Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Reexamination Certificate
1999-01-28
2001-02-06
Wilson, James O. (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
C560S055000, C560S075000, C560S087000, C560S089000, C560S095000
Reexamination Certificate
active
06184411
ABSTRACT:
This invention pertains to an improved process for the removal of residual tin catalyst from substituted higher aliphatic esters of hydroxyhydrocinnamic acids made by the tin catalyzed transesterification reaction between the corresponding lower alkyl ester and higher alkanol.
BACKGROUND OF THE INVENTION
The aliphatic esters and polyesters of substituted sterically hindered hydroxy-hydrocinnamic acid are well-known as effective antioxidants for a wide variety of organic materials protecting them from oxidative and thermal degradation. Many of these esters have gained wide commercial acceptance as phenolic antioxidants.
An important known class of transesterification catalysts which may be used to prepare the above compounds include tin catalysts, particularly organotin catalysts. For example, U.S. Pat. No. 4,594,444 teaches a process for the preparation of sterically hindered hydroxyphenylcarboxylic acid esters by the transesterification of the corresponding methyl or ethyl ester with a higher aliphatic alcohol using an oxide or an organometallic compound of a metal of the fourth main group or subgroup of the periodic table as catalyst in an amount between 0.05 and 1.0 mol percent based on the methyl or ethyl ester. Higher dialkyltin oxides, particularly dibutyltin oxides, are taught as the preferred catalysts for this process.
However, as recognized in the art of antioxidants, if the amount of tin residue in the product is too high, the ultimate product stability may be compromised. Care is therefore taken to remove such residues. Unfortunately, one or more of the following disadvantages are commonly associated with known methods for removing tin residue from substituted hydroxyphenylcarboxylic acid esters: product degradation and/or color formation; additional processing steps (including, for example, crystallization or adsorption techniques) which inevitably result in yield loss and increased waste generation; and increased expense due to the need for rather sophisticated equipment which may be required for the separation of product from residual tin catalyst.
Japanese Hei 01 316389 (Takee et al.) provides for the removal of organotin compounds from general ester exchange reactions by making the organotin compounds insoluble in organic media with the use of aqueous carboxylic acid solutions. In particular, the Japanese reference requires the use of an organic solvent to make the carboxylic acid derivative of the tin compound insoluble in the ester mixture, which technique increases equipment requirements as well as waste generation. The Japanese reference further requires use of an aqueous solution of a carboxylic acid. Unfortunately, the presence of a large amount of water leads to the formation of the undesirable toxic by-product, 3-(3,5-di-tert-butyl4-hydroxy)hydrocinnamic acid (HCA), the presence of which becomes problematic for the instant hydrohydroxycinnamate esters when employed in food contact applications. The reference further teaches the added step of using auxiliary filter aids, such as cellulose or activated charcoal, which are needed in order to effectively remove the reacted tine compound.
Clearly, need continues to exist in the industry for a simplified and improved process of removing residual tin from the substituted higher aliphatic esters of hydrohydroxycinnamic acids made by the tin catalyzed transesterification reaction between the corresponding lower alkyl ester and higher alkanol. It is the object of the present invention to satisfy this need.
BRIEF SUMMARY OF THE INVENTION
The invention is directed to an improved process for the preparation of substituted higher aliphatic esters of hydroxyhydrocinnamic acids by transesterifying the corresponding lower alkyl ester with a higher alkanol of the formula A-(OH)
m
in the presence of a tin catalyst. In particular, the invention provides for an improved method to remove the residual tin by reacting the tin catalyzed transesterification reaction mass with a carboxylic acid or hydrate thereof neat, in the absence of an aqueous medium, until the tin catalyst forms an insoluble derivative, and then separating the insoluble derivative from the reaction by filtration without the assistance of a filtration aid.
DETAILED DESCRIPTION
The invention is directed to an improved process for the preparation of a compound of formula (I)
wherein R is an alkyl of 1 to 4 carbon atoms, n is 0 to 2, m is 1 to 4; and when m is 1, A is a straight or branched chain alkyl of 4 to 18 carbon atoms;
when m is 2, A is a straight or branched chain alkylene of 2 to 12 carbon atoms, or said alkylene interrupted by one to five O or S atoms, or A is 2,2-bis(4-ethyleneoxyphenyl) propane;
when m is 3, A is a straight or branched chain alkanetriyl of 3 to 6 carbon atoms; and
when m is 4, A is pentaerythrityl, by transesterifying the corresponding lower alkyl ester with a higher alkanol of the formula
A-(OH)
m
(II)
in the presence of a tin catalyst;
wherein the improvement comprises reacting the tin catalyzed transesterification reaction mass with a carboxylic acid or hydrate thereof neat, in the absence of an aqueous medium, until the tin catalyst forms an insoluble derivative, and separating the insoluble derivative from the reaction mass by filtration without the assistance of a filtration aid.
Preferably, the lower alkyl ester is a compound of formula (I) where m is 1 and A is methyl or ethyl, most preferably methyl.
Preferably, R is methyl or tert-butyl.
When m is 1, A is preferably alkyl of 8 to 18 carbon atoms; most preferably isooctyl, lauryl or n ocladecyl; especially nectadecyl.
When m is 2, A is preferably hexamethylene, —CH
2
CH
2
SCH
2
CH
2
—or —CH
2
CH
2
OCH
2
CH
2
OCH
2
CH
2
—.
When m is 3, A is preferably CH
3
C(CH
2
—)
3
, CH
3
CH
2
C(CH
2
—)
3
or glyceryl.
Both organic and inorganic tin catalysts may be employed in the transesterification reaction and removed according to the instant invention. Representative tin catalyst classes include monoalkyltin esters, dialkyltin esters, monoalkyltin oxides, dialkyltin oxides, tin tetrachlorides, monoalkyltin trichloride, dialkyltin dichloride, diaryltin dichlorides, organotin sulfides, organotin sulfates, organotin mercaptans, organotin carboxylic acid or esters thereof, and stannoxanes.
Preferred tin catalysts include monobutyltin tris(2-ethylhexoate), dibutyltin bis(2-ethylhexoate), stannous bis(2-ethylhexoate), dibutyltin diacetate, dibutyltin oxide, butyltin trichloride, butyltin trimethylate, dibutyltin dichloride, and diphenyltin dichloride. In particular, FASCAT® 4215A organotin catalyst, of proprietary structure belonging to the stannoxane family and containing 18.5-20.5% tin is preferred. FASCAT® 4215A organotin catalyst is available in an aromatic hydrocarbon solution from Elf Atochem, headquartered in Philadelphia, Pa. Other particularly preferred catalysts are monobutyltin tris(2-ethylhexoate) and stannous bis(2-ethylhexoate), both available from Elf Atochem under the names FASCAT™ 9102/4102 and FASCAT™ 2003, respectively.
The transesterification reaction may be one which is known in the literature. For example, U.S. Pat. No. 4,594,444 teaches a process for the preparation of sterically hindered hydroxyphenylcarboxylic acid esters by the transesterification of the corresponding methyl or ethyl ester with a higher aliphatic alcohol using an oxide or an organometallic compound of a metal of the fourth main group or subgroup of the periodic table as catalyst in an amount between 0.05 and 1.0 mol percent based on the methyl or ethyl ester. Higher dialkyltin oxides, particularly dibutyltin oxides, are taught as the preferred catalyst for this process.
The instant process has been found to be particularly effective under conditions where the transesterification reaction proceeds neat in the absence of solvent and where the amount of tin catalyst is minimized, i.e., on the order of about 50 to about 120 ppm tin, based on the starting lower alkyl ester, at a temperature of 150-200° C.
In general, the carboxylic acid compounds that react with the tin transesterifica
Ciba Specialty Chemicals Corporation
Deemie Robert W.
Hall Luther A. R.
Kovaleski Michele A.
Wilson James O.
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