WO1999003869A2

WO1999003869A2 - Method for producing alkyl glycosides

Info

Publication number: WO1999003869A2
Application number: PCT/EP1998/004283
Authority: WO
Inventors: Oliver Rhode; Sandra Witt; Ingo Hardacker
Original assignee: Henkel Kommanditgesellschaft Auf Aktien
Priority date: 1997-07-18
Filing date: 1998-07-10
Publication date: 1999-01-28
Also published as: WO1999003869A3; DE19730836A1

Abstract

The invention relates to a method for producing alkyl glycosides by acetalising glucoses with alcohol using microwave radiation. The invention also relates to a method for producing dehydrated glucoses from glucose preparations containing water using microwave radiation.

Description

"Process for the Production of Alkyl Glycosides"

The invention relates to the production of alkyl glycosides by acetalization of glycoses with alcohols under microwave radiation and to a process for the production of dried glycoses from water-containing glycose preparations under microwave radiation.

Alkyl glycosides are nonionic surfactants, which are becoming increasingly important due to their excellent detergent properties and high ecotoxicological compatibility. They are usually prepared from glycoses and fatty alcohols, which are acetalized in the presence of acidic catalysts. The catalyst is then neutralized with a base. In order to shift the reaction equilibrium to the side of the products, the water of reaction which forms is distilled off. To avoid the polymerization of the glycoses, the fatty alcohol is used in a large excess. The acetalization is therefore usually followed by a step in which the unreacted alcohol is removed by distillation.

Both during the acetalization itself and during the subsequent removal of the unreacted fatty alcohol by distillation, undesired formation of dark-colored decomposition products can occur. For this reason, attempts are made to minimize the content of undesired dark decomposition products by gentle process control. However, the known processes, which have been gentle to date, always require relatively long reaction times, which is about 6 to 8 hours for the acetalization. There is therefore a need for gentle processes for the production of alkyl glycosides which, on the one hand, minimize the dark decomposition products and nevertheless have only short reaction times. It was therefore an object of the present invention to provide a gentle process for the direct production of alkyl glycosides, the color quality of the alkyl glycosides obtained being improved, ie the dark decomposition products being minimized, and this with overall shorter reaction times.

Surprisingly, the task could be solved if the acetalization reaction is carried out under microwave radiation.

The present invention therefore relates to a process for the preparation of alkyl glycosides by acetalization reaction of aliphatic alcohols with glycoses in the presence of an acidic catalyst, characterized in that the acetalization reaction is carried out under microwave radiation.

For the purposes of the present invention, the term alkyl glycosides means reaction products of glycoses such as glucose, fructose, mannose, galactose, talose, gulose, allose, old rose, idose, arabinose, xylose, lyose and ribose with aliphatic primary alcohols, the alcohol being more than an acetal bond is bound to the glycose and the glycose can in turn be linked to one another by glycosidic linkage. The number of linked glycoses is characterized by the so-called degree of oligomerization and is within the scope of the invention at values between 1 and 10, preferably between 1 and 3 and in particular between 1.1 and 1.5. The degree of oligomerization is a quantity to be determined analytically, which can also assume fractional numerical values.

In the process according to the invention, the glycoses, in particular glucose, are reacted with the aliphatic alcohols, preferably with aliphatic primary alcohols having 6 to 22 carbon atoms. Examples of suitable alcohols are capronic alcohol, caprylic alcohol, 2-ethylhexyl alcohol, capric alcohol, lauryl alcohol, isotridecyl alcohol, myristyl alcohol, cetyl alcohol, palmoleyl alcohol, stearyl alcohol, isostearyl alcohol, oleyl alcohol, elaidyl alcohol, petroselyl alcohol, linoleyl alcohol, linoleyl alcohol, linoleyl alcohol, linoleyl alcohol, linoleyl alcohol, linoleyl alcohol, linoleyl alcohol. Behenyl alcohol, erucyl alcohol and brassidyl alcohol as well their technical mixtures, which are obtained, for example, in the high-pressure hydrogenation of technical methyl esters based on fats and oils or aldehydes from Roelen's oxosynthesis and as a monomer fraction in the dimerization of unsaturated fatty alcohols.

Technical fatty alcohols with 12 to 18 carbon atoms such as coconut, palm, palm kernel or tallow fatty alcohol are preferred.

Glucose is preferably used as glycose in the process according to the invention. Glucose is available on the market as an anhydrous, finely divided powder, as a glucose monohydrate with one mole of crystal water and as a glucose syrup. The glucose syrup is a syrup-like glucose / water mixture with an active substance content of glucose which varies between 70 and 97% by weight. All of these forms of glucose can be used in the process according to the invention. If water-containing glucose products are involved, it is preferred to dry them with the acid catalyst before bringing them into contact and to convert them into the anhydrous form. Drying can be carried out, for example, by thermal treatment, but dark-colored decomposition products often occur.

Another object of the present invention therefore relates to a process for the preparation of dried glycoses, in particular glucose, by drying water-containing glycose preparations, characterized in that the water-containing glycose preparations are first suspended in aliphatic alcohols and then dried under microwave radiation.

The already mentioned glucose monohydrates and glucose syrups are suitable as water-containing glycose preparations, in particular glucose preparations. Suitable aliphatic alcohols are the alcohols already mentioned in connection with the acetalization, in particular those which are liquid at room temperature (about 20 to 25 ° C.). For drying, the water-containing glycose preparations are suspended in the alcohols in a weight ratio of 1: 2 to 1:10, in particular 1: 2.5 to 1: 4.5. The suspension can be carried out in the usual way, for example by means of a stirrer or by means of ultrasound. The suspensions obtained are then subjected to microwave radiation, preferably the microwave radiation is carried out with a high-frequency power of 5 to 100 Wh / kg, preferably 10 to 50 Wh / kg. The high-frequency power is given in watt-hours (Wh) per kilogram batch. The drying is particularly advantageously carried out at temperatures below the melting point of the glycoses, in particular below the melting point of glucose, particularly preferably at temperatures from 30 to 80 ° C. It has proven to be useful if the drying is carried out in vacuo, preferably at 10 to 50 mbar. During the drying process, the water is preferably continuously removed by distillation, the drying being considered complete when no further water separates. The amount of water separated can be determined, for example, by freezing the collected water in a cold trap. After drying has ended, the excess alcohol is generally distilled off in a gentle manner known per se. The dried glycoses generally have residual water contents below 5, preferably below 3% by weight.

If desired, the drying of the water-containing glycose preparations can also be combined with the usual thermal drying. In this case, drying is first carried out thermally in the customary manner and, to remove the remaining amounts of water, the drying described above is used under microwave radiation.

The glycoses dried in the manner according to the invention or in the customary manner can be used for the acetalization according to the invention under microwave radiation. For the acetalization under microwave irradiation, the preferably dried glycoses are reacted with the alcohols already described in a molar ratio of 1: 2 to 1:10, preferably 1: 3 to 1: 6. The acetalization takes place after addition of the acidic catalysts. All acidic compounds, including the so-called Lewis acids, are generally suitable as catalysts. Sulfuric acid, phosphoric acid, aliphatic and / or aromatic sulfonic acids, in particular p-toluenesulfonic acid, and the sulfonic acid ion exchange resins are particularly suitable. The quantities of acidic catalysts used correspond the usual amounts and are preferably in the range from 0.001 to 1% by weight, based on the total batch.

The acetalization reaction of the glycose with the alcohol in the presence of the catalyst can be carried out in a variety of ways. Thus, according to a variant of the method according to the invention, it is possible to present a mixture of the total amounts of all components and to initiate the reaction by microwave radiation, preferably together with the heating. According to another variant, a partial amount of the alcohol is initially charged with the catalyst and a suspension of the glycose in the remaining amount of alcohol is gradually added. According to the preferred variant, a suspension of the glycose in a partial amount of the alcohol is introduced and about one third of the required amount of catalyst, suspended in a part of the alcohol, is added. The rest of the required amount of catalyst is metered in later in portions.

The acetalization is carried out under microwave radiation, preferably under microwave radiation with a high-frequency power of 10 to 200 Wh / kg, in particular of 20 to 90 Wh / kg. The microwave radiation is preferably carried out unpulsed. The acetalization is favored by heating the reaction mixture to temperatures from 70 to 140, preferably from 100 to 120 ° C. The water of reaction formed is preferably continuously distilled off. To ensure this, a vacuum of 10 to 50 mbar is preferably applied. The end of the reaction is considered reached when no further water of reaction separates out. To determine the amount of water of reaction, the water can be collected, for example, by freezing it in a cold trap. The end of the reaction is usually reached after 2 to 3 hours and is therefore much faster than the usual production methods.

According to the above statements, the acetalization is preferably carried out batchwise. The microwave laboratory systems commonly used on the market for synthesis, for example M Lavis 1000 from MLS, can be used for the microwave radiation. After the reaction has ended, the catalyst can be neutralized, as usual, by adding organic or inorganic basic compounds; if desired, a pH of at least 8, preferably 8 to 10, can be set in addition to the neutralization of the acid catalyst. The excess alcohol can also be distilled off in a conventional manner, for example by means of falling film evaporators or thin film evaporators, to residual amounts of preferably less than 5% by weight. Information on suitable basic catalysts and the gentle distillation of the excess alcohol can be found, for example, in European patent application EP-A-362 671.

According to a particularly preferred embodiment of the present invention, the drying of the glycoses is carried out under microwave irradiation and the acetalization in the presence of an acidic catalyst under microwave irradiation in a joint reaction. For this purpose, the water-containing glycose preparation is first suspended with the aliphatic alcohols in the manner described above and, as described, freed of water (dried) with microwave radiation. The water which has been freed from water is not freed from the excess alcohol, but instead is used immediately for the acetalization reaction which takes place in the manner described above in the presence of an acidic catalyst and under microwave radiation. It may be necessary to replenish some of the alcohol so that the molar ratios of glycose to alcohol required for the acetalization reaction are present. The same alcohol is expediently used for drying and for the acetalization reaction under microwave radiation.

In the process according to the invention, light-colored, solid alkyl glycosides are obtained in a gentle and rapid manner and have degrees of oligomerization from 1 to 10, preferably from 1 to 3 and in particular from 1.1 to 1.5. Examples

Example 1 Drying Glucose Syrup

62.5 g of commercially available glucose syrup (70% by weight glucose, 30% by weight water) were suspended with 200 g dodecanol at 50 ° C. in the presence of ultrasound. At a vacuum of 30 mbar, the temperature was slowly raised to 70 ° C. with microwave radiation between 10 and 50 Wh / kg. The heating, microwave radiation and the vacuum were controlled by a computer-controlled microwave laboratory system from MLS, equipped with internal and external temperature control and vacuum sensors.

The distilled water was frozen out in a cold trap. The calculated maximum

The amount of water had been obtained after 1.5 hours. The excess alcohol was removed by distillation. Powdery glucose with a melting point of 140 ° C. was obtained.

Example 2 Acetalization

45 g (0.25 MOL) of commercially available dried glucose were mixed with 195 g (1.04 MOL) of dodecanol. A total of 0.58 g of dodecylbenzenesulfonic acid, dissolved in 15 g (0.08 mol) of dodecanol, was added. The mixture was heated to 80 ° C. by means of microwave radiation and 1/3 of the catalyst solution mentioned was added. A vacuum of 30 mbar was then applied. The temperature was slowly increased to 100 to 120 ° C and the remaining 2/3 amount of the catalyst solution was added in portions. The microwave radiation was 20 to 90 Wh / kg. After 2 hours the maximum calculated amount of water that had been frozen out in a cold trap was reached. The device mentioned in Example 1 was used to control the temperature, the vacuum and the microwave radiation. After the reaction had ended, the mixture was neutralized with 0.093 g of a 50% by weight sodium hydroxide solution and with 0.1 g of magnesium oxide. The excess alcohol was removed by distillation. A dodecanol glucoside with a degree of oligomerization of 1.43 was obtained.

Claims

Patent claims

1. A process for the direct production of alkyl glycosides by acetalization reaction of aliphatic alcohols with glycoses in the presence of an acid catalyst, characterized in that the acetalization reaction is carried out under microwave radiation.

2. The method according to claim 1, characterized in that the acetalization reaction is carried out with primary alcohols having 6 to 22 carbon atoms.

3. The method according to claim 1, characterized in that the acetalization reaction with glucose, preferably with glucose syrup, with glucose monohydrate or with anhydrous glucose powder, is carried out.

4. The method according to claim 1 to 3, characterized in that the acetalization reaction is carried out under microwave radiation with a high frequency power of 10 to 200 Wh / kg, preferably 20 to 90 Wh / kg.

5. The method according to claim 3, characterized in that the acetalization reaction is carried out at temperatures from 70 to 140 ° C, preferably from 100 to 120 ° C.

6. The method according to claim 1, characterized in that the acetalization reaction is preferably carried out in vacuo at 10 to 50 mbar.

7. A process for the preparation of dried glycoses, in particular glucose, by drying water-containing glycose preparations, characterized in that the water-containing glycose preparations are first suspended in aliphatic alcohols and then dried under microwave radiation.

8. The method according to claim 7, characterized in that the drying is carried out below the melting point of the glycose, in particular below the melting point of the glucose, particularly preferably at temperatures from 30 to 80 ° C.

9. The method according to claim 7, characterized in that the drying under microwave radiation with a high frequency power of 5 to 100 Wh / kg, preferably 10 to 50 Wh / kg, is carried out.

10. The method according to claim 7, characterized in that the drying in vacuo is preferably carried out at 10 to 50 mbar.