热带气候的化学反应被重新审视:HO2*启动的氧化作为一个高效的乙沉降器
Ive Hermans1, Thanh L Nguyen, Pierre A Jacobs
1Department of Chemistry, Celestijnenlaan 200F, B-3001 Heverlee, Belgium.
Journal of the American Chemical Society
|August 12, 2004
概括
乙与HO2基发生反应,形成一个新的化合物. 这种反应在热带期附近变得显著,解释了酸的丰富性,并充当了酸沉降剂.
科学领域:
- 大气化学 大气化学
- 上层热带层和下层层层 (UTLS) 研究.
- 化学动力学 化学动力学
背景情况:
- 乙是上层热层和下层平流层化学中的关键分子.
- 在此之前,人们忽略了乙和HO2基之间的反应.
- 酸是一种丰富的有机酸,在热带地区观察到.
研究的目的:
- 为了研究乙与HO2基的反应.
- 确定该反应在UTLS中的意义.
- 为了解释在热带期附近观察到的酸的丰富性.
主要方法:
- 使用验证的计算方法的理论研究.
- 在不同温度条件下分析化学平衡的变化.
- 涉及乙,HO2和NO的反应途径的动态建模.
主要成果:
- 乙和HO2基之间的反应形成了一个快速的平衡, (CH3) 2C=O + HO2* <=> (CH3) 2C(OH) OO*.
- 在室温下,平衡有利于反应物,使反应无关紧要.
- 在接近热带期 (T <= 220 K) 时,平衡转向产品,从而有效地去除乙.
- 该产品与氧化 (NO) 的后续反应导致乙酸的形成.
结论:
- 乙与HO2基的反应是UTLS中乙去除的重要途径.
- 这种反应途径解释了在热带期附近观察到的高度酸.
- 空中交通产生的NO在这种乙沉积机制中起作用.
相关概念视频
Hydroboration-Oxidation of Alkenes
In addition to the oxymercuration–demercuration method, which converts the alkenes to alcohols with Markovnikov orientation, a complementary hydroboration-oxidation method yields the anti-Markovnikov product. The hydroboration reaction, discovered in 1959 by H.C. Brown, involves the addition of a B–H bond of borane to an alkene giving an organoborane intermediate. The oxidation of this intermediate with basic hydrogen peroxide forms an alcohol.
Oxidation of Alkenes: Anti Dihydroxylation with Peroxy Acids
Diols are compounds with two hydroxyl groups. In addition to syn dihydroxylation, diols can also be synthesized through the process of anti dihydroxylation. The process involves treating an alkene with a peroxycarboxylic acid to form an epoxide. Epoxides are highly strained three-membered rings with oxygen and two carbons occupying the corners of an equilateral triangle. This step is followed by ring-opening of the epoxide in the presence of an aqueous acid to give a trans diol.
Oxidative Cleavage of Alkenes: Ozonolysis
In ozonolysis, ozone is used to cleave a carbon–carbon double bond to form aldehydes and ketones, or carboxylic acids, depending on the work-up.
Ozone is a symmetrical bent molecule stabilized by a resonance structure.
Ozone is a symmetrical bent molecule stabilized by a resonance structure.
Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation
Introduction
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
Oxidation of Alcohols
In this lesson, the oxidation of alcohols is discussed in depth. The various reagents used for oxidation of primary and secondary alcohols are detailed, and their mechanism of action is provided.
The process of oxidation in a chemical reaction is observed in any of the three forms:
The process of oxidation in a chemical reaction is observed in any of the three forms:
Oxidations of Aldehydes and Ketones to Carboxylic Acids
Oxidation of aldehydes and ketones results in the formation of carboxylic acids. Aldehydes, bearing hydrogen next to the carbonyl group, are easily oxidized compared to ketones. This is because an aldehydic proton can easily be abstracted during oxidation.
Aldehydes readily undergo oxidation in strong oxidizing agents such as potassium permanganate and chromic acid. The oxidation can also be carried out using mild oxidizing agents such as silver oxide. In fact, aldehydes can be easily oxidized...
Aldehydes readily undergo oxidation in strong oxidizing agents such as potassium permanganate and chromic acid. The oxidation can also be carried out using mild oxidizing agents such as silver oxide. In fact, aldehydes can be easily oxidized...


