Process for the preparation of condensed phosphoric esters

Details Process for the preparation of condensed phosphoric esters Process for the preparation of condensed phosphoric esters

2002-04-15

2003-08-12

McKane, Joseph K. (Department: 1626)

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

Organic compounds

Phosphorus esters

C568S016000

Reexamination Certificate

active

06605736

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a process for preparing a condensed phosphoric ester. More specifically, the present invention relates to a process for preparing a condensed phosphoric ester having a low content of volatile components, which is excellent as a flame retardant for resins.
BACKGROUND ART
Conventionally, various types of flame retardants are used for flame retardation of inflammable plastic materials, for example, halogen compounds such as decabromobiphenylether and tetrabromobisphenol A, and low molecular weight phosphorus compounds such as cresyl diphenyl phosphate and triphenyl phosphate.
Today, resin compositions are required to be non-halogenic from an environmental point of view, for example, due to the hazardous effects of dioxin. Flame retardants containing heavy metals cause problems due to their toxicity. Under these circumstances, phosphorus-based flame retardants have now become a target of attention. Among the phosphorus-based flame retardants, aromatic phosphoric ester-based flame retardants are a target of attention for their effectiveness especially in the applications of engineering plastics such as PC/ABS alloys and modified PPE since they have little adverse influence on the environment as well as superb physical properties. Actually, the industrial demand for phosphorus-based flame retardants, especially aromatic phosphoric ester-based flame retardants, is good and continues to increase at a high rate.
However, engineering plastics are molded at a very high temperature and therefore the following problems have occurred. When a low molecular weight monomer-type phosphoric ester such as triphenyl phosphate (TPP) or tricresyl phosphate (TCP) is used, the monomer-type phosphoric ester is thermally decomposed, bleeds out or volatizes during the molding process, which causes defective molding, contamination of the molds or the like.
It is known that use of a high molecular weight condensed phosphoric ester as a flame retardant is effective for avoiding these problems.
For example, Japanese Laid-Open Publication No. 63-227632 discloses a process for preparing a condensed phosphoric ester. According to this process, a condensed phosphoric ester is prepared by reacting a dihydroxy compound such as resorcin, hydroquinone, bisphenol A or the like with phosphorus oxychloride, thereafter removing unreacted phosphorus oxychloride, and then reacting the resultant product with phenol, cresol, xylenol or the like.
This process, however, has the problem that a significant amount, specifically about 4 to 7% by weight of monomer-type phosphoric ester is contained as an impurity, especially when the production is performed on an industrial scale. Therefore, the monomer-type phosphoric ester still volatizes or bleeds out, which causes defective molding, contamination of the molds or the like. As such, it is difficult to obtain a satisfactory molding efficiency.
More specifically, for example, Japanese Laid-Open Publication No. 63-227632 reports, in an example thereof, that a product having a content of a low molecular weight phosphate of equal to or less than 2% by weight was obtained in a small-scale test. However, when this technology is used for large-scale synthesis, the monomer-type phosphoric ester content is about 4 to 7% by weight.
Accordingly, production of a condensed phosphoric ester, especially on an industrial scale, requires that many conditions including the ratio of materials, reaction temperature, and reaction time should be carefully selected in order to reduce the content of the monomer-type phosphoric ester as an impurity.
Until today, details of such conditions have not been studied, and thus the relationship between the conditions and the amount of impurity in the resultant product has not been clarified at all. Especially regarding the ratio of materials, ratios obtained by theoretical calculations based on stoichiometry have been considered to be most efficient in order to reduce the impurity. Therefore, the ratios obtained by stoichiometric calculations have been loyally adopted.
Problems to be Solved by the Invention
An objective of the present invention is to solve the above-described problems by providing a process for stably preparing a condensed phosphoric ester formed from a low molecular weight monomer-type phosphoric ester and having a low content of impurities.
DISCLOSURE OF THE INVENTION
Means for Solving the Problems
The present inventors completed the present invention as a result of performing active studies based on the knowledge that the reaction between condensed phosphoric ester produced by the below-mentioned third step and an unreacted monophenol-based compound causes interesterification and thus produces a monomer-type phosphoric ester as an impurity.
The present invention provides the following processes.
1. A process for preparing a condensed phosphoric ester, comprising:
a first step of reacting a phosphorus oxytrihalide with a bisphenol-based compound to prepare a phosphorohalidate;
a second step of removing unreacted phosphorus oxytrihalide remaining after the first step; and
a third step of reacting the phosphorohalidate with a monophenol-based compound in a stoichiometrically excess amount with respect to the phosphorohalidate,
wherein the amount of the monophenol-based compound in the third step is greater, by equal to or less than 2 mol %, than the theoretically necessary amount for turning the entire amount of the phosphorohalidate into the condensed phosphoric ester.
2. A process according to aforementioned item 1, wherein the amount of the phosphorus oxytrihalide is equal to or greater than 3.6 mol times with respect to the amount of the bisphenol-based compound.
3. A process according to aforementioned item 1 or 2, wherein the bisphenol-based compound is bisphenol A.
4. A process according to any one of aforementioned item 1, 2 or 3, wherein the condensed phosphoric ester is 2,2-bis{4-[bis(phenoxy)phosphoryl]oxyphenyl}propane.
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be specifically described.
First Step
In the first step, a phosphorus oxytrihalide and a bisphenol-based compound are reacted, thereby preparing a phosphorohalidate.
In the present invention, a phosphorohalidate refers to a compound represented by the following formula (I):
(where X represents a halogen atom, R
5
and R
6
are the same as or different from each other and represent a hydrogen atom or an alkyl group containing 1 to 3 carbon atoms; R
7
represents —C(CH
3
)
2
—, —SO
2
— or CH
2
—; n represents an integer from 1 to 10; and n
1
and n
2
each represent an integer from 0 to 4.)
Examples of the phosphorus oxytrihalide include phosphorus oxychloride and phosphorus oxybromide.
A bisphenol-based compound refers to a compound containing two phenol groups (—PhOH) in a molecule. Specific examples of the bisphenol-based compound include bisphenol A, bisphenol S, and bisphenol F. A bisphenol A derivative is preferable, and bisphenol A is especially preferable.
The Bisphenol A derivative refers to bisphenol A or a derivative thereof, which is represented by the following formula (A):
(where R
5
and R
6
are the same as or different from each other and represent an alkyl group containing 1 to 3 carbon atoms; and n
1
and n
2
each represent an integer from 0 to 4.)
The usable amount of the phosphorus oxytrihalide and the usable amount of the bisphenol-based compound are not specifically limited.
According to general technical knowledge, it is not preferable that the amount of the phosphorus oxytrihalide is greater than a stoichiometrical reaction amount which is calculated from the amount of the bisphenol-based compound, i.e., 2.0 mol times the amount of the bisphenol-based compound. The reason is that the amount of remaining unreacted phosphorus oxytrihalide necessarily increases, which complicates the operation for recovering the unreacted phosphorus oxytrihalide.
According to the present invention, the amount of the phosphorus oxytrihalide is preferably equal to or

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