amount of ethyl
acetate containing a small amount of formic acid to remove
impurities from the surface and reactivate the catalyst. The air-
dried catalyst was then reused in the next reaction. The data of the
recycling experiments are shown in Fig. 1. The yields appear to
remain steady over five consecutive runs showing negligible decline
in activity indicating that the catalyst is recyclable in the
transformation.
Figure 1. Activity profile of the K-10 catalyst in five consecutive
applications using the solid phase one pot diazotization/coupling
reaction of aniline with mesitylene as nucleophile.
The reactions of diazonium salts commonly occur by ionic or
radical mechanisms. It is suggested that under acidic conditions the
diazonium salts react via a cationic intermediate, while the radical
mechanism is common under neutral or basic conditions in the
presence of an electron donor (e.g. Cu(0)).1 Since K-10 is considered
as a strong acid expecially at the reaction temperature, to explain
the likely mechanism of the reaction (Scheme 1) we propose that
the Brønsted acid centers of K-10 replace the Na-cation in the
nitrite and effectively produce HNO2 that initiates the diazotation
reaction. Once the diazonium salt is formed, the catalyst also serves
as a negative counterion to stabilize the it. We suggest that the
diazonium salt is highly reactive at this high temperature and
Scheme 1. Proposed reaction mechanism for the formation of
biphenyls via a one pot, domino K-10 montmorillonite catalyzed
solid phase diazotization and successive C-C bond formation
reaction of aniline and aromatics.
Conclusions
In conclusion we have developed an environmentally benign
solid acid catalyzed domino-style approach for the direct synthesis
of biaryls by diazotization and subsequent nucleophilic attack
leading to C-C bond formation. This new process represents several
advantages over the currently available methods such as (i) the
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(CDCl3, 100 MHz): δ(ppm) = 20.82, 21.26, 126.90, 127.75, 128.27,
intrinsic catalytic property of K-10 montmorillonite contributes to
both steps of the reaction (ii) the catalyst is commercially available,
stable and inexpensive; (iii) nobel metal assistance is not required,
reducing the overall toxicity of the system; (iv) the catalyst is
recyclable over repeated reactions; (v) the yields are nearly
quantitative; (vi) the easy work up procedure (simple filtration),
eliminates the need for typical purification processes; and finally
(vii) the high selectivity ensures that no (toxic or otherwise)
byproducts form. Based on the widespread industrial
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129.83, 134.31, 135.91, 137.17, 143.11. DMOIS::10C.103H9/CC7l:GC203208(0M4+K,
15 15
100%); 195(65%); 180(33%); 165(20%).
2'-fluoro-2,4,6-trimethylbiphenyl (Table 3, entry 4): 1H NMR
(CDCl3, 400 MHz): δ(ppm) = 2.05 (s, 6H), 2.36 (s, 3H), 6.98 (s, 2H),
7.15-7.20 (m, 2H), 7.21-7.23 (m, 1H), 7.32-7.38 (m, 1H). 13C NMR
(CDCl3, 100 MHz): δ(ppm) = 20.52, 21.12, 115.78 (d, JC-F = 23 Hz),
124.24, 128.22, 128.99 (d, JC-F = 9Hz), 132.45, 136.69, 137.50,
159.79 (d, JC-F = 252 Hz). 19FNMR (CDCl3, 376 MHz) δ(ppm) = -115.08
(pharmaceuticals, agrochemicals, and materials) interest in the - -115.14 (m) MS: C15H15F: 214(M+, 100%); 199(68%); 183(34%).
target compounds the new process could significantly decrease the
2,4,6-trimethyl-3'-(trifluoromethyl)biphenyl (Table 3, entry 5): 1H
environmental impact of traditional syntheses of biaryls.
NMR (CDCl3, 400 MHz): δ (ppm) = 2.00 (s, 6H), 2.35 (s, 3H), 6.98 (s,
2H), 7.36 (d, J= 8.0 Hz, 1H), 7.44 (s, 1H), 7.53-7.62 (m, 2H). 13C NMR
Experimental section
(CDCl3, 100 MHz): δ (ppm)= 20.08, 21.19, 123.64 (d, JC-F= 4.0 Hz),
All anilines and aromatics as well as the K-10 montmorillonite
125.73, 128.40 (d, JC-F= 3.0 Hz), 129.04 (t, JC-F= 8.0 Hz), 130.95 (d, JC-
were purchased from ThermoFisher Scientific and Sigma Aldrich
F= 32.0 Hz), 132.96, 135.91, 137.39, 137.59, 142.01. 19FNMR (CDCl3,
and used without further purification. Water used as solvent was
376 MHz) δ(ppm) = -62.5. MS: C16H15F3: 264(M+, 100%); 249(70%);
deionized water.
214(10%), 195 (40%), 179 (30%), 165(40%).
The mass spectrometric identification of the products has been
carried out by an Agilent 6850 gas chromatograph-5973 mass
4'-bromo-2,4,6-trimethylbiphenyl (Table 3, entry 6): 1H NMR
spectrometer system (70 eV electron impact ionization) using a 30
(CDCl3, 400 MHz): δ(ppm) = 2.01 (s, 6H), 2.34 (s, 3H) 6.96 (s, 2H),
1
m long DB-5 type column (J&W Scientific). The H and 13C spectra
7.03 (d, J= 8.0 Hz, 2H), 7.56 (d, J= 8.0 Hz, 2H). 13C NMR (CDCl3, 100
were recorded on a 400 MHz Agilent MR400DD2 spectrometer in
MHz): δ(ppm) =20.85, 21.19, 120.74, 128.30, 131.25, 131.74,
CDCl3, using tetramethylsilane or the residual solvent signal for
135.92, 137.07, 137.82, 140.09. MS: C15H15Br: 274(M+, 100%);
reference.
195(67%); 165(30%).
4'-ethyl-2,4,6-trimethylbiphenyl (Table 3, entry 7): 1H NMR (CDCl3,
General procedure K-10 montmorillonite (2.0 g), aniline (1.0
mmol) and NaNO2 (2.0 mmol) were suspended in 1.5 mL of water
and stirred for 5 min in a round bottom flask. Then the nucleophile
(2.0 mmol) was added into the reation mixture. After completing
the addition of nucleophile the reaction mixture was heated at
110°C for the desired time. After completion of the reaction, the
reaction mixture was allowed to cool to room temperature and
washed with 50 mL (2 X 25 mL) of hexane to dissolve the product
and the catalyst was removed by fitration. The biaryls were isolated
400 MHz): δ(ppm) = 1.30-1.34 (m, 3H), 2.05 (s, 6H), 2.36 (s, 3H),
2.72-2.75 (m, 2H), 6.97 (s, 2H), 7.08 (d, J= 8.0 Hz, 2H), 7.29 (d, J= 8.0
Hz, 2H). 13C NMR (CDCl3, 100 MHz): δ(ppm) =15.56, 20.84, 20.97,
28.71, 128.08, 128.18, 129.23, 136.31, 136.51, 138.31, 139.20,
142.36. MS: C17H20: 224(M+, 100%); 195(60%); 165(48%).
2,4,6-trimethyl-3'-propylbiphenyl (Table 3, entry 8): 1H NMR
(CDCl3, 400 MHz): δ(ppm) = 0.86-0.90 (m, 3H), 1.57-1.63 (m, 2H),
as oils after the evaporation of hexane and did not require further
purification. The spectral characteristics of the products are listed
below. The spectral data are in agreement with the structures.
1.91 (s, 6H), 2.23 (s, 3H), 2.52-2. 56 (m, 2H), 6.84 (s, 2H), 6.94 (d, J=
8Hz, 1H), 7.10-7.12 (m, 2H), 7.41 (d, J= 8Hz, 1H). 13C NMR (CDCl3,
100 MHz): δ(ppm) = 14.07, 20.94, 21.00, 24.65, 37.95, 128.13,
128.49, 129.20, 136.32, 136.50, 138.31, 141.86. MS: C18H22: 238(M+,
Catalyst recycling The portion of K-10 that was used in the
previous cycle was stirred in 5mL ethyl acetate and 200μL of formic
acid for 4h. The clay was then filtered and rinsed using two portions
of 15mL of ethyl acetate. Before reusing the catalyst for another
reaction, it was dried overnight at 90 °C.
100%); 209(64%); 165(37%).
3'-chloro-2,5-dimethylbiphenyl (Table 3, entry 9): 1H NMR (CDCl3,
400 MHz): δ(ppm) = 2.15 (s, 3H), 2.27 (s, 3H), 6.95 (s, 1H), 7.01 (d, J=
8.0 Hz, 1H), 7.07-7.13 (m, 2H), 7.23-7.28 (m, 3H) . 13C NMR (CDCl3,
100 MHz): δ(ppm) = 20.06, 21.12, 126.74, 127.33, 128.74, 129.20,
130.28, 132.19, 134.01, 135.47, 140.45, 144.04. MS: C14H13Cl:
216(M+, 100%); 181(100%); 165(100%).
1
biphenyl (Table 3, entry 1): H NMR (CDCl3, 400 MHz): δ (ppm) =
7.35 (t, J= 8.0 Hz, 2H), 7.44-7.46 (m, 4H), 7.58- 7.61 (m, 4H). 13C
NMR (CDCl3, 100 MHz): δ (ppm) = 127.31, 127.39, 128.90, 141.40.
MS: C12H10: 154.08 (M+, 100%).
2'-fluoro-2,5-dimethylbiphenyl (Table 3, entry 10): 1H NMR (CDCl3,
400 MHz): δ(ppm) = 2.19 (s, 3H), 2.38 (s, 3H), 7.07 (s, 1H), 7.13- 7.15
(m, 2H), 7.18-7.24 (m, 2H), 7.27-7.29 (m, 1H), 7.34-7.39 (m, 1H). 13
C
2,4,6-trimethylbiphenyl (Table 3, entry 2): 1H NMR: (CDCl3, 400
MHz): δ(ppm) = 2.01 (s, 3H), 2.03 (s, 3H), 2.34 (s, 3H), 6.97 (s, 2H),
7.14-7.16 (m, 2H), 7.17- 7.22 (m, 1H), 7.31-7.35 (m, 1H), 7.39-7.44
(m, 1H). 13C NMR: (CDCl3, 100 MHz): δ(ppm) = 20.52, 20.89, 126.63,
128.16, 128.48, 129.42, 136.11, 136.50, 139.18, 141.19. MS: C15H16:
196(M+, 100%); 181(67%); 165(48%).
NMR (CDCl3, 100 MHz): δ(ppm) = 19.58, 21.13, 115.43 (d, JC-F= 23.0
Hz), 123.85 (d, JC-F= 4.0 Hz), 128.66, 129.17 (d, JC-F= 29.0 Hz), 129.79,
129.91, 130.20 (d, JC-F= 4.0 Hz), 133.62, 135.19, 135.70, 159.77 (d,
JC-F= 247.0 Hz), MS: C14H13F: 200(100%), 185(67%), 165(37%).
4'-ethyl-2,5-dimethylbiphenyl (Table 3, entry 11): 1H NMR (CDCl3,
400 MHz): δ(ppm) = 1.29-1.33 (m, 3H), 2.26 (s, 3H), 2.36 (s, 3H),
2.71- 2.75 (m, 2H), 7.08 (s, 2H), 7.18 (t, J= 8.0 Hz, 1H), 7.28 (t, J= 8.0
Hz, 1H), 7.35-7.44 (m, 2H), 7.54 (d, J= 8.0 Hz, 1H). 13C NMR (CDCl3,
100 MHz): δ(ppm) = 15.78, 20.09, 21.16, 28.70, 127.13, 127.42,
3'-chloro-2,4,6-trimethylbiphenyl (Table 3, entry 3): 1H NMR:
(CDCl3, 400 MHz): δ(ppm) = 2.00 (s, 6H), 2.33 (s, 3H), 6.94 (s, 2H),
7.02-7.04 (m, 1H), 7.14-7.15 (m, 1H), 7.32-7.35 (m, 2H). 13C NMR:
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127.82, 129.03, 129.43, 130.58, 132.36, 135.25, 142.72. MS: C16H18:
210 (M+, 100%), 195 (100%), 181 (31%), 165 (37%).
6
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4'-ethyl-2,4-dimethylbiphenyl (Table 3, entry 12): H NMR (CDCl3,
400 MHz): δ(ppm) = 1.29 (t, J= 4.0 Hz, 3H), 2.26 (s, 3H), 2.36 (s, 3H),
2.67-2.72 (m, 2H), 7.05 (d, J=8.0 Hz, 2H), 7.27-7.35 (m, 3H), 7.52 (d,
J= 8.0 Hz, 2H). 13C NMR (CDCl3, 100 MHz) δ(ppm) = 15.71, 21.07,
21.28, 28.68, 126.8, 127.21, 128.34, 129.52, 131.38, 135.34, 136.41,
139.16, 141.37, 142.62. MS: C16H18: 210(M+, 100%); 181(67%),
165(37%).
7
8
9
4-ethyl-4'-methylbiphenyl (Table 3, entry 13): 1H NMR (CDCl3, 400
MHz): δ(ppm) = 1.27-1.31 (m, 3H), 2.28 (s, 3H), 2.68-2.74 (m, 2H),
7.20-7.25 (m, 4H), 7.46-7.51 (m, 4H). 13C NMR (CDCl3, 100 MHz)
δ(ppm) = 15.63, 20.71, 28.72, 126.80, 126.84, 128.24, 129.35,
135.93, 136.60, 138.32, 139.31, 142.98. MS: C15H16: 196(M+, 100%);
195(60%), 165(37%).
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4-bromo-4'-methylbiphenyl (Table 3, entry 14): 1H NMR (CDCl3,
400 MHz): δ(ppm) = 2.26 (s, 3H), 7.27 (d, J= 8.0 Hz, 2H), 7.40-7.52
(m, 4H), 7.75 (d, J= 8.0 Hz, 2H). 13C NMR (CDCl3, 100 MHz): δ(ppm) =
21.20, 122.43, 126.91, 128.67, 129.73, 131.90, 137.23, 137.67,
140.27. MS: C13H11Br: 246(M+, 100%); 248(100%); 168(81%),
165(37%).
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3,4-dichlorobiphenyl (major product, Table 3, entry 15): 1H NMR
(CDCl3, 400 MHz): δ (ppm) = 7.23 (s, 1H), 7.25 (d, J=8.0 Hz, 1H),
7.41-7.48 (m, 6H). 13C NMR (CDCl3, 100 MHz): δ (ppm) = 127.26,
128.27, 129.41, 129.62, 130.82, 133.72, 139.44, 141.40, MS:
C12H8Cl2: 222 (M+, 100%), 152 (50%)
4-bromobiphenyl (major product, Table 3, entry 16): 1H NMR
(CDCl3, 400 MHz): δ (ppm) = 7.34-7.38 (m, 1H), 7.41- 7.49 (m, 2H),
7.60-7.69 (m, 6H). 13C NMR (CDCl3, 100 MHz): δ (ppm) = 121.63,
126.92, 127.68, 128.73, 128.82, 131.93, 140.15, 140.32. MS:
C12H9Br: 232(M+, 100%), 234(M+2, 100%), 152(98%).
3-nitrobiphenyl (major product, Table 3, entry 17): 1H NMR (CDCl3,
400 MHz): δ (ppm) = 7.41-7.52 (m, 3H), 7.61-7.64 (m, 3H), 7.85-7.89
(m, 2H), 8.34-8.37 (m, 1H). 13C NMR (CDCl3, 100 MHz): δ (ppm) =
122.53, 127.49, 129.0, 129.97, 133.55, 136.62, 137.53, 148.91. MS:
C12H9NO2 : 199 (M+, 100%), 168(30%), 152(95%).
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