OXIDATION OF ALCOHOLS AND BENZYL HALIDES TO
CARBONYL COMPOUNDS USING QUATERNARY
‘ONIUIT BROMATES
Chapter 2
P art A
OXIDATION
OF
ALCO H O LS
AND
BENZYL
HALIDES
TO
THE
CO RRESPO NDING CARBONYL COMPOUNDS USING QUATERNARY
“ONIUM” BROM IDES
OXIDATION OF A LCO H O LS - A REVIEW
The oxidation of alcohols to a carbonyl compounds is a central
reaction in organic chemistry and several methods are available covering a
variety of experimental conditions. However, this reaction, due to its pivotal
role in synthetic chemistry, still continues to receive great attention from
synthetic organic chemists engaged in developing new oxidizing agents.
It is deemed appropriate at this stage to give a brief review of the
variety of oxidizing agents developed for oxidation of alcohols to the
carbonyl compounds. Among the variety of agents available for the oxidation
of alcohols , 1 the first reagent of wide applicability are the chromium based
oxidizing agents. Hexavalent chromium Cr(Vi) in the form of Cr03 or sodium
dichromate (Na2Cr2C>7) is used for such oxidation. Hexavalent chromium
oxidations have been run with a solution of sodium dichromate dihydrate in
glacial acetic acid ,2 with a solution of chromium trioxide in acetic anhydride,
or with a solution of the chromium trioxide complex in excess pyridine or in
methylene chloride3. Oxidation with acid solution of chromium trioxide is
unsuitable for alcohols containing sensitive groups. A useful and mild
reagent for the oxidation of primary and secondary alcohols to carbonyl
compounds is manganese dioxide. The main advantages of this reagent is
that acetylenic bonds are not affected by this reagent4 and the reaction can
be carried out at room temperature.
42
Chapter 2
Part A
Most of the methods for oxidation of alcohols utilize DMSO as
reagent, e.g. Dimethylsulfoxide-trifluoroacetic anhydride5 has been used for
the oxidation of a variety of allylic and benzylic alcohols. The reaction is
believed to proceed through the initial formation of acetoxydimethylsuifonium
acetate,
which
on
reaction
with
alcohol
is
converted
to
alkoxydimethylsulfonium acetate. Reaction of the alkoxysulfonium salts with
base yields the carbonyl compounds and dimethyl sulfide (Scheme A. 11.1).
Scheme A.II.1
/
H3C -S -C H , + (RC0)20-
+
1 RRCHOH
H3C -S -C H 3 OCOR — — ► CH3SCH2OCOR + r co 2h
OCOR
+
h 3c - -S -C H ,
I
///
OCOR + RCOzH
base
/
rrc =
o +c h 3s c h 3
OCHRR -
Other electrophilic reagents that have been used to activate dimethyl
sulfoxide include methane sulfonic anhydride6, tosyl chloride7, sulfur
trioxide/pyridine8, phosphorous pentoxide9, thionyl chloride10 and oxalyl
chloride11. The activation of DMSO can also be conveniently conducted with
the very cheap cyanuric chloride (TCT) [2,4,6-trichloro(1,3,5) triazine]12
under the so called Swern oxidation condition. It can be used even for large
scale synthesis simply using THF as solvent. The yields were quantitative
and the conversions was very high in most of the cases. Moreover, oxidation
proceeds at satisfactory rates even when the alcohol has steric constraints
and the methodology is applicable to N-protected p-amino alcohols.
However, the oxidation is not chemoselective.
43
Chapter 2
Part A
Phenyl dichlorophosphate (PDCP) has also been shown to be an
efficient DMSO-activating agent in the Pftizner-Moffatt oxidation13 (Scheme
A.II.2). It is believed that the complex salt ([PhOPOCIOS+(CH3]2Cr)
generated from PDCP and DMSO, serves as an oxidizing agent for the
conversion of primary and secondary alcohols to the corresponding
aldehydes and ketones.
Scheme A.II.2
/
PDCP, DMSO
RRCHOH---------------------Et3N, CH2CI2
-10 to 20°C, 30min
The methods of oxidations by DMSO have several disadvantages
because of their involvement under anhydrous14 and low temperature
conditions15, use of moisture sensitive and toxic reagents and bases and in
some cases occurrence of Pummerer rearrangements.16
Another alternative system for the oxidation of secondary alcohols to
ketones with DMSO/N2H4.H2O/I2/H2O/CH3CN in hydrated media has also
been reported17. (Scheme A.II.3).
Scheme A.II.3
d m s o / n 2h 4.h 2o / h 2o / i2
RRCHOH------------------------------- ► RRtC = O
CH3CH, 80°C, reflux
This method has the advantages that it can selectively oxidizes only
the secondary alcoholic groups in the presence of primary alcohols present
within the same molecule and it does not reduce the alcohols to the
corresponding saturated compounds.
44
Chapter 2
Part A
Hypervalent iodine reagents are also used for the oxidation of
alcohols to carbonyl compounds. These reagents are well known for their
selective, efficient, mild and environment friendly properties as oxidizing
agents.18 Of particular interest is the O-iodoxybenzoic acid (IBX) and DessMartin periodinane (DMP) of which IBX delivered very good results. IBX
smoothly oxidizes primary and secondary alcohols to aldehydes and
ketones, (Scheme A.II.4)19 respectively and also, 1,2-diois to a-ketols or adiketones without any oxidative cleavage of the glycol bond20.
Scheme A.il.4
The main disadvantages of IBX oxidation is that stericaliy hindered
alcohols are easily oxidized at room temperature in a few hours and
oxidation of chiral primary alcohols proceeds without epimerization. Double
bonds both conjugated and isolated are not affected. Moreover, the reagent
is stable against moisture and highly efficient. However, the main
disadvantages is that it is insoluble in most solvents. The limited solubility of
IBX has also led to many variations.21
Another elegant and simple methodology for the oxidation of a variety
of alcohols using IBX at room temperature with a water/ acetic mixture as
45
Chapter 2
Part A
solvent under supramolecular catalysis is reported by Rao et al.22a (Scheme
A.II.5). p-Cyclodextrin was used as catalyst because of its easy accessibility
and inexpensivity among the Cyclodextrins. The yield was impressive. This
methodology is compatible in the presence of other functionalities such as
methoxy, methylenedioxy, nitro, hydroxy and alkene double bonds.
Moreover, this reaction is highly selective for vicinal diols as it oxidizes only
the secondary hydroxy groups a to the benzene ring.
Scheme A.II.5
p-Cyclodextrin/H20/acetone
Room temp.
A serious disadvantage of such iodine (V) oxidants is their explosive
nature, which obliges their impromptu generation, as these potentially
dangerous reagents should not be stored.22b
A facile, safe to use, readily available and persistent iodine (III)
oxidant is the iodosobenzene diacetate [Phi (OAc)2], which is used for the
oxidation of a variety of alcohols to their carbonyl products (Scheme A.ll.6)
catalyzed
by
chromium
(III)
saien
conditions.220
46
complexes
under homogenous
Chapter 2
Part A
Scheme A.ti.6
CH2CI2i 20°C
H2O2 has also been used extensively for the oxidation of alcohols to
carbonyl compounds. Noyori et a/.23 reported a no solvent oxidation of 1°
and 2° alcohols under entirely halide free conditions using aq. H2O2. This
reaction was carried out by using sodium tungstate as a catalyst and methyl
trioctyl ammonium hydrogen sulfate [CH3(n-C8Hi7)3N+HS0 4 ] as a phasetransfer catalyst under heterogenous conditions. However, time required for
completion of the reaction is very long even at a very high stirring speed.
Tandon et al.24 overcome the limitation by using a quasi homogenous
system. The reaction were performed by dissolving alcohols in terf-butanoi
followed by addition of sodium tungstate and tetrabutyl ammonium hydrogen
sulfate (Scheme A.il.7). The main advantage of tert-butanol as a solvent is
that it has a better range of solubility for organic compounds and hence
makes the reaction easier and faster giving quantitative conversion of
alcohols into ketones.
Scheme A.11,7
CaCI2. 2 H20 has also been found to be an efficient reaction for the
acceleration of the oxidation of alcohols to their corresponding carbonyl
compounds with (NH4)2 (>207 in solution and under solvent free conditions.25
47
Chapter 2
Part A
The oxidation of p-amino alcohols to the corresponding a-amino
aldehydes is synthetically useful as the carbonyl group present in the amino
carbonyl compounds readily undergoes successive transformation. A novel
procedure for the mild oxidation of (3-amino alcohols to p-amino aldehydes
using commercially available manganese (IV) oxide is reported by Sergeev
at al.23 (Scheme A.II.8). The most important advantage of this procedure is
the absence of any organic by-products in the reaction and can be carried
out under very mild conditions and in very high yields. Besides, no
racemization at the stereogenic carbon atom takes place.
Scheme A.II.8
HN
PG
A ^
R
Mn02
oh
HN
PG
CHCI3
Another procedure is based on the addition of 1 molar equiv of 1,3,5trichloro-2,4,6-triazinetrione (trichloroisocyanuric acid), a very cheap reagent,
to a CH2CI2 solution of alcohol followed by catalytic amounts of 2, 2, 6, 6tetramethyl-1-piperidinyloxy (TEMPO) [Scheme A.II.9]27.
Scheme A.II.9
CH2CI2, r.t.
48
Chapter 2
Part A
The derivative of transition metal free and ecofriendiy synthetic
transformations is an area of current interest as such methods avoid the use
of toxic and expensive metals and their complexes.
A direct oxidation of methylarenes and benzylic bromides to the
corresponding aromatic carboxylic acid by a new transition metal free
reagent sodium metaperiodate28 (Nal04). Under the same reaction
conditions, benzylic alcohols are selectively oxidized to afford the
corresponding aldehydes in good yields without undergoing overoxidation
(Scheme A.II.10). Unreprecedentedly, oxidation of benzyl bromide, tolune or
benzyl alcohol with Nal04 underwent nuclear bromination followed by
oxidation to give 4-bromobenzoic acid in good yields.
Scheme A.II.10
Another transition metal free, efficient method for oxidation of
secondary alcohols to carbonyl compound is by using aqueous hydrogen
bromide (HBr) and hydrogen peroxide (H2O 2) as green oxidant system.29
(Scheme A. 11.11).
49
Chapter 2
Part A
Schem e A.II.11
R1
H
V
R
\
R
H20 2, HBr
O
OH
CH3CH, reflux
r2
H20 2 + H B r ------------- HOBr
1
R — |— R1
R — |— R
+ HOBr
+ H20
OBr
OH
I
R — ji— R
+ HBr
O
Another excellent system for the selective oxidation of benzylic and
secondary alcohols with hydrogen peroxide catalyzed by 1-methyl-3butylimidazolium decatungstate [bmim][BF4] ionic liquid (Scheme A.II.12)30.
The catalytic system is reusable and products are obtained under
environmentally benign conditions.
Schem e A.II.12
[bmim] [Br]
1
R"
OH
R
2
[bmim] [BFJ
[bmim]4 [W10O 233, H20 2
[bmim], [ B F J
50
R
R
Chapter 2
P a rt A
A variety of transition metals are well known to act as oxidant or
catalyst in the dehydrogenation of alcohols to carbonyl compounds. Metal
catalyzed aerobic oxidation of alcohols is regarded as the most attractive
and ideal technology considering its atom efficiency and many procedures
using metal catalysts such as Ru31, Pd32, Co33, Cu34, Ft35, Rh36, V37, Os38,
Ce39 and Ni40 have so far been reported.
Among the oxides of ruthenium, Ru04 is well-known as a powerful
oxidant for alcohol dehydrogenation. It is, however, too strong to be used for
selective
dehydrogenation.
Of allylic
alcohols
to
the
corresponding
unsaturated carbonyls. A lower oxidation state ruthenium oxide namely
RUO2 hydrate, acts as an oxidant with higher efficiency than M n02 and
effectively catalyzes aerobic oxidation for allylic alcohols. Some other
ruthenium based catalysts are hydrated RuCIs41, a combination of cobalt and
ruthenium42, tetrapropylammonium
perruthenate43,
Ru3+ -
exchanged
hydroxyapatite,44 a ruthenium complex along with Co-salen45, a zeolite
confined nanometer sized Ru02 (R u02-FAU)46, Ru-biomimetic-coupled
systems, Ru-AI-Mg hydrotalcities. (Scheme A. 11.13)47.
Scheme A.II.13
o
I
c-
R.
0 2 Ru-hydrotalciate
tolune
-R'
V
Some other catalytic systems, for example, M” - radical catalysts,48
CuCI-Phen49, Polyoxometalates50, bimetallic Mo-Cu51 and Os-Cu52 systems,
51
Chapter 2
Part A
Pt and Pt/Bi catalysts53, manganese oxide octahedral molecular sieves54
have also been reported for the aerobic oxidation of alcohols.
The use of heterogenous catalysts in the liquid phase offers several
advantages over homogenous ones such as ease of recovery and recycling,
atom utility and enhanced stability Uemura et al.55 reported a sophisticated
catalytic system for aerobic oxidation of alcohols in toluene using
atmospheric pressure of air as a sole oxidant using a heterogenous Pd
catalyst, Pd(ll)-hydrotalcite[Palladium(ll)acetate-pyridine complex supported
by hydrotalcite]. Another catalyst is the polyaniline-supported Mo02
(acac)256. The catalyst is recyclable and catalyzes efficiently the oxidation of
alcohols to aldehydes and ketones using molecular oxygen. Gold
nanoparticles have also been used as heterogenous catalysts to catalyze
the oxidation of alcohols with dioxygen (O2).57 Recently, Tsukuda and co­
workers also reported the application of colloidal gold nanoclusters (AuNCS)
to catalyze the aerobic oxidation of benzyl alcohols in water.58
The oxidation of alcohols to carbonyl compounds by photochemical
process also holds special promise and one of the widely used photocatalyst
is titanium dioxide (TiC>2). The photo-electro-oxidation on titanium dioxide
film of alcohols has delivered very good results as reported by Bilmes et al.59
Another photooxidation was reported by Itoh et al.60 where alcohols were
irradiated by a high-pressure mercury lamp in the presence of a catalytic
amount of lithium bromide (LiBr) in an oxygen atmosphere
(Scheme
A.II.14). Ethyl acetate was found to be the most efficient solvent to carry out
the reaction.
52
Chapter 2
Part A
Schem e A.II.14
O
0 2 (ballon)
lo^OH
LiBr, hv
The photosensitized oxidation of tellurides carrying bulky aromatic
substituents afforded the corresponding telluroxides which were found to
react with simple alcohols to give the corresponding carbonyl compounds in
excellent yields alongwith the starting tellurides (Scheme A.II.15).61 It is
believed that the bulky diaryl telluroxides which, due to the weak telluriumoxygen bond, efficiently transfer the oxygen atom to organic substrates.
Schem e A.II.15
0 2, Hv, rose bengal
* Ar2T = o
Ar2Te
r.t. 1h in EtOH
Ar,
\
-HoO
RRCHOH
RR C = O + Ar2Te
Te=0
Ar
/
R
Some polymer supported reagents have also been used for the
oxidation of alcohols to carbonyl compound. These reagents have the
advantages of simple work up by filtration and fast reaction optimization.
Polymer-supported IBX amides (IBX-amide resin) prepared by coupling of
2-iodobenzoic acid to amino functionalized polystyrene beads followed by
their subsequent activation has been used successfully for the oxidation of
alcohols.62 It has been found that the introduction of a spacer between the
polymer support and IBX amide group improved the yield dramatically.
53
Part A
Chapter 2
R ecently, R adem ann
et at.
have reported on the generation of
oxoam m onium halides as oxidizing reactive sp e cie s on a solid supp ort such
as po lystyren e and on the use of this reagent in the oxidation o f a lco h o ls
TEM PO
p o lystyre n e (T E M P O
.63
P S ) m ay also be used to catalyze the
oxidation o f alcohols with o xo n e in the p re se n ce o f a p h a se -tra n sfe r agent
such as tetrabutylam m onium brom ide
.64
A n o th e r m ethod o f using potassium h e xa cya n o fe rra te (III) m ediated
b y T E M P O p o lystyre n e resin a s catalyst u n d e r an o rg a n ic-a q u e o u s tw o ph ase solution system
has been
reported
recently65. T h is m ethod
is
prom ising from an environm ental, practical and sa fe ty view point. T h is
m ethod ha s the a d vantage o f not separating and T E M P O from a reaction
solution. P rim ary alco hols are oxid ized with no o v e r oxidation to ca rb o xylic
acids. Furtherm ore, this p ro ce ss exhibits an unpre ced ente d de g re e of
chem oselectivity for th e oxidation o f prim ary h yd ro xyl g ro u p s in the p re se n ce
o f s e c o n d a ry h yd roxyl groups.
A m o n g the w id e ly used m ethods fo r th e oxidation o f alcohols, the
solvent fre e
oxidation
undo ub ted ly ow ing
using
m icrow ave
to the va rio us
irradiation
a d va n ta g e s
e n jo ys
o v e r the
prom inence
conventional
hom ogenous and h e teroge nous reactions in v ie w o f the rapid reaction rates
and higher yie ld s o f the ensuing pure products.
1
“W e t precipitated m anganese d io xid e ha s been activated and is used
fo r ne ar quantitative co n ve rsio n o f a range o f conjugated unsaturated
alcohol to carbonyl
co m p o u n d s
.66
Silica supp orted
active m anganese
dioxide u n d e r so lve n t fre e conditions a lso offe rs e xce lle n t yield during the
54
Part A
Chapter 2
oxidation of alcohols.67 (Scheme A.II.16). The method is simple and
overoxidation to carboxylic acid was not observed.
Scheme A.II.16
1
R
%
R
1
MnOz — silica
OH ----------------------MW, 20-60 sec
O
It has been found that C r03 supported on alumina efficiently oxidizes
primary and secondary alcohols to the corresponding carbonyl compounds
under solvent free conditions.68 The presence of a small amount of f-butanol
in the reaction media is essential. Over-oxidation of aldehydes to carboxylic
acids and cleavage of carbon-carbon bond was not observed by this
method.
Another rapid and highly selective method for the oxidation of
alcohols by using clay supported ammonium nitrate has been reported
recently (Scheme A.II.17).69
Scheme A.II.17
R
R
R/L-L -O H + NO+----------- rM — o — n o
NO
R
■O
R-
2NO + H + R/;
\
H
55
N
II
O
M;
/ IN
Chapter 2
Part A
Benzimidazolium fluorochromate is also found to oxidize alcohols
under solvent free conditions,70This method has the advantages of oxidizing
primary alcohol in presence of secondary alcohol.
Finally, some quaternary “onium” based reagents have also been
used for the oxidation of alcohols to carbonyl compounds. For example,
pyridinium chlorochromate (PCC)71, pyridinium fluorochromate (PFC)72,
pyridinium
dichromate
(PDC)73,
2,2/~bipyridinium
chlorochromate74,
quinolinium chlorochromate (QCC)75, quinolinium fluorochromate (QFC)79,
quinolinium bromochromate (QBC)77, isoquinolinium fluorochromate78,
quinolinium
dichromate
3-carboxypyridinium
(QDC)79
and
isoquinolinium
dichromate80,
chlorochromate81,
tetramethyl
ammonium
fluorochromate82 and caffeinilium chlorochromate83. However most of the
reagents suffer from the drawback of over oxidation to carboxylic acid.
Very
recently,
oxidation
of
alcohols
by
trimethylammonium
fluorochromate (TrilVIAFC) have been reported.84 The reagent can be easily
synthesized by addition of a trimethylamine to an aqueous solution of CrC>3
and HF. It is soluble in water and can be stored for a long time without
decomposition. Moreover, the yield of the carbonyl compound obtained by
oxidation of alcohol is also impressive.
56
Part A
Chapter 2
E x p e r im e n ta l
In
the
present
study,
the
qu a te rn a ry
am m onium brom ates,
the
preparation of w hich have been described in detail in the pre vio us chapter,
have been su cce ssfu lly used for the oxidation o f a variety of prim ary and
se co n d a ry a lco h o ls to the carbonyl co m p ounds. T h e s e reagents w e re found
to be synthetically useful as the prim ary alco hols could be oxid ize d to the
a lde hyd es and overoxidation w a s not o b se rve d . In addition to the a b o ve
ob servatio ns it w a s also possible to o xid ize so m e b e n zyl halides to the
co rrespo nding a lde hyd es. T h is co n version is rarely o b se rve d with m ost
oxidizing agents. T h e
reaction conditions are sim ple and involves the
dissolution o f the alcohols and the tetra-n-alkylam m onium brom ate in equal
proportion in an appropriate organic solvent and refluxing the solution for a
particular duration till the ye llo w co lou r o f the solution ch anged to alm ost
colourless.
The
experim ental
details
are
d is c u s s e d
in
detail
in
the
experim ents section o f this chapter.
Experimental:
A ll a lco h o ls and benzylhalides w e re obtained from E . M erck Inc. and
used w ithout further purification. B e n zh yd ro l and som e alcohols w ere
prepared from appropriate substrates b y esta b lish e d procedure. T h e te tra -n propylam m onium brom ate
and
tetra-n-butylam m onium brom ates
prepared b y p ro ce d u re s described in
w ere
Chapterl. T h e product carb onyl
co m p ounds w e re identified by recording the m .p., IR , 1H -N M R spectra in
spectrom eters m entioned earlier and com paring the results with those
reported in literature.
57
Chapter 2
Experimental
Part A
Oxidation
of
alcohols
and
benzyl
halides
with
tetra-n-
a lk y la m m o n iu m b ro m a te s:
G e n e ra l p ro c e d u re :
0-01 mol of the alcohol was dissolved in 50 mL of an organic
solvent ( TabIeA.ll.1) and to this solution 0-01 mol of the quaternary
ammoniumbromate was added and the solution refluxed. On refluxing the
yellow colour of the solution turned to almost colourless. Further, the
progress of the reaction was followed by TLC in prepared silica gel plate.
Aliquots of the reaction solution was withdrawn at different time interval and
co-chromatographed. with pure sample of the starting alcohol using
ethylacetate; n-hexane (9:1) as eluent. The end of the conversion was
indicated by the disappearance of the starting alcohol from the reaction
mixture. In cases where the carbonyl compounds were liquids, they were
converted to their 2,4-dinitrophenylhydrazones. Evaporation of the solvent
gave the solid products which were washed several times with water to
remove the spent tetra-n-alkylammoniumbromates. The solid was then
washed with ethanol to remove the unreacted 2,4-dinitrophenyIhydrazine
and the phenylhydrazones in the pure form were crystallized out and
characterized by observing their melting points, UV-visible, IR and 1H-NMR
spectra, in those cases where the product carbonyl compound was a solid,
the reaction mixture was cooled to ambient temperature and poured into
crushed ice resulting in the precipitation of the product carbonyl compounds.
The product were washed several times with water, dissolved in minimum
58
Part A
Chapter 2
Experimental
quantity of ethanol and filtered directly into a large volume of water. The
latter procedure of dissolution in ethanol and reprecipitation was performed
several times so as to remove the last traces of by products. The target
carbonyl compounds were recrystallized from appropriate solvent and
characterized by recording their melting points, IR and 1H-NMR spectra and
comparison with those obtained from authentic samples. The conversions
were possible with both tetra-n-propylammoniumbromate as well as with
tetra-n-butylammoniumbromate and the results obtained as shown in
Table A. 11,1.
The conversion is shown in Schem e
Scheme A . II .18
R^NBrO,
solvent/reflux
X=-OH, halogen
59
A.li.18.
Part A
Experimental
Table A. II. 1
Physical characteristics of oxidized product
(Ref. Scheme A . II. 18)
60
Chapter 2
Part A
SI. No. substrate
11
Chapter 2
Experimental
Reflux time yield Solvent m.p./b.p.of products m.p.of2,4-DNP
(hr)
(%)
(Oq )
derivatives (cc)
I II
I
II
obs
lit
obs
lit
product
H
H
1
94 82 EtOH 41-43
42(mp
227
227
80 76 EtOH
56
57 (mp
243
244
91 73 EtOH
245
248(bp)
254
254
92 84 EtOH 177-78 179(bp)
238
240
236
240
1.5 85 79 EtOH 178-79
179(bp)
X = C l, Br
I Indicates reaction with tetra-n-propylammoniumbromate. II with tetra-n-butyiammoniumbromate
*
61
Part A
Chapter 2
Spectral Data
Some spectral characteristics o f the oxidized product o f alcohol
>
Product 1:
Benzophenone
UV: X max (95% EtOH) 282.6 nm ;
IR( K B r ): cm "1 1710.5 (> C = 0 );
1H NMR (300 MHz, C D C I3): 5 7.2(s, 10H).
>
Product 2:
Cinnamaldehyde
UV: Xmax (95% EtOH) 272.8 nm ;
IR(KBr): cm ~1 1677.5 (>C=0, a p-unsaturated);
1H NMR (300 MHz, C D C I3): 5 9.9 (s, 1H), 7.8(d, 1H),
7.3(m, 5H), 6.4(d, 1H).
> Product 3:
Camphor
UV: X max (95% EtOH) 271.3 nm ;
IR(KBr): cm ~1 1742.3(>C=0);
1H NMR (300 MHz, C D C !3): 5 1.4-2.3(m, 6H),
.83-.96(m, 9H).
> Product 4:
Benzil
U V: X max (95% EtOH) 288.3 nm ;
IR(KBr): cm "1 1692.4(>C=0);
1H NMR (300 MHz, C D C I3): 5 7.3-7.9(s, 10H).
62
Part A
Chapter 2
Spectral Data
> Product 5: Cyclohexanone
UV: Xmax (95% EtOH) 280.9 nm ;
IR{KBr): cm "1 1702.1(>C=O);
1H NMR (300 MHz, CDCI3): 5 2.3-3.1(s, 10H).
> Product 6: Acetophenone
UV: Xmax (95% EtOH) 244.3 nm ;
IR(KBr): cm "1 1695.5(>C=0);
1H NM R (300 MHz, CDCI3): 57.8 (m, 5H), 2.2(s, 3H).
> Product 7: 4-Phenylbut-3-ene-2-one
UV: Xmax (95% EtOH) 271.3 nm ;
IR(KBr): cm ~1 1728.2(>C=0);
1H NMR (300 MHz, CDCI3): 8 7.5(m, 5H), 7.8(d, 1H),
6.5(d, 1H), 2.1 (s, 3H).
> Product 8: Phenyl-( 2-phenyl )-2-propenylketone
UV: Xmax (95% EtOH) 287.9 nm ;
IR(KBr): cm ~1 1713.6(>C=0);
1H NM R (300 MHz, CDCI3): 8 7.6-7.7(m, 10H),
6.4(s, 4H),2.1(s, 3H).
> Product 9: Anisaldehyde
UV: Xmax (95% EtOH) 285.7 nm ;
IR(KBr): cm ~11682.9 (>C=0);
1H NMR (300 MHz, CDCI3): 8 9.8(s, 1H),
6.9-7.2(m, 10H),
3.6(s, 3H).
63
Part A
Chapter 2
Spectral Data
> Product 10 and 11 : Benzaldehyde
UV: Xmax (95% EtOH) 275.7 nm ;
IR(KBr): cm ~11730.4(>C=G);
1H NMR (300 MHz, CDCI3): 6 9.1(s, 1H),
7,2-7.6(m, 5H).
64
PartA
Conclusion
Chapter 2
Conclusion:
li m ay be concluded from the a b o ve stu d y that the prepared te tra -n alkylam m onium brom ates are excellent reage nt for the oxidation o f alcohols
to the ca rb on yl com pounds. A n o th e r interesting ob servatio n is the e a s e with
w hich som e b e nzyl halides could be o xid ized to the co rre sp o n d in g alde hyd e.
T h e oxidation o f halides and alco hols to a ld e h yd e s w ithout o v e r oxidation to
the co rre sp o n d in g acid b y this p ro ce d u re is notew orthy. M ore over, the
p ro ce du re for product re co ve ry is found to b e sim ple and requires o n ly
w ashing with w a te r as the byprod ucts of the reactions are w ater soluble and
he nce can be rem oved easily.
65
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