📚 Organic Nitrogen Compounds | 有机含氮化合物
Organic nitrogen compounds are a diverse group of molecules characterized by the presence of nitrogen atoms bonded to carbon. In A-Level Chemistry, the focus is on amines, amides, amino acids, and proteins, along with their preparation, properties, and reactions. Understanding these compounds is fundamental to grasping biological chemistry and industrial applications, from pharmaceuticals to dyes.
有机含氮化合物是一类种类繁多、分子中含有氮-碳键的化合物。在A-Level化学中，重点关注胺、酰胺、氨基酸和蛋白质，包括它们的制备、性质与反应。掌握这些化合物是理解生物化学和工业应用（从药物到染料）的基础。
1. Classification and Nomenclature of Amines | 胺的分类与命名
Amines are derived from ammonia (NH₃) by replacing one or more hydrogen atoms with alkyl or aryl groups. According to the number of carbon-containing groups attached to the nitrogen atom, amines are classified as primary (RNH₂), secondary (R₂NH), and tertiary (R₃N). Aromatic amines have the nitrogen directly bonded to a benzene ring, such as phenylamine (C₆H₅NH₂), also known as aniline.
胺是由氨（NH₃）中的一个或多个氢原子被烷基或芳基取代而成的衍生物。根据氮原子上所连烃基数目，胺可分为伯胺（RNH₂）、仲胺（R₂NH）和叔胺（R₃N）。芳香胺的氮原子直接连在苯环上，例如苯胺（C₆H₅NH₂），又称阿尼林。
Nomenclature: For simple aliphatic amines, the suffix '-amine' is added to the alkyl group name (e.g., ethylamine CH₃CH₂NH₂). When multiple alkyl groups are present, the prefixes di- and tri- are used (e.g., dimethylamine (CH₃)₂NH). The IUPAC system treats the amino group as a substituent using the prefix 'amino-' when other functional groups take priority.
命名：简单的脂肪胺在烷基名称后加“胺”（如乙胺 CH₃CH₂NH₂）。当有多个相同烷基时，使用“二”和“三”前缀（如二甲胺 (CH₃)₂NH）。在IUPAC命名中，当其他官能团优先时，氨基作为取代基，使用前缀“氨基”。
2. Preparation of Primary Aliphatic Amines | 脂肪族伯胺的制备
or primary halogenoalkanes, but further substitution can occur, leading to a mixture of secondary, tertiary amines, and quaternary ammonium salts. To improve yield, a large excess of ammonia is used. For example: CH₃CH₂Br + 2NH₃ → CH₃CH₂NH₂ + NH₄Br.
伯胺可以通过卤代烃与过量氨的亲核取代反应制备。伯卤代烃按Sₙ2机理进行，但会发生进一步取代，产生仲胺、叔胺及季铵盐的混合物。为提高产率，通常使用大大过量的氨。例如：CH₃CH₂Br + 2NH₃ → CH₃CH₂NH₂ + NH₄Br。
Another method is the reduction of nitriles. Nitriles (R-C≡ extra carbon atom compared to the starting halogenoalkane. This avoids further substitution and is a preferred route to pure primary amines. Example: CH₃CN + 4[H] → CH₃CH₂NH₂.
另一种方法是通过腈的还原。腈（R-C≡N）在无水乙醚中被氢化铝锂（LiAlH₄）还原，或经催化加氢（H₂，Ni催化剂），得到比原卤代烃多一个碳原子的伯胺。此方法避免了进一步取代，是制取纯净伯胺的优选途径。实例：CH₃CN + 4[H] → CH₃CH₂NH₂。
ed by alkali treatment. Alternatively, catalytic hydrogenation can be used. C₆H₅NO₂ + 6[H] → C₆H₅NH₂ + 2H₂O.
芳香伯胺如苯胺可通过硝基苯（C₆H₅NO₂）的还原制备，常用锡与浓盐酸后再加碱处理，也可采用催化加氢。C₆H₅NO₂ + 6[H] → C₆H₅NH₂ + 2H₂O。
3. Basicity of Amines | 胺的碱性
Amines act as Brønsted-Lowry bases because the lone pair of electrons on nitrogen can accept a proton (H⁺). The strength of basicity depends on the availability of this lone pair. Electron-donating alkyl groups increase the electron density on nitrogen, making aliphatic amines stronger bases than ammonia. In aqueous solution, basicity is often compared using pKb values or the Kb for the equilibrium: RNH₂ + H₂O ⇌ RNH₃⁺ + OH⁻.
胺作为布朗斯特-劳里碱，因为氮原子上的孤对电子可以接受质子（H⁺）。碱性的强弱取决于该孤对电子的可提供程度。给电子的烷基会增加氮上的电子密度，使脂肪胺的碱性比氨更强。在水溶液中，常用pKb值或平衡常数Kb来比较碱性：RNH₂ + H₂O ⇌ RNH₃⁺ + OH⁻。
| Compound | Kb (mol dm⁻³) | pKb |
|---|---|---|
| Ammonia NH₃ | 1.8 × 10⁻⁵ | 4.74 |
| Ethylamine CH₃CH₂NH₂ | 5.6 × 10⁻⁴ | 3.25 |
| Diethylamine (CH₃CH₂)₂NH | 9.6 × 10⁻⁴ | 3.02 |
| Phenylamine C₆H₅NH₂ | 4.0 × 10⁻¹⁰ | 9.40 |
For alkyl amines, the order of basicity in aqueous solution is generally secondary > primary > tertiary > ammonia, but solvation effects complicate the trend. In the gas phase, basicity increases with the number of alkyl groups due to inductive effects. Aromatic amines like phenylamine are much weaker bases than aliphatic amines and ammonia because the lone pair on nitrogen is delocalised into the π-system of the benzene ring, reducing its availability for protonation.
对于烷基胺，水溶液中的碱性大致为：仲胺 > 伯胺 > 叔胺 > 氨，但溶剂化效应使得顺序复杂。在气相中，由于诱导效应，碱性随烷基数目增加而增强。芳香胺如苯胺的碱性比脂肪胺和氨弱得多，因为氮上的孤对电子离域到苯环的π体系中，降低了接受质子的能力。
4. Reactions of Amines with Acids and Acyl Chlorides | 胺与酸及酰氯的反应
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