DE2305921C3 - Purification of 2-pyrrolidone - Google Patents

Description

a) in the starting product 0.1 to 0.8 percent by weight, based on the weight of the commercially available 2-pyrrolidone, analytically pure, practically anhydrous hydroxide of an alkali metal or alkaline earth metal dissolves,

b) the solution obtained in this way at a temperature of 90 to 120 ° C. and a maximum pressure of 5 mm Hg falling film molecular distillation at which the feed rate the solution is sized so that the non-volatile impurities of the solution on remain on the heated surface together with the metal hydroxide, and

c) the evaporated 2-pyrrolidone is condensed at a temperature of about 30 to 60 C and collects, after optionally first the commercially available liquid 2-pyrrolidone cooled to about 20 to 24 C, the crystalline 2-pyrrolidone formed from the liquid impurities separated and liquefied again.

2. The method according to claim 1, characterized in that the feed speed of the to evaporating solution is dimensioned so that up to 6% of the 2-pyrrolidone with the non-volatile Drain off any impurities in the solution on the heated surface of the apparatus.

3. Process according to Claims 1 and 2, characterized in that the metal hydroxide is used Potassium hydroxide used.

4. Process according to claims 1 to 3, characterized in that the hydroxide in an amount of about 0.5 percent by weight, based on the weight of the commercially available 2-pyrrolidone is used.

5. Process according to claims 1 to 4, characterized in that one works at about 110 ⁰ C and a maximum of 1 mm Hg.

Hydrides, hydroxides, pentoxides and various volatile solvents. However, some of these known methods are poorly effective which is due to the large amount of waste generated ai commercially available 2-pyrrolidone Some of these known processes are only to be used with 2-pyrrolidone, which after a certain Manufacturing process was obtained, and these known processes lead to a 2-Pyrro

ίο lidon, which is not really pure, as can be seen from it

Inability to enter into polymerization reactions

and its inability to maintain a stable clear color for longer than about 1 month.

From the USA.-Patent 28 06 856 is a Ver

\ 5 drive to the treatment of 2-pyrrolidone with an acid anhydride, subsequent vacuum distillation through a fractionation column, afterwards! Treatment of the distillate with an alkali carbon or hydroxide and a final, second

known as vacuum distillation. Furthermore, from dei USA.-Patent 28 02 777 a cleaning method known in which water trains to 2-pyrrolidone sets and the 2-pyrrolidone monohydra is crystallized out with cooling. This is followed by an azeo tropical distillation of the water from the crystals with toluene, whereupon the 2-pyrrolidone concludes is still distilled in vacuo. Furthermore, the German Auslegeschrift 12 95 556 is a cleaning known process in which the purification is carried out by recrystallization from an alkanol.

The object of the invention is therefore to provide an economical and very effective method for order Conversion of commercially pure 2-pyrrolidone into practically pure, practically anhydrous 2-pyrrolidone

its effectiveness from the method according to which the 2-pyrrolidone was produced independently and this results in a practically anhydrous 2-pyrrolidone sol rather purity leads to it being polymerizable in high yield.

The invention is based on the knowledge that. the specified problem can be solved in that untci precisely defined, coordinated and mutually influencing procedural conditions a hydroxide treatment with subsequent molecular distillation is carried out.

The inventive method for the preparation of practically pure, practically anhydrous 2-pyrro · lidone from commercially available liquid 2-pyrrolidor by treatment with a metal hydroxide unc Distillation under reduced pressure is characterized in that one

a)

The invention relates to a process for the preparation of practically pure, practically anhydrous 2-pyrrolidone from commercially available liquid 2-pyrrolidone.

As is well known, 2-pyrrolidone of commercial purity usually contains about 2 percent by weight of compound b) certain types of impurities, e.g. B. water, butyrolactone, bipolar mesomer, amino acids and other, unknown substances, depending on the method of manufacture and handling of the pyrrolidone malerials, with these impurities for certain end uses these - material do not pose a problem, but on the other hand for other purposes render the material unusable. c)

Numerous cleaning methods have therefore become known over the years. / .. B. a treatment with in the starting product 0.1 to 0.8 percent by weight based on the weight of the commercially available one 2-pyrrolidone, analytically pure, practically anhydrous hydroxide of an alkali metal or alkaline earth metal solves,

the solution thus obtained at a temperature of 90 to 120 C and a pressure of maxima Subjected 5 mm Hg to falling film molecular distillation at which the feed rate is the Solution is sized so that the non-volatile. ' Impurities in the solution on the heated Remaining area together with the metal hydroxide, and

the evaporated 2-pyrrolidone condenses and collects at a temperature of about 30 to (-0 C, after you first have the trade

conventional liquid 2-pyrrolidone at about 20 to 24 C wiper blades that the liquefied 2-pyrrolidone _On v

cooled and continuously strip the formed crystalline 2-pyrrolidone from the surface of the column

separated from the liquid contaminants cause it to flow more rapidly into the flask. the

and liquefied again. non-volatile impurities remain on the

⁵ surface of the heated outer wall and flow

To carry out the method of the invention in a separate flask connected thereto.
_W ith preferably in a first process stage, the speed at which the solution in the 2-Pyrrohdon is fed from serving as Ausgangsmatenal molecular distillation apparatus, should liquid 2-pyrrolidone from the commercial purity critical are preferably adjusted so that a certain itallisiert, after which the crystalline Material from the dark 10 small portion of 2-pyrrolidone is separated the entire length of the colored mother liquor. This mother-heated column or heated wall pass gelasbuge usually represents about 1 to 2 percent by weight sen and the contaminant flask is allowed to flow into the weight of the total starting material. Otherwise the impurities will solidify and the crystalline 2-pyrrolidone contains numerous genes and the metal hydroxide on the heated surface impurities that cannot be removed by washing and impair the smooth operation. the still The in this way

In the second process stage, 2-pyrrolidone, which was proposed according to the invention, acts as a solvent

According to the process, the crystalline 2-pyrrolidone is used for the impurities and for the metal hydroxide

liquefied, e.g. B. by increasing the temperature and represents only about 2 to 6% of the total amount.

the same to one above the melting point of ao. This embodiment is preferred. Self-evident

2-pyrrolidone lying temperature, preferably at borrowed, it is also possible to use all of the 2-pyrrolidone

a temperature between about 25 and 27-C to evaporate this, but in this case is a more common one

Melting the entire material to ensure cleaning of the apparatus is necessary because then the

whereupon in the liquid obtained about 0.1 to impurities, which are no longer liquid, of

0.8 percent by weight, based on the weight of the 25 walls that need to be scraped off,

liquefied 2-pyrrolidone, an alkali metal, water present in the starting solution is

hydroxyds or alkaline earth metal hydroxyds from analy- from the molecular distillation apparatus as steam

tic degree of purity and thus practically completely removed with the help of the vacuum line. Water is under

digfci anhydrous. The specified are those prevailing within the distillation apparatus

Quantities are so volatile for the process of the invention 30 temperature and pressure conditions that

This is critical, as is the practically complete temperature of the condensation wall or column

The metal hydroxide used is free of water and is much higher than the evaporation temperature

In the third stage of the process according to the invention, water.

The 2-pyrro-die containing the metal hydroxide is then applied to the surface of the heated columns or udon solution slowly into a falling film vacuum still- 35 heated wall in the molecular distillation apparatus brought in. The solution applied is preferably the metal hydroxide, Solution first degassed and then slowly to the dissolved in the impure 2-pyrrolidone, as well as the metal heated Surface of the molecular distillation apparatus hydroxide, which deals with the impurities fed, whereby the temperature of the heated has connected to form substances that are below Surface is 90 to 120 C and the pressure is non-volatile within 40 the prevailing conditions, the distillation apparatus maximum 5 mm Hg These non-volatile substances, together with the amounts Wrest amounts of liquid 2-pyrrolidone flow at the

One type of such a molecular distillation surface of the heated column or heated wall apparatus has a central heatable column as well as down and are collected in the connected column - a condensate arranged at a short distance therefrom. The bulk of the pure 2-Pyrrosationswand on, and in the intervening lidons evaporated from the surface of the heated interspace, the vacuum is maintained. Column and condenses on the condensation wall. The heated column has a flask in the column or column of the apparatus due to the fact that the bond used to hold the liquid is determined by the temperature of the condensation wall or column along the surface of the column below 5 ° is significantly below 9O ³ C, which the minimum flows without evaporating from this, ie that the evaporation temperature of the pure 2-pyrrolidone this flask takes the non-volatile constituents under the minimum reduced pressure inside the, and the outer condensation wall stands with system represents. The temperature of the condensation of a separate flask in connection, which the- area is between about 30 and 60 ⁼ C. The condensate absorbs the liquid that evaporates from the area of the 55 sated pure anhydrous 2-pyrrolidone flows on the central column and on the inner top - Condensation surface downwards and is thus condensed in the surface of the outer wall. connected flask collected.

Another type of such a molecular distilla- The weight of impurities plus that

tion apparatus makes use of a cooled hydroxide and the lost 2-pyrrolidone,

central condensation column and a heated ^6o which in the one connected to the heated column

outer wall or jacket between which pistons are collected is 5 to 10% of the

there is a vacuum. The solution to be cleaned Weight of the starting material. The pure anhydrous

slowly the inner surface of the heated liquid 2-pyrrolidone, which is in the with the condensation

Wall supplied, whereby the 2-pyrrolidone is collected in a short flask connected to the sationsflächenc,

Time evaporates and the surface of the central con-65 is clear and colorless, has a density of 1.117 at

condensation column condensed. The condensed 2-Pyrro- 25 C, a melting point of 24.8 C, a Bre-

Lidone flows to a with the surface of the column chung index of 1.484 at 30 C, a pH of

connected piston, usually with the help of 10.2 and is stable and resistant to

cooled to the 2-P> rrolidone in a dark brown Completely crystallize out the mother liquor. The mother liquor, which was 1 to 2 percent by weight of the starting material was poured off from the crystals.

The crystalline material was reduced to 25 b ^; It was heated to 27 ° C. in order to completely liquefy it, whereupon HOg was drawn off and 0.6 g of analytical grade potassium hydrochloride was dissolved in it.

The resulting solution was then poured into the Trichier

Discoloration when exposed to light for more than 6 months.

The use of falling film molecular vacuum reading apparatus is found to be used
of the process of the invention as essential, since prolonged heating of the 2-pyrrolidone in the presence of
Alkali and even from traces of water to one
Hydrolysis, a breakdown of the pyrrolidone ring and
for the formation of amino acids and / or amino acid
»Alzen can lead. In the molecular distillation - in a falling film molecular distillation apparatus - the heated element has a top and degassed for 10 minutes. The surface temperature used, which is the same as the evaporation distillation apparatus, had a centrally arranged temperature or that slightly above the evaporation column, which was heated inside by toluene vapors to a temperature of the 2-pyrrolidone below the reduced constant temperature of 110.6 C. . The pressure of the system is so that most of the space between the central heated 2-pyrrolidone evaporates on contact with the heated column and the outer condensation wall or immediately. In this way, the duration of the coating was kept at a vacuum pressure of 0.5 γρφ on heating the 2-pyrrolidone in the presence of the alkali mercury pressure.

The degassed solution was transferred to the distillation apparatus.

Water limited to a few seconds or less. 20 added dropwise onto the surface of the door The usable falling film molecular distillation heated column, where the volatile 2-pyrrolidone apparatuses are known, commercially available device vapors, while the non-volatile impurities. on the heated column in a liquid state

A small amount of 2-pyrro remained useful in carrying out the process of the invention Metal hydroxides are the alkali metal lidone that acted as a solvent. The small amount hydroxides, e.g. B. Sodium hydroxide, potassium hydroxide in water, which is present in the solution, was also and lithium hydroxide, as well as the alkaline earth metal- evaporates, and the water vapor that volatilizes as the hydroxyde, e.g. B. barium hydroxide and calcium 2-pyrrolidone vapor could not condense and hydroxide. Most advantageously, the use has been removed through the vacuum line and out of it Potassium hydroxide and sodium hydroxide are given in the 3 ° half of the distillation apparatus in a liquid Proven order. The metal trap collected. The 2-pyrrolidone vapors condensing hydroxide must rot in a practically dry state on the inner surface of the condensation wall and should never be exposed to water or coating that has a temperature of around contained, as in the special used, handeis- 50 C exhibited due to the fact that the external moderately available metal hydroxide of an analytical surface of the casing room temperature of about Degree of purity «is present. So contains z. B. Was exposed to potassium-27 C. If desired, the hydroxyd of analytical purity 10 to 13% coating is cooled by cold water. Water, sodium hydroxide of analytically pure- The non-volatile impurities run off

Degree of unity 1 to 3% water, lithium hydroxide and were in that with the area of the heated column 1% analytical purity water and barium 40-connected flask collected; they made OK hydroxide of analytical purity 10 to 11% by weight of the initial solution. That condensed Water. These metal hydroxides are practically 2-fyrrolidone and flowed off the condensation wall Denoted anhydrous in the context of the invention was collected in the associated flask; Procedure. it made up 100 parts by weight of the starting solution.

The presence of these small amounts of water in the resulting 2-pyrrolidone was odorless and colorless iMetal hydroxides of analytical grade and remained odorless and colorless after 6 months

long exposure to light. It had a pH value of 10.2, a refractive index of 1.484 at 30 C, a density of 1.117 at 25 ³ C, a melting point

Substantial amounts of amino acids, e.g. B. at 50 of 24.8 C and a boiling point of 248 C. 4-aminobutyric acid, resulting in a loss of substantially 760 mm.

- j ο

makes these materials more soluble in 2-pyrrolidone, ice if they were absolutely anhydrous. The presence On the other hand, larger amounts of water lead to formation

borrowed amounts of 2-pyrrolidone and one decreased

Effectiveness of the cleaning process.

The pure 2-pyrrolidone which can be prepared according to the invention

Example 2

5.5 g of potassium hydroxide of analytical purity is particularly suitable for such 55 degrees were dissolved in 1100 g of liquefied 2-pyrrolidone known uses of 2-pyrrolidone, and the resulting solution was in the funnel from the use of the pure, practically water - Benefit from a 4 inch molecular still free material container. One of the heatable wall type introduced in this regard. The solution of particularly important use is the poly- was degassed for 10 min and then the heated tnerization of this material with the formation of poly- ⁶ ° wall of the distillation apparatus, which electrically converts to fibers, which has a wide application a temperature of 110 was heated to 115 C, in

In the presence of a vacuum of a maximum of 2 mm pressure slowly fed. The majority of the 2-pyrrolidone flash-evaporated from the heated wall and condensed ⁶ 5 catalyzed on the cold surface of the condensation central column in the interior with the aid of cold water

develop area, are extrudable.

The following examples are intended to explain the process according to the invention in more detail.

Example I.

Commercially available 2-pyrrolidone was brought to a temperature of around 23 to 24 C in the transport container

was chilled. Spiral rotor blades wiped the liquid contaminants from the heated wall and

7 8

acted a more rapid drainage of the same in those with (94.3%) 2-pyrrolidone with d ' ^M = 1.1099 and

flask connected to the heated wall. The ver ηυ '^1!> ■ - 1.4861. The values given for pure 2-pyrrolidone

Impurities flowed together with a small new value corresponding to 1.1110 and 1.4860, respectively. The attainable

Amount of liquid 2-pyrrolidone which was the contaminated product was clear with no yellow color, which also

and kept the hydroxide in solution, which 5 did not appear later. The polymerization of 100 g in

heated wall downwards using the spiral- the same way as before gave 95.9% of a poly-

rotor blades and were in an associated merisats with an inherent viscosity

collected separate flask. The pure liquid of 10.3.
2-pyrrolidone flowed down the condensation surface

in the associated piston. The isolated pure * ° comparative experiment 2

2-pyrrolidone weighed 979 g, and the impurities, nc »η ■. u -r "-.o" -. -n-> x

plus the hydroxide and the lost (USA.-Patentschnft 28 02 777)

2-pyrrolidone accounted for about 126 grams. According to the information in this publication

The stated crystallization level was only as 150 g (1.76 mol) of commercially available 2-pyrrolidone

Any measure carried out, namely 15 mixed with 31.7 g (1.76 mol) of water and placed on OC

usually only in those cases where the output has cooled down. The cold, crystallized mixture became

material had a color that filtered the presence of. The crystals turned into water

removed substantial amounts of the bipolar mesomer azeotropic distillation with toluene. The back

or other impurities. The darker the constant toluene was distilled off, and the 2-pyrro-

This coloration was all the more advantageous because 2 ° lidone was obtained by vacuum distillation. the

the initial crystallization to apply to this yield was 115.7 g (77.13%) of 2-pyrrolidone, which

Way to separate the mother liquor. were still a little stained. The total treatment

. . treatment time was 4.5 hours. During the polymerization

Example 3 _{to e} j _nem homopolymer as previously resulted

The procedure of Example 1 was carried out using 46.0% of a soft, low-quality polymer

Use of barium hydroxide and calcium hydroxide of low molecular weight.

instead of the potassium hydroxide used previously. For comparison, the same starting product was used repeated. In this case, however, only half the amount was again made according to the procedure of the following by weight of the alkaline earth hydroxide added as game 2 treated. For this purpose 150 g with 0.75 g This behydroxid compared to the previously used alkali metal potassium hydroxide at room temperature (25 C) have a value of 2. acts and subjected to molecular distillation. the

A purified 2-pyrrolidone was obtained, the yield was 144.0 g (95.5%) of 2-pyrrolidone, where

showed the same analytical values as that for which the product obtained was colorless and odorless. the

Example 1. The total treatment time was only 0.5 hours. In the

The superiority of the polymerisation according to the invention to a homopolymer, which, like rens, results over what was previously described, 94.5% of a prior art polymer was obtained from the following comparative drawings,
to attempt:

Comparative experiment 1 4o comparative experiment 3

(USA.-Patent 28 06 S56) (German Auslegeschrift 12 95 556)

First, 300 ε of commercially available 2-pyrrolidone .. ® ™ ^a ' ^s "starting product used, commercial

with a density at 30 ° C. of 1.1131 and a standard 2-Pyrrohdon had the following physical properties

Refractive index at 25 C of 1.4587 with 1% (3 g) 45 Switching on:

reagent grade KOH mixed. The mixture became d ³⁰ = 1.1131

divided into two portions of 151.5 g each. «O ²⁵ = 1.4587

The first serving was made from an Ordinary Coloring (APHA) = 25

Distillation flask at 20 mm pressure without using _. . _. . . ... ,. ,

distilled manure of a fractionating column. The result of the decision, this starting product after

booty was 100g (66%) 2-pyrrolidone with rf »= 1.1127 ^the inventive method with 0.3 weight ·

and _ηο «= 1.4699. The product started after 1 percent potassium hydroxide at room temperature

Day storage to turn yellow. In the polymerization, carried out according to the procedure of the following

from 100 g of the product there was 51.3% poly- ^ ^{ite] s 2 in 300} ° 8 ^product ' ^er 8 ^{aben sldl fol} g ^final

merisat with an inherent viscosity 55 ^{a en}

from 4.1. Cleaning time (1) lh

The second portion was in the same apparatus Yield (2837.49 g) 94.3%

distilled at 0.5 mm pressure. The yield was Coloration (APHA) 1

105 g (69.31%) 2-pyrrolidone with d ³⁰ = 1.1125 and odor hardly noticeable

n _D 2s ₌ i ₅ 4702, which is also yellow when left to stand 6 ° pyrrolidone content 99.99%

would. The polymerization of 100 g gave 55.8% solidification temperature 24.5 ° C

Polymer with an inherent viscosity number water content (azeotropic

of 4.2. Determination) 0.01%

For comparison, 300 g of the same handeis refractive index at 25 ° C (2) 1.4861

usual 2-pyrrolidone with 1.5 g of analytically pure KOH 65 density at 3O ⁰ C (3) 1.1099

mixed and processed by molecular distillation apparatus,% conversion (4) .95.9%

temperature below the logarithmic viscosity number of the described in Example 2 below

Conditions sent. The yield was 282.9 g of polymer (5) 10.2

Remarks

1) from start to finish

2) theoretical value 1.4860 at 25 ° C

(J.CS. 1382 [1955] Fisch) '

3) theoretical value 1.1100 at 30 C (Ber. [1900])

4) homopolymerization

5) Viscosity measured in formic acid

When cleaning by the crystallization method according to German Auslegeschrift 12 95 556, Example 5, using n-butanol at -f-4'C, which were run on five separate samples, at reasonable average yields and treatment times the following were obtained for samples of 300 g each of commercially available 2-pyrrolidone Data:

Cleaning time (1) average. . 3.5 h

Yield (2) average 79.0%

Staining (APHA) (3) 20

Strong smell

Pyrrolidone content 98.15%

Solidification temperature 23.2 C

Water content (azcotropic determination) 0.98%

Refractive index at 25 C 1.4571

Density at 30 C 1.1125

Polymerization,% Conversion .. .70.2% inherent viscosity des Polymer 5.8

Remarks

1) from the beginning to the end including the Purification of the solvent

2) the commercially available 2-pyrrolidone contains 5 to 8 ° _{t of} impurities including water; the yield is the average of 5 purifications of 300 g of 2-pyrrolidone each time by crystallization, the lowest value being 75.0 "

3) the color becomes stronger if the sample is exposed to light; i.e. H. the product is not stable

Claims (1)

Patent claims: 1. Process for the production of practically pure, practically water-free 2-pyrrolidone from commercially available, liquid 2-pyrrolidone by treatment with a metal hydroxide and distillation under reduced pressure, thereby marked that one