JP2002105010A - Method for producing methallyl alcohol - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing methallyl alcohol, by which the methallyl alcohol can profitably be produced from methacrolein as a starting raw material at a low cost. SOLUTION: This method for producing the methallyl alcohol, characterized by hydrogenating the aldehyde group of methacrolein in a hydrogen atmosphere condition in the presence of a divalent ruthenium compound and a phosphite compound represented by the general formula (I) R1, R2 and R3 are each independently an aliphatic hydrocarbon group which may have a substituent, or either two of R1, R2 and R3 are combined to form an alkylene group which may have a substituent, and the remaining one is an aliphatic hydrocarbon group which may have a substituent).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing methallyl alcohol. The methallyl alcohol obtained in the present invention is useful as a raw material for medicines, agricultural chemicals, various chemicals and the like. For example, by subjecting methallyl alcohol to a hydroformylation reaction and hydrogenating the resulting aldehyde compound, 2-methyl-1,4-butanediol can be derived. 2-Methyl-1,4-butanediol is an intermediate of 3-methyltetrahydrofuran used as a raw material of a polyether polyol which is a constituent component of a thermoplastic polyurethane.

[0002]

2. Description of the Related Art Conventionally, as a method for producing methallyl alcohol by reducing methacrolein, a hydrogen transfer reduction reaction using an alcohol such as isopropanol as a hydrogen source in the presence of a catalyst includes the steps of:
Magnesium oxide-zirconium oxide mixed oxide (Mg
O-ZrO ₂ ) (eg, The Chemical Society of Japan, 1
56 (1993)), and magnesium oxide - a method of using a boron oxide mixed oxide _{(MgO-B 2 O 3)} ( e.g., Chemistry Letters (Chem.Let
t. ), Pages 1345-1348 (1992)).

On the other hand, as a method for producing a β, γ-unsaturated alcohol by selectively reducing an aldehyde group of an α, β-unsaturated aldehyde compound with hydrogen, ruthenium, cobalt-ruthenium, platinum ruthenium-tin, etc. A method using a solid catalyst supporting a transition metal (for example,
JP-A-3-18506; JP-A-10-236995; Journal of Chemical Faraday Trans (J. Chem. Soc., Far)
day Trans. ), 90 volumes, 2803-280
7 (1994)), a method of reacting in a homogeneous system using a transition metal complex catalyst (for example, JP-A-50-880).
No. 10; Journal of Molecular Catalysis (J. Mol. Catal.), Vol. 24, 217
-220 (1984); see JP-A-2-220 and the like).

[0004]

The above-mentioned methods require a high temperature of 300 ° C. or more, and in fact, require alcohol in an amount equivalent to methacrolein in an excess amount. It is necessary to use an amount of the carbonyl compound as a by-product of the reaction with hydrogen, and an equimolar amount of a carbonyl compound is produced as a by-product (for example, acetone is produced as a by-product from isopropanol). There are problems such as an increase in equipment burden.
Further, the catalyst used in the above method is easily deactivated by water, and there is a problem that even if a small amount of water is present in methacrolein or alcohol, the activity of the catalyst is significantly reduced. Therefore, these methods cannot be said to be industrially advantageous methods for producing methallyl alcohol.

The above method is limited to a specific range of α, β-unsaturated aldehyde compounds, and the conversion and selectivity of the desired product are not industrially satisfactory.
Further, there is no known example using methacrolein as a raw material. Is selectively hydrogenating various α, β-unsaturated aldehydes such as crotonaldehyde, prenal, cinnamylaldehyde, and citral using, for example, a ruthenium-based catalyst, and converting the corresponding β, γ-unsaturated alcohol to Manufacturing is disclosed. However, even in these methods, there is no known example of producing methallyl alcohol using methacrolein as the α, β-unsaturated aldehyde compound. Accordingly, an object of the present invention is to provide a method for producing methallyl alcohol inexpensively and industrially advantageously using methacrolein as a starting material.

[0006]

According to the present invention, the above-mentioned object is to provide a divalent ruthenium compound and a compound of the formula (I)

[0007]

Embedded image

(Wherein R ¹ , R ² and R ³ each independently represent an aliphatic hydrocarbon group which may have a substituent, or any one of R ¹ , R ² and R ³ Two together represent an alkylene group which may have a substituent, and the other one represents an aliphatic hydrocarbon group which may have a substituent. This is achieved by providing a method for producing methallyl alcohol, characterized by hydrogenating an aldehyde group of methacrolein in the presence of hydrogen atmosphere in the presence of phosphite (I).

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the above general formula, R ¹ , R ² and R
Examples of the aliphatic hydrocarbon group represented by ³ , for example, a methyl group,
Ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, s-butyl group, t-butyl group, n
-Pentyl group, n-hexyl group, n-heptyl group, n-
Examples include an alkyl group such as an octyl group, a 2-ethylhexyl group, an n-nonyl group, a decyl group, an isodecyl group, an undecyl group, and a dodecyl group. These alkyl groups may have a substituent. Examples of the substituent include an alkoxyl group such as a methoxy group, an ethoxy group and a propoxy group; a halogen atom such as a fluorine atom, a chlorine atom and a bromine atom; Groups, ethoxycarbonyl groups, and alkoxycarbonyl groups such as propoxycarbonyl groups.

The alkylene group represented by any ^{two of} R ¹ , R ² and R ³ together includes, for example, an ethylene group, a propylene group, a butylene group and a 2,2-dimethylpropylene group. These alkylene groups may have a substituent. Examples of the substituent include an alkoxyl group such as a methoxy group, an ethoxy group, and a propoxy group; a halogen atom such as a fluorine atom, a chlorine atom, and a bromine atom; Groups, ethoxycarbonyl groups, and alkoxycarbonyl groups such as propoxycarbonyl groups.

As the divalent ruthenium compound, for example, dichlorotris (triphenylphosphine) ruthenium, dichlorotetrakis (triphenylphosphine) ruthenium, dihydridotetrakis (triphenylphosphine) ruthenium, dichloro (1,5-cyclooctadiene) Ruthenium, tetrachlorobis (η-benzene)
Biruthenium, tetrabromobis (η-benzene) biruthenium, tetrachlorobis (η-p-cymene) biruthenium, tetrachlorobis (η-hexamethylbenzene) biruthenium, carbonylchlorohydridotris (triphenylphosphine) ruthenium , Dinitrate carbonyl bis (triphenylphosphine) ruthenium,
Acetatohydride tris (triphenylphosphine) ruthenium, dichlorobis (acetonitrile) bis (triphenylphosphine) ruthenium, chloro (cyclopentadienyl) bis (triphenylphosphine) ruthenium, bromo (cyclopentadienyl) bis (triphenylphosphine) ) Ruthenium, chloro (cyclopentadienyl) (1,5-cyclooctadiene) ruthenium, bromo (cyclopentadienyl) (1,5-cyclooctadiene) ruthenium, bis (η-cyclopentadienyl) ruthenium, Bis (η-pentamethylcyclopentadienyl) ruthenium; There is no particular limitation on the amount of the divalent ruthenium compound to be used, but industrially, it is preferable to use the divalent ruthenium compound in an amount that gives a concentration of 0.05 to 50 milligram atoms of ruthenium atoms per liter of the reaction mixture. An amount that results in a concentration of 1 to 10 milligram atoms is more preferred.

The phosphite (I) acts as a catalyst component together with the divalent ruthenium compound, and enables good selective hydrogenation of the aldehyde group of methacrolein. Examples of the phosphite (I) include trimethyl phosphite, triethyl phosphite, dimethylethyl phosphite, tri-n-propyl phosphite, triisopropyl phosphite, tri-n-butyl phosphite, tripentyl phosphite, and trihexyl phosphite. , Tricyclohexyl phosphite, trioctyl phosphite, tri (2-ethylhexyl) phosphite, triisodecyl phosphite and the like. One of these phosphites (I) may be used alone, or two or more thereof may be used in combination. The amount of the phosphite (I) to be used is generally 1 mol or more, preferably 4 mol or more, more preferably 10 mol or more, per 1 gram atom of ruthenium. There is no strict upper limit on the amount of phosphite (I) used, but usually it is preferably used in a range of 150 mol or less per gram atom of ruthenium, more preferably in a range of 100 mol or less.

The divalent ruthenium compounds containing phosphite (I) as a ligand component, for example, dichlorotetrakis (trimethylphosphite) ruthenium, dichlorotetrakis (triethylphosphite) ruthenium, etc., are themselves used in the present invention. It can be used as an effective catalyst for the method.

[0014] The method of the present invention can be carried out in the presence or absence of a solvent. The solvent is not particularly limited as long as it does not adversely affect the reaction, and examples thereof include aliphatic hydrocarbons such as pentane, hexane, heptane, octane and petroleum ether; benzene, toluene, xylene, mesitylene, cumene, pseudocumene, , 2,
Aromatic hydrocarbons such as 4-trimethylbenzene, 1,3,5-trimethylbenzene and diethylbenzene; halogenated hydrocarbons such as chloroform and trichloroethane;
Methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, n-pentanol, t-amyl alcohol, n-hexanol,
alcohols such as n-octanol and cyclohexanol; diols such as ethylene glycol and propylene glycol; ethers such as tetrahydrofuran, dioxane, diphenyl ether, diethyl ether and diisopropyl ether; monoesters such as methyl acetate and ethyl acetate; dibutyl phthalate and phthalic acid Diesters such as dioctyl and dimethyl adipate; amides such as N, N-dimethylformamide and N, N-dimethylacetamide; cyclic imides such as 1,3-dimethyl-2-imidazolidinone; sulfoxides such as dimethylsulfoxide; sulfolane; And the like. Among them, aromatic hydrocarbons such as benzene, toluene, xylene, mesitylene, cumene, pseudocumene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene and diethylbenzene are preferred. One of these solvents may be used alone, or two or more thereof may be used as a mixture. When a solvent is used, there is no particular limitation on the amount of the solvent used, but the amount of the solvent is 0.1% with respect to methacrolein.
It is preferably in the range of 1 to 100 times by weight.

In the method of the present invention, a salt containing a halogen ion may be further coexisted in the reaction system. Examples of the salt containing a halogen ion include lithium fluoride, lithium chloride, lithium bromide, lithium iodide, sodium fluoride, sodium chloride, sodium bromide, sodium iodide, potassium fluoride, potassium chloride, and potassium bromide. And alkali metal halides such as potassium iodide;
Alkaline earth metal halides such as magnesium chloride, magnesium bromide, magnesium iodide, calcium chloride, calcium bromide, calcium iodide, barium chloride, barium bromide, barium iodide; aluminum chloride, titanium trichloride, tetrachloride Titanium, manganese chloride, manganese bromide, ferrous chloride, ferric chloride, ferrous bromide, ferric bromide, cobalt chloride, cuprous chloride, cupric chloride, zinc chloride, tin dichloride And transition metal halides such as tin tetrachloride; N-alkylpyridinium halides such as methylpyridinium chloride, ethylpyridinium chloride, butylpyridinium chloride, cetylpyridinium chloride, methylpyridinium bromide, ethylpyridinium bromide, and cetylpyridinium bromide; Methylquinolinium chloride, ethylquinolinium chloride, chloride Chirukinoriniumu such as N-
Alkylquinolinium halides; quaternary phosphonium halides such as triphenylbenzylphosphonium chloride; and the like, among which lithium chloride, lithium bromide, ferrous chloride and cetylpyridinium chloride are preferred. The reaction rate can be improved by coexisting a salt containing these halogen ions. When a salt containing a halogen ion is allowed to coexist, the amount of the salt is not particularly limited, but 0.1 to 0.1 g as a halogen atom per 1 gram atom of ruthenium contained in the divalent ruthenium compound.
It is preferably in the range of 500 equivalents, more preferably in the range of 1 to 100 equivalents.

[0016] The reaction temperature is preferably in the range of 30 to 200 ° C, more preferably in the range of 70 to 150 ° C. When the reaction temperature is lower than 30 ° C., the reaction tends to proceed extremely slowly. When the reaction temperature is higher than 200 ° C., side reactions such as dimerization of methacrolein increase or the stability of the catalyst decreases. It tends to be impaired.

The method of the present invention is performed under a hydrogen atmosphere condition.
The pressure of hydrogen is not particularly limited, but is 0.01 to 20 MPa.
(Gauge pressure; 0.1 to 200 kg / cm ² G), preferably 0.1 to 10 MPa (gauge pressure; 1
To 100 kg / cm ² G range) is more preferable. Further, the reaction system may be further pressurized with an inert gas such as argon, nitrogen, helium or the like for this reaction.

The reaction is carried out by mixing a divalent ruthenium compound, phosphite (I), methacrolein, a salt containing a halogen ion if necessary, and a solvent, pressurizing the mixture with hydrogen to a predetermined pressure, and stirring at a predetermined temperature. It is preferable to carry out the following. As the reaction device, a known gas-liquid contact type reaction tank such as a stirring type reaction tank or a bubble column type reaction tank can be used. The reaction can be carried out by any of a batch method and a continuous method.

The obtained methallyl alcohol can be separated from the reaction solution by using a conventional separation and purification means such as distillation.

[0020]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention.

Example 1 Under an argon atmosphere, 28 mg (0.1 mmol) of dichloro (1,5-cyclooctadiene) ruthenium, 201 mg (0.4 mmol) of triisodecyl phosphite,
40 ml of toluene and 3.5 g of methacrolein (50
mmol) at room temperature, and the solution is mixed with a magnetic stirrer,
Equipped with pressure gauge, gas inlet tube and needle valve,
The system was charged in an autoclave (material: manufactured by Hastelloy C) having a capacity of 100 ml in which the inside of the system had been replaced with argon in advance. After replacing the inside of the system with hydrogen, the system was sealed, and the temperature of the mixture was increased while stirring. When the internal temperature reached 110 ° C., hydrogen was introduced into the reaction system to evacuate the reaction system to 3 MPa (30 kg / cm). ^The reaction was carried out for 1.5 hours while maintaining the pressure in the system at 3 MPa. After cooling the autoclave to room temperature, the pressure was released, the reaction solution was taken out, and a part thereof was analyzed by gas chromatography. The conversion of methacrolein was 84.7% and the selectivity of methallyl alcohol was 78. 0.1%. In addition, as other products,
Isobutyraldehyde was formed at a selectivity of 5.6%, and isobutyl alcohol was formed at a selectivity of 12.9%.

Example 2 In Example 1, dichlorotetrakis (triphenylphosphine) ruthenium (24 mg, 0.025 mmol) was used in place of dichloro (1,5-cyclooctadiene) ruthenium (28 mg, 0.1 mmol), and triisopropane was used. Decyl phosphite is used in an amount of 201 mg (0.4 m
mol) to 50.5 mg (0.1 mmol), and the reaction operation was carried out in the same manner as in Example 1 except that the reaction time was changed from 1.5 hours to 0.5 hours. When a part of the obtained reaction solution was analyzed by gas chromatography, the conversion of methacrolein was 84.7%, the selectivity of the product was methallyl alcohol of 87.2%,
It was 1.9% isobutyraldehyde and 7.0% isobutyl alcohol.

Example 3 Under an argon atmosphere, dichlorotris (triphenylphosphine) ruthenium 48 mg (0.05 mmol) and triisodecylphosphite 100.5 mg (0.2 mm
ol), 38 ml of toluene and methacrolein.
5 g (150 mmol) are mixed at room temperature and the solution is
Equipped with an electromagnetic stirrer, a pressure gauge, a gas inlet tube and a needle valve.
The mixture was placed in a ml autoclave (material: made of Hastelloy C). After replacing the inside of the system with hydrogen, the system was sealed, and the temperature of the mixture was increased while stirring. When the internal temperature reached 110 ° C., hydrogen was introduced into the reaction system to evacuate the reaction system to 3 MPa (30 kg / 30 kg / kg).
cm ² ) and reacted for 0.5 hour while maintaining the pressure in the system at 3 MPa. After cooling the autoclave to room temperature, the pressure was released, the reaction solution was taken out, and a part thereof was analyzed by gas chromatography. The conversion of methacrolein was 59.0%, and the selectivity of the product was methalyl. The alcohol content was 82.3%, isobutyraldehyde 6.6%, and isobutyl alcohol 4.7%.

Example 4 Under an argon atmosphere, dichlorotris (triphenylphosphine) ruthenium 48 mg (0.05 mmol), triisodecylphosphite 503 mg (1 mmol),
Lithium chloride 21mg (0.5mmol), toluene 3
8 ml and methacrolein 3.5 g (50 mmol)
Was mixed at room temperature, and this solution was charged into an autoclave (material: made of Hastelloy C) having a magnetic stirrer, a pressure gauge, a gas inlet tube and a needle valve, and having a 100 ml internal volume in which the system had been previously purged with argon. After replacing the inside of the system with hydrogen, the system was sealed, and the temperature of the mixture was increased while stirring. When the internal temperature reached 110 ° C., hydrogen was introduced into the reaction system to evacuate the reaction system to 3 MPa (30 kg / cm). ² ) Press up to
The reaction was carried out for 0.5 hour while maintaining the pressure in the system at 3 MPa. After the autoclave was cooled to room temperature, the pressure was released, the reaction solution was taken out, and a part thereof was analyzed by gas chromatography. As a result, the conversion of methacrolein was 6%.
The product selectivity was 83.5% for methallyl alcohol, 1.6% for isobutyraldehyde, and 9.0% for isobutyl alcohol.

Example 5 In Example 4, 21 mg of lithium chloride (0.5 mm
ol) instead of 63.4 mg (0.3 mm) of ferrous chloride
ol), except that the reaction operation was carried out in the same manner as in Example 4. When a part of the obtained reaction solution was analyzed by gas chromatography, the conversion of methacrolein was 71.8%, the selectivity of the product was 83.0% of methallyl alcohol, and the selectivity of isobutyraldehyde was 1.0%. 6% and isobutyl alcohol 10.7%.

Example 6 In Example 4, 21 mg of lithium chloride (0.5 mm
ol) instead of cetylpyridinium chloride 177mg
(0.5 mmol), and the same reaction procedure as in Example 4 was performed. When a part of the obtained reaction solution was analyzed by gas chromatography, the conversion of methacrolein was 93.3%, and the selectivity of the product was 67.3% for methallyl alcohol and 2.73% for isobutyraldehyde.
1% and isobutyl alcohol 10.5%.

Example 7 Under an argon atmosphere, dichlorotris (triphenylphosphine) ruthenium 48 mg (0.05 mmol), triisodecylphosphite 503 mg (1 mmol),
Lithium chloride 21mg (0.5mmol), toluene 1
9 ml, pseudocumene 19 ml and methacrolein 10.5 g (150 mmol) were mixed at room temperature, and the solution was placed in an autoclave equipped with a magnetic stirrer, a pressure gauge, a gas inlet tube and a needle valve and having a 100 ml internal volume in which the system had been previously purged with argon. (Material: Hastelloy C)
Was charged. After replacing the inside of the system with hydrogen, the system was sealed, and the temperature of the mixture was increased while stirring. When the internal temperature reached 110 ° C., hydrogen was introduced into the reaction system to evacuate the reaction system to 5 MPa (50 MPa).
kg / cm ² ) and reacted for 0.5 hour while maintaining the pressure in the system at 5 MPa. After cooling the autoclave to room temperature, the pressure was released, the reaction solution was taken out, and a part thereof was analyzed by gas chromatography. The conversion of methacrolein was 88.0%, and the selectivity of the product was methalyl. 66.0% of alcohol, 1.2% of isobutyraldehyde, and 25.7% of isobutyl alcohol.

Example 8 66.7 mg (0.1 mmol) of dichlorotetrakis (trimethylphosphite) ruthenium under an argon atmosphere
l), 40 ml of toluene and 3.5 g of methacrolein
(50 mmol) was mixed at room temperature, and this solution was charged into an autoclave (material: made of Hastelloy C) having a magnetic stirrer, a pressure gauge, a gas inlet tube and a needle valve, and having a 100 ml internal volume in which the system was previously purged with argon. .
After replacing the inside of the system with hydrogen, the system was sealed, and the temperature of the mixture was increased while stirring. When the internal temperature reached 110 ° C., hydrogen was introduced into the reaction system to evacuate the reaction system to 3 MPa (30 kg / c).
m ² ) and reacted for 0.5 hour while maintaining the pressure in the system at 3 MPa. After cooling the autoclave to room temperature, the pressure was released, the reaction solution was taken out, and a part thereof was analyzed by gas chromatography. As a result, the conversion of methacrolein was 87.2%, and the selectivity of the product was methalyl. Alcohol 73.9%, isobutyraldehyde 3.2%, isobutyl alcohol 19.4%.

Comparative Example 1 Under an argon atmosphere, 115.2 mg (0.1 mm) of dihydridotetrakis (triphenylphosphine) ruthenium
ol), 40 ml of toluene and 3.5 of methacrolein.
g (50 mmol) was mixed at room temperature, and this solution was equipped with an electromagnetic stirrer, a pressure gauge, a gas introduction tube and a needle valve, and was internally replaced with argon in an internal volume of 100 ml in advance.
(Material: Hastelloy C). After replacing the inside of the system with hydrogen, the system was sealed, and the temperature of the mixture was increased while stirring. When the internal temperature reached 110 ° C., hydrogen was introduced into the reaction system to evacuate the reaction system to 3 MPa (30 kg / c).
m ² ) and reacted for 6 hours while maintaining the pressure in the system at 3 MPa. After cooling the autoclave to room temperature,
The pressure was released, the reaction solution was taken out, and a portion thereof was taken and analyzed by gas chromatography. The conversion of methacrolein was 57.9%, and the selectivity of the product was 13.7% of methallyl alcohol, Aldehyde 47.
4% and isobutyl alcohol 20.8%.

Comparative Example 2 In Example 1, triisodecyl phosphite 201 was used.
The reaction operation was performed in the same manner as in Example 1 except that 124 mg (0.4 mmol) of triphenyl phosphite was used instead of mg (0.4 mmol), and the reaction time was changed to 4 hours. When a part of the obtained reaction solution was analyzed by gas chromatography, the conversion of methacrolein was 22.7%, the selectivity of the product was 53.6% of methallyl alcohol, and 19. 5
% And isobutyl alcohol 10.4%.

Comparative Example 3 A reaction operation was carried out in the same manner as in Example 2 except that triisodecyl phosphite was not used and the reaction time was changed to 0.5 hour. When a part of the obtained reaction solution was analyzed by gas chromatography, the conversion of methacrolein was 90.0%, the selectivity of the product was 1.4% for methallyl alcohol, and 42. 5%, isobutyl alcohol
4%.

Comparative Example 4 In Example 1, 39.8 mg of ruthenium triacetylacetonate was used instead of 28 mg (0.1 mmol) of dichloro (1,5-cyclooctadiene) ruthenium.
(0.1 mmol) and the reaction operation was carried out in the same manner as in Example 1 except that the reaction time was changed to 6 hours. When a part of the obtained reaction solution was analyzed by gas chromatography, the conversion of methacrolein was 5.6%.
The formation of methallyl alcohol was not observed, and the selectivity for isobutyraldehyde was 35.6%.

[0033]

According to the present invention, methallyl alcohol can be produced inexpensively and industrially advantageously using methacrolein as a starting material.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Hideharu Iwasaki 2045-1, Sazu, Kurashiki-shi, Okayama F-Term in Kuraray Co., Ltd. (Reference) 4G069 AA06 BA21B BA27A BA27B BB08A BB08B BC04B BC66B BC70A BC70B BD12B BE25B BE29A BE29B BE02B BE33B CB02 4H006 AA02 AC41 BA02 BA03 BA06 BA23 BA37 BA39 BA48 BA53 BE20 FC74 FE11 4H039 CA60 CB20

Claims (2)

[Claims] 1. A divalent ruthenium compound and a compound represented by the general formula (I): (Wherein, R ¹ , R ² and R ³ each independently represent an aliphatic hydrocarbon group which may have a substituent, or any ^{two of} R ¹ , R ² and R ³ are taken together. Represents an alkylene group which may have a substituent, and the other one represents an aliphatic hydrocarbon group which may have a substituent.) A method for producing methallyl alcohol, comprising hydrogenating an aldehyde group of methacrolein under a hydrogen atmosphere condition. 2. The method for producing methallyl alcohol according to claim 1, further comprising a salt containing a halogen ion.