Studies on the solvent dependence of the carbamic acid formation from ω-(1-naphthyl)alkylamines and carbon dioxide
Studies on the solvent dependence of the carbamic acid formation from ω-(1-naphthyl)alkylamines and carbon dioxide
复制标题
DOI：
10.1016/j.tet.2004.10.033
复制
发表时间：
2005-01-03
期刊：
影响因子：
2.1
通讯作者：
Fujita, H
中科院分区：
文献类型：
--
作者：
Masuda, K;Ito, Y;Fujita, H
利用核磁共振（H-1, C-13， HMBC）和红外光谱原位测定了胺和二氧化碳在多种溶剂中生成氨基甲酸。在DMSO、DMF或吡啶（亲原性、高度偶极性、非质子溶剂）溶液中对萘烷基胺1-3进行CO2鼓泡，使其完全转化为相应的氨基酸4-6。在二氧六环（亲原性、偶极性、非质子性溶剂）中，氨基甲酸和少量氨基甲酸铵生成。相比之下，在men（疏原、偶极、非质子溶剂）、苯或CHCl3（极性、非质子溶剂）、2-PrOH或MeOH（偶极、两质子溶剂）中，形成氨基甲酸铵7-9而不是4-6，尽管在MeOH中会竞争性地形成碳酸氢铵/碳酸酯。氨基甲酸铵在许多情况下沉淀，因此它们可以被分离。在亲原性、偶极性、非质子性溶剂（DMSO、DMF、吡啶和二恶烷）中选择性生成未解离的氨基甲酸而非氨基甲酸铵是通过考虑胺1-3和氨基甲酸4-6在非水介质中的酸碱平衡来合理化的。所获得的选择性可能是由于在这些溶剂中，4-6的pK(a)值比胺1-3大。有趣的是，在DMSO或DMF中，1-3的荧光强度在引入CO2后显著增强（4-50倍），而在二氧六烷、MeCN、苯、CHCl3、2-PrOH和MeOH中，除了I在二氧六烷、MeCN、2-PrOH和MeOH中有小到中等的增强（1.3-3倍）外，它们的荧光强度在引入CO2后没有太大的变化。总的来说，这些荧光研究中观察到的溶剂效应与上述核磁共振和红外研究中观察到的溶剂效应一致。最后，在CO2存在下，用（三甲基硅基）重氮甲烷成功地将胺3甲氧羰基化成氨基甲酸甲酯。(C) 2004 Elsevier Ltd.版权所有。
Carbamic acid formation from amine and carbon dioxide in a variety of solvents was investigated by measuring NMR (H-1, C-13, HMBC) and IR spectra in situ. Bubbling Of CO2 through solutions of naphthylalkylamines 1-3 in DMSO, DMF or pyridine (protophilic, highly dipolar, aprotic solvent) resulted in complete conversion of the amines to the corresponding carbamic acids 4-6. In dioxane (protophilic, dipolar, aprotic solvent), the carbamic acid and a small amount of the ammonium carbamate were formed. By contrast, in MeCN (protophobic, dipolar, aprotic solvent), in benzene or CHCl3 (apolar, aprotic solvent), or in 2-PrOH or MeOH (dipolar, amphiprotic solvent), ammonium carbamates 7-9 rather than 4-6 were formed, although the ammonium bicarbonates/carbonates were competitively formed in MeOH. The ammonium carbamates precipitated in many cases and hence they could be separated. The selective generation of the undissociated carbamic acids in preference to the ammonium carbamates in protophilic, dipolar, aprotic solvents (DMSO, DMF, pyridine, and dioxane) is rationalized by considering the acid-base equilibria between the amines 1-3 and the carbamic acids 4-6 in nonaqueous media. The obtained selectivity is likely due to the larger pK(a) values for 4-6 than the amines 1-3 in these solvents. Interestingly, the fluorescence intensities for 1-3 were dramatically enhanced (4-50 times) in DMSO or DMF upon introduction Of CO2, while they were not altered very much in dioxane, MeCN, benzene, CHCl3, 2-PrOH, and MeOH, except small to medium increases (1.3-3 times) for I in dioxane, MeCN, 2-PrOH and MeOH. As a whole, the solvent effects observed in these fluorescence studies are consistent with those observed in the above NMR and IR studies. Finally, methoxycarbonylation of amine 3 into the methyl carbamate was successfully accomplished by using (trimethylsilyl)diazomethane in the presence Of CO2. (C) 2004 Elsevier Ltd. All rights reserved.