FR2739850A1 - Process for manufacture of (meth)acrylic ester(s) of polyalkoxylated alcohol(s) with a hydrophobic chain - Google Patents

Abstract

A new process for the manufacture of a (meth)acrylic ester of a polyalkoxylated alcohol with a hydrophobic chain of formula: CH2=C(R<1>)H-C(=O)-O-C2H3(R<2>)On-R<3> (I), where R<1> = H or Me ; R<2> = H or Me ; R<3> = a hydrophobic radical ; and n = 3 - 60; -by the reaction of the anhydride of formula: CH2=C(R<1>)H-C(=O)-O-C(=O)-C(R<1>)H=CH2 (II); -with a polyalkoxylated alcohol of formula: R<3>OC2H3(R<2>)nOH (III), where R<1>, R<2>, and R<3> are as above. The alcohol contains up to 5% of glycols, in the presence of an esterification catalyst.

Description

PROCESS FOR MANUFACTURING ACRYLIC AND METHACRYLIC ESTERS
HYDROPHOBIC CHAIN POLYALKOXYL ALCOHOLS
The present invention relates to a process for the manufacture of (meth) acrylic monomers consisting of (meth) acrylic esters of hydrophobic chain polyalkoxylated alcohols. Such monomers have hydrophilic-hydrophobic sequences which give them interesting properties both in the field of polymerization and in that of thickeners.

The synthesis of amphiphilic acrylic monomers is described in the literature
American patent US-A-4 384 096 claims the synthesis of polyethoxylated acrylic monomers by esterification, catalyzed by sulfuric acid, of methacrylic acid with a polyethoxylated alcohol. This method of synthesis, in solution in toluene, is also described in European patent EP-B-113 836.

The synthesis of (meth) acrylates of polyethoxylated alcohols from (meth) acryloyl chloride is described in Izv. Vyssh. Uchebn. Zaved. Khim.

Teknol. 19 (5), 793-4, 1976, and in Makromol. Chem.

193 (6), 1377-85, 1992.

The other major synthetic route described in the literature relates to transesterification: the synthesis of n-dodecyloxypoly (ethyleneoxy) ethanol methacrylate by transesterification reaction, catalyzed by dibutyl tin oxide, of methyl methacrylate by a polyethoxylated alcohol, is described in the European patent
EP-B-13 836.

These different routes have a number of drawbacks
Synthesis by direct acid / alcohol esterification is generally difficult as soon as the degree of ethoxylation or propoxylation of the alcohol becomes greater than about 6.

The implementation of the acid chloride route is, for its part, very delicate because of the very high reactivity of the (meth) acryloyl chlorides. There is a strong ability of the polyalkoxylated chains to be cut under the action of hydrochloric acid generated during the synthesis.

The synthesis of (meth) acrylic esters of polyalkoxylated alcohols with a hydrophobic chain is very dependent on the content of ethylene glycol + polyethylene glycols (grouped under the abbreviation PEG) and of propylene glycol + polypropylene glycols (grouped under the abbreviation PPG) of the alcohols used. These alcohols, which form part of the family of anionic surfactants, obey the general formula (III), as defined below; they differ from each other by the nature of their hydrophobic part
R3 and their alkylene glycol sequences, as well as by their degree of alkoxylation; they are manufactured by alkoxylation of alcohol R30H with ethylene or propylene oxide in the presence of an alkaline catalyst and may contain up to 5% by weight of PEG or PPG, formed as by-products during The PEGs and PPGs, the content of which is difficult to control, can inhibit the action of most of the catalysts generally used in transesterification.

In addition, the synthesis of esters of polypropoxylated alcohols with a hydrophobic chain is made very difficult by the fact that the corresponding alcohols consist of a mixture of different isomers, the main ones of which are secondary alcohols, which therefore only react very much. poorly in conventional esterification reactions, performed from carboxylic acids, or in transesterification reactions, performed from esters.

The Applicant Company has now discovered that it is possible to synthesize (meth) acrylic esters of polyalkoxylated alcohols with a hydrophobic chain by esterification of polyethoxylated or polypropoxylated alcohols, starting from (meth) acrylic anhydride, without encountering any of the disadvantages of prior art.

dans laquelle
- R1 représente un atome d'hydrogène ou un groupe
méthyle
- les R2 représentent chacun indépendamment un atome
d'hydrogène ou un groupe méthyle
- R3 représente un radical hydrophobe ; et
- n a une valeur moyenne de 3 à 60, caractérisé par le fait que l'on fait réagir, en présence d'un catalyseur d'estérification, l'anhydride de formule (II)

dans laquelle R1 est tel que défini ci-dessus, avec un alcool polyalkoxylé de formule (III)
R3 [OC2H3 (R2) ]nOH (III) dans laquelle R2, R3 et n sont tels que définis ci-dessus, ledit alcool pouvant renfermer jusqu'à 5% en poids de glycols (lesquels sont les PEG et PPG définis ci-dessus).A subject of the present invention is therefore a process for the manufacture of a (meth) acrylic ester of polyalkoxylated alcohol with a hydrophobic chain represented by general formula (I).

in which
- R1 represents a hydrogen atom or a group
methyl
- the R2 each independently represent an atom
hydrogen or a methyl group
- R3 represents a hydrophobic radical; and
- has an average value of 3 to 60, characterized by the fact that the anhydride of formula (II) is reacted in the presence of an esterification catalyst

in which R1 is as defined above, with a polyalkoxylated alcohol of formula (III)
R3 [OC2H3 (R2)] nOH (III) in which R2, R3 and n are as defined above, said alcohol possibly containing up to 5% by weight of glycols (which are PEG and PPG defined above ).

In formulas (I) and (III) above, the writing "C2H3 (R2)" was used to encompass the isomeric forms "CH2-CHR2-" and "-CHR2-CH2-".

With the process according to the invention, it is possible to use polyalkoxylated alcohols (III) having a hydrophobic chain R3 of very varied nature, the nature of this chain R3 not influencing the synthesis. Thus, R3 can be an alkyl, aryl, alkylaryl, arylalkyl, polyarylphenyl, polyarylalkylphenyl group. These groups can moreover be substituted, inter alia, by halogens. They can for example be fluorinated or perfluorinated.

Furthermore, the starting alcohol (III) can be in the form of a pure product or of a mixture of several fatty alcohols.

Among the catalysts which can be used, mention may be made, for example, of Bronsted acids, such as sulfuric acid, alkyl- and aryl-sulfonic acids and cationic acid resins; Lewis acids, such as boron trifluoride; or even certain basic catalysts, such as amines of the diethylamine, triethylamine or 1-methylimidazole type, for example; as well as the supported forms of these catalysts on solid supports, for example on alumina, activated carbon, silica, weak cationic resin, etc.

The 1-methyl imidazole catalyst has the advantage of being more active and more selective than the acid catalysts, by generating fewer compounds resulting from cleavage of the alkoxylated chains. In accordance with a particularly advantageous mode of use, this catalyst can be used in a form supported on a solid support, for example such as those indicated above. The catalyst is generally used in an amount of 0.01 to 5% by weight relative to the reaction mass.

The reaction according to the invention is generally carried out at a temperature between 20 and 120-C and, more particularly, between 30 and 100-C. The duration of the reaction according to the invention, obviously depending on reaction conditions, such as the temperature and the quantity of catalyst (s) used, as well as the nature of the reagents used, is generally between 1 and 20 hours approximately.

The reagents are generally used in a (meth) acrylic (II) anhydride / alcohol (III) molar ratio, which is greater than 1: 1; being for example from 1.5: 1 to 10: 1, preferably from 1.5: 1 to 3: 1.

The reaction according to the invention is generally carried out in the presence of at least one polymerization inhibitor, such as hydroquinone monomethyl ether, hydroquinone, and hindered phenols of the 2,6-ditertiobutylparacresol type, 2, 4 -dimethyltertiobutylphenol or ditertiobutylcatechol for example. The inhibitor (s) are used, for example, in an amount of 0.01 to 0.2% by weight based on the weight of the reaction mixture.

To conduct the reaction, we can proceed as follows
The anhydride (II) in excess relative to the alcohol (III), the inhibitor (s), the alcohol (III) and the catalyst are successively introduced in this order, and the reaction mixture is maintained at the reaction temperature. , with stirring, until complete conversion of the alcohol.

At the end of the reaction step, the reaction crude is, where appropriate after having been filtered, if the catalyst is in the form of a solid dispersed within the reaction mass.
- or hydrolyzed by adding water and prolonged heating at
50-70 C, in order to obtain the final product in the form
an aqueous solution containing acid
(meth) acrylic, the initial excess of (II) anhydride having
been adjusted to have the desired acid content
(meth) acrylic after hydrolysis
- or purified by topping light products (water,
(meth) acrylic acid, anhydride) by distillation then
neutralization if necessary, in order to obtain the
final product in low acid form
(meth) acrylic or (meth) acrylic anhydride (these
contents can be of the order of 0.5 to 2% by weight).

The reaction and hydrolysis can be followed by assaying (meth) acrylic acid and anhydride (II) by HPLC.

The reaction generally lasts from 1 to 20 hours as indicated above. Hydrolysis typically lasts 3 to 20 hours.

In the case of obtaining the final product in a form with low acid or anhydride contents, the reaction crude is first filtered if the catalyst is in the form of a solid dispersed within the reaction mass, then topped by distillation under reduced pressure, for example using a thin film evaporator, in order to remove the water, most of the residual (meth) acrylic anhydride and the (meth) acrylic acid ) acrylic formed during the reaction, then, where appropriate subjected to a step of elimination by neutralization of the small amounts of (meth) acrylic acid and optionally of acid catalyst dissolved in the medium; conveniently and effectively, this last step can be carried out in the presence of an aliphatic hydrophobic solvent, such as heptane and cyclohexane, or aromatic, such as toluene, forming an azeotropic mixture with water, to the using a basic aqueous solution or an alkali carbonate or an anionic ion exchange resin, any residual water and the solvent then being removed by distillation.

The (meth) acrylic esters thus obtained can therefore be in the form of products with low acid and anhydride contents, or of aqueous solutions containing, in addition to the ester, (meth) acrylic acid originating from the hydrolysis. of the excess of anhydride used in the synthesis. Aqueous solutions, which are particularly suitable for certain applications, such as thickening dispersions, have the advantage of requiring a simpler synthesis process and of being easier to implement. However, this technique is more particularly advantageous in the case of polyethoxylated esters, which are more soluble in water than their polypropoxylated counterparts.

The following examples illustrate the present invention without, however, limiting its scope. In these examples, the percentages are by weight unless otherwise indicated.

EXAMPLE 1
In a stirred reactor, heated using a double jacket fed with water thermostatically controlled at 50 ° C., one introduces in the following order Ol acrylic anhydride ............. ................. 140 g O 2,6-Ditertiobutylparacresol ...................... 1 g Q3 Polyethoxylated fatty alcohol CpH2p + 1 [OCH2CH2] nOH
with p = 12 to 14 and mean n = 20, marketed
by the company "HULS" under the name
'9ARLIPAL 24/200 "................................. 320 g &commat; l-Methylimidazole fixed on a
weak acidic resin .............................. 1 g
The mixture is heated at 50 ° C. for 20 hours.

Then, the crude reaction mixture is topped on a thin film evaporator (LUWA), in order to remove therefrom the excess of anhydride and acrylic acid generated by the reaction.

The final crude product is, at room temperature, in the form of a solid having an acid number of 12 mg of KOH / g, and a saponification number of 1.8 equivalents / kg.

EXAMPLE 2
In the reactor described in Example 1, is introduced, in the following order
O Methacrylic anhydride ........................ 75 g Q Hydroquinone monomethyl ether .......... 0.6 g O Polyethoxylated fatty alcohol R3 [OCH2CH2] noH
with
- R3 - C16H33-C18H37 (30% of C16 alcohols
70% of C18 alcohols); and
- mean n = 18,
marketed by the company "HULS" under
the name "MARLIPAL 16 18/18" ............. 161.5 g Q4 1-Methylimidazole .................... .......... 0.5 g
The mixture is heated at 50 ° C for 10 hours.

The crude reaction mixture is then subjected to hydrolysis for 10 hours at 60 ° C. in the presence of 60 g of water.

The final product is in the form of a perfectly clear solution containing
Ester + residual alcohols: 60.2%
Methacrylic acid: 22.5%
Water: 17.3%
EXAMPLE 3
In the reactor described in Example 1, is introduced, in the following order
O Methacrylic anhydride ........................ 69.3 g O 2,6-Ditertiobutylparacresol ............. ....... 0.7 g 3 Tristyrylphenol with 12 moles of ethylene oxide
[C6H5CH2CH2] 3C6H2 [OCH2CH2j12OH ..................... 200 g O4 l-Methylimidazole ................. ............. 0.5 g
The mixture is reacted at 50 ° C for 15 hours, then it is subjected to hydrolysis with 60 g of water at 50 ° C for 8 hours.

The progress of the reaction and of the hydrolysis is followed by assaying the residual methacrylic acid by high performance liquid chromatography.

The final product obtained is in the form of a perfectly clear solution, having the following composition
Esters: 66.4%
Methacrylic acid: 16.6%
Water: 17%.

The residual acidity can be adjusted by adjusting the excess anhydride used in the feed.

EXAMPLE 4
Example 2 is repeated using the following charge Ol methacrylic anhydride at 95% purity ........ 126.4 g
2,6-Ditertiobutylparacresol .................... 0.9 g Q3 Tristyrylphenol with 16 moles of ethylene oxide
[C6H5CH2CH2] 3C6H2 [OCH2CH2] 16OH, marketed
by the company "RHÔNE POULENC" under
the name "SOPROPHOR BSU" ................. 222 g &commat; l-Methylimidazole .............................. 0.9 g
After 4.5 hours of reaction at 50 ° C., the crude reaction mixture contains 4.7% of methacrylic acid, which corresponds to a rate of progress of the reaction of 96%.

The reaction time at 50 ° C. is extended by 2 hours, then the excess methacrylic anhydride is hydrolyzed with 116 g of water at 50 ° C. for 10 hours.

The final crude product settles in two phases. The upper phase (397 g), which is perfectly clear, has the following composition
Esters: 55%
Methacrylic acid: 27.7%
Water: 17.3%.

EXAMPLE 5
Example 1 is repeated using the following charge Ol methacrylic anhydride ....................... 69.3 g Q Monomethyl ether of hydroquinone .. ...... 0.7 g O3 Alcohol CpH2p + 1 [OCH2CH2] nOH
with p = 12 to 14 and mean n = 20, marketed
by the Company "CECA" under the name
"REMCOPAL 20" ................................. 192 g 4 l-Methylimidazole ....... ....................... 0.9 g
The reaction and hydrolysis are carried out under the same conditions as those of Example 3. The final product has the following composition
Esters: 61.7%
Methacrylic acid: 21.6%
Water: 16.7%.

EXAMPLE 6
Example 1 is repeated using the following charge Ol methacrylic anhydride at 95% purity ....... 78.9 g O 2,6-Ditertiobutylparacresol .............. ..... 0.4 g 3 Octylphenoxypolyethoxyethanol with 13 moles of oxide
ethylene C8H17-C6H5- [OCH2CH2,] 13OH, marketed
by the company "UNION CARBIDE" under the
name "TRITON X-102" .................... 150 g &commat; l-Methylimidazole .............................. 0.7 g
The reaction and the hydrolysis are carried out under the conditions of Example 3. 77 g of water are used for the hydrolysis.

After settling, the final product has the following composition
Esters: 61.7%
Methacrylic acid: 20.6%
Water: 17.7%.

EXAMPLE 7
Example 1 is repeated using the following load
O Methacrylic anhydride ........................ 50 g Q 2,6-Ditertiobutylparacresol ............... ..... 0.5 g e3 Stearyl alcohol containing 20 moles of ethylene oxide
C18H37 [OCH2CH2] 20OH, marketed by
Company "SIDOBRE-SINNOVA" ...................... 145 g Q4 Triethylamine 2 g
The reaction and the hydrolysis are carried out under the conditions of Example 3. 45 g of water are used for the hydrolysis.

The final product has the following composition
Esters: 66.7%
Methacrylic acid: 17.3%
Water: 16.0%.

C4H9 étant le butyle normal, n moyen = 3 et indice OH = 230 g de KOH/kg, commercialisé par la Société "DOW", sous la dénomination "DOWANOL TpnB" ................... 740 g Q4 Résine commercialisée par la Société
"ROHM & HAAS" sous la dénomination
"AMBERLYST 15" .................................... 30 g
Le mélange est laissé sous agitation pendant 3 heures à une température de 80'C, puis filtré en vue de retirer le catalyseur.La plus grande partie de l'acide méthacrylique formé pendant la réaction et l'anhydride méthacrylique qui n'a pas réagi sont éliminés par distillation sur un évaporateur à film mince raclé, à une température de 150'C, sous une pression de 1,33x103 Pa (10 mm Hg). A l'issue de ce traitement, la teneur en acide méthacrylique résiduel n'est plus que de 1%.EXAMPLE 8
In a stirred reactor, electrically heated by a reactor heater, is charged, in the following order Qi Methacrylic anhydride .......................... 554 g
2,6-Ditertiobutylparacresol ...................... 3 g O3 Alcohol of formula

C4H9 being normal butyl, mean n = 3 and OH number = 230 g of KOH / kg, sold by the company "DOW", under the name "DOWANOL TpnB" .............. ..... 740 g Q4 Resin marketed by the Company
"ROHM &HAAS" under the name
"AMBERLYST 15" .................................... 30 g
The mixture is left under stirring for 3 hours at a temperature of 80 ° C., then filtered in order to remove the catalyst. Most of the methacrylic acid formed during the reaction and the unreacted methacrylic anhydride are removed by distillation on a scraped thin film evaporator, at a temperature of 150 ° C., under a pressure of 1.33 × 103 Pa (10 mm Hg). At the end of this treatment, the residual methacrylic acid content is no more than 1%.

500 g of heptane are added to the medium, and the residual acidity is neutralized with a 5.5 N sodium hydroxide solution. The basic aqueous phase is removed, and the solvent and the residual water are evaporated off at 90 ° C. under a pressure of 1.33x104 Pa (100 mm Hg), in the presence of air.

A methacrylic ester is thus obtained having an OH number of 4.5 g of KOH / kg and an acid number of less than 1 g of KOH / kg.

EXAMPLE 9
In a stirred reactor, electrically heated by a reactor heater, is charged, in the following order Qi Acrylic anhydride .......................... .. 200 g 2 2,6-Ditertiobutylparacresol .................... 1.2 g Q3 Alcohol of formula

C4H9 being normal butyl,
average n = 15 and OH index = 60 g of KOH / kg,
marketed by the company "HOECHST" under
the name "B01 / 40" ....................... 740 g Weak cationic resin marketed by the
BAYER company under the name "TP207", on
which 12 g of l-methylimidazole had been
previously fixed ............................ 80 g
The attachment of 1-methylimidazole to the resin was carried out by mixing 12 g of 1-methylimidazole and 75 g of dry resin in 100 g of methanol for 1 hour at room temperature, the resin having then been filtered, washed with methanol and dried.

The reaction medium is brought to a temperature of 45 ° C. for 24 hours.

For the purification, one proceeds according to the same procedure as in Example 7
- catalyst filtration
- elimination of most of the acid
formed acrylic and residual acrylic anhydride
by evaporation on a scraped film evaporator
- neutralization, in the presence of 500 g of heptane, using
of DOWEX anionic resins, then filtration of
resins; and
- elimination of heptane and traces of water by
air stripping on a rotary evaporator.

The acrylic ester obtained has an OH number of 0.7 g of KOH / kg and an acid number of less than 1 g of
KOH / kg.

EXAMPLE 10
In a stirred reactor, electrically heated by a reactor heater, is charged, in the following order
O Methacrylic anhydride ........................ 400 g O 2,6-Ditertiobutylparacresol ............... ..... 2.4 g Q3 Alcohol of formula

C4H9 being normal butyl,
average n = 11 and OH index = 80 g of KOH / kg,
marketed by the company "HOECHST" under
the name "B01 / 20" ....................... 800 g Q4 Boron trifluoride in acetic solution ....... 5 g
The reaction medium is brought to a temperature of 90 ° C. for 3 hours.

For the purification, one proceeds according to the same procedure as in Example 7
- catalyst filtration
- elimination of most of the acid
formed acrylic and methacrylic anhydride
residual by evaporation on a scraped film evaporator
- neutralization in the presence of 800 g of heptane, using
of DOWEX anionic resins, then filtration of
resins; and
- elimination of heptane and traces of water by
air stripping on a rotary evaporator.

The methacrylic ester obtained has an OH number of 2 g of KOH / kg and an acid number of less than 1 g of
KOH / kg.

EXAMPLE 11:
Example 1 is repeated using the following charge Qi Acrylic anhydride at 96.3% purity .......... 74 g O 2,6-Ditertiobutylparacresol .................. ......... 0.2 g Q3 Perfluorinated alcohol containing 13 moles of ethylene oxide
of formula: C6F13CH2CH2 [OCH2CH2] 13OH,
marketed by the company "ELF ATOCHEM"
under the name "FORAFAC 1110" ............. 150 g 4 1-Methylimidazole ........................ ...... 0.7 g
The reaction time is 20 hours at 50 ° C.

The hydrolysis is carried out by adding 21 g of water and it is carried out for 10 hours at 50 ° C.

The crude product is diluted with acrylic acid at the end of hydrolysis (target content for acrylic acid: approximately 50%).

The final product has the following compositions
Acrylic anhydride: 49.5%
Esters: 50%
Water: 0.5%

Claims (11)

1 - Process for the manufacture of a (meth) acrylic ester of polyalkoxylated alcohol with a hydrophobic chain represented by the general formula (I)

in which - R1 represents a hydrogen atom or a group methyl - the R2 each independently represent an atom hydrogen or a methyl group - R3 represents a hydrophobic radical; and - n has an average value of 3 to 60, characterized in that the anhydride of formula (II) is reacted in the presence of an esterification catalyst

in which R1 is as defined above, with a polyalkoxylated alcohol of formula (III) R3 [OC2H3 (R2)] nOH (III) in which R2, R3 and n are as defined above, said alcohol possibly containing up to 5% by weight of glycols. 2 - Process according to claim 1, characterized in that R3 is an alkyl, aryl, alkylaryl, arylalkyl, polyarylphenyl, polyarylalkylphenyl radical, these radicals possibly being substituted, in particular by halogens. 3 - Method according to one of claims 1 and 2, characterized in that an esterification catalyst is used, chosen from Bronsted acids, such as sulfuric acid, alkyl and aryl sulfonic acids and resins cationic; Lewis acids, such as boron trifluoride; and amines, such as 1-methyl imidazole, diethylamine, and triethylamine; as well as the forms supported on solid supports of these catalysts. 4 - Method according to one of claims 1 to 3, characterized in that the catalyst is introduced in an amount of 0.01 to 5% by weight relative to the reaction mass. 5 - Method according to one of claims 1 to 4, characterized in that the reaction is carried out at a temperature between 20 and 120'C, more particularly between 30 and 100'C. 6 - Method according to one of claims 1 to 5, characterized in that the reagents are used in an anhydride (II) / alcohol (III) molar ratio greater than 1/1, more particularly between 1.5: 1 and 10: 1. 7 - Method according to one of claims 1 to 5, characterized in that the reaction is carried out in the presence of at least one polymerization inhibitor, chosen in particular from the monomethyl ether of hydroquinone, hydroquinone and hindered phenols of the 2,6ditertiobutylparacresol, 2, 4-dimethyltertiobutylphenol or ditertiobutylcatechol type. 8 - Process according to claim 6, characterized in that, in order to carry out the reaction, the anhydride (II) is successively introduced in excess relative to the alcohol (III), the inhibitor (s), the alcohol (III ) and the catalyst in that order, and the reaction mixture is maintained at the reaction temperature, with stirring, until complete conversion of the alcohol. 9 - Process according to claim 8, characterized in that at the end of the reaction step, optionally after having filtered the crude reaction if the catalyst is in the form of a solid dispersed within the reaction mass, the reaction crude is hydrolyzed by adding water and prolonged heating at 50-70 ° C., for a period generally of between 3 and 20 hours, in order to obtain the final product in the form of a solution aqueous solution containing (meth) acrylic acid, the initial excess of anhydride (II) having been adjusted to have the desired content of (meth) acrylic acid after hydrolysis. 10 - Process according to claim 8, characterized in that at the end of the reaction step, optionally after having filtered the crude reaction if the catalyst is in the form of a solid dispersed within the reaction mass, the reaction crude is purified by topping the light products by distillation and then optionally neutralization, in order to obtain the final product in a form with low contents of (meth) acrylic acid or (meth) acrylic anhydride. 11 - Process according to claim 10, characterized in that the neutralization is carried out in the presence of an aliphatic or aromatic hydrophobic solvent forming an azeotropic mixture with water, using a basic aqueous solution or an alkali carbonate or an anionic ion exchange resin, the possible residual water and the solvent then being removed by distillation.