Entrainment method

Organometallics. Pentachloropyridiae (47) forms Grignard reagent (48) by the entrainment method (eq. 15) (46). Addition of CO2 produces 4-carboxy-2,3,5,6-tetrachloropyridine [19340-26-2]. 

Vapor-liquid separators (drums) are used to separate a liquid from a vapor-liquid stream with a minimum of liquid carryover. The separator size is determined by the vapor velocity which depends on the entrainment method used. The working equation is ... 

The usefulness of the Grignard reagent of 3-bromothiophene is somewhat limited as it can only be prepared by the entrainment method. The simultaneous formation of Grignard reagents from 3-bromothiophene and a fivefold molar excess of ethyl bromide gave, however, a 55% yield of 3-thiophenecarboxylic acid upon carbona-tion. With acetaldehyde, a 55% yield of methyl 3-thienyl carbinol... 

This is of great preparative importance as the Grig-nard reagent of 3-bromosubstituted thiophenes and the dibromothio-phenes can be obtained only by the entrainment method and with inferior The mechanism of the entrainment reaction... 

Certain halides, notably fluorides, are comparatively inert under these reaction conditions. In such cases the entrainment method, can be used, and reduction can be accomplished in the presence of a reactive halide such as 1-bromonaphthalene or 1-bromobutane. Also with certain halides, such as chlorocyclo-hexane, the tendency for dehydrohalogenation is diminished by the use of such entraining agents. 

Although pentacblorophenylmagnesium chloride can be made in tetrahydrofuran without the use of the entrainment method, the Grignard reagent in this solvent does not react with carbon dioxide to give pentachlorobenzoic acid in good yield.10... 

The chemical entrainment method was used by Ono et al. (1979) to eliminate the nitro group in nitroalkene derivatives. On simple mixing with thiophenol and sodium sulfide in DMF, nitro aryl olefins substitute hydrogen for the nitro group (Scheme 5.9). 

If the compound under consideration proves unsuitable for the entrainment method, either because it does not form a conglomerate or because the crystallization process itself is unsatisfactory, suitable derivatives, such as salts or esters, may be used for the resolution and then these derivatives reconverted to the original compound (Table 1). 

We adopt AjH (298.15 K) = -189.0 1.5 kcal mol" and A H 341.4 3 kcal mol" based on Aj.H (298.15 K) = 0.5 1 kcal mol" for 2/3 AlClg(g) + 1/3 AlFg(g) = AlCl2P(g). Krause and Douglas ( ) obtained this result by an entrainment method which measured enhanced volatility of AlFg In the presence of AlCI. Corrections were made for all the possible dimers which can form in this system. The entrainment data establish that aluminum fluoride-chloride exchange reactions are almost thermoneutral. 

Figure 13 Proposed mechanism for the reaction of 1,2-dibromoethanc with magnesium in the entrainment method of magnesium activation.

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