MXPA99000136A - Method to stabilize aldehi - Google Patents

Abstract

The present method makes possible the stabilization of aliphatic C3-C14 aldehydes against self-condensation polymerization, including the addition of alkaline substances to aldehydes where the alkaline substances used are alkali metal hydroxides, alkaline earth metal hydroxides, alkali metal carbonates , alkaline earth metal carbonates or alkaline earth metal carboxylates and are added to the aldehyde to be stabilized in amounts of 0.005-20 ppm, based on the aldehyde.

Description

METHOD FOR STABILIZING ALDEHYDES DESCRIPTIVE MEMORY The present invention relates to a method for stabilizing aldehydes against polymerization and self-condensation. Due to its high reactivity, aldehydes have a tendency toward polymerization and self-condensation. The polymerization mainly forms trimeric products. For example, isobutyraldehyde forms 2,4,6-triisopropyl-1,3,5-trioxane, although other aliphatic aldehydes having from 3 to 14 carbon atoms are also polymerized to form the cyclic trimeric aldehyde (trialkyltrioxane). Trimerization is catalyzed by chemical substances such as chlorine or bromine, phosphorus pentoxide, sulfuric acid, hydrogen sulfide, hydrogen chloride, hydrogen fluoride, boron trifluoride, aluminum chloride or zinc chloride. When said acidic compounds are present, the polymerization of the aldehydes begins spontaneously. If the concentration of the acid compound is sufficiently high, this results in the formation of crystalline trimeric aldehydes within a few minutes. At concentrations of up to 10 ppm of the acid compound, the formation of the trimer occurs more slowly over a period of a few days. In addition, low temperatures, i.e., temperatures of about 0 ° C or lower, or ultraviolet light promote the polymerization of the aliphatic aldehydes. An additional problem is the tendency for the aldehydes to undergo the condensation of aldol when alkaline substances are present. Due to their transformation into such compounds with such relatively high molecular weights, the aldehydes can not be stored for indefinite periods. Although the products of the polymerization and self-condensation of the aldehydes are redissociated at a relatively high temperature, their formation is an obstacle to the unlimited industrial use of the aldehydes. Therefore, efforts are made to avoid the formation of products with relatively high molecular weights from aldehydes. This is possible in a limited period by preparing and storing the aldehydes in a highly pure form. However, the purification operations required for this are so complicated that they are not feasible for the commercial preparation of the aldehydes. . It is known that polymerization and self-condensation reactions can be suppressed by adding certain substances. In practice, these substances have to meet a series of requirements if the objective is to use the aldehyde without any restriction in a wide range of applications. Among them is the requirement that the substance used must remain active for a prolonged period even at low concentration and also that it must not cause any interference in the processing of the aldehyde as a result of chemical reactions. Stabilizers which have been described for isobutyraldehyde are, for example, mercaptobenzimidazole and 2,2-methylene-nenedi (4-methyl-6-tert-butylphenol). However, these stabilizers are effective only for an insufficient time. Thus, according to DE-A-29 05 267, when 100 ppm of mercaptobenzimidazole is added to isobutyraldehyde, a considerable degree of trimerization is observed again after the stabilized aldehyde has been stored only for 5 weeks. According to another method, a solution of diphenylamine in ethanol is added to the aldehydes to avoid polymerization. However, similarly, this procedure does not ensure the removal of the polymerization for a long period. It is known from DE-A-29 05 267 and DE-A-29 17 789 that isobutyraldehyde and other aliphatic aldehydes possessing from 3 to 14 carbon atoms can be stabilized against polymerization and self-condensation by adding triethanolamine or dimethylethanolamine. When using these stabilizers, good stabilization over a prolonged period can be obtained even when relatively low concentrations are used. Holds, for example, that 10 ppm of the aforementioned ethanolamines, based on the aldehyde, can prevent the formation of compounds with high molecular weights due to polymerization and autocondensation, for example when oxygen is present, over a period of 30 weeks. When 20-100 ppm are added, based on the aldehyde, the stabilizers suppress the formation of the condensation product of the trimer > 5 or aldol when the aldehyde is stored for a period of about one year. However, these stabilizers have the disadvantage that they can be removed from the aldehydes again only with considerable expense in terms of distillation. Similarly, JP 45 012282 B4 faces the problem of stabilizing isobutyraldehyde against the formation of trimers. It is established that the treatment of isobutyraldehyde with an aqueous alkaline solution is completely ineffective. Stabilization can only be achieved if the substance Alkaline is added to the isobutyraldehyde as a solid or in the form of a highly concentrated aqueous solution; In the second case, it is critical that the amount of water is under the? Saturation limit of isobutyraldehyde. The alkaline compounds that are used are alkali metal compounds (salts carbonate, bicarbonate salts, silicates and fatty acid salts) alkaline earth metal compounds, oxides, hydroxides, carbonate salts, bicarbonate salts and salts of fatty acid and ammonium or ammonium carbonate. However, the amounts of alkaline compound that are added are very large. In the case of sodium hydrogen carbonate, sodium carbonate, potassium carbonate, ammonium carbonate, calcium carbonate and calcium hydroxide, sodium acetate and magnesium oxide as stabilizers, 500 ppm is added in each case to isobutyraldehyde, amount that is considered small in the context of JP 45 012282 B4. Although the use of such large amounts of the alkaline stabilizer suppresses trimer formation, problems caused by the increasing occurrence of aldol condensation of the alkali-catalyzed isobutyraldehyde are unavoidable. In addition, the addition of the alkaline substance as a solid to relatively large amounts of aldehyde, for example, stored in tanks, is associated with the problem of completely dissolving, dispersing and uniformly distributing the alkaline substance throughout the entire volume of the aldehyde. Therefore, an object of the invention is to provide an improved method that makes it possible to avoid the polymerization and self-condensation reactions of the aldehydes for as long as possible. This objective is achieved by means of a method in which aliphatic C3-C4 aldehydes are stabilized by the addition of alkaline substances, which includes adding alkali metal hydroxides, alkaline earth metal hydroxides, alkali metal carbonates, alkaline earth metal or alkaline earth metal carboxylates as alkaline substances to the aldehyde to be stabilized in amounts of 0.05-20 ppm, preferably 0.05-5 ppm, particularly preferably 0.05-2.5 ppm, based on the aldehyde. The process of the invention is notable for the fact that the stabilizers that are used are effective even at extremely low concentrations. Even 0.05 ppm of the stabilizer prevents the formation of compounds with a high molecular weight due to aldol polymerization or condensation when the aldehyde is stored, even at very low temperatures and without additional precautions for a period of several weeks. It should also be emphasized that the substances used to stabilize the aldehydes do not interfere with the further processing of the aldehydes. If, however, it is desired to remove the alkaline substance before further processing of the aldehydes, this can be obtained by simple distillation in which the alkaline substance remains in the distillation bottoms. It should be noted that, although the stabilizers are alkaline, they do not trigger any condensation reaction of aldol in the aldehydes. The preferred alkali metal hydroxides are sodium and potassium hydroxide, and the preferred alkaline earth metal hydroxide is calcium hydroxide. The preferred alkali metal carbonates are sodium and potassium carbonate and the preferred alkaline earth metal carbonates are magnesium carbonate and calcium carbonate. For alkali metal carboxylate, particular preference is sodium butyrate.

The alkaline substances are generally used as an aqueous solution 0.01-1M, preferably 0.05-0.5M and in particular 0.1-0.25M. In particular cases, it may also be advantageous to add the alkaline substances, in particular the alkali metal carboxylates and preferably sodium butyrate in solid form among them. Examples of the aldehydes that can be stabilized by the method of the invention are: propanal, n- and i-butanal, n- and i-pentanal, n- and i-hexanal, n- and i-heptanal, n and i-octanal , n- and i-nonanal, n- and i-decanal, undecanal, dodecanal, lauric aldehyde, methylnonyl aldehyde (MNA), tridecyl aldehyde, and myristyl aldehyde. These aldehydes can contain up to 3% by weight of water, preferably from 0.5 to 2% by weight of water and in particular from 0.75 to 1.25% by weight of water. In one embodiment of the method of the invention, the stabilizer is initially charged in the form of the aqueous solution and the aldehyde, which may also contain water, is added thereto. On the contrary, the aqueous solution of the stabilizer can also be added to the anhydrous aldehyde or containing water.

EXAMPLES EXAMPLES 1-3 The sodium hydroxide used for the stabilization is placed in the form of 0.1M aqueous solution, in the appropriate amount within polyethylene bottles, it is subsequently mixed with the appropriate amount of aldehyde and covered under a blanket of nitrogen. The isobutyraldehyde in Examples 1 and 2 contains, initially, 2% deionized water in each case and butyraldehyde n in Example 3 contains 1% deionized water. The polyethylene bottles are subsequently mixed in a rotary mixer for 20 minutes to obtain optimum mixing. In example 2, the bottle is mixed during the entire 4 weeks of the experiment. The bottles are stored in a place where there is no light during the respective times of the experiments. Sampling after the various storage times is carried out in each case with the addition of 100 ppm triethanolamine to ensure that the respective sample remains in the same state as at the time of sampling. The samples are analyzed by means of gas chromatography. All work is carried out under nitrogen.

TABLE 1 ^ TEMPLES 4-10 Sodium hydroxide, potassium hydroxide or sodium carbonate, used for the stabilization is put, in the quantity indicated in table 2 and in the form of an aqueous solution having the concentration indicated in the table, in polyethylene bottles, subsequently mix with the appropriate amount of butyraldehyde-n and put under a blanket of hydrogen. The polyethylene bottles are subsequently mixed in a rotary mixer for 20 minutes to obtain optimum mixing. The bottles are stored in a place where there is no light during the respective times of the experiments. Sampling after the various storage times is carried out in each case with the addition of 100 ppm of triethanolamine to ensure that the respective sample remains in the same state as at the time of sampling. The samples are analyzed by means of gas chromatography. All work is carried out under nitrogen. , 1st year The abbreviations used in the table have the following meanings: -C4 ~ al: n-Butyraldehyde Trim C4-al Kl: 2,4,6-Tri-n-propyl-1,3,5-trioxane with eee or aaa Trim configuration C4-al Ka: 2, 4, 6, Tri-n-propyl-1, 3, 5-trioxane. with configuration eea or aae Tetramer epsilon: Tetrameric polymerization product of butyraldehyde-nn Aldol epsilon: Total aldol condensation products EXAMPLES 11-14 In all examples 11-14, butyraldehyde containing 1% by weight of water is first acidified to an acid content of 1 ppm by adding sulfuric acid. Example 11 is a control to which no alkaline substance has been added as a stabilizer. In examples 12 and 13, 20 ppm and ppm, respectively, of solid sodium butyrate are subsequently added to butyraldehyde-n; in example 14, ppm of sodium hydroxide are subsequently added to the butyraldehyde-n. The bottle, which is placed under a blanket of nitrogen, is subsequently stirred in a rotary mixer for 20 minutes to ensure optimum mixing. The bottles are stored in a place where there is no light during the respective times of the experiments. Samples of 250 ml of each of the bottles are taken after the different storage times in each case with the addition of 100 ppm of trietonolamin to ensure that the respective sample remains in the same state as it was at the time of sampling. All work is carried out under nitrogen. The samples are analyzed by means of gas chromatography.

TABLE 3 EXAMPLES 15 TO 18 Example 15 is a control to which no alkaline substance has been added as a stabilizer. In Examples 16, 17 and 18, 0.5 ppm of solid sodium butyrate, solid calcium butyrate and sodium hydroxide are subsequently added in the form of 0.05 M solution to n-butyraldehyde. The bottle that is under a blanket of nitrogen, is subsequently agitated on a rotary shaker for 20 minutes to ensure optimal mixing. The bottles are stored in a place without light during the respective times of the experiments. Samples of 250 ml of each of the bottles are taken after the different storage times in each case with the addition of 100 ppm of triethanolamine to ensure that the respective sample remains in the same state as at the time of sampling. All work is carried out under nitrogen. The samples are analyzed by means of gas chromatography.

EXAMPLE 19-21 Example 19 is a control to which no alkaline substance has been added as a stabilizer. In Examples 20 and 21, 0.5 ppm and 0.25 ppm, respectively, of sodium hydroxide is subsequently added in the form of 0.1M solution to n-butyraldehyde. The bottle, which has been placed under a blanket of hydrogen, is subsequently agitated on a rotary shaker for 20 minutes to ensure optimum mixing. The bottles are stored in a place with no light during the respective times of the experiments. Samples of 250 ml of each of the bottles are taken after the different storage times in each case, with the addition of 100 ppm of triethanolamine to ensure that the respective sample remains in the same state as at the time of sampling. All work is carried out under nitrogen. The samples are analyzed by means of gas chromatography.

• • TABLE 4 TABLE 5

Claims (7)

NOVELTY OF THE INVENTION CLAIMS

1. - A method for stabilizing aliphatic C3-C1 aldehydes by addition of alkaline substances, including adding alkali metal hydroxides, alkaline earth metal hydroxides, alkali metal carbonates, alkaline earth metal carbonates or alkaline earth metal carboxylates as alkaline substances aldehyde which must be stabilized in amounts of 0.05-20 ppm, preferably 0.05-5 ppm, particularly preferably 0.05-2.5 ppm, based on the aldehyde.

2. The method according to claim 1, further characterized in that alkali metal hydroxides which are used are sodium or potassium hydroxide, the alkaline earth metal hydroxide which is used is calcium hydroxide, the alkali metal carbonates which are used are sodium or potassium carbonate, the alkaline earth metal carbonates which are used are magnesium carbonate or calcium carbonate and the alkali metal carboxylate which is used is sodium butyrate.

3. The method according to claim 1 or 2, further characterized in that the alkaline substance is used in the form of aqueous solution 0.01-1M, preferably 0.05-0.5M and in particular 0.1-0.25 M.

4. - The method of according to one or more of claims 1 to 3, further characterized in that aliphatic C3-C14 aldehydes which are used are propanal n- and i-butanal, n- and i-pentanal, n- and i-hexanal, n- and i-heptanal, n- and i-octanal, n- and i-nonanal, n- and i-decanal, undecanal, dodecanal, lauric aldehyde, methytonic aldehyde (MNA), tridecyl aldehyde or myristyl aldehyde.

5. The method according to claim 4, further characterized in that the aldehydes contain up to 3% by weight of water, preferably from 0.5 to 2% by weight of water and in particular from 0.75 to 1.25% by weight of water.

6. - The method according to one or more of claims 1 to 5, wherein the alkaline substance is initially charged in the form of the aqueous solution and the aldehyde, which may also contain water, is added thereto.

7. - The method according to one or more of claims 1 to 6, further characterized in that the aqueous solution of the alkaline substance is added to the anhydrous aldehyde or containing water.