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Nucleophilic Aromatic Substitution: Elimination–Addition01:11

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Simple aryl halides do not react with nucleophiles. However, nucleophilic aromatic substitutions can be forced under certain conditions, such as high temperatures or strong bases. The mechanism of substitution under such conditions involves the highly unstable and reactive benzyne intermediate. Benzyne contains equivalent carbon centers at both ends of the triple bond, each of which is equally susceptible to nucleophilic attack. This 50–50 distribution of products is...
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The benzylic position describes the position of a carbon atom attached directly to a benzene ring. Benzene by itself does not undergo oxidation. In contrast, the benzylic carbon is quite reactive in the presence of strong oxidizing agents such as KMnO4 or H2CrO4. Therefore, alkylbenzenes are readily oxidized to benzoic acid, irrespective of the type of alkyl groups.
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Sulfonation of benzene is a reaction wherein benzene is treated with fuming sulfuric acid at room temperature to produce benzenesulfonic acid. Fuming sulfuric acid is a mixture of sulfur trioxide and concentrated sulfuric acid.
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All meta-directing substituents are deactivating groups. These substituents withdraw electrons from the aromatic ring, making the ring less reactive toward electrophilic substitution. For example, the nitration of nitrobenzene is 100,000 times slower than that of benzene because of the deactivating effect of the nitro group. The first step in an electrophilic aromatic substitution is the addition of an electrophile to form a resonance-stabilized carbocation. The energy diagrams for...
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  9. Air Pollution Modelling And Control
  11. Combating Regional Air Pollution Significantly Enhance The Photodegradation Of Atmospheric Benzo(a)pyrene

Combating regional air pollution significantly enhance the photodegradation of atmospheric benzo(a)pyrene

Kai Shi1, Xiaohan Feng2, Chunqiong Liu1

  • 1College of Environmental Sciences and Engineering, China West Normal University, Nanchong 63700, China; Key Laboratory of Nanchong City of Ecological Environment Protection and Pollution Prevention in Jialing River Basin, China West Normal University, Nanchong 63700, China.

The Science of the Total Environment
|December 4, 2024

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View abstract on PubMed

Summary
This summary is machine-generated.

Air pollution control may accelerate Benzo(a) pyrene (BaP) degradation, creating toxic byproducts. This study quantifies BaP photodegradation trends in Hong Kong, revealing increased rates since 2019 due to specific atmospheric factors.

Area of Science:

  • Atmospheric Chemistry
  • Environmental Science
  • Pollution Control

Background:

  • Air pollution control strategies can alter atmospheric photochemistry.
  • This alteration may unexpectedly enhance the photodegradation of Benzo(a) pyrene (BaP).
  • The photodegradation of BaP can produce more toxic derivatives, posing new environmental risks.

Purpose of the Study:

  • To quantitatively assess the degree of Benzo(a) pyrene (BaP) photodegradation in Hong Kong's real atmosphere.
  • To investigate the temporal trends and influencing factors of BaP photodegradation.
  • To determine the relative contributions of atmospheric oxidants (NO2 and O3) to BaP photodegradation.

Main Methods:

  • Utilized Coupling Detrended Fluctuation Analysis (CDFA) on field observation data from 1998 to 2021.
Keywords:
Benzo(a)pyreneHong KongNitrogen dioxideOzone

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  • Analyzed temporal evolution of BaP photodegradation.
  • Performed correlation analysis with atmospheric factors (temperature, relative humidity, solar radiation, O3, NOx, PM2.5/PM10).

    • Main Results:

    • A significant increasing trend in BaP photodegradation was observed in Hong Kong starting in 2019.
    • BaP photodegradation positively correlated with temperature, relative humidity, solar radiation, O3, and NO2/NOx, but negatively with PM2.5/PM10.
    • Nitrogen dioxide (NO2) showed a greater contribution to BaP photodegradation than ozone (O3), with O3's contribution gradually increasing.

    Conclusions:

    • Air pollution control strategies may inadvertently increase Benzo(a) pyrene (BaP) photodegradation rates.
    • Atmospheric factors like temperature, humidity, solar radiation, and oxidants significantly influence BaP photodegradation.
    • Findings provide crucial insights for ecological risk assessment related to air quality management.
    Photodegradation