DE1211643B - Process for the vapor phase esterification of optionally halogen-substituted aliphatic carboxylic acids - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. α .:

C07c

German class: 12 ο-27

Number: 1211643

File number: B 66259IV b / 12 ο

Filing date: March 8, 1962

Opening day: March 3, 1966

It is known that carboxylic acid esters can be obtained by reacting carboxylic acids with alcohols in the liquid state and in the presence of an acidic catalyst such as sulfuric acid or p-toluenesulfanic acid, receives. In general, the esterification is carried out at the boiling point of the reaction mixture. Also the use of solid Catalysts which do not dissolve in the reaction mixture are already known. Such catalysts are z. B. ion exchange resins containing sulfonic acid groups. These catalysts have the advantage that they can be easily separated by filtration and do not require neutralization of the reaction mixture.

The esterification of carboxylic acids is known to be an equilibrium reaction in which equilibrium occurs is often only reached after hours. One can move the balance towards the desired one Shift esters if the carboxylic acid or alcohol is used in excess or the resulting water continuously, optionally with the help of an entrainer, from the Balance away. In any case, the esterification requires a long reaction time.

The esterification of carboxylic acids in the vapor state has also been carried out over solid catalysts. Thus, methods are known, for example for the production of ethyl acetate, are reacted in which acetic acid and ethanol at a temperature of 200 to 25O ⁰ C or of 250 to 300 ⁰ C on silica gel as a catalyst. At temperatures lower than 200 ° C, e.g. B. 150 ° C, the yields are still unsatisfactory, but even at the temperatures mentioned, a substantial degree of esterification is only achieved if one of the two components is used in a considerable excess.

In another known process, the carboxylic acid and the alcohol are reacted at a temperature between 250 and 320 ^° C. in the presence of a salt of a metal which is above hydrogen in the voltage series. In this process, too, good yields of ester are achieved only with a considerable excess of one of the two reactants. So z. B. the conversion of acetic acid and n-butanol a 90% yield only if alcohol and acid are used in a molar ratio of 2: 1.

Other known catalysts for the esterification of carboxylic acids in the vapor state are zirconium dioxide, vanadium pentoxide, cobalt oxide, cerium oxide, titanium dioxide, magnesium oxide and manganese processes for the vapor phase esterification of
optionally substituted halogen
aliphatic carboxylic acids

Applicant:

Aniline & Soda Factory in Baden

Aktiengesellschaft, Ludwigshafen / Rhein

Named as inventor:

Dr. Konrad Rauch, Limburgerhof (Palatinate)

dioxide. These catalysts, too, generally require a temperature of over above 250 ^° C. None of them has achieved industrial importance.

It has now been found that carboxylic acid esters are advantageously obtained by reacting aliphatic carboxylic acids having 1 to 6 carbon atoms, which may be saturated or mono- olefinically unsaturated and substituted by halogen, with alcohols in the vapor state over solid, acidic catalysts if the esterification is carried out in a temperature between 80 and 200 ⁰ C, preferably between 100 and about 18O ⁰ C, strongly acid in a, inorganic catalyst, optionally using an inert entraining agent for water, performing.

An essential advantage of the method according to the invention over the methods which work in the liquid state is that the equilibrium position is reached significantly more quickly. While this, as already mentioned, in a liquid state often requires several hours, can be found in the esterification of acetic acid with n-butanol in the vapor phase at 125 ⁰ C on an acid-activated montmorillonite already after 7.7 seconds of contact time 90.8 ° / o the theory ester in the reaction product. In a similar manner ethyl acetate to obtain ° / cent yield 90.2 when acetic acid and ethanol in a molar ratio 1: 1.1 passes at 104 ⁰ C in vapor form via an acid-activated bentonite.

It is a particular advantage of the process according to the invention that high ester yields and good Space-time yields can also be obtained

609 510/444

when carboxylic acid and alcohol are reacted in approximately stoichiometric amounts. the This is because this makes working up the reaction mixtures much easier. One obtains z. B. at the Reaction of acetic acid with n-butanol a mixture that turns into an aqueous after liquefaction and separates an organic layer. The organic layer is separated off, neutralized and distilled them fractionally. First of all, a ternary mixture of water and n-butanol goes into it and n-butyl acetate. This is followed by the binary mixture of n-butanol-n-butyl acetate with 53 percent by weight n-butyl acetate. It is understandable that considerable amounts of n-butyl acetate in the form of this Azeotropes must be removed if the reaction mixture contains large amounts of n-butanol, d. i.e., when n-butanol was used in larger excess in the reaction. A way of working with Butanol and acetic acid in a molar ratio of 2: 1, as in one of the known processes mentioned has been proposed is therefore extremely uneconomical. In the method according to the invention n-butyl acetate is obtained in yields of 90% of theory even when the alcohol is in only a little, d. H. about 10% excess over the stoichiometric amount is used. Man then distilled off the ternary and binary azeotropes and obtained more than 50% of the theoretical pure n-butyl acetate. The n-butyl acetate and butanol that were present in the mentioned azeotropes, after the water has been separated off, it is returned to the process, so that the overall yields of pure n-butyl acetate are 90% of theory.

Since the method according to the invention is carried out at lower temperatures than known processes that work using solid catalysts can also be many esterify sensitive acids and alcohols.

Carboxylic acids that can be converted by the process are, for example: formic acid, Acetic acid, butyric acid, isovaleric acid, caproic acid, crotonic acid, chloroacetic acid, «-bromopropionic acid and α-chloro-isobutyric acid.

The best results are obtained with the implementation of aliphatic alcohols like the Carboxylic acids contain 1 to 6 carbon atoms in the molecule and are saturated or simply olefinically unsaturated are. These alcohols can contain groups or atoms which, under the conditions of the Process inert, such as alkoxy groups having 1 to 4 carbon atoms or halogen atoms. Suitable Alcohols include methanol, ethanol, isopropanol, butanol, isoamyl alcohols, Ceryl alcohol, allyl alcohol, ethyl glycol, ethylene chlorohydrin and l-bromopropanol- (2).

The alcohol and the carboxylic acid are expediently used in a molar ratio of 1: 1 to 1.5: 1. The preferred molar ratios are between 1: 1 and 1.2: 1, or vice versa.

It is advantageous to use an inert entrainer in amounts of up to about 20 percent by weight to the sum of the weights of alcohol and acid. Suitable entrainers are z. B. benzene, toluene, cyclohexane, n-heptane, chloroform and trichlorethylene. It is surprising that even with the esterification in the vaporous state, the addition of an entrainer for water causes a further increase in the degree of esterification. So can the yield of ethyl acetate by adding 10% benzene to the reactants from 87.3% to 90.5% of theory increase. It is not known which processes are the basis for this increase in yield.

Suitable catalysts are, for. B. those obtained by impregnating an inert carrier material, such as Pumice stone, with a high-boiling strong or

ίο medium-strength inorganic acid, such as 90% Phosphoric acid, followed by heating to 200 to 380 ° C. Also acid boron phosphate is a suitable catalyst. Particularly high yields of esters and high reaction rates is achieved if an acid-activated clay, such as bentonite or montmorillonite, is used as the catalyst, used. These acid-activated clays give space-time yields of up to 50 moles of ester per liter of catalyst space and day. Space-time

The yield is thus considerably higher than that which is comparable with the known processes Conditions is achieved.

It is necessary that the reaction is carried out in the vapor state because the time required to establish equilibrium increases considerably and, moreover, the position of the equilibrium is shifted noticeably to the detriment of ester formation when the catalyst becomes moist. It is therefore carried out in the vapor state, ie at a temperature which is above the dew point of the reaction mixture and below the respective reaction pressure. If you put z. B. whose boiling point is a Carbonsäureester forth at the reaction pressure below 100 ⁰ C, a Rekationstemperatur is recommended above 100 ⁰ C. When the reaction product boiling above 100 ⁰ C, is advantageously chosen reaction temperature is between 100 ° C and the boiling point of the pure ester produced. This is because the boiling point (or dew point) of the reaction mixture is generally below the boiling point (or dew point) of the pure components of the mixture as a result of the formation of azeotropes.
If, on the one hand, it is necessary to select the reaction temperature so high that the catalyst remains dry, then, on the other hand, excessively high reaction temperatures also lead to poor yields. This can be seen from the following table, in which the yield of n-butyl acetate in the reaction of n-butanol and acetic acid in a molar ratio of 1.1: 1 under atmospheric pressure of acid-activated montmorillonite as a catalyst is given as a function of the temperature:

55 temperature Yield of n-butyl acetate ⁰ C ° / o of theory 100 71.7 125 90.8 60 130 87.9 200 59.3 300 12.6 400 0.9

You can see that the best yields
n-Butyl acetate at 125 to 130 ⁰ C can be achieved.

The process according to the invention is carried out at a temperature between 80 and 200 ° C, in particular

particular between 100 and 18O ⁰ C. The most favorable reaction temperature for the preparation of a certain ester and for a certain reaction pressure can easily be determined by a preliminary test.

Since the esterification is slightly exothermic in the vapor state, no heat is usually required to be added once implementation has started. The reaction lets through Appropriate feeding and preheating of the reaction components with a suitable design and autothermal control of the insulation of the reaction space against heat radiation.

The process is preferably carried out under atmospheric pressure. Reduced pressure is especially in the esterification of higher molecular weight carboxylic acids and / or higher molecular weight Alcohols recommended. The dew point is then reduced accordingly, so that one can also with can work relatively low temperatures. Sometimes, e.g. B. in the implementation of lower carboxylic acids with lower alcohols, the equilibrium position and the throughput are also determined by applying increased pressure, d. H. up to 20 at, favorably influenced.

The process is carried out continuously by adding the vaporous mixture of the starting materials passes over the solid, strongly acidic catalyst and liquefies the reaction mixture Worked up distillation and the binary and / or ternary condensates after separation of the water returned to the esterification vessel.

example 1

35

A montmorillonite is used as the catalyst. After activation with three times the amount by weight of 10% hydrochloric acid (8 hours at room temperature) and thorough washing with water, it is shaped into spheres 4 mm in diameter and dried. The activity of the catalyst is determined by titration. To remove adhering acid, a sample is ^{heated to 500 °} C. for 1 hour and allowed to cool in the desiccator. 1.00 g of the sample is ^{shaken with 50.0 cm 3 of} N potassium hydroxide solution for 1/2 hour. After filtering off, an aliquot of the filtrate is back-titrated with 0.1 N hydrochloric acid. The acid content of the catalyst corresponds to 0.7 milliequivalents per gram.

410 cm ^:! this catalyst are filled into a tube 1000 mm long and 25 mm in diameter. The catalyst is heated to 130 ° C. and 150 cm ³ per hour of a mixture of n-butanol and acetic acid in a molar ratio of 1.1: 1, which is evaporated in a preheater, over the catalyst. As soon as the reaction has started, the heating is switched off. The temperature then remains at 122 to 125 ^° C. The vaporous reaction mixture is liquefied. The condensate separates into two layers, the organic layer is worked up by distillation. The ternary mixture, which is obtained as the lowest-boiling fraction, and the binary azeotropic mixture of butanol-n-butyl acetate are returned to the esterification vessel after the aqueous layer has been separated off.

After 850 hours of running time, the experiment was terminated without any deterioration in the Yield was observed. The average yield of n-butyl acetate was 90.8% of theory, based on on acetic acid, with peaks up to 95% of theory.

Example 2

Ethanol and acetic acid are esterified on the catalyst used in Example 1 in a molar ratio of 1.1: 1, the hourly throughput being 50 cm ^{3 of} the starting mixture. The temperature adjusts to 104 ° C. The procedure described in Example 1 is followed and ethyl acetate is obtained in a yield of 87.3% of theory, based on acetic acid.

If 10 percent by volume of benzene is added to the mixture of starting materials, the yield is in ethyl acetate under otherwise identical conditions 90.5% of theory.

Example 3

N-butanol and acetic acid are reacted in a molar ratio of 1.1: 1 over 410 cm ³ of the catalyst described in Example 1 at various pressures and temperatures. For this purpose, a silver-lined pressure pipe with an internal diameter of 22 mm and a length of 2 mm is used. The pipe is surrounded by a heating jacket through which a heating fluid heated to 165 or 175 ° C - in the present case triglycol - is pumped. The 108 cm long catalyst layer, corresponding to 410 cm ^{3 of} catalyst, is located in the middle part of the tube.

The upper part of the tube is filled with glazed porcelain rings and is used for heating and Evaporation of the acetic acid-butanol mixture pumped in from above. The lower part of the tube is also filled with ceramic rings. By having the catalyst in the middle of the furnace, there is one ensures a uniform temperature along the entire catalyst layer. At the top of the A feed line for nitrogen, which is compressed to 100 atm in a storage bottle, is connected to the pipe. The required pressure can be set using a pressure reducing valve.

The product emerging at the lower end of the tube is ^{brought to room temperature via a cooler operated with water at 15 to 20 °} C. and fed into a pressure separator with a sight glass. If the level in the sight glass is kept constant, the product is continuously expanded to atmospheric pressure.

The feed is 150 cm ^{3 of a} liquid mixture of alcohol and acid. The following results are obtained.

pressure temperature yield at ⁰ C Before theory 3 165 88.3 3 175 87.9 5 165 91.2 5 175 93.8 6th 175 87.5 7th 175 85.8 10 175 82.8 12th 175 71.2 14th 175 70.6

Example 4

170 g of 85% phosphoric acid are mixed with 82 g of boric acid to form a homogeneous mass, which solidifies to a jelly after about 24 hours. This is ^{dried at HO 0} C and pressed into cylindrical bodies 8 mm in diameter and 8 mm in length. The catalyst is ^{heated to 350 °} C. for several hours.

650 cm ^{3 of} the catalyst are filled into a tube 1400 mm in length and 28 mm inside diameter and heated to 140.degree. ^{The vapors of 150 cm 8 of} a n-butanol / acetic acid mixture in a molar ratio of 1.1: 1 are passed over the catalyst per hour. The yield of n-butyl acetate in a single pass is 87.2% of theory.

With 20% phosphoric acid on silica rods, the degree of esterification is otherwise the same Conditions 84% of theory.

Example 5

The procedure is as in Example 1, except that 50 cm ³ / hour are passed. liquid n-butanol-propionic acid mixture in a molar ratio of 1.1: 1 in vapor form over the catalyst, the temperature of which is kept at 140 ° C. The esterification is 89.3%, the space-time yield 1.76 kg of ester per liter of catalyst and day.

If the throughput is increased to 150 cm ^s / hour, the degree of esterification goes to 86.8%. return. However, the space-time yield increases to 5.14 kg / l catalyst and day.

Example 6

The procedure is as in Example 1, except that 30 cm ^{3 of} a mixture of α-chloroacetic acid and n-butanol in a molar ratio of 1: 1.1 are passed over the catalyst heated ^{to 200 ° C. every hour.} The yield of n-butyl α-chloroacetate is 80% of theory.

Example 7

The procedure is as in Example 1, except that 30 cm ^{3 of} a mixture of allyl alcohol and acetic acid in a molar ratio of 1: 1.1 are converted every hour. The temperature at the catalyst is 134 ^° C. Allyl acetate is obtained in a yield of 59% of theory.

Example 8

Substituting hour in the manner described in Example 1. 30 cm ³ of a mixture of acetic acid and ethylene chlorohydrin in the molar ratio 1: 1.1 to and maintains a reaction temperature of 150 ⁰ C, then one achieves a yield of acetic acid-yS-chloräthylester of 51 % of theory.

Claims (5)

Patent claims: 1. A process for the vapor phase esterification of aliphatic carboxylic acids having 1 to 6 carbon atoms, which can be saturated or mono- olefinically unsaturated and substituted by halogen, with alcohols over solid, acidic catalysts, characterized in that the esterification is carried out at a temperature between 80 and 200 ⁰ C, preferably between 100 and about 180 ^° C., on a strongly acidic, inorganic catalyst, optionally using an inert entrainer for the water. 2. The method according to claim 1, characterized in that the solid, inorganic, strongly acidic catalyst an acid activated clay, such as bentonite or montmorillonite, or a acid boron phosphate is used. 3. The method according to claim 1 or 2, characterized in that the carboxylic acid and the alcohol in approximately molar amounts or one of the starting compounds mentioned used in a stoichiometric excess up to about 50%. 4. The method according to any one of claims 1 to 3, characterized in that at a pressure up to 20 at works. 5. The method according to any one of claims 1 to 4, characterized in that the inert entrainers in an amount of up to 20 percent by weight, based on the sum of the Weights of alcohol and carboxylic acid, used. Considered publications: Gattermann, »The Practice of Organic
Chemikers', 23rd edition (1933), p. 1; L. F. Fieser and M. Fieser, "Textbook of Organic Chemistry", 3rd edition (1957), p. 190.