Intermolecular Dehydration with HX
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Intermolecular Dehydration with HX

Another kind of intermolecular dehydration reaction is shown here (and in Example 11 in your workbook).
H H
| |
H-C-C-OH
| |
H H 		 + HBr ¾¾¾® H H
| |
H-C-C-Br
| |
H H 		+ H2O

In this case the ethyl group from ethyl alcohol attaches to the bromine atom from hydrogen bromide to make ethyl bromide. Since water is formed from parts of two molecules, it is considered an intermolecular dehydration reaction. By the way, you can also look at this as either a double displacement reaction or a substitution reaction.

Even though a different product is formed, the process is the same. The -OH comes off of the alcohol and attaches to the H- from the other molecule. What is left from the alcohol attaches to what is left from the other molecule.

Equation for the intermolecular dehydration of an alcohol with an alkyl halide. [63rxn09.JPG]

 

As an aside, I might point out that you can see why the non-IUPAC names remain in vogue, especially for simple compounds. To say that the ethyl group from one molecule combines with the bromide from the other to make ethyl bromide gives a very simple and succinct summary of the reaction.
H H 
| |
H-C-C-OH
| |
H H 		 + HBr ¾¾¾® H H
| |
H-C-C-Br
| |
H H 		+ H2O

 

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