Study On The Synthesis Of Neopentyl Glycol Dimethylacrylate Over Solid Acid Catalysts

Neopentyl glycol dimethylacrylate (NPGDA) like other multifunctional methacrylates is industrially important monomers for anaerobic adhesives, diluent monomer in dental composites, thread lockers, sealants and components for making soft contact lenses. NPGDA is currently produced by the direct esterification of neopentyl glycol with methacrylic acid using conventional acids as catalysts such as sulfuric acid. However due to it's problems of toxic, contaminative to the environment and the product separation requires tedious work up procedures, it becomes a must to find an eco-friendly alternative.In this paper, the process for synthesizing NPGDA by directly esterification over four kinds of solid acid catalysts (NaHSO4·H2O,DVB, SO₄^2-/TiO₂, SO₄^2-/TiO₂/La3+) were employed. The effects of reaction conditions on reaction results were studied and the catalytic activities of them were compared. The researching content was as follows:1. Neopentyl glycol dimethacrylate was synthesized by esterification of methacrylic acid and neopentyl glycol over sodium bisulfate and DVB as the catalysts. Esterification reaction conditions on the yield were investigated and the catalytic activities of the two catalysts were compared. The experimental results indicated that sodium bisulfate exhibited higher catalytic activity. The optimum conditions were obtained as follows: methacrylic acid-to-neopentyl glycol molar ratio is 2.3:1; sodium bisulfate 7.5% ; cyclohexane 60% ;hydroquinone 0.625% ; reaction temperature 110¹15℃;refluxing and water segregating for 2.0h, under which the yield of the ester could reach more than 94%.2. The preparing and reaction conditions of SO₄^2-/TiO₂/La3+ and SO₄^2-/TiO₂ were particularly studied and the catalytic activities of the two catalysts were compared. The experimental results indicated that SO₄^2-/TiO₂/La3+ exhibited higher catalytic activity. The optimum conditions were obtained as follows: the concentration of H2SO4 0.9mol/l ; calcination temperature 450℃; activation time 3h;methacrylic acid-to-neopentyl glycol molar ratio is 2.3:1; sodium bisulfate 7.5% ; cyclohexane 60% ;hydroquinone 0.625% ; reaction temperature 110¹15℃;refluxing and water segregating for 2.5 h, under which the yield of the ester could reach 60.9%. 3. The SO₄^2-/TiO₂/La3+ and SO₄^2-/TiO₂ catalysts were charactered by many methods including FT-IR, TEM, XRD, BET and so on. The results showed that the SO₄^2-/TiO₂/La3+ exhibited higher acid intensity and catalytic activity than SO₄^2-/TiO₂, the Lewis acid sites on it were more than SO₄^2-/TiO₂ by adding La3+, then the Br?nsted acid sites were more at the same time.