NL8103401A - METHOD FOR TREATMENT OF TWO-BASIC ESTERS WITH ALKALIMETALBOR HYDRIDES, PERMANGANATES OR METHYLATES - Google Patents

Description

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Process for the treatment of dibasic esters with alkali metal borohydrides, permanganates or methylates.

The invention relates to reducing the tendency for coloration of certain esters and more particularly to the treatment of esters with an alkali metal borohydride in the presence of water, an alkali metal permanganate in the presence of water and / or an alkali metal metal methylate.

Borohydrides are known to be compounds which can be used for the selective reduction of a wide range of functional groups, for example, aldehydes, ketones, imines, esters and amides, etc. The use of borohydrides is described in detail in the publication entitled Process Stream Purification, Bulletin No. BA-8UG,

Ventron Corp., September 1978. This publication discloses six patents pertaining to the purification of esters, but does not mention any publication relating to the removal of colourants from aliphatic dibasic esters.

U.S. Patent 2,957,023 describes a process for stabilizing alcohols contaminated with carbonyl and / or unsaturated compounds, such as olefins, by adding a borohydride to the alcohol during or before the esterification. In said US patent it is stated that a solvent is preferred because of the relatively insolubility of the borohydride, but it is also pointed out that the choice of the solvent is not essential for the described process. Said solvents include water, isopropanol ether, low molecular weight amines and the like.

The preparation of colorless polyvinyl alcohol according to U.S. Pat. No. 3,679,646 is accomplished by pretreatment of an alcohol solution of an 8103401 -2-% polyvinyl ester by about 0.03% to about 3% by weight based on weight of the polyvinyl ester, of an alkali metal boron hydride, followed by alkaline hydrolysis. Said United States Patent Specification states that the borohydride 5 is preferably used in a finely divided form, for example in powder form.

U.S. Patent 3,681,482 describes a method for improving the color of phosphate esters by contacting the esters with 0.002-10 0.05 wt% sodium or lithium borohydride. In said US patent it is stated that the borohydride is preferably in solid form, but that it can also be used in aqueous solution.

West German Patent 2,556,258 15 describes the stabilization of polyhydroxycarboxylate polymers by the addition of sodium borohydride.

US Patent 3,991,100 describes a process for the preparation of esters of dibasic acids, which exhibit a reduced tendency to color under alkaline or transesterification conditions. The process comprises heating the esters to remove water, nitrogen oxides and nitric acid, esterifying the product thus heated and finally distilling off volatile materials in the presence of a dry base such as sodium carbonate and calcium hydroxide. However, it should be noted that the use of this method does not completely eliminate the tendency for the esters to develop color during transesterification.

In the prior art, it has been reported that under common conditions aliphatic nitro compounds are not reactive with sodium borohydride and that such reaction to some degree requires transition metals, their salts and complexes of Lewis acids (Sodium Borohydride, Ventron Corporation, December 1979, p.

35 35-36).

U.S. Pat. No. 2,831,883 discloses 8103401-3% -3 - reduction of nitro impurities in alpha-alkane diacid esters prepared from diacids through the oxidation of organic. compounds with nitric acid. The said US patent discloses several methods for the reduction of the 5 nitro compounds, including the reduction with a metal and an acid, for example zinc dust and an alcoholic solution of an inorganic acid, the catalytic reduction with Raney nickel or with reduced precipitated nickel and the chemical reduction, for example, by catalytic reduction with palladium or platinum.

US Patent 3,991,100 describes a process for the preparation of esters of dibasic acids, which exhibit a reduced tendency to spin under alkaline or reverse reaction conditions. The process includes heating the esters to remove water, nitrogen oxides and nitric acid, esterifying the product thus heated, and finally distilling volatile materials in the presence of a dry base such as sodium carbonate or calcium hydroxide. The method described does not completely eliminate the tendency for the esters to color during transesterification.

Belgian patent 828,508 describes a process for the removal of organic nitrogen-containing compounds from dodecanedioic acid by treatment of the acid with potassium permanganate in an alkaline medium. This Belgian patent does not mention the treatment of acids other than dodecanedioic acids or the treatment of esters of acids.

A general method for the oxidation of the salts of mononitro compounds with neutral potassium permanganate is described in J. Organic Chem. 27, 3699 (1962). The described process involves the conversion of the nitro compounds into their potassium salts in an aqueous solution, which is then added to an aqueous solution of potassium permanganate. The aldehydes and / or ketones that are formed are removed by steam distillation from the aqueous reaction mixture 8103401 V.- * v-4-.

U.S. Patent 3,642,871 discloses the use of an alkali metal alkoxide, e.g. sodium methylate, necessarily combined with 5 phosphorus atoms, e.g. phosphoric acid, to improve the color stability of a wide range of organic esters, including diesters of aliphatic carboxylic acids, e.g. dimethyl adipate, dibutyl sebacate and diisopropyl .

The invention provides a method for reducing the tendency for coloration of alkane diacid esters, for example the esters derived from dicarboxylic acids with 4-12 carbon atoms, characterized in that the esters are contacted with an alkali metal borohydride in the presence of water an alkali metal permanganate in the presence of water and / or an alkali metal methylate. It is preferred to dissolve the borohydride and the permanganate in water before effecting contact with the esters.

The esters to which the invention is particularly applicable are those prepared from the acids isolated as co-products of the oxidation with air of cyclic hydrocarbons to cyclic ketones and alcohols, followed by oxidation of the ketones and alcohols with nitric acid . For example, the oxidation of cyclohexane to cyclohexanol and cyclohexanone can be carried out according to the method of US Pat. No. 3,530,185. Cyclohexanol and cyclohexanone prepared by the method of the above-mentioned U.S. Patent are then oxidized with nitric acid by the methods described in U.S. Pat. Nos. 3,359,308 and 3,365,490. Illustrative examples of the acids formed as co-products, which are formed together with adipic acid in the above-mentioned processes, are succinic acid and glutaric acid.

The preparation of alkanedicarboxylic acids of 8-12 carbon atoms by oxidation with nitric acid of the corresponding alcohols and ketones is described in U.S. Pat. No. 3,758,564. Illustrative examples of the acids formed as co-products in this process are pimeline acid, turmeric acid, azelaic acid, sebacic acid and undecanedioic acid.

The major acids formed in the processes described above, that is, adipic acid and dodecanedioic acid, are usually separated from the by-product acids by crystallization, and the by-product acids are then recovered from the mother liquor by known methods. These by-product acids can be converted to esters using known esterification processes.

10. Even after drastic distillation, these esters still show a marked tendency to turn yellow when exposed to alkaline conditions or when heated to temperatures, with the esters finally being used, for example, for the preparation of other esters and polyesters by transesterification.

The tendency to color esters treated in accordance with the method of the invention is believed to be due to the presence of small amounts of aliphatic nitro compounds, which are formed during the oxidation with nitric acid of the ketones or alcohols and / or or during the acid-catalyzed esterification in the presence of residual nitrate ion. These impurities distill along with the esters, are not adsorbed to any significant degree on activated carbon, and cannot be bleached, for example, with peroxides or aqueous hypochlorites.

The borohydrides useful in the method of the invention include sodium, potassium and lithium borohydride and mixtures thereof. Sodium borohydride is the preferred borohydride.

The methylates useful in the process of the invention include sodium, potassium and lithium methylate and mixtures thereof. Sodium methylate is preferred.

The permanganates useful in the method of the invention include sodium, potassium and 8103401

V

-6-

* V

Lithium permanganate and mixtures thereof. Potassium permanganate is preferred.

The method of contacting the additives described above with the esters is not essential to the invention, provided that water is present during the contact in the case of the permanganate and the borohydride. Stirring at low temperature at ambient temperature has been found to be completely satisfactory for mixing, but, as will be apparent to those skilled in the art, high shear mixing and / or the use of elevated temperatures will accelerate the reaction. The contacting can be carried out at temperatures in the range of 0-100 ° C and preferably 20-75 ° C for times ranging from about 0.5-2 hours. The time can be reduced by increasing the agitation and / or raising the temperature. The borohydride and / or permanganate and water can be added separately to the esters, but preferably they are dissolved in the water before the addition. In the case of the borohydride, the minimum amount of water required to form the solution depends on the solubility of the borohydride at the temperature of the water, but the amount of water may be up to twice the weight of the borohydride or more.

In any case, it is desirable to add only the minimum amount of water that is necessary, so that the drying required after the reaction can be reduced as much as possible.

The presence of water markedly decreases the effectiveness of the methylate, and it is preferred to maintain the water content at the lowest practical value, for example, less than 0.1% by weight based on the weight of the esters.

Since the borohydrides decompose rapidly in the presence of acid, the esters must be neutral or slightly basic in order to achieve optimum utilization of the hydride and optimum color reduction. This also applies to the treatment with the methylate. Usually, a precipitate is formed during the contact of the ester and the 8103401 - 7 - methylate, which can be removed if desired by known methods, for example, by filtration, before further treatment of the treated esters.

The amount of additive required will of course depend on the amount of coloring agents present, which is determined by the conditions used in the preparation of the acids and / or the esters. It has been found that 2 parts by weight of borohydride per 1000 parts by weight of ester are usually sufficient for complete color reduction. In many cases, however, less than "1 part borohydride per 1000 parts ester can effect complete color reduction. Generally, 0.05-5 wt%, and preferably about 0.1-0.3 wt%, of borohydride based on the weight of the ester is used. It has been found that 2-25 parts by weight and usually about 5 wt. 15 parts of methylate per 1000 parts by weight of ester is usually sufficient for complete color reduction. In many cases, however, less than 1 part methylate per 1000 parts ester can effect complete color reduction. It has been found that 6.6 parts by weight of permanganate per 1000 parts by weight of ester is usually sufficient for complete color reduction. In many cases, however, less than 6.6 parts of permanganate per 1000 parts of ester can effect complete color reduction. Generally, 0.1-2 wt%, and preferably about 0.4-0.8 wt%, of permanganate based on the weight of the ester is used. In each of the 25 cases, the amount of additive required is easily determined by increasing or decreasing the amount until the desired color level is obtained. An excess additive can be used to ensure a nearly complete reduction in the tendency to color.

The invention is further illustrated but not limited by the examples below, wherein, unless otherwise indicated, the parts and percentages are parts by weight and percentages by weight. The tendencies to color the esters, treated according to the method of the invention, were determined by adding two drops of a 40% by weight solution of benzyl trimethyl ammonium hydroxide in methanol to 81 03 4 0 1 v V-8. - 5 ml of the esters, followed by shaking the solution. All esters mentioned in the examples were treated in this way before determining the color. The polyesters were not treated before determining the color. The color was assessed using a Sacred Color Comparator equipped with a

Gardner Color Disc (Institute of Paint and Varnish Research Color System). According to this technique, the yellowness of samples is measured on a scale from 1 (very light yellow) to 10 (dark yellow). A colorless sample shows a Gardner color 10 of less than 1.

Example I

To a 12 liter flask equipped with a simple distillation head and a suitable heating device, 10 kg of the mixed methyl esters of succinic, glutaric and adipic acids were added with the analyzes indicated in Table A below a Gardner color of 6.

Table A

Dimethyl succinate 2%

Dimethyl glutarate 71 Z

20 Dimethyl adipate 27%

This ester mixture was prepared in the manner described above by esterification of the acids obtained by oxidation with nitric acid of a mixture of cyclohexanol and cyclohexanone, followed by removal of the largest amount of adipic acid by crystallization.

About 10 g of sodium borohydride were dissolved in 20 g of water and the resulting solution was added to the flask. After standing overnight at room temperature (about 16 hours at 20 ° C), the ester had a Gardner-30 number of less than 1. This ester was then distilled in a vacuum of 25 mm Hg. A small head was removed and 9.5 kg of distillate boiling in the range 1-18 ° C was collected. The distillate also exhibited a Gardner color of less than 1, and when a polyester was prepared from this material by transesterification with ethylene glycol in the presence of n-butyl stannic acid, a polyester with an 8103401 s-9-

Gardner color of less than 1 obtained.

Comparative example A

Example X was repeated with the exception that 10 g of powdered sodium borohydride (no water) were thoroughly mixed with the esters. The Gardner color of the distillate was 4, which indicates that only a small amount of the colorants were removed in the absence of water.

Comparative example B

Example I was repeated with this exception that 40 g of sodium borohydride (no water) were used.

A polyester prepared from this ester had a Gardner color of 6.

The above example shows that even a significant excess of sodium borohydride does not result in a satisfactory color reduction in the absence of water.

Example II

To a 12 liter flask equipped with a simple distillation head and a suitable heating apparatus, 8153 g of the mixed methyl esters of succinic, glutaric and adipic acids were added with an analysis as shown in Table A of Example I and a Gardner - color of 6.

This ester mixture was prepared as described in Example I25.

About 57 g of potassium permanganate were dissolved in 323 g of water at 85 ° C, the resulting solution was added to the flask and the mixture was kept at 77-93 ° C for 65 minutes. The mixture was then distilled off in a vacuum of 25 mm Hg. A small precursor containing water was removed and 7264 g of distillate boiling in the range 110-115 ° C was collected. The distillate exhibited a Gardner color of less than 1, and when a polyester was prepared from this material by transesterification with ethylene-35 glycol in the presence of n-butyl stannic acid, a polyester with a Gardner color of less than 1 was obtained. An analog of 8103401 Τ '**> - JO - polyester prepared from the untreated esters was dark orange.

Example III

To a 500 ml flask equipped with a simple distillation head and a suitable heating apparatus, 227 g of the mixed methyl esters of succinic, glutaric and adipic acids were added with an analysis as shown in Table A of Example I and a Gardner - color of 4.

This ester mixture was prepared as described in Example 10.

About 3.5 g of sodium methylate were added to the flask. The resulting suspension was heated to 75 ° C with stirring for 1 hour, after which the contents of the flask turned yellow. This ester was then distilled without any significant fractionation in a vacuum of 25 mm Hg.

About 215 g of distillate with a Gardner color of less than 1 were collected.

Example IV

A mixture of straight chain C18-dibasic acids, recovered from the oxidation with nitric acid of cyclododecanone and cyclododeanol, as described above, was esterified with methanol using dodecylbenzenesulfonic acid as a catalyst. The resulting esters were then distilled under a pressure of 1 mm Hg and a distillate with boiling points in the range of 99-150 ° C and a Gardner color of 7 was recovered. This ester distillate had the composition shown in Table B below.

Table B

Dimethyl pimelate 0.5% Dimethyl sebacate 7.0% 30 Dimethyl suberate 2.4% Dimethyl undecanedioate 47.6% Dimethyl azelate 3.3% Dimethyl dodecanedioate 39.2%

To 150 parts of this ester distillate was added 6 parts of a 25% by weight aqueous solution of sodium borohydride. The mixture was then stirred at room temperature for 1 hour and then redistilled under the conditions indicated above. A small pre-8103401 yr-11-r loop with a boiling point below 99 ° C was taken off and discarded.

A product was collected with a boiling range of 99-155 ° C, which had a Gardner color of less than 1.

Example V

To 124 parts of the ester distillate as described in Example IV with a Gardner color of 9, 1.6 parts of potassium permanganate dissolved in 4.8 parts of hot water (85 ° C) were added with gentle stirring at room temperature. The mixture was then distilled at a pressure below 1 mm Hg.

After a small aqueous precursor was discarded, 87 parts of the treated esters were collected, which showed a Gardner color of less than 1.

Example VI

To 124 parts of the ester distillate of Example V, 2 parts of sodium methylate were added with gentle stirring at room temperature. The mixture was then distilled at a pressure below 3 mm Hg. After a small lead was rejected, 104 parts of the treated esters were collected, which showed a Gardner color of less than 1.

20 81 03 4 0 1

Claims (5)

1. A method of reducing the tendency to color esters obtained from alkanedioic acids of 4-12 carbon atoms, prepared by nitric acid oxidation of cycloaliphatic hydrocarbons selected from ketones, alcohols and mixtures thereof, characterized, these esters are contacted with a compound selected from an alkali metal borohydride in the presence of water, an alkali metal permanganate in the presence of water and / or an alkali metal methylate, and the esters thus treated are then recovered. Process according to claim 1, characterized in that the borohydride is sodium borohydride, the permanganate is potassium permanganate and the methylate is sodium methylate. Process according to claim 1, characterized in that the borohydride and / or permanganate are dissolved in water before effecting contact with the ester. 4. A method according to claim 3, characterized in that the borohydride is sodium borohydride and the permanganate is potassium permanganate. 5. Methods as described in the description and / or examples. 8103401