Quenching with alcohol

The principal impurity in potassium metal is sodium. Potassium s purity can be accurately deterrnined by a melting point test (Fig. 2) or atomic absorption if necessary after quenching with alcohol and water. Traces of nonmetallic impurities such as oxygen, carbon, and hydrogen can be deterrnined by various chemical and physical methods (7,8). 

The standard method for synthesis of polysilanes follows the original preparation of (Me2Si) by Burkhard. Diorganodichlorosilanes are treated with finely dispersed sodium metal in an inert diluent, usually above the melting point of sodium. Homopolymers are obtained from single dichlorosilanes, while cocondensation of mixtures of dichlorosilanes yields copolymers (equation 33). Toluene is the most commonly used solvent, but other aliphatic or aromatic solvents are also effective. After completion of the reaction, the mixture is quenched with alcohol and/or water to destroy any excess sodium and silyl anion, then filtered and... 

Polymerizations are typically quenched with water, alcohol, or base. The resulting polymerizates are then distilled and steam and/or vacuum stripped to yield hard resin. Hydrocarbon resins may also be precipitated by the addition of the quenched reaction mixture to an excess of an appropriate poor solvent. As an example, aUphatic C-5 resins are readily precipitated in acetone, while a more polar solvent such as methanol is better suited for aromatic C-9 resins. 

Homoallyl alcohol (3) Metalation of (E) butene (1 05 equiv) with n BuLI (t equiv) and KOtBu (1 equiv) in THF at SO C for 15 mm followed by treatment of (E)-crotyl potassum salt with B(OiPr)3 at 79°C gave after quenching with 1 N HCI and extraction with EtjO containing 1 equiv of diisopropyl tartarate. the crotyl boronate 2 A solution of decanall (156 mg 1 mmol) was added to a toluene solution of 2 (1 1 15 equiv) (0 2 M) at 78 C containing 4A molecular sieves (15-20 mg/L) After 3 h at -78°1 N NaOH was added, followed by extraction and chromatography to afford 208 mg of 3 (90%), anti syn 99 1... 

Me2BBr, TEA, BH3-THF, —78° warm to —20° over 1 h, 70-97% yield. These conditions cleave the benzylidene acetal, to leave the least hindered alcohol as a free hydroxyl. If diborane is omitted from the reaction mixture and the reaction is quenched with PhSH and TEA, the benzylidene group is cleaved to give an (9,5 -acetal [ROCH(SPh)Ph]. Acetonides are cleaved similarly." ... 

Durst and coworkers were the first to report the condensation of chiral a-sulphinyl carbanions with carbonyl compounds477. They found that metallation of ( + )-(S)-benzyl methyl sulphoxide 397 followed by quenching with acetone gives a mixture of dia-stereoisomeric /i-hydroxy sulphoxides 398 in a 15 1 ratio (equation 233). The synthesis of optically active oxiranes was based on this reaction (equation 234). In this context, it is interesting to point out that condensation of benzyl phenyl sulphoxide with benzaldehyde gave a mixture of four / -sulphinyl alcohols (40% overall yield), the ratio of which after immediate work-up was 41 19 8 32478. 

Previous syntheses of terminal alkynes from aldehydes employed Wittig methodology with phosphonium ylides and phosphonates. 6 7 The DuPont procedure circumvents the use of phosphorus compounds by using lithiated dichloromethane as the source of the terminal carbon. The intermediate lithioalkyne 4 can be quenched with water to provide the terminal alkyne or with various electrophiles, as in the present case, to yield propargylic alcohols, alkynylsilanes, or internal alkynes. Enantioenriched terminal alkynylcarbinols can also be prepared from allylic alcohols by Sharpless epoxidation and subsequent basic elimination of the derived chloro- or bromomethyl epoxide (eq 5). A related method entails Sharpless asymmetric dihydroxylation of an allylic chloride and base treatment of the acetonide derivative.8 In these approaches the product and starting material contain the same number of carbons. 

A porphinatoaluminum alkoxide is reported to be a superior initiator of c-caprolactone polymerization (44,45). A living polymer with a narrow molecular weight distribution (M /Mjj = 1.08) is ob-tmned under conditions of high conversion, in part because steric hindrance at the catalyst site reduces intra- and intermolecular transesterification. Treatment with alcohols does not quench the catalytic activity although methanol serves as a coinitiator in the presence of the aluminum species. The immortal nature of the system has been demonstrated by preparation of an AB block copolymer with ethylene oxide. The order of reactivity is e-lactone > p-lactone. 

On reaction with Li-HMDS 492 and subsequent treatment with MegSiCl 14 a-ketoesters such as 512 afford N-silylated Schiff bases such as 513, which can be reduced to amino acids 514 or amino alcohols 515 and dimerized with methanol or H2O to give the imidazolone 516 [95]. Analogous treatment of benzil with Li-HMDS 492 and quenching with Me3SiCl 14 gives 517, which reacts with the Li-enolate of methyl isobutyrate 498 at 78 °C in THF to give the adduct 518 in 75%... 

Photocycloaddition of allene to cyclohexenone (341) gave the (3,y-enone (342), which reacted with vinyl magnesium bromide to produce the tertiary alcohol (343) in 79% yield. When the compound (343) was treated with KH and 18-crown-6 in THF at room temperature for two hours and quenched with aq. NH4C1, the cyclobutene (344) was obtained. The thermal ring opening of the cyclobutene (344) proceeded in toluene in a sealed-tube at 180 °C for twelve hours to give a readily separable 5 1 mixture of the civ-olefin (345), and the trans-olefin (346) respectively in 95 % yield. Moreover, (345) could be converted to a mixture of (346) and (345) in the ratio of 10 1 by irradiation. The compounds (345) and (346) possess the skeleton of the germacranes (347), (348) and (349) 122). 

A single example of allene formation was briefly described for a reaction of 2-methylbut-l-en-3-yne (148) with catecholborane (149) [116]. The allenylborane 150 was not isolated but converted into the homopropargyl alcohol 151 in 57% yield by quenching with benzaldehyde (Scheme 3.76). 

Method B (catalysed by polymer-supported chiral fl-hydroxyamines) The aldehyde (1 mmol) is added to the polymer-supported catalyst (0.298 g) in n-C6Hu (2 ml) at 0°C and the mixture is stirred for 15 min. The dialkylzinc (1M in rt-C6H 4, 2.2 ml) is added and the mixture is stirred for 1-8 days at 0°C. The reaction is quenched with aqueous HCI (1M, 5 ml) and the mixture is filtered and extracted with CH2C12 (3x10 ml). The dried (Na2S04) extracts are evaporated to yield the chiral secondary alcohol. 

Oxidation of alcohols to the corresponding carbonyl compounds using (COCl)2, DMSO, and quenching with EtsN. 

---