Processes for producing triaryl phosphite

Details Processes for producing triaryl phosphite Processes for producing triaryl phosphite

2002-08-02

2003-11-25

McKane, Joseph K. (Department: 1626)

Organic compounds -- part of the class 532-570 series

Organic compounds

Phosphorus esters

Reexamination Certificate

active

06653494

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to processes for producing triaryl phosphite. More particularly, this invention relates to processes for producing large quantities of hindered triaryl phosphite.
BACKGROUND OF THE INVENTION
The commercial use of triaryl phosphites in relation to latex is well known in the art. Triaryl phosphites containing alkyl-substituted phenyl rings are found to be effective synthetic latex stabilizers and are preferred over simpler aryl phosphites for several various reasons. One such reason is that it is non-discoloring. Yet another reason is that it imparts fewer odors to the finished polymer. Further, it is also more resistant to hydrolysis, which makes its addition possible to the latter as aqueous emulsions.
These important commercial uses of the triaryl phosphites have given rise to the development of research in this area intended to produce the same at cost efficient manners.
The preparation of ortho tertiary alkyl aryl phosphites is more difficult than the preparation of phosphites containing less hindered substituents. In fact it has been proved that it impossible to obtain acceptable yields of good quality hindered aryl phosphites in the absence of heterocyclic catalysts.
The following diagram illustrates the preparation of tris dietary alkyl aryl phosphite of general formula P(OR)
3
by reacting a di alkyl substituted phenol of formula ROH where R represents C
6
H
3
R
a
R
b
.
R
a
is tertiary alkyl, R
b
is lower alkyl or tertiary alkyl.
Various processes for the preparation of triaryl phosphite have been disclosed in prior patent disclosures. The U.S. Pat. No. 3,533,989 to Wescott Jr. discloses a process for the preparation of triaryl phosphite. According to this patent, certain basic materials such as triethylamine have been used in stoichiometric quantities as a hydrogen chloride scavenger so as to give yields as high as 80% of the theory of the desired product. It is not desirable to use a stoichiometric quantity of triethylamine in the preparation of the cited phosphite compound.
U.S. Pat. No. 4,312,818 to Maul et al. describes a process for producing triaryl phosphite from phosphorous trihalides and alkyl substituted phenol in the ring of formula ROH of where R=C
6
H
3
R
a
R
b
(R
a
is tertiary alkyl, R
b
is lower alkyl or tertiary alkyl) with the use of specific phosphorous-, nitrogen and/or sulfur containing compounds as catalysts has been disclosed.
U.S. Pat. No. 4,440,696 to Maul et al. describes another process for producing triaryl phosphite. According to this process, the catalyst is selected from the group consisting of an amide of a carboxylic acid.
The use of alkylated triaryl phosphites as stabilizers against thermo-oxidative and light-induced degradation of organic material has been disclosed in U.S. Pat. No. 4,321,218 to Rasberger et al.
U.S. Pat. No. 4,360,617 to Muller et al. describes the use of triaryl phosphite in combination with phenolic antioxidants for stabilizing organic polymers. The corresponding German Patent No. 2,702661 also discloses stabilizer systems of triaryl phosphite and phenols.
European Patent Application EP0455092 to Gregory et al. describes suspensions of polymer additives in functional fluids and thermoplastic resin compositions containing the same.
A process for the preparation of tris (2,4-ditertiary butyl phenyl) phosphite involving the heating of 0.8 mole of required phenol with 0.2 mole of PCl
3
for 1 hour at 80° C. and for 8 hour at 200° C. has been disclosed in German Patent No. 2,046,200.
German Patent No. 2,940,620 to Mayer et al. describes the preparation of tris (2,4-ditertiary butyl phenyl) phosphite by treating corresponding phenol with PCl
3
at 50° C. and then at 130° C. The process disclosed in this case requires a temperature level of 130° C. for a continuous period. Also the process requires evolution of hydrogen chloride gas which requires scrubbing.
SUMMARY OF THE PRESENT INVENTION
An improved one pot process for the preparation of sterically hindered triaryl phosphites is provided, which produce high yields and quality products, which are free of disadvantages and complications associated with prior art processes.
It is an aspect of the invention to provide for an improved process for the manufacture of hindered aryl phosphites by mixing a substantially stoichiometric amount of 2,4-dialkyl phenol with a phosphorous trihalide in methylene chloride with a relatively large amount of pyridine. Reaction is carried out in at 0-5° C. which takes 1 h for the completion and one hour for isolation in isopropanol.
It is well recognized to the persons skilled in the art that the amount of Lewis base used in synthesis of sterically hindered triaryl phosphites have traditionally been only several mole percent, or a fraction of a mole percent, compared to aryl reagents. However, according to the present invention, the use of a relatively large amount of Lewis base results in the ability of the reaction to go to its completion at a faster rate, and at a lower temperatures. This unexpected result has a technological and economic advantage over the prior art. Large amount of Lewis base means 10 mole percent or more of the Lewis base compared to the substituted phenol, preferably over 20 mol %, more preferably over 50 mol %, and most preferably the amount of the Lewis base is about stoichiometrically equivalent to the substituted phenol.
In yet another aspect a process for producing triaryl phosphite of (Structure 2) has been provided wherein R
a
is tertiary alkyl, R
b
is lower alkyl or tertiary alkyl, the process comprises reacting PCl
3
with 2,4-dialkyl phenol of formula ROH where R=C
6
H
3
R
a
R
b
(R
a
is tertiary alkyl, R
b
is lower alkyl or tertiary alkyl) (Structure 1) wherein the reaction is carried out by adding PCl
3
to a solution of 2,4-dialkyl phenol in methylene chloride and pyridine at 0-5° C. under nitrogen atmosphere over a period of one hour. After methylene chloride has been distilled out and isopropanol has been added to precipitate white crystalline solid, which is filtered out and is washed with cold methanol.
In still another aspect, the invention provides for a process of reacting 2,4-ditertiary butyl phenol with PCl
3
to produce tris-(2,4-ditertiaryl butyl phenyl) phosphite as illustrated in Structure 3.
In yet another aspect, the invention provides for a process of reacting 2,4-di tertiary amyl phenol with PCl
3
to produce tris(2,4-ditertiaryl amyl phenyl)phosphite as illustrated in Structure 4.
In still another aspect, the invention provides for a process of reacting 2-tertiary butyl-4-methyl phenol with PCl
3
to produce tris (2-tert butyl-4-methyl phenyl) phosphite as illustrated in Structure 5.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates a novel process for the production of tris (2,4-ditertiary butyl phenyl) phosphite, tris (2,4-ditertiary amyl phenyl) phosphite and 2-tertiary butyl-4-methyl phenyl phosphite especially in large scale manufacturing. Large scale manufacturing requires the production of title compound in a cost efficient manner. This led to the enquiry into producing the title compound with lesser impurity and with a better yield. Also one of the concerns was to achieve the desired lower temperature so as to have high yield with shortened reaction time.
The hydrogen chloride formed in the reaction PCl
3
with the phenol is removed by one of the following methods:
by removing HCl time to time by applying vacuum,
by passing CO
2
gas,
by refluxing at high temperatures,
by using a Lewis base.
All the above methods are laborious and time consuming. Therefore they are not suitable for commercial production of the title compound. The method employing the use of a Lewis base is more suitable in this case. The bases that can be conveniently used are triethylamine, trimethylamine and pyridine. Results were found to be good in the case of pyridine as base compared with the other two.
A process for producing triaryl phosphite has been provided. The process involves making triaryl phosphite of formula

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