TITLE OF THE INVENTION

A method for synthesis of dibenzylidene sorbitol in high yields Field of Invention

The invention relates to a method for synthesis of dibenzylidene sorbitol by reacting dimethyl benzaldehyde and D-sorbitol under microwave irradiation.

Background of Invention To impart crystallinity and to improve the mechanical and optical properties, polymers are treated with clarifiers and nucleating agents. Dibenzylidene sorbitol is a widely used clarifier and nucleating agent for polypropylene. Conventionally, dibenzylidene sorbitol is prepared by heating dimethyl benzaldehyde with D-sorbitol using thermal fluid in a jacketed reactor. The conventional heating method is, however, less energy efficient and the product yield obtained by the conventional method is usually low. Further, the product formed by the conventional method is usually contaminated with unreacted benzaldehyde and reaction side products. These contaminants are undesirable as they can generate unpleasant odours in the product.

There is a need for a method for synthesis of dibenzylidene sorbitol without the above mentioned drawbacks.

Detailed description

Accordingly, the invention provides a method for synthesis of dibenzylidene sorbitol by heating dimethyl benzaldehyde and D-sorbitol wherein the heating is carried out by microwave irradiation.

In one embodiment, the invention provides a method for synthesis of dibenzylidene sorbitol, in high yields, the method comprising heating dimethyl benzaldehyde and D-sorbitol in the presence

of a bronsted acid catalyst at a temperature in the range of 50 to 150 degrees wherein the heating is carried out by microwave irradiation.

In another embodiment, the invention provides a method for synthesis of dibenzylidene sorbitol, in high yields, the method comprising heating dimethyl benzaldehyde and D-sorbitol in the presence of a bronsted acid catalyst at a temperature in the range of 50 to 150 degrees wherein the heating is carried out by microwave irradiation having a frequency in the range of 2000 to 3000 MHz

In another embodiment, the invention provides a method for synthesis of dibenzylidene sorbitol, in high yields, the method comprising heating dimethyl benzaldehyde and D-sorbitol in a molar ratio of 1:2 in the presence of a bronsted acid catalyst at a temperature in the range of 50 to 150 degrees wherein the heating is carried out by microwave irradiation.

In another embodiment, the invention provides a method for synthesis of dibenzylidene sorbitol, in high yields, the method comprising heating dimethyl benzaldehyde and D-sorbitol in the presence of a bronsted acid catalyst used in the range of 10 to 200 parts by weight of dimethyl benzaldehyde and D-sorbitol, at a temperature in the range of 50 to 150 degrees wherein the heating is carried out by microwave irradiation.

In another embodiment, the invention provides a method for synthesis of dibenzylidene sorbitol, in high yields, the method comprising heating dimethyl benzaldehyde and D-sorbitol in the presence of a bronsted acid, at a temperature in the range of 50 to 150 degrees in a two solvent system comprising a hydrophobic solvent and a hydrophyllic solvent wherein the heating is carried out by microwave irradiation.

In another embodiment the invention provides clarified polypropylene prepared by using the dibenzylidene sorbitol synthesized by a method comprising heating dimethyl benzaldehyde and D-sόrbitol in the presence of a bronsted acid catalyst at a temperature in the range of 50 to 150 degrees wherein the heating is carried out by microwave irradiation.

In a further embodiment, the invention provides dibenzylidene sorbitol synthesized by the method comprising heating dimethyl benzaldehyde and D-sorbitol in the presence of a bronsted acid catalyst at a temperature in the range of 50 to 150 degrees wherein the heating is carried out by microwave irradiation

In a still further embodiment, the invention provides clarified polyolefin prepared by using dibenzyidene sorbitol synthesized by the method comprising heating dimethyl benzaldehyde and D-sorbitol in the presence of a bronsted acid catalyst at a temperature in the range of 50 to 150 degrees wherein the heating is carried out by microwave irradiation

High yield synthesis of dibenzylidene by the method of the invention is achieved by carrying out the reaction between dimethyl benzaldehyde and D-sorbitol under microwave irradiation. The synthesis yields dibenzylidene sorbitol in maximum yield of around 93%. A microwave generator operating at 100 to 1000 watts power and generating microwave frequency in the range of 2000 to 3000 MHz was used to irradiate the reaction mixture. Preferably, a microwave radiation having a frequency of 2450 MHz is used for irradiation. The dimethyl benzaldehyde to sorbitol molar ratio for the reaction is maintained at 1 :2. The reaction is carried out in the presence of a bronsted acid catalyst. Preferably, sulfuric acid is used as the bronsted acid. Further, the bronsted acid was used in the range of 10 to 200 parts by weight of dimethyl benzaldehyde and D-sorbitol. Dibenzylidene

synthesis by the method of the invention is carried out in a two solvent system comprising a hydrophobic solvent and a hydrophyllic solvent. Preferably, cyclohexane is used as the hydrophobic solvent. Hydrophyllic solvent is that which forms an azeotropic mixture with water formed during the reaction. Isopropyl alcohol is the preferred hydrophyllic solvent

The method of the invention could be used for the synthesis of dibenzylidene sorbitol as well as of the derivatives of dibenzylidene sorbitol. The synthesis is carried out in isopropyl alcohol under microwave irradiation. The water formed during the synthesis forms azeotropic mixture with isopropyl alcohol and the mixture is efficiently removed by distillation under microwave irradiation. In the method of the invention, the loss of solvent is compensated by the intermittent addition of fresh solvent to the reactor. Further the moisture content of the azeotropic mixture is analysed to determine the reaction progress. The synthesis proceeds by high conversion and yield thereby ensuring that the reaction product is less contaminated by bezaldehyde and reaction side products.

The invention is further illustrated by way of the following examples

Examples:

Example 1: Synthesis of Dibenzylidene sorbitol by microwave irradiation 5.0 gm of 3,4- Dimethylbenzaldehyde and 3.39 gm of D-Sorbitol was solublized in 25 ml cyclohexane and added to the reactor fitted in microwave oven. The reactor was fitted with Dean- Stark assembly for continuous removal of water from the system. 0.08 gm of sulphuric acid was added to the reactor. Microwave oven was programmed to use 300 Watt power and to take the reaction temperature from 30 ⁰ C to 80 ⁰ C in 5 minutes. As soon as water removal from the system is started, a mixture of 1:4 by volume of isopropanol and cyclohexane was added intermittently in

the reactor so as to compensate the solvent loss from the reactor. Moisture of the distilled solvent is measured to check for the separated water from the reaction. Reaction is completed in about 2 hours. Reaction mass is worked up by neutralization, washing, filtration and drying to collect a white powder of 3, 4- Dibenzylidene Sorbitol.

Example 2: Conventional synthesis of Dibenzylidene sorbitol

5.0 gm of 3,4- Dimethylbenzaldehyde and 3.39 gm of D-Sorbitol was solublized in 25 ml cyclohexane and added to a jacketed reactor heated by thermal fluid. The reactor was fitted with Dean-Stark assembly for continuous removal of water from the system. 0.08 gm of sulphuric acid was added to the reactor. As soon as water removal from the system is started, a mixture of 1 :4 by volume of Isopropanol and cyclohexane was added intermittently in the reactor so as to compensate the solvent loss from the reactor. Moisture of the distilled solvent was measured to check for the separated water from the reaction. Reaction was continued for 4 hours. Reaction mass was worked up by neutralization, washing, filtration and drying to collect 3, 4- Dibenzylidene sorbitol.

Table 1: Comparative yields and batch time of dibenzylidene sorbitol obtained by the conventional process and by the process of the invention

From table 1 it is clear that there is significant improvement in the yield of dibenzylidene sorbitol when the synthesis is carried out by microwave irradiation. Further there is improvement in batch

time for the reaction under microwave irradiation. Higher yields of the product increases the efficiency of the synthesis and simplifies the purification procedures whereas decrease in batch time for the reaction improves the overall productivity of the synthesis. Furthermore, the method of the invention provides ease of operation as well as reduces the process cost.