DE1103335B - Process for the production of carboxylic acid esters - Google Patents

Description

GERMAN

The invention relates to a novel process for the preparation of esters in the presence of a titanium-containing one Catalyst by direct esterification of carboxylic acids and alcohols or by transesterification of Carboxylic acid esters with alcohols in the liquid state in the presence of hydrated titanium oxides.

Esterification reactions of carboxylic acids with alcohols in the liquid state were previously carried out by adding a strong mineral acid, ζ. B. of hydrochloric acid or sulfuric acid or arylsulfonic acids, such as also of metal salts of strong mineral acids that hydrolyze easily in the presence of water, such as zinc and tin chlorides, catalyzed to the reactants. In the esterification reactions in the liquid State, sulfuric acid was the most widely used technical catalyst as it was in most cases a faster rate of ester formation and a greater percentage conversion of the organic Acid to ester effects as other well known esterification or transesterification catalysts.

However, acid catalysis has in esterification reactions in the liquid state by sulfuric acid as well as certain disadvantages caused by other strongly acidic catalysts, such as considerable dehydration of the alcohol component, thereby reducing the cost of the process due to alcohol loss and consequently Reduction of the ester yield can be increased considerably. Another disadvantage is that the obtained Esters are strongly acidic due to trapped acid. Before the esters as plasticizers for vinyl halide polymers just as other halogen-containing polymers can be used, it is necessary to that the catalytic acid residue of the ester is neutralized in order to accelerate the degradation of the plasticized Avoid polymers that would otherwise occur in the presence of free acid. The cost of Protection of the processing plant for the ester synthesis against the corrosive effects of the mineral acids or other strong acids is another disadvantage of the acid catalysts.

This invention relates to a process for the esterification of carboxylic acids with alcohols and for Transesterification of esters with alcohols in the liquid state under the catalytic action of hydrated Titanium oxides, in which the rate of ester formation and the percentage conversion of Acids to esters is equal to or greater than that obtained using strong acid catalysts is achieved in which practically neutral esters are obtained which do not contain an entrapped acid, and in which the ester synthesis proceeds without catalytic dehydration of the alcohols.

So far, the use of titanium compounds as catalysts for esterifications was based on the contact method of manufacture
of carboxylic acid esters

Applicant:

The BF Goodrich Company,
New York, NY (V. St. A.)

Representative: Dr.-Ing. H. Ruschke, Berlin-Friedenau,

and Dipl.-Ing. K. Grentzenberg,
Munich 27, Pienzenauer Str. 2, patent attorneys

Claimed priority:
V. St. v. America October 13, 1955

Frank Xavier Werber, North Royalton, Ohio,

and Seward Junior Averill, Boston, Ohio (V. St. A.),

have been named as inventors

catalysis of heterogeneous reactions in the vapor state is limited, the application of titanium compounds was dependent on the adsorption properties of the surface of the anhydrous titanic acid as the reaction between a carboxylic acid and an alcohol by adsorption of the components on the catalyst surface and causing desorption of the ester formed.

It has now been found that titanium compounds of the general formula TiR ₄ , in which R represents an OH group, can be used in the finely divided state as catalysts for esterification reactions of carboxylic acids and alcohols in the liquid state and that the above-mentioned advantages and the disadvantages described are thereby achieved be avoided. The titanium compound of the above general formula which is suitable according to the invention is hydrated titanium dioxide.

According to the invention, hydrated titanium dioxide which is suitable as a catalyst can be prepared according to one of the known Process are produced. For example, the treatment of titanium-containing minerals, such as rutile, Ilmenite or bauxite pulp, with concentrated sulfuric acid, adding an oxide, sulfate or carbonate one divalent metal to an acid solution to form titanium salts, whose hydrolysis at normal temperatures or elevated temperatures provides hydrated or partially hydrated titanium dioxide gels.

Titanium dioxide gels, sometimes called hydrated titanium dioxide, titanium hydroxide, or orthotitanic acid, can also be achieved by hydrolysis of titanium salts

109 538/575

3 4

with ammonium or alkali hydroxide solutions obtained displacing alcohol, or the one to be displaced

will. Preferably, the alcohol during manufacture should form an azeotropic mixture, which is below

the salts formed in the titanium gel boil to the boiling point of the alcohol to be introduced before the gel is added,

to the carboxylic acid and the alcohol or the ester In all of the above formulas, the symbols R, R 'and

and alcohol removed. The preparation of the above 5 R "aliphatic, cycloaliphatic or aromatic

titanium gels mentioned by partial dehydration by groups.

Extraction of the excess water with alcohol, carboxylic acids esterifiable according to the invention are by drying in vacuo, by heating or by saturated aliphatic carboxylic acids, halogen and oxy pressure filtration to evaporate part of the water, carboxylic acids, unsaturated aliphatic carboxylic acids is another method of production of titanium diio and halocarboxylic acids, saturated or unsaturated oxide, which is suitable as an active catalyst according to this invention, cycloaliphatic carboxylic acids and aromatic carbons. Hydrated titanium dioxide that has been obtained by other acids, amino, halogen and oxycarboxylic acids and known processes, such as by the anhydrides of dibasic acids such as succinic, hydrolysis of titanium halides or by decomposition of glutaric, adipic, pimeline, - maleic -, mesaconic, citracon and titanium halides at elevated temperatures by means of glutaconic, itaconic and phthalic anhydride.
Reacting with oxygen, air and water is also suitable as a catalyst to the alcohols, those with carboxylic acids, carbonator according to this invention. Colloic acid anhydrides and carboxylic acid esters are reacted hydrated titanium dioxide, which can be added by adding a divalent anion to an aqueous solution of titanium R (OH) _M , in which R is an organic radical and η a dioxide or through mechanical peptization of hydrati- 20 integer, such as methanol, chloroethanol, cyanoethanol, titanium dioxide sated has been obtained, ethoxyethanol, phenylethanol, 2-chloro-1-propanol, can also be used as a catalyst. 3-bromo-1-propanol, 2,2-dichloro-1-propanol; Ethyl-,

The method preferred according to the invention for h-n-propyl, isopropyl, η-butyl, secondary-butyl alcohol,

provision of hydrated titanium dioxide catalysts 2-nitro-l-propanol, l-chloro-2-propanol, 2-nitro-l-butanol,

consists in that one ammonium or alkali metal hydroxide 25 2-methyl-1-pentanol, 2-methylpentanol-3, primary and secondary

solutions with solutions of titanium sulfate or titanium chloride octanol, n-dodecanol, 6-dodecanol, lauryl, myristyl,

in dilute acids to form a hydrated titanium stearyl alcohol, 2-propen-1-ol; 2-buten-l-ol, 3-pentene

dioxydgel converts, the ammonium or alkali salts l-ol and similar alcohols, also the polyvalent ones

removed by filtration and the gel a few times to saturated and unsaturated alcohols and aryl

Removal of practically all impurities with 30 tuated aliphatic alcohols.

Water washes. This process is used because of the ease with which the esters, which react with alcohols in the presence of

Accessibility of the titanium salts mentioned is preferred. hydrated titanium dioxide to form esters

The concentration of that which can be used in accordance with the invention with other alcohol proportions than those of the ester reaction titanium catalyst can be implemented within a wide range of participants, include e.g. B. the to be changed. Preferred catalyst concentrations of the following groups of compounds: Esters from getionen are 0.01 to 1.0 percent by weight, based on the saturated or unsaturated monocarboxylic acids and one weight based on the esterifiable carboxylic acid. There are valuable saturated or unsaturated alcohols as well but can optionally also include concentrations of esters of saturated or unsaturated mono-2,0,5,0 and even 10.0% or more can be used. carboxylic acids and polyvalent saturated or un-

Esterification and transesterification reactions in which 40 saturated alcohols and esters from saturated or

the above-mentioned hydrated titanium dioxide as catalyzed unsaturated polycarboxylic acids and monohydric acids

Sator can be used are the formation of esters alcohols.

from carboxylic acids or carboxylic acid anhydrides and the reaction conditions, such as temperature, pressure Alcohols, also the transesterification reactions, in which and proportions of the reactants can be in an ester is reacted with an alcohol, the 45 of which can be varied over a wide range; in the main boiling point is higher than that of the alcohol content of the thing, this depends on the nature of the individual reaction ester. Accordingly, the invention comprises the catalyst and the desired end products, table conversions of organic compounds, with the reaction elements in the liquid state that contain at least one acyloxy group must be kept with one. Since the implementations at Alcohol, which compounds with at least 5 ° room temperature are slow, is preferred Acyloxy group according to the invention, carboxylic acids, carboxylic acids at elevated temperatures, especially under acid anhydrides and should be esters of carboxylic acids. worked river temperature. To ensure the completeness of the The following reactions can be ensured by hydrated reaction in a known manner Titanium oxide catalyzes: uninterrupted or interrupted one or more

1. Reaction of a carboxylic acid with an alcohol 55 reaction products are removed. This includes the formation of an ester after the general implementation of the reactions in the presence of formula diluents to form azeotropic Ge-RCOOH + ROH > RCOOR'4-HO mix that at a lower temperature than that

^{Boil 2} desired end product, by removing one

2. Reaction of the carboxylic acid anhydrides with alcohols 60 unwanted by-product or by removal according to the general formula of the desired end product by adding superheated steam

(RCO) O -4-2 R'OH > 2RC00R '+ HO ^{0 <} ^ ^{he merged} gases, such as nitrogen, through the reaction

^{2 2} mix, or by executing the

3. Alcoholysis or transesterification reactions between reactions under reduced or increased pressure, Carboxylic acid esters and other alcohols after 65, in which case ventilation is carried out from time to time, general formula to help the unwanted by-products escape

RCOOR '+ R "0H > RCOOR" + ROH ^read ^ ⁿ ·. , _,. . ,. " _{Tr x} ,

The following examples illustrate the process for

In the last-mentioned reaction, the alcohol is intended to produce esters in the presence of a catalyst

of the formula R "O H a higher boiling point than that of 70 from hydrated titanium dioxide and the effectiveness

of the titanium catalysts which can be used according to the invention. Unless otherwise stated, all parts are parts by weight.

example 1

A glass flask equipped with a reflux condenser and a separator for water displaced by alcohol was charged with 420 parts of octanol-2.148 parts of phthalic anhydride and 40 parts of hydrated titanium dioxide gel containing about 5% TiO ₂ and 95% water. The mixture was heated to reflux temperature, which was maintained until 99.0% of the phthalic anhydride had been converted to di (2-octyl) phthalate. The water was continuously removed during the course of the reaction. For comparison purposes, the same reaction was carried out without a catalyst.

The hydrated titanium oxide gel was prepared by dissolving titanium tetrachloride in water and hydrolyzing it with the addition of sufficient quantities of NH ₄ OH to precipitate hydrated titanic acid or the hydrated titanium dioxide gel. The precipitated gel was filtered off from the aqueous solution and washed several times with water until no more chloride ions could be detected.

Amounts of the same alcohol and anhydride were also used with 2 g of p-toluenesulfonic acid for comparison implemented as a catalyst.

In the table below, in which the catalyst, the carboxylic acid esterified in the specified time in Percentages and the dehydrated alcohol content in percentages are those with the various Values obtained from esterifications are given.

35

40

catalyst % Ver
esterification
the acid Duration
in
hours Excess
dehydrated
alcohol no 90
99
93 37
13th
6th 10%
after 37 hours
15%
after 13 hours
92%
after 6 hours TiO ₂ p-toluenesulfone
acid

Examples 3 to 7

The titanium dioxide used as a catalyst in Examples 3 and 4 below was prepared in gel form from commercially available titanium sulfate which contained the equivalent of about 50% titanium sulfate, 25% sulfuric acid and 25% water. The titanium salt was _{hydrolyzed with NH 4} OH to form a hydrated titanium dioxide gel which was then washed with water until no sulfate ions could be detected in the filtrate.

The titanium dioxide catalysts used in Examples 5, 6 and 7 were made as follows:

Example 5: Titanium dioxide in gel form with a calculated concentration of TiO ₂ of 18.1 percent by weight, produced by hydrolysis of titanium sulfate, was ^{dried at 120 °} C. for 1.5 hours.

Example 6: Titanium dioxide in gel form, which had been produced by hydrolysis of titanium sulfate, was dried in vacuo at 26.7 ° C., a moist powder being obtained which, when dispersed in water with stirring, is no longer returned to the gel state. The concentration of TiO ₂ in the moist powder was 76 percent by weight according to the analysis.

Example 7: Titanium dioxide in gel form, which had been obtained by hydrolysis of titanium sulfate, was dehydrated by heating at 177 ° C. for 2 hours, a practically anhydrous TiO _{2 being} obtained.

In each experiment, 1 mole of phthalic anhydride was reacted with 3 moles of 2-ethylhexanol at reflux temperature. The amount of catalyst was calculated so that it corresponded to 2 g of dry TiO ₂ in each case.

In the following table, in which the catalyst and the time required to convert 99% of the phthalic acid to di- (2-ethylhexyl) phthalate are noted, the values obtained are given.

When using p-toluenesulfonic acid as a catalyst, it is very difficult to achieve a 99% esterification of the Acid without a very large loss of alcohol through dehydration. Without a catalyst it is The final rate of esterification is very low, so that a very long reaction time is required to achieve a To achieve 99% esterification of the carboxylic acid.

Example 2

A glass flask equipped with a reflux condenser, stirrer and trap for water displaced by alcohol was charged with 148 parts of phthalic anhydride, 390 parts of 2-ethylhexanol and 40 g of hydrated titanium dioxide gel catalyst containing _{about 5% TiO 2.} The batch was heated to reflux temperature and held there until 99.0% of the phthalic anhydride had been converted to di- (2-ethylhexyl) phthalate. The water was continuously removed in the course of the reaction. The carboxylic acid was 99% esterified in a little over an hour.

example

45 comparison
3
4th
5
6th

Catalyst concentration

TiO ₂
(4 to 5 «/ ₀ TiO ₂ )

TiO ₂ gel
(10 percent by weight Ti O ₂ )

TiO ₂ gel
(18 percent by weight Ti O ₂ )

TiO ₂ , moist powder (76 percent by weight Ti O ₂ )

TiO ₂

anhydrous powder
(100 percent by weight TiOg)

Duration in

Hours up to

a conversion

of 99% of the acid

to the diester

19.0 (about 90% ester)

1.83

1.83 to 2.00 2.50 4.66

19.0 (about 90% ester)

60 These examples show that the aggregated gels of the hydrated titanium oxides which are in a higher swelling state show the highest level of catalytic activity and that the catalytic activity of the titanium oxides in the gel state is reduced as the water content of the gels decreases. The examples further illustrate the fact that the titania gels, although dehydrated to the extent that the characteristic gel form is converted into that of a moist powder

Claims (4)

(Example 6) still retain some catalytic activity as long as they are not completely dehydrated (Example 7). The exact reason why titanium oxide water gels with a TiO2 content of about 4 to 5 percent by weight show a higher catalytic effectiveness than partially dehydrated or fully dehydrated titanium oxide gels is not known. It is believed that the finely divided state of TiO2 obtained by the precipitation of titanium from an aqueous solution to form an elastic gel causes the formation of TiO2 aggregates which are easily dissolved or strongly dispersed in an organic solvent and that the reduction or lack of catalytic effectiveness caused by partially 1S or fully dehydrated titania gel is due to the formation of larger TiO2 aggregates and not to the removal of the water itself, as very long aging without loss gives the same type of aggregation in water. Conversely, a fresh titanium dioxide gel with a small particle size and a high TiO2 content has a high catalytic activity. Examples a5 A mixture of 142 parts (0.55 mol) of dibutyl adipate, 45 parts (0.50 mol) of 1,3-butanediol and 2.85 parts of titanium dioxide gel obtained from titanium sulfate by hydrolysis and neutralization and from 30 to 40 parts % TiO2 and 60 to 70% water, was heated in a three-necked flask connected to a reflux column filled with Berl bells until the reaction mixture had reached a temperature of 1960C, whereupon it slowly increased to 172C with continuous removal of butanol has been cooled. After 3 hours, 37 parts of butanol had been collected. The pressure was reduced to 40 mm Hg in 1.5 hours. Heating was continued during the depressurization and an additional 16 parts of butanol was collected. A polyester was obtained as a reaction product as a viscous oil. Analysis of the oil indicated that the polyester had a hydroxyl content of 1%. The initial reaction mixture had a hydroxyl content of 18%. From this analysis it was concluded that 95% of the available diol had been transesterified to form the polyester. A reaction mixture analogous to that just described was treated in the same way without the addition of hydrated titanium dioxide gel. A negligible amount of butanol was obtained, indicating that no transesterification had occurred. If terephthalic acid and ethylene glycol are reacted in the presence of hydrated titanium dioxide, a solid polymer with a high molecular weight and a melting point of about 250 to 260 ° C. is obtained. Example 9 This example illustrates the synthesis of a polyester by direct esterification in the presence of titanium dioxide gel. 146 parts of adipic acid, 113 parts of 1,3-butanediol, parts of lauric acid and 40 parts of titanium dioxide gel, which contained up to 5% TiO2 and had been prepared as in Example 8, were reacted for 40 minutes at normal pressure and at a temperature of 148 to 250.degree collecting 65 ecm of water. Of this, about 30 to 35 ecm of water came from the titanium dioxide gel. The reaction mixture was then heated to 167-205 ° C. at mm pressure for about 1.5 hours, an additional 10 ecm of water being collected. According to the analysis, the product had an acid number of 6.3. The acid number of the starting material was 428. Dimethyl terephthalate can also be transesterified with a glycol. When the glycol is ethylene glycol, a solid polymer of high molecular weight is obtained (see Example 8). Glycols with a higher molecular weight provide polyesters that are liquid or a solid substance with a lower melting point. PaT ENT ANSJ1ROCH E: 1. A process for the preparation of carboxylic acid esters by reacting an organic compound containing at least one acyloxy group with an alcohol in the liquid state at elevated temperature in the presence of esterification or transesterification catalysts and with immediate removal of the water or alcohol from the reaction mixture, characterized in that, that the reaction is carried out in the presence of 0.01 to about 10 percent by weight of hydrated titanium dioxide, based on the compound containing acyloxy groups. 2. The method according to claim 1, characterized in that the catalyst is used in an amount from about 0.01 to 1 percent by weight, based on the compound having at least one acyloxy group, used. 3. The method according to claim 1 and 2, characterized in that the connection with at least an acyloxy group is a carboxylic acid, a carboxylic acid anhydride or an ester of an alcohol and is a carboxylic acid. 4. The method according to claim 1 to 3, characterized in that that one a polycarboxylic acid and a polyhydric alcohol to form a polyester implements. © 109 538/575 3.61