Reduction of Ethers and their Derivatives

In bromohydrins, hydrogenation over Raney nickel may lead to epoxides rather than to alcohols since regular Raney nickel contains enough alkali to cause dehydrobromination. Pure hydrogenolysis of bromine can be achieved over Raney nickel which has been washed free of alkah by acetic acid [631]. 

Nitro alcohols were reduced to amino alcohols by catalytic hydrogenation over platinum [632] and with iron [JJ9], and nitrosophenols [255] and nitro-phenols [256] to aminophenols with sodium hydrosulfite, sodium sulfide [238] or tin [176]. Bromine atoms in 2,6-di-bromo-4-nitrophenol were not affected [176]. 

Open-chain aliphatic ethers are completely resistant to hydrogenolysis. Cyclic ethers (for epoxides, see p. 83) may undergo reductive cleavage under strenuous conditions. The tetrahydrofuran ring was cleaved in vigorous hydrogenations over Raney nickel [420] and copper chromite [420] to give, ultimately, alcohols. 

Tetrahydrofuran itself is not entirely inert to some hydrides although it is a favorite solvent for reductions with these reagents. A mixture of lithium aluminum hydride and aluminum chloride produced butyl alcohol on prolonged refluxing in yields corresponding to the amount of alane generated [633]. 

Under reasonable conditions tetrahydropyran ring is not affected. Catalytic hydrogenation of 1,2-dihydropyran over Raney nickel at room temperature and 2.7 atm saturated the double bond to give quantitative yield of tetrahydropyran [634.  

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