Hydration Of α,β- Unsaturated Aldehyde Catalyzed By Amino Acids In Aqueous Solution

Organocatalysts such as amino acids are a new type of green catalysts used for catalytic asymmetric synthesis, which demonstrate effective catalytic activity and high stereoselectivity,Unlike enzymes and chiral metal complexes, organocatalysts can reduce environmental pollution and the cost of production. The hydration product β-hydroxyaldehyde is an important intermediates for chemical synthesis. At present, β-hydroxyaldehyde is synthesized via. asymmetric Aldol reaction.The method has the drawback of low yields and low stereoselectivity.In this dissertation, amino acid catalyted hydration of α,β- unsaturated aldehyde at room temperaturea for the synthesis of β- hydroxyaldehyde has been investigated. The reaction mechanism has also been studied.1. Synthesis of β-hydroxybutanal from hydration of crotonaldehyde catalyzed by amino acids at room temperature has been discussed firstly.The effect of different conditions e.g. concentration, p H and reaction time etc. on the hydration reaction has been studied. The optimum reaction conditions are as follows: crotonaldehyde(0.1338 mol/L),L-proline(0.5mol/L), p H 10.0, reaction time 2.0 h, reaction temperation 40℃. The conversion of crotonaldehyde could reached 97% and the selectivity for3-hydroxybutyraldehyde was 54.29%.2. Five different amino acids of glycine(Gly), L-proline(Pro), Lglutamate(Glu), L-threonine(Thr) and L-lysine(Lys) have been employed as organocatalyst for the hydration reaction. The effects of amino acid structure on the conversion of crotonaldehyde have been investigated. It was found that all the amino acids can effectively promote the hydration reaction of crotonaldehyde at room temperature in aqueous solution. Based on the comparation of activation energy, L-proline is the most effective catalyst for the hydration reaction.3. Crotonaldehyde, trans-2-hexenal and 3-methyl-2-butene aldehyde have been investigated as the reaction substrates. It was found that the charge density of β-C affects the hydration reaction rate directly.4. A plausible hydration mechanism of α,β-unsaturated aldehyde catalyzed by amino acids have been proposed with intermediate() and(Ⅱ).5. The stereoselectivity of the hydration reaction catalyzed by amino acids has been investigated. With the acidic amino acids Lglutamic acid, basic amino acid L-lysine, L-proline and the two enantiomers of L-phenylalanine and D-phenylalanine as the catalyst for the hydration of crotonaldehyde, The ee value for the hydration product3-hydroxy butyraldehyde has been measured on a chiral column( Chiralcel® OD-H). The results demonstrated that the highest ee values of 38% was from the product catalyzed by L-lysine. and the structure of amino acids has contribution on the stereoselectivity of the hydration product. The ee values of the hydration products were all over30% except for glucine.