FORM 2
THE PATENTS ACT 1970
(39 OF 1970)
&
The patent Rules, 2003
COMPLETE SPECIFICATION
A Process for Preparation of Tris(2,4-di-tert-butylphenyl) phosphite
SeQuent Scientific Limited
A Company Incorporated Under The Companies Act, 1956
Having Registered Office at 301, 'Dosti Pinnacle', 3rd Floor,
Plot No.E7, Road No.22, Wagle Industrial Area,
Thane (W)-400 604
The following specification particularly describes the nature of the invention and the manner in which it has to be performed:

FIELD OF INVENTION
The present invention relates to a novel process for the preparation of triaryl phosphite, specifically it relates to the process for the preparation of tris(2,4-di-tert-butylphenyl) phosphite, an antioxidant.
BACKGROUND OF THE INVENTION
The triaryl phosphites are commercially used as a stabilizer for producing synthetic rubber. Triaryl phosphites containing more alkyl groups attached to benzene rings are found to be effective synthetic rubber stabilizers and are preferred over simpler aryl phosphites because they are non-discoloring, they impart less odour to the finished polymer and also they are more resistant to hydrolysis, which makes their addition possible to latter as aqueous emulsions.
These important commercial uses of triaryl phosphites have given rise to the development of research in this area intended to produce the same at cost efficient manner. The preparation of ortho tertiary alkyl aryl phosphites is more difficult than the preparation of phosphites containing less hindered substituents. The commercial significance of the tris(2,4-di-tert-butylphenyl) phosphite thereby requires the need to bring out novel processes for production of the tris(2,4-di-tert-butylphenyl)phosphite.
Tris(2,4-di-tert-butylphenyl)phosphite is represented by below formula I:


There are number of literatures available which describe the process for preparation of of triaryl phosphite. The US Patent 3533989 discloses a process for the preparation of triaryl phosphite. According to this patent, triaryl phosphite is prepared from phosphorous trihalides and alkyl substituted phenol using triethylamine in stoichiometric quantity as a hydrogen chloride scavenger so as to give yields as high as 80% of the desired product. It is not desirable to use a stoichiometric quantity of triethylamine in the preparation of the cited phosphite compound.
US Patent 4312818 describes a process for producing triaryl phosphite from phosphorous trihalides and alkyl substituted phenol in the ring of formula ROH of where R=C6H3RaRb (Ra is tertiary alkyl, Rb is lower alkyl or tertiary alkyl) with the use of specific phosphorous, nitrogen and /or sulfur containing compounds as catalysts has been disclosed.
US Patent 4440696 describes a process for producing triaryl phosphite. According to this process, the catalyst is selected from the group consisting of an amide of a carboxylic acid for example DMF.
EP0413661B1 describes a process for the preparation of tris (2,4-ditertiary butyl phenyl) phosphite from 2,4-di-tert-butylphenol and phosphorus trichloride in the presence of catalysts in the absence of solvent in three steps. In this process workup for the isolation of product is very complicated.
The major drawbacks of the prior art process is the use of catalysts such as DMF for the reaction, which is teratogen. Moreover, the workup for the isolation of product is very complicated. These drawbacks provide a good opportunity to develop a process which will overcome them. The present inventors have developed a process, which overcome most of the drawbacks of the prior art.
SUMMARY OF THE INVENTION
Accordingly, the main aspect of the invention is to provide a process for the preparation of tris (2,4 -di-tert-butyl phenyl) phosphite formula I, comprising:

a) reacting 2,4 -di tert butyl phenol with phosphorous trichloride using di-butylamine as a base in presence of a solvent to obtain crude tris(2,4-di-tert-butyl phenyl) phosphite of formula I; and
b) washing the obtained crude tris (2,4 -di-tert-butyl phenyl) phosphite using a solvent to form pure tris (2,4 -di-tert-butyl phenyl) phosphite formula I.
BRIEF DESCRIPTION OF THE FIGURE Figure 1: X-Ray diffractogram of tris (2,4 -di-tert-butyl phenyl) phosphite
DETAIL DESCRIPTION OF THE INVENTION Accordingly in an embodiment of the invention, the reaction of 2,4 -di tert butyl phenol with phosphorous trichloride is carried out using di-butylamine as a base in presence of a solvent which is an organic solvent selected from toluene, benzene, xylene, monochlorobenzene and the like, preferably xylene to obtain crude tris(2,4-di-tert-butyl phenyl)phosphite. The reaction is carried out at reflux temperature in the range of about 150-180°C, preferably at 160-170°C.
In another embodiment of the invention, the purification of crude tris(2,4-di-tert-butyl phenyl) phosphite is done by washing the crude tris(2,4-di-tert-butyl phenyl) phosphite using a solvent which is an alcohol selected from methanol, ethanol, propanol, butanol, isopropanol, preferably methanol.
In another embodiment of the invention, tris(2,4-di-tert-butyl phenyl) phosphite obtained after purification is crystalline and characterised by X-ray powder diffraction pattern as given in figure 1 and having major 20 peaks at 7.44, 13.93, 14.87, 15.14, 16.79, 17.08, 17.24,17.39, 17.51, 18.01, 18.97 and 20.76±0.2. This is carried out using X-ray diffractometer using Cu anode having 45kV, 40mA at 25 °C. This crystalline form is very stable and the form doesn't change with time for a considerably long time.
In another embodiment, the present invention avoids the use of teratogenic dimethyl formamide as catalyst for the preparation of tris(2,4-di-tert-butyl phenyl)

phosphite and uses di-butylamine as a catalyst which function as hydrogen chloride gas scavenger too and leads to the formation of stable product.
The present invention can be illustrated by the following example, which is not to limit the scope of invention.
Example: Preparation of tris(2,4-di-tert-butyl phenyl)phosphite of formula I
2,4-Di tert butyl phenol(100 g) was charged into a cleaned and dried RBF under nitrogen, heated to get clear solution at 50-55°C. Dibutylamine(2.5g) and xylene ( 15.7 ml) were charged to above reaction mass at 50-55°C, slowly heated to I10°C under nitrogen and maintained for 15 minutes. The reaction mass was gradually cooled to 80-85°C and further cooled to 55-60°C under vacuum. Phosphorous trichloride (21.6 g) was slowly added at 55-60°C in 2-3 hours under stirring. The reaction mass was heated slowly to 165°C and maintained for some time under nitrogen at 165°C. The reaction mass was further heated to 180°C under vacuum and maintained for 60-90 minutes. The reaction mass was cooled to 162°C. Xylene (30 ml) and DBA (2.5 g) was added to the reaction mass at 162-165°C and refluxed for 30 minutes under nitrogen. The reaction mass was again further heated to 180°C under vacuum and maintained for 90 minutes. The reaction mass was slowly quenched to another RBF containing pre-heated methanol (200.0ml). The reaction mass was refluxed for 30 minutes, cooled to 25-30°C and filtered. The product obtained was washed with methanol (25ml) twice and dried under vacuum.
Yield: 90-93 gm
Purity: NLT 98%
Colour of solution 425 (nm%): min 99

We Claim:
1. A process for the preparation of tris(2,4-di-tert-butyl phenyl) phosphite formula I, comprising:

a) reacting 2,4-di-tert-butyl phenol with phosphorous trichloride using di-butylamine as a base in presence of a solvent to obtain crude tris(2,4-di-tert-butyl phenyl) phosphite of formula I; and
b) washing the obtained crude tris(2,4 -di-tert-butyl phenyl) phosphite using a solvent to form pure tris (2,4 -di-tert-butyl phenyl) phosphite of formula I.

2. A process according to claim 1, wherein the solvent used in step (a) is selected from toluene, benzene, xylene, monochlorobenzene and the like.
3. A process according to claim 1, wherein the solvent in step (a) is xylene.
4. A process according to claim 1, wherein the reaction in step (a) is carried out at temperature in the range of 150-180°C.
5. A process according to claim 1, wherein the reaction in step (a) is carried out at temperature in the range of 160-170°C.
6. A process according to claim 1, wherein the washing in step (b) is done using a solvent selected from methanol, ethanol, propanol, butanol or isopropanol.

7. A process according to claim 1, wherein the washing in step (b) is done using methanol.