Synthesis of alkyl polyglycosides: Effect of catalyst-type on reaction rate and product composition

Abstract

Alkyl glycoside surfactants are of great importance due to their excellent environmental, physico-chemical and dermatological properties [1]. The technical synthesis is performed by reaction of a mixture of C8-C14-fatty alcohols and D-glucose using the Fischer-glycosidation to give a mixture of glycosides of glucose and oligomers of glucose (Scheme 1). Usually, sulfonic acids with aromatic or aliphatic groups are employed as catalysts [2]. The following problems have to be avoided in the technical process: Darkly coloured products and the formation of polymeric byproducts (polydextrose), which can be formed depending on the reaction conditions. It is known that -at a given ratio glucose/fatty alcohol -not only reaction temperature and time but also type and concentration of catalyst are the major factors with regard to product quality [1d, 1e, 2]. In this respect it was important to investigate if the use of bi-or oligofunctional sulfonic acids like sulfosuccinic acid would improve the glycosidation by an intermediate formation of esters of glucose or the fatty alcohol. The few systematic investigations on the Fischer-glycosidation deal with the glycosidation of short-chained alcohols in a homogenous phase, thus, very little basic knowledge is available about the Fischer-glycosidation using medium-chain fatty alcohols like octanol [3]. This paper describes our investigation into the influence of the acid used [4] as a function of its concentration and type in the formation of dodecyl glycosides. It is important to know that this glycosidation takes place as a heterogeneous reaction. The reaction was performed in a laboratory scale synthesis using dodecanol and D-glucose in a ratio of 3:1 at 110°C. The rates of the reaction were determined by using newly defined parameters for the rate of water formation (removal of water from the reaction mixture under reduced pressure). These parameters were correlated with the concentration and the Taft-constants of the substituents of the catalysts. The catalytic activities of the acids were correlated with the composition of the products.Finally, the influence of the particle size of glucose [5] was investigated. The average particle size correlated to the rate of water formation and the composition of the products. 2 Methods 2.1 General procedure for preparing dodecyl glycosides in a laboratory scale 131 g of dodecanol (704 mmol, Henkel) and 45.0 g of anhydrous D-glucose (250 mmol, Cerestar) are placed in a 21 three necked, round bottom flask equipped with a mechanical stirrer, a thermometer, a dropping funnel for catalyst-36

Chemical Routes for the Transformation of Biomass into Chemicals

“…The glycosylation described by Fischer involves the use of mineral acids such as HCl, HF, and H 2 SO 4 . − p -Toluenesulfonic and sulfosuccinic acids can also be used. The reaction rate is dependent on the concentration of the acid and on the acidity of the catalyst . The formation of oligomers is also catalyzed by acids, and oligomerization takes place mainly in the polar phase (sugar phase) of the heterogeneous reaction mixture.…”

“…Therefore, the oligomerization of glucose can be reduced by using hydrophobic acids such as alkylbenzenesulfonic acids, which will be preferentially dissolved in the less polar phase. The use of homogeneous acids presents the problems of neutralization and washing steps, together with the inconvenience of possible corrosion in the unit. , Solid acids are thus attractive catalysts for this process, and direct glycosidation of carbohydrates with aliphatic alcohols using heterogeneous acid catalysts has recently been reviewed by Corma et al…”

“…The reaction rate is dependent on the concentration of the acid and on the acidity of the catalyst. 680 The formation of oligomers is also catalyzed by acids, and oligomerization takes place mainly in the polar phase (sugar phase) of the heterogeneous reaction mixture. Therefore, the oligomerization of glucose can be reduced by using hydrophobic acids such as alkylbenzenesulfonic acids, which will be preferentially dissolved in the less polar phase.…”

Oil-in-Water Nanocontainers as Low Environmental Impact Cleaning Tools for Works of Art: Two Case Studies

“…Synthesis of commercial AGE was performed by Fisher glycosidation of a mixture of C10−C14 fatty alcohols . As indicated in the literature, − the AGE is obtained under acidic catalysis through a direct reaction between technical grade fatty alcohols and anhydrous glucose, where the excess of alcohols constitutes the reaction medium. The water produced in the reaction was collected in a cooling trap.…”

Catalytic glycosylation of glucose with alkyl alcohols over sulfonated mesoporous carbons

“…The catalytic Fischer glycosylation of glucose with fatty alcohols is one of the important sugarbased reactions deployed at an industrial scale. [14][15][16][17][18][19][20][21] This reaction is catalyzed by sulfuric acid and yields amphiphilic alkyl glycosides (AAG) that are valuable biosurfactants, with current applications in the cosmetic and detergence industries. The price of AAG is about 1.5-2 €/kg, which is still too high to compete with fossil derived surfactants exhibiting similar performances.…”