The only real difference is how to produce the appropriate electrophile for reaction. If you do not produce a lot of crystals, you might try evaporating some of the solvent by heating the mixture to the boiling point of methanol about 68 oC. The purpose of this cooling is to prevent a large increase in temperature when the concentrated sulfuric acid is added. Also, when a Pasteur pipet was used to remov e the solvent from the reactio n tube, many crystals were lost. Iron-Catalyzed Synthesis of Tetrahydronaphthalenes via 3,4-Dihydro-2 H-pyran Intermediates R.
Your sample should be a free flowing slurry, meaning that there is enough liquid to keep the solid moving around. Continue to swirl the mixture occasionally during the warming up process. A valuable, two-step alternative is Friedel-Crafts Acylation followed by a carbonyl reduction. Very carefully, add a drop of water to the mixture. Conversion of 2-Alkylcinnamaldehydes to 2-Alkylindanones via a Catalytic Intramolecular Friedel-Crafts Reaction G. Remove the solvent liquid layer using a glass Pasteur pipet with a.
Day 1: This is a small scale experiment, so it is crucial that you are careful, or you will end up with no product. Wash the solid chemical collected on the filter with water in order to remove any water-soluble chemicals e. Further Information Related Reactions Friedel-Crafts Alkylation This Lewis acid-catalyzed electrophilic aromatic substitution allows the synthesis of alkylated products via the reaction of arenes with alkyl halides or alkenes. You do not want to add too much methanol, but if you do, you can always evaporate some of it away. Add about 10 g of ice to the reaction mixture which would be approximately the volume of the reaction mixture; too much ice is not a problem as it just melts. Day 2: Re-crystallize the dried product using methanol as your re-crystallization solvent. A t-butyl cation will be used and since no carbocation rearrangement can occur, any method can be used to produce this cation.
Add the cold sulfuric acid drop wise about 1 drop per second or slower to the cooled reaction mixture from above. After your sample is completely dry at the beginning of the next lab period , remove a small amount of the dried crude product for melt point analysis remove a sample of the crude material at the beginning of the second day. Since alkyl substituents activate the arene substrate, polyalkylation may occur. Electrophilic Aromatic Substitution: Friedel-Crafts Alkylation Objectives Substitution reactions are really at the heart of most organic reactions. Mechanism of the Friedel-Crafts Alkylation Using alkenes : Recent Literature Iron Oxide Nanoparticles Grown on Carboxy-Functionalized Graphite: An Efficient Reusable Catalyst for Alkylation of Arenes V.
After this 15-min period of drying your sample, you can use the crystalline material directly in a melt temp. In order to collect your solid material, you will do a vacuum filtration. When you add your filter paper to the Buchner Funnel, do not wet with water, you must keep it dry. How the alkyl cation is produced is not important. Benzylic Phosphates in Friedel-Crafts Reactions with Activated and Unactivated Arenes: Access to Polyarylated Alkanes G.
These amounts will be your yield of both the crude and re-crystallized material. Allow the tube to remain at 20-25°C for approximately 10 minutes in order to complete the reaction. Dicationic Electrophiles from Olefinic Amines in Superacid Y. If the methanol is boiling, and all the solid has not dissolved add more methanol in 2-mL quantities until the boiling mixture is free of solid material. Weigh your solid and determine a yield. The percent yield of the product was 57. Remove the flask containing the reaction mixture from the ice bath and set in on the bench top.
The purpose of this experiment is to synthesize 1, 4-Di-t-butyl-2, 5 — dimethoxybenzene by reacting 1, 4 — dimethoxybenzene w ith tertiary-butyl alcoho l in the presence of sulfuric acid as a Lew is acid catalyst. While addition reactions occur for compounds containing either double or triple bonds, most reactions actually occur when one chemical or atom replaces something already on the molecule. Stir with a glass stirring rod, then continue to add water dropwise with both cooling and mixing until 2. Remove the beaker and let it sit again at room temperature until crystals form. The important part is that a carbocation is used for this reaction. In the experiment we conduct today, we use a Friedel-Crafts Alkylation. When only liquid is present, you should place the flask very briefly into an ice bath to cool its contents, but do not let it sit in the ice bath too long as solids may reform.
The electron cloud on the aromatic rings functions as the nucleophile as usually something positively charged functions as the electrophile. Let the vacuum continue to draw air over your sample, letting it dry by evaporating all of the methanol about 15 min. Methanol is a flammable liquid, and is toxic no flames will be allowed in lab, wear gloves while handling it, and avoid breathing its vapors. The reaction we will be performing actually takes advantage of that fact, as the dialkylation product shown above is not only the desired product, but it is the only product. Samarium Triflate-Catalyzed Halogen-Promoted Friedel-Crafts Alkylation with Alkenes S. This is a Friedel-Crafts Alkylation reaction. What factors are responsible for producing this as the only dialkylation product? However, as this reaction illustrates, one of the problems with Friedel-Crafts alkylations is that it is often difficult to avoid producing significant amounts of dialkylation substitution products because the alkyl group being attached to the aromatic ring is electron-donating.
Allow the reaction mixture to gradually warm up to room temperature. Isolate the solid product by vacuum filtration using a Büchner funnel. In the current experiment, we will use a different electrophile the t-butyl cation to alkylate 1,4-dimethoxybenzene. Add enough methanol to dissolve the product. Use a dry and clean 125-mL Erhlenmeyer flask for this reaction.
You should dry your sample in the dessicator drying oven until the next lab period. The ob served melting point of the product was 96 - 98°C, which is considerably lower than the literature value of 104 — 105°C. Wash your beaker with a little methanol, to attempt to add as much of your solid as possible to the funnel. You should keep the reaction mixture in the ice bath and swirl it occasionally during the addition of all of the sulfuric acid. As we have done before, we can generate these carbocations using reactions where acid is present, as we have seen before: As long as the carbocation is stable, and does not undergo rearrangements, this is actually a very good way to generate an electrophile for a Friedel-Crafts alkylation reaction. Take your time, do not rush this step. Procedure Safety: Concentrated sulfuric acid is a strong oxidizer, and both it and acetic acid are highly corrosivewear gloves while handling them, and avoid breathing their vapors.