friedel crafts alkylation – Flashcards
Unlock all answers in this set
Unlock answersquestion
What is the purpose of a friedel crafts alkylation?
answer
Reactions in which the electrophile is an acylium ion or a carbocation, and creates carbon carbon bonds by substituting alkyl and acyl groups onto an aromatic benzene ring.
question
Why is sulfuric acid added to the 1,4-dimethoxybenzene and t-butyl alcohol dissolved in acetic acid?
answer
The sulfuric acts as an acid catalyst to aid the reaction. Friedel crafts does not go forward without an acid catalyst present.
question
Why is water added after the mixture is cooled and crystallization begins to occur?
answer
Water is added to make sure that all sulfuric acid, t-butyl alcohol, and acetic acid are washed away from the product.
question
Why does the reaction of 1,4-di-t-butylbenzene with t-butyl chloride and aluminum chloride gives 1,3,5-tri-t-butylbenzene?
answer
Because even though the two t-butyl groups are ortho/para directors, steric hindrance favors the 1,3,5 product.
question
Why must AlCl3 be protected from exposure to the air?
answer
Because AlCl3 reacts with the air and forms hydrochloride and other aluminum chlorohydroxides in the air that do not allow for Friedel Crafts reactions to occur.
question
Would you expect to find two strong peaks at 690 and 770 in your product from alkylation of m-xylene?
answer
If the starting material m-xylene fully reacts you would not see those peaks which are characteristic of only 1,3-disubstituted aromatic rings. (xylene)
question
Suggest two other compounds that might be used in place of t-butyl alcohol to form 1,4-di-tert-butyl-2,5-dimthoxybenzene.
answer
t-butyl chloride, t-butyl bromide, isobutylene. You basically need a leaving group on the end of a t-butyl molecule so the butyl molecule can be substituted onto the benzene ring.
question
For the friedel crafts dialkylation of 1,4-dimethoxy benzene with t-butyl alcohol and sulfuric acid, draw the structure of all possible dialkylation products. Which one do you expect to isolate and why?
answer
You could have the X at the 3,5 positions, both ortho contributors to one of the methoxys. You could have the X at the 3,6 positions, ortho to one methoxy, ortho to the other methoxy. You could have the X at the 2,3 positions, ortho to both methoxys. You would chose the 3,6 positions because they are ortho/para contributors so the ortho products would be produced. This one would be chosen over the others because the others would be too streakily hindered.
