Preparation of alkyl glycosides

Details Preparation of alkyl glycosides Preparation of alkyl glycosides

1995-02-01

1996-12-17

Kight, John

Organic compounds -- part of the class 532-570 series

Organic compounds

Carbohydrates or derivatives

53612313, 536124, C07G 300, C07H 1500, C07H 1700

Patent

active

055854729

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a process for preparing alkyl glycosides by reacting alcohols with monosaccharides or compounds which, under the reaction conditions, form monosaccharides, in the presence of acid catalysts, and subsequently neutralizing the reaction mixture with bases.
Surface-active alkyl glycosides, which are mainly used for detergents and cleaners, have been known for a long time. They are prepared on the industrial scale by two different processes, either by direct synthesis in which the long-chain alcohol component is directly linked to the sugar component with elimination of water, or by the transacetalization method in which a short-chain alkyl glycoside is initially prepared and then, in a second stage, reacted with long-chain alcohols to give the surface-active alkyl glycoside. Acid catalysts are required for both processes. Thus, for example, U.S. Pat. No. 3 598 865 discloses the use of sulfuric acid, hydrochloric acid, phosphoric acid, phosphorous acid, toluenesulfonic acid or boron trifluoride as catalyst. As is evident from U.S. Pat. No. 3 839 318, direct reaction of saccharides and long-chain alcohols can also be carried out in the presence of acid ion exchangers. EP-B-132 043 discloses the use of anionic surfactants in the acid form as catalyst for preparing alkyl glycosides. DE-A-3 927 919 discloses the use of sulfosuccinic acid as catalyst in the preparation of alkyl glycosides. WO-A-90/07 516 discloses the use of dialkylnaphthalenesulfonic acids as catalyst in the preparation of alkyl glycosides. The abovementioned catalysts have various disadvantages. In particular, sulfuric acid and phosphoric acid lead to the formation of polysaccharides during the reaction of the alcohols with monosaccharides. In addition, the products obtained on use of these catalysts are highly colored. Other catalysts, such as anionic surfactants in the acid form, eg. dodecylbenzenesulfonic acid, likewise yield alkyl glycosides with relatively high color numbers.
It is an object of the present invention to provide a process for preparing alkyl glycosides in which the formation of polyglycosides from the monosaccharides is greatly reduced and in which the reaction products have a very low iodine number.
We have found that this object is achieved by a process for preparing alkyl glycosides by reacting alcohols with monosaccharides or compounds which, under the reaction conditions, form monosaccharides, in the presence of acid catalysts, and subsequently neutralizing the reaction mixture with bases, wherein amphoteric surfactants in the acid form are employed as catalysts. Amphoteric surfactants which are particularly preferably used are quaternary eminoalkylsulfonates, quaternary aminoalkyl sulfates or mixtures thereof.
In the literature, the emphoteric surfactants are also called sulfo betaines or sulfato betaines. They can also be employed in the form of the alkali metal or ammonium salts as catalyst. However, in this case it is necessary to liberate the free acid therefrom by adding a strong acid, eg. sulfuric acid or hydrochloric acid. The liberation of the acid can be carried out separately from the preparation of the alkyl glycosides or else take place in the reaction medium itself.
The amphoteric surfactants in the acid form are suitable for preparing all alkyl glycosides disclosed to date. The alkyl glycosides may be described by the formula RO(G).sub.m where glucose, fructose, mannose, galactose, talose, gulose, allose, altrose, idose, arabinose, xylose, lyxose and ribose. Also possible are saccharide mixtures, oligosaccharides, eg. maltose, lactose and palatinose, or mixtures of mono- and oligosaccharides. The saccharides can be employed both in anhydrous form and with water of crystallization or else as aqueous syrup. The use of an aqueous saccharide syrup is preferred for economic reasons. The water content of the aqueous saccharide syrup is from 10 to 80, preferably from 15 to 60, % by weight. Industrial solutions with water contents of 20-40% by weight are preferably used. The sacchari

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