GB2172887A - Purification of 1,4-dioxane - Google Patents

Abstract

1,4-dioxane is purified by azeotropic distillation of a mixture of crude 1,4-dioxane and an aqueous solution of an alkali-metal hydroxide.

Description

SPECIFICATION Purification of dioxane The present invention relates to a new process for the purification of the 1 ,4-dioxane, enabling a product of a very high purity grade to be obtained. The main impurities present in the commercial 1 ,4-dioxane are, as is known, water, acetic acid, glycol acetal

and peroxides.

Furthermore, depending upon the synthetic method employed for preparing 1,4-dioxane (hereinafter dioxane), other impurities may be present such as, for instance, aldehydes.

The aldehyde content in dioxane is often due to acetal hydrolyzation upon prolonged storage. Peroxides also may form under normal storage conditions and their production is accelerated by heat, light, air and moisture.

Many purification methods have been developed in the attempt of obtaining a 1,4-dioxane free from impurities, e.g. of the kind specified above.

Most methods are based on hot treatment with aqueous hydrochloric acid in the purpose of removing the acetal: indeed the so formed acetaldehyde can be then easily eliminated. To remove the acetal, particularly when this is present in only small amounts, other methods suggest prolonged heating with sodium: Hess and Fram, Ber.Deut.Chem.Gesell, 71B,2627(1938).

Basic treatment, obviously, allows elimination also of acidic impurities, such as, e.g., acetic acid.

Water can be, e.g., removed by a multi-step-procedure which may involve, e.g., first treatment of purified dioxane with potassium hydroxide, separation of the organic layer, drying of the latter over potassium hydroxide, then over sodium, and, final distillation from sodium. According to Russian patent 256,780 (Chemical Abstract 72, 132750), water is eliminated by a drying process involving azeotropic distillation of hydrated dioxane with benzene. According to Brown, J.Am.Chem.Soc. 81,3232 (1959), dioxane is dehydrated by treatment with anhydrous magnesium sulphate, refluxing over sodium and subsequent fractional distillation, and final storage over sodium wires.

Aldehydes, such as may be present, e.g., when dioxane is obtained from 1,2-ethanediol by heating with concentrated sulfuric acid, may be removed, for instance, by boiling with silver oxide followed by several distillations over freshly fused potassium hydroxide and final fractional crystallization over sodium: Hepworth, J.Chem.Soc., 1249(1959).

Other, somewhat different, approaches to the purification of dioxane are based on passage of the solvent through activated absorbing supports such as, for instance, charcoal and silica gel.

For example, J.Tu and M.Menge in Chinese journal Huanjing Baohu (Beijing), 27 (1984) find the passage through activated charcoal to be a superior method, over the analogous ones using silica gel, in order to eliminate U.V. absorbing impurities from organic solvents: purification of dioxane by such method allows, indeed, to eliminate many impurity absorptions in the near U.V. regions.

J.Habdas et al in the Polish journal Czas. Tech. (Kracow), M, 48 (1970) indicate that purification of dioxane by shaking with sodium hydroxide and following absorption with silica gel allows to eliminate impurities absorbing near 3580 cm-' and 240 nm, and Russian patent 515,749 (Chemical Abstract 85-123934) reports about dioxane purification by way of absorption on anhydrous activated charcoal followed by distillative evaporation and crystallization of the solvent.

Finally, Polish patent 69,944 (Chemical Abstract 82-43430) describes a continuous method for dehydration and purification of crude dioxane involving azeotropic distillation with a mixture of benzene and cyclohexane in a particular proportion. According to the latter method three subsequent rectifications are performed: the first allows to eliminate water and acetals, as azeotrope, the second leads to remove the benzene-cyclohexane mixture and the third allows to finally purify the residual dioxane.

The methods until now developed for the purification of dioxane present, however, drawbacks of various kinds.

It is indeed very difficult to obtain by the known methods, e.g. those mentioned above, a highly purified solvent or, better, a solvent which is sufficiently qualified for use not only in spectrophotometric determinations but also in other fields of analytical chemistry, e.g. liquid chromatography, where purity requirements are essential or very striking.

Generally not all of the impurities are removed with the said known methods which, moreover, present additional problems when considered separately.

Thus, for example, problems of corrosion are encountered with methods involving an acid treatment, particularly hot treatment, e.g. with hydrochloric acid: problems of this kind become of particular relevance when the purification is carried out on large production scale.

Toxicity problems are encountered in methods wherein toxic solvents such as, e.g. benzene, are employed. Cost problems are a drawback of methods requiring use of precious reagents such as, e.g., silver derivatives.

The methods using activated absorbing supports generally allow to eliminate only a limited range of impurities and, moreover, the obtained solvent is often found to contain traces or greater amounts of the used absorbent as an additional impurity. Furthermore, the use of chromatographic columns carries, as is known, problems of time (due to the long times required for passage of the solvent through the absorbing support) and of space, especially in large scale productions, due to the particular equipment involved.

The new method of the present invention is very cheap and simple process avoiding the drawbacks of the methods previously described in the art.

Accordingly, the invention provides a new process for the purification of 1,4-dioxane comprising azeotropic distillation of a mixture of crude 1 ,4-dioxane and an aqueous solution of an alkali metal hydroxide.

In accordance with the process of the invention a central fraction ofafirstazeotropicdistillation is collected and submitted to further treatment with an aqueous solution of an alkali metal hydroxide and further azeotropic distillation. A central fraction of the further azeotropic distillation is then collected and dehydrated. The so obtained dehydrated product may be finally submitted to normal distillation.

Preferably the alkali metal hydroxide employed in the process of the invention is potassium hydroxide or sodium hydroxide, most preferably potassium hydroxide; in any case a freshly fused hydroxide is preferred.

To prepare the aqueous solution of the alkali metal hydroxide it is preferred to use purified water: purification of this is preferably carried out by passage through a column filled with an ion exchange resin.

The relative proportions between the water and the hydroxide are preferably 20 to 100 parts by weight of water per part by weight of hydroxide. Preferably also, the amount of the water in relation to the crude dioxane is about 0.3 to 1.5 parts by weight per part by weight of the crude dioxane. The dioxane-water azeotrope which forms during distillation has a boiling point of 87.8"C and a conposition, expressed in volume by volume percentages, corresponding to 81.6 percent of dioxane and 18.4 percent of water.

Before beginning the azeotropic distillation, it is generally preferred to maintain the dioxane-aqueous alkali mixture under refluxing conditions for sometime, e.g. from about 1 hour to about 5 hours.

In order to know how much azeotrope is to be discarded before collecting the central fraction, the progress of the distillation may be monitored by an U.V. spectrophotometer recording the transmittance percent values of the various distilled fractions in the range between about 210 and about 300 nanometers.

Thus, it has been found suitable to start collecting the central fraction when the transmittance percent values in the range indicated above are increased by, at least, ten percent with respect to the transmittance percent values of the raw material in the same wavelength range.

A check on peroxide content of the different fractions separated during the azeotropic distillation generally indicates a decrease of peroxides of about ten percent with respect to the raw material, and an anaiogous decrease is also observed in the residue of the distillation.

In orderto avoid any mixing between the central fraction to be collected and the residue, which is characterized by very low transmittance percent values, the azeotropic distillation is preferably stopped when the column temperature exceeds 88-90"C.

As already said, the collected central fraction of the first azeotropic distillation is then treated with an aqueous solution of an alkali metal hydroxide, with the properties and in the proportions indicated before, and submitted to a further azeotropic distillation under the conditions previously described.

This second azeotropic distillation is thus carried out in a similar manner as the first one and the central fraction of the second distillation is recovered in the same general manner as the central fraction of the first distillation.

The central fraction of the second azeotropic distillation is then dehydrated.

Dehydration may be, e.g., carried out by stirring on pellets of an alkali metal hydroxide, such as, e.g.

potassium hydroxide or sodium hydroxide.

To avoid excessive and uncontrolled heating, the alkali metal hydroxide pellets must be added very carefully. After separation of the hydroxide pellets, the dehydrated dioxane is preferably submitted to a careful normal distillation and normally stored, preferably in sealed containers away from heat, light and moisture.

If desired an antioxidant may be added such as, for instance, butyl hydroxy toluene (BHT), i.e.2,6-ditert.butyl-4-methylphenol.

As already said, the new process provided by the invention for the purification of 1,4-dioxane, is a quite simple and cheap process devoid of the drawbacks of the prior methods. In fact, corrosive conditions, as those arising from acid treatments, are avoided; toxicity problems connected with the use of toxic solvents are eliminated; no expensive reagents are employed so that costs are kept at very low levels; and, finally, no activated absorbing supports are used so that the related additional purity problems and time- and equipment-problems are not encountered.

On the other hand the new process of the invention is quite effective in removing impurities.

Indeed, since the boiling point of the dioxane/water azeotrope is, as already said, 87.8"C whilst the boiling point of the acetal is 82.5"C, the acetal impurity is easily removed, according to the process of the invention, by discarding the first fractions of distillate in the course of the azeotropic distillation.

Aldehydes, if present, acetaldehyde in particular, will be fully eliminated with the process of the invention because they will react with the alkali metal hydroxide to form resinous products retained in the residue of the azeotropic distillation: Krauts and Vingee, J. Am.Chem.Soc., 56, (1934).

The use of an alkali metal hydroxide in the process of the invention allows easy removal of the acid impurities: alkali metal salts of the acids are formed, which remain in the residue of the distillation. Also peroxides are quickly decomposed, as is known, by alkaline hot treatment, and this is, indeed, achieved by the process of the invention. Accordingly, the new process of the invention leads to a 1,4-dioxane of a very high purity grade, i.e. to a solvent which, besides being certainly qualified for any spectrophotometrical determination, is also equally useful for any other determination in the field of the analytical chemistry wherein purity requirements are essential.

The following example illustrates but does not limit the invention.

Example In a four liter round bottom flask, equipped with an adiabatic column (h = 60 cm - int.lZi = 3 cm.) packed with Rashig rings, 1 liter of purified water and 28 g of potassium hydroxide (reagent grade) were added to 2 liters of raw 1 ,4-dioxane. After refluxing for 2 hours, the mixture was distilled. The first fraction (150 ml, head of the distillate) was separated and then 2.2 liters of central fraction were collected in a time of 15 hours.

The distillation was stopped when the temperature inside the column was observed to exceed 88-90 C. In fact, very low trasmittance percent values were found for the product distilling immediately after the increasing of the temperature over the said values (first fraction of the residue).

Table 1 shows the transmittance percent values referring to 7 fractions separated before starting to collect the central fraction. Table 2 shows the transmittance percent values referring to the raw material, the central fraction and the first fraction distilled after separation of the center fraction (first fraction of the residue).

In both tabies, as well in the following ones, the transmittance percent values are given for increasing wavelength values in the range between 210 and 300 nanometers.

TABLE 1 1st azeotrnpTransmittance percent values measured on 7 fractions of the head of the distillate (150 ml total) 1,4-dioxane 1 2 3 4 5 6 7 Mnm) (raw material) 50 my 20ml 20ml 15ml 10 my 15ml 20ml 210 0.20 0.16 0.19 0.22 0.21 0.22 0.23 0.22 220 0.10 0.08 0.10 0.11 0.12 0.12 0.12 0.12 230 0.07 0.06 0.07 0.08 0.08 0.09 0.10 0.09 240 0.06 0.05 0.06 0.09 0.13 0.19 0.35 0.61 245 0.07 0.06 0.09 0.28 0.57 0.95 1.64 2.64 250 0.58 0.04 0.32 1.21 2.13 3.17 4.69 6.44 260 11.65 0.05 4.02 8.18 10.95 13.25 16.33 19.26 270 22.05 0.16 12.26 20.62 25.32 29.10 33.97 38.32 280 27.02 2.36 34.44 45.60 50.74 54.36 59.00 62.23 290 51.54 18.94 61.73 70.65 73.77 76.53 78.80 80.34 300 77.66 34.52 76.31 83.42 85.68 87.84 89.27 90.01 TABLE 2 1 st azeotrope-Transmittance percent values measured on the central fraction of the distillate and on the first fraction from the residue.

1,4 Dioxane Central fraction 1 st fraction )ç(nm) (raw material) (2200 ml) from the residue 210 0.20 0.31 0.15 220 0.10 1.89 0.07 230 0.07 11.74 0.05 240 0.06 24.59 0.02 245 0.07 29.01 0.04 250 0.58 32.48 0.04 260 11.65 49.54 0.04 270 22.05 78.09 0.40 280 27.02 87.05 3.13 290 51.54 93.09 7.78 300 77.66 97.66 15.27 A check on peroxides in the raw material, first distilled fraction, central fraction and residue of the distillate showed the following values:: 1,4-dioxane (raw material) = 0.0014% first distilled fraction (150 ml) = 0.00017% central fraction (2.2 liters) = 0.00017% aqueous residue = 0.00017% The central fraction of the distillate (2.2 liters) was transferred into another four liter round bottom flask, equipped with an adiabatic column filled with Rashig rings. 1.1 liters of purified water and 28 g of potassium hydroxide were added. After 2 hours refluxing distillation was started. The first distillate (500 ml) was separated and 1.7 liters of central fraction were collected in a distillation time of 12 hours. The distillation was stopped when the temperature was going to exceed 80-90 C.

Table 3 reports the transmittance percent values relating to the last five fractions separated before starting to collect the central fraction.

Table 4 reports the transmittance percent values of the central fraction from the 1st azeotropic distillation, the central fraction from the 2nd azeotropic distillation and the first fraction distilled after the central fraction of the 2nd distillation.

TABLE 3 2nd azeotropeTransmittance percent values measured on five fractions of the head of the distillate (480 ml total) 1 2 3 4 5 (nm) 10ml 25ml 10ml 15ml 10ml 210 0.26 0.28 0.28 0.30 0.29 220 0.73 0.85 1.21 1.31 1.52 230 6.65 7.22 8.61 9.14 9.72 240 16.14 16.73 17.72 18.10 18.55 245 18.94 19.57 20.16 20.47 20.85 250 21.09 21.76 22.21 22.55 22.88 260 38.16 38.95 39.67 40.04 40.37 270 75.74 76.35 77.26 77.67 77.87 280 85.47 86.13 86.51 86.74 86.85 290 91.83 91.91 92.33 92.44 92.39 300 98.09 97.97 98.54 98.33 98.29 TABLE 4 2nd azeotropeTransmittance percent values of the central fraction and of the first fraction from the residue, in comparison with the transmittance percent values of the central fraction from the 1st azeotropic distillation.

Central fraction from Central fraction from 1 st fraction from the k(nm) 1st az.distillation 2nd az.distillation residue of the 2nd az.

(2200 ml) (1700 ml) distillation 210 0.31 0.86 0.09 220 1.89 34.21 0.05 230 11.74 46.34 0.04 240 24.59 47.75 0.03 245 29.01 48.95 0.03 250 32.48 51.92 0.03 260 49.54 68.55 0.03 270 79.09 92.24 0.03 280 87.05 97.46 0.03 290 93.09 100 0.04 300 97.66 100 0.74 Potassium hydroxide (1009) was added to the central fraction from the 2nd azeotropic distillation.

After shaking, further potassium hydroxide (100 g) was added and shaking was repeated several times.

After separation of the aqueous layer so formed, drying was completed by adding potassium hydroxide pellets (100 g). A portion (1.4 liters) of the so obtained dehydrated and purified dioxane was separated and then, after refluxing, carefully distilled. 50 ml of the first distillate were discarded to eliminate water possibly still present, and 1.2 liters of central fraction were collected in a time of 8 hours; 150 ml of residue were discarded.

Butyl hydroxytoluene (BHT), i.e. 2,6-di-tert.butyl-4-methyl-pheno!, (2.5 p.p.m.) was added to the obtained product to prevent peroxide formation.

Claims (5)

1. A process for the purification of 1 ,4-dioxane comprising azeotropic distillation of a mixture of crude 1 ,4-dioxane and an aqueous solution of an alkali-metal hydroxide.

2. A process according to claim 1 wherein a central fraction of a first azeotropic distillation is collected and submitted to a further treatment with an aqueous solution of an alkali metal hydroxide and further azeotropic distillation.

3. A process according to claim 2 wherein a central fraction of the further azeotropic distillation is collected and dehydrated.

4. A process according to any one of the preceding claims wherein the alkali metal hydroxide is potassium hydroxide or sodium hydroxide.

5. A process for the preparation of 1 ,4-dioxane substantially as hereinbefore described in the Example.