The reactions of the halogenoalkanes

1 Reaction with aqueous alkali

It is important to ensure that the reaction mixture is fully neutralized with dilute nitric acid before testing with silver nitrate solution. If this is done, a white precipitate of silver chloride is formed. What type of organic reaction has occurred here? Try to write an equation for the reaction.

Video - the reaction of a halogenoalkane with aqueous alkali

2 Reaction with alcoholic alkali

This reaction uses 20% potassium hydroxide in ethanol. This is extremely corrosive. We have used this type of apparatus before in the alkanes practical - care needs to be taken in this experiment because of the possibility of suck back.

We test the gaseous product for combustion and with bromine water. Given the results for these tests suggest the reaction type and write an equation for the reaction.

Video - the reaction of a halogenoalkane with ethanolic alkali

3 A comparison of halogenoalkanes

This experiment compares the rate of reaction in experiment 1 (above) using a range of halogenoalkanes. In the video we have added the hot silver nitrate solution to the three samples simultaneously, and checked for the order in which the silver halide precipitate is produced. As halogenoalkanes are not soluble in aqueous solutions, we have added some ethanol as a common solvent in which aqueous solution and halogenoalkane both dissolve. Make a note of the order in which the halogenoalkanes react, and try to explain it in terms of the differences in their molecular structure.

Video - rate of reaction in different 1-halobutanes

The experiment is now repeated with three isomers of chlorobutane. If you have not met types of halogenoalkane before, check it out. Again make a note of the order in which they react and try to explain any difference. This is not so easy!

Video - rate of reaction in primary, secondary and tertiary halogenoalkanes

Results and equations