Process for preparing ester compounds

Details Process for preparing ester compounds Process for preparing ester compounds

1999-12-03

2001-03-20

Ambrose, Michael G. (Department: 1626)

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

Organic compounds

Phosphorus esters

C558S094000, C558S102000

Reexamination Certificate

active

06204404

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a process for preparing ester compounds. More particularly, it relates to a process for preparing phosphoric ester compounds of high purity containing less coloring components without using an antioxidant.
RELATED ART
Phosphoric ester compounds among ester compounds have been used not only as additives to various resins such as a plasticizer, a flame-retardant and a resin modifier but also as a lubricant and a stabilizer. On the other hand, according to recent technologic innovations in automobile industry, electronics and so forth, higher performances have been kept demanded with resins. From such background, phosphoric ester compounds having highly improved basic performances are required as the additives to resins, and a development of a new method for preparing such phosphoric ester compounds is requested by its industry.
The ester compounds are generally produced by reacting a hydroxy compound with an acid or its reactive derivative in the presence or absence of a condensating agent such as sulfuric acid and p-toluenesulfonic acid. However, when the reactivity of these starting materials in the aforesaid reaction is not sufficient, the reaction needs to be conducted at a high temperature. In such case, particularly in the case where the ester compound is to be produced in industrial scale and an impurity is contained in the hydroxy compound of the starting material, it causes the coloration of the desired ester compound.
To solve such problem, for example, an antioxidant is added into the reaction system in order to prevent an oxidation of an impurity contained in the hydroxy compound as the starting material. Further, various antioxidants are put into market. This suggests that addition of the antioxidant is an effective means for preventing the coloration of the ester compound.
However, antioxidants on the market are expensive and a cost for product rises when antioxidants are used in preparing the ester compound, which causes economical disadvantage. Moreover, it is a difficult and complicated work to select an optimum condition for using antioxidants.
Japanese Unexamined Patent Publication No. SHO 51 (1976)-88944 discloses a treatment method for preventing coloration of alkyliphenyl phosphates. This publication discloses addition of an effective amount of phosphorus trichloride to an alkylated mixture in the case of producing an alkylphenyl phosphate by adding an olefin to phenol, then adding phosphorus oxychloride thereto and reacting the mixture in the presence of Friedel-Crafts catalyst under warming.
Further, this publication also describes that phenols having alkyl groups at both ortho positions with respect to hydroxyl group, that is, hindered phenols become quinones through oxidation in the presence of air, and that these phenols cause coloring of the ester compounds when these phenols are used for synthesizing the ester compounds.
Another problem in addition to the above-described coloration is as follows. That is, purification by a crystallization method is regarded as essential for preparing tris(tribromoneopentyl)phosphate as phosphoric ester compound of high quality. However, the crystallization method is complicate for operation, requires an apparatus of a large scale, and results in much loss of product. Therefore, a use of the crystallization method is disadvantageous in industrial production of tris(tribromoneopentyl)phosphate, resulting in an increase of the cost for product.
DISCLOSURE OF THE INVENTION
It is a subject of the present invention to provide a process for preparing phosphoric ester compounds of high purity containing less coloring components without using an antioxidant.
That is, according to the present invention, provided is a process for preparing an ester compound comprising reacting a halogen-substituted aliphatic hydroxy compound or aromatic hydroxy compound with a phosphorus oxyhalide or phosphorus pentahalide in the presence of 0.005 to 10 mol % of a phosphorus trihalide with respect to the said hydroxy compound to obtain a phosphoric ester compound.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The halogen-substituted aliphatic hydroxy compounds or the aromatic hydroxy compounds to be used in the present invention are not particularly limited. However, even if the hydroxy compounds contain impurities resulted from a preparing process thereof (for example, aldehydes or the like), such hydroxy compounds may suitably be used for the process of the present invention.
Further, in the case of synthesizing general-purpose phosphoric ester compounds used as additives to resins, halogen-substituted aliphatic hydroxy compounds of 4 to 20 carbon atoms or aromatic hydroxy compounds of 6 to 20 carbon atoms may be used.
The halogen-substituted aliphatic hydroxy compounds are aliphatic hydroxy compounds substituted by a halogen atom such as chlorine atom, bromine atom or the like. Specifically, chloromethyl alcohol, 2-chloroethyl alcohol, 1-chloro-2-propanol, 3-bromo-2,2-dimethyl-1-propanol [bromoneopentyl alcohol], 2-bromomethyl-3-bromo-2-methyl-1-propanol [dibromoneopentyl alcohol] and 2,2-di(bromomethyl)-3-bromo-1-propanol [tribromoneopentyl alcohol] are mentioned.
In the present invention, “the aromatic hydroxy compounds” mean mono- or polyvalent phenols which may be substituted by other substituent than alkyl group. Specific examples are given as follows;
aromatic hydroxy compounds such as; monovalent phenols such as phenol, (2-, 3-, or 4-)phenylphenol [oxybiphenyl] and (1- or 2-)naphthol; and substituted phenols such as chlorophenol, dichlorophenol, trichlorophenol, bromophenol, dibromophenol, tribromophenol and nitrophenol; and
aromatic dihydroxy compounds such as; polyvalent phenols such as catechol, resorcinol (resorcin), hydroquinone, pyrogallol and fluloroglucinol; and bisphenols such as 2,2-bis(4′-oxyphenyl)propane [bisphenol A], bis(4-hydroxyphenyl) sulfone [bisphenol S] and biphenyldiol.
In the case where the above-mentioned hydroxy compounds are used solely, phosphoric triester compounds can be obtained. Also when two or more kinds of the hydroxy compounds are reacted stepwise, mixed phosphoric ester compounds and condensed phosphoric ester compounds can be obtained.
Among the above-mentioned hydroxy compounds, the halogen-substituted aliphatic hydroxy compounds such as tribromoneopentyl alcohol and the aromatic hydroxy compounds such as phenol, resorcinol and hydroquinone are particularly preferable.
In the process of the present invention, the phosphorus oxyhalide or phosphorus pentahalide is used. Examples of the phosphorus oxyhalide are phosphorus oxychloride and phosphorus oxybromide. Examples of the phosphorus pentahalide are phosphorus pentachloride and phosphorus pentabromide. Among them, in the case where phosphoric ester compounds are produced industrially, phosphorus oxychloride can generally and preferably be used.
The present invention is characterized by adding the phosphorus trihalide when phosphoric ester compounds are produced using the above-described starting materials.
As the phosphorus trihalide, phosphorus trichloride and phosphorus tribromide are preferable, and can be used just as they are on the market or after purification as the needs arise. Further, in the case of industrial production of the phosphoric ester compounds, phosphorus trichloride can generally and preferably be used. Additionally, phosphorous acid can be used instead of the phosphorus trihalide.
The addition amount of the phosphorus trihalide varies in accordance with the types of the hydroxy compounds as the starting materials and the combination with the phosphorus oxyhalide or the phosphorus pentahalide, but generally, the amount of the phosphorus trihalide with respect to the hydroxy compound is 0.005 to 10 mol %, preferably 0.01 to 5 mol %, and more preferably 0.02 to 2 mol %.
When the above-mentioned addition amount is less than 0.005 mol %, it is not preferable because the prevention effect for coloration is not suff

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