FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See Section 10; Rule 13)
1. TITLE OF THE INVENTION: A novel route for preparation of
l,3:2,4-bis-(3,4-dimethylbenzylidene)sorbitol
2. APPLICANT(S)
(a) NAME: Excel Industries Limited
(b) NATIONALITY: An Indian Company
(c) ADDRESS:
184-87, Swami Vivekanand Road, Jogeshwari(West), Mumbai 400 102, Maharashtra, India.
3. PREAMBLE TO THE DESCRIPTION:
The following COMPLETE specification particularly describes the nature of this invention and the manner in which it is to be performed.

A NOVEL ROUTE FOR PREPARATION OF l,3:2,4-BIS-(3,4-DIMETHYLBENZYLIDENE)SORBITOL
FIELD OF INVENTION
This invention relates to a novel route for preparation of l,3:2,4-bis-(3,4-dimethylbenzylidene)sorbitol [DMDBS]. More particularly, this invention relates to a novel route for preparation of DMDBS comprising: bromination of o-xylene to obtain a mixture of 4-bromo-o-xylene as a major product and 3-bromo-o-xylene; conversion of bromo-o-xylenes into corresponding dimethylbenzaldehydes by Grignard reaction; and reaction of 3,4-dimethylbenzaldehyde, without separating 2,3-dimethylbenzaldehyde therefrom, with sorbitol, in presence of catalyst and solvent to obtain DMDBS.
BACKGROUND AND PRIOR ART
DMDBS is used as a nucleating agent and clarifier in the crystallization of isotactic polypropylene. DMDBS has an excellent nucleating efficiency in the low concentration range which leads to very small crystallites that impart clarity to the material. DMDBS crystallizes within molten polymer matrix forming a percolated network, the surface thereof provides a large number of uniformly spaced nucleation sites. It is possible to obtain fiber-like polymer morphologies with as little as 0.5% DMDBS.

Several methods for preparation of DMDBS are reported in the
literature [US5731474, US3721682, US4429140, US4562265,
US4902807, EP0497976, EP2663569, US2002137953,
WO02079124]. These methods involve reaction of substituted benzaldehyde with alditols such as sorbitol. In these methods, use of 3,4-isomer of dimethylbenzaldehyde as starting material is mentioned for production of DMDBS as shown in the following reaction:

This leads to assumption by a person having ordinary skill in the art that the other isomer needs to be separated in order to obtain isomerically pure DMDBS end-product. 3,4-Dimethylbenzaldehyde with high isomeric purity is a comparatively costlier intermediate.
The intermediate 3,4-dimethylbenzaldehyde can be prepared from 4-bromo-o-xylene by Grignard reaction as shown below:


4-Bromo-o-xylene is prepared by bromination of o-xylene. However, bromination of o-xylene results in the formation of mixture of isomers. A method for preparation of bromo-o-xylene containing a high ratio of the 4-bromo-o-xylene to the 3-bromo-o-xylene isomer is disclosed in EP 0492594, wherein it is prepared by reacting o-xylene with Br2 in complete darkness, in the presence of a catalyst. However, to achieve said high ratio, the reaction needs to be carried out at very low temperature such as -60 to -70°C.
Thus, unless the reaction is carried out under stringent conditions, bromination of o-xylene results in a mixture of 4-bromo-o-xylene and 3-bromo-o-xylene. When bromo-o-xylenes thus produced are converted into corresponding benzaldehydes, the outcome is a mixture of 3,4-dimethylbenzaldehyde and 2,3-dimethylbenzaldehyde.
As mentioned earlier, in the prior art methods, use of 3,4-isomer of dimethylbenzaldehyde as starting material is mentioned for the production of DMDBS. This leads to assumption by a skilled person that other isomer needs to be separated in order to obtain isomerically pure DMDBS end-product.

Therefore, there is a need for developing a route for preparation of DMDBS which is cost-effective and which obviates the need to separate desired isomer of the intermediate.
As per S.2(l)(ja) of the Patents Act, the definition of "inventive step" includes a feature of an invention that involves economic significance that makes the invention not obvious to a person skilled in the art.
OBJECTS OF INVENTION
Main object of invention is to provide a new route for production of DMDBS which offers economic advantage over prior art.
Another object of invention is to provide a method for production of DMDBS which utilizes cheaper starting material and obviates the need for using isomerically pure intermediate 3,4-dimethylbenzaldehyde.
DETAILED DESCRIPTION OF INVENTION
The inventors of present invention have found that it is possible to prepare DMDBS starting from bromination of o-xylene to produce a mixture of 4-bromo-o-xylene (major product) and 3-bromo-o-xylene, conversion of bromo-o-xylenes into a mixture of corresponding benzaldehydes, and reaction thereof with sorbitol to produce DMDBS, wherein the product of the reaction of only 3,4-isomer of dimethylbenzaldehyde with sorbitol is selectively isolated. This method is more economic compared to conventional methods.

It should be noted that bromination of o-xylene for preparation of bromo-o-xylene results in a mixture of isomers. Hence further reaction to produce corresponding dimethylbenzaldehyde also results in a mixture of isomers. However, in spite of getting mixture of isomers of dimethylbenzaldehyde, as per present invention, there is no need of purification step to obtain isomerically pure 3,4-dimethylbenzaldehyde for preparation of DMDBS. Thus, in addition to providing a cost-effective route, present invention eliminates purification step.
DMDBS is prepared in three steps.
In the first step, bromination of o-xylene is carried out in presence of iodine and solvent whereby a mixture of 4-bromo-o-xylene (major product) and 3-bromo-o-xylene (up to 15%) is obtained. This step per se is not claimed as it is reported in the prior art. Any conventional method may be used for preparation of bromo-o-xylene wherein a mixture of isomers is produced.
It should also be noted that a method for preparation of bromo-o-xylene containing a high ratio of the 4-bromo-o-xylene to the 3-bromo-o-xylene isomer is disclosed in EP 0492594 wherein it is prepared by reacting o-xylene with Br2 in complete darkness, in the presence of a catalyst. However, to achieve said high ratio, the reaction needs to be carried out at very low temperature such as -60 to -70°C. Present invention obviates the need to use 4-bromo-o-xylene with high purity.

In the second step, bromo-o-xylenes produced in step-1 are reacted with magnesium turnings and DMF in presence of tetrahydrofuran as solvent to obtain corresponding benzaldehydes. Third step involves reaction of 3,4-dimethylbenzaldehyde obtained in the second step with sorbitol to produce DMDBS.
EXAMPLE-1
(i) Bromination of o-xylene
17.1 gm o-xylene, 0.1 gm iodine and 20 ml methylenedichloride were charged in the reactor. The mixture was stirred and cooled to -10°C. A mixture of 31 gm of bromine and 20 ml methylenedichloride was added dropwise over 7 hrs. with stirring into the above mixture maintaining the temperature below -5°C. The reaction mass was stirred for 15 min and then it was allowed to attain room temperature and was stirred at room temperature for another 20 min. It was then cooled to 10°C. pH of the reaction mass was brought to 8-9 by adding 162 ml 4% aqueous NaOH solution and it was stirred for another 15 min. The reaction mass was taken in a separating funnel. The lower organic layer was taken out. Aqueous layer was extracted with 15 ml of methylenedichloride. Organic layer and solvent-washings were mixed and were washed with 2x25 ml water. Organic layer was separated and dried over Na2SO4 and filtered. Solvent was removed by distillation at atmospheric pressure to obtain a mixture comprising 4-bromo-o-xylene in 75% yield and 3-bromo-o-xylene in 15% yield.

(ii) Preparation of 3,4-dimethylbenzaldehyde by Grignard reaction:
4.33 gm magnesium turnings, 75 ml tetrahydrofuran (THF) and 0.15 gm iodine were charged into a reactor. The mixture was heated at 57-68°C with stirring. 5.6 gm bromo-o-xylene mixture prepared in accordance with process described in step (i), and 5 ml THF were added dropwise with stirring to initiate the reaction. Then another 23 gm of bromo-o-xylene mixture and 20 ml THF was added dropwise over 5 hrs with stirring, maintaining the temperature 57-68°C. The reaction mass was cooked for 8 hrs to complete the reaction. It was then cooled to -5°C and a mixture of 9.71 gm DMF and 25 ml THF was added in 10 min maintaining the temperature -5 - 0°C. The reaction mass was stirred for 1 hr. It was then cooled to 10°C and 108 ml aqueous HC1 solution (1:3) was added dropwise. Aqueous and organic layers were separated. Aqueous layer was extracted with THF. Organic layer and THF extraction were given washing with 5% NaHC03 solution, filtered and the solvent was removed by distillation under reduced pressure to obtain 20 gm of a mixture of 3,4-dimethylbenzaldehyde and 2,3-dimethylbenzaldehyde in an isomeric ratio of 85:15 respectively.
(iii) Preparation of l,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol
[DMDBS]
14.2 gm D-Sorbitol and 58 ml methanol were taken in the reactor and mixture was stirred. 20 gm Dimethylbenzaldehyde mixture of isomers as obtained in step (ii) above, 3.55 gm ethylene glycol, 1.68

gm p-toluenesulfonic acid and 62 ml cyclohexane were added with stirring. The reaction mass was heated to reflux temperature (55-60°C) for 10 hrs. It was then filtered at 50°C to obtain 26.2 gm of crude DMDBS. It was treated with 70% aqueous methanol followed by 2% sodium bicarbonate solution and was kept for 2 hrs. It was Altered hot and washed with methanol and was dried to obtain DMDBS in 75% yield and 99% purity.

WE CLAIM:
1. A method of manufacturing l,3:2,4-bis(3,4-
dimethylbenzylidene)sorbitol comprising steps of:
(i) bromination of o-xylene to obtain 4-bromo-o-xylene as a major product, wherein 3-bromo-o-xylene is also produced simultaneously; (ii) conversion of 4-bromo-o-xylene and 3-bromo-o-xylene produced in step (i) above into a mixture of corresponding 3,4-dimethylbenzaldehyde and 2,3-dimethylbenzaldehyde respectively; (iii) reacting 3,4-dimethylbenzaldehyde produced in step (ii) above with D-sorbitol to obtain l,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol; wherein the reaction in step (iii) mentioned above is carried out without separating 2,3—dimethylbenzaldehyde from 3,4-dimethylbenzaldehyde .
2. A method as claimed in claim 1, wherein conversion of 4-bromo-o-
xylene and 3-bromo-o-xylene into corresponding 3,4-
dimethylbenzaldehyde and 2,3-dimethylbenzaldehyde respectively is
carried out by Grignard reaction.
3. A method of manufacturing l,3:2,4-bis(3,4-
dimethylbenzylidene)sorbitol as claimed in claim 1, wherein the
reaction of 3,4-dimethylbenzaldehyde with D-sorbitol is carried out in
presence of 2,3-dimethylbenzaldehyde.
4. A method as claimed in claim 1, wherein l,3:2,4-bis(3,4-
dimethylbenzylidene)sorbitol obtained is purified by treatment with

aqueous methanol followed by sodium bicarbonate solution, filtering hot followed by washing with methanol and drying.