Title of Invention

"A PROCESS FOR PREPARATION OF POLYTHIOL"

Abstract This invention relates to a process for the preparation of polythiol which may advantageously be employed for producing plastic lense having a high refractive index comprising in the steps of preparing diol by heating at 20° to 35°C mixture of 1:1 to 1:1.5 of mercaptoethanol and epichlorohydrin in the presence of a catalyst, adding drop wise hydrated sodium sulphide to said diol so that the temperature is maintained at 30 to 45°C, preparing a salt of isothiouronium by reacting the tetrol with hydrochloric acid and thiurea, reacting the salt of step (c) with ammonia in solution to obtain the polythiol.
Full Text FIELD OF INVENTION
This invention relates to a process for the preparation of polythiol. The polythiol made by the process of the present invention may advantageously be employed for producing ophthalmic lenses.
BACKGROUND OF INVENTION
Plastic ophthalmic lenses are classified by their refractive index, and the refractive index defines the power of the lense. Thus, if a lense having a low refractive index is used for high power, the lense would need to be of substantial thickness, which adds discomfort to a wearer due to the weight of such a lense. In such an instance, it is preferable to use a lense having a high refractive index.
Hitherto, lenses having a high refractive index was normally made from a polythiol. The process consisted in first preparing a diol from mercaptoethanol and epichlorohydrin in the presence of triethylamine as a catalyst. The ratio of the catalyst and active ingredients was 1:1 and the reaction is carried out at a temperature of above 40°C.
The diol is then reacted with anhydrous sodium sulphide to give a tetrol. The tetrol is reacted with thiourea and concentrated hydrochloric acid for a period of 9 hours at 120°C to produce a salt of isothiouronium. Such a salt is reacted with ammonia in toluene as a solvent to produce polythiol.
Several disadvantages are associated with such a known process. One such distinct disadvantage is that of low yields. Yet another disadvantage is that the yield, even though low, is obtained at high temperatures. A further disadvantage is the time of synthesis.
OBJECTS OF THE INVENTION
An object of this invention is to propose a process for the preparation of polythiol which may advantageously be used for the manufacture of opthalmic lenses.
Another object of this invention is to propose a process for the preparation of polythiol which may advantageously be used for the manufacture of opthalmic lenses, and which is heat resistant.
Still another object of this invention is to propose a process for the preparation of polythiol which may advantageously be used for the manufacture of opthalmic lenses having good optical properties.
Yet another object of this invention is to propose a process for the preparation of polythiol which may advantageously be used for the manufacture of opthalmic lenses, which has a yield of 90% and above.
A further object of this invention is to propose a process for the preparation of polythiol which may advantageously be used for the manufacture of opthalmic lenses, which has yields at lower operating temperatures.
A still object of this invention is to propose a process for the preparation of polythiol which may advantageously be used for the manufacture of opthalmic lenses, and wherein the time of synthesis is shorter than that of the known art.
DESCRIPTION OF INVENTION
According to this invention there is provided a process for the preparation of polythiol which may advantageously be employed for producing plastic lense having a high refractive index comprising in the steps of:-
a) preparing diol by heating at 20° to 35°C mixture of 1:1 to 1:1.5 of mercaptoethanol and epichlorohydrin in the presence of a catalyst,
b) adding drop wise hydrated sodium sulphide to said diol so that the temperature is maintained at 30 to 45°C,
c) preparing a salt of isothiouronium by reacting the tetrol with hydrochloric acid and thiurea,
d) reacting the salt of step (c) with ammonia in solution to obtain the polythiol.
In accordance with this invention the process comprises in the first step of preparation of diol. The known process also envisaged the first step of preparation of the diol. However, in the preparation of the diol in accordance with the present invention, the reactant epichlorohydrin is added drop wise to the reactant mercaptoethanol and ethanol in the presence of a catalyst and such as to maintain the reaction mixture at room temperature. However, depending upon the catalyst, the reaction mixture may be heated to 35°C. Preferably, the ratio of mercaptoethanol to epichlorohydrin is 1:1 to 1:1.5. An excess amount of epichlorohydrin may be added, but which constitutes a waste. The catalyst is selected from triethanolamine, triethylamine, tributylamine and tripropylamine. Epichlorohydrin is added to mercaptoethanol such that the reaction mixture is maintained at a temperature of 20 to 35°C. Heating of the reaction may be carried at 35°C for one hour, if necessary. The diol has a refractive index of 1.534.
The diol produced by the first step is subjected to a second step to produce tetrol. Thus, diol is reacted with hydrated sodium sulphide. It has now been found that sodium sulphide in a hydrated form in distinction to an anhydrous form of the known art has definite advantages. Hydrated sodium sulphide helps in the reaction as the reaction is quicker. Hydrated sodium sulphide is added dropwise as the reaction is exothermic and so that the temperature is maintained at 30 to 45°C. Such a reaction is completed within 1 to 1 '/2 hours in comparison to 2 hours of the known art. The tetrol has a refractive index of 1.488.
The third step consists in reacting tetrol with hydrochloric acid at 90 to 100°C for 6 to 7.5 hours in comparison to 9 hours of the known art. The salt of isothiouronium has a refractive index of 1.522.
Finally the salt of isothiouronium is reacted with ammone in toluene as a solvent to produce polythiol has a refractive index of 1.421.
Further objects and advantages are apparent from the ensuing examples : EXAMPLE 1
To a mixed solution of 1.0 mole of mercapto ethanol, 1.0 mole of ethanol, and 2.0 g of triethanol amine were added 1.0 mole of epichlorohydrin dropwise over an hour while maintaining the temperature between 20-25 degree centigrade.
An aqueous solution, formed in advance by dissolving 1.0 mole of sodium sulphide nonahydrate in 100 ml of distilled water was added dropwise to the reaction liquid over an hour while maintaining the temperature at 30-35 degree centigrade. After addition, the reaction is allowed to cool for three hours at 45 degree centigrade thereby obtaining the tetrafunctional compound.
Identification was made by of reversed phase chromatography and NMR. Then 3.0 moles (303.6gm) of 36% hydrochloric acid and 2.5 moles (190.3 gm) of thiourea were added to the reaction liquid.
The mixture cooled to room temperature 400ml of toluene and then slowly 306.5 gm (4.5 moles) of 25% aqueous ammonia was added followed by hydrolysis at 35-45°C for 3 hours.
The layer thus separated from the aqueous layer was subjected to washing. The organic layer was washed in sequence with 100 ml of water, 100 ml of 36% hydrochloric acid, 100 ml of water, 100 ml of dilute aqueous ammonia (50%) and with 100 ml of water till the washing become neutral to litmus. The toluene was distilled off, under an atmosphere of nitrogen and under normal atmospheric pressure to 174.6 gm of colorless, hazy viscous liquid.
The liquid was further filtered on a to give a colorless, clear and transparent liquid.
The liquid was subjected to elemental analysis, IR, MS, NMR and colour determination by tristimulus values.
EXAMPLE 2
To a mixed solution of 1.0 mole of mercapto ethanol and 2 gms of triethylamine were added 1.0 mole of epichlorohydrin dropwise in 15 minutes while maintaining the temperature at 20° centigrade. This was followed by heating the reaction upto 35° and maintaining it for an hour.
The identification was done by NMR.
An aqueous solution, formed in advance by dissolving 0.5 mole of sodium sulphide nonahydrate in 100 gms of distilled water was added dropwise to the reaction liquid over an hour while maintaining the temperature at 40-45c, followed by reaction at 450c for an hour. The following tetrafunctional compound was obtained which was identified by neans of NMR and reversed gas phase chromatography.
To 303.6 gms of 36% hydrochloric acid and 190.3 gms of thiourea were added to the reaction liquid and the mixture was heated to 110 for 9hs under stirring.
The mixture was cooled to room temperature to which were added 400 ml of toluene and then slowly 306.5 gms (4.5 moles) of 25% aqueous ammonia, followed by hydrolysis at 600 c for three hours.
The organic layer thus obtained was washed in sequence with 100 ml of 36% hydrochloric acid, 10 ml of water, 100 ml of dilute aqueous ammonia and 100 ml of water repeatedly till the washings become neutral.
Toluene was distilled off under atmospheric pressure to get a residue which was filtered using a whatman 40 filter paper. A colorless, clear and transparent liquid was obtained which was subjected to identification by NMR, MS, IR and reversed phase chromatography.
In an amount of 36.7 gms of polythiol was mixed uniformly with 37.6 gms of toluene diisocyanate. The mixture was charged into a mold consisting of a glass mould and a gasket made of thermoplastic elastomer such as PVC where the mixture cured by holding at60-100°Cforl2hours.





WE CLAIM:
1. A process for the preparation of polythiol which may advantageously be employed for producing plastic lense having a high refractive index comprising in the steps of:-
a) preparing diol by heating at 20° to 35°C mixture of 1:1 to 1:1.5 of mercaptoethanol and epichlorohydrin in the presence of a catalyst,
b) adding drop wise hydrated sodium sulphide to said diol so that the temperature is maintained at 30 to 45°C,
c) preparing a salt of isothiouronium by reacting the tetrol with hydrochloric acid and thiurea,
d) reacting the salt of step (c) with ammonia in solution to obtain the polythiol.
2. A process as claimed in claim 1 wherein said catalyst is selected from triethanol amine, triethylamine, tributylamine, and tripropylamine.
3. A process for the preparation of polythiol substantially as herein described and illustrated.

Documents:

2342-DEL-2004-Abstract-(21-02-2011).pdf

2342-del-2004-abstract.pdf

2342-DEL-2004-Claims-(21-02-2011).pdf

2342-del-2004-claims.pdf

2342-DEL-2004-Correspondence-Others-(21-02-2011).pdf

2342-DEL-2004-Correspondence-Others-(21-10-2010).pdf

2342-del-2004-correspondence-others.pdf

2342-del-2004-correspondence-po.pdf

2342-DEL-2004-Description (Complete)-(21-02-2011).pdf

2342-del-2004-description (complete).pdf

2342-del-2004-form-1.pdf

2342-del-2004-form-18.pdf

2342-del-2004-form-2.pdf

2342-DEL-2004-Form-3-(21-10-2010).pdf

2342-DEL-2004-GPA-(21-10-2010).pdf

2342-del-2004-gpa.pdf


Patent Number 248781
Indian Patent Application Number 2342/DEL/2004
PG Journal Number 34/2011
Publication Date 26-Aug-2011
Grant Date 24-Aug-2011
Date of Filing 22-Nov-2004
Name of Patentee SHRIRAM INSTITUTE FOR INDUSTRIAL RESEARCH
Applicant Address 19, UNIVERSITY ROAD, DELHI-110 007, INDIA.
Inventors:
# Inventor's Name Inventor's Address
1 RAKESH KUMAR KHANDAL SHRIRAM INSTITUTE FOR INDUSTRIAL RESEARCH, 19, UNIVERSITY ROAD, DELHI-110 007, INDIA.
2 GEETHA SESHADRI SHRIRAM INSTITUTE FOR INDUSTRIAL RESEARCH, 19, UNIVERSITY ROAD, DELHI-110 007, INDIA.
3 GAURI SHANKAR JHA SHRIRAM INSTITUTE FOR INDUSTRIAL RESEARCH, 19, UNIVERSITY ROAD, DELHI-110 007, INDIA.
PCT International Classification Number C08G 75/04
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA