Field of the Invention
The present invention relates to a purification process of 4-Fluoro-3-phenoxy-benzaldehyde.
Background of the Invention
U.S. Patent No. 4,424,168 discloses a process for the preparation of a known pesticidal a-cyano-
3-phenoxy-benzyl 3-alkenyl-2,2-dimethyl-cyclopropanecarboxylate comprises reacting a 3-
alkenyl-2,2-dimethyl-cyclopropanecarboxylic acid-chloride with a 3-phenoxy-benzaldehyde of
the or an adduct thereof with an alkali metal bisulphite (hydrogen sulphite or pyrosulphite) and
an alkali metal cyanide, using an.alkyl ester and water as diluents.
U.S. Patent No. 4,162,269 discloses a process for 3-phenoxybenzaldehyde, reacting crude 3-
phenoxybenzaldehyde with an alkali metal or ammonium bisulfite, or metabisulfite in the
presence of an organic quaternary ammonium salt, an inorganic acid salt or a macrocyclic
polyether used as a catalyst, isolating the resulting 3-phenoxybenzaldehyde alkali metal or
ammonium bisulfite adduct, and decomposing it by using an acid or a base, or by heating.
An Indian Journal of Chemistry. Vol. 43B. pp. 1798-1801 discloses the use of the compound 4-
Fluoro-3- phenoxybenzaldehyde in the synthesis of oxadiazoles but does not reveal of any
purification process of said compound.
Thus, there is a need to develop an improved process for purification of 4-Fluoro-3-
phenoxybenzaldehyde which is commercially viablc and cost effective.
Summary of the Invention
The present invention relates to a process for purifying 4-fluoro-3- phenoxybenzaldehyde of
Formula I by bisulphite adduct formation.
Detailed Descrivtion of the Invention
In an aspect, the present invention provides a process for purification of 4-Fluoro-3-
phenoxybenzaldehyde, comprising
a.) contacting 4-fluoro 3-phenoxybenzaldchdye and sodium hyclrogen sulphite in the
presence of an alcohol solvent,
b.) contacting the mixture obtained fiom step a) with alkali metal hydroxide in the presence
of solvent, and
c.) isolating 4-Fluoro-3- phenoxybenzaldehyde from reaction mixture.
The 4-fluoro 3-phenoxybenzaldehdye and sodium hydrogen sulphite are reacted in the presence
of alcohol solvent. The starting material 4-fluoro 3-phenoxybenzaldehdye may be prepared by
any method known in the art. The starting material 4-fluoro 3-phenoxybenzaldehdye has a purity
less than 99.0% by HPLC. The alcohol solvent may be selected from methanol, ethanol, npropanol,
iso-propanol and n-butanol or mixture thereof. The reaction may take place at a
temperature of about 10°C to about 50°C, for example, 20°C to about 30°C for about 10 minutes
to about 6 hours. The mixture may be cooled to about.-O°C to about 5OC .and 4-fluoro 3-
phenoxybenzaldehyde bisulfite adduct may be isolated from the mixture. The 4-fluoro 3-
phenoxybenzaldehyde bisulfite adduct is contacted with alkali metal hydroxide in the presence of
solvent. The solvent may be selected from ether hydrocarbon solvent. The alkali metal hydroxide
may be selected from sodium hydroxide, potassium hydroxide and cesium hydroxide or mixture
thereof. The hydrocarbon solvent may be selected from toluene and xylene or mixture thereof.
The contacting of 4-fluoro 3-phenoxybenzaldehyde bisulfite adduct is contacted with alkali
metal hydroxide may take place at a temperature of about 10°C to about 50°C, for example, 20°C
to about 30°C for about 10 minutes to about 6 hours. The pure 4-fluoro 3-phenoxybenzaldehyde
is isolated from the mixture.by distillation, precipitation, decantation, crystallization and layer
separation or mixture thereof.
The 4-Fluoro-3-phenoxy-benzaldehyde, obtained by present invention, has a purity greater than
99.0%, more preferably greater than 99.5%.
It will be appreciated that many steps can be made and that many changes can be made in the
preferred steps without departing from the scope of the invention. These and other changes in the
preferred steps of the invention will be apparent to those skilled in the art from the disclosure
herein.
Example
PURIFICATION OF 4-FLUORO 3-PHENOXYBENZALDEHDYE
4-Fluoro 3-phenoxybenzaldehdye (200 g, 98.57% purity), ethanol (104.8 g) were taken together
in a reaction vessel. The temperature was maintained at 22'C -25OC and sodium hydrogen
sulphite (1 12.0g in 400.0 g of purified water) was added drop wise over a period of 30 minutes to
40 minutes. The reaction mixture was stirred to obtain 4-fluoro 3-phenoxybenzaldehyde bisulfite
adduct. The mixture was cooled to 0-5OC for two hours. The mixture was filtered, washed with
ethanol (3 15.6 g) and with 1 : 1 mixture of ethanol: methanol (320.3 g) and dried under reduced
pressure for 3 hours to 4 hours. The filtered product, toluene (692.8 g) and sodium hydroxide
(36.0 g) were taken together and purified water (400.0 g) was added drop wise for 30 minutes to
40 minutes at 22-25' C. The mixture was stirred for 2 hours, the layers were separated, washed
with fresh toluene (346.4 g) and distilled under reduced pressure at 65-70' C to obtain the title
compound.
Purity: 99.7% (GC purity)

We claim:
1. A process for purification of 4-fluoro-3- phenoxybenzaldehyde, comprising:
a.) contacting 4-fluoro-3-phenoxybenzaldehdye and sodium hydrogen sulphite in the
presence of an alcohol solvent to obtain a bisulfite adduct,
b.) contacting the bisulfite adduct from step a) with an alkali metal hydroxide in the presence
of a solvent, and
c.) isolating 4-fluoro-3- phenoxybenzaldehyde.
2. The process of claim 1, wherein the alcohol solvent is selected fiom methanol, ethanol, npropanol,
iso-propanol and n-butanol or mixture thereof.
3. The process of claim 1, wherein step a) takes place at a temperature in the range of 20°C to
30°C.
4. The process of claim 1, wherein the solvent in step b) is selected fiom toluene and xylene or
mixture thereof.
5. The process of claim 1, wherein the alkali metal hydroxide in step b) is selected from sodium
hydroxide, potassium hydroxide and cesium hydroxide or mixture thereof.
6. The process of cla& 1, wherein the 4-fluoro 3-phenoxybenzaldehyde is isolated from the
mixture by distillation, precipitation, decantation, crystallization and layer separation or mixture
thereof.
7. The 4-Fluoro-3-phenoxy-benzaldehyde, as obtained by claim 1, has a purity greater than
99 .O%.