1 - -1 -propyne, hydration

Acetylenic compounds may in some cases be suitable sources of 1,3-dioxo precursors as shown for propynal in the synthesis of 85a-d.62,l27 131 Similarly, the preparation of probable 4//-pyran derivative 91 (61.7%) may be explained by a hydration catalyzed with Zn2+ ions, which leads to a 1,5-dicarbonyl intermediate.138... 

The syntheses of findersine (92a) and its methoxy derivative 92b (28 and 35%, respectively) starting from thallous salts of corresponding 2,4-dihy-droxyquinolines and 3-chloro-3-methyl-l-propyne, on the other hand, did not apparently involve a hydration step. 

The so-called trimerization of propynal in the presence of piperidine acetate provides a synthesis of 4-ethynyI-4//-pyran-3,5-dicarbaldehyde (149) (50LA(568)34> it should be noted that the structure proposed for the product in the original work has been corrected (64CB1959). In the absence of moisture, the reaction fails and it seems likely that the synthesis involves hydration of the alkyne to the divinyl ether. Finally, condensation with the third molecule of the aldehyde results in cyclization to the product (Scheme 20). 

In aqueous 5M HC1, solutions of ruthenium chloride catalyze the hydration of acetylene, giving acetaldehyde (equation 166).614 Propyne reacted to give acetone. The reaction is inhibited by high or low chloride concentrations. The mechanism proposed is given in Scheme 60. 

The addition of water to an alkyne leads to the formation of an unstable vinyl alcohol. These unstable materials undergo keto-enol tautomerization to form ketones. The hydration of propyne forms 2-propanone, as the following figure illustrates. 

Problem 8.6 Hydration of propyne yields the ketone acetone, CH3COCH3, rather than the aldehyde CH3CH2CHO. What docs this suggest about the orientation of the initial addition ... 

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. ... 

The mechanism of this reaction is illustrated by the hydration of propyne to give... 

Problem 6.12. What are the products obtained on the mercury (Il)-catalyzed hydration of (a) ethyne (acetylene, HC=CH), (b) propyne (methylacetylene, CHjC CH), and (c) 2-butyne (dimethylacetylene, CHsC CCHs) Because ethyne (acetylene, HC=CH) and 2-butyne (dimethyl-acetylene, CHsC CCHs) are symmetrical, the carbon-carbon triple bond stretching frequency is IR inactive (Raman active) and... 

On one hand, the aliphatic acetylenic alcohols are relatively stable in the acid itself (in protonated form) and undergo reaction only in the presence of an electroactive metal surface. On the other hand, aromatic acetylenic alcohols tend to react further with the acid, as well as with the metal surface, forming products which themselves are active inhibitors. - These secondary products may function as intermediates and continue to react, either on the surface or in solution, to yield an adherent low-molecular-weight polymer film. For example, 3-phenyl-2-propyn-1-ol undergoes acid-catalyzed hydrolysis (protonation and hydration) in the solution to... 

In contrast, 1-phenyl-2-propyn-1-ol undergoes protonation and dehydration, followed by hydration and deprotonation. ... 

Give the products of mercuric ion-catalyzed hydration of (a) ethyne (b) propyne (c) 1-butyne (d) 2-butyne (e) 2-methyl-3-hexyne. 

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