Study On The Application Of Modified Ldhs In The Synthesis Of Acetysalicylic Acid

Acetylsalicylic acid is also called aspirin, which is a common nonsteroidal anti-inflammatory drug with a long history. It has the anti-inflammatory, antipyretic and analgesic effects. Low dose aspirin may could inhibit platelet aggregation and treat coronary heart disease. Recently, it has been found that the drug can reduce the morbidity and mortality of digestive tumor.Currently, the synthesis of acetylsalicylic acid from salicylic acid and acetic anhydride, using concentrated sulfuric acid as catalyst has been widely used in industrial production. The disadvantages have many side-reactions, corrosion of equipments, low purity of products and environmental pollution. Directed to this problem, many substances have been substituted for concentrated sulfuric acid as catalyst in recent years. One is paratoluene sulphonic acid,silicotungstic acid,vitamin C, potassium carbonate or sodium bisulfate, but it is difficult to reuse. Another is SO₄^2-/M_xO_y solid superacid, but it exist that the loss of the active component, deactivity and poor stability. Therefore, it is important to seek for a new-type catalyst with high catalytic activity, environmental friendly and stability.Layered double hydroxides (LDHs), also known as hydrotalcite-like compounds (HTLCs), is a sort of layered anionic clays. Because of LDHs'lamellar structure and anion exchange properties, LDHs are potentially interesting in various fields of application such as anion exchangers , adsorbents, catalysts and medicine stabilizers. In this thesis, cis-[Cr(C₂O₄)₂(H₂O)₂]^– pillared Mg–Al layered double hydroxides (LDHs) was assembled by anion exchange using NO₃–LDHs as a precursor. The structure of the materials were characterized by using modern physical and chemical techniques, such as X-ray diffraction(XRD), Fourier transformation infrared spectra (FT-IR), Thermogravimetry-differential thermal analysis (TG-DTA), UV–vis diffuse reflectance spectra (UV–vis), Nitrogen adsorption-desorption isotherms and Elemental analysis. And the catalytic activity was investigated in the synthesis of acetylsalicylic acid. The optimum reactconditions for the catalytic synthesis of acetylsalicylic acid were obtainas follows: the reaction time was 25min, the reaction temperature was 70℃, the molar ratio of salicylic acid to acetic anhydride was 1:2, the amount of catalyst was equal to 10% salicylic acid. Under theseconditions, the yield of acetylsalicylic acid reached 79.32%. In athree kinds of tungstomolybdophosphate heteropolyanions[PW_xMo_12-xO₄₀]^3– (x = 1,3,6) pillared Mg–Al layered double hydroxide(LDHs) were prepared by anion exchange using NO₃–LDHs as aprecursor. The structure of the materials were characterized by X-raydiffraction (XRD) and Fourier transformation infrared spectra (FT-IR).And the catalytic activity was further investigated in the synthesis ofacetylsalicylic acid. The optimum reaction conditions for the catalyticsynthesis of acetylsalicylic acid on the PWMo₁₁–LDHs catalyst wereobtained as follows: the reaction time was 10min, the reactiontemperature was 75℃, the molar ratio of salicylic acid to acetic anhydridewas 1:2, the amount of catalyst was equal to 10% salicylic acid. Underthese conditions, the yield of acetylsalicylic acid reached 82.02%.