化工专业英语lesson8翻译

仅供参考

Lesson 8-1 Alcohol Alcohols are characterized by the presence of OH (hydroxyl group) attached to a carbon atom. Aliphatic alcohols may be considered to be derived from hydrocarbons in which an sp3 bonded hydrogen atom has been replaced with OH:

R —H (Alkane) R — OH (Alcohol)

They may also be considered as derivatives of water in which one of the hydrogens has been replaced with an alkyl group, R—.

H —O —H (Water) R — 0—H (Alcohol)

Since hydrocarbons may contain primary, secondary, or tertiary hydrogens, the same classes of alcohols are capable of existence. The following examples illustrate the typical members of each class:

CH3CH2OH (CH3)2CHOH (CH3)3COH

l°Alcohol 2°Alcohol 3°Alcohol

Ethyl alcohol (Isopropyl alcohol) (t-butyl alcohol)

1. Oxidation Reaction of C—H Bond

Alcohols may be considered to be the first product of oxidation of the alkanes in the oxidation scheme, which eventually produces carbon dioxide and water. Alcohols might be expected to be subject to further oxidation .This has been found to be the case as long as a hydrogen atom (a -hydrogen) remains bonded to the carbon atom which has already been partially oxidized.1 The following equations illustrate the structural changes which occur; it should be emphasized that they do not illustrate the mechanistic steps of the reactions [(1) and (2)].

The above reaction involve the C—H bond. Since 3° alcohol have no a-hydrogen atom bonded to the partially oxidized carbon atom, they resistant to further oxidation.

2. Reaction of O—H Bond

The proton bonded to oxygen of an alcohol is much more acidic than protons bonded to carbon. This difference can be readily accounted for on the greater electronegativity of oxygen, which polarizes the 0—H bond." The hydrogen on oxygen is replaceable by sodium for example (3).

This reaction is analogous to the liberation of hydrogen by reaction of an acid and a metal. The order of reactivity of alcohols in this reaction is : l°>2°>3°.The reason for this order of reactivity is believed to be the result of the inductive effects of alkyl groups. Utilizing the relative electronegativity value of 2.1 for hydrogen and 2.5 for carbon, the H—C may be represented as follows: Hδ+ -> Cδ-. Thus, the larger the number of such bonds, as in the i-butyl group, the greater the combined electron release effect would be expected. As the combined electron

release effect increases, the greater the destabilizing effect on the alkoxide anion, which thus accounts for the observed order of reactivity: 1°>2°>3°.

Lesson 8-1 Alcohol

醇的特点是碳原子上连接着羟基。脂肪醇可能被认为是由烃上的sp3键合的氢被羟基取代得到的。

脂肪醇也可以被认为是由水中的一个氢（原子）被烷基取代来得到，R-

因为烃中可能有一级、二级或三级的氢，所以同一类的醇是可能存在的。下面的例子说明了每一类的典型代表：

乙醇 异丙醇 叔丁醇

碳氢键的氧化反应

醇可能被认为是在氧化体系中烷烃氧化的第一产物，最后生成二氧化碳和水。醇可能会被进一步氧化。已经发现只要部分氧化的碳原子上仍有氢原子（α-氢），就有进一步氧化的可能。下面的方程式说明了出现的结构上的变化，需要强调的是他们并不说明反应（1）（2）的机械步骤。

以上反应涉及到碳氢键。因为叔丁醇部分氧化的碳原子上没有α氢原子，（所以）他们抵抗进一步氧化。

氧氢单键的反应

结合在醇上的氧的质子的酸性比结合在碳上的强。这种差别很容易用氧的电负性较大，因而它极化了O-H 键而进行解释。例如氧上的氢可以被钠取代。

这个反应类似于酸和金属释放出氢一样。醇反应活性顺序是：伯仲叔。反应活性顺序的原因被认为是烷基诱导效应的结果。利用氢的电负性是2.1和碳的电负性是2.5的关系，碳氢键可以表示如下：H →C

因此，这种键的数目越多，如在叔丁基中，则结合电子的释放效应越大。随着结合电子的释放效应增强，对醇盐阴离子的不稳定影响越大，作为观察到反应活性顺序的解释：伯仲叔。