Title of Invention

A PROCESS FOR THE PREPARATION OF NEUTRAL DIESTERS

Abstract This invention relates to a process for the preparation of neutral diesters such as Bis-(2-ethyl hexyl) adipate, Bis-(2-ethyl hexyl) azelate, Bis-(2-ethyl hexyl) sebacate, Bis-(isodecyl) adipate, Bis-(isodecyl) azelate, Bis-(isodecyl) sebacate, comprising the steps of preparing metal oxide of the catalyst by dissolving the lower valent chloride salt of titanium, zinc or tin concentrated hydrochloric acid, quenching with an aq solution of alkali metal salt preferably sodium carbonate, precipitating the metal oxide by increasing the alkalinity and heating for 1-5 hours at a temperature of 100-120°C followed by filtration and washing the precipitated tin oxide with deoxygenated distilled water till the pH of the water is neutral, and then drying in an inert atmosphere at a temperature of 100-120°C; mixing of metal oxide catalyst prepared in step a) in 1-6% amount to that of a dibasic acid selected from OXALIC ACID, MALONIC ACID, SUCCINIC ACID, GLUTERIC ACID, ADIPIC ACID, PIMALIC ACID, SUBERIC ACID, AZELAIC ACID, SEBASIC ACID mechanically in controlled atmosphere preferably inert atmosphere; esterification by mixing the acid mixture of step b) and 2-6 mol monohydric alcohol selected from 2-ethyl hexyl alcohol, n-octanol and isodecyl alcohol which may be linear or branched chain, heating to the refluxing temperature of the solution till 2.0 mol of water is collected in the dean-stark assembly; separating the diester and catalyst by cooling the reaction mixture of stem c) by filtration under vacuum at 20-110 mm followed by the fractional distillation under vacuum of about 0.1 mm of the filtrate and collecting the excess alcohol and the diester separately.
Full Text FIELD OF INVENTION
This invention relates to a process for the preparation of complete neutral diesters as base stock of synthetic lubricants for thermal resistant applications in the area of avionics, air compressors, bearings, hydraulics and gears etc.
PRIOR ART
To meet the requirement of lubricants for aircraft engines, the synthetic esters are used extensively. These synthetic esters are mainly the diesters of dibasic carboxylic acids with monohydric alcohols or esters of polyols with monobasic acids. These esters have an edge over conventional lubricating oils based on mineral oils due to more favourable viscosity temperature behavior, high temperature resistance and low pour point with high viscosity etc..
Synthetic ester lubricants are also utilized in a wide variety of other applications like air compressor, bearings, hydraulics, gears and greases etc.
The utility of synthetic esters, however, can be significantly improved by increasing the oxidation life of the lubricant, reducing the acid forming tendency of a lubricant, reducing the volatility of the lubricant and in particular reducing the varnish/deposit formation of the esters. By improving these characteristics, the synthetic esters lubricants can be utilized in even more applications and provide greater useful life for the lubricant.
Though the diesters are generally synthesized either by the esterification of acid and alcohol in presence of catalysts or by trans esterification reactions of fower alcohol esters with higher alcohols using appropriate catalysts yet to obtain complete neutral esters is difficult and require manipulative skills.
The mineral acids and organic acids have been used widely as catalyst for the direct esterification of acids and alcohols to obtain diesters and polyol esters.
The disadvantage of the above known process is that to remove acid for obtaining neutral esters a number of processing steps are required.
Another disadvantage is the side reactions which result in unreactive diluents which reduce the efficiency of the final product.
Yet another disadvantage is the formation of colour bodies which cannot be removed from the finished product.
Besides acids, the metals, metal halides and their and their acid salts have also been used to facilitate the esterification process.
But this process also suffers from certain disadvantages like it requires excess use of carboxylic acid to complete the reactions. The excess carboxylic acid cannot be recovered or recycled thus increases raw material cost.
The tetrakisacetylacetonate zirconium or tetrabutoxy titanium or dibutylin oxide has also been used as catalyst synthesizing various other esters.
The disadvantage in the use of tetra alkoxy zirconium and titanium salts as catalyst is that they are moisture sensitive and get hydrolyzed easily thus reducing its catalytic activities.
Another disadvantage of the above known process is that stannic chloride which is highly fuming liberates toxic hydrochloric acid.
Yet another disadvantage of the above process is that the dibutylin oxide is very pungent and toxic.
The diesters and polyol esters have also been prepared using alcohols, carbon mono oxide, olefins and oxygen under pressure in presence of catalysts.
The main disadvantage of synthesizing esters using carbon monoxide is the use of high pressure and temperature reactor. To handle pressure reactor a very precise and specific skill is required which makes the process more difficult and complicated.
The complete mixed polyol esters were prepared generally by the reaction of partial polyol mono carboxylic acid esters with an acidic anhydride in presence of catalysts viz. stannic chloride, ferric chloride, zinc chloride, tin oxalate, hydrogen bromide, cobalt, nickel or sodium salt along with pyridine as co-catalyst and perfluoroalkyi sulfonic acid. The organic diesters have also been prepared using epoxide and acid anhydride.
The disadvantage of using anhydride in the preparation of esters is that the anhydrides are prepared from the acid dehydration, which involves one more reaction step thus increasing the cost.
Another disadvantage of the above known process is that the anhydrides in tropical conditions react with moisture forming acid.
Yet another disadvantage of the above known process is that the remains of metal halides and their side products after hydrolysis cause corrosion.
In another process the transesterification reactions are facilitated by the catalyst such as aluminium propoxide, sodium methoxide, tetraisopropyltitanate, a catalyst made from dialkyltin dichloride and lead oxide.
The disadvantage of the above known process is that the catalysts used in this process are generally metal alkoxides which are moisture sensitive thus making their handling and storage difficult.
Another disadvantage of the above known process is that the catalysts used in this process are non reusable.
Yet another disadvantage of the above known process is that the removal of catalysts from the finished product especially on industrial scale is cumbersome.
OBJECTS OF THE INVENTION
The main object of the present invention is to provide a process for the preparation of complete neutral diesters.
Another object of the present invention is to provide a process for the preparation of complete neutral diesters which are free from acid and colour embodies.
Still another object of the present invention is to provide a process for the preparation of complete neutral diesters which does not make use of moisture sensitive reagents and catalyst.
Yet another object of the present invention is to provide a process for the preparation of complete neutral diesters which utilises a catalyst which can be easily removed from the reaction mixture and reused.
Further object of the present invention is to provide a process for the preparation of complete neutral diesters which makes use of a non-toxic catalyst.
Yet another object of the present invention is to provide a process for the preparation of complete neutral diesters where the completion of reaction is easily known thus avoiding excess time and energy consumption.
Still further object of the present invention is to provide a process for the preparation of complete neutral diesters wherein, there are minimum side reactions.
Yet further object of the present invention is to provide a process for the preparation of complete neutral diesters which requires simple equipment and is carried out at ambient pressure condition.DETAILED DESCRIPTION OF THE INVENTION
According to this invention there is provided a process for the preparation of neutral diesters such as Bis-(2-ethyl hexyl) adipate, Bis-(2-ethyl hexyl) azelate, Bis-(2-ethyl hexyl) sebacate, Bis-(isodecyl) adipate, Bis-(isodecyl) azelate, Bis-(isodecyl) sebacate, comprising the steps of:
a) preparing metal oxide of the catalyst by dissolving the lower valent chloride salt of titanium, zinc or tin concentrated hydrochloric acid, quenching with an aq solution of alkali metal salt preferably sodium carbonate, precipitating the metal oxide by increasing the alkalinity and heating for 1-5 hours at a temperature of 100-120°C followed by filtration and washing the precipitated tin oxide with deoxygenated distilled water till the pH of the water is neutral, and then drying in an inert atmosphere at a temperature of 100-120°C;
b) mixing of metal oxide catalyst prepared in step a) in 1-6% amount to that of a dibasic acid selected from OXALIC ACID, MALONIC ACID, SUCCINIC ACID, GLUTERIC ACID, ADIPIC ACID, PIMALIC ACID, SUBERIC ACID, AZELAIC ACID, SEBASIC ACID mechanically in controlled atmosphere preferably inert atmosphere;
c) esterification by mixing the acid mixture of step b) and 2-6 mol monohydric alcohol selected from 2-ethyl hexyl alcohol, n-octanol and isodecyl alcohol which may be linear or branched chain, heating to the refluxing temperature of the solution till 2.0 mol of water is collected in the dean-stark assembly;

d) separating the diester and catalyst by cooling the reaction mixture of stem c) by filtration under vacuum at 20-110 mm followed by the fractional distillation under vacuum of about 0.1 mm of the filtrate and collecting the excess alcohol and the diester separately.
In accordance with the present invention, the process for the preparation of complete neutral diesters comprises of the steps of:
a) Preparation of the metal oxide of the catalyst
A lower valent chloride salt of titanium, zinc or tin preferably tin chloride in a weight/volume ratio of about 7.5:0.1 is dissolved in concentrated hydrochloric acid (-36%), under inert atmosphere. The clear solution of tin chloride is then quenched with 10% aqueous solution of alkali metal salt preferably sodium carbonate, by continuous stirring with a glass rod for 15-45 minutes preferably 25-30 minutes, to obtain a neutral solution of tin chloride. To this neutral solution of tin chloride a small amount about 5.0 ml of aqueous alkaline solution is added to marginally increase the alkalinity of the solution due to which the oxide of tin is precipitated. This solution is heated for 1-5 hours preferably for about 3 hours at a temperature of 100-120°C preferably at 110°C. The precipitated tin oxide is filtered and washed with deoxygenated distilled water till the pH of the water is neutral. This washed residue of tin oxide is dried in an inert atmosphere at a temperature of 100-120°C preferably at 110°C.
b) Mixing of the catalyst with acid
The tin oxide catalyst prepared in step a) is mixed in 1-6% preferably 3-4% amount to that of a dibasic acid having C2 to C10 carbon atoms. The mixing is done mechanically in controlled atmosphere preferably inert atmosphere.
c) Esterification of the acid
The mixture of stem b) is taken in a R.B. flask and monohydric alcohol having carbon atom from C4 to C15 preferably C4 to do, which may be linear or branched chain, is taken in excess amount, 2-6 mol preferably 4-5 mol to that of acid in the flask. The flask is then fitted to a dean-stark assembly and heated on an oil bath or electrical heating mantle to the refluxing temperature of the solution. When about 2.0 mol of water is collected in the deanstark assembly the heating is stopped to stop the reaction.
d) Separation of the diester and catalyst
The reaction mixture of stem c) is cooled and the catalyst is separated by filtration by any filtration device preferably through sintered buchner funnel under vacuum (20-110 mm). The filtered solution is fractionally distilled under vacuum of about 0.1 mm and the excess alcohol and the diester are collected separately.
This invention will now be illustrated with working examples which are intended to be typical examples to explain the technique of the present invention and are not intended to be taken restrictively to imply any limitation to the scope of the present invention.
Working Example
1. 7.5 gm of lower valent tin oxide as catalyst was mixed mechanically with
188g (~1.0 mol) of azeleic acid in a one litre flask. To this mixture 512 gm
(~4.0mol) of 2-ethy! hexyl alcohol was added. A dean-stark assembly with a
condenser was fitted to the flask and the reaction mixture was heated to reflux
on an electrically operated heating mantle. The reaction was stopped after about
1 hour when 36 ml ("2.0 mol) of water was collected in the dean-stark
assembly. It was then cooled to room temperature to about 25°C. The solution
was filtered through G-4 sintered funnel to remove particulate matters and the
catalyst. The filtrate was then fractionally distilled (0.1mm) to separate unreacted
alcohol and diester about 392 gm, 96%, b.p. 201 °C/0.1mm.
2. 6.0 gm of lower valent tin oxide as catalyst was mixed mechanically with
146g (~1.0 mol) of adipic acid in a one litre flask. To this mixture 512 gm
(~4.0mol) of 2-ethyl hexyl alcohol was added. A dean-stark assembly with a
condenser was fitted to the flask and the reaction mixture was heated to reflux
on an electrically operated heating mantle. The reaction was stopped after about
1 hour when 36 ml (~2.0 mol) of water was collected in the dean-stark
assembly. It was then cooled to room temperature to about 25°C. The solution
was filtered through G-4 sintered funnel to remove particulate matters and the
catalyst. The filtrate was then fractionally distilled (1 .0mm) to separate unreacted
alcohol and diester about 349 gm, 96%, b.p. 168 °C/1.0mm.
3. 8.0 gm of lower valent tin oxide as catalyst was mixed mechanically with
202g (-1.0 mol) of sebasic acid in a one litre flask. To this mixture 512 gm
(~4.0mol) of 2-ethyl hexyl alcohol was added. A dean-stark assembly with a condenser was fitted to the flask and the reaction mixture was heated to reflux on an electrically operated heating mantle. The reaction was stopped after about 1 hour when 36 ml (~2.0 mol) of water was collected in the dean-stark assembly. It was then cooled to room temperature to about 25°C. The solution was filtered through G-4 sintered funnel to remove particulate matters and the catalyst. The filtrate was then fractionally distilled (1 .0mm) to separate unreacted alcohol and diester about 405 gm, 96%, b.p. 214 °C/1.0mm.
It is to be understood that the process of the present invention is susceptible to modifications, changes, adaptations by those skilled in the art. Such modifications, changes, adaptations are intended to be within the scope of the present invention which is further set forth under the following claims:




















WE CLAIM;
1. A process for the preparation of neutral diesters such as Bis-(2-ethyl hexyl) adipate, Bis-(2-ethyl hexyl) azelate, Bis-(2-ethyl hexyl) sebacate, Bis-(isodecyl) adipate, Bis-(isodecyl) azelate, Bis-(isodecyl) sebacate, comprising the steps of:
a) preparing metal oxide of the catalyst by dissolving the lower valent chloride salt of titanium, zinc or tin concentrated hydrochloric acid, quenching with an aq solution of alkali metal salt preferably sodium carbonate, precipitating the metal oxide by increasing the alkalinity and heating for 1-5 hours at a temperature of 100-120°C followed by filtration and washing the precipitated tin oxide with deoxygenated distilled water till the pH of the water is neutral, and then drying in an inert atmosphere at a temperature of 100-120°C;
b) mixing of metal oxide catalyst prepared in step a) in 1-6% amount to that of a dibasic acid selected from OXALIC ACID, MALONIC ACID, SUCCINIC ACID, GLUTERIC ACID, ADIPIC ACID, PIMALIC ACID, SUBERIC ACID, AZELAIC ACID, SEBASIC ACID mechanically in controlled atmosphere preferably inert atmosphere;
c) esterification by mixing the acid mixture of step b) and 2-6 mol monohydric alcohol selected from 2-ethyl hexyl alcohol, n-octanol and isodecyl alcohol which may be linear or branched chain, heating to the refluxing temperature of the solution till 2.0 mol of water is collected in the dean-stark assembly;
d) separating the diester and catalyst by cooling the reaction mixture of stem c) by filtration under vacuum at 20-110 mm followed by the fractional distillation under vacuum of about 0.1 mm of the filtrate and collecting the excess alcohol and the diester separately.
2. A process as claimed in claim 1 wherein the step (b) the metal oxide catalyst is mixed in an amount of 3-4% of said dibasic acid.
3. A process for the preparation of neutral diesters substantially as described and illustrated herein.

Documents:

1379-DEL-2003-Abstract-(11-02-2010).pdf

1379-DEL-2003-Abstract-(26-11-2009).pdf

1379-del-2003-abstract.pdf

1379-DEL-2003-Claims-(11-02-2010).pdf

1379-DEL-2003-Claims-(26-11-2009).pdf

1379-del-2003-claims.pdf

1379-DEL-2003-Correspondence-Others (11-02-2010).pdf

1379-DEL-2003-Correspondence-Others (26-11-2009).pdf

1379-del-2003-correspondence-others.pdf

1379-del-2003-correspondence-po.pdf

1379-DEL-2003-Description (Complete)-(11-02-2010).pdf

1379-DEL-2003-Description (Complete)-(26-11-2009).pdf

1379-del-2003-description (complete).pdf

1379-del-2003-form-1.pdf

1379-del-2003-form-18.pdf

1379-del-2003-form-2.pdf

1379-DEL-2003-Form-3-(11-02-2010).pdf

1379-DEL-2003-GPA-(11-02-2010).pdf

1379-DEL-2003-GPA-(26-11-2009).pdf


Patent Number 239820
Indian Patent Application Number 1379/DEL/2003
PG Journal Number 15/2010
Publication Date 09-Apr-2010
Grant Date 01-Apr-2010
Date of Filing 10-Nov-2003
Name of Patentee DIRECTOR GENERAL, Defence Research & Development Organisation
Applicant Address DEFENCE RESEARCH & DEVELOPMENT ORGANISATION MINISTRY OF DEFENCE, GOVT OF INIDA, B-341, SENA BHAWAN, DHQ P.O. NEW DELHI-110011
Inventors:
# Inventor's Name Inventor's Address
1 CHANDRA SWAROOP BISARIA DEFENCE MATERIALS AND STORES R&D ESTT. G.T. ROAD, KANPUR-208013.
2 ARVIND KUMAR SAXENA DEFENCE MATERIALS AND STORES R&D ESTT. G.T. ROAD, KANPUR-208013.
3 OM PRAKASH DEFENCE MATERIALS AND STORES R&D ESTT. G.T. ROAD, KANPUR-208013.
4 GYANESH NARAIN MATHUR DEFENCE MATERIALS AND STORES R&D ESTT. G.T. ROAD, KANPUR-208013.
PCT International Classification Number C07C 67/03
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA