One-step conversion of acetophenones to α-haloacetophenone dimethyl acetals using DCDMH/DBDMH and molecular sieve in methanol

Article abstract of DOI:10.1080/00397911.2010.540696

Using DCDMH/DBDMH as N-halo reagent, piperidine as catalyst, and 4-A molecular sieve as water-removing agent, α-haloacetophenone dimethyl acetals were directly obtained from the solvent of methanol. As to the substrates with electronwithdrawing groups, the conversions were 80-100%. Copyright Taylor & Francis Group, LLC.

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One-Step Conversion of Acetophenones
to α-Haloacetophenone Dimethyl Acetals
Using DCDMH/DBDMH and Molecular
Sieve in Methanol
Bin Zhou a , Zizhan Chen a , Zubiao Zheng a , Bingbing Han a &
Xinzhuo Zou a
a Department of Chemistry , East China Normal University ,
Shanghai , China
Accepted author version posted online: 21 Oct 2011.Published
online: 25 Jan 2012.
To cite this article: Bin Zhou , Zizhan Chen , Zubiao Zheng , Bingbing Han & Xinzhuo Zou
(2012) One-Step Conversion of Acetophenones to α-Haloacetophenone Dimethyl Acetals Using
DCDMH/DBDMH and Molecular Sieve in Methanol, Synthetic Communications: An International
Journal for Rapid Communication of Synthetic Organic Chemistry, 42:10, 1445-1453, DOI:
10.1080/00397911.2010.540696
To link to this article: http://dx.doi.org/10.1080/00397911.2010.540696
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Synthetic Communications1, 42: 1445–1453, 2012
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.540696
ONE-STEP CONVERSION OF ACETOPHENONES
TO a-HALOACETOPHENONE DIMETHYL ACETALS
USING DCDMH/DBDMH AND MOLECULAR SIEVE
IN METHANOL
Bin Zhou, Zizhan Chen, Zubiao Zheng, Bingbing Han, and
Xinzhuo Zou
Department of Chemistry, East China Normal University, Shanghai, China
GRAPHICAL ABSTRACT
Abstract Using DCDMH/DBDMH as N-halo reagent, piperidine as catalyst, and 4-A
molecular sieve as water-removing agent, a-haloacetophenone dimethyl acetals were
directly obtained from the solvent of methanol. As to the substrates with electron-
withdrawing groups, the conversions were 80–100%.
Keywords Acetophenone; 1,3-dibromo-5,5-dimethylhydantoin; 1,3-dichloro-5,5-dimethyl-
hydantoin; a-haloacetophenone dimethyl acetals; molecular sieve; one-step conversion;
piperidine
INTRODUCTION
Halogenated organic compounds have received much attention because they
can be easily converted into other functional molecules as synthetic intermediates
and precursors.[1] Recently, many research papers with wonderful results focus on
the formation of acetophenone dimethyl acetals.[2] a-Haloacetophenone dimethyl
acetals are a kind of halogentated molecules with acetal structure, and they constitute
an interesting class of synthetic intermediates that can be used to prepare novel flavor
material and other sorts of functional compounds.[3] However, as to the preparation
of a-haloacetophenone dimethyl acetals, the reports are rare.[4]
Both 1,3-dichloro-5,5-dimethylhydantoin (DCDMH) and 1,3-dibromo-5,5-
dimethylhydantoin (DBDMH) are disinfecting agents and bleaching agents that
Received September 10, 2010.
Address correspondence to Xinzhuo Zou, Department of Chemistry, East China Normal
University, 3663 Zhongshan Road (N), Shanghai 200062, China. E-mail: xzzou@chem.ecnu.edu.cn
1445

1446
B. ZHOU ET AL.
have been extensively used in industrial and domestic water and fruit storage.[5]
Application of DCDMH or DBDMH in some aspects has been widely researched,
and some methods about DCDMH or DBDMH have been described by our
group.[6] a-Chloroacetophenone dimethyl acetals were found as by-products when
DCDMH was refluxed with acetophenones and methanol during our research.[6c]
Generally speaking, there is a chemical equilibrium between ketones and ketals.
Acids are used as catalysts to prepare ketals from ketones, and trimethyl orthofor-
mate is widely used to prepare acetophenone dimethyl acetals.[7] Additionally, if
a-haloacetophenone dimethyl acetals need to be prepared from acetophenones, there
are two steps to reach the target molecules, halogenation and acetalization. In our
research, the a-haloacetophenone dimethyl acetals as by-products were obtained
without trimethyl orthoformate and acids in just one step so we decided to develop
and optimize a method for preparation of a-haloacetophenone dimethyl acetals
based on our findings (Scheme 1).
First, p-nitroacetophenone 1a was chosen as a model for the reaction of a-
chlorination and acetalization in one step. Various amounts of DCDMH were tested,
and 2 equiv. of DCDMH were beneficial to the reaction. Compound 1a was treated
with 2 equiv. of DCDMH in the presence of silica gel (1 g) and CH3OH under reflux
by various catalysts. The amount of catalyst was 10 mmol, and the results were shown
in Table 1. When Et3N was used as catalyst, only 65% of substrate was converted into
the corresponding product 2a and the remaining of 1a was transformed into the
a-chloro-4-nitroacetophenone. Only trace of a,a-dichloro-4-nitroacetophenone was
1
found, which was determined by H NMR (Table 1, entry 1). When the reaction
was catalyzed by pyridine, Et2NH, or 1-butylamine, the conversions to a-chloro-4-
nitroacetophenone dimethyl acetals were 74%, 80%, and 84% (Table 1, entries 2–4).
As to piperidine, the conversion reached 89%, the highest among our experimental
results (Table 1, entry 5). We thought piperidine was helpful to this reaction in that
the substrate was a-chlorinated and acetalizated in one step. Molecular sieve (4A)
replaced silica gel as water-removing agent, and interestingly the conversion increased
to 100%. The 4A moleculor sieve can be reused during our experiments. Because 1a
was very reactive, 1d with mild reactivity was selected to be the tested compound to
optimize the amount of the amine. Compound 1d was heated with 4A molecular
Scheme 1. One-step conversion of acetophenones to a-haloacetophenone dimethyl acetals using
DCDMH=DBDMH and molecular sieve in methanol. I: piperidine, 4-sieves, MeOH, reflux, 12 h. Conver-
sions: 50–100%. II: piperidine, 4-A sieves, MeOH, 50–52ꢀC, 12h. Conversions: 50–100%.

ONE-STEP CONVERSION OF a-HALOACETOPHENONE ACETALS
Table 1. Conversion of 1a catalyzed by various aminesa
1447
Entry
Catalyst
Conversion (%)b
1
2
3
4
5
Et3N
Pyridine
65
74
80
84
89
Et2NH
1-Butylamine
Piperidine
a1a (10 mmol), DCDMH (20 mmol), silica gel (1 g),
MeOH 35 mL, reflux for 12 h.
bThe conversion to 2a was determined by 1H NMR
analysis of the crude reaction mixture.
sieves, and 10, 5, 2.5, 1, or 0 mmol of piperidine were added to the reaction mixture.
The conversions of 1d were from 81% to 92%, and the conversion that used 2.5 mmol
piperidine was 92%, higher than the other experimental results.
Various acetophenones were examined, and the substrates were heated with 2
equiv. of DCDMH, 2.5 mmol piperidine, and 15 g 4A molecular sieve in MeOH at
reflux for 12 h. We found the chemical conversions of most of substrates were high,
and most of the substrates could be converted to the corresponding products in good
yield. The conversions of 1a–1h were 92–100%, and the isolated yields of 2a–2h were
from 82% to 94% (Table 2, entries 1–8). In the mixture of the crude products of 1j,
1
25% of a,a-dichloro-p-methylacetophenone was found by H NMR (Table 2, entry
10). The conversion and isolated yield of 1i were respectively 86% and 72% (Table 2,
entry 9). In our new chemical process of a-chlorination and acetalization in one pot,
the substrates with electron-withdrawing groups seem to offer products with good
yields, and the yields of the substrates with electron-donating groups were less than
the substrates with electron-withdrawing groups.
When DBDMH was used instead of DCDMH and other conditions remained,
some a,a-dibromoacetophenones were found. We adjusted the temperature to 50–
52ꢀC, and the a,a-dibromoacetophenones almost disappeared; the conversion of
the tested substrate 1f was 86%. When the reaction was carried out at room tempera-
ture, the product was not detected. Various substrates were tested, and the substrates
were mixed with 2 equiv. of DBDMH, 2.5 mmol piperidine, and 15 g 4A moleculor
sieve in MeOH at 50–52ꢀC for 12h. The conversions of 1a–1h were 70–100%, and
the isolated yields of 3a–3h were from 62% to 93% (Table 2, entries 1–8). The yields
of 3i were 38%, which was lower than 3a–3h (Table 2, entry 9). As to the substrate 1j,
the conversion of 1j was very low (< 1%) (Table 2, entry 10). In the process of a-bro-
mination and acetalization in one pot, the substrates with electron-withdrawing
groups could also offer products with good yields. On the whole, the yields of the sub-
strates in the process of a-chlorination and acetalization were greater than those in
the process of a-bromination and acetalization.
Xu et al. gave the mechanism about keto-enol tautomerism in the process of the
bromination of substituted acetophenones using DCDMH in the presence of p-TsOH
(see Ref. [6a] and references therein). Analogously, we propose the following mech-
anism (Scheme 2) for the reaction, in which piperidine was used as a catalyst and
4A molecular sieves were used in methanol. In this reaction, DCDMH=DBDMH

1448
B. ZHOU ET AL.
Table 2. a-Halogenation and acetalization of various acetophenones
in one step
Conversion (%)c
Entry
Substrate
2a
3b
1
2
1a
1b
1c
1d
1e
1f
100 (94)
100 (91)
100 (87)
92 (82)
100 (93)
98 (92)
80 (70)
3
4
70 (62)
77 (68)
5
98 (85)
6
100 (85)
100 (86)
100 (85)
86 (72)
86 (79)
89 (84)
7
1g
1h
1i
8
89 (84)
50e (38)
<1 (Trace)
9
10
1j
50d (40)
aSubstrate (10 mmol), DCDMH (20 mmol), 4-A molecular sieves
(15 g), piperidine (2.5 mmol), MeOH (35 mL), reflux for 12 h.
bDBDMH (20 mmol) and the reaction mixture was heated to
50–52ꢀC for 12 h.
cThe conversion to a-haloacetophenone dimethyl acetals was
determined by 1H NMR analysis of the crude reaction mixture. The
isolated yields were in the brackets.
d2j, a-chloro-p-methyl-acetophenone and a,a-dichloro-p-methylace-
tophenone were found in the products and the ratio of the three
compounds determined by 1H NMR was 2:1:1.
e7% of the a,a-dichloroacetophenone was also found in the products
determined by 1H NMR.
Scheme 2. Possible mechanism for one-step conversion of acetophenones to a-haloacetophenone dimethyl
acetals using DCDMH=DBDMH and molecular sieve in methanol.

ONE-STEP CONVERSION OF a-HALOACETOPHENONE ACETALS
1449
could emit Clþ or Brþ twice, so maybe CH3OCl or CH3OBr was helpful to the process
and CH3OCl or CH3OBr was involved in not only a-halogenation but also acetaliza-
tion. Piperidine and molecular sieves played an important role in the reaction
respectively as acid and water-removing agent.
In conclusion, we developed a simple and efficient method to prepare a-haloa-
cetophenone dimethyl acetals directly from acetophenones in one pot in mild
conditions. The method to prepare an important and interesting class of synthetic
intermediates is combined with two reactions (a-halogenation and acetalization) in
a one-step process with some cheap and clean reagents such as DCDMH and
DBDMH. The method is a novel route to a-haloacetophenone dimethyl acetals in
the methodology of organic synthesis.
EXPERIMENTAL
Typical Experimental Procedure of a-Halogenation and Acetalization
Piperidine (2.5 mmol) and 4A molecular sieves (15 g) were added into a mixture
of substrate (10 mmol), DCDMH=DBDMH (20 mmol), and methanol (35 mL). After
reflux for 12 h (or heating to 50–52 ꢀC when DBDMH was used), the mixture was fil-
tered, and the solvent of methanol was removed from the filtrate under reduced press.
After MTBE (50 mL) was added to the residue, the organic layer was washed by water
(40 mL) and brine (50 mL) several times, and the organic layer was dried on Na2SO4.
After that, the organic layer was filtered, and the solvent was removed under reduced
pressure. The product was obtained.
1-(2-Chloro-1,1-dimethoxyethyl)-4-nitrobenzene (2a)
1
Light yellow solid; mp 48–49ꢀC; H NMR (500 MHz, CDCl3): d: 8.23 (d, 2H,
J ¼ 8.6 Hz, Ar-H), 7.70 (d, 2H, J ¼ 8.6 Hz, Ar-H), 3.73 (s, 2H, -CH2), 3.24 (s, 6H,
-OCH3); 13C NMR (125 MHz, CDCl3): d: 148.1, 145.5, 128.6, 123.2, 101.5, 49.4,
45.9; m=z: 214, 196, 150; IR (KBr, cmꢁ1): 1528, 1352, 1287, 1126, 1073, 1053. EA
calculated for C10H12NO4Cl: C, 48.89%; H, 4.92%; N, 5.70%, found: C, 48.85%;
H, 5.12%; N, 5.72%.
1-(2-Chloro-1,1-dimethoxyethyl)-3-nitrobenzene (2b)
1
Light yellow solid; mp 51–52ꢀC; H NMR (500 MHz, CDCl3): d: 8.39 (s, 1H,
Ar-H), 8.22–8.24 (m, 1H, Ar-H), 7.84–7.86 (m, 1H, Ar-H), 7.58–7.60 (m, 1H, Ar-H),
3.74 (s, 2H, -CH2), 3.26 (s, 6H, -OCH3); 13C NMR (125 MHz, CDCl3): d: 148.3,
140.8, 133.4, 129.1, 123.5, 122.8, 101.3, 49.4, 45.9; m=z: 214, 196, 150; IR (KBr,
cmꢁ1): 1530, 1350, 1127, 1097, 1073, 1054. EA calculated for C10H12NO4Cl: C,
48.89%; H, 4.92%; N, 5.70%, found: C, 48.95%; H 5.04%; N 5.71%.
1-(2-Chloro-1,1-dimethoxyethyl)-4-trifluoromethylbenzene (2c)
Light yellow oil;1H NMR (500 MHz, CDCl3): d: 7.64 (s, 4H, Ar-H), 3.74 (s,
2H, -CH2), 3.24 (s, 6H, -OCH3); 13C NMR (125 MHz, CDCl3): d: 142.4, 130.4,
127.9. 125.0, 125.0, 101.5, 49.3, 46.1; m=z: 237, 219, 173; IR (KBr, cmꢁ1): 1384,
1125, 1075, 1002.

1450
B. ZHOU ET AL.
1-Bromo-4-(2-chloro-1,1-dimethoxyethyl)benzene (2d)
Light yellow oil; 1H NMR (500 MHz, CDCl3): d: 7.49 (d, 2H, J ¼ 7.8 Hz,
Ar-H), 7.37 (d, 2H, J ¼ 7.8 Hz, Ar-H), 3.70 (s, 2H, -CH2), 3.22 (s, 6H, -OCH3);
13C NMR (125 MHz, CDCl3): d: 138.8, 132.6, 132.3, 130.0, 129.7, 126.6, 101.1,
49.3, 46.0; m=z: 249, 229, 183; IR (KBr, cmꢁ1): 1124, 1073, 1051, 1011.
1-Chloro-4-(2-chloro-1,1-dimethoxyethyl)benzene (2e)
Light yellow oil; 1H NMR (500 MHz, CDCl3): d: 7.45 (d, 2H, J ¼ 8.4 Hz,
Ar-H), 7.36 (d, 2H, J ¼ 8.4 Hz, Ar-H), 3.70 (s, 2H, -CH2), 3.21 (s, 6H, -OCH3).[8]
1-Chloro-2-(2-chloro-1,1-dimethoxyethyl)benzene (2f)
1
Light yellow oil; H NMR (500 MHz, CDCl3): d: 7.86–7.88 (m, 1H, Ar-H),
7.38–7.40 (m, 1H, Ar-H), 7.28–7.30 (m, 2H, Ar-H), 3.84 (s, 2H, -CH2), 3.23 (s, 6H,
-OCH3); 13C NMR (125 MHz, CDCl3): d: 134.4, 132.3, 131.1, 131.0, 129.8, 126.4,
101.1, 48.8, 42.7; m=z: 203, 185, 139; IR (KBr, cmꢁ1): 1384, 1127, 1082, 1063, 1002.
2,4-Dichloro-1-(2-chloro-1,1-dimethoxyethyl)benzene (2g)
Light yellow oil; 1H NMR (500 MHz, CDCl3): d: 7.80 (d, 1H, J ¼ 8.5 Hz,
Ar-H), 7.40 (s, 1H, Ar-H), 7.29 (d, 1H, J ¼ 8.5 Hz, Ar-H), 3.93 (s, 2H, -CH2), 3.23
(s, 6H, -OCH3); 13C NMR (125 MHz, CDCl3): d: 135.1, 133.4, 132.0, 130.6, 130.6,
126.7, 101.0, 48.9, 42.5; m=z: 237, 219, 173; IR (KBr, cmꢁ1): 1383, 1125, 1081,
1059, 1002, 984.
1,2-Dichloro-4-(2-chloro-1,1-dimethoxyethyl)benzene (2h)
1
Light yellow oil; H NMR (500 MHz, CDCl3): d: 7.62 (s, 1H, Ar-H), 7.46 (d,
1H, J ¼ 8.4 Hz, Ar-H), 7.33 (d, 1H, J ¼ 8.4 Hz, Ar-H), 3.69 (s, 2H, -CH2), 3.22 (s, 6H,
-OCH3); 13C NMR (125 MHz, CDCl3): d: 137.4, 131.1, 129.1, 122.6, 101.6, 49.1,
46.2; m=z: 237, 219, 173; IR (KBr, cmꢁ1): 1290, 1121, 1076, 1055.
(2-Chloro-1,1-dimethoxyethyl)benzene (2i)
1
Light yellow oil; H NMR (500 MHz, CDCl3): d: 7.51–7.53 (m, 2H, Ar-H),
7.38–7.40 (m, 3H, Ar-H), 3.75 (s, 2H, -CH2), 3.24 (s, 6H, -OCH3).[9]
1-(2-Chloro-1,1-dimethoxyethyl)-4-methylbenzene (2j)
Light yellow oil; 1H NMR (500 MHz, CDCl3): d: 7.42 (d, 2H, J ¼ 8.4 Hz,
Ar-H), 7.24 (d, 2H, J ¼ 8.4 Hz, Ar-H), 3.70 (s, 2H, -CH2), 3.21 (s, 6H, -OCH3),
2.54 (s, 3H, -CH3).[10]
1-(2-Bromo-1,1-dimethoxyethyl)-4-nitrobenzene (3a)
1
Light yellow solid; mp 49–50ꢀC; H NMR (500 MHz, CDCl3): d: 8.25 (d, 2H,
J ¼ 9 Hz, Ar-H), 7.71 (d, 2H, J ¼ 9 Hz, Ar-H), 3.62 (s, 2H, -CH2), 3.25 (s,

ONE-STEP CONVERSION OF a-HALOACETOPHENONE ACETALS
1451
6H, -OCH3); 13C NMR (125 MHz, CDCl3): d: 148.0, 145.7, 128.5, 123.2, 101.0, 49.6,
34.5; m=z: 258, 196, 150; IR (KBr, cmꢁ1): 1522, 1352, 1282, 1114, 1047. EA calc.
for C10H12NO4Br: C, 41.40%; N, 4.83%; H, 4.17%, found: C, 41.45%; N, 4.81%;
H, 4.15%.
1-(2-Bromo-1,1-dimethoxy-ethyl)-3-nitrobenzene (3b)
1
Light yellow solid; mp 68–69ꢀC; H NMR (500 MHz, CDCl3): d: 8.38 (s, 1H,
Ar-H), 8.19–8.21 (m, 1H, Ar-H), 7.82–7.84 (m, 1H, Ar-H), 7.58–7.60 (m, 1H, Ar-H),
3.62 (s, 2H, -CH2), 3.25 (s, 6H, -OCH3); 13C NMR (125 MHz, CDCl3): d: 148,3,
141.1, 133.4, 129.1, 123.5, 122.8, 100.8, 49.6, 34.7; m=z: 258, 196, 150; IR (KBr,
cmꢁ1): 1529, 1350, 1271, 1121, 1089, 1043. EA calc. for C10H12NO4Br: C, 41.40%;
N, 4.83%; H, 4.17%, found: C, 41.47%; N, 4.83%; H, 4.27%.
1-(2-Bromo-1,1-dimethoxyethyl)-4-trifluoromethylbenzene (3c)
1
Light yellow oil; H NMR (500 MHz, CDCl3): d: 7.55 (s, 4H, Ar-H), 3.53 (s,
2H, -CH2), 3.15 (s, 6H, -OCH3);13C NMR (125 MHz, CDCl3): d: 142.6, 130.2,
127.8, 125.0, 124.9, 101.0, 49.4, 34.9; m=z: 281, 219, 173; IR (KBr, cmꢁ1): 1326,
1166, 1127,1068, 1049.
1-Bromo-4-(2-bromo-1,1-dimethoxyethyl)benzene (3d)
Light yellow oil; 1H NMR (500 MHz, CDCl3): d: 7.52 (d, 1H, J ¼ 8.5 Hz,
Ar-H), 7.39 (d, 1H, J ¼ 8.5 Hz, Ar-H), 3.60 (s, 2H, -CH2), 3.21 (s, 6H, -OCH3);13C
NMR (125 MHz, CDCl3): d: 137.7, 131.1, 129.1, 122.7, 101.1, 49.4, 35.1; m=z: 293,
229, 183; IR (KBr, cmꢁ1): 1282, 1108, 1065, 1043, 1008.
1-(2-Bromo-1,1-dimethoxyethyl)-4-chlorobenzene (3e)
Light yellow oil; 1H NMR (500 MHz, CDCl3): d: 7.46 (d, 2H, J ¼ 8.4 Hz,
Ar-H), 7.37 (d, 2H, J ¼ 8.4 Hz, Ar-H), 3.60 (s, 2H, -CH2), 3.23 (s, 6H, -OCH3).[11]
1-(2-Bromo-1,1-dimethoxyethyl)-2-chlorobenzene (3f)
1
Light yellow oil; H NMR (500 MHz, CDCl3): d: 7.83–7.85 (m, 1H, Ar-H),
7.35–7.37 (m, 1H, Ar-H), 7.27–7.29 (m, 2H, Ar-H), 3.94 (s, 2H, -CH2), 3.23 (s,
6H, -OCH3);13C NMR (125 MHz, CDCl3): d: 134.7, 132.4, 131.3, 131.1, 130.1,
126.3, 100.7, 49.1, 31.6; m=z: 249, 185, 139; IR (KBr, cmꢁ1): 1116, 1074, 1059, 1041.
1-(2-Bromo-1,1-dimethoxyethyl)-2,4-dichlorobenzene (3g)
Light yellow oil; 1H NMR (500 MHz, CDCl3): d: 7.78 (d, 1H, J ¼ 8.5 Hz,
Ar-H), 7.39 (s, 1H, Ar-H), 7.27 (d, 1H, J ¼ 8.5 Hz, Ar-H), 3.88 (s, 2H, -CH2), 3.21
(s, 6H, -OCH3).[12]
4-(2-Bromo-1,1-dimethoxyethyl)-1,2-dichlorobenzene (3h)
1
Light yellow oil; H NMR (500 MHz, CDCl3): d: 7.61 (s, 1H, Ar-H), 7.43
(d, 1H, J ¼ 8.5 Hz, Ar-H), 7.31 (d, 1H, J ¼ 8.5 Hz, Ar-H), 3.56 (s, 2H, -CH2), 3.21

1452
B. ZHOU ET AL.
(s, 6H, -OCH3); 13C NMR (125 MHz, CDCl3): d: 139.0, 132.6, 132.3, 130.0, 129.7,
126.6, 100.6, 49.4, 34.7; m=z: 283, 219, 173; IR (KBr, cmꢁ1): 1117, 1069, 1047, 1026.
(2-Bromo-1,1-dimethoxyethyl)benzene (3i)
1
Light yellow oil; H NMR (500 MHz, CDCl3): d: 7.57–7.59 (m, 2H, Ar-H),
7.34–7.36 (m, 3H, Ar-H), 3.62 (s, 2H, -CH2), 3.22 (s, 6H, -OCH3).[10]
ACKNOWLEDGMENT
The authors thank Shanghai Foundation of Science and Technology for
finacial support (No. 073919106).
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