Alkoxides potassium

Williamson ether synthesis Alkyl halides react with sodium or potassium alkoxides or phenox-ides to give ethers. 

Select the combination of alkyl bromide and potassium alkoxide that would be the most effective in the syntheses of the following ethers... 

Both reactants m the Williamson ether synthesis usually originate m alcohol pre cursors Sodium and potassium alkoxides are prepared by reaction of an alcohol with the appropriate metal and alkyl halides are most commonly made from alcohols by reaction with a hydrogen halide (Section 4 7) thionyl chloride (Section 4 13) or phosphorus tri bromide (Section 4 13) Alternatively alkyl p toluenesulfonates may be used m place of alkyl halides alkyl p toluenesulfonates are also prepared from alcohols as their imme diate precursors (Section 8 14)... 

Potassium Alkoxides. The most widely used potassium bases are potassium tert-hu. oAde [865-47-4] (KTB) and potassium / i -amylate [41233-93-6] (KTA). These strong alkoxide bases offer such advantages as base strength (pX = 18), solubiUty (Table 5), regio/stereoselectivity because of bulky alkyl groups, and stabiUty because of the lack of a-protons. On storage, KTB and KTA have long shelf Hves under inert atmosphere (see... 

KTB and KTA are superior to alkaU metal hydrides for deprotonation reactions because of the good solubiUties, and because no hydrogen is produced or oil residue left upon reaction. Furthermore, reactions of KTA and KTB can be performed in hydrocarbon solvents as sometimes requited for mild and nonpolar reaction conditions. Potassium alkoxides are used in large quantities for addition, esterification, transesterification, isomerization, and alkoxylation reactions. 

The heat of hydrolysis, MOR + HOH — MOH + ROH (exothermic), is capable of igniting alkaU alkoxides, especially potassium alkoxides, on exposure to air. Such fires must be extinguished with sand or foam but not with water. 

Williamson reaction is the synthesis of ethers by action of heat on a mixture of alkyl haldie and sodium or potassium alkoxide... 

The most common conditions employed in the Madelung process are sodium/potassium alkoxide or sodium amide at elevated temperature (200-400 C). The Madelung reaction could be effected at lower temperature when -BuLi or LDA are employed as bases/ The useful scope of the synthesis is, therefore, limited to molecules which can survive strongly basic conditions. The process has been successfully applied to indoles bearing alkyl substituents. ... 

The directive effect of allylic hydroxy groups can be used in conjunction with chiral catalysts to achieve enantioselective cyclopropanation. The chiral ligand used is a boronate ester derived from the (VjA jA N -tetramethyl amide of tartaric acid.186 Similar results are obtained using the potassium alkoxide, again indicating the Lewis base character of the directive effect. 

N-benzyl-sulfonamides are cleaved under "relatively mild conditions" with potassium alkoxide (19). 

Figure I indicates the approach used to synthesize poly(oxyethylene)-b-poly(pivalolactone) telechelomers. An acetal capped anionic initiator, X (13) polymerizes ethylene oxide (EO) to give 2> a potassium alkoxide of a masked polyether, and this "new" initiator is to be used to polymerize pivalolactone (PVL). Since potassium alkoxides are strong nucleophiles, they can randomly attack at both the carbonyl carbon and the 3-methylene carbon in lactones, (Figure 2) such a random attack would result in a pivalolactone segment containing irregularities. Lenz (15), and Hall (16), and Beaman (17) have investigated PVL polymerization and have shown that the less nucleophilic carboxylate anion is preferable in polymerizing PVL smoothly. The weaker carboxylate anion will attack only at the methylene...

AuMe2(OR)(PPh3)] (R = Ph, /Viol, CH2CF3, CH(CF3)2) have been prepared by metathesis of czs-dimethyliodo(triphenylphosphine)gold(III) with potassium alkoxides (Equation (15)) 1786... 

Attempted formation of sodium tetrafluoropropoxide by adding the alcohol to sodium (40 g) caused ignition and a fierce fire which melted the flask. This was attributed to alkoxide-induced elimination of hydrogen fluoride, and subsequent exothermic polymerisation. In an alternative preparation of the potassium alkoxide by adding the alcohol to solid potassium hydroxide, a vigorous exotherm occurred. This was not seen when the base was added slowly to the alcohol. 

A combination of an anionic oxy retro-ene and an aldol reaction to give annulated cyclopentenones 4-361 from 4-358 was described by Jung and coworkers (Scheme 4.80) [126]. It can be assumed that, in the presence of KH, the potassium alkoxide 4-359 is first formed this leads to 4-360 and finally to 4-361 in an intramolecular aldol reaction. 

Sodium (and potassium) alkoxides are usually prepared by using excess of alcohol, and the excess alcohol becomes the solvent for the reaction. 

Sodium and potassium alkoxides are often used as bases in organic synthesis. 

Notes 0 Potassium alkoxides (2.5 equiv) prepared in situ from the corresponding alcohols with KH in THF were allowed to reoctwith PhCHCI2 (1 equiv) and t-BuOK (equivalent to alkoxide) at 0°C for the period indicated. b Except entry 7, yields refer to the isolated one based on PhCHCI2. c Paladini, J. Chuche, J. Bull. Chim. Soc. Fr. 1974, 192. d Manat, P. Dieter, S. Angew. Chem. 1977, 89, 333. eMauz6, B. J. Organomet. Chem. 1979, 365, 1 70. f Tamura, Y. Bayomi, S.M. Sumoto, K. Ikeda, M. Synthesis 1977, 693. 

Ketone homoenolatesAddition of BuLi to the potassium alkoxide (2) of a 3-hydroxy-l-alkene (1) results in partial isomerization via a to the corresponding... 

Potassium acetate, 20 629-630 Potassium acid tartrate, 20 637 Potassium alkoxides, 20 604-605 Potassium a-hydrohexafluoroisobutanoyl fluoride, 13 724 Potassium amides, 20 605 Potassium analysis, of water, 26 31 Potassium arsenite (Fowler s solution), 3 276... 

In this method, attack by an anionic initiator ( -BuLi, potassium alkoxides/cryptand[2.2.2],62 or silyl anions in benzene)63 occurs regioselectively on the less hindered silicon of 9, resulting in an anionically terminated disilanyl-lithium which then attacks another monomer at the less hindered silicon atom. The process continues rapidly (the reaction is usually complete within a few minutes) in a living polymerization fashion to yield 10 on alcohol workup. 

Roitman and Cram (1971) have shown that the kinetic basicity of potassium alkoxide increases on complexation with dicyclohexyl-18-crown-6 ([20] + [21]). Both the rate of isotopic exchange and the rate of racemization of (—)-4-biphenylylmethoxydeuteriomethane [163] by t-BuOK in t-BuOH were found to increase by factors between 30 and 17 000. Isotopic exchange was... 

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