Synthesis Of Alkyl Polyglucosides Using SO₃H-founctionalized Ionc Liquids As Catalysts

Alkyl polyglycosides?APG?,produced from natural D-glucose and fatty alcohols under acid catalysis,are one kind of renewable green surfactants.Its degradation products are carbon dioxide and water,which is called“new type green surfactant”in the international society.APG have a broad application prospects in cosmetic,detergents,food,pharmacy and other fields,which has a potential to replace conventional petroleum based surfactant.At present,concentrated sulfuric acid and p-toluenesulfonic acid are common catalysts in the synthesis of APG.Owning to low catalytic efficiency,fatty alcohol must excess four times than glucose so that most of glucose could be converted to APG.On the one hand,excess fatty alcohol don't participate in the reaction,which makes reactor low utilization rate and the additional energy consumption.On the other hand,it is necessary to remove excess fatty alcohol for obtaining high purity APG,implying that separation process would be complexity.Therefore,the development of efficient catalyst is a key technical problem in the clean production of APG.Owning to their negligible volatility,excellent thermal stability,acid controllability and hydrogen bond acid-base controllability,ionic liquids?ILs?could meet the requirement of the synthesis of APG for catalyst.?1?By analyzing the reaction mechanism of hemiacetal and the unique properties of ionic liquids,four SO₃H-founctional ionic liquids?SFILs?catalysts are designed from three aspects of high acidity,easy formation of hydrogen bond and excellent thermal stability:1-?3-sulfonic group?propyl-3-methyl imidazolium hydrosulfate?[PSmim][HSO₄]?,1-?3-sulfonic group?propyl-3-methyl imidazolium p-toluenesulfonate?[PSmim][pTSA]?,1-?3-sulfonic group?propyl pyridine hydrosulfate?[PSPy][HSO₄]?and 1-?3-sulfonic group?propyl pyridine p-toluenesulfonate?[PSPy][pTSA]?.Then,characterization?FT-IR,¹H NMR,ESI,TGA and acidity?of four SFILs were evaluated and the results of characterization showed the synthesized four SFILs have correspondence with their structure.?2?The catalytic performance of four SFILs were studied systematically.[PSmim][HSO₄]?92.8%?exhibited the best catalytic performance than other three SFILs,which is higher than the reported literature?74%?.Then,experimental conditions for the synthesis of APG are optimized systematically from the aspect of reaction temperature,reaction time,catalyst dosage,molar radio of n-octanol to D-glucose when[PSmim][HSO₄]is used as catalyst.The optimized reaction conditions were:reaction temperature 353.15 K,reaction time 8 h,catalyst dosage 5mol%,molar ratio of n-octanol to D-glucose 3:1.The reaction time decreases from 24 h to 8 h,and molar ratio of n-octanol to D-glucose decrease from 5:1 to 3:1 when the conversion rate of D-glucose is 87.5%.In addition,the catalytic performance of[PSmim][HSO₄]had decrease when[PSmim][HSO₄]was recycled above four times,which is due to the loss of[PSmim][HSO₄]in the regenation process.Through the molecular simulation the synthesis of APG,catalyst combined with the C1 position of hydroxyl oxygen in the glucose ring firstly with a molecule water off,and the presence of hydrogen bond between catalyst and n-octanol contributes to the fracture of hydrogen from the hydroxyl and be near to between n-octanol and D-glucose,which promote the reaction process between n-octanol and D-glucose.?3?To solve the loss of[PSmim][HSO₄]in the regeneration,there are four kinds of porous materials were selected to evaluated the catalytic performance of supported[PSmim][HSO4].The catalyst performance of four supported[PSmim][HSO4]were investigated under the condition of reaction temperature 353.15 K,reaction time 8 h,catalyst dosage 5 mol%,molar ratio of n-octanol to D-glucose 3:1.The results show that solid silica gel supported[PSmim][HSO₄]has the highest catalytic performance,the conversion rate of D-glucose is 89.8%and catalytic performance has not obvious decline after five times recycling,implying the problem of catalytic loss has been solved in the regeneration process of[PSmim][HSO₄].