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
Two new systems of liquid crystalline glucose derivatives 5a-d, 6a, b are prepared, studied and compared with reference compounds. The a-and P-D-dodecyl glucofuranosides 6a, b show smectic A phases. The clearing points of the fura-nosides are of the same magnitude as those of the pyranosides. The alkyl glucose acetals 5a-d show columnar discotic phases. The clearing points are about 30°C lower than those of the corresponding thioacetals. -I , , Dahlhoff, Liebigs Ann. chem. 1991, 463-467. [220/93] Chem.
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