Chapter 3 Aerobic Oxidation of Benzyl...

Chapter 3

Aerobic Oxidation of Benzyl Alcohols

Application of solid supported----------- Chapter 3

115

Application of solid-supported palladium catalyst for oxidation reaction

3.1 Introduction:

Oxidation of organic compounds is important and widely used reaction in organic

chemistry [Tsuji (2000)]. Among various oxidation reactions, oxidation of alcohols (Figure

1) is a fundamental organic transformation in synthetic organic chemistry [Hudlicky

(1990); Larock (1999); Smith and March (2001)] since carbonyls have huge industrial

applications as solvents, perfumes, intermediates in the manufacture of dyes and in

pharmaceuticals [Pillai and Sahle-Demessie (2003)].

R OHR

H

O1o alcohols

Oxidising agent

R1 OH

R2

R1

R2

O

Oxidising agent

2o alcohols ketone

aldehyde

Figure 1. General Scheme for the oxidation of alcohols

Traditionally, stoichiometric oxidants having transition metals notably chromium based

reagents (such as PCC, PDC etc.) [Lee and Spitzer (1970), Cainelli and Cardillo (1984);

Muzart (1992)], permanganates [Regen and Koteel (1977); Menger and Lel (1981)],

ruthenium (VIII) oxide [Berkowitz and Rylander (1958); Griffith (1992)], DMSO-coupled

reagents [Mancuso and Swern (1981)], Dess-Martin periodinane [Dess and Martin (1983)],

tert-butylhydroperoxide [Krohn et al.(1996)] and TPAP/NMO system [Ley et al. (1994)]

are used to affect the oxidation of alcohols which are often toxic and demonstrate poor

atom efficiency and their use causes significant environmental issues which render them

impractical. For this reason, there has been a strong move toward the development of

catalytic reactions using benign oxidizing reagents.

3.2 Different metal catalyzed protocols using green oxidants:

From economical and environmental viewpoint, there is a definite need for catalytic

oxidation reactions that use dioxygen (O2) or hydrogen peroxide as oxidants. The use of

oxygen has great benefits from both economic and green chemistry viewpoints in oxidation

reactions because oxygen is relatively cheap and produce water as the only by product. In

this context, significant progress has been made in the field of transition metal catalyzed

oxidations [Chen et al. (2010); Ji et al. (2007); Li et al. (2007); Kockritz et al. (2006)]


116

particularly utilizing molecular oxygen as green oxidant. The catalysts including

heterogenized complexes, mixed oxides and nanoparticles, containing transition metals

such as vanadium [Jiang and Ragauskas (2007)], cobalt [Sharma et al. (2003)], copper

[Marko et al. (1996)], ruthenium [Yamaguchi and Mizuno (2002)], palladium [Jensen et al.

(2003)], platinum [Wang et al. (2007)], iron [Martin and Suarez (2002)] etc. have been

screened for oxidation reactions. Among them, palladium based catalysts have very

interesting and promising catalytic activity and different types of palladium based

homogeneous and heterogeneous catalysts in the form of metal complexes or nanoparticles

have been developed for oxidation reactions which are discussed in details as below:

3.2.1 Homogeneous palladium-catalyzed aerobic oxidation of alcohols:

Oxidation of primary and secondary allylic and benzylic alcohol to aldehyde and ketone

has been achieved [Peterson and Larock (1998)] using catalytic Pd(OAc)2 in dimethyl

sulfoxide (DMSO) with oxygen gas as the sole oxidant. Nishimura et al. have described an

improved system of simple combination of commercially available reagents,

Pd(OAc)2/pyridine/MS3Ao for aerobic oxidation of benzylic and aliphatic alcohols using

O2 [Nishimura et al. (1999)]. This apparoach could also be employed using catalytic

amount of a novel perfluoroalkylated-pyridine as a ligand in a fluorous biphase system

(FBS) composed of toluene and perfluorodecalin [Nishimura et al. (2000)]. The fluorous

phase containing the active palladium species reused several times without significant loss

of catalytic activity. Further Schultz et al. have developed a convenient aerobic alcohol

oxidation using Pd(OAc)2/TEA system at room temperature and found that triethylamine

(TEA) is best additive or base for oxidation than pyridine. The initial mechanistic studies

provided evidence that the active catalyst may be a palladium complex of TEA (Scheme 1)

[Schultz et al. (2002)].

R1 OH

R2

R1

R2

O

Pd(OAc)2, O2

Ligand / Toluene

80 oC

R2 = H, CH3

R1 = alkyl, aryl

Scheme 1. Palladium-catalyzed aerobic oxidation of alcohols

Brink et al. have demonstrated that water-soluble complexes of palladium (II) with

phenanthroline derivatives are stable and recyclable catalysts for the selective aerobic


117

oxidation of a wide range of alcohols in a biphasic liquid-liquid system and the active

catalyst found to be a dihydroxy-bridged palladium dimer (Scheme 2) [Brink et al. (2002)].

R1 OH

R2

R1

R2

O

R2 = H, CH3

R1 = alkyl, arylair, NaOAc, H2O

PhenS*Pd(OAc)2

Scheme 2. PhenS*Pd(OAc)2-catalyzed aerobic oxidation of alcohols

Buffin et al. have described the application of an aqueous palladium catalyst that is

stabilized by a water-soluble biquinoline-based ligand for the aerobic oxidation of primary

and secondary alcohols in water and air as oxidant. The catalyst system was recycled

(Scheme 3) [Buffin et al. (2005)].

R1 OH

R2

R1

R2

O

Pd(II) biquinoline catalyst

R2 = H, CH3

R1 = alkyl, arylO2, NaOAc, H2O

Scheme 3. Palladium(II)biquinoline catalyzed aerobic oxidation of alcohols

Steinhoff et al. have studied the effect of molecular sieves on the Pd(OAc)2/pyridine and

Pd(OAc)2/DMSO catalystic systems for aerobic oxidation of alcohols. It has been found

that molecular sieves enhance the rate of the Pd(OAc)2/pyridine-catalyzed oxidation due to

ability of molecular sieves to serve as a bronsted base, but no rate enhancement was

observed for the Pd(OAc)2/DMSO catalyzed reaction [Steinhoff et al. (2006)]. It has been

observed that both catalytic systems exhibit improved catalytic stability in the presence of

molecular sieves. The performances of palladium complexes with phenanthroline ligands

have been studied for alcohol oxidation in water as well as in water/polar co-solvent

mixtures [Arends et al. (2006)]. The Pd(OAc)2-neocuproine catalyst has been found

efficient in water or polar co-solvents for oxidation of alcohols and tolerates a wide variety

of functional groups in the alcohol (Scheme 4).

R1 OH

R2

R1

R2

O

Pd (II) neocuproine, air

DMSO/ H2O

80 oC

R2 = alkyl, aryl

R1 = aryl, alkyl

Scheme 4. Palladium-neocuproine catalyzed aerobic oxidation of alcohols


118

Zhou et al. have investigated the use of palladium-diamine catalyst in the aerobic oxidation

of alcohols (Scheme 5). The electronic properties, rigidity and steric hindrance of ligands

have remarkable influence upon the catalytic activity of the palladium complexes [Zhou et

al. (2008)]. It has been found that the catalyst showed high efficiency for the oxidation of

benzylic alcohols than secondary aliphatic and cyclic alcohols.

R1 OH

R2

R1

R2

O

Pd (OAc)2 / diamine, O2

K2CO3, DMA

100 oC

R2 = alkyl, aryl

R1 = aryl, alkyl

Scheme 5. Palladium-diamine catalyzed aerobic oxidation of alcohols

Water-soluble palladium nanoparticles stabilized by the functionalized-poly(ethylene

glycol) [Feng et al. (2010)] as a protective ligand has been demonstrated for aerobic

oxidation of alcohols (Scheme 6). UV/Vis and XPS study proved the electronic

interactions between the bidentate nitrogen ligand and palladium atoms. It has been found

that both the size and surface properties of palladium nanoparticles are important in

affecting catalytic performance and the catalyst can be recycled at least four times without

any loss of catalytic activity.

R1 OH

R2

R1

R2

O

R2 = H, CH3

R1 = alkyl, arylO2, K2CO3, 80 oC

Pd nanoparticles

Scheme 6. Aerobic oxidation of alcohols using water soluble palladium nanoparticles

Palladium pincer complexes have been used as catalysts for aerobic oxidation of secondary

benzyl alcohols in PEG-400 and showed good catalytic activity (Scheme 7) [Urgoitia et al.

(2011)].

R1 OH

R2

R1

R2

O

Pd pincer complex, O2

NaOAc,PEG-400

120 oC

R2 = alkyl, aryl

R1 = aryl

Scheme 7. Oxidation of secondary benzyl alcohols using palladium pincer complex

Although homogeneous catalyst (typically a soluble metal complex) acquire the advantage

of having all catalytic sites accessible to all reagents. However, their use in industrial


119

applications is limited by the difficulties encountered in catalyst separation from the final

products. To overcome the separation problems encountered in homogeneous catalysis,

efforts have been made to develop heterogeneous catalysts which can be easily separated

from the reaction mixture and reused several times.

3.2.2 Heterogeneous palladium-catalyzed aerobic oxidation of alcohols:

Kakiuchi et al. have described the aerobic oxidation of primary and secondary alcohols

into the corresponding aldehydes and ketones with atmospheric pressure of air under mild

conditions in toluene using a heterogeneous Pd(II)-hydrotalcite catalyst (Scheme 8)

[Kakiuchi et al. (2001)].

R1 OH

R2

R1

R2

O

Pd(II)hydrotalcite, O2

Pyridine/ Toluene

R2 = H, alkyl, aryl

R1 = aryl, alkyl

Scheme 8. Aerobic oxidation of alcohols using palladium hydrotalcite catalyst

Mori et al. have described the formation of palladium hydroxyapatite (PdHAP-0) as a

heterogeneous catalyst by grafting of monomeric PdCl2 species on the surface of

stoichiometric hydroxyapatite and its application in aerobic alcohol oxidation (Scheme 9)

[Mori et al. (2004)].

R1 OH

R2

R1

R2

O

PdHAP-0, O2

TFT, 90 oC

R2 = H, alkyl, aryl

R1 = aryl, alkyl

Scheme 9. Aerobic oxidation of alcohols using palladium hydroxyapatite catalyst

Kwon et al. have prepared a recyclable aluminium hydroxide-supported palladium catalyst

by a one-pot synthesis through nanoparticle generation and gelation which have catalytic

activity for aerobic alcohol oxidation (Scheme 10) [Kwon et al. (2005)]. A silica-based

Pd(II) interphase catalyst having high thermal stability has also been applied for the

oxidation of alcohols [Karimi et al. (2005)].

R1 OH

R2

R1

R2

O

Pd catalyst, O2

Toluene or TFT

80-100 oCR2 = H, CH3, alkyl, aryl

R1 = alkyl, aryl

Scheme 10. Oxidation of alcohols using supported palladium catalyst with O2


120

Alumina supported palladium (Pd/Al2O3) catalyst has been prepared by the adsorption

method [Wu et al. (2005)] which results in mononuclear or oligonuclear palladium species

stabilized on Al2O3 surface after calcination and found to be efficient in the solvent-free

selective oxidation of alcohols (Scheme 11). The catalyst was recycled and palladium

species transformed to small Pd nanoparticles during the course of oxidation.

R1 OH

R2

R1

R2

O

R2 = H, CH3

R1 = alkyl, aryl

150 oC

Pd/ Al2O3, O2

Scheme 11. Aerobic oxidation of alcohols using Pd/Al2O3

The biphasic aerobic oxidation of alcohols by using palladium nanoparticles in a

poly(ethylene glycol) (PEG) matrix as the catalyst and supercritical carbon dioxide

(scCO2) as the substrate and product phase has been established (Scheme 12) [Hou et al.

(2005)]. It was observed that the PEG matrix effectively stabilizes and immobilizes the

active particles, whereas the solubility and mass-transfer properties of scCO2 allow

continuous processing at mild conditions.

R1 OH

R2

R1

R2

O

Pd nanoparticles, O2

R2 = H, CH3

R1 = alkyl, aryl

scCO2 / PEG

Scheme12. Aerobic oxidation using PEG stabilized palladium nanoparticles

An efficient and recoverable palladium-based catalyst for the aerobic oxidation of alcohols

has been developed [Karimi et al. (2006)]. It has been demonstrated that the combination

of an organic ligand and ordered mesoporous channels resulted in an interesting synergistic

effect that led to enhanced activity, the prevention of the agglomeration of the Pd

nanoparticles and the generation of a durable catalyst. Choudhary et al. have prepared a

series of silica-supported palladium catalysts bearing N-N, N-S and N-O chelating ligands

for the aerobic oxidation of alcohols [Choudhary et al. (2006)] and found that N-N ligands

were highly selective for oxidation without forming over-oxidation products (Scheme 13).

R1 OH

R2

R1

R2

O

Palladium catalyst, O2

K2CO3,Toluene,

80-90 oCR2 = H, alkyl, aryl

R1 = alkyl, aryl

Scheme 13. Aerobic oxidation of alcohols using palladium catalyst


121

An amphiphilic polystyrene-poly(ethylene glycol) (PS-PEG) resin-dispersion of palladium

nanoparticles [Uozumi and Nakao (2003); Uozumi et al. (2007)] has been prepared by

Uozumi et al. and the catalytic oxidation of alcohols has been achieved in water under

atmospheric pressure of molecular oxygen (Scheme 14). The catalyst was recycled up to

four runs and catalyst leaching into the aqueous phase under the reaction conditions was

not observed.

R1 OH

R2

R1

R2

O

ARP-Pd, O2

K2CO3, H2O,reflux

R2 = H, alkyl, aryl

R1 = aryl, alkyl

Scheme 14. Aerobic oxidation of alcohols using ARP-Pd

Chen et al. have prepared SiO2-Al2O3-supported Pd nanoparticles by adsorption of PdCl42-

ions onto the support followed by calcination and reduction with either hexanol or H2. The

supported Pd nanoparticles catalyzed the aerobic oxidation of benzyl alcohols under

solvent free conditions [Chen et al. (2008)]. The Pd/SiO2-Al2O3 catalyst with appropriate

Si/Al ratios showed significantly higher benzyl alcohol conversions than both the Pd/SiO2

and the Pd/Al2O3. Hara et al. have synthesized a NiZn-Pd nanocomposite catalyst

containing highly stable divalent Pd species by simple intercalation of the anionic Pd(II)

hydroxyl complex. The intercalated anionic palladium hydroxide complex rigidly fixed by

the strong electrostatic interactions between the NiZn host and anionic Pd(II) species could

act as an efficient heterogeneous catalyst for the oxidation of alcohols under an air

atmosphere (Scheme 15) [Hara et al. (2009)].

R1 OH

R2

R1

R2

O

Pd/SiO2-Al2O3, O2

R2 = H, CH3

R1 = alkyl, arylTFT

orPd/ NiZn, air

Scheme 15. Pd/SiO2-Al2O3 or Pd/ NiZn catalyzed aerobic oxidation of alcohols

Palladium catalysts supported on TUD-1 mesoporous molecular sieves functionalized with

various organosilanes (APS, ATMS, HMDS and MPTMS) have been prepared using a

post-synthesis grafting method combined with a metal adsorption-reduction procedure. The

catalytic activity has been explored in the solvent-free selective oxidation of benzyl alcohol

using molecular oxygen (Scheme 16). Among all the catalysts, 1Pd/1.2APS-TUD


122

(containing 1 wt% Pd and 1.2 mmol of APS/g TUD) showed high catalytic activity for

benzyl alcohol conversions [Chen et al. (2010)].

OH

R2

R1

R2

O

R1

O2, 160 oC

R1=H, Me,NO2,BrR2= H,Me

1Pd/1.2APS-TUD

Scheme 16. 1Pd/1.2APS-TUD catalyzed aerobic oxidation of benzyl alcohols

Palladium-charcoal (Pd/C) has been used as a heterogeneous catalyst along with NaBH4 in

aqueous ethanol or methanol and either K2CO3 or KOH as base at room temperature under

molecular oxygen or air for oxidation of alcohols (Scheme 17). The catalyst was recycled

upto ten times without the loss of activity [An et al. (2010)].

OH

R2

R1

R2

O

R1

K2CO3, EtOH-H2O

R1=H,OMe,Me,NO2,FR2= H,Me,Ph

Pd/ C, NaBH4, O2

Scheme 17. Pd/C catalyzed aerobic oxidation of alcohols

Karimi et al. have demonstrated the efficiency of ionic liquid based PMO material in the

production and stabilization of active palladium species for aerobic oxidation of alcohols

(Scheme 18). The catalyst was easily recovered and reused even after ten runs [Karimi et

al. (2011)]. The hot filtration test, atomic spectroscopy and the results of the effect of

poisons have confirmed that the Pd@PMO-IL catalyst operated through a heterogeneous

pathway.

R1 OH

R2

R1

R2

O

Pd@PMO-IL, O2

K2CO3,TFT, 95 oC

R2 = H, alkyl, aryl

R1 = alkyl, aryl

Scheme 18. Pd@PMO-IL catalyzed aerobic oxidation of alcohols

Nanocrystalline magnesium oxide-stabilized palladium(0) [NAP-Mg-Pd(0)] as an efficient

catalytic system has been employed for the selective oxidation of alcohols using

atmospheric oxygen as a oxidant at room temperature (Scheme 19). This catalyst was

recovered and reused for several cycles without any significant loss of catalytic activity

[Layek et al. (2011)].


123

R1 OH

R2

R1

R2

O

NAP-Mg-Pd(0), O2

K2CO3,Toluene

R2 = H, alkyl, aryl

R1 = alkyl, aryl

Scheme 19. NAP-Mg-Pd(0) catalyzed aerobic oxidation of alcohols

The supported palladium catalyst based on ligand functionalized amorphous and ordered

mesoporous silica (SBA-15) has been prepared and applied for the oxidation of alcohols

[Karimi et al. (2009)]. Recently Zang et al. have prepared mesoporous SBA-15 supported

catalyst PdLn@SBA-15 via click route in which the click-triazole acted as a stable linker

and good chelator [Zang et al. (2012)]. The obtained solid catalyst demonstrated a

promising catalytic activity for the aerobic oxidation of benzyl alcohols (Scheme 20). The

catalyst was recovered by simple filtration and reused upto seven cycles with a consistent

catalytic activity.

OH

R2

R1

R2

O

R1

K2CO3, Toluene

80-100 oC

R1=H,OMe,Me,NO2,FR2= H,Me,Ph, Et

PdLn$SBA -15, O2

Scheme 20. Aerobic oxidation of benzylic alcohols using PdLn$SBA-15

In view of the above literature precedents, it would be apparent that a majority of the

prevalent oxidation approaches employ additives and basic conditions. Although there

have been noteworthy efforts to devise more benign oxidation conditions with various

improvements, but these have also been found to be constrained by the use of complicated

ligands which are not commercially available or require multiple steps for their synthesis.

On the other hand, various metal free approaches mainly employ oxidants such as TEMPO

or hypervalent iodine based reagents. But the utility of TEMPO mediated system is limited

due to its expensiveness and lengthy work up procedures [Jiang and Ragauskas (2005);

Mannam et al. (2007); He et al. (2009)]. In this context, it would be highly desirable to

develop a mild methodology for oxidation of benzyl alcohols using green oxidants.

Hence, we have investigated the scope of our previously synthesized heterogeneous SS-

Pd(0) catalyst in the oxidation of benzyl alcohols to the corresponding aldehydes and

ketones using molecular oxygen as the oxidant. Moreover, the catalyst system was

recycled up to five runs without significant loss of activity.


124

3.3 Results and discussion:

Initially concentration based studies of solid supported palladium catalyst were performed

to optimize the concentration of palladium required to give best performance of the

catalyst for aerobic oxidation of benzyl alcohols. In this regard, solid supported palladium

catalysts (SS-Pd) were prepared following our previously described procedure with

different concentrations of Pd(OAc)2 on solid surface (5 mg/g and 10 mg/g) and analyzed

by scanning electron micrographs (SEM) (Figure 2 and 3). With the change of

concentration, no significant particle size changes were observed but 10 mg Pd(OAc)2 on 1

g solid surface gave the best result with good recyclability. Through these studies, we

realized that 10 mg/g concentration of catalyst occupied sufficient space of the solid

surface which showed highest interaction with the substrate required for heterogeneous

catalyst to give high performance of the catalyst. With decrease of concentration (5mg/g)

huge space of the solid surface remained unoccupied by the catalyst and decrease the

optimal interaction with substrate, thereby, decreasing the rate of reaction.

SS-Pd

5um

a b

Figure 2. (a) SS-Pd (10 mg Pd(OAc)2/g solid surface) (b) SEM of SS-Pd (10 mg

Pd(OAc)2/g solid surface)

Figure 3. (a) SS-Pd (5 mg Pd(OAc)2/g solid surface) (b) SEM of SS-Pd (5 mg Pd(OAc)2/g

solid surface)


125

The solid surface of the catalyst (SS-Pd) behaves as an interface where liquid and gaseous

molecules such as alcohols and oxygen interacted with each other to produce

corresponding carbonyls (Figure 4).

Figure 4. Performance of reaction on solid surface of catalyst which act as interface

Using the standard SS-Pd catalyst (10 mg/g), further optimization studies were performed

for oxidation of 2-ethoxybenzylalcohol 1a as the model substrate (Table 1). The progress

of reaction was monitored by TLC and GC-MS analysis. From standard SS-Pd catalyst (10

mg/g), different loadings of SS-Pd containing 1-6 mol% palladium with respect to

substrate were investigated for the aerobic oxidation of 2-ethoxybenzyl alcohol. Highest

turnover number (TON, 2266) and turnover frequencies (TOF, 453 h-1

) were calculated

when SS-Pd (3 mol % Pd) was used for the oxidation reaction of 1a (Table 1, entry 2).

However, only 68% yield of 2a was observed by GC-MS analysis. SS-Pd with 5 mol% Pd

in toluene afforded 80% yield of 2a and TON/TOF was calculated as 1600/320 h-1

(Table

1, entry 3). No further improvement of yield was observed by enhancing the catalyst

loading up to 6 mol% Pd (Table 1, entry 4). Different solvents were investigated to see

their effect on the product yield. Dioxane and THF were not found to be good solvents

under the reaction condition. Moderate yield of product was obtained in benzene and

acetonitrile. Among different solvents, toluene gave the best result under standard reaction

condition. Comparative studies of different catalytic systems were also performed. The

reaction with Pd/C and Pd2C6H10Cl2 gave poor yield of product while moderate yields


126

were obtained in presence of Pd2(dba)3 and Pd[P(C6H5)3]4. Pd(OAc)2 was also found to be

good but the best result was obtained using SS-Pd under the standard reaction condition.

Hence SS-Pd (5 mol% Pd) in the presence of toluene was found to be optimum under the

reaction conditions.

Table1. Effect of catalysts and solvents for the oxidation of 2-ethoxybenzylalcohol

OH OSolvent, 110 0C

1a 2a

OC2H5 OC2H55h

Catalyst,O2

Entry Castalyst (mol % Pd) Yield (%)aTON TOF h-1

2

3

4 SS-Pd (6)

SS-Pd (3)

SS-Pd (1)

68

11

2266 453

1100 220

Solvent

Toluene

Toluene

2

69

80

Pd/C

Pd(OAc)2

6

5

Toluene

Toluene

Toluene

1333 267

1380 276

(5)

(5)

40 8

aDetermined by means of GC,based on the 2-ethoxy benzyl alcohol

TON = % conversion x mmole of substrate /mmole of catalyst, TOF = TON / time

1

SS-Pd (5)

i. Toluene 80 1600 320ii. THF 9 180 36iii.Dioxane 3 60 12iii. C6H6 55 1100 220iv. CH3CN 23 460 92

7 Pd2C6H10Cl2(10) Toluene 1

8 Pd2(dba)3(10)

9 Pd[P(C6H5)3]4(5)

Toluene

Toluene

20

39

20 4

400 80

780 156

Further investigations were performed to enhance the scope of oxidation reactions in

different substituted primary and secondary benzyl alcohols (Table 2).


127

Table 2. Oxidation of primary and secondary benzyl alcohols to aldehydes and ketones

OH

R2

R1

R2

O

R1

SS-Pd, O2

Toulene, 110 0C

1a-1m 2a-2m

3-5 h

Entry Product Yield (%)a

1

2b1b

90

Substrate

2

1d

1e

3

4

5

6

1f

1g

1h

70

2c

7

8

9

10

80

83

85

2d

2e

2f

1i

1j

11

2g

96

12

1k

1l

1m

2h

2i

2j

2k

2l

2m

90

90

90

93

90

74

aIsolated Yield

Time (h)

5

3

3

3

3

3

5

5

5

5

5

513

5

2a

78CHO

OC2H5

1a

CH2OH

OC2H5

OH O

1c

CH2OHO2N CHOO2N

CH2OH

MeO

CHO

MeO

CH2OHBr CHOBr

CH2OHCl CHOCl

CH2OH

Br

CHO

Br

OH O

OHMeO

OMe

OMeO

OMe

OHOMe

MeO

OOMe

MeO

OHMeO

OMeO

C6H5

OHCl

C6H5

OCl

OHBr

OBr

TON /TOF-h

1963/393

1400/467

1800/600

1600/533

1660/553

1700/567

1800/360

1860/372

1800/360

1800/360

1480/296

1800/360

1560/312


128

Both the primary and secondary benzyl alcohols on oxidation gave satisfactory to good

yields of the corresponding aldehydes and ketones. Secondary benzyl alcohol was also

found to be reactive toward oxidation under the same reaction condition and the product 2b

was obtained in excellent yield (Table 2, entry 2). Primary benzyl alcohols with electron

donating and withdrawing groups afforded products 2c and 2d in good yields (Table 2,

entries 3 and 4). Primary benzyl alcohols bearing halogen groups were also successfully

oxidized to benzaldehydes 2e-g with satisfactory yields (Table 2, entries 5-7). Secondary

benzyl alcohols with electron donating groups afforded products 2h-k in good yields

(Table 2, entries 8-11) and halogen substituted secondary benzyl alcohols also gave

products 2l and 2m in satisfactory yields (Table 2, entries 12 and 13).

Evaluation of recyclability was done on the same test substrate 1a. After completion of

reaction, the product was extracted with ethyl acetate and the recovered catalyst was

washed with acetone, dried and used for further reactions. The catalytic activity of SS-Pd

remained almost the same upto five runs as indicated by the yields of the corresponding

aldehyde 2a. Gradual decrease in yield was encountered after six to seven runs of SS-Pd

catalyst. As shown in Table 3, on recycling, from the first to the seventh run the TONs

drop from 1600 to 1000 and total turnover number over the seven cycles was 10400.

Table 3. Recyclability experiments of 2a using SS-Pd

1st2nd 3rd

80 79

4th Run

79 78

5th

Yield (%)a

aDetermined by means of GCbIsolated Yield

TTON = total turnover number; procedure followed as described for 2a

6th 7th

74b50b

TON

TTON over seven cycles

1600 1600 1580 1580 1560

10400

1480 1000

80

3.4 Conclusion:

Aerobic oxidation of benzyl alcohols using SS-Pd has been developed. Different primary

and secondary benzyl alcohols afforded corresponding products in good yields. Due to the

stability of SS-Pd catalyst in moisture and air, it is very easy to handle under reaction

conditions. This methodology will find interest in both academic as well as industry due to


129

its atom-economy and cost-effective process by using heterogeneous nano and

microparticles as a ligand free catalyst.

3.5 Experimental section:

3.5.1 General procedure:

Reagents of high quality were purchased from Sigma Aldrich. Silica gel (60-120 mesh

size) for column chromatography was procured from SD Fine-Chem. Ltd. Commercial

reagents and solvents were of analytical grade and were purified by standard procedures

prior to use. Thin layer chromatography was performed using precoated silica gel plates 60

F254 (Merck) in UV light detector. 1H and

13C NMR spectra were recorded using a Bruker

Avance 300 spectrometer operating at 300 MHz (1H) and 75 MHz (

13C). Spectra were

recorded at 25 °C in CDCl3 [residual CHCl3 (δH 7.26 ppm) or CDCl3 (δC 77.00 ppm) as

international standard] with TMS as internal standard. Chemical shifts were recorded in δ

(ppm) relative to the TMS and CDCl3 signal, coupling constants (J) are given in Hz and

multiplicities of signals are reported as follows: s, singlet; d, doublet; t, triplet; m,

multiplet; br, broad singlet.

3.5.2 Procedure of aerobic oxidation:

O 1-Phenyl ethanone (2b): A mixture of 1-phenyl ethanol 1b (100 mg, 0.818

mmol), SS-Pd (918 mg, 0.04 mmol Pd) and 3 ml of toluene was purged with molecular

oxygen and stirred at 110 0C for 5h. The progress of reaction was monitored by TLC. After

completion of reaction, the reaction was cooled, diluted with ethyl acetate and filtered

through cotton bed. The combined organic layer was evaporated under reduced pressure

and crude residue was purified by silica gel (mesh 60-120) column chromatography

(hexane:EtOAc :: 95:5) afforded 1-Phenyl ethanone 2b as colourless liquid (94 mg, 96%);

1H NMR (300 MHz, CDCl3-d1) δ 2.59 (s, 3H), 7.44-7.55 (m, 3H), 7.93-7.96 (m, 2H);

13C

NMR (75 MHz, CDCl3-d1) δ 26.49, 128.22 (2C), 129.48 (2C), 133.01, 137.06, 198.07.

CHO

OC2H5

2-Ethoxy benzaldehyde (2a): Prepared as described for 2b; starting from 2-

ethoxybenzyl alcohol 1a (100 mg, 0.66 mmol) gave, after purification with silica gel

column chromatography (hexane:EtOAc :: 95:5) 2a as colourless liquid (81 mg, 78%); 1H

NMR (300 MHz, CDCl3-d1) δ 1.27-1.35 (m, 3H), 4.10-4.21 (m, 2H), 6.97-7.05 (m, 2H),


130

7.52-7.57 (m, 1H), 7.85 (d, J = 7.6 Hz, 1H), 10.53 (s, 1H); 13

C NMR (75 MHz, CDCl3-d1)

δ 35.02, 64.92, 113.16, 116.67, 121.28, 125.66, 129.06, 136.64, 190.77.

CHOO2N 4-Nitro benzaldehyde (2c): Prepared as described for 2b; starting

from 4-nitrobenzyl alcohol 1c (100 mg, 0.66 mmol) gave, after purification with silica gel

column chromatography (hexane:EtOAc :: 97:3) 2c as a brown solid (70 mg, 70%), mp

106-107 oC;

1H NMR (300 MHz, CDCl3-d1) δ 8.09 (brs, 2H), 8.41 (brs, 2H), 10.17 (s, 1H);

13C NMR (75 MHz, CDCl3-d1) δ 124.29 (2C), 130.71 (2C), 140.04, 151.12, 190.23.

CHO

MeO 3-Methoxy benzaldehyde (2d): Prepared as described for 2b; starting

from 3-methoxy benzylalcohol 1d (100 mg, 0.72 mmol) gave, after purification with silica

gel column chromatography (hexane:EtOAc :: 95:5) 2d as colourless liquid (89 mg, 90%);

1H NMR (300 MHz, CDCl3-d1) δ 3.90 (s, 3H), 7.20-7.21 (m, 1H), 7.42-7.49 (m, 3H),

10.01 (s, 1H); 13

C NMR (75 MHz, CDCl3-d1) δ 55.48, 112.02, 121.55, 123.57, 130.03,

137.81, 160.16, 192.13.

CHOBr4-Bromo benzaldehyde (2e): Prepared as described for 2b; starting

from 4-bromobenzyl alcohol 1e (100 mg, 0.54 mmol) gave, after purification with silica

gel column chromatography (hexane:EtOAc :: 96:4) 2e as white solid (80 mg, 80%), mp

56-57 oC;

1H NMR (300 MHz, CDCl3-d1) δ 7.61-7.71 (m, 2H), 7.75-7.78 (m, 2H), 9.99 (s,

1H); 13

C NMR (75 MHz, CDCl3-d1) δ 129.77, 130.95 (2C), 132.43 (2C), 135.06, 191.04.

CHOCl4-Chloro benzaldehyde (2f): Prepared as described for 2b; starting

from 4-chlorobenzyl alcohol 1f (100 mg, 0.70 mmol) gave, after purification with silica gel

column chromatography (hexane:EtOAc :: 96:4) 2f as white solid (82 mg, 83%), mp 46-47

oC;

1H NMR (300 MHz, CDCl3-d1) δ 7.43-7.46 (m, 2H), 7.45-7.77 (m, 2H), 9.91 (s, 1H);

13C NMR (75 MHz, CDCl3-d1) δ 129.45 (2C), 130.89 (2C), 134.71, 140.96, 190.84.

CHO

Br

2-Bromo benzaldehyde (2g): Prepared as described for 2b; starting from 2-

bromobenzyl alcohol 1g (100 mg, 0.54 mmol) gave, after purification with silica gel

column chromatography (hexane:EtOAc :: 95:5) 2g as colourless liquid (85 mg, 85%); 1H

NMR (300 MHz, CDCl3-d1) δ 7.40-7.45 (m, 2H), 7.60-7.63 (m, 1H), 7.86-7.89 (m, 1H),


131

10.31 (s, 1H); 13

C NMR (75 MHz, CDCl3-d1) δ 126.88, 127.73, 129.68, 132.82, 133.37,

135.12, 191.48.

O 4-Methyl acetophenone (2h): Prepared as described for 2b; starting from

4-methyl phenyl ethanol 1h (100 mg, 0.72 mmol) gave, after purification with silica gel

column chromatography (hexane:EtOAc :: 95:5) 2h as colourless liquid (88 mg, 90%); 1H

NMR (300 MHz, CDCl3-d1) δ 2.43 (s, 3H), 2.60 (s, 3H), 7.27-7.29 (m, 2H), 7.87-7.89 (m,

2H); 13

C NMR (75 MHz, CDCl3-d1) δ 21.61, 26.49, 128.44, 129.23, 134.78, 143.85,

197.81.

OMeO

OMe 2,4-Di-methoxy acetophenone (2i): Prepared as described for 2b;

starting from (2,4-di-methoxy phenyl) ethanol 1i (100 mg, 0.54 mmol) gave, after

purification with silica gel column chromatography (hexane:EtOAc :: 95:5) 2i as white

solid (92 mg, 93%), mp 46-48 oC;

1H NMR (300 MHz, CDCl3-d1) δ 2.53 (s, 3H), 3.80 (s,

3H), 3.84 (s, 3H), 6.34-6.48 (m, 2H), 7.73-7.79 (m, 1H); 13

C NMR (75 MHz, CDCl3-d1) δ

31.57, 55.20, 55.25, 98.00, 104.95, 120.84, 132.74, 160.90, 164.36, 197.37.

OOMe

MeO

2,5 Di-methoxy acetophenone (2j): Prepared as described for 2b; starting

from (2,5 di-methoxy phenyl) ethanol 1j (100 mg, 0.54 mmol) gave, after purification with

silica gel column chromatography (hexane:EtOAc :: 95:5) 2j as colourless liquid (88 mg,

90%); 1H NMR (300 MHz, CDCl3-d1) δ 2.64 (s, 3H), 3.80 (s, 3H), 3.90 (s, 3H), 6.90-7.06

(m, 2H), 7.28-7.30 (m, 1H); 13

C NMR (75 MHz, CDCl3-d1) δ 31.75, 55.79, 56.02, 113.20,

113.82, 120.31, 128.42, 153.41, 153.50, 199.34.

O

MeO

4-Methoxy acetophenone (2k): Prepared as described for 2b; starting

from (4-methoxy phenyl)ethanol 1k (100 mg, 0.64 mmol) gave, after purification with

silica gel column chromatography (hexane:EtOAc :: 95:5) 2k as white solid (87 mg, 90%),

mp 37-39 oC;

1H NMR (300 MHz, CDCl3-d1) δ 2.54 (s, 3H), 3.85 (s, 3H), 6.91 (d, J =

8.72, 2H), 7.92 (d, J = 8.70 Hz, 2H); 13

C NMR (75 MHz, CDCl3-d1) δ 26.65, 55.75, 113.96

(2C), 130.57, 130.89 (2C), 163.77, 197.12.


132

C6H5

OCl

4-Chlorobenzophenone (2l): Prepared as described for 2b; starting

from (4-chlorophenyl)-phenylethanol 1l (100 mg, 0.44 mmol) gave, after purification with

silica gel column chromatography (hexane:EtOAc :: 95:5) 2l as white solid (73 mg, 74%),

mp 76-78 oC;

1H NMR (300 MHz, CDCl3-d1) δ 7.46-7.53 (m, 3H), 7.60-7.64 (m, 2H),

7.76-7.80 (m, 4H); 13

C NMR (75 MHz, CDCl3-d1) δ 128.38 (2C), 129.61 (2C), 129.90

(2C), 131.44 (2C), 132.62, 135.86, 137.23, 138.87, 195.46.

OBr

4-Bromo acetophenone (2m): Prepared as described for 2b; starting

from (4-bromophenyl) ethanol 1m (100 mg, 0.48 mmol) gave, after purification with silica

gel column chromatography (hexane:EtOAc :: 95:5) 2m as white solid (87 mg, 90%), mp

47-49 oC;

1H NMR (300 MHz, CDCl3-d1) δ 2.60 (s, 3H), 7.60-7.63 (m, 2H), 7.82-7.84 (m,

2H); 13

C NMR (75 MHz, CDCl3-d1) δ 26.52, 128.28, 129.82 (2C), 131.87 (2C), 135.81,

197.00.

3.6 References:

An, G., Ahn, H., Castro, K. A. D. and Rhee, H. (2010). Pd/C and NaBH4 in basic aqueous

alcohol: an efficient system for an environmentally benign oxidation of alcohols

Synthesis 477-85.

Arends, I. W. C. E., Brink, G-J. T. and Sheldon, R. A. (2006). Palladium-neocuproine

catalyzed aerobic oxidation of alcohols in aqueous solvents. Journal of Molecular

Catalysis A: Chemical 251: 246-54.

Berkowitz, L. M. and Rylander, P. N. (1958). Use of ruthenium tetraoxide as a multi-

purpose oxidant. Journal of American Chemical Society 80: 6682-84.

Brink, G. T., Arends, I. W. C. E. and Sheldon, R. A. (2002). Catalytic conversions in

water. Part 21: mechanistic investigations on the palladium-catalyzed aerobic

oxidation of alcohols in water. Advanced Synthesis and Catalysis 344: 355-69.

Buffin, B. P., Clarkson, J. P., Belitz, N. L. and Kundu, A. (2005). Pd(II)-biquinoline

catalyzed aerobic oxidation of alcohols in water. Journal of Molecular Catalysis A:

Chemical 225: 111-16.

Cainelli, G. and Cardillo, G. (1984). Chromium Oxidants in Organic Chemistry. Springer,

Berlin.


133

Chen, J., Zhang, Q., Wang, Y. and Wan, H. (2008). Size-dependent catalytic activity of

supported palladium nanoparticles for aerobic oxidation of alcohols. Advanced

Synthesis and Catalysis 350: 453-64.

Chen,Y., Guo, Z., Chen, T. and Yang, Y. (2010). Surface-functionalized TUD-1

mesoporous molecular sieve supported palladium for solvent-free aerobic oxidation

of benzyl alcohol. Journal of Catalysis 275: 11-24.

Chen, Y., Lim, H., Tang, Q., Gao, Y., Sun, T., Yan, Q. and Yang,Y. (2010). Solvent-free

aerobic oxidation of benzyl alcohol over Pd monometallic and Au-Pd bimetallic

catalysts supported on SBA-16 mesoporous molecular sieves. Applied Catalysis A:

General 380 (1-2): 55-65.

Choudhary, D., Paul, S., Gupta, R. and Clark, J. H. (2006). Catalytic properties of several

palladium complexes covalently anchored onto silica for the aerobic oxidation of

alcohols. Green Chemistry 8: 479-82.

Dess, D. B. and Martin, J. C. (1983). Readily accessible 12-I-5 oxidant for the conversion

of primary and secondary alcohols to aldehydes and ketones. Journal of Organic

Chemistry 48 (22): 4155-56.

Feng, B., Hou, Z., Yang, H., Wang, X., Hu, Y., Li, H., Qiao, Y., Zhao, X. and Huang, Q.

(2010). Functionalized poly(ethylene glycol)-stabilized water-soluble palladium

nanoparticles: property/activity relationship for the aerobic alcohol oxidation in

water. Langmuir 26(4): 2505-13.

Griffith, W. P. (1992). Ruthenium Oxo complexes as organic oxidants. Chemical Society

Reviews 21: 179-85.

Hara, T., Ishikawa, M., Sawada, J., Ichikuni, N. and Shimazu, S. (2009). Creation of highly

stable monomeric Pd(II) species in an anion-exchangeable hydroxy double salt

interlayer: application to aerobic alcohol oxidation under an air atmosphere. Green

Chemistry 11: 2034-40.

He, X., Shen, Z., Mo, W., Sun, N., Hu, B. and Hu, X. (2009). TEMPO-tert-butyl nitrite: an

efficient catalytic system for aerobic oxidation of alcohols. Advanced Synthesis and

Catalysis 351: 89-92.

Hou, Z., Theyssen, N., Brinkmann, A. and Leitner, W. (2005). Biphasic aerobic oxidation

of alcohols catalyzed by poly(ethylene glycol)-stabilized palladium nanoparticles in

supercritical carbon dioxide. Angewandte Chemie International Edition 44: 1346-

49.


134

Hudlicky, M. (1990). Oxidations in Organic Chemistry. American Chemical Society,

Washington, DC.

Jensen, D. R., Schultz, M. J., Mueller, J. A. and Sigman, M. S. (2003). A well-defined

complex for palladium-catalyzed aerobic oxidation of alcohols: design, synthesis

and mechanistic considerations. Angewandte Chemie International Edition 42:

3810-13.

Ji, H. B., Yuan, Q. L., Zhou, X. T., Pei, L. X. and Wang, L. F. (2007). Highly efficient

selective oxidation of alcohols to carbonyl compounds catalyzed by ruthenium (III)

meso-tetraphenylporphyrin chloride in the presence of molecular oxygen.

Bioorganic & Medicinal Chemistry Letters 17: 6364-68.

Jiang, N. and Ragauskas, A. J. (2005). TEMPO-catalyzed oxidation of benzylic alcohols to

aldehydes with the H2O2/HBr/ionic liquid [bmim]PF6 system. Tetrahedron Letters

46: 3323-26.

Jiang, N. and Ragauskas, A. J. (2007) Vanadium-catalyzed selective aerobic alcohol

oxidation in ionic liquid [bmim]PF6. Tetrahedron Letters 48: 273-76.

Kakiuchi, N., Maeda, Y., Nishimura, T. and Uemura, S. (2001). Pd(II)-hydrotalcite-

catalyzed oxidation of alcohols to aldehydes and ketones using atmospheric

pressure of air. Journal of Organic Chemistry 66: 6620-25.

Karimi, B., Abedi, S., Clark, J. H. and Budarin, V. (2006). Highly efficient aerobic

oxidation of alcohols using a recoverable catalyst: the role of mesoporous channels

of SBA-15 in stabilizing palladium nanoparticles. Angewandte Chemie

International Edition 45: 4776-79.

Karimi, B., Elhamifar, D., Clark, J. H. and Hunt, A. J. (2011). Palladium containing

periodic mesoporous organosilica with imidazolium framework (Pd@PMO-IL): an

efficient and recyclable catalyst for the aerobic oxidation of alcohols. Organic and

Biomolecular Chemistry 9: 7420-26.

Karimi, B., Zamani, A. and Clark, J. H. (2005). A bipyridyl palladium complex covalently

anchored onto silica as an effective and recoverable interphase catalyst for the

aerobic oxidation of alcohols. Organometallics 24: 4695-98.A

Karimi, B., Zamani, A., Abedi, S. and Clark, J. H. (2009). Aerobic oxidation of alcohols

using various types of immobilized palladium catalyst: the synergistic role of

functionalized ligands, morphology of support and solvent in generating and

stabilizing nanoparticles. Green Chemistry 11: 109-19.


135

Kockritz, A., Sebek, M., Dittmar, A., Radnik, J., Bruckner, A., Bentrup, U., Pohl, M. M.,

Hugl, H. and Magerlein, W. (2006). Ru-catalyzed oxidation of primary alcohols.

Journal of Molecular Catalysis A: Chemical 246: 85-99.

Krohn, K., Vinke, I. and Adam, H. (1996). Transition-metal catalyzed oxidations. 7.

Zirconium-catalyzed oxidation of primary and secondary alcohols with

hydroperoxides. Journal of Organic Chemistry 61: 1467-72.

Kwon, M. S., Kim, N., Park, C. M., Lee, J. S., Kang, K. Y. and Park, J. (2005). Palladium

nanoparticles entrapped in aluminum hydroxide: dual catalyst for alkene

hydrogenation and aerobic alcohol oxidation. Organic letters 7 (6): 1077-79.

Larock, R. C. (1999). Comprehensive Organic Transformations. 2nd

ed. p.1197. Wiley-

VCH, New York.

Layek, K., Maheswaran, H., Arundhathi, R., Kantam, M. L. and Bhargavab, S. K. (2011).

Nanocrystalline magnesium oxide stabilized palladium(0): an efficient reusable

catalyst for room temperature selective aerobic oxidation of alcohols. Advanced

Synthesis and Catalysis 353: 606-16.

Lee, D. G. and Spitzer, U. A. (1970). Aqueous dichromate oxidation of primary alcohols.

Journal of Organic Chemistry 35: 3589-90.

Ley, S. V., Norman, J., Griffith, W. P. and Marsden, S. P. (1994). Tetrapropylammonium

perruthenate, Pr4N+RuO4

-, TPAP: a catalytic oxidant for organic synthesis.

Synthesis 639-66.

Li, S., Lin, Y., Cao, Y. and Zhang, S. (2007). Guanidine/Pd(OAc)2-catalyzed room

temperature Suzuki cross-coupling in aqueous media under aerobic condition.

Journal of Organic Chemistry 72 (11): 4067-72.

Mancuso, A. J. and Swern, D. (1981). Activated dimethyl sulfoxide: useful reagents for

synthesis. Synthesis 3: 165-85.

Mannam, S., Alamsetti, S. K. and Sekar, G. (2007). Aerobic, chemoselective oxidation of

alcohols to carbonyl compounds catalyzed by a DABCO-copper complex under

mild conditions. Advanced Synthesis and Catalysis 349: 2253-58.

Marko, I. E., Giles, P. R., Tsukazaki, M., Brown, S. M., Urch, C. J. (1996). Copper-

catalyzed oxidation of alcohols to aldehydes and ketones: an efficient, aerobic

alternative. Science 274: 2044-46.

Martin, S. E. and Suarez, D. F. (2002). Catalytic aerobic oxidation of alcohols by

Fe(NO3)3-FeBr3. Tetrahedron Letters 43: 4475-79.


136

Menger, F. M. and Lee, C. (1981). Synthetically useful oxidations at solid sodium

permangate surfaces. Tetrahedron Letters 22: 1655-56.

Mori, K., Hara, T., Mizugaki, T., Ebitani, K. and Kaneda, K. (2004). Hydroxyapatite-

supported palladium nanoclusters: a highly active heterogeneous catalyst for

selective oxidation of alcohols by use of molecular oxygen. Journal of American

Chemical Society 126: 10657-666.

Muzart, J. (1992). Chromium-catalyzed oxidations in organic synthesis. Chemical Reviews

92: 113-40.

Nishimura, T., Maeda, Y., Kakiuchi, N. and Uemura, S. (2000). Palladium(II)-catalyzed

oxidation of alcohols under an oxygen atmosphere in a fluorous biphase system

(FBS). Journal of Chemical Society, Perkin Tranactions1 4301-05.

Nishimura, T., Onoue, T., Ohe, K. and Uemura, S. (1999). Palladium(II)-catalyzed

oxidation of alcohols to aldehydes and ketones by molecular oxygen. Journal of

Organic Chemistry 64: 6750-55.

Peterson, K. P. and Larock, R. C. (1998). Palladium-catalyzed oxidation of primary and

secondary allylic and benzylic alcohols. Journal of Organic Chemistry 63: 3185-

89.

Pillai, U. R. and Sahle-Demessie, E. (2003). Oxidation of alcohols over

Fe3+

/montmorillonite-K10 using hydrogen peroxide. Applied Catalysis A: General

245 (1): 103-09.

Regen, S. L. and Koteel, C. (1977). Activation through impregnation. Permanganate-

coated solid supports. Journal of American Chemical Society 99: 3837-38.

Schultz, M. J., Park, C. C. and Sigman, M. S. (2002).IA convenient palladium-catalyzed

aerobic oxidation of alcohols at room temperature. Chemical Communications

3034-35.

Sharma, V. B., Jain, S. L. and Sain, B. (2003). Cobalt phthalocyanine catalyzed aerobic

oxidation of secondary alcohols: an efficient and simple synthesis of ketones.

Tetrahedron Letters 44: 383-86.

Smith, M. B. and March, J. (2001). Advanced Organic Chemistry, Reactions, Mechanisms,

and Structure. 5th

ed, Wiley-Interscience, New York.

Steinhoff, B. A., King, A. E. and Stahl, S. S. (2006). Unexpected roles of molecular sieves

in palladium-catalyzed aerobic alcohol oxidation. Journal of Organic Chemistry

71: 1861-68.


137

Tsuji, J. (2000). Transition metal reagents and Catalysts. John Wiley & sons, New York.

Uozumi, Y. and Nakao, R. (2003). Catalytic oxidation of alcohols in water under

atmospheric oxygen by use of an amphiphilic resin-dispersion of a nanopalladium

catalyst. Angewandte Chemie International Edition 42: 194-97.N

Uozumi, Y., Nakao, R. and Rhee, H. (2007). Development of an amphiphilic resin-

dispersion of nanopalladium catalyst: design, preparation, and its use in

aquacatalytic hydrodechlorination and aerobic oxidation. Journal of

Organometallic Chemistry 692: 420-27.

Urgoitia, G., Martin, R. S. Herrero, M. T. and Dommguez, E. (2011). Palladium NCN and

CNC pincer complexes as exceptionally active catalysts for aerobic oxidation in

sustainable media. Green Chemistry 13: 2161-66.

Wang, T., Xiao, C. X., Yan, L., Xu, L., Luo, J., Shou, H., Kou,Y. and Liu, H. (2007).

Aqueous-phase aerobic oxidation of alcohols by soluble Pt nanoclusters in the

absence of base. Chemical Communication 4375-77.

Wu, H., Zhang, Q. and Wang, Y. (2005). Solvent-free aerobic oxidation of alcohols

catalyzed by an efficient and recyclable palladium heterogeneous catalyst.

Advanced Synthesis and Catalysis 347: 1356-60.

Yamaguchi, K. and Mizuno, N. (2002). Supported ruthenium catalyst for the

heterogeneous oxidation of alcohols with molecular oxygen. Angewandte Chemie

International Edition 41: 4538-42.

Zhang, G., Wang, Y., Wen, X., Ding, C. and Li, Y. (2012). Dual-functional click-triazole:

a metal chelator and immobilization linker for the construction of a heterogeneous

palladium catalyst and its application for the aerobic oxidation of alcohols.

Chemical Communications 48: 2979-81.

Zhou, J., Li, X. and Sun, H. (2008). Palladium-catalyzed aerobic alcohol oxidation

supported by a new type of α-diimine ligands. Canadian Journal of Chemistry

86(8): 782-90.


138

NMR spectra of some compounds

1H NMR (in CDCl3) spectrum of 4-Bromo benzaldehyde

13

C NMR (in CDCl3) spectrum of 4-Bromo benzaldehyde


139

1H NMR (in CDCl3) spectrum of 4-methoxy acetophenone

13

C NMR (in CDCl3) spectrum of 4-methoxy acetophenone


140

1H NMR (in CDCl3) spectrum of 4-chlorobenzophenone

13

C NMR (in CDCl3) spectrum of 4-chlorobenzophenone

Chapter 3 Aerobic Oxidation of Benzyl...

Documents

Transcript of Chapter 3 Aerobic Oxidation of Benzyl...