Potassium with tetrahydrofuran

Preliminary Experiments. Initial work centered on the study of the reaction of potassium with tetrahydrofuran and with naphthalene in tetrahydrofuran. 

Formation of asphaltenes during solubilization of low-rank bituminous coals has been attributed to cleavage of open ether-bridges (6). But while the presence of such configurations in high- and medium-rank bituminous coals is well established (7), their existence in less mature coals remains to be demonstrated. From reactions of low-rank bituminous coals with sodium in liquid ammonia or potassium in tetrahydrofuran, it has, in fact, been concluded that open ether-bonds are absent (8) or only present in negligible concentrations (9). 

The radical anions 1, anti-2, anti,anti-3, and anti,anti,anti-4 were generated by the reduction of the corresponding ladder polysilanes with potassium (Scheme 8). When the ladder poly silanes were treated with potassium in tetrahydrofuran (THF) at ca. — 70 °C, the solutions were immediately colored 1, purple anti-2, brown anti,anti-3, blue and anti,anti,anti-4, black. In the UV-visible-NIR spectra, several absorption bands appeared (Fig. 15). The intense absorption of anti,anti-3 and anti,anti,anti-4 in the near-infrared region is noted because it has been... 

Potassium tetrafluorocobaltate(III) at 200°C reacts with tetrahydrofuran to give82 unsaturated products the major ones are 5 and 6, although the overall yield is poor (< 30%). Furan itself gives no products at all over cobalt(IIl) fluoride it presumably polymerizes. This does not, however, rule furan out as an intermediate in the tetrahydrofuran fluorinations (it could form by desaturation, as does benzene in the fluorination of cyclohexane, vide supra). 2-Methyl-and 2,5-dimethyltetrahydrofuran83 have also been fluorinated with similar results to tetrahydrofuran. 

The lithium anion of chloromethyl phenyl sulfoxide reacts with tetrahydrofuran-2-ones 1011 to afford a diastereo-meric mixture of hemiacetal adducts 1012, the potassium enolate of which is treated with /-BuLi followed by addition of a proton source leading to to-hydroxyalkyl ketenes 1013, which themselves cyclize to 6-substituted tetrahydropyran-2-ones in excellent overall yield (Scheme 263) <1998TL9215>. 

Reduction of pyrazine with potassium in 1,2-diethoxyethane at — 70° gives the paramagnetic radical anion. Anions have also been generated from the low-temperature reaction of pyrazine, methyl-pyrazine, 2,5- and 2,6-dimethylpyrazines with sodium or potassium in tetrahydrofuran or 1,2-dimethoxyethane. From measurements of their ESR spectra, ion-pair formation is proposed between the alkali metal cation and the pyrazine anion.96-101... 

Tris(N-methylanilino)borane has previously been prepared by the reaction of boron trifluoride-ether complexes with three equivalents each of N-methylaniline and a suitable Grignard reagent,1,2 by the reaction of (N-methylanilino)potassium with boron trifluoride-ether complexes,2 and by aminolysis of boron trichloride by N-methylaniline.3 The present general procedure describes a convenient preparation of tris(N-methylanilino)-borane by the reaction of (N-methylanilino)lithium and boron trifluoride-diethyl ether in tetrahydrofuran-hexane as solvent. 

The rates of reduction of tetrahydrofuran (Curve A), naphthalene in tetrahydrofuran (Curve B), and a mixture of naphthalene and Illinois No. 6 coal in tetrahydrofuran (Curve C) are shown in Figure 1. These preliminary experiments established that potassium reacted only very slowly with tetrahydrofuran under the experimental conditions used for the formation of the coal polyanion. Naphthalene was rapidly converted to a mixture of anion radicals and dianions under the same conditions. The initial reaction between the electron transfer reagent and the Illinois No. 6 coal was quite rapid. However, the reaction slowed to nearly constant rate after about 12 hr. During the last 4 days of reaction the coal molecules acquired about 0.1 negative charge per 100 carbon atoms per hour. 

The Alkylation Reaction. Ether solvents and naphthalene often are employed in the Sternberg alkylation reaction. Inasmuch as these substances are reactive in strongly basic solution, concern has been expressed about their polymerization reactions and about their incorporation into the alkylation product. In view of these potential problems we examined the reaction of potassium with carefully purified tetrahydrofuran at 25 C. The results shown in Figure 1, Curve A, indicate that the reaction is insignificant. On the other hand, the results shown in Figure 1, Curve B, indicate that potassium reacts rapidly with naphthalene to form naphthalene anion radical and naphthalene dianion. The reduction to the dianion is about 80% complete after 4.5 hr. 

Addition of two electrons to cyclooctatetraene would lead to a 10ji-electron system, the cyclooctatetraenyl dianion, Cyclooctatetraene, which is non-planar, reacts with potassium in tetrahydrofuran to give dipotassium cyclooctatetraenide, which is planar. The C-C bond lengths are all the same (141 pm). At low temperatures, a dication is formed when cyclooctatetraene reacts with SbF.. This also has some aromatic characteristics in keeping with a 6jt-electron system. 

Starting from the 1,3,5-triazines, few syntheses of dihydro-1,3,5-triazines have been reported. Although many versatile synthetic approaches are available, most of them are yet to be tried. The known reactions involve preparation of dihydro-1,3,5-triazine derivatives from 2,4,6-triphenyl-1,3,5-triazine (153) via (a) lithium aluminum hydride reduction264 (b) treatment with potassium in tetrahydrofuran, followed by hydrolysis265 and (c) reaction with organolithium compounds and hydrolysis266 [Eq. (81)]. 

Compound C is synthesized from the pentaethyl-1,5-dicarba-c/oso-pentaborane(S) (A) by a dimerization that has not yet been fully clarified mechanistically 1 mol of A (5"B = + 13.5) reacts with 1.2 mol of metallic potassium in tetrahydrofuran (THF) at room temperature according to the above equation, slowly forming a dark brown solution. The metal does not react faster when the mixture is heated. If > 0.5 mol of potassium per mole of A ( "B = 13.5) are taken up, four new "B NMR signals of the weakly paramagnetic solution (ESR measurementsf) appear at = 26.8, — 14.2, — 16.2, and — 37.1 (see Fig. 1). The intensity of the "B NMR signal of A decreases to ca. 50% after reaction of > 1.0-1.2 mol of potassium per mol of A. Correspondingly, we presume that a potassium salt of the dianionic species B is formed in an equilibrium with A and a small amount of the radical anion salt B (see equation). 

When lithium cyclononatetraenide is treated with iodine it is converted into a thermolabile, air-sensitive bis(cyclononatetraenyl) which reacts with potassium in tetrahydrofuran, in the absence of air and moisture, to give deep brown crystals of dipotassium bis(cyclononatetraenido) 182]. Addition of further potassium cleaves this dianion slowly to form potassium cyclononatetraenide ... 

Carbanionic species in solution are strongly influenced by the counterion and by any added species such as bases that can coordinate a metallic counterion. For example, Kronzer and Sandel reported NMR studies of 1-and 2-naphthylmethyllithium, -sodium, and -potassium in tetrahydrofuran (THF) and in hexamethylphosphoramide (HMPA) solution. In THF the spectra showed a strong dependence on the metal, suggesting that there was close association of the carbanionic carbon with the metal. The spectra of the lithium and sodium species were identical in HMPA solution, however, suggesting that the carbanions were significantly separated from the cation, either as free ions or as ion pairs separated by solvent molecules. 

Reduction of 1,1-dichlorotetraphenylsilole with lithium, sodium or potassium in tetrahydrofuran affords the polysilole of a moderate molecular... 

PO also reacts with active hydroxyl hydrogen derived from the ring opening of other compounds such as EO and tetrahydrofuran thus, a copolymer polyol is obtained. Typically, polyols are obtained from base-catalyzed reactions with aqueous ammonia, sodium or potassium hydroxide, or lower alkyl tertiary amines such as trimethyl- and triethylamine. The reaction of PO with tetrahydrofuran is catalyzed by boron trifluoride etherate. The molecular weights of polyols prepared according to the reactions described earlier range from 200 to 7000. 

With potassium in tetrahydrofuran (84) gives 2-phenylpyrrole. The proposed mechanism for this rearrangement is shown in Scheme 18. Under the same conditions the N-methyl analogue of (84) gives a mixture of naphthalene and N-methyl-l-naphthylamine. Azabullvalene reacts with Fe2(CO)9 as shown in scheme 19. 

The phenomena described here are strongly dependent on the solvent and the alkali metal. No disproportionation occurred in tetrahydrofuran and 1,2-dimethoxyethane, irrespective of the alkali metal used. The reaction of sodium or potassium with naphthalene in 2-methyltetrahydrofuran leads exclusively to the mononegative ion in the whole temperature range from -120° to +25°C. 

Isocratic elution with 5% methanol, 3% acetonitrile, 0.5 mmol/1 sodium acetate, 0.012 mol/1 potassium dihydrogen orthophosphate and 0.148 mmol/1 phosphoric acid in distilled water a 349 nm emission) bicartxmate buffer (pH = 10.5) and extraction with tetrahydrofuran prior to SPE with Zeolite Y column ... 

Under phase transfer conditions (boiling benzene, 50% aquous sodium hydroxide solution and tetia-n-butylammonium hydrogenphosphate) benzamides are monoalkylated. In the solid-liquid PTC system potassium hydride, tetrahydrofuran and 18-crown-6, acidic trifluoroacetamides are rapidly deprotonated and alkylated with lower kyl, allyl and benzyl halogenides in high yield. Methylation of trifluoroacetamides is carried out under less basic conditions in KOH/acetone. A similar reaction in KOH/DMSO generally allows the efficient reaction of benzamide and acetanilide with primary alkyl halides with secondary halides only moderate yields are accomplished, whereas tertiary halogenides are not alkylated due to dehydrohalogenation. ... 

Metal specificity. p-Biphenylyl n-decyl ether treated 2 hrs. at room temp, with 5 moles potassium in tetrahydrofuran containing biphenylyl as electron carrier n-decanol. Y ca. 90%. F. e., also with Na and Li, formation of phenols particularly with Li, s. M. Itoh et al., Chem. Lett. 1976, 271. 

The n-butyllithium/potassium ferf-butoxide mixture and butylpotassium also exhibit striking differences in their stability toward ethereal solvents. The latter reagent is instantaneously destroyed when brought in contact with tetrahydrofuran even at temperatures below — 100°C to give 2-tetrahydrofurylpotassium as the main product, which then undergoes decomposition at around —50 °C to ethane and the potassium enolate of acetaldehyde. In contrast, the n-butyllithium/potassium ferf-butoxide mixture survives in the same solvent almost indefinitely at —75 °C and can be briefly exposed to —50... 

There are fewer reports of linear, acyclic, ion-binding polymers. It has been reported that poly(oxyethylene) improves the solubility of alkali metals in ethers such as tetrahydrofuran, dime thoxy ethane, and diglyme, stabilizes fluorenyl alkali metal compounds, accelerates Williamson reactions and accelerates several other nucleophilic reactions.All of these effects were attributed to the ability of poly(oxyethylene) to complex with cations in solution. Yanagida and coworkers studied the alkali metal cation complexation of poly(oxyethylene), using a picrate salt extraction technique similar to the one used by Pedersen and Frensdorff. Polymers with more than 23 oxyethylene units were effective iono-phores for potassium, with degrees of extraction (percent extracted) comparable to crown ethers. The extractability per oxyethylene unit was nearly constant, and the complex stability increased linearly with increasing numbers of repeating oxyethylene units. Seven oxyethylenes were the minimum number of repeat units necessary to bind potassium ion effectively in the aqueous phase. The less efficient extraction of short-chain poly(oxyethylene) is apparently caused by its hydrophilic character. 

The non-aromatic non-planar hydrocarbon cyclo-octatetraene adds two electrons on reaction with potassium in tetrahydrofuran, forming a planar aromatic dianion. The equilibrium... 

Tetrahydrofuran is polymerized to poly(tetramethylene glycol) with fuming sulfuric acid and potassium biduoride (29). 

These reactions are usehil for the preparation of homogeneous difunctional initiators from a-methylstyrene in polar solvents such as tetrahydrofuran. Because of the low ceiling temperature of a-methylstyrene (T = 61° C) (26), dimers or tetramers can be formed depending on the alkaU metal system, temperature, and concentration. Thus the reduction of a-methylstyrene by sodium potassium alloy produces the dimeric dianionic initiators in THF (27), while the reduction with sodium metal forms the tetrameric dianions as the main products (28). The stmctures of the dimer and tetramer correspond to initial tail-to-tail addition to form the most stable dianion as shown in equations 6 and 7 (28). 

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