DESC:PROCESS FOR THE PREPARATION OF HALOFLUORENES

Field of the invention

The present invention provides a process for the preparation of halofluorenes of Formula I.

Formula I

Background of the invention

The fluorene and fluorene derivatives find utility in the preparation of resinous materials, dyestuffs, and as insecticides. Particularly, the bromofluorenes are useful as intermediate in pharmaceutical and organic light emitting diode.

The literature provides processes for preparation of bromofluorenes which use halogenated hydrocarbons as solvents to brominate fluorene compounds. One such method is disclosed in Synthetic Communications, 38:1888-1895, 2008, which provides a process for the preparation of bromide derivatives of fluorene and spirobifluorene using sodium bromide, hydrogen peroxide, and sulphuric acid in the presence of ethylene dichloride as solvent. The process has yield as low as 33%. As the process involves the use of halogenated hydrocarbon as solvent, it has deleterious effects on the environment. Also, handling of such solvent is burdensome and it is enormously costly to dispose them off as well as the waste water containing these solvents. Additionally, the paper discloses the use of petroleum ether for recrystallization to obtain the final product. The use of petroleum ether is industrially unfavourable as they are extremely volatile, have very low flash points, and present a significant fire hazard. Also due to its low boiling point there will be difficulty in separation of the desired product. Moreover, the paper does not disclose the purity of the bromofluorene.

The paper Chemical Communication 2009, Issue 33, pp 4950-4952, discloses the use of ethanol/water for recrystallization to obtain 2-bromofluorene. The ethanol/water, in isolation, is not effective in removal of dibromofluorene and residual fluorene.

An European Patent No. 1,298,117 discloses a process of preparation of bromofluorenes. The process discloses the use of toluene in work-up. The inventors have observed that use of toluene with bromofluorene will lead to the formation of a thick slurry and thereby filtration of the same will result in choking of the filter and thus leading to difficulty in handling.

The inventors have surprisingly found a novel method for carrying out oxidative bromination of fluorenes, with high selectivity to obtain the mono-brominated fluorene. The present invention provides a process for the preparation of halofluorenes represented by Formula I. The process of the present invention is simple, safe, environmental friendly and suitable for industrial production.

Summary of the invention

The present invention provides a process for the preparation of halofluorenes of Formula I, comprising;
a) contacting a compound of Formula II with an acid, alkali bromide and an oxidizer to obtain halofluorenes of Formula I,
b) isolating the halofluorenes of Formula I from step a),
c) washing step b) product with ethanol and water,
d) washing step c) product with an alcohol, and
e) isolating the halofluorenes of Formula I from step d)

Formula I Formula II

Detailed description of the invention

The present invention provides a process for the preparation of halofluorenes of Formula I, comprising;
a) contacting a compound of Formula II with an acid, alkali bromide and an oxidizer to obtain halofluorenes of Formula I,
b) isolating the halofluorenes of Formula I from step a),
c) washing step b) product with ethanol and water,
d) washing step c) product with an alcohol, and
e) isolating the halofluorenes of Formula I from step d)

Formula I Formula II

The compound of Formula II is commercially obtained.
The step a) may be carried out at a temperature in the range of 20oC to 80oC. The acid used in the step a) is selected from acetic acid or sulphuric acid. The oxidizer used in step a) is selected from the group consisting of hydrogen peroxide, molecular oxygen and organic peroxide. The organic peroxide may be selected from the group consisting of benzoyl peroxide, tert-butyl hydroperoxide, di-tert-butyl peroxide, diacetyl peroxide and peracetic acid.

The acid, alkali bromide and oxidizer in step a) may be added sequentially or in one go.

The alkali bromide is selected from the group consisting of lithium bromide, sodium bromide, potassium bromide, caesium bromide and rubidium bromide or mixture thereof. The step a) may be carried out in the presence of water, dimethyl formamide, propylene carbonate, acetonitrile and tetrahydrofuran or a mixture thereof.

The alcohol in step d) is selected from aliphatic alcohols having from 1 to 10 carbon atoms, preferably from 1 to 4 carbon atoms, such as, for example, methanol, ethanol, propanol, isopropanol, n-butanol, isobutanol, and t-butanol or a mixture thereof.

The isolation of the halofluorenes of Formula I is carried out by any method known in the art.

While the present invention has been described in terms of its specific embodiments, certain modifications and equivalents will be apparent to those skilled in the art and are intended to be included within the scope of the present invention.

The following examples are given by way of illustration and therefore should not be construed to limit the scope of the present invention.

Examples
Example 1: Preparation of 2-bromofluorene
In a round bottom flask, glacial acetic acid (1500g), water (500g), sodium bromide (310g) and fluorene (100g) were added to obtain a reaction mixture. The reaction mixture was heated to 40°C. The hydrogen peroxide (189g) was added to the reaction mixture in two batches with intermittent stirring for 1 hour at 55°C. The reaction mixture was stirred for additional 4 hours after complete hydrogen peroxide addition. Progress of the reaction was monitored by high-performance liquid chromatography. After completion of the reaction, the mass was cooled to 25°C and filtered. The solid was slurry washed with fresh water (1000g) and then washed twice with ethanol (720g) and water (80g) followed with pure n-butanol (600g). The solid was filtered and dried under vacuum at 45°C to obtain the title compound.
Yield (g) = 65
Purity (%) = 97.2

CLAIMS:
We claim:
1. A process for the preparation of halofluorenes of Formula I, comprising;
a) contacting a compound of Formula II with an acid, alkali bromide and an oxidizer to obtain halofluorenes of Formula I,
b) isolating the halofluorenes of Formula I from step a),
c) washing step b) product with ethanol and water,
d) washing step c) product with an alcohol, and
e) isolating the halofluorenes of Formula I from step d).

Formula I Formula II

2. The process as claimed in claim 1, wherein the step a) is carried out at a temperature in the range of 20oC to 80oC.

3. The process as claimed in claim 1, wherein the acid used in the step a) is selected from acetic acid or sulphuric acid.

4. The process as claimed in claim 1, wherein the oxidizer used in step a) is selected from the group consisting of hydrogen peroxide, molecular oxygen and organic peroxide.

5. The process as claimed in claim 4, wherein the organic peroxide is selected from the group consisting of benzoyl peroxide, tert-butyl hydroperoxide, di-tert-butyl peroxide, diacetyl peroxide and peracetic acid.

6. The process as claimed in claim 1, wherein the alkali bromide is selected from the group consisting of lithium bromide, sodium bromide, potassium bromide, caesium bromide and rubidium bromide or mixture thereof.

7. The process as claimed in claim 1, wherein the step a) is carried out in the presence of water, dimethyl formamide, propylene carbonate, acetonitrile and tetrahydrofuran or a mixture thereof.

8. The process as claimed in claim 1, wherein the alcohol in step d) is selected from the group consisting of methanol, ethanol, propanol, isopropanol, n-butanol, isobutanol, and t-butanol or a mixture thereof.