Oxidation of benzoin catalyzed by oxovanadium(IV) schiff base complexes.

0.75 MB·English

by  Alsalim, Tahseen A

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RESEARCH ARTICLE Open Access
Oxidation of benzoin catalyzed by oxovanadium
(IV) schiff base complexes
Tahseen A Alsalim1, Jabbar S Hadi1, Omar N Ali1, Hanna S Abbo2 and Salam JJ Titinchi2*
Abstract
Background: The oxidative transformation ofbenzoin to benzil has been accomplishedby the useof a wide
variety of reagents or catalysts and different reactionprocedures. The conventional oxidizing agents yielded mainly
benzaldehyde or/and benzoic acid and only a trace amount ofbenzil. The limits ofpractical utilization of these
reagents involves theuse of stoichiometric amounts of corrosive acids or toxic metallic reagents, which inturn
produce undesirable waste materials and required high reaction temperatures.
Inrecent years, vanadiumcomplexeshave attracted much attention for their potential utility as catalystsfor various
types ofreactions.
Results: Active and selective catalyticsystemsof new unsymmetricaloxovanadium(IV) Schiff base complexes for
theoxidation ofbenzoin is reported. The Schiff base ligands are derived between 2-aminoethanol and 2-hydroxy-1-
naphthaldehyde (H L1) or 3-ethoxy salicylaldehyde (H L3);and 2-aminophenol and 3-ethoxysalicylaldehyde (H L2) or
2 2 2
2-hydroxy-1-naphthaldehyde (H L4).The unsymmetrical Schiff bases behave as tridentate dibasic ONO donor
2
ligands. Reaction of theseSchiff base ligands with oxovanadyl sulphate afforded the mononuclear oxovanadium(IV)
complexes (VIVOLx.H O), which are characterized by various physico-chemical techniques.
2
The catalytic oxidation activities ofthese complexes for benzoin were evaluated using H O as an oxidant. The best
2 2
reaction conditions are obtained byconsidering the effect ofsolvent,reactiontime and temperature. Under the
optimized reaction conditions, VOL4 catalyst showed high conversion (>99%) with excellent selectivity to benzil
(~100%) ina shorterreactiontime comparedto the other catalysts considered.
Conclusion: Four tridentate ONO type Schiff base ligands were synthesized. Complexation of theseligands with
vanadyl(IV) sulphate leads to the formation of new oxovanadium(IV) complexes oftypeVIVOL.H O.
2
Elemental analyses and spectral data of thefree ligands and theiroxovanadium(IV) complexeswere found to be in
goodagreement with their structures, indicating high purity of allthecompounds.
Oxovanadium complexeswere screened for the oxidation of benzoin to benzil using H O as oxidant. The effectof
2 2
time, solventand temperature were optimizedto obtain maximum yield. The catalytic activity resultsdemonstrate
that these catalytic systems are both highly active and selective for the oxidation of benzoin under mild reaction
conditions.
Keywords: Tridentate ONO Schiff base ligands, Oxovanadium(IV) complexes,Benzoinoxidation, Benzil
Background importantsyntheticintermediatesinthesynthesisofmany
Liquidphasecatalyticoxidationofalcoholsisafascinating heterocyclic compounds. α-Dicarbonyl compounds have
reaction and is one of the most important synthetic reac- diverse applications in organic and pharmaceutical indus-
tionsinorganicchemistry.Oxidationof benzointobenzil tries such as photosensitive and synthetic reagents [7,8]
has been extensively studied for the production of fine and photo initiators for radical polymerization [9]. Benzil,
chemicals [1-6]. In general α-dicarbonyl compounds are in particular, is a standard building block in organic syn-
thesisandisutilizedasanintermediateinthesynthesisof
*Correspondence:[email protected] chiralligandsandbiologicallyactivecompounds.
2DepartmentofChemistry,UniversityoftheWesternCapeBellville,Private The oxidative transformation of an α-hydroxy ketone
BagX17,Bellville,CapeTown7535,SouthAfrica to the corresponding α-diketone (benzoin to benzil) has
Fulllistofauthorinformationisavailableattheendofthearticle
©2013Alsalimetal.;licenseeChemistryCentralLtd.ThisisanOpenAccessarticledistributedunderthetermsoftheCreative
CommonsAttributionLicense(http://creativecommons.org/licenses/by/2.0),whichpermitsunrestricteduse,distribution,and
reproductioninanymedium,providedtheoriginalworkisproperlycited.
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been accomplished by the use of a wide variety of act as tridentate dibasic ligands. These ligands can co-
reagents or catalysts and different reaction procedures. ordinate through the imino nitrogen and two oxygen
Several reagents have been used for this transformation atoms from the deprotonation of the phenolic groups as
such as nitric acid, Th(III) and Y(III) nitrate [10] and well as from the aliphatic hydroxyl group. The ligands
bismuth(III) nitrate-copper(II) acetate [11]. The conven- react with V(IV) to fill three of the four equatorial co-
tional oxidizing agents viz., permanganate, dichromate ordination sites with a water molecule coordinating to
or chromic acid yielded chiefly benzaldehyde/benzoic theremainingsite.
acid and only a trace of benzil. The limits of practical The IR spectra of the ligands and their complexes
utilization of these reagents involves the use of stoichio- were compared to determine any changes during com-
metric amounts of corrosive acids or toxic metallic plexation and to confirm their structures (Additional file
reagents, which inturn produceundesirablewastemate- 1: Figure S1-S3). The IR spectra of the ligands showed a
rialsandrequiredhigh reaction temperatures. broad absorption band at 3230–3117 cm-1 attributed to
In recent years, vanadium complexes have attracted the stretching vibration of intramolecular hydrogen
much attention for their potential utility as catalysts for bondedOHgroups[28].Thisbanddisappeared oncom-
various types of reactions. Oxovanadium complexes plexation indicating the coordination of vanadium metal
catalyze various oxidation reactions viz., hydroxylation through OH groups after deprotonation. A new medium
of phenols [12,13], oxidation of sulfides to sulfoxides intensity band near 3400–3500 cm-1 is attributed to the
[14,15], oxidation of alcohols [15], epoxidation of olefins νOH stretching vibration of the coordinated water mol-
[15-19], hydroxylation of benzene to mono- and dihy- ecule to the central metal ion [29]. A strong band at
droxybenzenes [12,20,21] including reactions such as the 1648–1629 cm-1 of the spectra of the ligand was
coupling of 2-naphthols as well as Mannich-type reac- assigned to the azomethine (C=N) stretching vibration.
tions [22-25]. Most recently, the application of various This band shifted to lower frequency (by 10–30 cm-1) in
oxovanadium complexes as catalysts in different oxida- the complexes, indicating that the nitrogen atom of the
tion reactions hasbeenreviewed[26,27]. azomethine group is coordinated to the metal centre
In this report we describe the synthesis of Schiff base [30,31]. The phenolic ν(C–O) band at 1114–1116 cm-1
ligands derived by reaction between 2-aminophenol or in the free ligand is shifted towards lower frequency by
2-aminoethanol and 2-hydroxy-1-naphthaldehyde or 3- 10 ± 15 cm-1 in the complexes, verifying coordination
ethoxysalicylaldehydetoformtridentatedibasicligands via the deprotonated phenolic oxygen. The complexes
of the ONO type. Complexation of these ligands with show a new strong band in the region between 975–987
vanadyl sulphate produced oxovanadium(IV) com- cm-1 assigned to stretching vibration of V=O [32,33]
plexes.Tothebestofourknowledge,thisisthefirstre- which indicates its monomeric nature [34]. The absence
port describing the synthesis of these oxovanadium(IV) of significant bands in the frequency range below 900
complexes. cm-1 demonstrates no V=O····V bridge vibration [35,36].
Aspartofourcontinuinginterestinoxidationreactions A similar monomeric nature of related complexes has
by vanadiumcomplexes [13] andconsideringthe demand also been well established crystallographically [37,38].
ofmoreefficientcatalyticsystems,weundertookaninves- The appearance of two to three new moderately intense
tigation of these oxovanadium(IV) complexes as catalysts bands in the low-frequency region of 350–500 cm-1 in
forbenzionoxidationforthefirsttime. the complexes are assigned to stretching frequencies of
ν(V–N) and ν(V–O) bonds i.e. coordination of azo-
Results and discussion methine nitrogen as well as phenolic oxygen to the van-
Synthesisandcharacterization adium metal after deprotonation. The C=C stretching
Facile condensation of 2-aminophenol or 2-aminoethanol modes of the benzene ring of the ligand around 1600
and 2-hydroxy-1-naphthaldehyde or 3-ethoxy salicylalde- cm-1 does not show any significant shift on complex-
hyde in 1:1 molar ratio afforded four Schiff base ligands ation. Thus, the IR data indicates that the Schiff bases
viz. H L1, H L2, H L3 and H L4, respectively (Scheme 1). behave as dibasic tridentate ligands coordinating
2 2 2 2
These tridentate ligands reacted readily with vanadyl sul- through phenolic and alcoholic oxygens and the azo-
fateinmethanoltoformtheoxovanadiumcomplexeswith methinenitrogen.
thesamegeneralstructure(Scheme2). The 1H NMR spectra of ligand H L1 and ligand H L3
2 2
Spectral data and elemental analysis of all the synthe- displayed a broad signal corresponding to the OH pro-
sized ligands and their oxovanadium(IV) complexes ton of the ethanol amine moiety at 5.00 and 5.32 ppm,
were in good agreement with their structure, indicating respectively. The phenolic OH protons appeared as
thehigh purity ofallthe compounds. broad signals at 13.88 and 13.70 ppm, respectively. The
The analytical data of the complexes indicates a 1:1 1H NMR spectra of ligands H L2 and H L4 displayed the
2 2
metal: ligand stoichiometry, and hence the Schiff bases OH phenolic groups as singlets at 9.77 and 14.2, and
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OH
N OH
N OH
N OH
OH N
OH
OH
OH
O
O
CH3
CH3
L1 L2 L3 L4
Scheme1Structureoftheligands.
10.35 and 15.7 ppm, respectively [39]. In all the ligands Catalyticactivitystudies
the azomethine HC=N proton appeared as a singlets at The catalytic activity of oxovanadium complexes for the
8.35−9.43 ppm. Allthe otheraromatic and aliphatic pro- oxidation of benzoin to benzil has been studied and the
tons were observed in the expected regions (Additional effect of time, solvent and temperature were optimized
file1:FigureS4-S7). to produce maximum yield. Oxidation did not proceed
The elemental analyses of the ligands and the com- when the reaction was carried out in the presence of ei-
plexes are in agreement with their formulation. The ther hydrogen peroxide or oxovanadium complexes
elemental analysis of the complexes confirms a 1:1 only.
(metal: ligand) stiochiometry. Progressof the reaction (asdetermined bythe concen-
The result of mass spectra further indicates that theV tration of benzil) was monitored spectrophotometrically
(IV) complexes have a monomeric form of 1:1 stiochio- and identification of the product was confirmed by GC-
metry, where the observed molecular ion peak (m/z) MS analyses which showed that benzil was the only
values are consistent with the calculated value in the product detectable. No oxidative cleavage products were
proposed structure (Additional file 1: Figure S8-S11). observed.
The complexes were non-volatile and difficulties were The electronic spectrum of benzil is characterized by
experiencedtorecord theirmassspectra byE1methods. an absorption at 283 nm, which is readily differentiated
from the other absorption bands of benzil at 260 nm
and benzoin 247 nm [40]. Accordingly, the band at
283 nm was used to determine the concentration of the
produced benzil (Figure 1).
In order to screen the catalytic oxidative potential of
the prepared complexes, they were tested for oxidation
of benzoin using H O as an oxidant under different re-
2 2
action conditions viz., temperature, reaction time and
type of solvent in order to optimise the conditions for
thebestperformance ofthe catalyst.
Figure2showsthattheabsorbanceat283nmincreases
with reaction time as an indication of the increasing con-
centration of benzil by using one of the catalysts, namely
VOL1. The maximum benzil yield was found to depend
upon the type of catalyst used (Figure 3). It is clear from
Figure 3 that VOL4 and VOL1 give higher benzil yields
compared to VOL3 and VOL2 with the same reaction
Scheme2Generalstructureofoxovanadium(IV)complexes.
time. VOL4 gave 100% yield after 2 h, while VOL1 gave
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Figure1Absorptionspectraofbenzoinandbenzilinacetonitrile.
98.9% after a longer reaction time (4 h). The order observedusingthepolaraproticsolvent,acetonitrile,com-
of catalytic activity was found to be as follows: VOL4 > pared to the other two solvents. On the other hand, the
VOL1>VOL3>VOL2. protic solvent, methanol, was not tried as it retards the
oxidation of benzoin due to hydrogen bonding with the
Effectofsolvent methanol[41].
The influence of three different solvents viz. benzene, In general, in these solvents, the order of the catalytic
carbon tetrachloride and acetonitrile on the rate of ben- performance of these catalysts after 6 h reaction time as
zoin oxidation wasnext studied. thefollowingVOL1≅VOL4>VOL3>VOL2.
Figures4,5,6,7illustratetheeffectofsolventuponthe
rateandyieldof benzoinusingcatalysts(VOL1−VOL4).It
isclearfromthefiguresthatthesolventhasnosignificant Effectoftemperature
effect on the yield and selectivity. However, the reaction The performance of the catalysts was investigated at two
rateduringthefirstfourhoursincreasesslightlyasthepo- different temperatures viz. 30°C and 50°C in benzene
larity of the solvent decreases. Lower reaction rates were after5hreactiontime(Figure8).
Time
Figure2ChangeintheabsorptionspectrawithtimeusingVOL1.
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100 100
80 80
%) 60
%) 60 d (
d ( 40 VOL1 Yiel 40 MeCN
el VOL2 CCl4
Yi 20 Benzene
VOL3
20
VOL4
0
0 2 4 6 8 10
0
0 1 2 3 4 Time (h)
Time (h) Figure5Effectofsolventon%yieldofbenzilusingVOL2
Figure3Catalyticperformanceofthedifferentcatalystswith at50°C.
timefortheformationofbenzilinbenzeneat50°C.
as a function of time in benzene at 50°C. The reaction
In general, the catalytic activity of the four catalysts profiles (Figure 3) showed that the yield of benzil
increased with increasing temperature. Figure 8 shows increased with increasing reaction time until a steady
that there was a significant increase in benzil yield using state was reached after 2-4 h. However, maximum yield
VOL1, VOL2 and VOL3 when the reaction temperature of benzil (>99.9%) was obtained using VOL1 and VOL4,
wasincreasedfrom 30°Cto50°C; whileVOL4 gaveahigh and ca. 90% using VOL2 and VOL3. VOL4 achieved the
benzil yield (97%) even at the lower temperature i.e. 30°C maximum conversion within a shorter reaction time
andaminorincreaseat50°C.At30°C,moderateyieldsof than the other catalysts. The selectivity of all the cata-
benzil were observed in all three solvents. However, the lysts was found to be unaffected with increasing reaction
increase in reaction temperature to 50°C led to almost time i.e.>99.9% benzil.
completeconversionofbenzointobenzil.Excellentselect-
ivity was observed with all the catalysts. Thus from the
results above it is clear that 50°C is the optimum Experimentalsection
temperature for this oxidation. All the catalysts possess Materials
excellentselectivitytowardsbenzilformation. Oxavanadium sulfate trihydrate, 2-aminophenol and 2-
hydroxy-1-naphthaldehyde were obtained from Fluka, 2-
Effectoftime aminoethanol, 3-ethoxysalicylaldehyde and benzoin were
The catalytic oxidation of benzoin using H O as oxi- obtained from Merck 30% H O . All other chemical
2 2 2 2
dant in the presence of the four catalysts was followed reagents were used as such. Solvents were used after
beingpurifiedaccordingtothe standard methods.
100
100
80
80
%)60
( MeCN %)60
Yeild40 CCl4 Yield (40 MeCN
CCl4
Benzene
20 Benzene
20
0
0
0 2 4 6 8 10 0 2 4 6 8 10
Time (h) Time (h)
Figure4Effectofsolventon%yieldofbenzilusingVOL1 Figure6Effectofsolventon%yieldofbenzilusingVOL3
at50°C. at50°C.
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mp 148–150°C. Anal. Found: C, 71.69; H, 5.73; N, 6.09.
100
C H NO requires C, 72.54; H, 6.09; N, 6.51%. IR
13 13 2
(KBr, cm-1), 3167br (νOH), 3056 (νC-H Ar), 2917 (νC-H
80
aliph.), 1641 (νC=N); 1H NMR (DMSO-d , δ/ppm): 3.65
6
%) 60 (m, 4 H, 2CH2), 5.00 (br, 1H, OH), 6.64-8.00 (m, 6H,
d ( Ar-H), 9.02(s, 1H, HC=N), 13.88 (br, 1H, phenolic OH);
Yiel 40 MeCN m/z M.+ = 215 (85%), 214 (66%), 184 (base peak), 170
(42%).Found215.00,C H NO requires215.25.
CCl4 13 13 2
20 H L22-ethoxy-6-{[(2-hydroxyphenyl)imino]methyl}phenol
Benzene 2
3-Ethoxysalicylaldehyde(1.66g), 2-aminophenol (1.09g),
0 (87% yield) as reddish orange needles (from ethanol); mp
0 2 4 6 8 10
172-174°C. Anal. Found: C, 69.17; H, 5.41; N, 5.13.
Time (h)
C H NO requires C, 70.02; H, 5.88; N, 5.44%. IR (KBr,
Figure7Effectofsolventon%yieldofbenzilusingVOL4 15 15 3
cm-1), 32100 (νOH), 3060 (νC-H Ar), 2986 (νC-H aliph.),
at50°C.
1629 s(νC=N). 1H NMR (DMSO-d , δ/ppm): 1.3 (t, 3H,
6
CH ),4.06(q,2H,2CH ),6.78-7.38(m,7H,Ar-H),8.94(s,
3 2
Physicalmethodsandanalysis 1H,HC=N),9.77(s,1H,OH;aminophenolmoiety),14.20
InfraredspectrawererecordedasKBrpelletsonaBUCK- (s, 1H, OH; 3-ethoxysalicylaldehyde moiety). m/z M.+ =
500 FT-IR spectrometer. 1H NMR spectra were recorded 257 (86%), 242 (41%) [M-CH ].+, 212 (24%) [M-
3
onaBruker500(500MHz)spectrometerusingDMSO-d OCH CH ].+, 120 (55%), 69 (base peak). Found 257.00,
6 2 3
as a solvent and TMS as internal standard. GC-MS were C H NO requires257.29.
15 15 3
recorded on a Hewlett Packard E1 mass spectrometer at H L32-ethoxy-6-{[(2-hydroxyethyl)imino]methyl}phenol
2
70 eV. Elemental analysis was performed on Euro Vectro 3-Ethoxysalicylaldehyde (1.66 g), 2-aminoethanol
EA 3000A analyzer. All catalyzed reaction products were (0.61 g), (81% yield) as yellow crystals (from ethanol);
analyzedusingUV–visPGInstrumentT-80+. mp 88-90°C. Anal. Found: C, 62.25; H, 6.91; N, 6.41.
C H NO requires C, 63.14; H, 7.23; N, 6.69%. IR
11 15 3
Preparationmethods (KBr, cm-1), 3230 (νOH), 3050 (νC-H Ar), 2953–2866
GeneralmethodforpreparationofSchiffbaseligands (νC-H aliph.), 1652 (νC=N). 1H NMR (DMSO-d , δ/
6
Methanolic solutions of the aldehyde and amine were ppm): 1.6 (t, 3H, CH ), 3.70 (t, 2H, CH of CH N=CH),
3 2 2
mixed at room temperature in a 1: 1 molar ratio using 3.90 (t, 2H, CH of CH OH), 5.32 (s, 1H, OH), 6.70-7.91
2 2
glacial acetic acid as acatalytic agent. Theresulting mix- (m, 3H, Ar-H), 8.35(s, 1H, HC=N), 13.70 (br, 1H, OH
ture was refluxed for 2 h. The crystalline product was phenolic OH); m/z M.+ = 209 (13%) C H NO , 194
11 15 3
obtained from the deep-yellow coloured solution after (20%) [M-CH ].+, 164 (25%) [M-OCH CH ].+, 69 (base
3 2 3
standing for a few hours at 25°C. The precipitate was fil- peak) (C H NO+). Found 209.00, C H NO requires
2 5 11 15 3
tered off and washed with ice-cold methanol. The pure 209.23.
compound was obtained by recrystallization from a suit- H L41-{[(2-hydroxyphenyl)imino]methyl}-2-naphthol
2
ablesolvent. 2-Hydroxy-1-naphthaldehyde (1.72 g), 2-aminophenol
H L11-{[(2-hydroxyethyl)imino]methyl}-2-naphthol (1.09 g), (63% yield) as orange needles (from ethanol);
2
2-Hydroxy-1-naphthaldehyde (1.72 g), 2-aminoethanol mp 247-249°C. Anal. Found: C, 76.64; H, 4.34; N, 4.96.
(0.61 g), (69% yield) as orange needles (from ethanol); C H NO requires C, 77.55; H, 4.98; N, 5.32%. IR
17 13 2
(KBr, cm-1), 3117 (νOH), 3053 (νC-H Ar), 2960 (νC-H
aliph.), 1622 (νC=N). 1H NMR (DMSO-d , δ/ppm):
100 98.9 97.2100 6
89.3 91.1 6.74-8.35 (m, 10H, Ar-H), 9.43 (s, 1H, HC=N), 10.35
80 (s, 1H, OH phenolic), 15.70 (s, 1H, OH naphthoyl); m/z
61.1 M.+ = 263 (75%), 262 (base peak) [M-H].+. Found
eld (%) 4600 54.8 38.6 3500°°CC 263.00.C17H13NO2requires263.30.
Yi
20 Preparationoftheoxavanadium(IV)complexes
All complexes were prepared according to the following
0
VOL1 VOL2 VOL3 VOL4 procedure: a hot methanolic solution of VOSO .3H O
4 2
Figure8Catalyticperformanceofthecatalystsforthe (0.217 g, 1 mmol), was added drop wise to a hot metha-
oxidationofbenzoinattworeactiontemperaturesinbenzene nolic solution of the ligand (1.5 mmol). The resulting
after5hreactiontime.
mixture was stirred for 3 h and the products obtained
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were filtered, washed with hot water then methanol and in good agreement with their structures, indicating high
driedinairat 90°C. purity ofallthe compounds.
VOL1 Dark green ppt., mp>300°C, IR (KBr, cm-1); Oxovanadium complexes were screened for the oxida-
3050 (νC-H arom.), 2936 (νC-H aliph.) 1614 (νC=N), tion of benzoin to benzil using H O as oxidant. The ef-
2 2
1512 (νC=C), 1322 (νC-N), 1198 (ν-O), 975 (νV=O). fect of time, solvent and temperature were optimized to
Anal. Calcd. for C H NO V: C, 52.35; H, 4.36; N, 4.69. obtain maximum yield. The catalytic activity results
13 13 4
Found: C,52.51;H,4.23;N, 4.51.m/zM.+=298. demonstrate that these catalytic systems are both highly
VOL2 Brown ppt., mp>300°C, IR (KBr, cm-1); 3053 active and selective for the oxidation of benzoin under
(νC-H arom.), 2969–2890 (νC-H aliph.), 1601 (νC=N), mildreactionconditions.
1582 (νC=C), 1294 (νC-N), 1248 (νC-O), 987 (νV=O).
Anal. calcd. for C15H15NO5V: C, 52.95; H, 4.41; N, 4.11. Additional file
Found: C,52.51;H,4.23;N, 4.39.m/zM.+=340.
VOL3 Green ppt., mp>300°C, IR (KBr,cm-1); 3080 (υC- Additionalfile1:FigureS1.Ft-IRspectrumofHL1.FigureS2:FT-IR
2
H arom.), 2951 (υC-H aliph.), 1608 (νC=N), 1505 spectrumH2L2.FigureS3:FT-IRspectrumVOL2.FigureS4:H-NMR
(νC=C), 1334 (νC-N), 1212 (νC-O), 981 (νV=O). Anal. spectrumH2L1.FigureS5:H-NMRspectrumH2L2.FigureS6:H-NMR
spectrumHL3.FigureS7:H-NMRspectrumHL4.FigureS8:Mass
2 2
calcd. for C11H15NO5V: C, 45.21; H, 5.31; N, 4.79. spectraH2L1.FigureS9:MassspectraH2L2.FigureS10:Massspectra
Found: C,45.54;H,5.23;N, 4.57.m/zM.+=292. H2L3.FigureS11:MassspectraH2L4.
VOL4 Dark green ppt., mp>300°C, IR (KBr,cm-1); 3067
(νC-H arom.), 2961 (νC-H aliph.), 1592 (νC=N), 1575 Competinginterests
(νC=C), 1338 (νC-N), 1177 (νC-O), 978 (νV=O). Anal. Theauthorsdeclarethattheyhavenocompetinginterests.
calcd . for C H NO V: C, 58.96; H, 3.75; N, 4.04.
Found: C,58.5117;H13,3.494;N, 4.19.m/zM.+=346. Authors’contributions
OAcarriedouttheexperimentalwork.TAhelpedinexperimentaland
discussionpart.JHhelpedinexperimentalanddiscussionpart.HAhelpedin
Catalyticactivitystudy thediscussion,characterizationanddraftthemanuscript.SThelpedinthe
discussion,characterizationanddraftthemanuscript.Allauthorsreadand
The catalytic oxidation of benzoin to benzil was carried
approvedthefinalmanuscript.
out ina25 ml flask.In atypicalreaction, an aqueousso-
lution of30%H O (0.015mmol)(0.5mLofH O stock Authordetails
2 2 2 2 1Departmentchemistry,CollegeofEducation,UniversityofBasrah,Basrah,
solution; 0.017 g in 5 mL CH CN) and benzoin (0.01 g,
3 Iraq.2DepartmentofChemistry,UniversityoftheWesternCapeBellville,
0.047 mmol) were mixed in 3 mL of the solvent used PrivateBagX17,Bellville,CapeTown7535,SouthAfrica.
and the reaction mixture was magnetically stirred and
Received:13November2012Accepted:2January2013
heated at 30°C or 50°C in an oil bath. An appropriate
Published:7January2013
amount of catalyst (0.003 g) was added to the reaction
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