JPH04198166A - Production of maleimides - Google Patents

Abstract

PURPOSE:To obtain a maleimide compound in high yield at a remarkably improved catalytic performance by adding and reacting a tert. amine to recovered catalyst in the dehydrative imidation of an N-substituted maleinamic acid in the presence of a tin-based catalyst. CONSTITUTION:An N-substituted maleimide is produced by using metallic tin or a tin compound as a catalyst, heating and dehydrating an N-substituted maleinamic acid in a mixed solvent consisting of an organic solvent forming an azeotropic mixture with water and an organic aprotic polar solvent and carrying out the dehydrative imidation of the acid while removing the formed water by azeotropic distillation. The catalyst is recovered from the reaction liquid, added with 0.01-10mol (preferably 0.1-5mol) of a tert. amine based on 1g-atom of tin and reused in the dehydrative imidation reaction.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing N-substituted maleimides. Maleimides are useful as raw materials for various resins, agricultural chemicals, medicines, etc. In recent years, they have been used in large quantities especially to improve the heat resistance of styrene resins, and are also used as comonomers for modifying other resins and copolymers for polymer blends. It is about to be used as such.

[Prior Art] Several methods have been known for a long time as methods for producing N-substituted maleimides. -The direct production method is a method in which maleic anhydride and aniline are reacted to form N-phenylmaleamidic acid, which is dehydrated and ring-closed to imide. This can be roughly divided into two methods: methods using dehydrating agents and methods using catalysts.

A method using a dehydrating agent is described, for example, in US Pat. No. 2444
As is known from No. 53 and Organic Synsense, Vol. 41, p. 93, the reaction is carried out using a dehydrating agent such as acetic anhydride in an amount equal to or more than the same molar amount. Although this method is excellent because the reaction conditions are mild and the reaction yield is relatively high, it requires the use of large amounts of expensive dehydrating agents and complicated product separation treatment after the reaction. As a result, the cost of the maleimide product increases, making it difficult to achieve an economical mass production method.

In comparison, the catalytic dehydration imidization method does not consume a large amount of expensive auxiliary raw materials, so it can basically be an excellent economical production method.

As this method, there are
Known examples include JP-A-5-46394, JP-A-60-11465, JP-A-5]-40078, JP-A-51-5066, and JP-A-62-63562.

An essential element common to these known catalytic dehydration imidization methods is a strong Bronsted acid catalyst, such as inorganic protonic acids such as sulfuric acids, phosphoric acids, hydrobromic acid, fluorosulfonic acid, etc. Alternatively, a Brønsted acid with strong acid strength, typified by organic protonic acids such as chloroacetic acid, fluoroacetic acid, trifluoromethanesulfonic acid, and sulfone type ion exchange resin, is used as the acid catalyst.

The catalytic dehydration imidization method is a direct reaction that does not consume large amounts of expensive auxiliary raw materials, so it can basically be an excellent economical production method. However, judging from the industrial use of maleimides, none of the conventionally known methods using acid catalysts has been technically or economically satisfactory for the following reasons.

(1) Even when the above-mentioned known inorganic or organic strong acids are used as catalysts, the selectivity or yield of the reaction is not sufficient.

(2) Inorganic acids and expensive organic acids that are used in large amounts as catalysts have poor liquid separation properties such as organic phases, so it is not easy to separate and recover them after the reaction.

(3) Acid catalysts tend to contaminate products, and because of their relatively low selectivity, many by-products are mixed in. In order to remove stiffness from the product, complicated purification such as water washing and separation is essential.

(4) Because of (3) above, a large amount of washing water must be treated as waste water.

(5) Since the strong acid of the catalyst is used in large amounts at high temperatures, the reactor and peripheral equipment are made of corrosion-resistant materials, making them expensive.

The present inventors conducted a catalyst search in order to fundamentally solve the five problems of conventional acid catalysts, and as a result,
We have discovered that dehydrated imidization can be carried out in accordance with the purpose by simply adding at least one catalyst selected from metal tin and compounds containing the tin element, without using the aforementioned acid catalyst. Prior to the invention, a patent application was filed (Japanese Patent Application No. 1i52432 and No. 2-108769).
).

[Problems to be Solved by the Invention] The present inventors discovered that in a method using at least one type of catalyst selected from metal tin and compounds containing the tin element, when the catalyst was reused as it was, the performance of the catalyst was improved. was found to be decreasing. Therefore, in order to reuse the catalyst, it became necessary to find an effective method for activating the catalyst.

[Means for Solving the Problems] The present inventors have conducted extensive studies to solve the above problems. As a result, they found that when the recovered catalyst is reused, the performance of the catalyst can be significantly improved by carrying out the dehydration imidization reaction in the presence of a tertiary amine, and the present invention has been completed.

That is, the present invention dehydrates and imidizes N-substituted maleamic acid in the presence of at least one catalyst selected from metal tin and compounds containing the tin element, and
This is a method for producing N-substituted maleimide, which is characterized in that the recovered catalyst obtained from the reaction solution for producing J-substituted maleimide is subjected to the above dehydration imidization reaction by adding a tertiary amine. I can do what I do.

The present invention will be specifically explained in detail below.

In the reaction according to the present invention, in the absence of an acid catalyst and in the presence of at least one selected from metal tin and compounds containing the tin element as a catalyst, the N-substituted maleamic acid is reacted with water. Dehydration is carried out by heating in a mixed solvent consisting of an azeotropic organic solvent and an organic aprotic polar solvent, and dehydration imidization is carried out while the produced water is azeotropically removed to produce an N-substituted maleimide. For example, N- as maleamic acid
When phenylmaleamide acid and stannous oxide are used as a catalyst, the white slurry of PMA gradually dissolves and becomes an orange-yellow solution as the dehydration reaction progresses, but on the other hand, at the end of the reaction, most of the PMA is dissolved. catalytic components precipitate.

Examples of the N-substituted maleamic acid used as a raw material in this case include the following.

A typical example of N-substituted motumaleamic acid is N-
Methyl maleamic acid, N-butyl maleamic acid, N-octyl maleamic acid, N-dodecyl maleamic acid, N~stearyl maleamic acid, N-cyclohexyl maleamic acid, N-phenyl maleamic acid, N -(o-toile λ-maleamic acid, N
-dodecyl phenyl maleamic acid, N-chlorophenyl maleamic acid, N-dichlorophenyl maleamic acid, N-(o- or p-hydroxyphenyl)
Examples include maleamic acid, N-(o- or m-methoxyphenyl)maleamic acid, N-(m-hydroxycarbonylphenyl)maleamic acid, and N-(m-nitrophenyl)maleamic acid.

Further, as an example of N-substituted bis-maleamidic acid,
N,N'-(m- or p-phenylene)bis-maleamidic acid, N,N'-<2,4-tolylene)his-maleamidic acid, N,N'-(4,4'-diphenylmethane) Bis-maleamidic acid, N, N'-
(4,4°-diphenyl ether)bis-maleamidic acid, N,N'-(4,4°-diphenylketone)
His-maleamidic acid, N,N'-(4,4''-diphenylcisulfi'r:)bis-maleamidic acid, N,N'-(4,4°-diphenylsulfone)bis-maleamidic acid, etc. There is.

These N-substituted maleamic acids can be prepared by mixing and reacting the corresponding maleic anhydride or its substituted product with a primary anhydride or seaamine in a solvent according to a known method. It is a compound that can be obtained easily and quantitatively. These maleamic acids synthesized in this manner can be isolated and used in a dehydration reaction.

The recovery catalyst used in the method of the present invention is at least one selected from the following metal tin and compounds containing the tin element, and maleamic acid is dehydrated and imidized through the reaction. Obtained from the reaction solution.

Examples of such compounds containing metal tin and the tin element include the following.

There are no restrictions on the shape of metal tin, but fine powder is preferred.

Examples of compounds containing the tin element include divalent and tetravalent tin oxides, hydroxides, carboxylates, alkoxides, halides, mineral salts, and organic tin compounds.

Examples of tin oxides and hydroxides include stannous oxide,
Stannous oxide, stannous hydroxide, and stannic hydroxide can be used.

The organic carboxylic acid salt of tin is a tin salt of an aliphatic, alicyclic or aromatic monovalent or polyvalent carboxylic acid.

Representative examples of such carboxylic acids include acetic acid,
Propionic acid, butyric acid, 2-ethylhexanoic acid, octylic acid, lauric acid, stearic acid, glycine, lactic acid, succinic acid, glutaric acid, adipic acid, acelaic acid, maleic acid, fumaric acid, citric acid, cyclohexylcarboxylic acid , naphthenic acid, benzoic acid, tolylic acid, chlorobenzoic acid,
Examples include phthalic acid and terephthalic acid.

Further, examples of tin alkoxide include tin methoxide, ethoxide, n-propoxide, i-propoxide, n-butoxide, sec-butoxide, ter
Examples include t-butoxide, pentaoxide, hexoxide, phenoxide, and hensyloxide.

Tin halides include stannous chloride, stannic chloride, stannous bromide, stannic bromide, stannous iodide, stannic iodide, dichlorotin bisacetylacetonate, dichlorodi-n- These are halogen-containing tin compounds such as butyltin, dichlorodimethyltin, dichlorodivinyltin, trichloromethyltin, trichlorophenyltin, triethylbromostin, and trimethylbromostin.

Examples of tin W and acid salts include tin sulfate, nitrate, phosphate, and bis(triethyltin) sulfate.

Examples of the organic tin compound include allyltriphenyltin, his(trimethyltin)acetylene, hexamethyldistin, tetramethyltin, tetra-1-propyltin, and triphenyltin hydroxide.

Among these metallic tin and compounds containing the element tin, stannous oxide, stannous hydroxide, stannic hydroxide, stannous chloride, stannic chloride, and divalent tin organic carboxylates Acid salts and alkoxides are preferred.

These catalysts are usually used alone or, if necessary, two types of catalysts may be used in combination.

The amount of catalyst used is not particularly limited, but it is usually 0.1 to 20 mol% (0.001 to 0.2 crum atoms as tin), preferably 0.5 to 20 mol % (0.001 to 0.2 crum atoms as tin) per 1 mol of raw maleamic acid.
~10 mol % (0.005 to 0.1 crum atom as tin).

The recovered catalyst of the present invention can be obtained, for example, by the following method.

That is, after the reaction is completed, the catalyst component insoluble in the reaction solution can be separated and recovered as a precipitate by using a conventional separation means such as filtration or centrifugation to obtain a recovered catalyst.

In addition, in the same way as above, as a method for separating and recovering the catalyst component insoluble in the reaction solution and recovering the catalyst component contained in the solution, the solution containing the maleimide and the catalyst component can be evaporated, etc. After concentrating to dryness and removing the solvent, the maleimides are extracted with a suitable organic solvent, and the recovered catalyst can be obtained as a raffinate.

On the other hand, after recovering the solvent from the reaction solution, the component containing the catalyst can also be separated and recovered. That is, after the reaction solution is concentrated to dryness by means such as evaporation to recover the solvent, the maleimides can be extracted with a suitable organic solvent to obtain the recovered catalyst as a raffinate.

The catalyst-containing component recovered in this manner cannot be reused as a catalyst as it is or, after drying, as a catalyst.

However, as shown in Comparative Example 1, even if the component containing the catalyst recovered in this way is reused as a catalyst without adding anything special, either as it is or after drying, it is still not the same as the original catalyst. In comparison, the reaction rate is slow and the yield of N-substituted phenylmaleimito is low.

In the method of the present invention, when the component containing the catalyst recovered by the above method is reused as a catalyst, a tertiary amine is added thereto and used in the dehydration imidization reaction.

The following may be cited as examples of tertiary amines used in the method of the present invention. Trimedelamine, triethylamine, tri-n-propyla.

trimy propylamine, tri-n-butylamine, tri-5ec-butylamine, tri-t-butylamine, triamylamine, to-so-1-amylamine, trihexylamine, trioctylamine, tri-2-ethylhexyl amine,
Symmetric aliphatic tertiary amines such as tridotesylamine, triotadecylamine, triallylamine, tribenzylamine, tripropargylamine, towas(trimethylsilyl)amine, dimethylethylamine, dimethylpropylamine, dimethylisopropylamine, dimethyl-
5ec-butylamine, dimethyl-t-butylamine,
Dimethylophtatecylamine, diethylmethylamine,
Methylethylpropylamine, methylethylisopropylamine, methylethylbutylamine, methylethylisobutylamine, methylethyl-butylamine, methyldibrobylamine, methyldiisopropylamine,
Asymmetric aliphatic tertiary amines such as methylpropylbutylamine, methylbrobyltecylamine, edylcibrobylamine, N,N,N',N'-tetramethylethylenecyamine, N,N,N',N '-cyamines such as tetraethylethylenecyamine, N,N-dimethylaniline, N-methyl-N-ethylaniline, p-N,N~
Dimethyltoluidine, p-N-methyl-N-ethylchloroaniline, aromatic tertiary amines such as triphenylamine, N-methylpyrrolidine, N-ethylpyrrolidine,
Alicyclic tertiary amines such as N-methylmorpholine, N-ethylmorpholine, N-methylpiperidine, N-ethylpiperidine, N,N'-dimethylpiperazine, N,N'-dimethylpiperazine, pyridine, biritazine, pyrimidine Examples include heterocyclic tertiary amines such as pyrazine, quinoline, isoquinoline, quinazoline, quinoxaline, phthalazine, phenanthroline, acridine, 1,10-phenanthroline, and 2.2'-bipyridyl.

Among the stiff tertiary amines, aliphatic, alicyclic and heterocyclic tertiary amines are preferred.

The amount of these tertiary amines added varies depending on the basicity of the tertiary amine added, but is 0.01 to 10 mol, preferably 0.01 to 10 mol, per 1 gram atom of tin contained in the catalyst-containing component. It ranges from 1 to 5 moles.

If the amount of tertiary amine added is too small, the effect of the addition will be small, and if the amount added is too large, it will have a negative effect on the reaction.

There are no particular restrictions on the method of adding the tertiary amine, but usually a predetermined amount of the tertiary amine is added together with the recovered catalyst to a solution containing the maleamic acids. may be added separately together with the solvent.

The organic solvent is used to azeotropically remove water produced by the reaction from the reaction system. This azeotropic solvent has a molecular weight of 50 to 200
It is sufficient that the material is azeotropic with water at a temperature in the range of °C and is inert to the reaction. Examples include hensen, toluene, ethylbenzene, xylenes, cumene, chlorobenzene, anisole, dichloroethane, jetoxyethane, cyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, trioxane, etc., and xylenes are preferable considering the properties and price of the solvent. is often used.

In addition, organic aprotic polar solvents are used to increase the solvent concentration of maleamic acid and catalyst, such as dimethylformamide, dimethylacetamide, dimethyl sulfoxide, sulfolane, methyl isobutyl ketone,
Gamma butyrolactone, hexamethylphosphoramide,
Selected from N-methylpyrrolidone, tetramethylurea, 1,3-dimethyl-2-imidasisodinone, etc., preferably dimethylformamide, dimethylacetamide,
Dimethyl sulfoxide and the like are used.

In the dehydration imidization reaction, a solvent prepared by adding or mixing an organic aprotic polar solvent to an organic solvent that is azeotropic with water is used. The amount of mixed solvent used is usually 0.0% as the raw material concentration of maleamic acid. ] to 5 mol/L, preferably 0.5 to 3 mol/L. The composition of the polar solvent in the mixed solvent is usually selected from the range of 0.1 to 50% by volume, preferably 1 to 20%.

Reaction temperature is 50-200°C, preferably 80-160°C
range is used. There is no particular restriction on the reaction pressure, and the reaction is usually preferably carried out at normal pressure. Reaction time is usually 0.5~
It is in the range of 10 hours, preferably in the range of 1 to 5 hours.

The process of the invention can be carried out batchwise, semi-continuously or continuously. Usually, maleamic acid, an organic solvent azeotropic with water, an organic aprotic polar solvent, a recovered catalyst and tertiary amines are mixed together prior to the reaction, or maleamic acid, recovered catalyst and tertiary The amines are fed separately into the reactor along with the solvent. The reactor is heated afterwards or in advance, and the azeotropic solvent is heated and refluxed for a predetermined period of time, and water produced is azeotropically separated from the reactor to advance the dehydration reaction, thereby converting maleamic acid into 7-reimite.

At this time, the raw material maleamic acid does not need to be synthesized and used separately, but a primary amine corresponding to maleic anhydride or its substituted product is added in the above mixed solvent or a mixed solvent of this and a polar solvent. Synthesized by a known method,
Subsequently, it is also possible to directly add a catalyst and a tertiary amine to the mixture, reflux it, and carry out an azeotropic dehydration reaction in the same manner as above. Since maleamic acids can be synthesized almost quantitatively, this method is usually more economical.

The resulting reaction mixture is subjected to simple extraction, crystallization, distillation, etc. after both solvents are evaporated and recovered using an evaporator or the like to obtain a crude product of maleimide. On the other hand, the extraction, crystallization, or distillation material is supplied to the dehydration imidization reaction system as a recovered catalyst and reused.

[Example] Next, the present invention will be explained in more detail with reference to Examples.
The present invention is not limited to these.

In the examples, the yield of N-phenylmaleimide was calculated by 4 based on aniline used as a raw material. Furthermore, when calculating the yield, the amount of N-phenylmaleamic acid contained in the recovered catalyst was corrected.

Example 1 1! Equipped with a reflux condenser with a water separator, a stirrer, and a thermometer! Maleic anhydride (hereinafter abbreviated as VAN) 208 into the flask
．． Item g, xylene (hereinafter abbreviated as T"
l and dimethylformamide (hereinafter abbreviated as DMF) 70
Mfl was charged, and aniline (hereinafter A) was added under stirring at 40°C.
A mixture of 97.79g (abbreviated as N) and
The mixture was aged for 15 minutes at C to synthesize N-phenylmaleamic acid (hereinafter abbreviated as PMA).

Add 7% stannous oxide to this white powder slurry as a catalyst.
．． 06g was added, and the temperature was raised while stirring to heat the contents to reflux. Refluxing was continued for 2 hours at about 140° C. while azeotropically separating water produced by the reaction.

During this time, as the dehydration reaction progressed, the white slurry of PMA gradually dissolved to become an orange-yellow solution, while catalyst components precipitated at the end of the reaction.

After the reaction was completed, was the reaction solution concentrated to dryness? & X y180
Extracted with 0 aQ and extracted with N-phenylmaleimide (hereinafter PM
The extract containing r) was concentrated to dryness, and the raffinate was dried.
As a result of quantitative determination by liquid chromatography, the PMr yield was 92.0%, and 4.0% of unreacted PMA was recovered.

On the other hand, after drying the raffinate residue, the amount of tin was determined and used as a recovered catalyst.

2.2 g of recovered catalyst obtained in the above reaction (7.5 g as tin)
The following reaction was carried out using Iog atoms (containing Iog atoms) as a catalyst.

Equipped with a reflux condenser with a water separator, a stirrer, and a thermometer.
+on7 M A N 15.44g into Lasco, X
Prepare 70 ml of Y and DMFIOmu and heat to 80℃.
While stirring, a mixed solution of 13.97 g of AN and Xy20mj2 was quantitatively supplied over 15 minutes, and the mixture was aged for another 15 minutes to synthesize PMA.

To this white powder slurry, 2.2 g of recovered catalyst (containing 7.5 mg of tin atoms) was added as a catalyst, and 0.76 g of triethylamine (7.5 mmol,
After adding triethylamine/tin molar ratio 1.0), the temperature was raised while stirring to heat the contents to reflux. After the water produced by the reaction was azeotropically separated, the reaction was completed in 1 hour and 45 minutes by continuing to reflux at about 14 (1'C). After the reaction was completed, the reaction solution was concentrated to dryness, and then subjected to liquid chromatography. As a result, the PMI yield was 83.5%, and 5.6% of unreacted PMA was recovered.

Comparative Example 1 In the reaction using the recovered catalyst of Example 1, the reaction was carried out in exactly the same manner as in Example 1, except that triethylamine was not added. As a result, the time required to complete the reaction was 4.5 hours. In addition, the reaction results showed that the PMI yield was 70.8%, and 6.7% of unreacted PMI was recovered.

Example 2 In Example 1, the amount of triethylamine used was 0.38
The reaction was carried out in exactly the same manner as in Example 2, except that the reaction mixture was changed to g(3.8m101) (triethylamine/tin molar ratio 0.5). As a result, the reaction time was 2.5 hours, and PMI
The yield was 81.9%, and 8.6% of unreacted PMA was recovered.

Example 3 In Example 1, 0.76 g (7,5111 mol) of N-methylmorpholine was used instead of triethylamine (
The reaction was carried out in exactly the same manner as in Example 1, except that N-methylmorpholine/tin molar ratio (1.0) was used. As a result, the reaction time was 1 hour and 30 minutes, the PMI yield was 86.1%, and 5.5% of unreacted PMA was recovered.

Example 4 In Example 1, N-te was used instead of triethylamine.
rt-butylmorpholine], 07g (7.5mmol)
(N-tertbutylmorpholine/tin molar ratio 1.0
) The reaction was carried out in exactly the same manner as in Example 1, except that .

As a result, the reaction time was 1 hour and 30 minutes, and the PMI yield was 91.
．． 8%, and 4.6% of unreacted PMA was recovered.

Example 5 In Example 1, instead of triethylamine, 2.2°
-0.59g (3.8mmol) of bipyridyl (2,
The reaction was carried out in exactly the same manner as in Example 1 except that 2'-bipyridyl/tin molar ratio (0.50) was used. the result,
The reaction time was 1 hour and 30 minutes, and the PMI yield was 87.3%, and 6.2% of unreacted PMA was recovered.

Example 6 In Example 1, instead of triethylamine, 1.10
- 0.68 g (3.8 mmol) of phenanthroline (
The reaction was carried out in exactly the same manner as in Example 1, except that the molar ratio of 1,10-phenanthroline/tin was 0.5). As a result, the reaction time was 2 hours, the PMI yield was 83.6%, and 7.7% of unreacted PMA was recovered.

Example 7 The reaction for obtaining the recovered catalyst in Example 1 was carried out in the same manner as in Example 1, except that 04.1 g of cyclohexylamine was used instead of aniline. As a result, N-
The yield of cyclohexyl maleimide was 86.5%, and 9.3% of unreacted N-cyclohexyl maleamic acid was recovered.

Next, 2.4 g of recovered catalyst obtained from this reaction (7.0 g as tin)
5 mg atoms) as catalyst, 14.9 g of cyclohexylamine instead of aniline and 1.07 g of N-tert-butylmorpholine (7 mg atoms) instead of triethylamine.
,5mmol) (N-tert-butylmorpholine/
A catalyst reuse experiment was conducted in the same manner as the reaction using the recovered catalyst in Example 1, except that a tin molar ratio of 1.0) was used.

As a result, the yield of N-cyclohexylmaleimide was 87.
At 3%, unreacted N-cyclohexyl maleamic acid is 8
．． 5% recovered.

Comparative Example 2 Using the recovered catalyst obtained in Example 7 as a catalyst, N-ter
A catalyst reuse experiment was carried out in the same manner as the reaction using the recovered catalyst in Example 7, except that t-butylmorpholine was not added.

As a result, the time required to complete the reaction was 4 hours. The N-cyclohexylmaleimide yield was 76.
At 2%, unreacted N-cyclohexyl maleamic acid is 1
2.9% was recovered.

[Effect of the invention] The present invention dehydrates and imidizes N-substituted maleamic acid in the presence of at least one catalyst selected from metal tin and compounds containing the tin element to produce N-substituted maleimide. In the reaction, N
- A method for producing a substituted maleimide.

According to the method of the present invention, it is easy to recover the catalyst, and when the recovered catalyst is reused, the catalyst performance can be greatly improved simply by adding a tertiary amine and carrying out the reaction. It's a big one.

Patent applicant: Mitsui Toatsu Chemical Co., Ltd.

Claims (4)

[Claims] (1) A reaction solution in which N-substituted maleamic acid is dehydrated and imidized to produce N-substituted maleimide in the presence of at least one catalyst selected from metal tin and compounds containing the tin element. 1. A method for producing an N-substituted maleimide, which comprises recovering a catalyst component from a catalytic converter and adding a tertiary amine thereto to carry out the dehydration imidization reaction. (2) The method according to claim 1, wherein the recovered catalyst component is a solid that is separated from the reaction liquid and is insoluble in the reaction liquid. (3) The method according to claim 1, wherein the recovered catalyst component is a raffinate obtained by distilling off the solvent of the solution after separating the solid from the reaction solution and further extracting with an organic solvent. (4) The method according to claim 1, wherein the recovered catalyst component is a raffinate obtained by extracting the residue obtained by distilling off the solvent from the reaction solution with an organic solvent.