Iodination of Durene Lab Notes

Iodination of Durene Lab Notes - Laboratory B:...

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Laboratory B: Electrophilic Aromatic Substitution Laboratory Techniques: Using Handbooks p. 25-36 (skip section on Lange’s p. 28-30) Recrystallization p. 104-110, 115-119 Refluxing a reaction p. 203-204 Organic Chemistry Concepts: Electrophilic Aromatic Substitution Carey, p. 471-474, 496-498 FF p. 488-491 J p. 687-688 When bromine is added to a double bond, a rapid reaction occurs and the orange color of the bromine quickly disappears. In fact, this reaction is rapid enough that bromine can be used to determine if a molecule contains a double bond. If the orange bromine color disappears, it can be concluded that the molecule contains a double bond. However, this same reaction does not occur with the double bonds in an aromatic ring. While the halogens bromine and iodine can add to an aromatic ring, harsher conditions are required and the mechanism is different. In this experiment, we will be using the oxidizing agent HIO 4 to oxidize I 2 to I + , which is a strong enough electophile to undergo an aromatic substitution reaction. The HIO 4 is in turn reduced to H 2 O and I + , which is also used for electrophilic aromatic substitution. We will then be using this to add to durene, which is the common name of 1,2,4,5-tetramethylbenzene. The first step of the mechanism of the reaction is for the I + to add to one of the double bonds of the aromatic ring leading to the formation of a carbocation on the adjacent carbon. Due to resonance, this carbocation can be delocalized onto two of the other carbons in the ring. However, in the next step of the mechanism a proton is lost in order to regain aromatic stabilization. In evaluating such a reaction, it is always necessary to balance the reaction. I 2 I HIO 4 . 2H 2 O H 2 SO 4 aq HOAc In planning and developing chemical reactions, it is important to consider everything that is present in solution. Molecules look for other molecules for which it is energetically favorable for them to react; they do not know how to follow instructions to do one reaction first and the next one second. They are also not able to look at the reaction stoichiometry that we write on a piece of paper to determine how many times a reaction can occur. Therefore, when we are doing a chemical reaction in solution, we
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need to consider all of the possible reactions that can occur. In particular, we need to consider if any of the reactants can react with the products. In this particular reaction, when we consider the I + that is generated in solution, we need to determine if it will react more favorably with the durene starting material or the iododurene product. The redox reaction to form I
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This note was uploaded on 03/24/2009 for the course CHEMISTRY 030.225 taught by Professor Janegreco during the Spring '09 term at Johns Hopkins.

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Iodination of Durene Lab Notes - Laboratory B:...

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