Acetylene Active hydrogen

Gas-phase photolysis of diazoethane results in mixtures of ethylene, acetylene, and cis- and frans-2-butene. A mechanism involving the initial formation of ethylidene followed by formation of activated ethylene [which is collisionally deactivated or decomposes to produce acetylene and hydrogen— Eqs. (11.26(b,c,d)] or alternate attack on diazoethane to produce 2-butene [Eq. 11.26(e)] is proposed ... 

All the above-mentioned initiators are very sensitive towards substances with active hydrogen. Care must therefore be taken to exclude acids, water, thiols, amines, and acetylene derivatives. Oxygen, carbon dioxide, carbon monoxide, carbonyl compounds, and alkyl halides which can react with the initiator, also interfere with the reaction. Careful purification and drying of the starting materials and apparatus is, therefore, absolutely essential, especially when dealing with living polymers (see Example 3-19). 

The [Con(bipy)2 ]2+ species has also been reported to activate hydrogen peroxide and ter -butyl hydroperoxide for the selective ketonization of methylenic carbons, the oxidation of alcohols and aldehydes, and the dioxygenation of aryl olefins and acetylenes (36). Later reports (37), however, while confirming that the cobalt complexes did indeed cata-... 

Adsorption studies revealed that both reactants can be adsorbed on active catalysts. For the reaction of acetylene with hydrogen chloride, the... 

Hexafluoroacetone is a reactive electrophile. It reacts with activated aromatic compounds (e.g., phenol), and can be condensed with olefins, dienes, ketenes, and acetylenes. It forms adducts with many compounds containing active hydrogen (e.g., H.,0 or HCN). Reduction of HFA with NaBH or LiAlH affords the useful solvent hexafluoroisopropyl alcohol. The Industrial importance of HFA arises largely from its use 1n polymers and as an... 

Table I summarizes the application of various low-valent titanium metallocenes as catalysts for olefin hydrogenation. Compounds 10 and 37 are very effective hydrogenation catalysts for C2H4 and cyclohexene. Since different researchers have used widely varying conditions, we can only estimate that the polystyrene-supported (7j-C8H8)2Ti (142) is comparable in activity to compounds 10 and 37. When one recalls that 37 was prepared by a formal oxidation of the Ti centers in 10, it is remarkable that 37 is as good a catalyst as 10. Solutions prepared by reaction of l-methyl-17-allylbiscyclopentadienyltitanium (54) with H2 do appear to be more active hydrogenation (126) catalysts than 10 and 37. The dicarbonyl complex, (17-CsH5)2Ti(CO)2 (39), has been shown to be a catalyst for the hydrogenation of acetylene at —50 atm of H2 (143). It does not catalyze the hydrogenation of simple olefins. However, Floriani and Fachinetti discovered that if...

Finally a carbene compound with a U=C bond is Cp3U=CHPMe3.61 Various alkyl and hydrido Cp species can catalyze oligomerization of terminal acetylenes, activate C-H bonds, hydrogenate alkenes, and so on.62... 

Condensation of Acetylenes with Compounds Containing Active Hydrogen (Vinylation)... 

Acetylene is condensed to vinylacetylene and divinylacetylene by cuprous chloride and ammonium chloride. Similar additions of other compounds containing an active hydrogen atom occur in the presence of various catalysts. Mercury salts ate most effective in the vapor-phase reaction of acetylene with hydrogen chloride to give vinyl chloride (100%). Basic catalysts such as potassium hydroxide, potassium ethoxide, or zinc oxide are used for the vinylation of alcohols, glycols, amines, and acids. Most of these reactions involve the use of acetylene under pressure, and few have been described as simple laboratory procedures. Chloroacetic acid, however, reacts with acetylene at atmospheric pressure in the presence of mercuric oxide to yield vinyl chloro-acetate (49%). ... 

It is sometimes necessary to protect active sites of acetylenic compounds to achieve the desired reactions. Acetylenic compounds that have an active hydrogen tend to react with heavy-metal salts to form explosive metal acetylides. However, when treated with potassium mercuric tetraiodide or mercuric acetate in organic amines, monosubstituted terminal ethynyl compounds give stable crystalline mercuric salts. These mercuric salts can be purified by recrystallization in organic solvents and used for identification. They can be further converted to lithium acetylides, which are useful tools for chemical synthesis [Eq. (62) 156]. 

The formation of vinyl chloride from acetylene and hydrogen chloride is catalyzed by activated carbon impregnated with mercuric and mercurous chlorides.54- 5S The catalyst is prepared by saturating activated carbon with mercury vapor at 200° C and then adding hydrogen chloride to form mercuric and mercurous chlorides. 

However, conversion of the acetylenic into the olefinic bond makes special preparative demands. This half-reduction can be effected by chemical reagents as well as by catalytically activated hydrogen the stable fra .s-ethylenic stereoisomers are usually obtained by the first method, whereas the second of these methods gives predominantly the metastable cis-isomers of higher energy content. 

I Preparation of Chloroolefins and Diolefins by Hydrochlorination. When ia gaseous mixture of acetylene and hydrogen chloride is passed through a reaction chamber packed with highly activated charcoal or silica gel I impregnated with a solution containing about 20 per cent calcium chloride,... 

Activated carbon 600-1200 vinylation with acetylene, selective hydrogenation with noble metal catalysts (fine chemicals)... 

It is believed that a strong base such as KOH or potassium alkoxide will deprotonate the active hydrogen from the reactants, such as alcohols, thiols, amines, carboxylic acids, and phenols, to generate the nucleophiles that add to acetylene, as illustrated by the formation of vinyl ether from alcohol and acetylene. This can qualitatively explain the reactivity order among primary, secondary, and tertiary alcohols, without considering the steric hindrance. It is known that tertiary alcohol is less acidic than secondary and primary alcohol, therefore, less potassium f-butoxide will be formed than primary potassium alkoxide from KOH. ... 

Grignard reagents are prepared mainly by the reaction shown in eq. (4.3). The others are prepared by the reactions shown in eqs. (4.6)-(4.8). The reactions shown in eq. (4.6) are reactions with compounds having an active hydrogen. For example, the reactions with acetylenes, cyclopentadiene, indene, fluorene. 

Organomagnesium compounds easily react with compounds having an active hydrogen such as water, alcohols, amines and acetylenes, halides and carbonyl compounds. 

Isonitriles, acetylenes having an active hydrogen or alcohols react easily with platinum compounds to afford the organoplatinum compounds. For example, reactions are shown in eqs. (21.28)-(21.31) [11,90-94]. The reaction with ethyl alcohol shown in eq. (21.30), yields the Zeise salt by dehydration. This is the reaction that Zeise published in 1830 [93]. 

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