Selective Synthesis Of Monoacetals From Bio-Based Polyol And Their Surfactant Properties

Many chemicals used by the chemical industry can be derived from biomass,potentially reducing the industry's reliance on petroleum.Bio-based polyols can be used as hydrophilic groups to synthesize various types of surfactants,and acetal can serve as surfactants and intermediates.Previous research indicated that glycerol acetals exhibited poor aqueous solubility and unsatisfactory surfactant properties due to its strong hydrophobic properties and required a larger hydrophobic moiety.In this paper,diglycerol and xylitol were used as the reactant,monoacetals were selectively obtained by direct reaction with long-chain aldehydes in the presence of Lewis acid catalysts.The structure of products was characteristic by gas chromatograph?GC?,gas chromatograph-mass spectrometer?GC-MS?,infrared spectrometer?FT-IR?and high-resolution mass spectrometer?HR-MS?.The surfactant properties of the monoacetal products were determined.The main research contents and conclusions are as follows:1?Under the solvent-free condition,the reaction of diglycerol and n-octanal with traditional Br?nsted acids was showed low selectivity of monoacetal.By screening a series of Lewis acid catalysts,higher monoacetal selectivity was obtained in the presence of Zn Cl₂.Various reaction parameters,the ratio of the reactants,the catalyst loading,temperature and time,were evaluated.The optimized synthetic conditions involved treating diglycerol?1.3equiv?with n-octanal in the presence of 2 mol%Zn Cl₂ at 100°C for 4 h.The selectivity to monoacetal was 84.4%,and the conversion of octanal was 80.3%.According to the reaction process,the two-phase incompatible system of diglycerol and octanal was emulsified by the monoacetal formed in the first 2 h.But the emulsion was very unstable,which caused the monoacetal to eventually transfer to the octanal phase.The Zn content in the two phases during the reaction was analyzed by ICP.Most of the Zn Cl₂ remained in the diglycerol phase.Since the monoacetal and the catalyst had opposite directions of movement,the catalyst was separated from the monoacetal and Zn Cl₂ exhibited high selectivity.2.The surfactant properties of diglycerol monoactal were estimated by the critical micelle concentration?CMC?,foaming volume,dynamic wetting angle,alkali resistance and cloud point.The CMC of diglycerol monoacetal was 0.029g/L and the surface tension under CMC was 27.4 m N/m.In the presence of 1g/L surfactant solution,the initial foaming volume at room temperature was 250m L,the foam stability was 80%after 5 min.At the same concentration,the advancing angle of diglycerol monoacetal on the first wetting canvas was74.47°.And it can be stored for more than one week in a 7.5 wt%alkaline solution.Compared with the traditional nonionic surfactants AEO-3 and AEO-7,the surfactant properties of the monoacetal were close to AEO-7 in terms of CMC and the wetting property.Due to the high cloud point of monoacetal?more than 95°C?,the monoacetal was showed better foaming properties at high temperatures.At 40°C,the diglycerol monoacetal had the same initial foaming volume with AEO-7,but the foam volume after 5 min was 250 m L for monoacetal and 80 m L for AEO-7.Diglycerol monoacetal had superior properties in alkali tolerance than AEO-7.3.Considering the high melting point of xylitol and poor solubility of Lewis acid catalysts,water was chosen used in the reaction of xylitol and octanal.A series of Lewis acid catalysts were screened in a xylitol aqueous solution.It was found that the selectivity and conversion of reaction kept an approximately linear relationship with the metal hydrolysis constant.Although Cu Cl₂ had a high monoacetal yield in the screened catalyst,it had lower selectivity and higher conversion than the data obtained by the fitting.When different amounts of water were added to the catalytic system in the presence of Cu Cl₂,the solution obtained after reaction was analyzed by UV-vis spectrometry,the peak at 325 nm indicated the[Cu Cl_x]^2-x?x>2?complex was rated to the selectivity.By adding different amounts of Na Cl,using different cationic chlorides,conducting different reaction temperatures and time,it was proved that Cl^-promoted the formation of[Cu Cl_x]^2-x?x>2?complex in Cu Cl₂which promoted the formation of diacetal rather than monoacetal.4.In order to further increase the yield of monoacetal,higher monoacetal selectivity and yield were obtained in the presence of Cu SO₄.Various reaction parameters,the ratio of the reactants,the catalyst loading,temperature and time,were evaluated.The optimized synthetic conditions involved treating xylitol?1.5 equiv.?with n-octanal in the presence of 4 mol%Cu SO₄ at 110°C for 4 h.The selectivity of monoacetal was 76.6%,and the conversion of n-octanal was56.7%.Upon adding the corresponding sodium salt to inhibit the hydrolysis reaction,Cu SO₄ was less efficient at promoting the reaction when compared to other soluble copper salts?Cu Cl₂,Cu?NO₃?₂ and Cu?OTf?₂?because of its low Lewis acid activity in water.The reaction process was controlled by H⁺produced during the Cu²⁺hydrolysis process.Compared with the outcome under different p H,Cu SO₄ was able to selectively prepare the monoacetal because the initial reaction rate was controlled using gradual hydrolysis.5.The surfactant properties of the three xylitol monoacetals obtained from n-hexanal,n-octanal and n-decanal were characterized by surface tension,foaming volume and emulsifying time.Because the hydrophobic chain of xylitol monoacetal of n-hexanal?C6-monoacetal?is too short,CMC was not showed at a low concentration,and foaming properties were not exhibited in a high concentration of 1 g/L.The CMC of xylitol monoacetal of n-octanal?C8-monoacetal?was 0.14 mmol/L,and the surface tension under CMC was27.6 m N/m.Although a maximum foaming volume was 50 m L at a concentration of 0.25 g/L,the stability of the foam was poor.The CMC of xylitol monoacetal of n-decanal?C10-monoacetal?was 0.03 mmol/L and surface tension of 26.4 m N/m under CMC.At room temperature,the initial foaming volume of C10-monoacetal was 160 m L at 0.25 g/L,and the foam stability after 5 min was 75%.When the temperature was up to 40°C,the initial foam volume was the same as the foam under room temperature,but the foam stability after 5 min was 93.8%.Finally,the emulsion stabilization times of these three products increased with increasing hydrophobic chains.