The second electrophilic aromatic substitution

This preview shows 3 out of 8 pages.

The second electrophilic aromatic substitution utilized in the synthesis of musk ketone is Nitration. This mechanism is extremely useful for attaching a nitro group to the benzene, and the mechanism can be examined below:
Image of page 3

Subscribe to view the full document.

The nironium ion, which is formed through the activation of nitric acid by sulfuric acid, attacks the benzene ring. After the nitro is attached to the benzene ring it becomes a directing group for further substituents that will be added to the molecule. Specifically, benzene rings can be substituted in three positions: ortho, para, and meta. The position to which substituents are substituted on the ring is determined by electron rich or electron poor substituents that are already bonded to the benzene ring. Electron rich substituents direct further substituents to the ortho or para positions on the ring, while electron poor substituents, such as a nitro group, direct further substituents to the meta position of the benzene ring 1 . The third electrophilic substitution utilized in this synthesis was Sulfonation. This reaction is generated from concentrated sulfuric acid and its mechanism is described below:
Image of page 4
This reaction was fuming within this lab because at room temperature the sulfuric acid would not go through substitution, and the heat is what allows the SO 3 to attack the benzene ring. This step of the reaction can be reversed, and is often used to control further aromatic substitution through the use of the sulfonic acid group as a direct blocking group for future added substituents. Via reverse sulfonation the sulfonic acid group can be removed from the benzene ring 1 . As mentioned before the synthesis of synthetic muck ketone involves the use of the Friedel-Crafts alkylation. This mechanism forms carbon-carbon bonds between the desired substituent and the benzene ring through the use of various alkylating agents and catalytic amounts of Lewis acids. These are important to the reaction because they give a polar addition complex by coordinating themselves to the alkylating agent. Thus, allowing for proton loss by the attack of the benzene ring concluding in the desired carbon-carbon bond. The complete mechanism is outlined below:
Image of page 5

Subscribe to view the full document.

The most common Lewis acids used are AlCl 3 and BF 3 followed by lanthanide trihalides and alkyl aluminum halides. The reactivity pattern for the Friedel-Crafts alkylation of the used alkyl halides is F>Cl>Br>I. The branching of the alkyl groups also plays an important role in this reaction with the reactivity order consisting of the following 3° > 2° > 1°. Two disadvantages that are common to this mechanism is that only electron rich substituents can be used, and that the product is more nucleophilic than the reactant because of the electron donating alkyl-chain which can lead to overalkylation of the molecule 1 . Friedel-Crafts acylation is similar to the alkylation outlined above utilizes similar reaction conditions. In addition to the formation of carbon-carbon bonds this reaction can also form ketones. The mechanism can be examined below:
Image of page 6
Acylation requires approximately 2 equivalents more of catalyst than alkylation does. The first
Image of page 7

Subscribe to view the full document.

Image of page 8
You've reached the end of this preview.
  • Fall '07
  • crandall
  • Organic chemistry, pH, Benzene, final product, Sulfuric acid, Electrophilic aromatic substitution, Friedel-Crafts Acylation, musk ketone

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern