WO2012046114A1

WO2012046114A1 - Preparing higher trialkyl phosphites

Info

Publication number: WO2012046114A1
Application number: PCT/IB2011/002228
Authority: WO
Inventors: Jaidev Rajnikant Shroff; Vikram Rajnikant Shroff; Birja Shanker
Original assignee: United Phosphorus Ltd
Current assignee: UPL Ltd
Priority date: 2010-10-07
Filing date: 2011-09-26
Publication date: 2012-04-12
Anticipated expiration: 2013-04-07
Also published as: GB201213971D0; WO2012046114A8; TW201221521A; GB2489896A; GB2489896B

Abstract

According to an aspect of the invention, there is provided an improved process for the preparation of trialkyl phosphite of Formula (I): said process comprising reacting trialkyl phosphite of Formula (II) with alkanol of formula (III) R¹-OH III such that R¹ represents an alkyl moiety having 8 to 16 carbon atoms and R represents an alkyl moiety having 1 to 3 carbon atoms. Also disclosed is the compound of formula (I) that is substantially free of a phenolic impurity.

Description

PREPARING HIGHER TRIALKYL PHOSPHITES

TECHNICAL FIELD OF INVENTION

The present invention relates to an improved process for preparation of trialkyi phosphites and to trialkyi phosphites made therefrom.

BACKGROUND OF THE INVENTION

Various uses of trialkyi phosphites are reported in the art, such as its use as a stabilizer for synthetic resins, additives to lubricants, antifoaming agents, intermediates for producing various chemicals, etc. Numerous processes have been developed for the preparation of trialkyi phosphites. For example, triethyl phosphite is prepared by the reaction of phosphorus trichloride with ethanol in the presence of hydrogen chloride acceptors such as ammonia or amines. However, various problems are associated while preparing triethyl phosphite by this technique. For example, the reaction is highly exothermic and expensive cooling means must therefore be employed to control the reaction temperature. The product formed is not obtained in pure form, and hence lengthy procedure which is not economically viable is employed to get pure product.

More recently trialkyi phosphites have been prepared by the transesterification of triaryl phosphites, such as triphenyl phosphite, with an alkyl alcohol in the presence of a basic catalyst. However, when this technique is applied to some of the lower alkyl alcohols, such as ethanol, the separation of the trialkyi phosphite, such as triethyl phosphite, from the other reaction products is not easily obtained. The product requires isolation from the reaction mixture by tedious and expensive procedure.

Moreover, it has been found that the trialkyi phosphites prepared by this process invariably includes 0.1 % to 0.3% or more of a phenolic impurity, which is undesirable for its intended use due to its inherent toxicity. There is a need in the art for a process that leads to the preparation of trialkyi phosphites that are substantially free of a phenolic impurity. The term "substantially free of is intended herein to denote trialkyi phosphites being completely free of phenolic impurity or comprises less than 100 ppm of a phenolic impurity. This phenolic impurity originates from the aryl moiety of the triaryl phosphite starting material and is very undesirable. Thus, there is clearly a need within the art for trialkyl phosphites that are substantially free of a phenolic impurity and a process for the preparation thereof.

U.S.Pat.No. 3636145 discloses a process for preparing a trialkenyl phosphite by the transesterification reaction involving trimethyl phosphite and alkenol. According to the claimed process, the essential element of this disclosed invention is the presence of alkaline catalyst in the process and presence of non-azeotropic solvent.

U.S. Pat.No.3184496 discloses a method of preparing and recovering trimethyl phosphite and to the preparation of derivatives of trimethyl phosphite. The process also discloses the use of basic catalysts in the reaction. The above mentioned processes either involve a lengthy and tedious work-up procedure to get pure product or use a catalyst and a solvent thus making these processes uneconomical and less eco-friendly.

Hence there is a need in the art to develop an ecofriendly, efficient and economical process for the manufacture of trialkyl phosphite without using any solvents and/or alkaline catalysts to obtain the product in high yield and purity.

OBJECT OF THE INVENTION

It is one object of this invention to provide an improved process for preparation of trialkyl phosphite compounds. A further object of the present invention is to provide an improved process for preparation of trialkyl phosphite in high yield and percentage utilization of phosphorus content.

A further object of the present invention is to provide an improved process for preparation of trialkyl phosphite which is environmentally friendly.

Yet another object of the invention to provide an improved process for preparation of trialkyl phosphite which is economically viable and less time consuming. Yet another object of the present invention is to provide an improved process that leads to the preparation of trialkyi phosphites that are substantially free of a phenolic impurity.

Another object of the present invention is to provide trialkyi phosphites that are substantially free of phenolic impurity or comprises less than 100 ppm of a phenolic impurity.

These and other objects of this invention will become apparent from the detailed description which follows.

SUMMARY OF THE INVENTION

According to an aspect of the invention, there is provided an improved process for the preparation of trialkyi phosphite of Formula I:

R O— R

\ /

O— P

\

O

R

I said process comprising reacting trialkyi phosphite of Formula

^R O— R

\ /

O— P

\

o

R

with alkanol of formula III

R -OH such that R¹ represents an alkyl moiety having 8 to 16 carbon atoms and R represents an alkyl moiety having 1 to 3 carbon atoms.

In another aspect, there is provided a compound trialkyi phosphite of Formula I: R O— -R

\ /

O— P

\

O

R

such that R¹ represents an alkyl moiety having 8 to 16 carbon atoms wherein said compound of formula I is substantially free of a phenolic impurity.

DETAILED DESCRIPTION

The present invention provides an improved process for preparation of trialkyi phosphite of Formula I by reacting trialkyi phosphite of Formula II with alkanol of Formula III as described above, wherein R¹ represents an alkyl moiety having C₈-C₁₆ carbon atoms, and R represents alkyl moiety having C C₃ carbon atoms.

The reaction is represented in the form of Schematic diagram below. Without wishing to be bound by theory, it is believed that the reaction presumably proceeds via the intermediates monoalkylphosphites and dialkylphosphites to give the trialkylphosphite compound of formula I.

REACTION PATHWAY FOR THE PREPARATION OF TRIALKYLPHOSPHITE OF

FORMULA I

Λ

According to an aspect, the invention relates to an improved process for the preparation of trialkyl phosphite of Formula I by reacting trialkyl phosphite of Formula II with alkanol of Formula III as described above, wherein the reaction is carried out in the absence of a catalyst and/or a solvent.

In an embodiment, the improved process of the present invention comprises reacting the trialkyl phosphite of formula II with the alkanol R -OH in the absence of a catalyst or in the absence of a solvent or in the absence of a catalyst and a solvent.

In one embodiment, the R¹ moiety of trialkyl phosphite of Formula I is selected from carbon chain ranging from C₈-C₁₆, preferably C₉-Ci₅ and more preferably Ci₀-C₁₃ In an embodiment, alkanol of Formula III is selected from alkanol having carbon chain ranging from C₈-C₁₆, preferably C₉-C ₅ and more preferably Ci₀-Ci₃.

In further embodiment, the R group in trialkyl phosphite of Formula II is selected from an alkyl moiety having d-C₃ carbon atoms, and most preferably R is methyl.

According to an embodiment, trialkyl phosphite of Formula II is added to the alkanol of Formula III at a temperature range between 75°C-180°C. In yet another embodiment, trialkyi phosphite of Formula II is added to the alkanol of Formula III with stirring for 0.5-7 hrs.

In further embodiment, the alkanol of Formula III is in the molar ratio of 5:1-3:1 with respect to the trialkyi phosphite of Formula II, preferably the ratio is 4:1.

In another embodiment, subsequent to the addition of trialkyi phosphite, the reaction mass is heated to a temperature between 180°C -220°C. The reaction mass is maintained at this temperature for a predetermined period of time that allows the reaction to be completed.

In an embodiment, the reaction mass is maintained at a temperature of about 180°C -220°C and maintained at this temperature for a period of about 2-4 hours. It has been found that maintaining the reaction mass at an elevated temperature leads to an increase in the yield of the target product.

In an embodiment, the aforesaid elevated temperature to which the reaction mass is maintained for 2-4 hours is at least above the boiling point of the alcoholic by-product R— OH of formula IV generated during the reaction. It has been found that maintaining the temperature of the reaction mass at least above the boiling point of the alcoholic by-product leads to a simultaneous removal of the by-product from the reaction system, which has been found to increase the yield of the target product of formula I.

Therefore, in this embodiment, the alcoholic by product R— OH of formula IV generated during the reaction is simultaneously removed from the reaction system. The alcoholic by- product is preferably recovered by condensing it at lower temperature by circulating cold water through a condenser without letting the alcohol going out of the system. This is an added advantage in the operation of the reaction that makes the process cost effective as well as environmentally safe. Thus, in this embodiment, the present invention provides an improved process for the preparation of trialkyi phosphite of Formula I: /

\

o

R¹

I said process comprising: (a) reacting trialkyi phosphite of Formula II

^R _x O— R

\ /

O— P

\

o

R

II with alkanol R¹-OH of formula III such that R¹ represents an alkyl moiety having 8 to 16 carbon atoms and R represents an alkyl moiety having 1 to 3 carbon atoms, by adding the compound of formula II to the alkanol R -OH at a temperature of between 75°C-180°C;

(b) maintaining the reaction mass at least at a temperature above the boiling point of an alkanol having 1 to 3 carbon atoms for a predetermined period of time while simultaneously removing the alcoholic by-product R— OH of formula IV generated during the reaction; and

(c) recovering the target compound of formula I by filtration; wherein the improvement comprises reacting the trialkyi phosphite of formula II with the alkanol in the absence of a catalyst or in the absence of a solvent or in the absence of a catalyst and a solvent. In an embodiment, subsequent to the completion of step (b) above, the reaction mass is cooled under an inert atmosphere. The preferred inert atmosphere is nitrogen. The cooled reaction mass is subjected to a vacuum at 80-100°C to remove any residues of the alcoholic by-product.

In an embodiment, the reaction mass is again heated to 190-200°C for a sufficient period of time at 1-2 mm vacuum to remove any remaining traces of alcohol.

In an embodiment, the reaction is thereafter cooled, preferably to a temperature of about 40°C and the target compound is recovered by filtration.

Thus, in another embodiment, the present invention provides an improved process for the preparation of trialkyl phosphite of Formula I: O-R¹

\ /

O— P

\

o

R¹

said process comprising:

(a) reacting trialkyl phosphite of Formula II

II with alkanol R¹-OH of formula III such that R¹ represents an alkyl moiety having 8 to 16 carbon atoms and R represents an alkyl moiety having 1 to 3 carbon atoms, by adding the compound of formula II slowly over a period of at least 0.5 hours to the alkanol R¹-OH of formula III at a temperature of between 75°C-180°C, and subsequent to the complete addition of the compound of formula II to said alkanol,

(b) maintaining the reaction mass at least at a temperature above the boiling point of an alkanol having 1 to 3 carbon atoms for a predetermined period of time while simultaneously removing the alcoholic by-product R— OH generated during the reaction;

(c) optionally, cooling the reaction product under an inert atmosphere; (d) heating the cooled reaction product to 190-200°C for a sufficient period of time at 1-2 mm vacuum pressure; and

(e) cooling the reaction product to a temperature of about 40°C and recovering the compound of formula I by filtration; wherein the improvement comprises reacting the trialkyl phosphite of formula II with the alkanol in the absence of a catalyst or in the absence of a solvent or in the absence of a catalyst and a solvent.

In a further embodiment, the trialkyl phosphite of Formula II is added to the alkanol of Formula III at an elevated temperature of about 75°C -180°C, optionally maintained at the same temperature for 0-6 hours, the reaction temperature is then raised to about 195°C - 210°C, and stirred at the same temperature for about 2-4 hours to get the desired trialkyl phosphite of Formula I in high yield and purity.

In yet another embodiment, trimethyl phosphite is added to the alkanol at 170°C -180°C, in 3-7 hrs followed by stirring at 195°C -210°C for about 2-4 hours. In an embodiment, the product is isolated by methods known in the art.

In an embodiment, the trialkyl phosphite of Formula I is obtained in more than 85% yield.

The process described herein in this specification is completely solvent free and catalyst free which makes the process ecofriendly. It has been surprisingly found that in the absence of a solvent and/or a catalyst, the target compound of formula I is formed in a surprisingly higher yield as compared to the conventional processes using a catalyst and/or a solvent. Therefore, it has been surprisingly found that percentage utilization of the initial phosphorus content originating from the starting trialkyi phosphite is maximized in the absence of a catalyst and/or a solvent.

Thus, the process of the present invention completely eliminates the use of a starting reactant having an aryl moiety. The present inventors have found that eliminating a starting material having an aryl moiety leads to the formation of a trialkyi phosphite compound that is substantially free of a phenolic impurity.

Thus, in this aspect, the present invention provides a compound trialkyi phosphite of Formula I:

O— P

\

O

R¹

I such that R¹ represents an alkyl moiety having 8 to 16 carbon atoms wherein said compound of formula I is substantially free of a phenolic impurity. The term "substantially free of" is intended herein to denote trialkyi phosphites being completely free of phenolic impurity or comprises less than 100 ppm of a phenolic impurity. The term "phenolic impurity" denotes all compounds that are derivable from phenol and/or includes a hydroxyl group substituted to a phenyl ring or a phenolic compound being more highly substituted than the starting triaryl phosphite compound.

The embodiments of the present invention are explained in the tables below.

The following examples are presented to define the invention more fully without any intention of being limited thereby. All percentages and ratios are by weight unless otherwise specified. EXAMPLE 1

Preparation of tri-isodecyl phosphite in the presence of sodium methoxide.

In a clean dry reaction flask, 316 gm of isodecanol was charged under N₂ atmosphere and stirred for 5 minutes. 0.45 gm of sodium methoxide was then added and stirred. The temperature was then raised to 75° C. 63 gm of trimethyl phosphite was then added to isodecanol in 0.5 hours while maintaining the temperature. The reaction temperature was then raised to 195-200° C and the reaction mass was stirred at the same temperature for 2 hours. During the process, methanol generated as byproduct was removed simultaneously. The reaction mass was cooled under N₂ atmosphere to 80-100° C while applying vacuum to recover the isodecanol. The reaction mass was then maintained at 190-200° C under 1-2 mm vacuum to remove the traces of isodecanol. The temperature was then allowed to come to 40° C under N₂, and the product was recovered after filtration.

Yield of the product: 82.47%

Phenolic content: NIL

Example 2 Preparation of tri-isodecyl phosphite without the use of sodium methoxide.

In a clean dry reaction flask, 316 gm of isodecanol was charged under N₂ atmosphere and stirred for 5 minutes. The temperature was then raised to 75° C. 63 gm of trimethyl phosphite was then added to isodecanol in 0.5 hours while maintaining the temperature. The reaction temperature was then raised to 195-200° C and the reaction mass was stirred at the same temperature for 2 hours. During the process, methanol generated as byproduct was removed simultaneously. The reaction mass was cooled under N₂ atmosphere to 80- 100° C while applying vacuum to recover the isodecanol. The reaction mass was then maintained at 190-200° C under 1 -2 mm vacuum to remove the traces of isodecanol. The temperature was then allowed to come to 40° C under N₂, and the product was recovered after filtration.

Yield of the product: 93.82%

Phenolic content: NIL Example 3

Preparation of tri-isodecyl phosphite: In a clean dry reactor, 2743 Kgs isodecanol was charged under N₂ atmosphere and stirred for 5 minutes. The temperature was then raised to 95° C. 542 Kgs of trimethyl phosphite was then added to isodecanol in such a way that the temperature was maintained between 95-98° C (total addition time 5 hrs.). The reaction temperature was then raised to 190°C - 200°C and the reaction mass was stirred at the same temperature for 2 hours. During the process, methanol generated as byproduct was removed and recovered by condensation simultaneously. The reaction mass was cooled under N₂ atmosphere to 80-100°C while applying vacuum to recover the traces of alcohol. The reaction mass was then maintained at 190-200°C under 1-2 mm vacuum to remove the last traces of isodecanol. The temperature was then allowed to come to 40°C under N₂, and the product was recovered after filtration.

Yield of the product. : 92%

Specific gravity at 25°C: 0.88-0.905

Refractive index at 25°C: 1.45-1.4610

Phenolic content: NIL

The following examples were also carried out using the process described above in examples 1-3.

Table 1

Sr.No. Formula Alkanol (gm) Reaction Recovered alkanol Yield gm

II (gm) conditions (%)

1 TMP; Isodecanol ; Addition of TMP at Methanol - 90 gm; 474

125 632 95-100° C in 5 isodecanol - 179 (94.42) hrs; stirring at 195- gm

207° C for 2 hrs.

2 TMP; Isodecanol ; Addition of TMP at Methanol - 90 gm; 471

125 632 70-80° C; stirring isodecanol - 179 (93.82) for 0.5 hrs; stirring gm

at 195-207° C for

2 hrs.

3 TMP; Isodecanol ; Addition of TMP at Methanol - 82 gm; 472 (94) 125 632 70-80° C; stirring Isodecanol - 181

for 9.5 hrs; stirring gm

at 195-207° C for

2 hrs.

4 TMP; Isotridecanol; Addition of TMP at Methanol - 95 gm; 583

125 800 80-140° C, stirring Isotridecanol - 237 (92.83) for 3 Hr 45 mins; gm

stirring at 195-

200° C for 2 hrs.

TMP: Referred herein is Trimethyl Phosphite

U.S.Pat.No. 3636145 discoses the process for preparing trialkyl phosphite, in high yield, high purity and at extremely rapid reaction rate, and by a process suitable for large scale production involving the transesterification of trimethyl phosphite and alkanol. The said reaction is conducted essentially in the presence of an alkaline catalyst and in the presence of non-azeotropic solvent. Surprisingly the inventors of the present invention have found that the yield of the final product is deteriorated in the presence of catalyst and/or a solvent. Table 2

It is evident from Table 2 that higher yield of the product was obtained when the reaction was carried out in the absence of alkaline catalyst. The reaction yield was higher even in the absence of the non-azeotropic solvent. Examples 4-14:

The below table shows that experiments are carried out using aikanol of Formula III having carbon chain ranging from C₈-C₁₆ and using trialkyl phosphite of Formula II which were selected from an alkyl moiety having C C₃ carbon atoms. The trialkyl phosphite was added to the aikanol at an elevated temperature of about 75°C -1 10°C, the reaction temperature was then raised to about 195°C -210°C, and stirred at the same temperature for about 2-4 hours to get the desired trialkyl phosphite. The respective trialkyl phosphites were obtained in more than 85% yield. It was observed that the reaction did not proceed with desired rate and in desired yield when higher alcohols like C₁₈ were used.

Table 3

TMP: Referred herein is Trimethyl Phosphite

TEP: Referred herein is Triethyl Phosphite

TIPP: Referred herein is Tri isopropyl Phosphite

Phenol content

All the samples prepared above were analyzed for their purity. It was found that Acid Number (in mgKOH/gm) varied from 0.0072-0.041. The specific gravity of the samples varied from 0.8866 to 0.8905. Surprisingly, the phenol content in all the prepared samples was found to be NIL.

The aforegoing reference has been made to components having known equivalents and then such equivalents are herein incorporated as if individually set forth. Accordingly, it will be appreciated that changes may be made to the above described aspects and embodiments of the invention without departing from the principles taught herein. Additional advantages of the present invention will become apparent for those skilled in the art after considering the principles in particular form as discussed and illustrated. Thus, it will be understood that the invention is not limited to the particular embodiments described or illustrated, but is intended to cover all alterations or modifications which are within the scope of the invention.

Claims

1. An improved process for the preparation of trialkyi phosphite of Formula O-R¹

\ /

O— P

\

o

R¹

said process comprising reacting trialkyi phosphite of Formula II

O— R

\ /

O— P

\

O

R

with alkanol R¹-OH of formula III such that R represents an alkyl moiety having 8 to 16 carbon atoms and R represents an alkyl moiety having 1 to 3 carbon atoms.

2. The process as claimed in claim 1 , wherein said trialkyi phosphite of formula II is reacted with the alkanol R¹-OH in the absence of a catalyst or in the absence of a solvent or in the absence of a catalyst and a solvent.

3. The process as claimed in claim 1 , wherein said trialkyi phosphite of formula II is added to said alkanol at a temperature range between 75°C-180°C.

4. The process as claimed in claim 3, wherein said alkyl phosphite is added to the alkanol of formula III over a period of 0.5-7 hrs.

5. The process as claimed in claim 1-4, wherein said alkyl phosphite and said alkanol are added in a mole ratio of 1 :3 to 1 :5.

6. The process as claimed in claim 1 , wherein the alkanol of formula III is selected from the group comprising isodecanol, isotridecanol, octanol, tetradecanol and hexadecanol.

7. The process as claimed in claim 1 , wherein the trialkyi phosphite of formula II is selected from the group comprising triethyl phosphite, trimethyl phosphite and tri- isopropylphosphite.

8. The process as claimed in claim 1 further comprising the step of recovering the alcoholic by-product R-OH of formula IV of the reaction by condensation.

An improved process for the preparation of trialkyi phosphite of Formula I: O-R¹

\ /

O— P

\

said process comprising:

(a) reacting trialkyi phosphite of Formula II

R o-

\ /

O— P

\

o

R with alkanol R¹-OH of formula III such that R¹ represents an alkyl moiety having 8 to 16 carbon atoms and R represents an alkyl moiety having 1 to 3 carbon atoms, by adding the compound of formula II to the alkanol R¹-OH at a temperature of between 75°C-180°C; (b) maintaining the reaction mass at least at a temperature above the boiling point of an alkanol having 1 to 3 carbon atoms for a predetermined period of time while simultaneously removing the alcoholic by-product R— OH generated during the reaction; and

(c) recovering the target compound of formula I by filtration.

10. The process as claimed in claim 9, wherein said trialkyl phosphite of formula II is reacted with the alkanol in the absence of a catalyst or in the absence of a solvent or in the absence of a catalyst and a solvent.

11. The process as claimed in claim 9, wherein said temperature above the boiling point of the alcoholic by-product is from 180°C to about 220°C.

12. The process as claimed in claim 9, wherein said predetermined period of time is from about 2 hours to about 4 hours.

13. The process as claimed in claim 9 comprising cooling the reaction mass obtained at the end of step (a) in an inert atmosphere before subjecting it to step (b).

14. An improved process for the preparation of trialkyl phosphite of Formula I:

R .1

O— R

\ /

O— P

o

R

said process comprising:

(a) reacting trialkyl phosphite of Formula II R O— R

\ /

O— P

\

o

R

II with alkanol R¹-OH of formula III such that R¹ represents an alkyl moiety having 8 to 16 carbon atoms and R represents an alkyl moiety having 1 to 3 carbon atoms, by adding the compound of formula II slowly over a period of at least 0.5 hours to the alkanol R¹-OH at a temperature of between 75°C-180°C, and subsequent to the complete addition of the compound of formula II to said alkanol;

(c) optionally, cooling the reaction product under an inert atmosphere;

(d) heating the cooled reaction product to 190-200°C for a sufficient period of time at 1 -2 mm vacuum; and

(e) cooling the reaction product to a temperature of about 40°C and recovering the compound of formula I by filtration.

15. The process as claimed in claim 14, wherein said trialkyi phosphite of Formula II is added to the alkanol of Formula III at an elevated temperature of about 75°C -180°C over a period of about 0.5 hours to about 6 hours.

16. The process as claimed in claim 14, wherein said trialkyi phosphite of formula II is reacted with the alkanol in the absence of a catalyst or in the absence of a solvent or in the absence of a catalyst and a solvent.

17. The process as claimed in claim 14, wherein said temperature above the boiling point of an alkanol having 1 to 3 carbon atoms is from about 195°C -210°C.

18. The process as claimed in claim 14, wherein the reaction mass is maintained at said temperature for about 2 to about 4 hours.

19. TrialkyI phosphite of Formula I:

O— P

\

O

R¹

I such that R represents an alkyl moiety having 8 to 16 carbon atoms wherein said compound of formula I is substantially free of a phenolic impurity.

20. TrialkyI phosphite of formula I as claimed in claim 18, wherein said compound of formula I is completely free of a phenolic impurity.

21. TrialkyI phosphite of formula I as claimed in claim 19, wherein said compound of formula I comprises less than 100 ppm of a phenolic impurity. 22. An improved process for the preparation of trialkyi phosphite _. of Formula I substantially as described herein with reference to the examples.