Organic compounds -- part of the class 532-570 series – Organic compounds – Carbohydrates or derivatives
Patent
1995-09-11
1997-10-28
Peselev, Elli
Organic compounds -- part of the class 532-570 series
Organic compounds
Carbohydrates or derivatives
536 41, 536 185, 536124, C07H 100
Patent
active
056819382
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates essentially to a novel process for the preparation of weakly colored alkylpolyosides having a low content of acid degradation products, obtained by reaction of a saccharide with an excess of a fatty alcohol in the presence of an acid catalyst, followed by neutralization with a base.
Alkylpolyosides are non-ionic surfactants which are already used in a wide range of industrial applications.
The preparation of alkylpolyosides from a reducing sugar and a fatty alcohol has been amply described in the literature.
The most commonly used processes involve the reaction of a monosaccharide (or a source of monosaccharide) with a fatty alcohol in the presence of an acid catalyst.
A variant of these processes consists in performing a transetherification, i.e. introducing a low-molecular alcohol, for example methanol or butanol, before or at the same time as the fatty alcohol, to give a short-chain alkylpolyoside, which reacts with the fatty alcohol to give a long-chain alkylpolyoside.
In all cases the reaction is carried out with a molar excess of fatty alcohol (generally 2 to 8 mol of fatty alcohol per monosaccharide unit), so it is subsequently necessary to remove the excess alcohol.
The excess fatty alcohol is generally removed by vacuum distillation.
However, as the alcohols used have high boiling points (of the order of 120.degree. C. to 220.degree. C. under residual pressures of between 0.5 and 20 mm of mercury), the distillation has to be carried out at a relatively high temperature, which can lead to problems regarding the color of the products obtained.
To limit the risks of coloration when the alcohol is removed, the currently most satisfactory industrial method consists in employing a falling film or rotating film evaporator or a flash evaporator. This technique, the main advantage of which is to reduce the product overheating times, has been described for example in the documents U.S. Pat. No. 3,565,885 and EP 0418458.
During the alcohol removal phase, the pH of the reaction medium is another parameter, apart from the temperature, which influences the final coloration of the products.
Before distillation of the alcohol, it is essential to neutralize the catalyst residues present in the reaction product. This neutralization must be effected within an optimum pH range. Thus an alkaline pH favors the degradation of the residual sugars present in the reaction medium with, in particular, the formation of very highly colored aldolic polycondensation products, whereas distillation at an excessively acid pH, albeit beneficial in terms of coloration, detracts from the stability of the alkylpolyosides to hydrolysis. In an acid medium, glucose, whether residual or formed by hydrolysis, is dehydrated to 5-hydroxymethylfurfural, which can degrade to give acids like formic acid or levulinic acid. Traces of acetic, lactic or glycolic acid are also found in certain commercial alkylpolyosides.
The catalyst is generally neutralized with a strong mineral base such as sodium or potassium hydroxide, which, given the anhydrous nature of the medium, makes pH adjustment more difficult.
Various neutralizing agents have been proposed in order to overcome these disadvantages.
The following may thus be mentioned: alcoholates (EP 0132046); acetate (U.S. Pat. No. 4,939,245).
All the solutions proposed hitherto do indeed make it possible to improve the coloration of the finished products.
Nevertheless these solutions prove inadequate when it is desired to obtain very weakly colored products.
It is for this reason that it has been proposed also to resort to more or less complex decolorization and/or color stabilization processes:
Processes for limiting the formation of colored products, by removal of the residual sugars from the reaction medium upstream, have also been proposed:
SUMMARY OF THE INVENTION
One object of the present invention is to solve the technical problem which consists in providing a novel process for the preparation of alkylpolyosides which yields very weakl
REFERENCES:
patent: 4939245 (1990-07-01), Rascle et al.
Boiteux Jean-Pierre
Rolland Herve
Peselev Elli
Societe D'Exploitation de Produits pour les Industries Chimiques
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