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Ether And Epoxides
Part-4
(iv) Alcohol with diazomethane
(v) Alkyl halide with dry Ag2O
This reaction is not carried out with moist Ag2O because moist Ag2O is actually AgOH where
substitution occurs and formation of alcohols from alkyl halide takes place.
Chemical properties
(i) Oxidation
Ether are less reactive due to absence of polarity, along with an ability to soluble in nonpolar
substances like CCl4, that makes ethers so often used as solvents when carrying out many
organic reactions. Nevertheless, most ethers are explosive and hazardous materials, and
precautions must be taken when using them. Diethyl ether is extremely flammable and because
of its high volatility can form explosive mixtures in air very quickly. Open flames must never be
present in laboratories where diethyl ether is being used regularly.
A second dangerous property of ethers is when they undergo oxidation in presence of air to
form explosive peroxides. Where air oxidation of diethyl ether gives explosive strained
peroxide proceeds according to the following equation.
The reaction is a free-radical type, and oxidation occurs at the carbon that contain the ether
oxygen to form a hydroperoxide, a compound of the type ROOH. Hydroperoxides tend to be
unstable and shock-sensitive due to molecular strain. On standing, they form related peroxidic
derivatives, which are also. Due to this, one should never use old bottles of dialkyl ethers, and
extreme care must be taken in their uses.
(ii) Acid–catalyzed fission of ethers
When the carbon-oxygen bond of alcohols is undergo fission on reaction with hydrogen halides,
just similar to an ether linkage undergo breaking with hydrogen halides.
The fission of ethers is generally carried out under conditions like excess hydrogen halide, cold
or hot HX, such that the alcohol formed as one of the original products and by heating
converted to an alkyl halide. Thus, the reaction with hot HX finally gives two alkyl halide
molecules :
Cyclic ethers yield one molecule of a dihalide :
The order of hydrogen halide reactivity is HI>HBr >HCl. Hydrogen fluoride is not effective so
normally not considered in organic chemistry.
A mechanism for the cleavage of diethyl ether by hydrogen bromide is given below where the
key is an SN2-like attack on a dialkyloxonium ion by bromide