Acetylenic acids, catalytic hydration

Acetaldehyde is obtained by the catalytic hydration of acetylene or by the catalytic dehydrogenation of ethanol. Formic acid and formaldehyde are by-products of acetic acid synthesis. They are removed by distillation. Chemically pure acetic acid is diluted with water to 60-80% by volume to obtain the vinegar essence. The essence is a strongly corrosive liquid and is sold with special precautions. It is diluted further with water for production of food grade vinegar. 

A highly regioselective, efficient, and clean anti-Markovnikov hydration of terminal acetylenes has been realized through the use of catalytic amounts of Ru complexes.561 Typically, [CpRu(dppm)Cl] catalyzes the reaction at 100°C to give aldehydes in high yields (81-94%). Triflic acid or trifluoromethanesulfonimide effectively catalyzes the hydration of alkynes without a metal catalyst to afford Markovnikov products (ketones).562... 

Catalysts used to convert ethylene to vinyl acetate are closely related to those used to produce acetaldehyde from ethylene. Acetaldehyde was first produced industrially by the hydration of acetylene, but novel catalytic systems developed cooperatively by Farbwerke Hoechst and Wacker-Chemie have been used successfully to oxidize ethylene to acetaldehyde, and this process is now well established (7). However, since the largest use for acetaldehyde is as an intermediate in the production of acetic acid, the recent announcement of new processes for producing acetic acid from methanol and carbon monoxide leads one to speculate as to whether ethylene will continue to be the preferred raw material for acetaldehyde (and acetic acid). 

Catalytic conversions were experimentally studied in Russia toward the end of the nineteenth century, and especially in the twentieth century, and regularities were empirically established in a number of cases. The work of A. M. Butlerov (1878) on polymerization of olefins with sulfuric acid and boron trifluoride, hydration of acetylene to acetaldehyde over mercury salts by M. G. Kucherov (1881) and a number of catalytic reactions described by V. N. Ipatieff beginning with the turn of the century (139b) are widely known examples. S. V. Lebedev studied hydrogenation of olefins and polymerization of diolefins during the period 1908-13. Soon after World War I he developed a process for the conversion of ethanol to butadiene which is commercially used in Russia. This process has been cited as the first example of commercial application of a double catalyst. Lebedev also developed a method for the polymerization of butadiene to synthetic rubber over sodium as a catalyst. Other Russian chemists (I. A. Kondakov I. Ostromyslenskif) were previously or simultaneously active in rubber synthesis. Lebedev s students are now continuing research on catalytic formation of dienes. 

The work of Nazarov on vinyl ethynyl carbinols involves condensation of vinylacetylene with ketones in the presence of caustic potash and also their conversions, many of which are catalytic in nature. A review of his work involving polymerization, isomerization, hydrogenation, and other conversions was published by him (252). Hydration of divinylacetylenes in methanol solution in the presence of mercuric sulfate and sulfuric acid gave vinyl alkyl ketones. These can be reacted with hydrogen sulfide, amines, etc., to yield heterocyclic compounds. Substituted vinyl alkyl ketones underwent spontaneous cyclization to cyclopentenones. Nazarov summarized a decade of this research in this field in 1951 (253). His general review of organic syntheses based on acetylene is also of interest in this connection (254). 

In general, the acetylenic triple bond is highly reactive toward hydrogenation, hydroboration, and hydration in the presence of acid catalyst. Protection of a triple bond in disubstituted acetylenic compounds is possible by complex formation with octacarbonyl dicobalt [Co2(CO)g Eq. (64) 163]. The cobalt complex that forms at ordinary temperatures is stable to reduction reactions (diborane, diimides, Grignards) and to high-temperature catalytic reactions with carbon dioxide. Regeneration of the triple bond is accomplished with ferric nitrate [164], ammonium ceric nitrate [165] or trimethylamine oxide [166]. 

The catalytic activity of mercuric salts in sulfuric acid solutions for hydration of acetylenes doubtless proceeds by routes similar to the above the overall reaction is... 

Despite its own valuable synthetic potential, the use of [ C2]acetylene as a starting material for various building blocks is of much higher relevance. Mercury(II)-catalyzed hydration, for example, gives [ C2]acetaldehyde (Figure 8.5, Route 1) The same reaction carried out in the presence of ammonium persulfate furnishes [ 2] acetic acid (Route 2). Trapping of its mono- or dianion with formaldehyde or carbon dioxide affords [2,3- C2]propynol, [2,3- C2]butyne-l,4-diol, [2,3- C2]propiolic acid " and [2,3- C2]acetylenedicarboxylic acid, respectively (Routes 3-6). UV irradiation of a mixture of HBr and [ C2]acetylene produces l,2-dibromo[ C2]ethane (Route 8) . Reduction with chromium(II) chloride followed by a two-step epoxidation of the initially formed [ C2]ethylene converts [ 2]acetylene into [ C2]ethylene oxide (Route 7) . Finally, catalytic homotrimerization or co-trimerization with other alkynes provides [ " C ]benzene or substituted [ " C ]benzenes, respectively, the central starting materials for the vast majority of substituted benzenoid aromatic compounds (Route 9). 

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