Methods To Accelerate Organic Chemical Reactions In High Temperature Liquid Water

High temperature liquid water, which stands for the pressurized liquid water under the condition of 180-350 ℃, is also called Near-critical water. As temperature and pressure goes to critical point, there is a dramatic increase in ionization constant. It is about three orders magnitude higher than that at ambient temperature and pressure, so HTLW has a strong tendency to ionize and can act as an acid and/or base catalyst. Besides, it has excellent dissolve ability similar to ambient acetone because of lower dielectric constant and appropriate density, which can dissolve organic substance to some extent to allow homogeneous reaction in high temperature liquid water. As an environmentally benign medium, high temperature liquid water can discard the use of large tons of catalysts and poisonous solvent. Meanwhile, It has good tunability, namely we can design the reaction medium according to different reaction system by tuning temperature and pressure.As a reaction media, high temperature liquid water has drawn increasing attention for acid or base catalyzed organic chemical reactions without any added acid or base and extensive research has been pursued on organic chemical reactions in HTLW. However, problems such as slow reaction rate and poor selectivity exist for these non-catalyzed organic syntheses in HTLW, which hinder the extensive use of HTLW in organic synthesis. The dissertation put forward two different ways to speed up the reaction rate according to two acid and base catalyzed reaction, namely introducing CO₂ or NH₃ into pure HTLW for acid or base catalyzed reaction respectively.We studied the aldol condensation of benzaldehyde and acetaldehyde in pure HTLW in 0.5 L high pressure reactor. The pressure was 15 MPa and temperature was within 220-300 ℃. The mole ratio of benzaldehyde and acetaldehyde was 1:5.7. Fitting the data by Arrhenius equation could yield activation energy of (64.3±5.9)kJ/mol.Aldol condensation of benzaldehyde and acetaldehyde in NH₃-Enriched HTLWwas investigated under the condition of 15 MPa, 220³00 °C. Addition of ammonia could enhance the reaction rate greatly and the reaction rate increased with the amount of ammonia. According to pseudo second rate reaction mechanism, the reaction activation energy is (67.9±6.5) kJ/mol with ammonia concentration at 105 mg/L. Estimation of pOH and discussion about reaction mechanism was made.Pinacol rearrangement reaction in pure HTLW and CO2-Enriched HTLW were investigated under the condition of 10 MPa and 180-220 °C. According to pseudo first rate reaction mechanism, activation energy of non-catalyzed and CO2-catalyzed pinacol rearrangement were (87.1±5.4) kJ/mol, (81.1±14.6)kJ/mol, respectively. Besides, estimation of pH of the reaction system and discussion about reaction mechanism was made.