Organopotassium compounds

A variety of organometallic compoundshave been used to couple with alkyl halides. " Organosodium and organopotassium compounds are more reactive than Grignard reagents and couple even with less reactive halides. Organolithium... 

Potash salt mining, 20 613-614 Potassium (K), 20 597-608. See also NaK entries KBr disks Organopotassium compounds... 

Gyclopentadienyl ring metathesis with organocalcium or organopotassium compounds constitutes a further method for the synthesis of decamethylplumbocene 34 and, for example, furnishes compound 34 in 59% or, respectively, 35% yield55 (Equation (17)). 

The alkylation of benzene by alkylpotassium compounds has been reported by Bryce-Smith (S9) and is probably due to the increased base strength of organopotassium compounds over organosodium compounds. The potassium hydride eliminated in the cyclization reaction may add to ethylene to form ethylpotassium, which then may react with the aromatic to yield ethane and a benzylic carbanion [Reactions (16) and (17)]. 

The negative charge distribution in the adducts was evaluated on the basis of the chemical shift values and found to be nearly 75% concentrated on the nitrogen atom. In the reactions of l-ethoxycarbonyl-l,4-dihydropyridines with organosodium and organopotassium compounds, the resulting metal-associated (j-adducts were not soluble in aliphatic hydrocarbons alone but were made so by addition of 18-crown-6. This behavior would support ionic structures for the potassium and sodium adducts. 

This represented the discovery of the first addition of an organometallic (organoalkali) compound to a C=C double bond. The organopotassium compound used had at that time been known for only 4 years. It was found by the author and Schnell (46) as the result of a systematic search for the simplest ether to be split by an alkali metal according to the equation... 

Factors governing orientation in metalation reactions. I. The metalation of ethylbenzene 437 with organosodium and organopotassium compounds./. Am. Chem. Soc. 1962, 84, 4971— 4975. 

Dissolving metals initially convert aldehydes, ketones, and esters into radical anions. Subsequently, proton donors may react with the latter, which leads to neutral radicals. This mode of reaction is used, for example, in the drying of THF or ether with potassium in the presence of the indicator benzophenone. Potassium and benzophenone react to give the deep-blue potassium ketyl radical anion A (Figure 14.45). Water then protonates ketyl A to the hydroxylated radical B as long as traces of water remain. Further potassium reduces B via another electron transfer to the hydroxysubstituted organopotassium compound C. C immediately tautomerizes to the potassium alkox-ide D. Once all the water has been consumed, no newly formed ketyl A can be pro-tonated so that its blue color indicates that drying is complete. 

The sodium used was in a very finely divided form, the diameter of the particles being about 5 to 25 microns. The organopotassium compounds are obtained in an analogous manner. 

The preparation of benzyllithium from benzyl halides and alkyllithiums is not feasible because the benzyllithium initially formed reacts with the starting benzyl halides, producing 1,2-diphenylethane. Metalation of toluene with n-BuLi in the presence of TMEDA at 30 °C results in a 92 8 ratio of benzyllithium and ring metalated products. Metalation of toluene with n-BuLi in the presence of potassium rert-butoxide, and treatment of the resultant organopotassium compound with lithium bromide, affords pure benzyllithium in 89% yield. Alternatively, benzyllithiums are accessible by cleavage of alkyl benzyl ethers with lithium metal. " ... 

Organopotassium compounds are still more reactive than the corresponding derivatives of sodium. Whereas phenylsodium can be obtained after reaction of sodium with chlorobenzene in toluene, reaction of potassium with chlorobenzene in toluene affords benzylpotassium in good yield, even at low temp-... 

A large number of patents and papers have been published since 1956 covering this technique(9-13). The initiator in most cases is an organolithium compound, Organosodium or organopotassium compounds can be used, but a much higher amount of the 1,2 addition product of the diene is found in the product. 

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