Modern Friedel-Crafts Chemistry. Part 24. Alkylation of Benzene with 1,2-Dibromo-3-chloro-2-methylpropane in the Presence of Lewis and Bronsted Acid Catalysts

Article abstract of DOI:10.1039/a603860c

The major alkylation products of benzene with 1,2-dibromo-3-chloro-2-methylpropane are 1-X-2-methyl-3,3-diphenylpropane (X = Cl, Br) with AlCl₃ and 1,4-bis-(1-bromo-3-chloro-2-methylpropyl)benzene with AlCl₃-CH₃NO₂ or K10 montmorillonite (K10 Clay); minor products include di- and tri-phenylated butanes and/or 2-methyl-1-phenylindane.

Full text of DOI:10.1039/a603860c

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20 J. CHEM. RESEARCH (S), 1997
J. Chem. Research (S),
1997, 20–21‡
Modern Friedel–Crafts Chemistry. Part 24.† Alkylation of
Benzene with 1,2-Dibromo-3-chloro-2-methylpropane in the
Presence of Lewis and Brønsted Acid Catalysts‡
Hassan A. Albar,* Ali A. Khalaf and Saleh O. Bahaffi
Department of Chemistry, Faculty of Science, King Abdulaziz University, P.O. Box 9028,
Jeddah 21413, Saudi Arabia
The major alkylation products of benzene with 1,2-dibromo-3-chloro-2-methylpropane are 1-X-2-methyl-
3,3-diphenylpropane (X = Cl, Br) with AlCl3 and 1,4-bis-(1-bromo-3-chloro-2-methylpropyl)benzene with AlCl3–CH3NO2 or
K10 montmorillonite (K10 Clay); minor products include di- and tri-phenylated butanes and/or 2-methyl-
1-phenylindane.
The alkylation of benzene with multifunctional reagents con-
stitutes an important part of Friedel–Crafts chemistry.1,2 In
this paper, we present the alkylation of benzene with
1,2-dibromo-3-chloro-2-methylpropane 1 under both Lewis
and Brønsted acid catalyses. The results are depicted in
Table 1 and their mechanistic rationale in terms of carboca-
tion transformations is formulated in Scheme 1.
butane 7c and 1,4-bis-(1-bromo-3-chloro-2-methylpropyl)-
benzene 8, depending on catalyst type and the reaction
conditions.
Commenting on these results, several points have to be
emphasized:
(1) The results of entry 4 are worthy of comparison with
earlier ones from the corresponding trichloride which report
Scheme 1 (X = Cl or Br)
With reference to Table 1 and Scheme 1, the alkylation of
benzene with 1 gave product mixtures consisting of varying
proportions of 1-chloro- and 1-bromo-2-methyl-3,3-diphe-
nylpropanes 3a,b, 1,1,2- and 1,1,3-triphenyl-2-methylpro-
panes 4a,b, 1-phenyl-2-methylindane 6, 1,1- and 1,2-di-
phenyl-2-methylpropanes 7a,b, (<)- and meso-2,3-diphenyl-
the product to be meso-7c (33.4% yield) mixed with two
unidentified liquid isomers.
(2) The formation of 8 as the major product in entries 5–7
may be attributed to the mild catalytic activity of AlCl3–
CH3NO2 and K10 montmorillonite (K10 Clay) which can
induce reaction only at the tertiary site. However, a longer
reflux time with K10 montmorillonite appears to enhance
dealkylation of 8 to 3b (see entry 8).
(3) The dominance of 3b over 3a in all the reactions is
explicable in terms of the known greater reactivity of Cl as
compared to Br in Friedel–Crafts reactions.1
*To receive any correspondence.
†Part 23: Reference 2.
‡This is a Short Paper as defined in the Instructions for Authors,
Section 5.0 [see J. Chem. Research (S), 1997, Issue 1]; there is there-
fore no corresponding material in J. Chem. Research (M).

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J. CHEM. RESEARCH (S), 1997 21
Table 1 Products from alkylation of benzene with compound 1
Product composition (%)a
Reactants
Conditions
Other products
Entry
no.
1
PhH
(mol)
Catalyst
(mol)
Time
(t/h)
Temp.
(T/°C)
(mol)
3a
3b
4a,b
7a
7b
7c
Identified
Unidentifiedb
1
2
3
4c
5
6
7
8
0.11
0.11
0.11
0.23
0.11
0.02
0.02
0.02
1.1
0.5
1.1
2.3
1.1
0.2
0.2
0.2
AlCl3 (0.011)
1
24
24
14
24
12
24
43
25
12
2
51
69
86
31
3
13
16
38
3
2
2
1
5
2
2
3
6 (13)
6 (2)
—
12
19
6
43
16
19
32
50
AlCl3 (0.011)
25
AlCl3 (0.02)
25
1
2
1
1
3
Al (2%)/HCl (g)
AlCl3/(0.02)/CH3NO2 (0.06)
K10 Clay (2.0 g)
K10 Clay (2.0 g)
K10 Clay (2.0 g)
25
8
4
2
5
7
—
25
2
—
—
3
—
—
1
—
—
2
—
—
—
—
8 (79)
8 (63)
8 (44)
8 (4)
Reflux
Reflux
Reflux
5
2
2
3
1
2
aProduct identifications and percentage compositions of various products are based on combined IR, 1H NMR, GC and GCMS
analyses. bMost FriedelCrafts reactions are complex and the presence of unidentifiable components is always expected; the number
of unidentifiable components ranged from 3 in some cases (e.g., entry no. 3) to 14 in other cases (e.g., entry no. 4). cParallels old work
by Dolgov and Larin3 in which 1,2,3-trichloro-2-methylpropane was the alkylating agent.
(4) The formation of 6 via intermediates 5 finds analogy in
3.84 (d, 1 H, J 7 Hz, C6H4CHPh) and 7.12–7.43 (m, 9 H, Ar-H); m/z
(%), 208 (Mǹ, 90), 193 (Mǹ ꢀCH3, 22), 180 (11), 179 (100), 165
(09), 149 (20), 130 (13), 115 (20), 105 (26), 91 (28), 77 (09), 57 (11)
(Found: Mǹ, 208.12520. C16H16 requires Mr, 208.304).
Compound 8: dH (CDCl3) 1.32 (s, 6 H, 2CH3), 3.63 (s, 8 H,
4CH2), and 7.09–7.22 (m, 4 H, Ar-H); m/z (%), 414/422 (Mǹ, 0/0),
370 [Mǹ ꢀ(Cl—CH2), 5], 335/341 [Mǹ ꢀ(ClCH2ǹ2CH3), 8],
300–304 [Mǹ ꢀ(ClǹBr), 12], 286–290 [Mǹ ꢀ(BrǹClCH2), 13],
256–260 (18), 221–223 (28), 179–181 (19), 143 (63), 125 (53), 105
(84), 91 (100), 77 (81), 65 (89), 53 (73).
an earlier paper co-authored by one of us.4
Experimental
IR spectra were recorded on a Nicolet Magna 520 FT-IR spec-
1
trometer, H NMR spectra were recorded on a Bruker DPX-400
FT-NMR spectrometer, GC–MS data were obtained with a Shim-
dazu QP-5000 mass spectrometer and microanalyses were per-
formed on a 2400 Perkin Elmer Series 2 CHNS analyser.
Preparation of 1,2-Dibromo-3-chloro-2-methylpropane 1.—Addi-
tion of bromine (0.2 mol) to stirred methallyl chloride (0.1 mol)
over 1 h followed by stirring at room temperature for 48 h gave the
desired product 1: dH (CDCl3) 1.98 (s, 3 H, CH3), 4.02 (s, 4 H,
2ÅCH2).
Received, 3rd June 1996; Accepted, 7th October 1996
Paper E/6/03860C
Alkylation Procedures.—These were similar to those published in
earlier papers.2
1
Spectral Data for New Alkylation Products.—The H NMR and
MS data for 3a, 3b, 6 and 8 are as follows:
References
Compound 3a: dH (CDCl3) 1.03 (d, 3 H, J 7 Hz, CH3), 2.53–2.89
(m, 1 H, CHCH3), 3.16–3.67 (m, 2 H, CHPh2 and HCHX), 3.79 (d,
1 H, J 9 Hz, CHX) and 7.03–7.41 (m, 10 H, Ar-H); m/z (%),
244/246 (Mǹ, 12/3), 208 (Mǹ ꢀHCl, 08), 193 (04), 178 (10), 167
(100), 152 (53), 115 (15), 103 (05), 91 (23), 77 (09), 65 (12), 51
(19).
Compound 3b: dH (CDCl3) identical with that of 3a; m/z (%),
288/290 (Mǹ, 06/06), 208 (Mǹ ꢀHBr, 04), 193 (02), 178 (04), 167
(100), 152 (23), 115 (08), 102 (02), 91 (12), 77 (07), 65 (05).
Compound 6: dH (CDCl3) 1.26 (d, 3 H, J 7 Hz, CH3), 2.48 (m,
1 H, CHCH3), 2.74 (m, 1 H, CHC6H4), 3.21 (dd, 1 H, CHC6H4),
1 For reviews see: (a) R. M. Roberts and A. A. Khalaf, Friedel–
Crafts Alkylation Chemistry, Marcel Dekker, New York, 1984; (b)
Friedel–Crafts and Related Reactions, ed. G. A. Olah, Wiley, New
York, 1963–1965.
2 (a) A. A. Khalaf and H. A. Albar, J. Indian Chem. Soc., 1995, 72,
87; (b) H. A. Albar, S. A. Basaif and A. A. Khalaf, Indian J. Chem.
B, 1996, 35, 161.
3 B. N. Dolgov and N. A. Larin, J. Gen. Chem. USSR, 1950, 20, 450
(Chem. Abstr., 1951, 45, 566f).
4 A. A. Khalaf and R. M. Roberts, J. Org. Chem., 1969, 34, 3571.