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Preparation of Ethyl bromide

There are main 2 methods for the Preparation of Ethyl bromide. These two are the most suitable laboratory methods for preparing ethyl bromide. They are,

  1. Prepare ethyl bromide by ethanol.
  2. Prepare ethyl bromide by Phosphorus bromide.

So, let’s discuss each of the above methods of preparation of ethyl bromide one by one.

1. Prepare ethyl bromide using ethanol (ethyl alcohol)

Firstly, 50ml of ethyl alcohol (rectified spirit) add in small amounts to an equal volume of concentrated sulfuric acid, cooling between additions. Then the mixture pours into a 1-liter distillation flask containing 100g of potassium bromide. The distillation flask connect to a Liebig condenser fitted with an adapter dipping underwater in a conical flask as below figure.

preparation of ethyl bromide with H2SO4

Also, the distillation flask heat over a sand bath when ethyl bromide distills over and collects as a colorless liquid underwater in a conical flask.

The ethyl bromide synthesis reaction with KBr

KBr + H2SO4 → HBr + KHSO4

HB + C2H5OH →C2H5Br + H2O

The above quantities use in the preparation of ethyl bromide are approximately calculated from the above equations. Also, it is necessary to maintain the temperature during preparation as low as possible to prevent oxidation of the hydrogen bromide by the concentrated sulfuric acid to liberate bromine. The oxidation is evident by the appearance of brown fumes.

2HBr + H2SO4 → 2H2O + Br2 + SO2

So, ethyl bromide may contain impurities acid fumes, ethyl alcohol, ether, and water. It first separates from the water. Also, the contents of the conical flask transfer to a separating funnel, collecting the lower layer of denser ethyl bromide. The ethyl bromide then shakes yup with aqueous sodium carbonate to remove any acid gases present. Also, the carbonate adds until there is no further effervescence. The ethyl bromide layer separates again.  

Also, a few pieces of calcium chloride adds, and then te mixture allows to stand for a few days in a stoppered vessel. The calcium chloride removes any water and also ethyl alcohol which may present. The remaining ethyl bromide distills over a water bath. The thermometer blub being opposite the side tube of the distillation flask. The boiling point of ethyl bromide is about 380C. Also, the fraction distilling can collect over between the temperatures of 350C and 430C.

Because of the low boiling point, it is advisable to surround the receiver by ice.

Under the preparation of ethyl bromide, let’s talk about the second method of preparation.

2. Prepare ethyl bromide by Phosphorus bromide

Firstly a distillation flask containing approximately 70ml of ethyl alcohol and 10g of red phosphorous, fit with a tap funnel and connect to a condenser and adapter as the below figure.

preparation of ethyl bromide with red phosphorous

Also, 20ml of bromine run in from the tap funnel drop by drop while the flask immerses in a trough of cold water. After the addition of bromine, the mixture is allowed to stand for some hours. Then the mixture distills over a water bath. Oily ethyl bromide collects in the receiver. It purifies as in method 1.

The phosphorous and bromine combine and the product reacts with the alcohol. Red phosphorous use instead of white allotrope which reacts rather violently.

Also, assuming the bromine and phosphorous combine to form the tribromide, the equations may write as follows. The quantities us in the preparation are approximately those calculated from the equations.

2P + 3Br2 → 2PBr3

Important: Great care is necessary when the use of bromine. The vapor attacks the throat and lungs. Also, the liquid can cause severe burns on the skin.

The ethyl bromide synthesis reaction with PBr3

PBr3 + 3C2H5OH → 3C2H5Br + P(OH)3 (Orthophosphorous accid)

Summary of Preparation of ethyl bromide

From this article, you knew that there are main two methods for the preparation of ethyl bromide. They are,

  1. Prepare ethyl bromide by ethanol.
  2. Prepare ethyl bromide by Phosphorus bromide.

I hope you will get a good knowledge of how to prepare ethyl bromide at the laboratory level by the above two methods. We discussed each of the ones by one.

Also if you like to read more about preparations, Read the Preparation of ethyl alcohol.

How many methods are there to prepare ethyl bromide?

2 methods

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