Organic compounds -- part of the class 532-570 series – Organic compounds – Phosphorus esters
Reexamination Certificate
2001-02-08
2002-06-11
Higel, Floyd D. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Phosphorus esters
Reexamination Certificate
active
06403820
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process for producing a phosphoric ester of low acid value. More particularly, it relates to a process for obtaining a phosphoric ester having a low acid value and excellent physical properties, such as heat resistance, storage stability, and hydrolysis resistance. The phosphoric ester obtained is useful as a plasticizer or a flame retardant for synthetic resins.
BACKGROUND ART
It is known that phosphoric esters are synthesized by processes comprising dehydrochlorination reaction between phosphorus oxychloride and an alcohol or a phenol. Because these processes do not accomplish perfect esterification, however, the resulting phosphoric esters have an acid value ascribed to a phosphoric acid radical or an acid chloride derived from the starting material. Phosphoric esters having an acid value are not satisfactory in heat resistance, hydrolysis resistance, and storage stability. When exposed to high temperature, they undergo considerable coloration and, when added to a resin as a flame retardant, invite reductions of the physical properties of the resin and coloration of the resin. Phosphoric esters having an acid value have another problem that they corrode a mold for molding the resin. To avoid these problems, it is desirable to control the acid value of phosphoric esters to 1.0 (mg/KOH) or smaller.
In order to obtain a phosphoric ester of low acid value, it has been a generally followed practice that a phosphoric ester is purified by neutralization with a basic substance, for example, in a wet process using an alkali metal hydroxide such as sodium hydroxide or in a dry process using an alkali metal compound such as calcium carbonate or magnesium hydroxide, followed by washing with water or distillation.
However, where a phosphoric ester having a high viscosity is purified, the wet neutralization with an alkali metal hydroxide meets difficulty in separation between an aqueous layer and an oily layer, which not only needs a long process time but results in incorporation of a trace amount (e.g., several ppm to several hundreds of ppm) of the alkali metal into the oily layer separated. If any alkali metal remains in the purification step of phosphoric esters, it adversely affects the heat resistance and hydrolysis resistance of the phosphoric esters and causes reductions of physical properties of some kinds of resins, such as a change in composition.
For the purpose of reducing the residual alkali metal content, a phosphoric ester may be diluted with an organic solvent to reduce the viscosity or subjected to salting out to improve separation into an aqueous layer and an oily layer. Nevertheless these manipulations still allow a trace amount of the alkali metal to remain in the product layer. Therefore, removal of the alkali metal is usually conducted by washing several times. The same problem arises in the case of dry neutralization.
Some phosphoric esters are not suitable to be wet neutralized with alkali metals because they get emulsified on wet neutralization and cannot be separated into an aqueous layer and a product layer.
Purification of phosphoric esters by distillation is also adopted. Purification by distillation is freed of the above-described problem of alkali metal remaining with respect to phosphoric esters having a low molecular weight but requires a distillation apparatus having a high fractionation effect, such as a rectifier, in order to remove impurities other than alkali metals which will reduce the physical properties of phosphoric esters (for example, heat resistance, storage stability and hydrolysis resistance). There is another problem that distillation purification is more difficult with a phosphoric ester having a larger molecular weight. Further, distillation purification has a poor yield, resulting in an increased cost of the phosphoric ester.
Japanese Patent Laid-Open No. 67685/96 discloses a process of producing a phosphoric ester, which comprises treating a crude phosphoric ester with an epoxy compound, followed by heat treatment in the presence of water. However, this process involves heat treatment in the presence of water (hereinafter “water/heat treatment”) after epoxy treatment, which makes the steps complicated. Further, should the water/heat treatment be insufficient, the product is deteriorated in both acid value and hue. Even when the water/heat treatment is sufficient, the product is unsatisfactory in hue and storage stability.
Accordingly, an object of the present invention is to provide a process for producing a phosphoric ester having a low acid value and excellent in heat resistance, hydrolysis resistance and storage stability.
DISCLOSURE OF THE INVENTION
The above object of the invention is accomplished by a process for producing a low acid value phosphoric ester characterized by treating a phosphoric ester having an acid value with an organic ortho-acid ester.
BEST MODE FOR CARRYING OUT THE INVENTION
The process of producing a low acid value phosphoric ester according to the present invention will be described in detail.
The phosphoric esters which can be treated by the process of the present invention are known in the art usually for use as plasticizers and/or flame retardants for resins. As far as they have such acid values as have to be reduced, the kinds, the process of making and the like are not particularly limited. Typical examples of the phosphoric esters used in the present invention are those represented by general formula (1):
wherein R
1
, R
2
, R
4
, and R
5
, which may be the same or different, each represent an alkyl group having 1 to 10 carbon atoms or an aromatic group represented by general formula (2) shown below; R
3
represents a divalent aromatic group represented by general formula (3) or (4) shown below; and n represents 0 to 30.
wherein A
1
and A
2
each independently represent a hydrogen atom or an alkyl group having 1 to 10 carbon atoms.
wherein A
3
, A
4
, A
5
, A
6
, A
7
, and A
8
each independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a cycloalkyl group, an aryl group, an alkoxy group, a nitro group, a halogen atom or a cyano group; and B represents a single bond, divalent S, a sulfone group, or an alkylidene or alkylene group having 1 to 5 carbon atoms.
In general formulae (1) and (2), the alkyl group as represented by R
1
, R
2
, R
4
, R
5
, A
1
, and A
2
includes methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, amyl, tert-amyl, hexyl, 2-ethylhexyl, n-octyl, nonyl, and decyl. The alkyl group having 1 to 4 carbon atoms as represented by A
3
, A
4
, A
5
, A
6
, A
7
, and A
8
includes methyl, ethyl, propyl, butyl, isobutyl, sec-butyl, and tert-butyl. The cycloalkyl group includes cyclohexyl. The aryl group includes phenyl, cresyl, xylyl, 2,6-xylyl, 2,4,6-trimethylphenyl, butylphenyl, and nonylphenyl. The alkoxy group includes methoxy, ethoxy, propoxy, and butoxy. The halogen atom includes a fluorine atom, a chlorine atom, and a bromine atom. The group represented by general formula (2) includes phenyl, cresyl, xylyl, 2,6-xylyl, butylphenyl, and nonylphenyl. The alkylidene group having 1 to 5 carbon atoms as represented by B includes ethylidene and 2,2′-propylidene. The alkylene group includes methylene, ethylene, trimethylene, and tetramethylene.
The acid value of a phosphoric ester to which the process of the present invention is applied includes one attributed to the acid radical remaining after the synthesis of the phosphoric ester and one attributed to the acid radical produced during storage.
The above-described phosphoric esters which can be used in the process of the present invention can be obtained by methods known in the art. They are usually obtained by allowing phosphorus oxychloride to react with an appropriate alcohol or phenol in the absence or presence of a catalyst such as a Lewis acid (e.g., aluminum chloride, magnesium chloride or titanium tetrachloride). Specifically, a phosphoric triester is produced by allowing phosphorus oxychloride to react with a phenol in the
Hayashi Kazuhiko
Kamimoto Tetsuo
Kimura Ryoji
Murase Hisashi
Asahi Denka Kogyo Kabushiki Kaisha
Higel Floyd D.
Sackey Ebenezer
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