Acta Chim. Slov. 2004, 51, 333-336.
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Short Communication
MICROWAVE-EXPEDITED SYNTHESIS OF AROMATIC ALDEHYDES AND
KETONES FROM ALKYL HALIDES WITHOUT SOLVENT USING WET
MONTMORILLONITE K 10 SUPPORTED IODIC ACID AS OXIDANT
Mohammed Mahmoudi Hashemi,*a Abdollah Ranimi,a and Yousef Ahmadibenib
a Department of Chemistry, Sharif University of Technology, P.O.Box 11365-9516, Tehran, Iran b Toda Pharmaceutical Co., No. 14, Farid Afshar Ave., Vahidi Dastgerdi Ave., Modarres Highway, P. O.
Box 19395-4978, Tehran, Iran
Received 22-11-2003
Abstract
The efficient microwave-assisted synthesis of aldehydes and ketones over wet montmorillonite K 10 using HI03 as oxidizing agent is described. This fast oxidation protocol is applicable to variety of alkyl halides.
Key words: alkyl halides, iodic acid, Montmorillonite K10
Introduction
Recently microwave-assisted solvent-free synthesis in organic reactions has been of growing interest as an efficient, economic and clean procedure (‘green chemist^’).1"9 Over the past few years, a considerable number of reactions have been developed in which inorganic solid supports such as alumina, silica gel and montmorillonite appeared to be useful in terms of mildness of conditions, yield and convenience.10"12
Synthesis of aldehydes and ketones from alkyl halides is an important method for the preparation of aldehydes and ketones. In this regard various reagents have been developed: dimethyl sulfoxide,13-14#,#-dimethyl-4-nitrosoaniline,15 nitronate anion and Pd(PPh3),16 pyridine #-oxides,17 and other amine oxides,18 chromate and dichromate systems,19 silver nitrate,20 hexamethylene tetraamine,21 pyrazinyl sulfoxides.22
Some of these reagents or catalysts give low yields,13'14'17'18'21 others require the use of high temperature,13'14'21 long reaction tirne,15'16'22 bulk requirement of the solid bed.12
Barbry and Champagne have reported a solvent free procedure under microwave irradiation for the oxidation of benzylic bromides to aromatic aldehydes using pyridine
M. M. Hashemi, A. Rahimi, Y. Ahmadibeni: Microwave-Expedited Synthesis of Aromatic Aldehydes...
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Acta Chim. Slov. 2004, 51, 333-336.
N-oxide as oxidant.23 By this method only benzylic bromides can be oxidized to their corresponding aromatic aldehydes.
Recently NaI04-DMF,24 bromate exchange resin,25 2-dimethylamino-#, #-dimethylaniline #-oxide26 and photooxidation of alkyl bromides with mesoporous silica FSM-1627 have been reported for the conversion of alkyl halides to the aldehydes and ketones. However these procedures have some limitations such as long reaction tirne.
Oxidation of alkyl halides and alkyl tosylates to their corresponding aldehydes and ketones by molecular oxygen catalyzed by Kieselghur supported CuCl is another method, which was developed by our group.28
Results and discussion
Herein we wish to report a fast and convenient procedure for the one step oxidation of alkyl halides to the aldehydes and ketones using HI03/wet montmorillonite K 10 under microwave irradiation and without solvent (Table 1). This method offers some advantages in terms of simplicity of performance, solvent-free conditions, no side product formation, very low reaction tirne and also a wide range of alkyl halides can be converted to their corresponding aromatic aldehydes and ketones. In addition the montmorillonite K 10 clay can be recycled after activation (yields remained 86% after 3 re-uses for the oxidation of benzyl chloride to benzaldehyde).
Some experiments have been performed to check the efficiency of microwave irradiation in our synthesis. When this reaction was done in methanol, or benzene under reflux condition, after 12 hours only starting materials were observed on the TLC plate. In the absence of the montmorillonite K 10 yields are much lower in longer tirne.
Conclusions
In summary we have extended successfully the application of montmorillonite K 10 supported iodic acid under microwave irradiation and without solvent. This method offers some advantages in terms of simplicity of performance, solvent free condition, no side product formation and very low reaction tirne. In addition, the montmorillonite K 10 clay can be recycled after activation.
M. M. Hashemi, A. Rahimi, Y. Ahmadibeni: Microwave-Expedited Synthesis of Aromatic Aldehydes...
Acta Chim. Slov. 2004, 51, 333-336.
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HI03/wet Montmorillonite K 10
RR'CHX---------------------------------------------*~          RR'C=0
MW
Scheme 1
Table 1. Microwave-assisted oxidation of alkyl halides to the corresponding aldehydes and ketones over wet montmorillonite K 10 using HI03 as oxidant.
Entiy	Substratea	Reaction time (sec.)	Product C6H5CHO	YieldJ%
1	CsHsCHzCl	60.0		91
2	CsHsCHzBr	50.0	C6H5CHO	97
3	p-BrC6H4CH2Br	60.0	p-Br-C6H4CHO	90
4	p-ClC6H4CH2Cl	120.0	p-Cl-C6H4CHO	87
5	p-NO2C6H4CH2Br	90.0	p-NO2-C6H4CHO	89
6	p-CH3C6H4CH2Cl	90.0	p-CH3C6H4CHO	85
7	m-NO2C6H4CH2Br	90.0	m-NO2C6H4CHO	93
8	p-FC6H4CH2Cl	90.0	p-FC6H4CHO	86
9	p-ClC6H4CH2I	40.0	p-ClC6H4CHO	90
10	(C6H5)2CHBr	90.0	(C6H5)2CO	94
11	(C6H5)2CHC1	120.0	(C6H5)2CO	88
12	(p-ClC6H4)2CHCl	120.0	(p-ClC6H4)2CO	93
13	a-C10H7CH2Br	100.0	a-C10H7CHO	87
14	a-C10H7CH2Cl	90.0	a-C10H7CHO	92
aa-C10H7 is l-naphtyl, *the yields of isolated products.
Experimental
Typical procedure for the oxidation of benzyl chloride to benzaldehyde: Wet
montmorillonite K 10 was prepared by the addition of 50 mL of distilled water into 450 g of dry montmorillonite K 10 (surface 200 m2/g, Fluka) followed by mixing for 30 minutes; it must be stored in a well closed container.
Benzyl chloride (0.56 g, 5 mmol), iodic acid (1.76 g, 10 mmol) and wet montmorillonite K 10 (5 g) were taken in a microwave oven (Butane household apparatus) and irradiated (1000 W) for 1 min. The progress of the reaction was monitored by thin layer chromatography (10% ethyl acetate in petroleum ether). After completion of the reaction, the product was extracted into dichloromethane (3x15 mL) followed by decolorisation with activated charcoal, then it was filtered after 5 minutes and dried over sodium sulfate. Evaporation of the solvent followed by distillation of the residue gave 0.48 g (91% yield) of benzaldehyde, which was identified by its boiling point, IR and 'H-NMR spectroscopic properties.
M. M. Hashemi, A. Rahimi, Y. Ahmadibeni: Microwave-Expedited Synthesis of Aromatic Aldehydes...
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Acknowledgements
Financial support from the research council of Sharif University of Technology is gratefully acknowledged.
References
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Povzetek
Opisana je sinteza aldehidov in ketonov z oksidantom HIO3 na vlažnem montmorilonitu K 10 s pomočjo mikrovalov. Metoda je uporabna na različnih alkil halidih.
M. M. Hashemi, A. Rahimi, Y. Ahmadibeni: Microwave-Expedited Synthesis of Aromatic Aldehydes...