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separating the reaction mixture into organic and aqueous layers by liquid-liquid extraction. removal of solvents by evaporation. purification by chromatography, distillation or recrystallization. The work-up steps required for a given chemical reaction may require one or more of these manipulations.
The resulting hydroquinone is poorly soluble in typical reaction solvents (dioxane, benzene, alkanes), which facilitates workup. Solutions of DDQ in benzene are red, due to the formation of a charge-transfer complex. [9]
The mechanism of the reaction involves two steps. The first step is a nucleophilic addition to the nitrile with the aid of a polarizing Lewis acid, forming an imine, which is later hydrolyzed during the aqueous workup to yield the final aryl ketone. Hoesch reaction mechanism
Grignard reagents serve as a base for non-protic substrates (this scheme does not show workup conditions, which typically includes water). Grignard reagents are basic and react with alcohols, phenols, etc. to give alkoxides (ROMgBr). The phenoxide derivative is susceptible to formylation by paraformaldehyde to give salicylaldehyde. [18]
Acid–base extraction is a subclass of liquid–liquid extractions and involves the separation of chemical species from other acidic or basic compounds. [1] It is typically performed during the work-up step following a chemical synthesis to purify crude compounds [2] and results in the product being largely free of acidic or basic impurities.
The general mechanism for primary alkyl halides is shown in the figure below. [8] Mechanism of Friedel–Crafts alkylation. For primary (and possibly secondary) alkyl halides, a carbocation-like complex with the Lewis acid, [R (+)---(X---MX n) (–)] is more likely to be involved, rather than a free carbocation.
The mechanism of the Stille reaction has been extensively studied. [11] [23] The catalytic cycle involves an oxidative addition of a halide or pseudohalide (2) to a palladium catalyst (1), transmetalation of 3 with an organotin reagent (4), and reductive elimination of 5 to yield the coupled product (7) and the regenerated palladium catalyst (1).
Upon workup by acidic hydrolysis the primary amine is liberated as the amine salt. [11] Alternatively the workup may be via the Ing–Manske procedure, involving reaction with hydrazine. This method produces a precipitate of phthalhydrazide (C 6 H 4 (CO) 2 N 2 H 2) along with the primary amine: C 6 H 4 (CO) 2 NR + N 2 H 4 → C 6 H 4 (CO) 2 N 2 ...