INTRODUCTION:
Aromatic aldehydes are important chemicals with applications such as chemical intermediates, pharmaceuticals, agricultural chemicals, pulp and paper chemicals dyestuff, and flavors and fragrance materials. Aldehydes may be prepared from a variety of starting materials such as alcohols, carboxylic acids, acid chloride salts, glycols and olefins etc by using different methods. However several known methods are limited to the preparation of specific aldehydes or they give low yields. The ready availability of alkyl substituted aromatic compounds makes it a possible starting material for synthesis of corresponding aldehydes.1-2 So, phase transfer catalyst is used for selective and controlled oxidation of alkyl aromatics to respective aldehydes.3 Phase transfer catalysis offers a number of advantages over the conventional processes:4-7
Enhanced reaction rates and/or mild reaction conditions such as lower temperature
§ Suppression of byproducts and increased yields and selectively with respect to desired product
§ Expensive aprotic solvents are not required
§ Inexpensive and safe oxidants are used
§ Workup of the reaction is easier
§ Reaction can be carried out with PTC which otherwise do not proceed
The transformation of these hydrocarbons to aldehydes may be accomplished by oxidizing agents.
Experimental:
The purity and structure of synthesized compounds was confirmed by thin layer chromatography, melting point/boiling point, 1H NMR and IR spectroscopy.
1H NMR was recorded on ‘Jeol My 60 FTNMR’ spectrometer in CCl4 / CDCl3 using TMS as an internal standard. IR spectra were recorded by using FTIR (KBr, cm-1) spectrophotometer. Melting points were determined in open capillary tube method and were uncorrected.
General Synthetic Procedure:
Substituted toluene (5mmole) was added to a mixture of sodium bromate (5mmole) and tetra butyl ammonium hydrogen sulphate (0.118mmole) in acetonitrile, water and glacial acetic acid (5:4:1). The mixture was stirred at 90 0C for completing the reaction, reaction was monitored by TLC. Then the reaction mixture was extracted with methylene dichloride. Evaporation of solvent gives product which was purified by recrystallization or by column chromatography if necessary. 8 -12
Results and Discussion:
A simple, industrially feasible, environmentally acceptable, selective method of oxidation from alkyl aromatics to aldehydes by phase transfer catalyst method is developed (Table no.1).
Spectral Data:
1H NMR and FTIR spectra of synthesized aromatic aldehydes:
Benzaldehyde: Bp: 178 0C, 1H NMR (60 MHz, CDCl3) 10.102 (1H, s) CHO, 7.963 (4H dd) Ar, IR (KBr, cm-1) 1656 (C=O), 2865 (C-H)