Spectrophotometric Determination of Secondary Amines
Spectrophotometric Determination of Secondary Amines
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分光光度法测定仲胺
DOI：
10.1021/ac60179a035
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发表时间：
1961
期刊：
影响因子：
--
通讯作者：
G. R. Umbreit
中科院分区：
文献类型：
--
作者：
G. R. Umbreit
图3显示了反应时间对三乙醇胺乙酰化的影响。在30分钟的乙酰化时间内，获得正常的滴定曲线，而拐点在90分钟内完全模糊。显然，三个羟基的乙酰化连续增加了具有乙酰氧基的原始三乙醇胺分子的链长，其吸电子倾向逐渐减少氮原子的碱性。滴定这些不同的碱性部分产生的结果类似于通过滴定含有少量不同碱性强度的其他胺的胺所获得的结果;也就是说，滴定曲线不产生明确定义的拐点。二甲基乙醇胺不以这种方式表现，因为只有一个乙酰氧基可以添加到分子中，并且这种效果不足以克服释放电子的V-甲基基团的碱性贡献。通过将乙酰化时间限制在30分钟，可以避免三乙醇胺问题。
Figure 3 shows this effect of reaction time on the acetylation oftriethanol-amine. Within a 30-minute acetylation time, a normal titration curve is obtained, whereas the inflection point is completely obscured in 90 minutes. Evidently, acetylation of the three hydroxyl groups successively increases the chain length of the original tri-ethanolamine molecule with acetoxy groups, whose electron-withdrawing tendencies progressively diminish the basic character of the nitrogen atom. Titration of these various basic moieties produces a result similar to that obtained by titrating an amine which contains small amounts of other amines of varying basic strengths; that is, the titration curve does not yield a well defined inflection point. Dimethyl-ethanolamine does not behave in this manner because only one acetoxy group can be addedto the molecule, and this effect is insufficient to overcome the basicity contributions of the electronreleasing V-methyl groups. The tri-ethanolamine problem can be avoided by restricting the acetylation time to 30 minutes.