Sulfanilic acid in just 3 minutes - Ácido sulfanílico en sólo 3 minutos (ESP sub)

[00:00:06]Hello again everyone. In this new video, I'll be synthesizing sulfanic acid through the microwave assistant reaction of sulfuric acid and analine as it described in this paper.

[00:00:17]Though I base my procedure on that article, I also did some modifications with respect to the purification steps.

[00:00:24]The traditional lab synthesis of sulfonilic acid is described in various old textbooks. It requires at least 8 hours of heating at a temperature near 200° in an oil bath or in a direct flame which is not only dangerous but also extremely energetically inefficient.

[00:00:42]I'm leaving those procedures here in case you want to check them. Let's move to the procedure.

[00:00:49]First we weigh 9.3 gram of analine in a 100ml erlin mer flask and 16 grams of sulfuric acid. Then we begin to gradually add the sulfuric acid into the analine. This procedure generates a lot of heat and toxic vapors. So it is important to work in a fume hood.

[00:01:09]It is also advisable to cool down the mixture with a bowl of cold water to avoid excessive loss of analine.

[00:01:17]It is very important to thoroughly stir the mixture so the reaction is as homogeneous as possible before we radiate the reaction.

[00:01:26]Well, at the end of the addition, the reaction mixture resembles a thick paste. We put a small beaker in the mouth of the flask and put the reaction inside the microwave.

[00:01:36]Then we have to adjust the power of the microwave to 400 W. I have a 1200 W household microwave, so I adjust the power to 30%.

[00:01:47]The majority of microwave ovens simply control the power by switching on and off the magnetron to different intervals of time. In new models of microwave ovens with inverter technology, the power can be in fact effectively adjusted.

[00:02:02]After 3 minutes of reaction, we open the door and observe some fumes and the changing color of the reaction. With a lot of care, we take out the hot flask and let it cool to room temperature.

[00:02:13]Optionally, we can monitor the reaction with TLC using a mixture of 2 to1 of one propanol to concentrated ammonia as eluent.

[00:02:22]In the UV light, we can clearly see that sulfanic acid has formed, but also there is some analine left. Fortunately, we can further purify the product and get rid of the analine easily.

[00:02:35]So next we prepare a solution of 0.2 mole or 8 g of sodium hydroxide in 80 ml of water. Carefully we pour the hot alkali into the product and stir it until all of it has dissolved.

[00:02:49]Then we transfer the product into a crystallizing dish and let evaporate about 20% of the water.

[00:02:56]This step is useful to get rid of some of the volatile laneline that is still present in the reaction mixture. Then we'll let it cool to room temperature and begin the addition of concentrated hydrochloric acid until the pH is strongly acidic.

[00:03:10]This will cause the sulfanic acid to precipitate and the mixture to heat up.

[00:03:15]So we cool it down in a bath of ice cold water.

[00:03:20]Finally, we vacuum filter and collect the product which could be used as it is without purification in some reactions.

[00:03:27]But I just wanted to have some nice pure crystals. So I followed a somewhat tiresome purification process.

[00:03:38]So to purify the product, we need to dissolve the silver leak crystals in 250 ml of boiling water. The dissolution is slow, so we have to boil it for a couple of minutes. Then we add 0.5 g of activated charcoal and let it boil for 10 minutes approximately.

[00:03:57]The sulfanilic acid is only soluble in very hot water. So we need to quickly filtrate the charcoal using a glass bna funnel. The crystals of sulfanic acid tend to constantly jam the filter. So I can assure you that it is not a pleasant procedure.

[00:04:14]After a long filtration process, we finally collect the filtrate and add 115 ml of ethanol to help the sulfanic acid to precipitate out of solution and also to decrease the melting point of the solution so we can safely put it in the freezer overnight.

[00:04:30]The next day, we are left with some nice and almost colorless crystal plates. So, we filter and wash them with ethanol and let them dry in a vacuum vicator.

[00:04:41]If we want to recover as much sulfanic acid as possible, it is necessary to evaporate almost all the water from the filtrate. At the end, we recovered from the mother liquor 1.5 extra g. So, at the end, the final weight of pure sulfanilic acid dihydrate was 9.8 g, which corresponds to a yield of 47%.

[00:05:02]And that's all for this video. See you next time.