Mercuric salts, reaction with alkynes

Direct mercuration of alkynes has also been achieved. " The interest in mercury alkynyls stems from their documented applications in the rapid separation and detection of toxic organomercurials (particularly, methylmercury derivatives). Upon reaction with alkynes, samples containing methylmercury salts yield Hg(C=CR)2 or Hg(Me)(C=CR) species that can then be analyzed using chromatographic techniques. 

The iodination reaction can also be conducted with iodine monochloride in the presence of sodium acetate (240) or iodine in the presence of water or methanolic sodium acetate (241). Under these mild conditions functionalized alkenes can be transformed into the corresponding iodides. AppHcation of B-alkyl-9-BBN derivatives in the chlorination and dark bromination reactions allows better utilization of alkyl groups (235,242). An indirect stereoselective procedure for the conversion of alkynes into (H)-1-ha1o-1-alkenes is based on the mercuration reaction of boronic acids followed by in situ bromination or iodination of the intermediate mercuric salts (243). 

The hydration of triple bonds is generally carried out with mercuric ion salts (often the sulfate or acetate) as catalysts.159 Mercuric oxide in the presence of an acid is also a common reagent. Since the addition follows Markovnikov s rule, only acetylene gives an aldehyde. All other triple-bond compounds give ketones (for a method of reversing the orientation for terminal alkynes, see 5-12), With alkynes of the form RC=CH methyl ketones are formed almost exclusively, but with RC=CR both possible products are usually obtained. The reaction can be conveniently carried out with a catalyst prepared by impregnating mercuric oxide onto Nafion-H (a superacidic perfluorinated resinsuifonic acid).160... 

The hydration reaction of alkynes leading to carbonyl compounds is generally carried out in dilute acidic conditions with mercuric 1on salts (often the sulfate) as catalysts (ref. 5). Only very reactive alkynes (phenylacety-lene and derivatives) can be hydrated in strong acidic conditions (HgSO ) without mercury salts (ref. 6). Mercury exchanged or impregnated sulfonic resins have also been used in such reactions (ref. 7). Nevertheless, the loss of the catalyst during the reaction and environmental problems due to the use of mercury make this reaction method not as convenient as it should be for the preparation of carbonyl compounds. 

This reaction was first reported by Fittig and Schrohe in 1875 and subsequently extended by Kutscheroff in 1881. It is an acid-catalyzed hydration of alkynes into ketones. In this reaction, dilute sulfuric acid and mercuric salt are used as catalysts, and mercuric chloride can form a complex with acetylene in aqueous solution. This reaction has been used to prepare ketones from higher alkynes, such as propyne, and vinylacetylene as well as in commercial production of acetaldehyde from acetylene. ... 

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