FORM 2
THE PATENTS ACT, 1970
(39 of 1970) The Patent Rules, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
"AN IMPROVED PROCESS FOR THE PREPARATION
OF ALDITOL ACETALS"
We, Reliance Industries Limited, of Reliance Technology Group, Reliance Corporate Park, 7B, Ground Floor, Thane - Belapur Road, Ghansoli, Navi Mumbai- 400 701, Maharashtra, India.
The following specification particularly describes the nature of the invention and the manner in which it is performed:

FIELD OF THE INVENTION
The present invention relates to process for the preparation of 4-methylbenzylidene sorbitol (MDBS) and 3,4-dimethylbenzylidene sorbitol (DMDBS). More particularly, the present invention relates to an improved process for the preparation of MDBS and DMDBS by reaction of 4-methylbenzaldehyde and 3,4- dimethylbenzaldehyde with sorbitol in a two solvent system in which the mother liquor obtained after crystallization of the MDBS and DMDBS is recycled back and reused continuously. The present invention also relates to 4-methylbenzylidene sorbitol and 3,4-dimethylbenzylidene sorbitol prepared by said process.
BACKGROUND OF THE INVENTION
4-methylbenzylidene sorbitol (MDBS) and 3,4-dimethyl dibenzylidene sorbitol (DMDBS) from acetal based compositions which are used as a clarifier, gelling agent or nucleating agent in polymer resins. The MDBS and DMDBS based compounds are typically prepared by the condensation reaction of two moles of an aromatic aldehyde with one mole of polyhydric alcohol such as sorbitol.
In the last three decades, many inventors have proposed various processes for producing of 4-methylbenzylidene sorbitol and 3,4-dimethylbenzylidene sorbitol. In 1973, Murai et. al. showed the preparation of DBS by an aqueous solution of sorbitol with benzaldehyde in the presence of a dehydrating catalyst and cyclohexane as a solvent (US Patent 3,721,682). This document teaches the manufacture of benzylidene sorbitols by reacting an aqueous solution of sorbitol with benzaldehyde in the presence of a dehydrating catalyst to produce a benzylidene sorbitol, a method of this invention comprises adding cyclohexane to the reaction system in an amount of 5 to 20 weight parts based on one weight part of the benzadehyde, heating with stirring the reaction system to effect the reaction sorbitol and benzaldehyde while boiling an azeotropic mixture of cyclohexane and water, said azeotropic mixture being condensed and separated to remove the water from the reaction system and recycle the cyclohexane to the system, and recovering the resultant benzylidene sorbitol thus produced.
Uchiyama (US Patent 4,267,110) teaches a process of preparing dibenzylidenesorbitol by dehydrocondensation of 1 mol of sorbitol with 2 mols of benzaldehyde in the presence of an acid catalyst, the improvement in which the reaction is carried out in two stages, the first-stage reaction comprising reacting the reactants with heating at a temperature of 50° to 70°C„ the first-stage reaction being shifted to the second-stage reaction by adding water and

additional amount of an acid when the conversion of sorbitol to dibenzylidenesorbitol reaches 10 to 40%, and the second-stage reaction comprising of reacting the mixture in the suspended state at ordinary temperature in 2.5 or more parts by weight, per part by weight of sorbitol, of an aqueous reaction medium and the resulting dibenzylidenesorbitol is obtained as an aqueous suspension. Although, the process is stated to be a two stage process, in effect it is a three stage process.
Similar work has done by Machell (US Patent 4,562,265). This patent document provides a method for producing di-acetal of sorbitol and an aromatic aldehyde wherein an aqueous solution containing a catalytic amount of a mineral acid and sorbitol is formed. Thereafter, an effective amount of an aromatic aldehyde such as benzaldehyde is incrementally admixed into the homogeneous aqueous admixture containing the sorbitol at a rate sufficient to allow a substantially spontaneous reaction to occur between the D-sorbitol and aromatic aldehyde; thus, forming an aqueous slurry containing crude di-acetal, e.g., dibenzylidene sorbitol. The amount of aromatic aldehyde employed is that amount sufficient to provide a molar ratio of D-sorbitol to aromatic aldehyde of from about 1:0.75 to about 1:1.75. Thereafter, the aqueous slurry is neutralized, and crude di-acetal is removed from the liquid phase and washed with water to remove mono-acetal, and the dried di-acetal may be further purified by washing with a relatively non-polar solvent.
Kobayashi et. al. (US Patent 4,902,807) discloses a process for batchwise production of a l,3:2,4-dibezylidene-sorbital or xylitol compound comprising subjecting a sorbitol or xylitol and a benzaldehyde compound to a condensation reaction in a reactor by feeding a homogeneous solution or suspension formed from sorbitol or xylitol, an aldehyde compound, a lower alcohol, and if necessary an acid catalyst to the reactor, together with a hydrophobic organic solvent, continuously or intermittently while adjusting the rate of feeding of said homogeneous solution or suspension such that sorbitol or xylitol and the benzaldehyde compound are fed to the reaction system in a total amount per hour of about 0.1 to about 2 parts by weight per part by weight of the l,3:2,4-dibenzylidene compound as found in the reaction system.
WO1992003439 discloses a method of producing acetal compounds by condensing at least one aromatic aldehyde such as unsubstituted or substituted benzaldehyde with a penta- or hexahydric alcohol such as sorbitol in a hydrophobic organic solvent in the presence of a lower alcohol and an acid catalyst, wherein the lower alcohol and water are

discharged from the reaction system at least thrice. JP 56108791 discloses the preparation of the compound useful as an additive for various applications, in high yield and selectivity, by reacting a lower alcohol continuously with a preliminary reaction product of sorbitol and benzaldehyde compound in the presence of a catalyst. The homogeneous liquid obtained by the preliminary reaction of sorbitol, a benzaldehyde compound and a lower alcohol in a preliminary reactor is charged continuously into the reactor together with a hydrocarbon reaction medium (e.g. cyclohexane, alkyl-substituted cyclohexane, etc.) and reacted to obtain the titled compound. The reaction temperature is preferable about 65-140°C. The vapor generated by heating is condensed with a cooler and separated into the reaction medium, the lower alcohol and water in a decanter.
Gardlik el. al. (US Patent 5,106,999) discloses a process for preparing dibenzylidene-D-sorbitol compounds, particularly meta substituted halogenated derivatives, by reacting D-sorbitol with an aromatic aldehyde, particularly those substituted at the 3 position with a halogen, in the presence of an acid catalyst, and C1-C3 aliphatic alcohol reaction medium. The resulting product is purified by subsequent washings with a C1-C3 aliphatic alcohol. Alkyl group substitution on bis-dibenzylidene sorbitols was studied by John W. R. (US Patent 5,049,605). This patent disclosed bis (3,4-dialkylbenzylidene) sorbitol acetals and compositions containing same and relates to plastic additives which are useful as nucleating agents and which are especially useful for improving the optical properties of polymeric materials. These bis-dialkylbenzylidene sorbitol acetals and polymer compositions thereof are useful as materials for food or cosmetic containers and packaging because they do not impart an objectionable taste or odor to the packaged materials. Thus acetals which contain lower alkyl groups in the 3 and 4 positions on benzylidene ring provide substantially improved odour properties.
In 2002, a surfactant route has been employed for the preparation of symmetrical or unsymmetrically substituted dibenzylidenesorbitols wherein DMB is reacted with sorbitol in the presence of a surfactant in aqueous mineral acid (US Patent 6,500,964). Lever el. al. (US Patent 6,500,964) discloses a method of producing high yield alditolacetals with mineral acids and surfactants. A process for preparing alditol acetals, such a dibenzylidene sorbitols, monobenzylidene sorbitols, and the like, through the reaction of unsubstituted or substituted benzaldehydes with alditols (such as sorbitol, xylitol, and ribitol) in the presence of a mineral acid and at least one surfactant having at least one pendant group of 6 carbon

chains in length is disclosed. Such a reaction provides a cost-effective, relatively safe procedure that provides excellent high yields of alditol acetal product. Furthermore, such a specific reaction is also the best known procedure for the production of certain compounds which can be easily separated from other formed isomers. Additionally, such a procedure facilitates the production of certain asymmetric alditol acetal compounds and a composition is acceptable yields as well. Such alditol acetals are useful as nucleating and clarifying agents for polyolefin formulation and articles.
A solvent route has also been employed for the preparation of DBS. Kawai et. al. (US Patent 4,314,039) discloses a polypropylene composition containing a 1.3,2.4-de(alkylbenzylidene) sorbitol having improved transparency and being substantially free from a bleeding phenomenon comprising 100 parts by weight of polypropylene and 0.005 to 8 parts by weight of a 1.3,2.4-di(alkylbenzylidene) sorbitol with each alkyl group having 2 to 18 carbon atoms.
Murai et. al. (US Patent 4,429,140) discloses a process for preparing dibenzylidene sorbitols or dibenzylidene xylitols by reacting sorbitols or xylitol with a substituted or unsubstituted benzaldehyde or alkyl acetal derivative thereof in the presence of an acid catalyst, a hydrophobic organic solvent and a water-soluble organic polar solvent, the process being characterized by using the hydrophobic organic solvent in an amount sufficient to permit the resulting dibenzylidene xylitols to separate out as crystals and capable of maintaining the reaction system in the form of a gel to solid phase and by conducting the reaction with forced agitation.
Scrivens et. al. (US Patent 5,731,474) discloses a method of making acetals is provided by condensing an aromatic aldehyde and a polyhydric alcohol having five or more hydroxyl groups in the presence of an acid catalyst, a hydrophobic organic liquid medium and a processing agent selected from dihydric, trihydric, and tetrahydric alcohols; Jones et. al. (US Patent 6,599,964) teaches symmetric substituted benzaldehyde alditol derivatives and compositions and articles containing same. This patent relates to certain symmetric DBS compounds comprising specific pendant groups, such as C3-C6alkyl, C1-C6 alkoxy, phenyl, and methylenedioxy (as the combination of two available sites on the pertinent ring system), as well as wherein the individual benzylidene ring systems may be Indan or tetralin. Because of the required symmetrical configuration, the pendant groups on each ring system of the dibenzylidene sorbitol compound must be located at the same positions. Such

compounds may be added to or incorporated within polymer compositions which may then be utilized within, as merely examples, food or cosmetic containers and packaging. OBJECTS OF THE INVENTION
It is an important object of the present invention to provide an improved process for the preparation of 4-methylbenzylidene sorbitol (MDBS) and 3,4-dimethylbenzylidene sorbitol (DMDBS) by the reaction of 4-methylbenzaldehyde and 3,4-dimethylbenzaldehyde with sorbitol respectively.
Another object of the present invention is to provide a process for the preparation of MDBS and DMDBS with complete recycling of mother liquor comprising mono-intermediates of MDBS and DMDBS and un-reacted raw material, leading to minimization of consumption of aldehyde, solvents, and catalyst.
Still another object of the present invention is to provide 4-methylbenzylidene sorbitol and 3,4-dimethylbenzylidene sorbitol with 99.5% purity. SUMMARY OF THE INVENTION
The above and other objects of the present invention are achieved by providing an improved process for the preparation of 4- methylbenzylidene sorbitol (MDBS) and 3,4-dimethylbenzylidene sorbitol (DMDBS).
The present invention discloses a process comprising the steps of adding 4-methylbenzaldehyde to a first solvent in the presence of a catalyst; stirring the reaction mixture at a suitable temperature; adding solution of sorbitol dissolved in a second solvent; stirring and heating under reflux the reaction mixture for a certain period; removing the azeotrope and treating the reaction mixture with fresh solvent; and filtering the reaction mixture to obtain mother liquor; recycling the mother liquor; neutralizing the product with a base with stirring at a suitable temperature; washing the product and filtering and drying the product.
The present invention discloses a process for the preparation of 4-methylbenzylidene sorbitol (MDBS) comprising the steps of reacting 4-methylbenzaldehyde with sorbitol; and filtering the reaction mixture to obtain mother liquor; recycling the mother liquor; neutralizing the product with a base with stirring at a suitable temperature; and optionally, washing the product and filtering and drying the product.
The present invention also discloses a process comprising the steps of reacting 3,4-dimethylbenzaldehyde in a first solvent in the presence of catalyst; stirring the reaction

mixture at a suitable temperature; adding solution of sorbitol dissolved in a second solvent; stirring and heating under reflux the reaction mixture for a certain period; removing the azeotrope and treating the reaction mixture with fresh solvent; and filtering the reaction mixture to obtain mother liquor; recycling the mother liquor; neutralizing the product with a base with stirring at a suitable temperature; washing the product and filtering and drying the product.
The present invention discloses a process for the preparation of 3,4-dimethylbenzylidene sorbitol (DMDBS) comprising the steps of reacting 3,4-dimethylbenzaldehyde with sorbitol; and filtering the reaction mixture to obtain mother liquor; recycling the mother liquor; neutralizing the product with a base with stirring at a suitable temperature; and optionally, washing the product and filtering and drying the product.
In a preferred embodiment, the present invention discloses a process for the preparation of 4-methylbenzylidene sorbitol (MDBS) comprising the steps of mixing 4-methylbenzaldehyde in a first solvent; in the presence of a catalyst; the mixture is stirred at a suitable temperature; adding solution of sorbitol dissolved in a second solvent; stirring and heating under reflux the reaction mixture for a certain period; removing the azeotrope and treating the reaction mixture with fresh solvent; and filtering the reaction mixture to obtain mother liquor; recycling the mother liquor, neutralizing the product with a base with stirring at a suitable temperature; washing the product and filtering and drying the product.
In a preferred embodiment, the present invention discloses a process for the preparation of 3,4-dimethylbenzylidene sorbitol (DMDBS) comprising the steps of mixing 3,4-dimethylbenzaldehyde in organic solvents in the presence of a catalyst; the mixture is stirred at a suitable temperature; adding solution of sorbitol dissolved in methanol; stirring and heating under reflux the reaction mixture for a certain period; removing the azeotrope and treating the reaction mixture with fresh solvent; and filtering the reaction mixture to obtain mother liquor; recycling the mother liquor, neutralizing the product with a base with stirring at a suitable temperature; washing the product and filtering and drying the product.
Preferably, said sorbitol is selected from 100% sorbitol or 70% aqueous solution of sorbitol.
Preferably, the first organic solvent of reaction is selected from group consisting of hydrophobic organic media such as benzene, toluene, xylene, cyclohexane and the like and

the second solvent is selected from group consisting of lower alcohols such as isopropyl alcohol, methanol and the like
Preferably, said catalyst is selected from group consisting of sulphuric acid, phosphoric acid, hydrochloric acid, alkyl benzene sulphonic acid, p-toluene sulphonic acid, m-toluene sulphonic acid, oxalic acid.
Preferably, said stirring is performed at temperature of 62 to 67 °C , preferably, 65°C and more preferably, said stirring is performed at 320-350 rpm with heating under reflux for five hours.
Preferably, said azeotrope is removed.
Preferably, said mother liquor comprises of mono-intermediates of MDBS and DMDBS, un-used reactants and catalysts.
Preferably, said recycling of mother liquor is replenished with all the raw materials
for the next batch.
. Preferably, said product neutralizing is performed by a base selected from the group
consisting of alkali or alkaline metal, hydroxides or salts like potassium hydroxide, sodium hydroxide, sodium carbonate.
Preferably, said product is first washed with water and then with methanol.
Preferably, said product is dried overnight in the vacuum oven at 100°C.
In another preferred embodiment, the present invention provides an improved process for the preparation of 4-methylbenzylidene sorbitol (MDBS) comprising the steps of mixing 4-methylbenzaldehyde with cyclohexane in the presence of p-toluene sulphonic acid; stirring the reaction mixture at temperature of 62 to 67 °C, preferably, 65°C; adding solution of sorbitol dissolved in methanol; stirring at 320-350 rpm with heating under reflux for five hours of the reaction mixture; removing the azeotrope and treating the reaction mixture with fresh solvent; and filtering the reaction mixture at reaction mixture temperature to obtain mother liquor comprising of un-used reactants, mono intermediate of MDBS and catalyst; recycling the replenished mother liquor for the next batch; neutralizing the product with sodium hydroxide with stirring at 60°C; washing the product with water and methanol; filtering and drying the product overnight in the vacuum oven at 100°C.
Preferably, the yield of MDBS is 90% and has a purity of 99.5%.
In another preferred embodiment, the present invention provides an improved process for the preparation of 3,4-dimethylbenzylidene sorbitol (DMDBS) comprising the

steps of mixing 3,4-dimethylbenzaldehyde with cyclohexane in the presence of p-toluene sulphonic acid; stirring the reaction mixture at temperature of 62 to 67 °C , preferably, 65°C; adding solution of sorbitol dissolved in methanol; stirring at 320-350 rpm with heating under reflux for five hours of the reaction mixture; removing the azeotrope and treating the reaction mixture with fresh solvent; and filtering the reaction mixture at reaction mixture temperature to obtain mother liquor comprising of un-used reactants, mono intermediate of DMDBS and catalyst; recycling the replenished mother liquor for the next batch; neutralizing the product with sodium hydroxide with stirring at 60°C; washing the product with water and methanol; filtering and drying the product overnight in the vacuum oven at 100°C.
Preferably, the yield of DMDBS is 90% and has a purity of 99.5%.
Preferably, the amount catalyst recycled with the mother liquor is in the range of 1 to 30 parts.
In another embodiment of the present invention, an environment friendly process with minimization of waste generation is disclosed".
In yet another embodiment of the present invention, 4-rnethylbenzylidine sorbitol (MDBS) and 3,4-dimethylbenzylidine sorbitol (DMDBS) prepared by said process is disclosed. DETAILED DESCRIPTION OF THE INVENTION
The present invention discloses the preparation of 4-methylbenzylidene sorbitol (MDBS) and 3,4-dimethylbenzylidene sorbitol (DMDBS) by the conversion of 4-methylbenzaldehyde and 3,4- dimethylbenzaldehyde respectively utilizing sorbitol in a two solvent system. The present invention further disclose processes for the preparation of MDBS and DMDBS where the mother liquor (from a batch production of MDBS and DMDBS) is reused/ recycled for the production of next batch MDBS and DMDBS and so on. The said recycled/ reusable mother liquor in the present invention is replenished with all the raw materials for the next batch. According to the prior art in place for existing processes, it has been ascertained that in a single pass operation regarding the production of MDBS and DMDBS from 4-methylbenzaldehyde and 3,4- dimethylbenzaldehyde respectively utilizing sorbitol, product is neutralized along with reaction mixture with caustic and obtained mother liquor wherein the concentration of the mono product and un-reacted 0-12 wt% aldehyde and catalyst is lost. But the present invention circumvent the losses of reactants andcatalyst and reduce the specific consumption of this raw-material including solvents.

It has now been found that mother liquor or part of the mother liquor can be recycled back to the MDBS and DMDBS production vessel. The recycled mother liquor is replenished with all the raw materials. Process does not suffer yield and quality of the final product provided said mother liquor is replenished with all raw materials. The amount of aldehyde fed to the process vessel is slightly more than to be reacted theoretically. On a molar basis, in the range of 0 to 60% excess 4-methylbenzaldehyde and 3,4- dimethylbenzaldehyde are used in the said process. MDBS and DMDBS are produced from 4- methylbenzaldehyde and 3,4-dimethylbenzaldehyde respectively with sorbitol and excess respective aldehydes as is conventional in the prior art and the desired products, the MDBS and DMDBS crystals separated from the mother liquor and the mother liquor is then recycled back to use as a starting material for the production of MDBS and DMDBS. It is noted that 50-95% of the mother liquor in both the processes contains 1-60% mono intermediate product in dissolved form and 1-30 parts of catalyst can be recycled back. Conditions utilized with regard to temperature and atmospheric pressure is those conventional in the prior art and include temperatures of from 0-80 DEG C for periods of time of 1-8 hours.
The present invention is based on an unexpected finding that use of the two solvent syatem and the recycling step which is an important characteristic feature of the present invention results in advantages, hitherto not thought possible. The prior art did not attach too much importance to the kinetics of the reaction. While, it is known that the reaction of 4-methylbenzaldehyde and 3,4- dimethylbenzaldehyde respectively with sorbitol takes place in two stages, not much attention was paid to the kinetics thereof. The reaction takes place in two statges, i.e., formation of momo-acetal followed by di-acetal compound. Kinetics of mono-actal and di-acetal are totally different. The moment the formation of di-acetal starts, the reaction changes from kinetic control regime to mass transfer regime. This has a huge implication on inter alia, total reaction time. By having higher stoichiometric ratio of aldehyde to sorbitol initially, the present invention has achieved further reduction in reaction time for mono-acetal intermediate formation and the excess is recycled. The prior art does not teach or even suggest recycling of unreacted aldehyde and mono-actetal intermediates.
The process of the present invention uses range of 1:2 to 1:3 mole ratios of sorbitol and aldehyde, respectively and gives two units of the product, based on 100% conversion. This clearly shows that any re-usage of aldehyde will keep the cost low, as major cost is contributed

by the aldehyde in the process. Essentially, in every recycle, 10% aldehyde and its cost are saved in addition to the excess aldehyde, if yields are 90%. Recycling of mother liquor has implications on total reaction time in view of the formation of mono intermediate initially which will be in dissolved state in mother liquor.
Stoichiometric equivalent aldehyde in the process of the present invention that is available in the mother liquor, converts into mono-acetal intermediate and free aldehyde will be in activated stage in the mother liquor in the presence of catalyst and will remain available for next reaction. At 65°C, mono-acetal product and active aldehyde are in soluble form and available for further use without loss. Recycling of mother liquor with catalyst and mono intermediates reduces the neutralization and washing load on the solid product in the process.
The present invention is illustrated and supported by the following examples. These are merely representative examples and optimization details and are not intended to restrict the scope of the present invention in any way. EXAMPLE-1
A 500 ml four necked round bottom flask equipped with a Dean-stark trap, condenser, thermometer, and a mechanical stirrer is charged with 130 ml of cyclohexane, 0.5gms of catalyst (p-toluene sulphonic acid) and 13.18.ml of 4 - methyldibenzylidene (2 equivalent molar based on sorbitol).
To the well stirred hot reaction mixture (65 C), a solution of 10 gms of sorbitol dissolved in 60 ml methanol is added over a period of 30 minutes. The reaction is stirred and heated under reflux for six hours. The reaction mixture is stirred at 350 rpm and the torque monitored constantly. The azeotrope is removed continuously and reaction vessel is replenished with fresh solvent. After six hours, reaction mixture is cooled, neutralized with sodium hydroxide (1.0 gms dissolved in 2 ml water). The product is filtered under vacuum to remove as much residual methanol, 4-Methyl Benzaldehyde and residual catalyst as
possible. The product is washed with hot water (65 C) (2 x 200 ml) and filtered. The product is finally washed with methanol (500 ml), filtered and dried over night in a vacuum oven at
100°C. MDBS is obtained with purity of 99.5% and 90% - 95% yield with melting point of in
the range of 260 C-265 C (DSC measurements). EXAMPLE-2
The procedure of Example 1 is followed, except after five hours the reaction mixture

having excess 4-methylbenzaldehyde to sorbitol molar ratio in the range of 2-3 is cooled and filtered under vacuum to separate the mother liquor containing mono intermediate of MDBS, unreacted aldehyde, catalyst along with solvents. The product is neutralized with aqueous solution of sodium hydroxide and the product is washed with hot water (65°C). The product is finally washed with methanol (IX 50 ml and IX 450 ml - 500 ml), filtered and
dried over night in a vacuum oven at 100°C. MDBS is obtained with purity of 99.5% and 90%
- 95% yield with the same melting point range as in Example 1.
EXAMPLE-3
The procedure of Example 2 is followed except, reaction is carried out with the mother
liquor (filtrate obtained from example 2) replenished with the reactants and solvents.
EXAMPLE-4
The procedure of Example 2 is followed except, reaction is carried out with the mother liquor (filtrate obtained from example 3) replenished with the reactants and solvents. EXAMPLE-5
The procedure of Example 2 is followed except, after five hours the reaction mixture having excess 4-methylbenzaldehyde to sorbitol molar ratio in the range of 2-3 is filtered under vacuum to separate the mother liquor at reaction temperature containing mono intermediate of MDBS, unreacted aldehyde, catalyst along with solvents. The product is neutralized with aqueous solution of sodium hydroxide and the product is washed with hot water (65°C). The product is finally washed with methanol (350 ml), filtered and dried over
night in a vacuum oven at 100°C MDBS is obtained with purity of 99.5% and 90% - 95% yield with the same melting point range as in Example 1. Obtained mother liquor is replenished with the reactants and solvents for further reactions. EXAMPLE - 6
The procedure of Example 5 is followed except/ reaction is carried out with the mother liquor (filtrate obtained from example 5) replenished with the reactants and solvents. EXAMPLE-7
The procedure of Example 5 is followed except, reaction is carried out with the mother liquor (filtrate obtained from example 6) replenished with the reactants and solvents. EXAMPLE - 8
Comparative example for recycling of mother liquor obtained from example 2

The procedure for synthesis of MDBS as per the example 1, needs fresh solvents and reactants in every batch. The used solvents in every batch are subjected to azeotropic distillation to recover the solvents and reused.
The procedure of example 2 is followed with aldehyde to sorbitol ratio of 2:1. 90% yield was obtained. The reactants are cooled, filtered and recycled for the subsequent batch. The recycled reactant mixture contained primarily 92% cyclohexane, 90% catalyst and is used directly for the subsequent batch. The solid product is neutralized aqueous solution of sodium hydroxide and washed with hot water at 65°C. The solid product is washed with 50 ml methanol initially and 10% of monointermediate is extracted. In the second step 450 ml of methanol is used to wash the solid product and 99.5% product purity was obtained.
The procedure of example 2 is followed in the next batch by replenishing the reactor contents; the mother is replenished with 90% of sorbitol and aldehyde, 100% methanol obtained from previous batch washing steps containing 10% of monointermedaite and 8% of cyclohexane and 10% of the catalyst. EXAMPLE-9
Comparative example for recycling of mother liquor obtained from example 5
The procedure for synthesis of MDBS as per the example 1, needs fresh solvents and reactants in every batch. The used solvents in every batch are subjected to azeotropic distillation to recover the solvents and reused.
The procedure of example 5 is followed with aldehyde to sorbitol ratio of 2:1. 90% yield was obtained. The reactants are filtered at reaction temperature and recycled for the subsequent batch. The recycled reactant mixture contained 10% of sorbitol, 10% of 4-methyldibenzaldehyde in the form of monointermediate, 92% cyclohexane, 90% catalyst and is used directly for the subsequent batch. The solid product is neutralized with aqueous solution of sodium hydroxide and washed with hot water at 65°C. The product is washed with 350 ml of methanol and 99.5% product purity was obtained.
The procedure of example 5 is followed in the next batch by replenishing the reactor contents; the mother is replenished with 90% of sorbitol and aldehyde, 100% methanol obtained from previous batch washing steps, 8% of cyclohexane and 10% of the catalyst.
It is thus evident that the utility of the inventive recycling method and its ability to reproduce the product quality shows the unexpected benefits available from such procedure. EXAMPLE-10

The procedure of Example 1 is followed except, 15.5 ml of 3,4-dimethyldibenzyIidene (2.1 equivalent molar based on sorbitol) is used in lieu of 4-methyldibenzylidene. DMDBS is obtained with purity of 99.5% and 85% - 90% yield with melting point of in the range of
272°C++-275°C (DSC measurements). EXAMPLE-11
The procedure of Example 10 is followed except, after five hours the reaction mixture having excess 3,4-dimethylbenzaldehyde to sorbitol molar ratio in the range of 2-3 is cooled and filtered under vacuum to separate the mother liquor containing mono intermediate of DMBDS, unreacted aldehyde, catalyst along with solvents. The product is neutralized with aqueous solution of sodium hydroxide and is washed with hot water (65°C). The product is finally washed with methanol (1X50 ml and 1X450 ml - 500 ml),
filtered and dried over night in a vacuum oven at 100 C. DMDBS is obtained with purity of 99.5% and 85% - 90% yield with the same melting point range as in Example 10 . EXAMPLE-12
The procedure of Example 11 is followed except, reaction is carried out with the mother liquor (filtrate obtained from example 11) replenished with the reactants and solvents. EXAMPLE-13
The procedure of Example 11 is followed except, reaction is carried out with the mother liquor (filtrate obtained from example 12 ) replenished with the reactants and solvents. EXAMPLE-14
The procedure of Example 11 is followed except, after five hours the reaction mixture having excess 3,4-dimethylbenzaldehyde to sorbitol molar ratio in the range of 2-3 is filtered under vacuum to separate the mother liquor at reaction temperature containing mono intermediate of DMDBS, unreacted aldehyde, catalyst along with solvents. The product is neutralized with aqueous solution of sodium hydroxide and is washed with hot water (65°C). The product is finally washed with methanol (350 ml), filtered and dried over
night in a vacuum oven at 100°C. DMDBS is obtained with purity of 99.5% and 85% - 90% yield with the same melting point range as in Example 8. Obtained mother liquor is replenished with the reactants and solvents for further reactions. EXAMPLE-15

The procedure of Example 14 is followed except, reaction is carried out with the mother liquor (filtrate obtained from example 14 ) replenished with the reactants and solvents. EXAMPLE-16
The procedure of Example 14 is followed except, reaction is carried out with the mother liquor (filtrate obtained from example 15 ) replenished with the reactants and solvents. EXAMPLE -17
Comparative example for recycling of mother liquor obtained from example 11
The procedure for synthesis of DMDBS as per the example 10, needs fresh solvents and reactants in every batch. The used solvents in every batch are subjected to azeotropic distillation to recover the solvents and reused.
The procedure of example 11 is followed with aldehyde to sorbitol ratio of 2.1:1. 85% yield was obtained. The reactants are cooled, filtered and recycled for the subsequent batch. The recycled reactant mixture contained primarily 92% cyclohexane, 90% catalyst and is used directly for the subsequent batch. The solid product is neutralized with aqueous solution of sodium hydroxide and washed with hot water at 65°C. The solid product is washed with 50 ml methanol initially and 15% of monointermediate and 5% of free aldehyde is extracted. In the second step 450 ml of methanol is used to wash the solid product and 99.5% product purity was obtained.
The procedure of example 11 is followed in the next batch by replenishing the reactor contents; the mother is replenished with 85% of sorbitol and aldehyde, 100% methanol obtained from previous batch washing steps containing 15% monointermedaite, 5% free aldehyde, 8% cyclohexane and 10% catalyst. EXAMPLE-18
Comparative example for recycling of mother liquor obtained from example 14
The procedure for synthesis of DMDBS as per the example 10, needs fresh solvents and reactants in every batch. The used solvents in every batch are subjected to azeotropic distillation to recover the solvents and reused.
The procedure of example 14 is followed with aldehyde to sorbitol ratio of 2.1:1. 85% yield was obtained. The reactants are filtered at reaction temperature and recycled for the subsequent batch. The recycled reactant mixture contained 15% sorbitol, 15% 3,4-

dimethyldibenzaldehyde in the form of monointermediate, 5% free aldehyde in activated stage, 92% cyclohexane, 90% catalyst and is used directly for the subsequent batch. The solid product is neutralized aqueous solution of sodium hydroxide and washed with hot water at 65°C. The product is washed with 350 ml of methanol and 99.5% product purity was obtained.
The procedure of example 14 is followed in the next batch by replenishing the reactor contents; the mother is replenished with 85% of sorbitol and aldehyde, 100% methanol obtained from previous batch washing steps, 8% cyclohexane and 10% catalyst.
It is thus evident that the utility of the inventive recycling method and its ability to reproduce the product quality shows the unexpected benefits available from such procedure.
The above examples clearly illustrate that operation within the parameters of this invention resulted in the synthesis of MDBS and DMDBS which have given comparable clarity in polypropylene.

We claim:
1. An improved process for the preparation of 4-methylbenzylidenesorbitol (MDBS) and 3,4-dimethylbenzylidenesorbitol (DMDBS) comprising the steps of reacting 4-methylbenzaldehyde and 3,4-dimethylbenzaldehyde respectively with sorbitol and filtering the reaction mixture to obtain mother liquor; recycling the mother liquor; neutralizing the product with a base with stirring at a suitable temperature; and optionally, washing the product and filtering and drying the product.
2. A process as claimed in claim 1, wherein said 4-methylbenzaldehyde is mixed a first solvent in the presence of a catalyst; the mixture is stirred at a suitable temperature; a solution of sorbitol dissolved in a second solvent is added to said mixture; said reaction mixture is stirred and heated under reflux; the azeotrope is removed and the reaction mixture is treated with fresh solvent followed by filtration to obtain mother liquor; the mother liquor is recycled to the process; the reaction product is neutralized and stirred; to obtain said MDBS.
3. A process as claimed in claim 1, wherein said 3,4-dimethylbenzaldehyde is mixed with a first organic solvent in the presence of a catalyst; the mixture is stirred at a suitable temperature; a solution of sorbitol dissolved in methanol is added to said mixture; said reaction mixture is stirred and heated under reflux; the azeotrope is removed and the reaction mixture is treated with fresh solvent followed by filtration to obtain mother liquor; the mother liquor is recycled to the process; the reaction product is neutralized and stirred; to obtain said DMDBS.
4. A process as claimed in any preceding claim wherein the aldehyde is employed in stoichiometric excess.
5. A process as claimed in claim 4 wherein the mole ratio of said sorbitol to said aldehyde is in the range of 1:2 to 1: 3.
6. The process as claimed in claims 1 to 5, wherein said first organic solvent of reaction is selected from group consisting of hydrophobic organic media such as benzene, toluene, xylene and cyclohexane and the second solvent is selected from group consisting of lower alcohols such as isopropyl alcohol and methanol.
7. The process as claimed in claims 1 to 5, wherein said catalyst is selected from group consisting of sulphuric acid, phosphoric acid, hydrochloric acid, alkyl benzene sulphonic acid, p-toluene sulphonic acid, m-toluene sulphonic acid, oxalic acid.

8. The process as claimed in any of the claims 2 to 7, wherein said reaction mixture stirring is performed at temperature of 60-80°C.
9. The process as claimed in claim 8, wherein said stirring is performed at 320- 350 rpm with heating under reflux during the reaction time for five hours.
10. The process as claimed in any preceding claim wherein said azeotrope is removed during the reaction time.
11. The process as claimed in any of the preceding claim, wherein said mother liquor comprises of mono-intermediates of MDBS, DMDBS, un-used reactants and catalysts.
12. The process as claimed in any one of the claims 2 to 11, wherein said recycling of mother liquor is replenished with the all the raw materials for the next batch.
13. The process as claimed in any one of the claims 2 to 11, wherein said neutralizing is performed by a base selected from the group consisting of alkali or alkaline metal, hydroxides or salts like potassium hydroxide, sodium hydroxide, sodium carbonate.
14. The process as claimed in any of the preceding claim, wherein said product is first washed with water and then with methanol.
15. The process as claimed in any of the preceding claim, wherein said product is dried overnight in the vacuum oven at 100°C.
16. An improved process for the preparation of 4-methylbenzylidene sorbitol (MDBS) comprising the steps of mixing 4-methylbenzaldehyde with cyclohexane in the presence of p-toluene sulphonic acid; stirring the reaction mixture at temperature of 62 - 67°C; adding solution of sorbitol dissolved in methanol; stirring at 250-350 rpm with heating under reflux for five hours of the reaction mixture; removing the azeotrope and treating the reaction mixture with fresh solvent; and filtering the reaction mixture at a temperature in the range of 62-67, preferably 65°C to obtain mother liquor comprising of un-used reactants and catalyst; recycling the mother liquor replenished with all the raw materials for the next batch; neutralizing the product with a sodium hydroxide with stirring at 60°C; washing the product with water and methanol; filtering and drying the product overnight in the vacuum oven at 100°C.
17. An improved process for the preparation of 3,4-dimethylbenzylidene sorbitol (DMDBS) comprising the steps of mixing 3,4-dimethylbenzaldehyde with

cyclohexane in the presence of p-toluene sulphonic acid; stirring the reaction mixture at temperature of 65°C; adding solution of sorbitol dissolved in methanol; stirring at 250- 350 rpm with heating under reflux for five hours of the reaction mixture; removing the azeotrope and treating the reaction mixture with fresh solvent; and filtering the reaction mixture temperature of 65°C to obtain mother liquor comprising of un-used reactants and catalyst; recycling the mother liquor replenished with all the raw materials for the next batch; neutralizing the product with a sodium hydroxide with stirring at 60°C; washing the product with water and methanol; filtering and drying the product overnight in the vacuum oven at 100°C.
18. The process claimed in any of the preceding claim, wherein the amount catalyst recycled with the mother liquor is in the range of 1 to 30 parts.
19. The process as claimed in any of the preceding claim, wherein the yields of MDBS and DMDBS are 90%.
20. 4-methylbenzylidine sorbitol (MDBS) prepared by a process as claimed in preceding claims.
21. 3,4-dimethylbenzylidine sorbitol (DMDBS) prepared by a process as claimed in preceding claims.
22. The MDBS as claimed in claim 18 has the melting point in the range of 260°C-265°C.
23. The DMDBS as claimed in claim 19 has the melting point in the range of 272°C-275°C.
24. The MDBS as claimed in claims 18 or 20 has a purity of 99.5%.
25. The DMDBS as claimed in claims 19 or 21 has a purity of 99.5%.