Quenching the reaction

Quench the reaction by adding filtered methanol. Wash the beads with filtered methanol. 

In an altogether different type of approach, the hydrazone is formed in situ as a lithium salt. Wilson et al. (80JHC389) described this approach in the one-pot synthesis of 5-aryl-2-phenylpyrazol-3-ones 72a-f from the corresponding hydrazones 65a-f (Scheme 20). The latter were obtained by condensing ketones 64a-f with phenylhydrazine. Treatment of hydrazones 65a-f with n-butyllithium in dry THF, followed by the addition of half a molar equivalent of diethyl carbonate 67 and then quenching the reaction mixture with hydrochloric acid, produced pyrazol-3-ones 72a-f, along with products 71. The yields of the products 72 are in the range 22-97%. Four intermediates—66a-f, 68a-f, 69a-f, and 70a-f— were proposed for this reaction. 

A dicarbocyanine dye, dithiazinine (79), is used as a broad-spectrum anthelmentic agent, although, interestingly, it seems to have been prepared initially for use in photographic emulsions. It is made by heating 2-methylbenzothiazole ethiodide (77) with the malondialdehyde equivalent, B(ethylmercapto)-acrolein diethylacetal (78) in the presence of pyridine. There apparently ensues a sequence of addition-elimination reactions quenching the reaction mixture with potassium iodide solution results in separation of green crystals of dithiazanine iodide (79). ... 

The reaction of butyllithium and /erf-butyl-1-naphthyl sulfone in diethyl ether at reflux for 5 hours followed by quenching the reaction mixture with water gives trans-X,2-dihydro-1-/m-butylsulfonyl-2-butylnaphthalene 2 3. 

The first report of the use of bromine for the oxidation of sulphoxides appeared in 1966116. Diphenyl sulphone was isolated in 0.5-1% yield when the sulphoxide was treated with bromine in aqueous acetic acid for several hours. The yield was increased to about 5% by quenching the reaction with sodium carbonate. A kinetic study117 of a similar reaction involving dimethyl sulphoxide showed no significant yield improvement but postulated that the mechanism proceeds via an equilibrium step forming a bromosulph-onium type intermediate which reacted slowly with water giving dimethyl sulphone as indicated in equation (35). 

The checkers found that this purification of ethylene was not necessary. Without the purification, the checkers obtained the product quantitatively after purification by chromatography and in 97% yield after distillation. Ethyl vinyl ether is added to quench the reaction.5... 

C. (.Z)-l-(l-Heptenyl)-l,l-dimethylsilanol. A solution of 13.0 g (58 mmol) of (Z)-1 -iodo-1 -heptene in 50 mL of ether is placed in a flame-dried, three-necked, 300-mL, round-bottomed flask equipped with stirbar, septum, temperature probe, and N2 inlet. The solution is cooled to -72°C and a solution of n-BuLi in hexane (Note 4) (35.6 mL, 1.63M, 58 mmol) is then added by syringe over 15 min. The mixture is stirred at -72°C for 30 min and then a solution of 4.30 g (19.3 mmol) of hexamethylcyclotrisiloxane (Note 17) in 50 mL of ether is added over 15 min. The cooling bath is removed, and the reaction solution is allowed to warm to room temperature and stirred for 14 hr. The solution is then cooled to 0°C and 50 mL of water is slowly added to quench the reaction. The aqueous layer is separated and extracted with three 50-mL portions of diethyl ether. The combined organic phases are washed with 30 mL of water and two 30-mL portions of brine, dried over anhydrous MgS04, filtered, and concentrated by rotary evaporator and vacuum drying to give a crude product which is distilled to afford 7.34 g (73%) of (Z)-1 -(1 -heptcnyl)-1,1 -dimcthylsilanol as a colorless liquid, bp 54-55°C at 0.15 mm (lit.3 120°C at 0.9 mm) (Notes 18, 19). 

Under the conditions of the Birch reduction, IV-Boc amides such as 60 can be reductively alkylated in high yields, presumably via a dianion intermediate which is protonated by ammonia at C-5 leaving an enolate anion at C-2 <96JOC7664>. Quenching the reaction with alkyl halides or ammonium chloride then affords the 3-pyrrolines 61. 

Fig. 9. The MoFe protein cycle of molybdenum nitrogenase. This cycle depicts a plausible sequence of events in the reduction of N2 to 2NH3 + H2. The scheme is based on well-characterized model chemistry (15, 105) and on the pre-steady-state kinetics of product formation by nitrogenase (102). The enzymic process has not been chsiracter-ized beyond M5 because the chemicals used to quench the reactions hydrolyze metal nitrides. As in Fig. 8, M represents an aji half of the MoFe protein. Subscripts 0-7 indicate the number of electrons trsmsferred to M from the Fe protein via the cycle of Fig. 8.

In order to get reliable information about the yield of organoaluminum compounds formed in a transition metal-catalyzed hydroalumination reaction it is essential to derivatize the organometallic products by quenching the reaction mixture with electrophiles like D2O, O2 or halogens. It is often observed that hydrogenation... 

A study aimed at optimizing yields in this reaction found that carbinol formation was a major competing process if the reaction was not carried out in such a way that all of the lithium compound was consumed prior to hydrolysis.113 Any excess lithium reagent that is present reacts extremely rapidly with the ketone as it is formed by hydrolysis. Another way to avoid the problem of carbinol formation is to quench the reaction mixture with trimethylsilyl chloride.114 This procedure generates the disilyl acetal, which is stable until hydrolysis. 

With the reaction performance improved, attention turned to isolation of 3. The work-up of this reaction was complicated by the solubility of TH F in water and the low solubility of 3 in most organic solvents. Using extraction to remove residual magnesium salts would have severely limited volumetric productivity. We found that 3 could be isolated by quenching the reaction into aqueous HC1. Crude 3 was isolated after concentrating the organic layer. Residual TH F and magnesium salts were then removed by recrystallization from AcOH/water with less than 1% loss of 3. 

The IR showed the complete disappearance of the OH stretch of 46 after 0.5 equiv of Red-AI was added. Quenching the reaction at this stage resulted only in the recovery of starting material. However, the addition of an additional 1.0 equiv of Red-Ad to intermediate 83 led to the rapid formation of 48 and 10. It was speculated that the addition of the excess Red-AI led to the formation of 84 [31], where... 

To obtain the polyurethanes, typically a prepolymer was first prepared by reacting the diisocyanate with various diols in dimethylformamide or dimethylacetamide in a two to one molar ratio at 100-110°C for two hours under nitrogen atmosphere. A solution of chain extenders, such as BEP, was then added to the prepolymer reaction mixture and further reacted another three hours. The polymer was isolated by quenching the reaction mixture in cold water. Fine white powder was obtained with a typical yield of around 90%. 

When we allowed pentafluorophenyl-lithium to decompose in ether in the presence of an excess of N, ZV-dimethy laniline we obtained the compounds (92) 70, X = F), (94), the latter as the major compound, and a product which was shown to be (97). That this latter compound did not arise by metallation of 2V,lV-dimethylaniline followed by addition to tetrafluorobenzyne was shown by quenching the reaction mixture with deuterium oxide. No deuterium incorporation was detected. The compound (97) provides a rare example of a product derived by a Stevens rearrangement in which aryl migration has occurred b>. 

It is important to quench the reaction into the acidic ethanol. If the quench solution is added to the reaction mixture, very little product is obtained. 

Quench the reaction by immediate gel filtration using a column of Sephadex G-25 (Pharmacia). Equilibrate the column and perform the chromatography using 0.2M sodium borate, pH 9.0, so that the protein will be at the proper pH for the reduction step. After the separation, a determination of the modification level may be done by measuring its absorbance at 428 nm. 

Add 2-mercaptoethanol to the reaction solution to obtain a final concentration of 20 mM. Mix and incubate for 10 minutes at room temperature. Note If the protein being activated is sensitive to this level of 2-mercaptoethanol, instead of quenching the reaction chemically, the activation may be terminated by desalting (step 5). 

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