Hydration of acetylenes

Much of the acetaldehyde of commerce is obtained by the hydration of acetylene in hot dilute sulphuric acid solution in the presence of mercuric sulphate as catalyst ... 

Since 1960, the Hquid-phase oxidation of ethylene has been the process of choice for the manufacture of acetaldehyde. There is, however, stiU some commercial production by the partial oxidation of ethyl alcohol and hydration of acetylene. The economics of the various processes are strongly dependent on the prices of the feedstocks. Acetaldehyde is also formed as a coproduct in the high temperature oxidation of butane. A more recently developed rhodium catalyzed process produces acetaldehyde from synthesis gas as a coproduct with ethyl alcohol and acetic acid (83—94). 

From Acetylene. Although acetaldehyde has been produced commercially by the hydration of acetylene since 1916, this procedure has been almost completely replaced by the direct oxidation of ethylene. In the hydration process, high purity acetylene under a pressure of 103.4 kPa (15 psi) is passed into a vertical reactor containing a mercury catalyst dissolved in 18—25% sulfuric acid at 70—90°C (see Acetylene-DERIVED chemicals). 

Acetaldehyde. Acetaldehyde [75-07-0] C2H4O, (qv) was formerly manufactured principally by hydration of acetylene. 

FIGURE 3.30 (a) Hydration of acetylene to acetaldehyde and (b) transformation of an isonitrile to... 

Schemes 6-20 Mechanism for transition metal-catalyzed hydration of acetylene...

The hydration of acetylenes, which usually gives aldehydes or ketones, has been widely used in industries for a long time. The hydration of acetylenes in aqueous media could date back to the 1930s, when it was reported that acetylene was converted into acetaldehyde in the presence... 

It is well known that Rh(I) complexes can catalyze the carbonylation of methanol. A heterogenized catalyst was prepared by ion exchange of zeolite X or Y with Rh cations.126 The same catalytic cycle takes place in zeolites and in solution because the activation energy is nearly the same. The specific activity in zeolites, however, is less by an order of magnitude, suggesting that the Rh sites in the zeolite are not uniformly accessible. The oxidation of camphene was performed over zeolites exchanged with different metals (Mn, Co, Cu, Ni, and Zn).127 Cu-loaded zeolites have attracted considerable attention because of their unique properties applied in catalytic redox reactions.128-130 Four different Cu sites with defined coordinations have been found.131 It was found that the zeolitic media affects strongly the catalytic activity of the Cd2+ ion sites in Cd zeolites used to catalyze the hydration of acetylene.132... 

Excess acidity correlations have been used to show that some aromatic sulfonic acid desulfonations have an A-SE2 mechanism.188,189 This mechanism (alternative terminologies are Ad-E2 and A(E) +A(N))190 has also been found to apply to the hydration of acetylene itself,191 to ynamines192 and to many other alkynes,193-195 as well as to many different alkenes196-199 and vinyl ethers.200-203 The excess acidity method has been used to evaluate aA values for several alkene hydrations.204 205... 

Although the process (a) is the only one which need he considered for laboratory purposes, the technically much more important hydration of acetylene is described here. From time to time this second process should he carried out in the laboratory.1... 

Investigations of base-catalyzed isomerizations of allene derivatives have been recently continued. For instance, the rearrangement of allene ethers 53 under superbasic conditions (KOH-DMSO) is considered as one of the steps in hydration of acetylene derivatives (equation 17)31,32. 

Oxidation of ethyl alcohol was one of the two important commercial routes to acetaldehyde until the 1950s, The other, much older route was the hydration of acetylene. The chemical industry was always after a replacement of acetylene chemistry, not just for acetaldehyde production, but all its many applications. Acetylene was expensive to produce, and with its reactive, explosive nature, it was difficult to handle. In the 1950s, acetylene chemistry and the ethyl alcohol oxidation route were largely phased out by the introduction of the liquid phase direct oxidation of ethylene. Almost all the acetaldehyde produced uses the newer process. 

Clinoptilolite Isomerization of n-butene, the dehydration of methanol to dimethyl ether, and the hydration of acetylene to acetaldehyde... 

The hydration of acetylene produces acetaldehyde which then can be converted to acetic acid and other derivatives. The process is similar to olefin hydration employing a sulfuric acid solution containing also a mercurous sulfate catalyst. 

Carboxylic esters, thiol esters, and amides can be made, respectively, by acid-catalyzed hydration of acetylenic ethers, thioethers,162 and ynamines, without a mercuric catalyst 163... 

However, the enzymology of alkene and alkyne hydration is not well known. Recently, Meckenstock et al. (1999) discovered that the enzyme responsible for anaerobic hydration of acetylene contains a tungsten atom and an [Fe-S] cluster. This may hint that the enzyme uses the tungsten as a Lewis acid to activate the double bond. Possibly, the [Fe-S] cluster then serves to deliver a hydroxide as known in many common metabolite hydrations (Flint and Allen, 1996). Having introduced an oxygen moiety in an initial hydration, anaerobic bacteria may now be able to continue the biodegradation of such compounds. 

Addition of water to unsaturated hydrocarbons (hydration) and the related addition of alcohols are important processes from both practical and chemical points of view. Alcohols and ethers are manufactured in industry by the addition of water and alcohols to alkenes. Hydration of acetylene to produce acetaldehyde, a once important process, has lost its practical importance. 

Both acid and metal catalysis are usually required to accomplish hydration of alkynes to yield carbonyl compounds.34 The addition is usually regioselective, allowing for conversion of terminal alkynes to ketones. Hydration of acetylene to produce acetaldehyde used to be an industrially significant process but was replaced by the Wacker synthesis. 

Acetaldehyde. The industrial production of acetaldehyde by the hydration of acetylene has lost its importance with the introduction of more economical petrochemical processes (dehydrogenation of ethanol, oxidation of ethylene see Section 9.5.2). At present it is practiced only in a few European countries where relatively cheap acetylene is still available.86-88... 

A RhCl3-Dowex 1 anion exchanger ion pair is an efficient and recyclable catalyst to induce hydration of acetylenes.560 Whereas the soluble ion pair mediates oligomerization, this solid catalyst transforms phenylacetylenes to the corresponding methyl ketones in high yields. 

For a long time, only a liquid phase process was employed industrially for the hydration of acetylene to acetaldehyde mercury salts in acidic solution were used as catalysts. Only recent reports can be found in the literature (e.g. ref. 300) on the industrial utilisation of the direct vapour phase hydration of acetylene over solid catalysts. 

It has been reported that solid acids and oxides or salts of different metals can catalyse the vapour phase hydration of acetylene. Most typical are phosphoric acid and phosphates of bivalent metals, such as Zn or Cd. Organic ion exchangers and synthetic zeolites exchanged for Zn2+, Cd2+, Hg2+ and Cu2+ ions were also employed. A survey of inorganic catalysts [254] or of organic ion exchangers [283] catalysing the hydration of acetylene or its derivatives can be found in literature. 

Again, these appear to resemble the corresponding Mo-dependent enzymes. The unique acetylene hydratase from the acetylene-utilizing Pelobacter acetylenicus catalyzes the hydration of acetylene to acetaldehyde.687... 

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). 

KUCHEROV REACTION. The hydration of acetylenic hydrocarbons with dilute sulfuric acid in the presence of mercuric sulfate or boron trifluoride as catalyst. 

Concerning alkynes, only the hydration of acetylene to acetaldehyde has been studied on X zeolites in Cu, Ag, Zn, Cd forms (ref. 11). These zeolites are active but they suffer fast deactivation. 

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. 

This side reaction seems to be common to all ketoximes, although the yield of other dipyrryl ethanes (98b,c) does not exceed 0.1% under normal conditions (88ZOR1789). It is likely that acetaldehyde formed due to the hydration of acetylene is involved in the condensation with pyrroles (Scheme 47). 

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