Tetrahydrofuran, ether degradation

Scheme 3 Ether degradation of tetrahydrofuran (top) and diethyl ether (middle and bottom) after initial deprotonation in a- or p-position...

Arylcalcium complexes are commonly prepared in ethereal solutions via reduction of aryl halides with finely divided and highly reactive calcium powder. Because diethyl ether has a rather low boiling point these exothermic reactions are advantageously carried out in tetrahydrofuran (THF) or tetrahydropyran (TEfP). Due to an operative Schlenk equilibrium usually three species are present in solution heteroleptic [(Ar) CaI(L) ] as well as homoleptic [Cal2(L) ] and [(Ar)2Ca(L)J. Fractionated crystalh-zation and subsequent recrystallization are mandatory in order to remove excess of calcium, imreacted substrates, and ether degradation products. 

Bernhardt D, H Diekmann (1991) Degradation of dioxane, tetrahydrofuran and other cyclic ethers by an environmental Rhodococcus strain. Appl Microbiol Biotechnol 36 120-123. 

While ethers react only slowly with dimethyldioxirane, they are efficiently hydroxylated by methyl(trifluoromethyl)dioxirane even at low temperatures. Thus r-butyl methyl ether [32] was converted to f-butyl alcohol through its hemiacetal. On the other hand, tetrahydrofuran gave butyrolactone [32] in which presumably the intermediary cyclic hemiacetal was oxidized to the lactone by an additional C —H insertion. The ketal was degraded into 2-butanone and the orthoformate into diethyl carbonate [32]. The latter transformation may serve useful for deketalation under neutral conditions. 

Homo and copolymers of tetrahydrofuran (THF) and alkylene oxides (AO) are used as soft segment glycols in the preparation of polyurethanes. In the process of producing the THF-AO homo and copolymers certain oligomeric cyclic ethers are also produced and can comprise 7-15 % of the polymer. These cyclic ethers are undesirable because when the polymers are used to prepare polyurethane the cyclic ethers tend to degrade the polyurethane s properties. 

Consequently, it appears likely fliat flie alcohols, ketones, o-cresol, ethyl acetate, and pyridine will degrade rapidly in soil if rapidly is defined as having a half-life of 10 days or less. Most ofthe benzene derivatives, F-11, and the chlorinated aliphatic hydrocarbons may be relatively persistent in soil. Analogous information was not located for diethyl ether, hexane, decane, or tetrahydrofuran. ATSDR for example, found that there was little information available for the degradation of n-hexane in soil. It was suggested that n-hexane can degrade to alcohols, aldehydes, and fatty acids under aerobic conditions. 

Grassie and co-workers a.l23, a.l24] found that under inert conditions at temperatures above about 210 °C the polyurethane linkage disappears without any volatile products being formed, and the initial degradation step is seemingly a simple depolymerisation reaction. The two monomers are the primary products, and all the other products, which include carbon dioxide, butadiene, tetrahydrofuran, dihydrofuran and water as volatile products and carbodiimide and urea amide in the condensed phase, are formed from the monomers in a complex set of secondary reactions while they are diffusing from the hot polymer. This is unlike under oxidative conditions, whereby the first step involves the scission of the polyurethane molecule into primary amine, carbon dioxide and propenyl ether species, the latter leading to propene formation. The mechanism is reduced to a... 

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