N-butyraldehyde Self-condensation Catalyzed By Chitosan

2-Ethylhexanol(2EHO)is an important organic chemical.n-Butyraldehyde self-condensation is a crucial step of carbon chain extention for industrial manufacture of 2EHO.In the present work n-butyraldehyde self-condensation was investigated in the presence of a biodegradable natural polymer chitosan.First of all,the catalytic performance of different functionalized chitosan samples on n-butyraldehyde self-condensation to 2-ethyl-2-hexenal(2E2H)was evaluated,and the results showed that there were little differences in the catalytic performance before and after chitosan was functionalized.The effect of reaction conditions on the n-butyraldehyde self-condensation catalyzed by non-functionalized chitosan was investigated,and the suitable reaction conditions were obtained as follows:a weight percentage of chitosan = 5%,a reaction temperature = 80℃ and a reaction time = 8 h.Under the above reaction conditions,n-butyraldehyde conversion attained 96.0%,the yield and selectivity of 2E2H were 86.0%and 89.6%,respectively.The recovered chitosan sample could be used for 5 times without a significant deactivation after being treated with ammonium hydroxide.Additionally,the reaction products obtained from chitosan catalyzed n-butyraldehyde self-condensation were indentified by GC-MS and several possible side-reactions were conjectured.Secondly,the adsorption and desorption of n-butyraldehyde on chitosan surface was studied by in-situ FT-IR.The mechanism of n-butyraldehyde self-condensation catalyzed by chitosan was proposed:a n-butyraldehyde molecule was adsorpted on a site of-NH2 to form an enamine and then the nucleophilic enamine attacked the carbonyl carbon of another n-butyraldehyde molecule to complete the aldol condensation reaction.Then the reaction process of n-butyraldehyde self-condensation was investigated by React IR TM IC-10 and the result showed that n-butyraldehyde self-condensation comprises two steps:n-butyraldehyde self-condensation to 2-ethyl-3-hydroxyhexanal followed by dehydration to 2E2H.The chitosan catalyzes not only the first step but also the second step reaction.Futhermore,there was a greater effect on the second step reaction when the reaction temperature was increased.Finally,the reaction kinetic of n-butyraldehyde self-condensation over chitosan catalyst was studied.It was found that the reaction was auto catalytic and the kinetic equations are as follows.rB=-dcB/dt=cB1.56[1.547×exp(-13.043×10~4/RT)+260.803×exp(-4.039×10~4/RT)]r2E2H=dc2E2H/dt=260.803×exp(-4.069×10~4/RT)×CB1.56 rB,r2E2H was the reaction rate of n-butyraldehyde and 2E2H,mol·L.-1·min-1 cB was the concentration of n-butyraldehyde,mol·L-1...