Synthesis of some 2-aminonitroethanes via tin(II)chloride mediated addition reaction of bromonitromethane to imines

Article abstract of DOI:10.1515/znb-2005-0717

In the presence of tin(II)chloride, bromonitromethane reacts with imines derived from aromatic aldehydes and ammonia to yield 2-amino-2-aromatic substituted nitroethane derivatives via an addition reaction in good yields.

Full text of DOI:10.1515/znb-2005-0717

Synthesis of Some 2-Aminonitroethanes via Tin(II)chloride Mediated
Addition Reaction of Bromonitromethane to Imines
Ali S. Mahasneh and Hazem Qaraqe
Department of Chemistry, Mutah University, PO. Box 7, Karak-Jordan
Reprint requests to Dr. A. S. Mahasneh. E-mail: asmahasneh@hotmail.com
Z. Naturforsch. 60b, 797 – 800 (2005); received December 19, 2004
In the presence of tin(II)chloride, bromonitromethane reacts with imines derived from aromatic
aldehydes and ammonia to yield 2-amino-2-aromatic substituted nitroethane derivatives via an addi-
tion reaction in good yields.
Key words: Bromonitromethane, Imines, Benzaldimines
Introduction
turn can be used as precursors for synthesis of α-amino
acids [8].
In chemical synthesis, bromonitromethane was re-
ported to behave as a versatile electrophile, for exam-
ple in the synthesis of nitrothiophenes and related com-
pounds [1]. It is a C-1 building block with the advan-
tage of bearing a nitro group [2]. A potential conver-
sion of the nitro group into an amino group via reduc-
tion and the ease of replacement of the nitro group by
a hydrogen atom (denitration) using tributyltin hydride
makes bromonitromethane a useful synthon.
Bromonitromethane was found to form β-
nitroalcohols via a tin(II)chloride mediated addition
reaction to aliphatic aldehydes [9]. Here the polarity
of bromonitromethane is reversed from an electrophile
to a nucleophile. Trichloronitromethane reacts with
acyl chlorides in the presence of tin(II) chloride
to produce dichloronitroketones via a substitution
reaction [10]. In this work the results of the reaction
of bromonitromethane with imines derived from
aromatic aldehydes and ammonia, in the presence
of tin(II)chloride using diethyl ether as solvent are
reported.
Imines (azomethines or Schiff bases) react with
electrophiles, HCl for example, under anhydrous con-
ditions to form iminium salts [3]. They were also re-
ported to allow 1,2-addition across the carbon-nitrogen
double bond; for example nitrosyl chloride (NOCl),
Results and Discussion
◦
at −30 C adds to imines to give N-nitrosoamines
Primary α-nitroamines 2 were obtained from ben-
zaldimines 1 and bromonitromethane in the pres-
ence of a stoichiometric amount of SnCl2 (Scheme 1,
Table 1).
with a chlorine atom bonded to the carbon atom of
the former imine carbon atom [4]. Alkylation of N-
alkyl-aldimines and -ketimines occurs at the N-atom to
give the corresponding iminium salts [5]. In general,
processes of this type are subject to steric hindrance
and electronic activation so that imines having bulky
groups or N-aryl substituents N-alkylate only with dif-
ficulty and require the use of more powerful reagents.
Nucleophilic reagents attack the imine function at the
carbon atom this was in fact found to be the case [6].
Imines lacking hydrogen atoms α- to the carbon-
nitrogen double bond react with Grignard and organo-
lithium reagents analogous to carbonyl compounds to
give adducts which on hydrolytic work up afford sec-
ondary amines in good to excellent yield [7]. The addi-
tion of hydrogen cyanide to imines occurs readily and
Scheme 1.
Tin(II)chloride changes the character of bromoni-
tromethane from a powerful electrophile to a nu-
cleophile leading to the formation of a carbon-
carbon bond between the CH2NO2 unit and the imine
function.
1
The H NMR spectrum of compound 2d shows a
provides a viable route to α-aminonitriles, which in broad signal at δ = 3.18 which could be quenched
c
0932–0776 / 05 / 0700–0797 $ 06.00 ꢀ 2005 Verlag der Zeitschrift fu¨r Naturforschung, Tu¨bingen · http://znaturforsch.com
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798 A. S. Mahasneh – H. Qaraqe · Synthesis of Some 2-Aminonitroethanes via Tin(II)chloride Mediated Addition Reaction
Table 1. Yields of amines 2 from the reaction of imines 1 and
bromonitromethane.
2
a
b
c
d
e
f
g
h
Ar
C6H5
Yield [%]
83
90
87
82
80
82
77
76
4-Nitro-C6H4
3-Nitro-C6H4
4-Methyl-C6H4
4-Ethyl-C6H4
2,4-Dimethyl-C6H4
2-Methyl-C6H4
4-Methoxy-C6H4
with deuterium oxide, for the NH2 proton, a multiplet
at δ = 4.55 (CH2NO2) and a multiplet at δ = 5.35
(benzylic CH). The 13C NMR spectrum showed char-
acteristic signals at δ = 70.1 (benzylic carbon) and
81.5 ppm (CH2NO2). The compound showed a strong
IR absorption at 1554 cm−1 for the NO2 group. All
Scheme 2.
Experimental Section
All reagents were of commercial grade, and reagent qual-
ity solvents were used without further purification. IR spec-
tra were determined on a Mattson 5000 spectrometer. NMR
spectra were determined on Bruker AC 200 MHz instrument.
In all cases, samples were dissolved in CDCl3 using TMS as
internal standard. The elemental analysis were performed at
the Middle East Technical University-Analyses Center.
1
other prepared products gave H NMR, 13C NMR and
IR signals consistent with the assigned structures. The
electron impact mass spectrum of compound 2d at
70 eV showed the M+ peak at m/e = 180 (4%), the
[M+-NO2] peak at 134 (65%), and a very intense peak
Bromonitromethane was prepared according to the fol-
lowing improved procedure [12]: A mixture of water
(500 ml), ice (200 g), NaOH (20 g, 0.5 mol) and ni-
tromethane (36.6 g, 0.6 mol) was vigorously stirred using a
mechanical stirrer f◦or 30 min during which the temperature
was kept around 0 C. Bromine (60 g, 0.4 mol) was added
to the solution at once with continuous stirring. After 4 h the
at 119 (98%) due to [M+-CH3NO2]; the base peak at
+
91 is possibly due to the a tropylium ion C7H7
.
When the reactions were performed in tetrahydro-
furan, dimethyl sulfoxide, or acetonitrile, no dramatic
increase in the yields was noticed. The yields were
enhanced when the amount of tin(II) chloride was
increased. As an example, the yield of 2d was in- solution was steam distilled. The product was isolated, dried
over anhydrous MgSO4 and fractionally distilled. Bromoni-
creased from 82% to 87% when the mole ratio was
changed from 1:1:1 to 1:1.2:1 (imine : tin(II) chlo-
ride : BrCH2NO2).
tromethane was collected at 134 – 136 ◦C; yield: 30 g (56%).
1
– H NMR: δ = 5.45 (s, CH2). IR (neat): ν = 1565, 1370,
1260 cm−1
.
Imines were prepared from aromatic aldehydes and am-
monia according to the literature general procedure [13]:
Conclusion
As can be seen from the results, bromonitromethane
can be considered a valuable C-1 unit in C-C bond for-
mation reactions. Functionalities present in the prod-
ucts may be suitable for a wide range of other chemi-
cal manipulations. The CH2NO2 unit, for example, can
be transformed into a carbonyl group by the Nef reac-
tion [11], and then to carboxylic acid, making prod-
ucts 2 precursors to some α-amino acids. High yields,
relatively short reaction time, low cost and easy han-
dling are additional advantages of this reaction. Imines
prepared from aromatic aldehydes and aniline deriva-
tives and aliphatic amines gave similar reaction prod-
ucts and the results will be sent to publication later on.
The mechanism of this reaction remains uncertain,
however, a proposed mechanism as shown in Scheme 2
is suggested.
General procedure for the synthesis of products (2a – h)
A mixture of SnCl2 (1.0 g, 5.3 mmol), CH3BrNO2 (0.7 g,
5 mmol) and Na-dried diethyl ether (50 ml) was stirred in
a 100 ml flask. To the flask another mixture of the imine
(5 mmol) in dry ether (10 ml) was added. The mixture was
left stirring for 5 h during which the reaction was monitored
by TLC using an ethyl acetate/hexane mixture (1:5) as elu-
ent. The mixture was then diluted with ether (50 ml), washed
successively with (3×20 ml) portions of 0.1 M aqueous HCl
solution, saturated aqueous NaHCO3 (30 ml) solution and
brine (30 ml), and dried over anhydrous MgSO4. The crude
product was purified by column chromatography (silica gel,
ethyl acetate/hexane mixture (1:4) as eluent). Solid products
were purified by recrystallization from saturated hot ethanol
solution.
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A. S. Mahasneh – H. Qaraqe · Synthesis of Some 2-Aminonitroethanes via Tin(II)chloride Mediated Addition Reaction 799
2-Amino-2-(4-ethylphenyl)-1-nitroethane (2e): Oil, IR
2-Amino-2-phenyl-1-nitroethane (2a): Oil. IR (film): ν =
3429 (NH2), 1554 (NO2), 1397, 1066, 765, 700 cm−1. – (film): ν = 3418 (NH2), 2924, 1554 (NO2), 1419, 1379,
1H NMR (200 MHz, CDCl3): δ = 3.1 (broad, 2H, NH2), 1082, 833 cm−1. – 1H NMR (200 MHz, CDCl3): δ =
4.6 (m, 2H, CH2NO2), 5.45 (m, 1H, C6H5CH), 7.4 (m, 1.25 (t, 3H, Me), 2.7 (q, 2H, CH2Me), 2.85 (broad, 2H,
5H, C6H5). – 13C{H} NMR (200 MHz, CDCl3): δ = 71.2 NH2), 4.55 (m, 2H, CH2NO2), 5.45 (m, 1H, C6H4CH), 7.15,
(C6H5CH), 81.5 (CH2NO2), 126.4, 128.2, 129.2, 138.0 7.4 (dd, 4H, C6H4). – 13C{H} NMR (200 MHz, CDCl3): δ =
(C6H5). – C8H10N2O2 (166.18): calcd. C 57.82, H 6.07, 15.5 (Me), 28.5 (CH2), 71.2 (C6H4CH), 81.5 (CH2NO2),
N 16.86; found C 57.79, H 6.68, N 16.92.
126.2, 128.5, 136.0, 145.5 (C6H4). – C10H14N2O2 (194.23):
calcd. C 61.84, H 7.27, N 14.42; found C 61.92, H 7.30,
N 14.66. – MS (EI, 70 eV): m/z (%) = 194 (2) [M+] 177 (4),
148 (66), 133 (84), 91 (63), 79 (68), 28 (100), 18 (38).
2-Amino-2-(2,4-dimethylphenyl)-1-nitroethane (2f): M. p.
2-Amino-2-(4-nitrophenyl)-1-nitroethane (2b): M. p. 54 –
56 ◦C. IR (KBr): ν = 3421 (NH2), 1554, 1536 (NO2),
1350, 1085, 856 cm−1. – 1H NMR (200 MHz, CDCl3):
δ = 3.2 (broad, 2H, NH2), 4.55 (m, 2H, CH2NO2), 5.6 (m,
1H, C6H4CH), 7.2, 8.3 (2 d, 4H, C6H4). – 13C{H} NMR
(200 MHz, CDCl3): δ = 70.0 (C6H4CH), 80.5 (CH2NO2),
124.1, 127.2, 145.0, 149.3 (C6H4). – C8H9N3O4 (211.18):
calcd. C 45.50, H 4.30, N 19.90; found C 45.56, H 4.32,
N 19.94. – MS (EI, 70 eV ): m/z (%) = 211 (4) [M+], 194 (5),
179 (2), 165 (78), 150 (45), 120 (12), 105 (24), 91 (67),
65 (27), 28 (89), 18 (100).
◦
52 – 55 C. IR (KBr): ν = 3469 (NH2), 2924, 1554 (NO2),
1465, 1379, 1072, 821 cm−1. – 1H NMR (200 MHz, CDCl3):
δ = 2.3 (s, 3H, Me), 2.35 (s, 3H, Me), 2.65 (broad, 2H,
NH2), 4.5 (m, 2H, CH2NO2), 5.65 (m, 1H, C6H4CH),
6.8 – 7.42 (m, 3H, C6H3). – 13C{H} NMR (200 MHz,
CDCl3): δ = 19.2 (Me), 21.5 (Me), 68.2 (C6H4CH),
81.3 (CH2NO2), 126.0, 128.0, 132.0, 133.5, 134.8,
2-Amino-2-(3-nitrophenyl)-1-nitroethane (2c): M. p. 69 – 139 (C6H4). – C10H14N2O2 (194.23): calcd. C 61.84,
72 ◦C. IR (KBr): ν = 3420 (NH2), 2926, 1556, 1540 (NO2), H 7.27, N 14.42; found C 61.92, H 7.30, N 14.66.
1354, 1072, 736 cm−1. – 1H NMR (200 MHz, CDCl3):
2-Amino-2-(2-methylphenyl)-1-nitroethane (2g): Oil. IR
δ = 3.1 (broad, 2H, NH2), 4.6 (m, 2H, CH2NO2), 5.6 (m, (film): ν = 3416 (broad NH2), 2930, 1550 (s, NO2), 1462,
1H, C6H4CH), 7.6 – 8.4 (m, 4H, C6H4). – 13C{H} NMR 1379, 1070 cm−1. – 1H NMR (200 MHz, CDCl3): δ =
(200 MHz, CDCl3): δ = 70.2 (C6H4CH), 80.5 (CH2NO2), 2.35 (s, 3H, Me), 2.85 (broad, 2H, NH2), 4.5 (m, 2H,
121.2, 124.0, 130.2, 1324, 140.1, 148.7 (C6H4).
–
CH2NO2), 5.68 (m, 1H, C6H4CH), 7.15, 7.60 (m, 4H,
C8H9N3O4 (211.18): calcd. C 45.50, H 4.30, N 19.90; found C6H4). – 13C{H} NMR (200 MHz, CDCl3): δ = 18.5 (Me),
C 45.43, H 4.43, N 19.95. – MS (EI, 70 eV ): m/z (%) = 211 68.5 (C6H4CH), 80.5 (CH2NO2), 126.1, 127.5, 129.0, 131.4,
(3) [M+] 179 (22), 165 (4), 151 (28), 133 (42), 105 (45), 134.5, 136.5 (C6H4). – C9H12N2O2 (180.39): calcd. C 59.93,
55 (84), 29 (100), 18 (42).
H 6.71, N 15.63; found C 59.94, H 6.68, N 15.70.
2-Amino-2-(4-methoxyphenyl)-1-nitroethane (2h): Oil. IR
2-Amino-2-(4-methylphenyl)-1-nitroethane (2d): M. p.
◦
47 – 49 C. IR (KBr): ν = 3477 (NH2), 2924, 1554 (NO2), (film): ν = 3416 (broad NH2), 2926, 1612, 1554 (s, NO2),
1379, 1249, 1178, 1030 cm−1. – 1H NMR (200 MHz,
1379, 1080, 819 cm−1. – 1H NMR (200 MHz, CDCl3):
CDCl3): δ = 3.08 (broad, 2H, NH2), 3.80 (s, 3H, Me),
δ = 2.35 (s, 3H, Me), 3.18 (broad, 2H, NH2), 4.55 (m,
2H, CH2NO2), 5.35 (m, 1H, C6H4CH), 7.15, 7.3 (dd, 4.55 (m, 2H, CH2NO2), 5.38 (m, 1H, C6H4CH), 6.90,
7.20 (dd, 4H, C6H4). – 13C{H} NMR (200 MHz, CDCl3):
4H, C6H4). – 13C{H} NMR (200 MHz, CDCl3): δ =
δ = 55.2 (OMe), 71.0 (C6H4CH), 81.5 (CH2NO2), 114.5,
21.1 (Me), 70.2 (C6H4CH), 81.5 (CH2NO2), 126.1, 130.5,
135.0,138.5 (C6H4). – C9H12N2O2 (180.39): calcd. C 59.93, 127.5, 130, 160.4 (C6H4). – C9H12N2O3 (196.38): calcd.
C 55.04, H 6.16, N 14.36; found C 55.10, H 6.22,
N 14.40.
H 6.71, N 15.63; found C 59.84, H 6.66, N 15.70. – MS (EI,
70 eV): m/z (%) = 180 (4) [M+], 134 (65), 119 (88), 91 (100).
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