To the round bottom flask containing calculated amount of nitrating mixture, 40 g of dinitrotoluene are slowly placed.
” (This doesn’t just apply to the synthesis of aromatic compounds – this is important for synthesis in general. Say we want to synthesize In the next post, we’ll add another wrinkle to this “order of operations”; changing the nature of the directing groups. How would you synthesize each of these three molecules? (The third example has three substituents – remember that when doing electrophilic aromatic substitution reactions on disubstituted benzenes, the most activating group “wins”.
Post: Disubstituted Benzenes – The Strongest Donor “Wins”) There is one complication, and since it isn’t addressed in many courses, I’m relegating it to this place at the bottom where relatively few people will read it.
The issue has to do with the Friedel Crafts alkylation and (to a slightly lesser extent) the Friedel-Crafts acylation reaction.
It turns out that Friedel-Crafts reactions don’t work particularly well when strong electron-withdrawing groups (i.e – it’s that the reaction with electron-poor aromatic groups tends to be slower than side-reactions between the carbocations themselves.
The solution in a tall beaker is warmed to 50° C, and a mixed acid, composed of 54.5 g each of nitric acid (d=1.50 g/ml) and sulfuric acid (d=1.84 g/ml), is added slowly drop by drop from a dropping funnel while the mixture is stirred mechanically.
The heat generated by the reaction raises the temperature, and the rate of addition of the acid is regulated so that the temperature of the mixture lies always between 90° C and 100° C.
If we just barrel along, doing bromination first and nitration second, what happens?
Since the first reaction (bromination) installs an you have a list of some of the reactions needed to form/break these bonds, you need to ask a third question when planning a synthesis: “In what order do we run these reactions?
One-half of it, corresponding to 50 g of toluene, is taken for the dinitration.
The mononitrotoluene is dissolved in 109 g of concentrated sulfuric acid (d=1.84 g/ml) while the mixture is cooled in running water.