Synthesis and oxidation of (E)-1,2-diphenyl-2-(arylimino) ethanol derivatives

Article abstract of DOI:10.1007/s11164-012-0761-0

The compounds (E)-1,2-diphenyl-2-(phenylimino)ethanol, (E)-1,2-diphenyl-2- (p-tolylimino)ethanol, and (E)-2-((4-chlorophenyl)imino)-1,2-diphenylethanol) were synthesized by reaction of a p-substituted aniline with benzoin then oxidized with chromium trioxide-triethylamine in chloroform to give (E)-1,2-diphenyl-2-(phenylimino)ethanone, (E)-1,2-diphenyl-2-(p-tolylimino) ethanone, and (E)-2-((4-chlorophenyl)imino)-1,2-diphenylethanone in very high yield. The products were characterized by IR and NMR spectral analysis.

Full text of DOI:10.1007/s11164-012-0761-0

Res Chem Intermed (2013) 39:2351–2355
DOI 10.1007/s11164-012-0761-0
Synthesis and oxidation of (E)-1,2-diphenyl-2-
(arylimino) ethanol derivatives
•
Zakaria H. Aiube Sabah T. Najiam
Abdul Amir H. Kadhum
•
Received: 18 July 2012 / Accepted: 6 August 2012 / Published online: 16 September 2012
Ó Springer Science+Business Media B.V. 2012
Abstract The compounds (E)-1,2-diphenyl-2-(phenylimino)ethanol, (E)-1,2-
diphenyl-2-(p-tolylimino)ethanol, and (E)-2-((4-chlorophenyl)imino)-1,2-diphenyl-
ethanol) were synthesized by reaction of a p-substituted aniline with benzoin then
oxidized with chromium trioxide–triethylamine in chloroform to give (E)-1,2-
diphenyl-2-(phenylimino)ethanone, (E)-1,2-diphenyl-2-(p-tolylimino)ethanone, and
(E)-2-((4-chlorophenyl)imino)-1,2-diphenylethanone in very high yield. The prod-
ucts were characterized by IR and NMR spectral analysis.
Keywords Chromium trioxide Á p,x-Substituted aniline Á Benzil Á Benzoin Schiff
base
Introduction
A variety of oxidizing agents and conditions can be used to oxidize secondary
alcohols to ketones [1–4]. Chromium trioxide–sulfuric acid in water, known as
Jones reagent [5, 6], can be used to oxidize secondary alcohols to ketones in high
yield without disturbing double or triple bonds which may be present, and
without epimerizing an adjacent asymmetric center [5, 6]. Chromium trioxide–
pyridine, known as Collins reagent, can be used to oxidize secondary alcohols,
similar to Jones reagent, but this reagent is more specific for acid-sensitive alcohols.
Corey [6–9] used Cr(VI)—oxidizing agents, for example pyridinium dichromate in
dimethylformamide and pyridinium chlorochromate in dichloromethane. Both
Z. H. Aiube Á S. T. Najiam
Department of Chemistry, College of Education (Ibn Al-Haithaim), Baghdad University,
Baghdad, Iraq
A. A. H. Kadhum (&)
Department of Chemical and Process Engineering, Universiti Kebangsaan Malaysia,
Bangi, Selangor, Malaysia
e-mail: amir@eng.ukm.my
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Z. H. Aiube et al.
reagents are characterized by extraordinary ease of product isolation, since
oxidizing agent removed by filtration and product obtained by evaporation.
The activity of these oxidizing compounds is strongly dependent on the nature of
the heteroatomic ring and the position of attachment to the ring [11]. These
compounds have been studied extensively because of their flexibility, selectivity,
and sensitivity toward the central metal atom, and structural similarities with natural
biological substances, and because of the presence of imine group (–N=CH–) which
imparts biological activity [13–15]. In this work, chromium trioxide–triethylamine
in chloroform was used for oxidation of (E)-1,2-diphenyl-2-(phenylimino)ethanol,
(E)-1,2-diphenyl-2-(p-tolylimino)ethanol, and (E)-2-((4-chlorophenyl)imino)-1,2-
diphenylethanol, because the secondary alcohol contains an azomethene double
bond (C=N) which is very sensitive to hydrolysis in acidic and basic medium.
Experimental
All chemicals used were of reagent grade (supplied by Sigma-Aldrich) and used as
supplied. Melting points were recorded on an Electrothermal Stuart apparatus and
are uncorrected. IR spectra were recorded on a Euro OV Ectro FTIR 8400s infrared
1
spectrophotometer and H NMR spectra were recorded on a dpx400 instrument,
with CDCl3 as solvent.
Synthesis of (E)-1,2-diphenyl-2-(phenylimino)ethanone derivatives (I), (x = H,
Me, Cl)
A mixture of equimolar amounts of benzoin and p,x-substituted aniline (x = H, Me, Cl)
inasmallamountofethylalcoholwasheatedat120 °Cfor1 h,thenthereactionmixture
was cooled. The residue obtained was crystallized from ethyl alcohol to give the
2-hydroxy-1,2-diphenyl-N-(p,x-substituted phenyl)-azomethene (I) (Table 1).
X
HO
N
X=H, Me, Cl
Compound I
Table 1 Physical and spectroscopic parameters of derivatives of compound I
Compound I
M.p. (°C)
Yield (%)
IR -m (cm-1
)
1H NMR (d, ppm)
OH
C=N
OH
CH
Ph
Me
A (x = H)
B (x = Me)
C (x = Cl)
124–6
76
79
87
3,400–3,375
3,380–3,360
3,400–3,370
1,680
1,665
1,670
–
–
–
–
118–120
123–4
4.6
4.5
6.0
5.9
7.2–7.9
7.2–8.0
2.2
–
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Synthesis and oxidation of (E)-1,2-diphenyl-2-(arylimino) ethanol
2353
Table 2 Physical and spectroscopic parameters of derivatives of compound II
Compound II
M.p. (°C)
Yield (%)
IR-m (cm-1
)
Crystallizing solvents
C=O
C=N
A (x = H)
B (x = Me)
C (x = Cl)
104–6
110–2
98–100
82
87
90
1,668
1,662
1,666
1,626
1,618
1,624
Ethyl alcohol
Methyl alcohol
Methyl alcohol
Oxidation of (E)-1,2-diphenyl-2-(phenylimino)ethanone derivatives (I), (x = H,
Me, Cl)
With concentrated nitric acid
A mixture of compound I (1 g) in 4 ml concentrated nitric acid was heated on steam
bath for 30 min. Then 20 ml water was added, the reaction mixture was cooled to
room temperature, and the precipitate formed was collected, washed with water, and
crystallized from ethanol to give benzil, m.p. 96. The melting point when mixed
with authentic benzil was not depressed [7], and the IR spectrum of the product was
identical with that of authentic benzil.
O
X
N
X=H, Me, Cl
With chromium trioxide–triethylamine in chloroform
A solution of 60 mmol triethylamine and 30 mmol anhydrous chromium trioxide in
75 ml chloroform was swirled until a clear dark red solution was formed. The
solution was cooled to room temperature, and 5 mmol IA, IB, or IC was added,
with stirring, for 20 min. The clear solution was decanted. The residue was washed
several times with chloroform and the chloroform was decanted. The combined
chloroform solution was evaporated and the residue obtained was re-crystallized
from a suitable solvent to give the 2-oxo-1,2-diphenyl-N(p,x-substituted
phenyl)azomethene (II). Melting points, crystallizing solvents, and IR spectral
data are given in Table 2.
Result and discussion
Condensation of the carbonyl groups of reducing sugars, for example aldoses and
ketoses as a-hydroxy aldehydes and ketones, with the primary amino group of amino
acids and proteins is known as the ‘‘Maillard reaction’’ [11]. It is a complicated
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reaction, well described by Hodge [12, 13]. The initial step is addition–elimination
reaction of the open chain aldoses and ketoses with the amine producing an unstable
Schiff base (imine) which undergo enolization and molecular rearrangement to give
1-amino-1-deoxy-2-ketoses (Amadori product [13, 14]) and 2-amino-2-deoxy-1-
aldoses (Heyns product [14]), respectively.
NH2
X
X
HO
HO
HO
N
N
H
O
X
X=H, Me, Cl
X
O
N
H
Benzoin as a-hydroxy ketone was condensed with p,x-substituted anilines
(x = H, Me, Cl) as primary aromatic amines; the product was a stable benzoin
Schiff base (imine) I, in contrast with the reducing sugar Schiff base.
IR spectral analysis of I revealed strong, broad OH-stretching bands in the range
3,400–3,360 cm-1 and sharp, medium intensity (C=N)-stretching bands at 1,680,
1
1,665, and 1,670 cm-1 for IA, IB, and IC, respectively. H NMR spectral analysis
revealed CH and OH protons signal at d (ppm) 6 (1H, d) and 4.6 (1H, d) for IB and
5.9 (1H, d) and 4.5 (1H, d) for IC.
Oxidation of benzoin Schiff base (IA) with concentrated nitric acid gave benzil,
which was characterized by its melting point (undepressed mixed point of oxidation
product with authentic benzil), also identity of its IR-spectrum with that of authentic
benzil [10]. Formation of benzil might be explained, that the benzoin Schiff base
(imine) (IA) is more easily to hydrolysis in acidic media which was oxidize to
benzil. Oxidation of the benzoin Schiff base (IA, IB, and IC) with chromium
trioxide–triethylamine in chloroform gave the 2-oxo-1,2-diphenyl-N(p,x-substituted
phenyl) azomethenes (IIA, IIB, and IIC) which were characterized by their melting
points (undepressed when IIA, IIB, and IIC were mixed with authentic samples
prepared by another methods [15]). IR spectral analysis showed the disappearance
of the strong, broad OH-stretching bands and the appearance of the strong, sharp
(C=O)-stretching bands at 1,668, 1,662, and 1,666 cm-1 and medium-intensity,
sharp stretching bands of C=N groups at 1,626, 1,618, and 1,624 cm-1
,
respectively. The IR spectra of IIA, IIB, and IIC were identical with those of
authentic samples prepared by other methods [15, 16].
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2355
Conclusion
It is clear that use of chromium trioxide–triethylamine in chloroform as oxidizing
agent for oxidation of benzoin Schiff base (IA, IB, and IC) did not disturb the
azomethene double bond (C=N), which is highly sensitive to hydrolysis in acidic
and basic media, and also gave very high yields with more rapid oxidation than by
use of the Jones and Collins oxidizing agents.
References
1. Fieser, Fieser’s Reagents for organic synthesis, Wiley, New York, 1967
2. Von L.F. Fieser, M. Fieser, Reagents for organic synthesis, Wiley, New York, 1969
3. H.C. Brown, C.P. Garg, K.-T. Liu, Org. Chem. 36, 387 (1971)
4. J. March, Advanced organic chemistry, 2nd edn. (McGraw-Hill, Tokyo, 1977), pp. 1073–1084
5. J.C. Collins, W.W. Hess, Org. Synthesis 52, 5 (1972)
6. K.B. Sharpless, K. Akashi, J. Am. Chem. Soc. 97, 5927 (1975)
7. Y.S. Cheng, W.L. Liu, S. Chen. Synthesis, 223 (1980)
8. J. Corey, J.W. Suggs, Tetrahedron Lett. 16, 2647 (1975)
9. J. Corey, G. Schmidt, Tetrahedron Lett. 20, 339 (1979)
10. L.F. Fieser, K.L. Williamson, Organic experiments, 5th edn. (D. C. Heath and Co., Lexington, Mass.,
1983), pp. 146–149 and 210–215
11. R. Mladenova, M. Ignatova, N. Manolova, T. Petrova, I. Rashkov, Eur. Polym. J. 38, 989–999
(2002). doi:10.1016/S0014-3057(01)00260-9
12. O.M. Walsh, M.J. Meegan, R.M. Prendergast, T.A. Nakib, Eur. J. Med. Chem. 31, 989 (1996)
13. A.A. Al-Amiery, Y. Al-Majedy, H. Abdulreazak, H. Abood, Bioinorg. Chem. Appl. 2011, 1–5 (2011)
14. A.A. Al-Amiery, R.I.H. Al-Bayati, K.Y. Saour, M.F. Radi, Res. Chem. Intermediate 38, 559–569
(2011)
15. A.A. Al-Amiery, Y.K. Al-Majedy, H.H. Ibrahim, A.A. Al-Tamimi, Org. Med. Chem. Lett. 2, 32
(2012). doi:10.1186/2191-2858-2-4
16. A.H. Kadhum, B.A. Wasmi, A.B. Mohamad, A.A. Al-Amiery, M.S. Takriff, Res. Chem. Interme-
diate 38, 659–668 (2012)
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