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Two moles of alkyl halide heated with two moles of dry silver oxide forms an ether and two moles of silver halide. The ether formed by this reaction will be symmetric. If the silver oxide is moist, the final product form will be alcohol instead of ether. When moisture is present, silver oxide forms silver hydroxide (actually, the silver hydroxide does not exist); that’s why the reaction does not move further to give the desired product.
Alkyl Halide
- When one hydrogen of alkane is replaced by halogens (such as Cl, Br, I, F), the compound formed is called alkyl halide
- In the ether, we see that two alkyl groups attached to the oxygen may either be symmetrical or not symmetrical
- That’s why we need two moles of alkyl halides so that the formation of ether can take place
- These are also three types based on no hydrogens attached to carbon:
- Primary alkyl halide – when three hydrogens are attached to the carbon. For example, CH3Cl, CH3Br, CH3I.
- Secondary alkyl halide – when two hydrogens are attached to the carbon For example: CH2Cl2, C2H4Cl2.
- Tertiary alkyl halide – when only one hydrogen is attached to the carbon. For example: CHCl3.
Silver Oxide
It is an inorganic compound. Silver oxide is an oxide whose molecular formula is Ag2O , formed by two elements, silver and oxygen. It is a fine, black-coloured powder. It is odourless and has a metallic substance. Usually, it is used for glass polishing. It is soluble in both water and alkali. When exposed to air or dust, it becomes toxic for the lungs.
Ether
Ether is a form of an organic compound. Two alkyl groups are attached to the oxygen. It is a highly volatile and flammable compound. It is colourless and has a sweet odour. Its boiling point is comparable to alkanes. Due to the difference in electronegativity between carbon and oxygen, the polarity occurs, showing some magnetic moment.
Ether can be of two types:
- Symmetric ether – Having the same alkyl group at both sides of oxygen.
e.g. Di-isopropyl ether, Diethylether, Dimethyl ether.
- Asymmetric ether – Having two different alkyl groups at both sides of oxygen.
e.g. Ethyl Methyl Ether
Silver Halide
Silver halide is a compound formed by silver and halogens when silver and chlorine form a bond. The white precipitate formed is called silver chloride. And when silver and bromine form a bond, we call it silver bromide. It gives a creamy colour precipitate. When silver and iodine form a bond, we call it silver iodide, which gives a yellow colour precipitate.
Reactions of different alkyl halides with dry silver oxide:
- 2CH3Cl +Ag2O —∆→CH3OCH3 + 2AgCl
- 2C2H5Cl +Ag2O —∆→ C2H5OC2H5 + 2AgCl
- 2CH3Br + Ag2O —∆→CH3OCH3 + 2 AgBr
- 2C2H5Br + Ag2O —∆→C2H5OC2H5 +2 AgBr
Mechanism
The SN2 mechanism executes this reaction. Carbon has a partially positive charge due to the difference in electronegativity between carbon and halogen. And silver oxide’s oxygen starts behaving like a nucleophile due to the presence of lone pairs. This oxygen attacks carbon and forms ether. When the halogen has a partial negative charge and silver a partial positive charge, they make a bond and form silver halide.
Limitations
(i) This method of ether preparation is most suitable for the formation of symmetric types of ethers.
Asymmetric ethers can not be produced by this method. To prepare asymmetric ether, we have to take two different alkyl halides as reactants. And then, the product is formed as a mixture of three compounds which are both symmetric and asymmetric.
(ii) Silver oxide should not be moist.
If moisture is present in the form of H2O, then the Ag2O forms AgOH silver hydroxide. And we wouldn’t be able to get the desired product. So dry silver oxide must be present.
Conclusion
Here, we have discussed alkyl halide, silver oxide, ether, silver halide, reactions with different alkyl halides with dry silver oxide, its mechanism, and limitations. Moreover, this is one of the most suitable methods of preparation for ether. We don’t need any specific catalyst or artificial environment to proceed with this reaction. We have to simply heat alkyl halides with dry silver oxide to form ether. But we should also always be aware of two limitations of this reaction. Only dry silver oxide can only be used, and only symmetric ethers are formed.
