DE1043316B - Process for the production of largely pure solutions of peracetic or perpropionic acid in organic solvents - Google Patents

Description

The invention relates to a process for the preparation of largely pure organic solutions of Peracetic acid or perpropionic acid by reacting the carboxylic acids with hydrogen peroxide. These solutions can be largely free of water in addition to hydrogen peroxide.

The conversion of hydrogen peroxide with carboxylic acids to produce peracids has been around for a long time known. The reaction, which is reversible, can be illustrated by the following equation, which the production of peracetic acid concerns:

CH ₃ COOH + HOOH

CH ₃ COOOH

H ₉ O.

The reaction can be carried out by adding a mixture of acetic acid and hydrogen peroxide in The presence of a strong mineral acid as a catalyst is heated. The balance can be right Page shifted if a much larger amount of acetic acid is used in the implementation than is necessary for the reaction with all of the hydrogen peroxide. As a result the instability of peracetic acid, however, difficulties arise when this from the im Reaction mixture also present water, hydrogen peroxide and acetic acid should be separated. the The presence of these substances is undesirable when the peracid is used to epoxidize unsaturated compounds should be used because these admixtures in conjunction with sulfuric acid or other catalysts catalyze the ring opening of epoxides. Although the sulfuric acid neutralizes to some extent can be, but the sulfuric acid salt obtained here is also a catalyst for the Epoxy cleavage.

Various measures have been proposed to overcome these difficulties. So is Attempts have already been made to deposit pure peracetic acid by crystallization, but this process is too dangerous for technical procedures. Peracetic acid is more explosive in crystal form than in solution; it can already be caused to explode by mechanical or thermal influences (»reports from German Chemical Society "Vol. 45, 1845-1853 [1912]).

Another known measure is to replace in the production of peracetic acid the whole or a part thereof by acetic anhydride (USA. Patent 2,490,800;. "Journal of American Chemical Society" Vol 67, p 413 [1945] ). Although in this way, as a result of the removal of water by reacting it with the anhydride, the preparation of anhydrous peracid solutions becomes possible, and although the solution can be prepared to be removed from the unreacted process of preparation

of largely pure solutions

of peracetic or perpropionic acid

in organic solvents

Applicant:

Union Carbide Corporation,
New York, NY (V. St. A.)

Representative: Dr. W. Schalk, Dipl.-Ing. P. Wirth,

Dipl.-Ing. G. E. M. Dannenberg

and Dr. V. Schmied-Kowarzik, patent attorneys,

Frankfurt / M., Große Eschenheimer Str. 39

Claimed priority:
V. St. v. America July 31, 1956

Benjamin Phillips, Paul Spencer Starcher,

Charleston, W.Va.,
and Bertrand Donahay Ash, St. Albans, W.Va.

(V. St. A.),
have been named as inventors

Hydrogen peroxide is free, so there is still the possibility that the anhydride with the peracid under Formation of diacetyl peroxide reacts. But diacetyl peroxide is not only very explosive, it is also annoying also the use of peracetic acid in epoxidation. For example, the diacetyl peroxide catalyzes Polymerizations.

Another known measure consists in adding the peracetic acid solution by fractional distillation concentrate and thereby increase the peracid content to a value of 60 to 75 percent by weight. In addition to the explosion hazard associated with such distillation, this process has the Another disadvantage is that greater losses of peracid occur due to the aqueous preliminary fraction, if not special precautionary measures are taken.

These statements apply mutatis mutandis to the production of perpropionic acid.

The method is based on the fact that solutions of peracetic or perpropionic acids, the largely free of water and hydrogen peroxide, can be produced if the reaction between the carboxylic acid and the hydrogen peroxide in the presence of a catalyst and an organic one Solvent is carried out, which under the

«09 6W414

3 4

Reaction conditions (temperature and pressure) with 4. Of the aromatic hydrocarbons, can

the existing water a heterogeneous azeotropic z. B. Benzene, which normally boils at 80 ° C, and

Forms mixture with the lowest boiling point, which is used toluene, which normally boils at 110 ° C

distilled off from the reaction mixture. will. For the production of perpropionic acid are

This solvent has a boiling point of 50 to 130 ° C at normal pressure, these two aromatic hydrocarbons dissolve the peracid, but suitable and they are therefore preferred
not the water with which it forms an azeotropic mixture. If these azeotrope formers are used for carrying out the process, the maximum no more than 0.5 mole of peracid used in each process can contain the mole of water and that at a temperature of when the water is removed used pressure of about 20 to 90 ° C from the reaction mixture is distilled i ° 6 mm (with one of the higher-boiling organic liquids, until all the water of the aqueous keiten used, such as butyl acetate) to atmospheric hydrogen peroxide and at least part of the or slightly elevated pressure (e.g. water formed from the reaction of chloroform during the use reaction). Preferably mixture is removed. however, the removal of the water in a vacuum

The organic solvent used should therefore be used * 5.

a boiling point at normal pressure of at least Preferably the carboxylic acid and the water are -50 ° C because in azeotropic mixtures forming peroxide used in equivalent amounts. Here-solvents, whose boiling point is below 50 ° C, can, at least in theory, be achieved by the water content of the azeotropic mixture is so low that there is no unreacted water in the end product, that when this mixture is distilled off, only a very small amount of substance peroxide has not yet reacted carboxylic acid in little water is removed. However, this will result in substantial amounts being present when the reaction occurs the duration of the expulsion of the water from the reac- is carried out to the end. For some mixed applications and thus also the reaction time of the peracid, however, is not intended for its manufacture prolonged, and it can also reduce the yield by using exactly equivalent amounts can thereby be reduced. 25 not required, such as for bleaching

In order to drive off the water from the reaction textiles or in the oxidation of sulfides to suI-

In the case of the blow-drying and the like, for which purposes the presence of a

drive at the respective working temperature used, a larger amount of carboxylic acid can be tolerated,

however, the boiling point of the azeotropic mixture below that of the so far known is of no particular advantage

the peracid to be produced. As by experiments 30 by the presence of hydrogen peroxide in the

was found to meet solvents whose boiling peracid achieved.

point is above 130 ° C at normal pressure, this conveyance- Since the reaction of the carboxylic acid with the water

tion not. Preferably, the boiling point of the substance peroxide should be reversible, not only through that

azeotropic mixture at least 10 ° C under the boiling point removal of the water as one of the reaction products,

point of the peracid are at the working temperature, 35 but also by the presence of the carboxylic acid in

and therefore, suitable solvents are those in the reaction mixture in an amount larger than them

preferred, whose boiling point is in the range from 70 to required for the reaction with the hydrogen peroxide

110 ° C. is borrowed, a greater reaction speed or resp.

Suitable solvents are, for example, and a more complete utilization of the hydrogen

the following in question: 40 peroxyds according to the known principles that the

L Saturated low molecular weight aliphatic carbon equilibrium in the case of reversible reactions

acid esters, e.g. B. the methyl, ethyl, propyl, isopropyl, regem, favors. Instead of draining all of the water

The n-butyl, isobutyl, sec-butyl and isoamyl esters distill to bring the reaction to a complete end

Formic acid, acetic acid, propionic acid, n-butyric acid, they can also lead to a desired location of the

and isobutyric acid, the normal boiling point of which is terminated in the reaction. For example, can

Range from 50 to 130 ° C. Esters, which are normal- the procedure will be canceled when the amount of

boiling between 70 and 110 ° C are preferred. dissolved peracetic or perpropionic acid about 20% or

The esters, which are at least 3% each, or distilling off the are also very suitable

2 carbon atoms in their alkyl and acyl groups water can continue until the reaction is up

included, e.g. B. ethyl acetate, propyl acetate, isopropyl 50 run to the end and the peracid solution practically

acetate and ethyl isobutyrate, as this is anhydrous against hydrolysis.

are more stable than the methyl esters and the ants are the starting materials in practically equivalents

acid ester. Quantities or the acid used in slight excess,

2. Saturated low molecular weight aliphatic simple, so is easily a symmetrical or mixed ether, according to the present process ^; n those at the 55 to about 90 ° / ₀ ige conversion of the hydrogen per ether oxygen atom obtained methyl, ethyl, propyl, iso-oxide. In processes in which the propyl, η-butyl, isobutyl, sec-butyl, tert-butyl, measures according to the invention are not carried out, cyclopentyl, neopentyl, tert-amyl, isoamyl , Prim.- on the other hand a ratio of about 10 moles of acetic acid isoamyl, 3-pentyl and n-amyl groups are bound per mole of hydrogen peroxide in the form of its 50 ° / ₀ igen and a normal boiling point in the range of 60 aqueous solution and of about 4.7 moles of acetic acid per mole of 50 to 130 ° C. Ethers which normally boil between hydrogen peroxide in the form of its 90 ° / ₀ igen aqueous 70 and 110 ° C are preferred. Ether, the solution required to achieve the same or a similar chlorine or fluorine solution, within the borrowed degree of conversion.

The concentration of the given range and boil below the reaction are stable (such as ether, 65 include hydrogen used as a starting product which the carbon atom on which the halogen peroxyds is not critical, and it can with is bound, not directly to the ether oxygen- good results the aqueous hydrogen peroxide atom adjacent) can also be used. solutions that are commercially available can be used.

3. Of suitable aliphatic chlorinated hydrocarbons with a hydrogen peroxide content of approx substances are called chloroform. However, 70% to 95% by weight is preferred.

5 6

The higher the concentration of the peroxide solution is to be added to the reaction vessel through lines not shown.

of course, the amount of water that is carried is thus less, and the reaction mixture obtained is carried out

is to be removed in the course of the reaction, so that the suitable heating devices, also not shown

The advantage is that the duration of the procedure and heated. The perder withdrawn from the reaction vessel Heat consumption can be reduced. Also at 5 acid vapors are liquefied in the column 14 and

Concentration of hydrogen peroxide of 25% and flow together with the other condensable

higher the tendency of the peracid as a component of the substances (water and entrainer) to enter the reaction

Distilling over azeotropic mixture reduces. get back. The non-condensed vapors

In the case of the present process, the catalysts can be cooled in the condenser 15. This here drive all the substances used whose suitability io resulting liquid condensate flows through a pipe, for example

is known as acidic esterification catalysts, i.e. at the bottom and below the liquid level,

for example sulfuric acid, alkylsulfonic acids and aryls which is maintained in the separator, in

sulfonic acids, phosphoric acid and acidic phosphoric acid - the separation vessel. Here the condensate separates into one

alkyl esters, trifluoroacetic acid and acetylsulfoacetic acid. aqueous and an organic layer. The upper orga-also with a number of ion exchange resins are 15 niche is through line 23 after the layer

good results have been obtained. Preferred catalyst column recycled, while the lower aqueous

gates are sulfuric acid and alkyl sulfone and aryl layers from the separation vessel from time to time

sulfonic acids, such as ethane, butane, hexane, decane, for example attached to their bottom, not shown

Benzene, toluene, xylene and naphthalenesulfonic acid, tube is withdrawn. For the implementation of the sulfonated Polystyrene and sulfonated styrene-divinyl 20 driving at reduced pressure can reduce the pressure in the

benzene copolymers, such as those under the commercial device through the vacuum pump 17, through which

designation "Dowex 50" and "Amberlite IR - 12Ck gases or vapors from the cutting device 16, for example

known cation exchange resins. at the head of which can be withdrawn through the pipe 24,

The catalyst is said to be used in such a large amount to reduce it.

be that at least a moderate reaction rate 25 The device of Fig. 2 consists of a reaction

age is preserved. The catalyst vessel 51, a still 52, and one attached to this are expediently

in amounts of at least 0.2 parts per 100 parts by weight of ordered fractionation or rectification column 53, a

the carboxylic acid used. In the absence of a catalyst condenser 54 and a separation vessel 55. As in the

Although a reaction takes place sators, it takes place Fig. 1 also here the acetic acid, the aqueous one

too slow to be of any technical importance 30 hydrogen peroxide, the organic solvent and

could. If appropriate, the catalyst, but also the acidic catalyst, can be fed to the reaction vessel 51,

in an amount of 5 parts per 100 parts of carboxylic acid, which is equipped with a stirrer 61 here.

to be used. The use of larger amounts than the contents of the reaction vessel can be based on normal,

5% has no advantages, especially not in cases where positive or negative pressure is maintained. That the per-

in which a neutralization of the catalyst before the 35 acid-containing reaction mixture flows through the

Use of the peracid is indicated. A lot of the line 62 connected to a flow regulating

Catalyst from 1 to 2 parts per 100 parts by weight of valve 63 is provided, in the fractionation column 53, about

So carboxylic acid is preferred. in the middle, one and from here down over in the

The process can be used both in batches and in columns, but not drawn trays or

be carried out continuously by a solution 40 similar devices. This downward flow stands

the hydrogen peroxide with the carboxylic acid in counter-the reaction mixture in intimate contact with the hot

War of the catalyst is heated and at the same time the water is steaming the solvent and that way

is removed from the reaction mixture. The implementation freed from its water content. The one from the water

can be carried out at a temperature of 20 to 90 ° C. The freed mixture passes from the bottom of the column into the

be, however, a temperature of 30 to 65 ° C 45 still 52, from where the solvent vapors

preferred. Below 30 ° C the reaction is too slow to get into the rectification device while

and at a temperature above 65 ° C, the waste becomes the hot, anhydrous bottoms product through line 64

active oxygen through the formation of mole- in the reaction vessel 51 by means of the pump 65-

Cular oxygen is passed through the decomposition of the hydrogen.

peroxyds or the peracid or both favored. 50 The expelled water rises as an azeotropic steam-preferential is also the expulsion of the water mixture with the organic solvent by the felt under reduced pressure. This has the column 53 upwards, passes through the top of the column Advantage that a lower temperature is maintained- line 66 out and then flows after the condensation and thus the decomposition of the peracid is reduced by sator 54 in which the azeotropic vapor mixture is congealed. 55 is condensed. The condensate is passed through the line 67. In the drawing, two devices are schematically guided into the separation vessel 55 as in FIG. 1 and shown, which for the implementation of the invention, the upper organic layer through the line 68 in the moderate procedure can be used. Recirculated column, while the lower aqueous Fig. 1 shows an apparatus in which the process is withdrawn from time to time from the separation vessel becomes 60 neither batch nor continuously and possibly 60. For working under reduced pressure is one vacuum pump 71 is also provided under reduced pressure, namely the suction can, and Fig. 2 shows a device in which the side of the pump through the line 72 approximately at the head of the Reaction mixture connected between the reaction vessel and separation vessel, a distillation column circulates. The method according to the invention is carried out by the following

According to Fig. 1, the device consists of a reaction 65 illustrates the examples

tion vessel 10, a fractionation arranged on this.

or rectifying column 14, a condenser 15, one example

Separation device 16 and a vacuum pump 17. The 144 g of a 35% aqueous hydrogen peroxide-acetic acid, the aqueous hydrogen peroxide, the organic solution (1.48 mol H ₂ O ₂ ), 88 g acetic acid (1.48 mol), 2, 4 g niche solvent and the acidic catalyst are 70 concentrated sulfuric acid and 1200 g chloroform

7 8

were in a still with a fraction of 80% of theory. The amount of unreacted aquatic animal attachment present in the distillation column and a decantation residue connected to it, which was designed so that the water without peroxide was 3.5 g (about 0.5 percent by weight), interruption of the vacuum could be drawn off, which shows that the reaction was practically over to the end, was brought to a flask temperature of 40 ⁰ C 5, heated and the pressure in the device to an example 4

Reduced value at which the distillation at the

Piston temperature took place (about 320 mm Hg). The acetic acid (234 g; 3.9MoI), hydrogen peroxide (103 g;

Distillate was divided into two layers, namely 3.02 mol) in the form of 114 g of an aqueous 90% strength, the upper layer of water, which came from the decanting ίο solution, 10 g of concentrated sulfuric acid and 660 g rate during the distillation continuously withdrawn. Ethyl acetate was added together with 1.5 ecm of a 30 ° / ₀ igen Within 11 hours, a total of 126 g of a solution of the polyphosphate used in Example 2 in water, which heated a small amount of hydrogen peroxide and acetic acid to a temperature of 50 ° C and held that , removed. The theoretical total amount of water distillation carried out at a pressure of 180 mm was calculated to be 121 g. Was (The fact that a 15 The distillation of the water was obtained by practically larger amount of water than the calculated, 7 terminates _^3/4 hours.

can be partly due to the decomposition of water The peracetic acid in an amount of 200 g (calculated)

substance peroxide in oxygen and water, was used as a residue in the form of. 853 g of an ethyl dung somewhat moist reactants and the anacetate solution with a peracetic acid content of 23.4 were present of impurities in the water obtained 20 percent by weight, which corresponds to a yield of 87% of the explain.) corresponds to theory. In the ethyl acetate solution only remained

A small amount of unreacted hydrogen peroxide was left in the reaction vessel as the distillation residue 1211 g of a 6.7% peracetic acid solution in chloroform, back (0.44% by weight = 3.8 g), which shows accordingly 72% of theory obtained, which is still 1.57 g, that the reaction practically led to the end contained unreacted hydrogen peroxide. Turned 25.

Example 2 Example 5

370 g (5MoI) propionic acid, 4MoI hydrogen peroxide, acetic acid (117g; 1.95MoI), hydrogen peroxide (51g;

in the form of 426 g of 32 ° / "aqueous H ₂ O ₂ solution, 1.5 mol) in the form of 56.5 g of a 90 ° / ₀ aqueous solution of 3.7 g concentrated sulfuric acid and 1193 g (800 cc ) 30 solution and 310 g of ethyl acetate were in the absence of chloroform, were in the apparatus of example 1 of a catalyst and in the presence of 0.5 cc together with a 0.5 g of a polyphosphate (under the 30 ° / ₀ solution of example 2 used PolyDesignation pVictawet 35 B «; its formula phosphates in acetic acid under a pressure of 130 mm is Na ₅ R ₅ (P ₃ O ₁₀ ) ₂ , where R is a 2-ethylhexyl radical heated to a temperature of 50 ° C The rectifier means; it serves to trap heavy metal ions, 35 column was kept at such a temperature that the decomposition of peracid or hydrogen peroxide only decatalyzes the water from the reaction mixture) to a flask temperature of 40 ° C, but the other components of the steam is heated and the pressure is increased f reduced by about 250 mm. Under the prevailing temperature and pressure conditions, a distilled water and chloroform nits flow back. The water that was deposited in the decanting azeotropic mixture, which deposited in the decanting attachment, was continuously collected from the detecting attachment system, in which it was removed, and after 3 hours 20 ecm had distilled off, two layers separated. The aqueous upper layer was and amounted After the flask temperature continuously removed at the appropriate Ändewährend the distillation is tion of the pressure to about 220 mm Hg at 6O ⁰ C increased within 20 hours 365 g. Theoretically calculated, an amount of water of 362 g was still present within a further 4.67 hours. 45 3 ecm received. According to analysis, the distillery contained

When the reaction was complete, a small amount of residue (375 g) formed 3.8 percent by weight peracetic acid Chloroform at a temperature of 33 ° C and one and 11% hydrogen peroxide, which is a reaction pressure drifted by 110 mm. The calculated amount corresponds to peracetic acid of 12.5%. The ge (240 g) Perpropionic acid was obtained as a residue in the form of a total recovery of peroxide was 95.5%. (Under of 449 g of their chloroform solution obtained, which has a peroxide "total recovery of peroxide" is the back propionic acid content of 53.4%. This corresponds to the amount of peracid + hydrogen peroxide obtained a yield of 67%, calculated in terms of hydrogen, i.e. the recovery of »active acid peroxide. A small amount of perpropionic acid (11 g; stoff «.)

0.12 mol) distilled off together with the chloroform. The flask temperature was then at the appropriate

55 Adjustment of the pressure to about 340 mm Hg at 70 ° C

Example 3 increases and the reaction continued for another 6 _^3/4 hours.

Hydrogen peroxide (2 mol) in the form of 194 g of a further 9 ecm of water were distilled off (a total of 35% aqueous solution, 120 g (2 mol) of acetic acid, 3.1 g including 32 ecm). The flask residue (343 g) contained concentrated sulfuric acid and 688 g of isopropyl acetate according to analysis 20.6 g or 5.96% of the peracetic acid, what were as in the previous examples at 40 ° C 60 corresponds to a degree of conversion of 18%. The warmed up and careful attention was paid that this rate of peroxide recovery was 64%. temperature was not exceeded. The heating was up. .

under such reduced pressure (about 10 mm Hg) Examples

carried out that during heating an azeotropic acetic acid (117 g; 1.95 mol), hydrogen peroxide

Mixture of water and isopropyl acetate distilled off. 65 (51.5 g; 1.5 mol) in the form of 96 g of an aqueous After 7 ¹ I ₂ hours, the distillate was free of water and corresponds 53.4% solution, 5 g of sulfuric acid and 300 g of n-Prohielt may only still traces of it. pyl acetate were added after adding 0.7 ecm of a 30%

The remaining product in the flask in an acetic acid solution of a polyphosphate (see FIG. 2 example) Quantity \ ^{τ οη} 709 g contained, according to analysis of 123 g (17.3 overall at 5O ⁰ C eiwarmt and the pressure to 85 mm reduced weight percent) Peracetic acid, resulting in a yield of 70. After 2 hours 50 minutes, 82 ecm of water were removed.

distilled. The flask residue (378 g) contained 25.2% (95.3 g) peracetic acid, which corresponds to a yield of 83.5% is equivalent to. A further 4.8 g of peracetic acid were found in the distilled propyl acetate, whereby the Overall yield increased by 4.2% to 87.7%. The residue still contained 0.04% (0.15 g) unreacted Hydrogen peroxide and about 2.3% of the hydrogen peroxide used (2.6 g) were in the form of peracetic acid found in the aqueous distillate.

IO

Example 7

Hydrogen peroxide (51.3 g; 1.5 mol) in the form of 96 g of a 53.4% strength aqueous solution, 117 g (1.95 mol) of acetic acid, 15 g of the acidic form of the sulfonic acid- ^{containing 1} S ion exchange resin »Amberlite IR - 120 ": and 300 g of n-propyl acetate were as in the previous examples in the presence of 0.7 ecm of a 30% solution of a polyphosphate (see. Example 2) at a pressure of 80 to 100 mm under reflux to a piston temperature. ^ao temperature of 50 ⁰ C warmed. After 2.67 hours, 86 ecm of water had distilled off. The cooled flask residue containing the peracetic acid was filtered to remove the ion exchange resin. The filtrate (344 g) consisted of a clear, colorless solution of peracetic acid in propyl acetate. The peracetic acid content was 24.7 percent by weight (86.2 g), which, calculated on hydrogen peroxide, corresponded to a yield of 75.6%. A further 6.9 g of peracetic acid were contained in the lower layer (propyl acetate layer) of the distillate, as a result of which the yield increased to 81.7% of theory.

The peracetic acid contained no catalyst acid and 0.09% (0.31 g) unreacted hydrogen peroxide. 3.8% of the originally used hydrogen peroxide was contained in the distilled water as peracetic acid.

Example 8

Hydrogen peroxide (51.3 g; 1.5 mol) in the form of 96 g of an aqueous 53.4% solution, 117 g (1.95 mol) of acetic acid, 5 g of concentrated sulfuric acid and 300 g of isopropyl acetate were, after the addition of 0, 7 ecm of a 30% solution of a polyphosphate (cf. Example 2) in acetic acid is ^{heated to a temperature of 50 ° C. under a pressure of about 120 to 125 mm to 4} ° C. and the azeotropic mixture of water and isopropyl acetate is removed under reflux. After 3.5 hours, a total of 79 ecm of water had distilled off. 374 g of a peracetic acid solution in isopropyl acetate were obtained as a residue. The peracetic acid content was 26.2 percent by weight (98 g). Based on the hydrogen peroxide, the yield was 86% of theory. The solution contained no more than 0.01 percent by weight hydrogen peroxide.

Claims (9)

Patent claims: 1. A process for the preparation of largely pure solutions of peracetic or perpropionic acid in organic solvents by reacting acetic or propionic acid with aqueous hydrogen peroxide in the liquid phase and in the presence of an acidic catalyst, characterized in that the reaction is carried out in the presence of an inert organic solvent that at atmospheric pressure, a boiling point of 50 to 13O ⁰ C has, peracids, but does not dissolve water and forms with this water, a heterogeneous azeotropic mixture containing not more than about 0.5 moles of peracid per mole of water, is carried out to give an amount of water which corresponds to the total amount of the water in solution of the hydrogen peroxide solution and at least part of the water which is formed during the reaction is ^{distilled off from the reaction mixture at a temperature of 20 to 90 °} C. as an azeotropic mixture. 2. The method according to claim 1, characterized in that there is a 25 to 95 percent by weight aqueous hydrogen peroxide solution is used. 3. The method according to claim 1 and 2, characterized in that the aliphatic monocarboxylic acid and reacting the hydrogen peroxide with one another in equivalent amounts. 4. The method according to claim 1 to 3, characterized in that the catalyst used is sulfuric acid, an alkyl or an aryl sulfonic acid is used. 5. The method according to claim 1 to 4, characterized in that 1 to 2 parts by weight of catalyst used per 100 parts by weight of carboxylic acid. 6. The method according to claim 1 to 5, characterized in that the reaction is carried out at a temperature from 30 to 65 ° C. 7. The method according to claim 1 to 6, characterized in that the reaction is carried out in vacuo performs. 8. The method according to claim 1 to 7, characterized in that a solvent with a boiling point of 70 to 110 ⁰ C is used as an entrainer for water. 9. The method according to claim Ibis 8, characterized in that that the entrainer for water is chloroform, benzene, toluene or a saturated low molecular weight aliphatic carboxylic acid ester used. 1 sheet of drawings