Lucas Reagent

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Lucas Reagent

Post by bigmack »

I was asked for this today to test for Primary and Secondary and Tertiary Alcohols .

It took a bit of finding so I thought I'd post it here in case anyone else is looking for a recipe .
We only needed about 5mls , so I just used a 1/10th of both .
It didn't foam, get hot or anything nasty . I did make it in the fume hood though as there was quite a chlorine smell .
One chemical method of determining the identity of an unknown is by using spot tests to determine how it reacts with particular compounds. These tests react with only one or two types of compounds, so you can glean information about the possible type of compound the unknown is. One test that identifies alcohols is the test with Lucas Reagent. The Lucas Reagent reacts differently with the alcohol depending on the number of carbon atoms bonded to the carbon atom that contains the alcohol group. To obtain valid results, the Lucas Reagent must be prepared fresh each day.

Put on all the safety equipment before beginning the preparation of Lucas Reagent. Due to the hazardous nature of the concentrated HCl, you must guard against injury. Put on the goggles, rubber apron and rubber gloves. Adjust these items to fit you and ensure they will not get in your way or hamper you from performing any of the tasks required during the preparation.

Place a 400 ml beaker on the bench and fill it half way with ice. Pour a small amount of water into the beaker with the ice.

Pour the concentrated HCl into the 50 ml graduated cylinder. Measure out 47 ml of concentrated HCl and pour it into the 100 ml beaker.

Place the 100 ml beaker in the ice bath in the 400 ml beaker. This will absorb the heat generated during the dissolution of the ZnCl2.

Weigh out 62.5 gm of anhydrous ZnCl2 from the cooled weighing bottle using a laboratory balance. Dry the stock ZnCl2 in an oven inside a weighing bottle for at least two hours. Cool the ZnCl2 anhydrous in a dessicator to prevent air contact.

Add the ZnCl2 to the hydrochloric acid in the beaker slowly. Stir the mixture with a glass stirring rod until the ZnCl2 dissolves. Add the ZnCl2 slow to avoid the mixture overflowing the sides of the small beaker. Adding the solid too fast will cause the solution to foam.

Pour the Lucas Reagent into the 150 ml brown storage bottle. Label the bottle immediately so that it doesn’t get mislabeled.
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