Alkynes mercuric acetate, reaction with

Alkynes react with mercuric acetate in acetic acid to give addition products. In the case of 3-hexyne, the product has -stereochemistry, but the Z-isomer is isolated from diphenylacetylene. The kinetics of the addition reaction are first-order in both alkyne and... 

The hydration of triple bonds is generally carried out with mercuric ion salts (often the sulfate or acetate) as catalysts. 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 15-16). With allqmes 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 resinsulfonic acid). ... 

The most synthetically valuable method for converting alkynes to ketones is by mercuric ion-catalyzed hydration. Terminal alkynes give methyl ketones, in accordance with the Markovnikov rule. Internal alkynes give mixtures of ketones unless some structural feature promotes regioselectivity. Reactions with Hg(OAc)2 in other nucleophilic solvents such as acetic acid or methanol proceed to (3-acetoxy- or (3-methoxyalkenylmercury intermediates,152 which can be reduced or solvolyzed to ketones. The regiochemistry is indicative of a mercurinium ion intermediate that is opened by nucleophilic attack at the more positive carbon, that is, the additions follow the Markovnikov rule. Scheme 4.8 gives some examples of alkyne hydration reactions. 

Alkenylmercury compounds can be prepared by hydroboration of an alkyne with catecholborane, followed by reaction with mercuric acetate.185... 

Cycloaddition approaches to pyrazole derivatives were employed extensively in 1997. Thus, aldhydrazones combine with mercuric acetate to form nitrileimines which react in situ with olefins to give 1,3,5-trisubstituted 2-pyrazolines <97SC3737>. Oxidation of the latter to pyrazoles with iodobenzene diacetate was reported <97SC2683>. The most common cycloaddition pathway, however, is from the reaction of alkenes or alkynes with diazo compounds. The facial selectivity of the regiospecific reactions of diazomethane (and other... 

Oxymercuration occurs with an alkyne as with an alkene, but differences in reactivity lead to a modification in the procedure. For reasons that will not be discussed, a mixture of mercuric sulfate (HgS04) and mercuric acetate [Hg(OAc)2] is used. When 1-heptyne is treated with this mixture in aqueous solvent, the initially formed enol (107) tautomerizes to 2-heptanone (108), which is isolated in 80% yield. Note that the ketone product mentioned in connection with vinyl chloride 92 in Section 10.4.5 results from formation of an enol. There is an important difference in the oxymercuration of alkynes and alkenes that is notable in this transformation. The mercury reacts with the alkyne, but the mercury is lost when the enol is formed and there is no need to add NaBH in a second step. This observation is general for oxymercuration of alkynes under these conditions. The more stable secondary vinyl carbocation is an intermediate, but the vinyl-mercury compound formed by reaction with the carbocation is unstable in the presence of water, so the enol is the product. 

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 reaction of alkynes with nitric acid or mixed acid is generally not synthetically useful. An exception is the reaction of acetylene with mixed acid or fuming nitric acid which leads to the formation of tetranitromethane. A modification to this reaction uses a mixture of anhydrous nitric acid and mercuric nitrate to form trinitromethane (nitroform) from acetylene. Nitroform is produced industrially via this method in a continuous process in 74 % yield. " The reaction of ethylene with 95-100 % nitric acid is also reported to yield nitroform (and 2-nitroethanol). The nitration of ketene with fuming nitric acid is reported to yield tetranitromethane. Tetranitromethane is conveniently synthesized in the laboratory by leaving a mixture of fuming nitric acid and acetic anhydride to stand at room temperature for several days. ... 

Methoxymercuration of diphenylacetylene by mercury(II) acetate in methanol results in a mixture of geometrical isomers 375 and 376. Internal aliphatic acetylenes yield mercurated ketones 2-nonyne, for example, gives a mixture of 377 and 378 2-heptyne behaves in an analogous fashion. The reaction of mercury(II) thiocyanate with terminal alkynes affords 379 (R = Pr, Bu, -Bu, hexyl or Ph), which are converted into unsaturated isothiocyanates 380 by acidolysis. ... 

On irradiation in the presence of alkynes the stable zwitterion (49) yields 5,7-dinitrobenzofuran (Equation (51)) <86JOC3453>. In an intramolecular alkoxymercuration reaction phenyl ethers of type (50) are cyclized with mercury(II) acetate to give mercurated benzofurans (Equation (52)) <84JA4218, 86JOC3453>. 

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