Organic compounds -- part of the class 532-570 series – Organic compounds – Phosphorus esters
Reexamination Certificate
2002-01-24
2004-03-16
Gerstl, Robert (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Phosphorus esters
C558S147000
Reexamination Certificate
active
06706907
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of purifying an organic phosphoric ester which is useful as a plasticizer or a flame retardant for a synthetic resin. More particularly, it relates to a purification method for obtaining an organic phosphoric ester which has a low acid value and is excellent in heat resistance, storage stability and hydrolytic resistance.
BACKGROUND ART
Organic phosphoric esters are synthesized by a method for reacting phosphorus oxychloride with an alcohol or phenol under dehydrochlorination, or the like. However, since it is difficult to complete the esterification by this synthesis method, the synthesized organic phosphoric esters show some acid value due to phosphoric acid and chloride derived from the starting materials.
Since the substances that generate the acid value have a bad influence on physical properties such as heat resistance, hydrolytic resistance and storage stability of the organic phosphoric esters, crude organic phosphoric esters are purified to remove the substances generating the acid value, thereby reducing the acid value of the organic phosphoric esters. The purification treatment may be carried out by neutralization using a basic substance, e.g., by wet neutralization using alkali metal hydroxide such as sodium hydroxide or dry neutralization using an alkali earth metal compound such as calcium carbonate and magnesium hydroxide, followed by washing with water, or by distillation.
However, in the case where a highly viscous organic phosphoric ester is subjected to the wet neutralization using alkali metal hydroxide, separation of an aqueous phase and an oily phase is not performed well and takes time. Moreover, there is a problem in that a relatively large amount (e.g., several tens to hundreds of ppm) of alkali metal remains in the separated oily phase. The remaining alkali metal is not preferable because it causes a bad influence on the heat resistance and the hydrolytic resistance of the organic phosphoric ester.
In order to reduce the amount of alkali metal remaining in the organic phosphoric ester, there has been proposed a method of diluting the highly viscous organic phosphoric ester with an organic solvent to reduce the viscosity or a method of salting-out the highly viscous organic phosphoric ester, thereby facilitating the separation of the aqueous phase and the oily phase. However, even in these methods, the alkali metal cannot be eliminated completely and washing with water needs to be carried out many times to get rid of the yet remaining alkali metal. The problem of the remaining alkali metal is also involved in the dry neutralization.
With respect to some organic phosphoric esters, the whole mixture including the crude organic phosphoric ester may be emulsified during the wet neutralization using alkali metal hydroxide, so that the aqueous phase and the oily phase may not be separated well.
In the case of purification by distillation, low molecular weight organic phosphoric esters are purified without suffering from the above-described problem of the remaining alkali metal. However, it is difficult to conduct the purification treatment itself for high molecular weight organic phosphoric esters.
There are other impurities than the alkali metal causing a bad influence on the physical properties such as heat resistance, hydrolytic resistance and storage stability of the organic phosphoric ester. Examples of such impurities include unreacted compounds in which the esterification is not completed, compounds in which phosphoric acid or alcohols and a reaction catalyst are combined and other impurities in a small amount derived from the starting materials.
To eliminate these impurities, only the above-described purification treatment by neutralization or distillation is insufficient and a purification apparatus of high fractionation efficiency is required. However, there is a problem in that the apparatus is expensive and reduces the product yield, thereby increasing the cost.
To solve the problem, there has been developed a purification method of the organic phosphoric ester by treating a crude organic phosphoric ester with an epoxy compound, subjecting the resulting product to thermal treatment in the presence of water, washing the obtained product with water, and then removing residual water (see Japanese Unexamined Patent Publication No. Hei 8(1996)-67685).
According to the method, impurities in the organic phosphoric ester are reacted with the epoxy compound, the reaction product is hydrolyzed in water to convert into a water-soluble compound and the obtained water-soluble compound is removed by washing with water, thereby removing the impurities in the organic phosphoric ester. In this method, it is important to selectively hydrolyze only the compound obtained by the reaction with the epoxy compound. If the hydrolysis is insufficient, the acid value of the organic phosphoric ester cannot be reduced. To the contrary, if the hydrolysis is carried out excessively, the organic phosphoric ester itself to be purified is also hydrolyzed.
Accordingly, in order to purify the organic phosphoric ester efficiently by the above-described method, it is necessary to set the optimum conditions such that the organic phosphoric ester itself is not hydrolyzed during the thermal treatment. The optimum conditions must be established in view of a kind and amount of the organic phosphoric ester, a kind of the epoxy compound, conditions of the thermal treatment (e.g., temperature, time, water amount and the like), as well as an apparatus used, which requires complicated work. Especially, in the case of purifying a large quantity of the organic phosphoric ester in an industry scale, there has been a problem in that the treatment conditions are difficult to establish and thus the acid value of the organic phosphoric ester cannot be reduced sufficiently.
DISCLOSURE OF INVENTION
To solve the above-mentioned problems, the present invention is intended to provide a method of purifying an organic phosphoric ester for stably obtaining the organic phosphoric ester having a low acid value and being excellent in heat resistance, hydrolytic resistance and storage stability, the method being free from the influence by the kind and amount of the organic phosphoric ester as well as the treatment conditions.
According to the present invention, provided is a method of purifying an organic phosphoric ester characterized in that the purification is carried out by treating a crude organic phosphoric ester with an epoxy compound and treating the treated organic phosphoric ester with an alkaline aqueous solution.
BEST MODE FOR CARRYING OUT THE INVENTION
The organic phosphoric esters to be treated by the method of the present invention are compounds that are known in the art and generally used as a plasticizer and/or a flame retardant for a resin. However, they are not particularly limited as long as they contain impurities generated through the synthesis thereof.
The organic phosphoric esters are represented by the general formula (I):
wherein n is an integer of 0 to 30, R
1
, R
2
, R
3
and R
4
, the same or different, are an aliphatic hydrocarbon residue or an aromatic hydrocarbon residue when n is 0 or an aromatic hydrocarbon residue when n is 1 to 30, and R
5
is a bivalent organic group.
The aliphatic hydrocarbon residue represented by R
1
, R
2
, R
3
and R
4
in the general formula (I) may preferably be a straight-chain or branched-chain alkyl group having a carbon number of 8 to 18. Examples thereof include 2-ethylhexyl, n-octyl, sec-octyl, decyl, dodecyl, hexadecyl, octadecyl and the like.
The aromatic hydrocarbon residue may preferably be an aryl group having a carbon number of 6 to 15. Examples thereof include phenyl, cresyl, xylyl, 2,6-dimethylphenyl, 2,4,6-trimethylphenyl, butylphenyl, nonylphenyl and the like.
The bivalent organic group of R
5
may be an alkylene group, an arylene group or the like. Examples thereof include an alkylene group such as methylene, ethylene, trimethylene, propylene, tetramethylene and ethylethylene,
Hirao Kiyoharu
Oda Masasuke
Daihachi Chemical Industry Co. Ltd.
Gerstl Robert
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