JPS6033901B2 - Method for producing 4-butanolides - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel method for producing 4-butanolides from acrylic acid esters and aldehydes, and particularly to a method for producing 4-butanolides by electrolytic reductive coupling reaction.

The 4-butanolides referred to in the present invention refer to 4-butanolide, that is, y-butyrolactone and its 4-position monosubstituted product.

4-Butanolides, particularly 4-alkyl-4-phthanolides, have a unique aroma and are used as fragrances for foods and cosmetics, and are also useful as intermediates in the production of fragrances, medicines, agricultural chemicals, and the like.

For example, 4-n-propyl-4-butanolide has a coumarin-like aroma, and 4-n-hexyl-4-butanolide has a nutty aroma when concentrated, and a peach-like aroma when diluted. Known as a fragrance. The following method has been proposed as a method for producing 4-butanolides by electroreductive coupling reaction of acrylic acid ester and aldehyde.

That is, using dimethylformamide as a solvent, aldehyde,
Tet is produced by electrolytically reducing a mixture of acrylic acid esters and trimethylchlorosilane in a homogeneous system using a lead electrode.
Rahedron Botte Dai”, Volume 21, No. 5029
~5032 Bage (198th King)] and Zh. ○rg. Khim
．． ”, Volume 11, No. 9, pages 1984-1985 (1973 edition)]. In the former case, electrolysis is performed in a homogeneous system, but generally speaking, when electrolysis is performed in a homogeneous system, three types of solvent systems are considered: water-protic solvent, water-abrotic polar solvent, and aprotic polar solvent. It will be done. As a result of various studies on electroreductive coupling reactions in a homogeneous system, the present inventors obtained the following knowledge disclosed in Tokuiso Sho 56-155746. That is, it was recognized that the current efficiency was extremely low in water-protic solvents. Although the reason for this is not well understood, it is thought that one of the causes is that a part of the aldehyde undergoes acetalization and hemiacetalization by the solvent. Furthermore, in the case of water-aprotic polar solvent, the selectivity of 4-butanolide based on aldehyde is extremely low. In this case, it is thought that the action of hydroxyl ions, which are thought to be slightly produced by water electrolysis, was strengthened by the aprotic polar solvent, and that undesirable side reactions occurred with aldehydes as well. Therefore, in order to perform electrolysis in a homogeneous system while maintaining both high yield and current efficiency, an aprotic polar solvent must be used alone, taking into consideration the compatibility with water and the solubility of the conductive supporting salt. , and the use of special reagents such as trimethylchlorosilane. However, an expensive solvent such as dimethylformamide must be used, and trimethylchlorosilane must be used in equimolar amounts with the aldehyde, which is expensive and easily hydrolyzed by moisture. There are problems such as the need to be careful when handling the product. On the other hand, in the latter case, the electrodes used are difficult to manufacture, and the carbon electrodes lack mechanical strength, resulting in them breaking or cracking when attached to filter-press type battery containers, etc., which are usually used industrially. There are drawbacks such as the need to solve the pollution problem caused by the use of mercury.

Furthermore, in this method, 4-butanolide is
Since it is obtained as a mixture of -butanolide and 4-ethyl-4-butanolide, it also has the disadvantage that separation and purification becomes complicated. The present inventors aimed to overcome the various drawbacks of the conventional manufacturing method of 4-butanolides and develop a method that can be easily implemented industrially. By using an inorganic salt and electrolytically reducing the pH in the aqueous layer in an aqueous emulsion state in the presence of an electrically conductive substance that has a phase transfer catalytic function, it is possible to easily reduce 4 with extremely high yield and high current efficiency. -Discovered scales for producing butanolides.

The present invention was made based on the above-mentioned knowledge, and it is possible to produce 4-butanolides in high yield and with high current effect under mild conditions without using expensive additives or additives that require careful handling. In addition, it is an industrially advantageous four-tube polymer that facilitates the isolation operation of the product, makes the cathode strong in mechanical strength and non-toxic, and facilitates the separation and recovery of conductive substances. The object of the present invention is to provide a method for producing /lidos.

The method for producing 4-butanolides of the present invention which achieves the above object uses a mixture of acrylic acid ester and aldehyde as an electrode and a supporting electrolyte in a battery cell separated by an intestinal ion exchange membrane. in an aqueous emulsion state using an inorganic salt having a phosphate ion in the presence of at least one conductive substance having a phase transfer catalytic function selected from the group consisting of quaternary ammonium salts and quaternary phosphonium salts. , and the pH in the aqueous layer of the aqueous emulsion is 6-6.
It is characterized in that electrolytic reduction is carried out within the range of 9.

The reaction of the present invention proceeds roughly according to the following reaction formula.

(R in the formula is a substituted or unsubstituted alkyl group, aryl group, aralkyl group, alkenyl group or alkynyl group, R'
is an alkyl group) In the present invention, it is necessary to carry out this reaction in an aqueous emulsion state, that is, in a heterogeneous phase consisting of an aqueous phase and an organic phase.

In this case, the pH in the aqueous layer has an important meaning in the present invention. That is, it is necessary to adjust the pH in the aqueous layer to a range of 6 to 9. In an acidic region with a pH of 6 or lower and an alkaline region with a pH of 9 or higher, acrylic acid esters and aldehydes become unstable, side reactions occur, and the reaction yield of 4-butanolides based on acrylic esters and aldehydes decreases. Especially pH
In the acidic range of 6 or less, the amount of propionate ester produced increases and the reaction yield based on acrylate ester decreases.
Also, electrode wear increases. The aqueous layer of the aqueous emulsion mainly contains inorganic salts having phosphate ions and conductive substances having a phase transfer catalytic function, which influence the pH.

Inorganic salts containing phosphate ions are particularly influential. In order to make the - of the aqueous layer in the range of 6 to 9, it is necessary to adjust the pH of the inorganic salt having phosphate ions, that is, the alkali metal salt of phosphoric acid, to 6 to 9. Alkali metal salt of phosphoric acid at pH 6-9
In order to achieve this, phosphoric acid or dihydrogen phosphate must be neutralized with an alkali, or an alkali metal hydroxide or phosphoric acid-hydrogen salt must be neutralized with phosphoric acid. The cations of the inorganic salts having phosphate ions used in the present invention include, for example, alkali metal cations such as sodium, potassium, lithium, cesium and rubidium, and ammonium ions, with sodium and potassium being preferred for economical reasons.

There is no particular restriction on the amount of inorganic salt containing phosphate ions used, as long as the electrical resistance of the emulsion is not extremely high and electrolysis can be carried out smoothly, and the concentration in the aqueous layer is usually 1.
It is used in a range of 30% by weight.

The aldehyde used in the present invention is not particularly limited, but from an industrial standpoint, aliphatic aldehydes having 2 to 13 carbon atoms are preferred, and saturated linear aldehydes are more preferred.

For example, propanal, futanal, bentanal, hexanal, hef. These include tanal, octanal, and nonanal. The yield can be significantly improved by carrying out electrolysis in an aqueous emulsion state using an inorganic salt having a phosphate ion and an electrically conductive substance having a phase transfer catalytic function, such as a quaternary ammonium salt or a quaternary phosphonium salt. The degree of effectiveness of the quaternary ammonium salt and quaternary phosphonium salt used in the present invention differs depending on the type thereof.

Furthermore, the degree of effectiveness of quaternary ammonium salts and quaternary phosphonium salts also differs depending on the type of aldehyde.
That is, when the aldehyde has a small number of carbon atoms, for example, when the aldehyde has 2 to 4 carbon atoms, a quaternary ammonium salt and a quaternary phosphonium salt in which the total number of carbon atoms in the general formula described later is 10 or more and 25 or less are used. It is preferable. 1
If it is less than 0 or more than 25, the current efficiency and reaction yield will decrease.

When the aldehyde has a large number of carbon atoms, for example, the number of carbon atoms is 5 to 1.
In the case of aldehyde No. 3, it is preferable to use one in which the total number of carbon atoms in the general formula described below is 10 or more and 20 or less,
It is more preferable to use one having a total number of carbon atoms of 16. When the total number of carbon atoms is 10 or less and 20 or more, current efficiency and reaction yield decrease. The above-mentioned quaternary ammonium salt and quaternary phosphonium salt have the general formula (quaternary ammonium salt) (quaternary phosphonium salt) (in the formula, R1, R2, R3, and R4 are respectively the same or different alkyl groups or Compounds that are aralkyl groups, the total number of carbon atoms in these groups is 10 to 25, × is an acid group, and n is an integer corresponding to the ionic valence of ×) It is.

In the quaternary ammonium salt and quaternary phosphonium salt, R1, R2, R3 and R4 are generally alkyl groups selected from the group consisting of methyl group, ethyl group, propyl group, butyl group, and amyl group. Some are preferred, especially at least three of R1, R2, R3, and R4.
More preferably, each group is an alkyl group having 3 or more carbon atoms. In particular, in the case of an aldehyde having 5 to 13 carbon atoms, it is preferable that all the alkyl groups are butyl groups. These include, for example, ammonium salts and phosphonium salts of tetra(n or iso)-propyl, tetra(n or iso)-butyl, tetra(n or iso)-amyl, ethyltripropyl, ethyltributyl, ethylpropyldibutyl. can be mentioned. The amount of quaternary ammonium salt and quaternary phosphonium salt in the aqueous layer of the aqueous emulsion may be 0.01% by weight or more, and 0.1% by weight or more.
It is preferably at least 5% by weight and at most 5% by weight.

If the amount of quaternary ammonium salt and quaternary phosphonium salt is too small, current efficiency and reaction yield will decrease. As the counteranion X (same as X shown in the general formula) of the quaternary ammonium salt or quaternary phosphonium salt, for example, phosphate ion, sulfate ion, halogen ion, etc. are used. Acid ions are preferred.

Sulfate ions, halogen ions, etc. cause a slight decrease in reaction yield and current efficiency. Among these, halogen ions are undesirable because they increase electrode wear. Examples of the cathode material used in the present invention include lead or alloys containing lead as a main component, such as hard lead containing antimony, lead-tin alloys, and the like. These cathode materials have sufficient mechanical strength and do not cause pollution problems. Even when used in bipolar filter press type lightning tanks, it is possible to continue stable operation for a long period of time. The anode material may be any material that has sufficient corrosion resistance against the anolyte, such as lead, lead alloys, platinum, silver, alloys mainly composed of these metals, or other metals containing these metals or alloys. A plated plate is used.

In the method of the present invention, during electrolysis, a diaphragm is used to prevent the possibility of the oxygen generated on the anode surface corresponding to the amount of current flowing and the hydrogen generated slightly on the cathode surface mixing and generating explosive gas. It is preferable to partition the chamber into an anode chamber and a cathode chamber.

As the diaphragm, a cation exchange membrane, an unglazed diaphragm, etc. can be used, but a cation exchange membrane is generally preferred. As the anolyte, an aqueous solution of an inorganic acid such as sulfuric acid or phosphoric acid is used. The catholyte contains substances derived from the reactants such as acrylic acid ester, aldehyde, and their electrolytic products such as 4-phthanolide, adipic acid diester, propionic acid ester, and alcohol, as well as water and a substance derived from the reactant to increase conductivity. It is a mixture of conductive substances and exists as a two-layer system consisting of an organic layer and an aqueous layer.

In some cases, it is also possible to add an acrylic acid ester polymerization inhibitor, and it is also possible to use an emulsifier to stabilize the emulsion, and to add a solvent as long as it does not adversely affect emulsion formation. However, it is usually preferable to perform electrolysis without using these additives or solvents. As the acrylic acid ester used in the present invention, lower alkyl esters of acrylic acid are preferable from the viewpoint of water solubility, and acrylic acid methyl ester (hereinafter abbreviated as methyl acrylate) is preferable because it is inexpensive and industrially easily available. do.

) is most preferred. The molar ratio of aldehyde to acrylic ester is preferably 1 to 10 from the viewpoint of yield, and more preferably 1 to 5 from the viewpoint of product separation.

The amount of aldehyde and acrylic ester relative to water is
It is sufficient that the amount is at least the dissolution amount in water and at least the amount at which the organic layer is separated and an emulsion is formed.

The volume ratio of the organic layer in the emulsion to the total emulsion is preferably 0.05 to 0.5 from the viewpoint of ease of product separation.

The temperature during electrolysis may be any temperature as long as it is below the boiling temperature of the aldehyde or acrylic acid ester, but it is usually preferably 20 to 60 qo, particularly 20 to 40 qo, in order to prevent thermal denaturation of the aldehyde and acrylic ester.

Regarding the current density on the cathode surface, IA/d~50A
/dMy preference.

If it is less than IA/d, productivity decreases and electrodes with a wide area are required, and if it is more than 50 A/d, heat generation is intense due to liquid resistance, making it impractical. Normally, it is carried out at 5 to 20 A/d. It is desirable that the electrolytic reaction solution be supplied onto the cathode surface in a state where the aqueous layer and organic layer are suspended as finely as possible. Therefore, in a tank-type electrolytic cell, it is necessary to sufficiently stir the electrolyte solution. In addition, in a filter press type electrolytic cell, the flow linear velocity of the electrolytic reaction solution is . The speed is preferably at least a speed at which an emulsion is sufficiently formed, and is usually carried out at a speed of 100 to 400 per second. In the present invention, the treatment of the catholyte after the electrolytic reaction is generally carried out as follows.

That is, first, the electrolytic solution is separated into two layers, an organic layer and an aqueous layer, and then the conductive substance distributed in the organic layer is extracted with a small amount of water. The organic layer is then distilled, first removing low-boiling by-products such as alcohol, then recovering unreacted raw materials, and then obtaining the product. On the other hand, for the aqueous layer, low-boiling byproducts such as alcohol are removed by distillation, water corresponding to the water transferred from the anolyte is removed by distillation, and the remaining liquid containing conductive substances is circulated as the aqueous layer of the catholyte. use. In the method of the present invention, the product can be separated very easily by such a treatment, and the conductive substance can also be recovered very easily. The advantages of the present invention are listed below. 1 In the emulsion state,
By adjusting the pH in the aqueous layer to a range of 6 to 9 and electrolyzing in the presence of a conductive substance that has a phase transfer catalytic function, 4-butanolides can be produced with extremely high current efficiency without using expensive reagents. and can be obtained with excellent selectivity.

Furthermore, adipic acid gester, which is partially a subsidiary, is also extremely important industrially. 2. Separation of the product is extremely easy.

In other words, by simply allowing the emulsion to leave the electrolytic tank, acrylic esters, aldehydes,
It can be easily separated into an organic layer mainly composed of 4-butanolide and an aqueous layer mainly composed of water and a conductive substance. The product can be easily isolated and purified by removing only this organic layer and distilling it. In this distillation, unlike in a homogeneous system, there is no need to distill and recover a large amount of solvent, and the utility costs are extremely low.
After separating the electrolyte into two layers, the aqueous layer can be subjected to subsequent electrolysis after some treatment. 3. The conductive substance in 4-butanolide can be easily separated and recovered.

That is, as described in 2 above, the organic layer and the aqueous layer can be easily separated, and the conductive substance in this organic layer can be separated and recovered very easily by extraction with water. As described above, the present invention provides 4-
This invention has great significance in that it provides a very advantageous industrial process for producing butanolides.

Next, Examples will be shown to further specifically explain the present invention. Note that the reaction rate, selectivity, and current efficiency were calculated using the following formulas. Reaction rate of acrylic ester Number of moles of acrylic ester consumed - Number of moles of acrylic ester charged x 100 [%] Selectivity of 4-butanolides based on acrylic ester Number of moles of 4-butanolide produced - Number of moles of acrylic acid ester consumed x 100 [%]
] Selectivity of 4-butanolides based on aldehyde generated 4
- Number of moles of butanolides - Number of moles of aldehyde consumed x 100 [%] Selectivity of adipic ester based on acrylic ester Number of moles of adipic ester produced x 2 - Number of moles of consumed acrylic ester x 100 [%] Current efficiency Number of moles of 4-butanolide produced x 2 Amount of current (in Faraday units) x 100 [%] However, the current effect is less than the amount of electricity produced by 2 Faradays.
It was calculated assuming that moles are produced.

Example 1 Lead electrodes with a current-carrying area of 0.04 d were used for both the anode and the cathode, and an intestinal ion exchange membrane obtained by sulfonating a divinylbenzene-styrene-butadiene copolymer with a thickness of 1.6 ribs was used as the anode chamber. A day-type cell partitioned into a cathode chamber was used as an electrolytic cell.

10% sulfuric acid was used as the anolyte. As catholyte,
Dissolve 2.73 g of potassium dihydrogen phosphate and 0.95 g of potassium hydroxide with a purity of 85% in water, and add 1.6 g of a 50% aqueous solution of tetra-n-butylammonium phosphate to this.
The pH of this aqueous solution was adjusted to 7 with phosphoric acid.
Then butanal 5.53 hours, methyl acrylate 2.2 hours
A mixture was used in which water was added to make a total liquid volume of 70. Electrolysis was carried out at a current density of 10 A/d while maintaining the temperature of the catholyte at 25 to 3,000 ℃ and thoroughly stirring with a magnetic stirrer. After starting electrolysis 3. When the electrolysis was finished at the end of the morning hours and the catholyte was analyzed by gas chromatography, the reaction rate of methyl acrylate was 9.
8%, 4-n-propyl-4- based on methyl acrylate
Butanolide selectivity 86.5%, dimethyl adipate selectivity 1%, butanal standard 4-n-propyl-4-
Selectivity of ptanolide 95.4%, 4-n-propyl-4
- The current efficiency of butanolide was 83.0%. Example 2 5.46 hours of sodium dihydrogen phosphate and 1.31 hours of sodium hydroxide were dissolved in water, 1.88 hours of a 50% aqueous solution of tetra-n-amylammonium phosphate was added thereto, and this aqueous solution was dissolved in phosphorus. The pH was adjusted to 7 with acid, and then 5.53 g of butanal and 2.20 g of methyl acrylate were added, and water was added to make the total liquid volume 70. When electrolysis was carried out in the same manner as in Example 1, the reaction rate of methyl acrylate was 86%, the selectivity of 4-n-propyl-4-butanolide was 92% based on methyl acrylate, and the selectivity of dimethyl adipate was less than 1%. The selectivity of 4-n-propyl-4-butanolide was 86.2% based on butanal, and the current efficiency of 4-n-propyl-4-butanolide was 76.4%.

Example 3 5 of tetra-n-butylammonium sulfate instead of tetra-n-butynoleammonium phosphate
Electrolysis was carried out in the same manner as in Example 1 except that 1.65% of the 0% aqueous solution was used, and the reaction rate of methyl acrylate was 9.
5%, 4-n-propyl-4- based on methyl acrylate
Selectivity of putanolide 81.0%, dimethyl adipate 1
%, butanal standard selectivity for 4-n-propyl-4-butanolide was 87.8%, and current efficiency for 4-n-propyl-4-butanolide was 77%.

Example 4 50% of tetra-n-butylphosphonium phosphate instead of tetra-n-butylammonium phosphate
When electrolysis was carried out in the same manner as in Example 1 except that a 1.66% aqueous solution was used, the reaction rate of methyl acrylate was 96%.
%, selectivity of 4-n-propyl-4-butanolide based on methyl acrylate 86%, selectivity of dimethyl adipate 1%, selectivity of 4-n-propyl-4-butanolide based on butanal 95.5%, 4 The current efficiency of 1-n-propyl-4-butanolide was 83.2%.

Example 5 Heptanal instead of butanal 8.76 pm, electrolysis time 3.5 hours 2. When electrolysis was carried out in the same manner as in Example 1 except that the field time was changed, the reaction rate of methyl acrylate was 56.0%, and the selectivity of 4-n-hexyl-4-butanolide based on methyl acrylate was 69. 4%, selectivity of dimethyl adipate 27.1%, 4-n based on heptanal
-Hexyl-4-butanolide selectivity is 78%, 4-n
The current efficiency of -hexyl-4-butanolide was 65.6%.

Example 6 50% of tetra-n-amylammonium phosphate instead of tetra-n-butylammonium phosphate
When electrolysis was carried out in the same manner as in Example 5 except that a 1.88% aqueous solution was used, the reaction rate of methyl acrylate was 68%.
．． 9%, 4-n-hexyl-4 based on methyl acrylate
-butanolide selectivity 54.7%, dimethyl adipate selectivity 22.0%, Hef.

The selectivity of 4-n-hexyl-4-butanolide based on tanal was 71%, and the current efficiency of 4-n-hexyl-4-butanolide was 54.0%. Example 7 50% of tetra-n-butylammonium sulfate instead of tetra-n-butylammonium phosphate
When electrolysis was carried out in the same manner as in Example 5 except that a 1.65% aqueous solution was used, the reaction rate of methyl acrylate was 57.
．． 1%, 4-n-hexyl-4 based on methyl acrylate
-Selectivity of butanolide 65.7%, selectivity of dimethyl adipate 24.1%, selectivity of 4-n-hexyl-4-butanolide based on heptanal 74%, 4-n-hexyl-4-butanolide The current efficiency was 62.1%.

Example 8 Electrolysis was carried out in the same manner as in Example 5, except that 1.66% of a 50% aqueous solution of tetra-n-butylphosphonium phosphate was used instead of tetra-n-butylammonium phosphate. Reaction rate 56.4%, selectivity of 4-n-hexyl-4-butanolide based on methyl acrylate 68.3%, selectivity of dimethyl adipate 27.0%, Hef.

The selectivity of 4-n-hexyl-4-butanolide based on tanal was 79.0%, and the current efficiency of 4-n-hexyl-4-phthanolide was 66.0%. Comparative Example Potassium dihydrogen phosphate 2.73 days, 50% aqueous solution of tetra-n-phthylammonium phosphate 1.6 days, water 54.71 days,
Methyl acrylate was 2.2 hours, hebutanal was 8.769 in the catholyte (pH in the aqueous layer was 4.2).

Claims (1)

[Claims] 1. A battery containing a mixture of acrylic ester and aldehyde with a lead or lead alloy as an electrode and separated by a cation exchange membrane, using an inorganic salt having phosphate ions as a supporting electrolyte, In the presence of at least one conductive substance having a phase transfer catalytic function selected from the group consisting of quaternary ammonium salts and quaternary phosphonium salts, the pH of the aqueous layer of the aqueous emulsion is reduced to 6. 9. A method for producing 4-butanolides, characterized by carrying out electrolytic reduction. 2. The method according to claim 1, wherein the inorganic salt having phosphate ions is an alkali metal salt of phosphoric acid. 3. The method according to claim 2, wherein the alkali metals are sodium and potassium. 4. The method according to claim 1, wherein the aldehyde is an aliphatic aldehyde having 2 to 13 carbon atoms. 5 The aldehyde is an aliphatic aldehyde having 2 to 4 carbon atoms, and the quaternary ammonium salt and quaternary phosphonium salt have the general formula. ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (Quaternary ammonium salt) ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (Quaternary phosphonium salt) (R^1, R^2, R^3 in the formula, and R^4 are the same or different alkyl groups or aralkyl groups, and the total number of carbon atoms in these groups is 10 to 25,
2. The method according to claim 1, wherein X is an acid group, and n is an integer with a value corresponding to the ionic valence of X. 6. Claim 5, in which R^1, R^2, R^3 and R^4 in the general formula are all alkyl groups, and the total number of carbon atoms in these alkyl groups is 14 to 20. Method described. 7 The aldehyde is an aliphatic aldehyde having 5 or more carbon atoms, and the quaternary ammonium salt and quaternary phosphonium salt have the general formula. ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (Quaternary ammonium salt) ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (Quaternary phosphonium salt) (R^1, R^2, R^3 in the formula, and R^4 are the same or different alkyl groups or aralkyl groups, and the total number of carbon atoms in these groups is 10 to 20,
2. The method according to claim 1, wherein X is an acid group, and n is an integer with a value corresponding to the ionic valence of X. 8. The method according to claim 7, wherein R^1, R^2, R^3, and R^4 in the general formula are all alkyl groups. 9. The method according to claim 8, wherein all the alkyl groups are butyl groups. 10. The method according to claim 5 or 7, wherein X in the general formula is a unit corresponding to a monovalent phosphate ion. 11. The method according to claim 1, wherein the acrylic ester is a lower alkyl ester of acrylic acid. 12. The method according to claim 11, wherein the lower alkyl ester of acrylic acid is methyl acrylate. 13 Claim 5 or 7, wherein the concentration of the quaternary ammonium salt and quaternary phosphonium salt in the aqueous layer of the aqueous emulsion is 0.01% by weight or more and 5% by weight or less
The method described in section.