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【英文名称】Barium Hydroxide
【分子式】BaH2O2
【分子量】171.35
【CA 登录号】17194-00-2
【物理性质】Ba(OH)2-H2O：白色固体，d 3.743 g/cm3，微溶于水。Ba(OH)2-8H2O：为透明晶体或者白色块状固体，mp78°C，d 2.180g/cm3。与水和甲醇以任意比互溶，微溶于乙醇，不溶于丙酮。
【制备和商品】国内外试剂公司有销售。
【注意事项】有毒和腐蚀性，对黏膜通道、上呼吸道、眼睛和皮肤有破坏性。不能与酸共存，能从空气中吸收水分和二氧化碳。
Ba(OH)2作为碱催化剂参与脱羰反应、缩醛或者缩醛类的反应、Claisen-Schmidt反应、Michael加成反应和Wittig-Horner反应等。最常见的氢氧化钡是Ba(OH)2-8H2O，升高温度到200-500 °C转化成无水形式。这种方法处理所得的固体氢氧化钡被称为“活性氢氧化钡”。最常用的活性氢氧化钡称为C-200 (200 °C的脱水形式)，其化学结构组成为 Ba(OH)2-0.8H2O。 羧酸的生成 在Ba(OH)2-8H2O作用下，酮式二羧酸酐可发生水解脱羧反应生成晶状的γ-酮酸（式1)[1]。 与α-氯代内酰胺的反应 用水合 Ba(OH)2 处理α-氯二环戊内酰胺有利于Favorskii类型的环收缩反应，生成八氢吲哚和八氢异吲哚。氯代内酰胺以非对映立体选择性方式重排可生成1:1的混合物（式2)[2]。 非均相Claisen-Schmidt缩合 在Claisen-Schmidt缩合反应中，活性Ba(OH)2(C-200)可以被用作非均相催化剂。使用这种方法，可以使甲基酮与不同的芳醛反应得到相应的苯乙烯酮，也可用于邻羟基查耳酮的合成。在少量水存在条件下，氢氧化钡能使苯甲醛和氯代苯乙酮室温反应生成环氧化合物（式3)[3]。 Michael加成 使用部分脱水的Ba(OH)2作为碱性试剂，能有效地催化活性亚甲基化合物的Michael加成反应生成查耳酮，产物的类型主要受到反应温度和催化剂用量的影响。在室温下，用少量的催化剂可以催化查耳酮与乙基乙酰乙酸反应的主要产物为Michael加成产物。增加催化剂的用量会生成环化产物，在回流温度下主要得到脱水环化产物。在固体Ba(OH)2 (C-200)的作用下，丙二酸二乙酯与香豆素没有发生Michael加成反应，而生成1,2-加成-消除产物（式4)[4]。 烯醚的合成 在室温下，氢氧化钡也能催化甲醇和丁烯酮发生加成反应生成烯醚（式5)[5]。 6β,19-环氧甾体的重排 6β,19-环氧-2,17-二羟基雄甾烷基-1,4-二烯-3-酮与Ba(OH)2-8H2O在嘧啶中加热回流反应后，经酸性条件处理生成呋喃吡喃酮。其重排过程包括B-环收缩反应、双键的异构反应及苯甲酸重排反应（式6)[6]。 Wittig-Horner反应 在活性Ba(OH)2 (C-200)催化下，醛与磷酰基乙酸三乙酯反应生成相应的3-取代的丙烯酸酯，常用于高位阻的醛反应。使用2-氧代烷基磷酸酯生成相应的（反)-α,β-不饱和酮，得到较高的产率和很好的立体选择性。使用经140 °C活化的Ba(OH)2，能够使可烯醇化的醛与磷酸酯之间的烯化反应时间缩短且产率提高（式7)[7]。 N-保护基苄氧基羰基的脱除 在Ba(OH)2-8H2O作用下，从氨基甲酸苄酯中消除N-保护基苄氧基羰基可以制备炔基胺（式8)[8]。 参考文献 1. Danishefsky, S.; Hirama, M.; Gombata, K,; Harayama, T.; Berman, E.; Schuda, V.Y.J. Am. Chem. Soc.1979,101，7020. 2. Henning, R.; Urbach, H. Tetrahedron Lett. 1983, 24, 5339. 3. Tanaka, K.; Shiraishi, R. Green Chem. 2001, 3, 135. 4. Sinisterra, J. V.; Marinas, J. M.Monatsh. Chem. 1986,117, 111. 5. Kabashima, H.; Katou, Tomokazu.; Hattori, H. Applied Catalysis，A: General 2001,214, 121. 6. Chorvat, R. J.; Bible, Jr. R. H.; Swenton, L. Tetrahedron 1975, 57, 1353. 7. Fiirstner, A.; Turet, L. Angew. Chem., Int. Ed. 2005, 44,3462. 8. Overman, L. E.; Sharp, M. J. Tetrahedron Lett. 1988, 29,901.
本文摘自---现代有机合成试剂
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