Acetylene, hydrocyanation

Xl80" Acetylene Hydrocyanic acid Band spectra... 

Hydrocyanation of acetylene is catalyzed by an aqueous solution of copper(I) chloride and ammonium chloride however, byproducts are also formed, viz., acetaldehyde and vinylacetylene, the latter arising by dimerization of acetylenes. Hydrocyanation, followed by reduction of alkynes leading to secondary nitriles, is catalyzed by Co(CN)5 in the atmosphere of H2 or by Ni(CN)4 in the presence of BH4 cyanide. 

Irradiation of ethyleneimine (341,342) with light of short wavelength ia the gas phase has been carried out direcdy and with sensitization (343—349). Photolysis products found were hydrogen, nitrogen, ethylene, ammonium, saturated hydrocarbons (methane, ethane, propane, / -butane), and the dimer of the ethyleneimino radical. The nature and the amount of the reaction products is highly dependent on the conditions used. For example, the photoproducts identified ia a fast flow photoreactor iacluded hydrocyanic acid and acetonitrile (345), ia addition to those found ia a steady state system. The reaction of hydrogen radicals with ethyleneimine results ia the formation of hydrocyanic acid ia addition to methane (350). Important processes ia the photolysis of ethyleneimine are nitrene extmsion and homolysis of the N—H bond, as suggested and simulated by ab initio SCF calculations (351). The occurrence of ethyleneimine as an iatermediate ia the photolytic formation of hydrocyanic acid from acetylene and ammonia ia the atmosphere of the planet Jupiter has been postulated (352), but is disputed (353). 

Nickel plays a role in the Reppe polymeriza tion of acetylene where nickel salts act as catalysts to form cyclooctatetraene (62) the reduction of nickel haUdes by sodium cyclopentadienide to form nickelocene [1271 -28-9] (63) the synthesis of cyclododecatrienenickel [39330-67-1] (64) and formation from elemental nickel powder and other reagents of nickel(0) complexes that serve as catalysts for oligomerization and hydrocyanation reactions (65). 

Acetylene, fulminic acid (produced in ethanol - nitric acid mixtures), ammonia Acetic acid, acetone, alcohol, aniline, chromic acid, hydrocyanic acid, hydrogen sulphide, flammable liquids, flammable gases, or nitratable substances, paper, cardboard or rags Inorganic bases, amines Silver, mercury... 

Chlorine dioxide Copper Fluorine Hydrazine Hydrocarbons (benzene, butane, propane, gasoline, turpentine, etc) Hydrocyanic acid Hydrofluoric acid, anhydrous (hydrogen fluoride) Hydrogen peroxide Ammonia, methane, phosphine or hydrogen sulphide Acetylene, hydrogen peroxide Isolate from everything Hydrogen peroxide, nitric acid, or any other oxidant Fluorine, chlorine, bromine, chromic acid, peroxide Nitric acid, alkalis Ammonia, aqueous or anhydrous Copper, chromium, iron, most metals or their salts, any flammable liquid, combustible materials, aniline, nitromethane... 

Acrylonitrile was first produced in Germany and the United States on an industrial scale in the early 1940s. These processes were based on the catalytic dehydration of ethylene cyanohydrin. Ethylene cyanohydrin was produced from ethylene oxide and aqueous hydrocyanic acid at 60°C in the presence of a basic catalyst. The intermediate was then dehydrated in the liquid phase at 200°C in the presence of magnesium carbonate and alkaline or alkaline earth salts of fonnic acid. A second commercial route to acrylonitrile was the catalytic addition of hydrogen cyanide to acetylene. The last commercial plants using these process technologies were shut down in 1970 (Langvardt, 1985 Brazdil, 1991). 

The interaction of unsaturated molecules, for example olefins and acetylenes, with transition metals is of paramount importance for a variety of chemical processes. Included among such processes are stereospecific polymerization of olefin monomers, the production of alcohols and aldehydes in the hydroformylation reaction, hydrogenation reactions, cyclo-propanation, isomerizations, hydrocyanation, and many other reactions. 

As shown in Appendix 1, the pKa value for hydrocyanic acid is approximately 9.3, and the pKa value for acetylene is approximately 25. Thus, the acetylene anion is more reactive than the cyanide anion and is therefore the better nucleophile. 

The union of acetylene and nitrogen to hydrocyanic acid takes place rather smoothly if the easy clecomposability of acetylene is lessened by dilution with hydrogen, as was already done by Berthelot.6 His experiments were recently again taken up by Gruszkiewicz.7 The electrodes were blackened by a deposition of carbon except with a maximum content of acetylene of 5 per cent, by volume (composition of tne gas mixture 5 per cent, acetylene, 5 per cent, nitrogen and 90 per cent, hydrogen). 

Cyanogen shows the same easy decomposability as hydrocyanic acid. Both Berthelot1 and Hofmann and Buff2 observed that cyanogen was decomposed into its elements by the action of the electric spark. The least trace of water in the gas caused the formation of hydrocyanic acid and acetylene. 

Aniline.—Destrem3 investigated the action of the electric-spark from an induction apparatus on aniline vapor, and observed a decomposition into acetylene, hydrogen, hydrocyanic acid, and nitrogen. 

The polymer of methyl methacrylate (MMA) is known as Perspex. It is a clear transparent glasslike material with high hardness, resistance to fracture, and chemical stability. The conventional route, as shown by reaction 4.10, involves the reaction between acetone and hydrocyanic acid, followed by sequential hydrolysis, dehydration, and esterification. This process generates large quantities of solid wastes. An alternative route based on a homogeneous palladium catalyst has recently been developed by Shell. In this process a palladium complex catalyzes the reaction between propyne (methyl acetylene), methanol, and carbon monoxide. This is shown by reaction 4.11. The desired product is formed with a regioselectivity that could be as high as 99.95%. 

M. HYDROCYANATION 01 UNSATURATED HYDROC ARBONS 2.1.1. Hytirocyanation of Acetylene... 

The first mechanism is. in fact, reminiscent of the well-known copper-catalyzed dimerization of acetylene viny(acetylene being the main by-product of this process. This side reaction can, however, be inhibited to some extent by the use of cobalt salts as additives [IS]. The cyanation of acetylene and of alkenyl halides is also promoted by Co and Ni cyanides and Pd catalysis. A reducing reagent, such as Zn or NaBll4, has been used in conjunction with cobalt cyanide complexes, and the formation of. succinonitrile has been reported to result from the basebase-catalyzed hydrocyanation of acrylonitrile. 

Catalytic hydrocyanalion of acetylenes. Acetylenes are hydrocyanated to saturated secondary nitriles by 1 with excess cyanide ion and either NaBH, (in ethylene glycol) or Zn (in water) as reducing agent. Terminal acetylenes RC=CH afford RCH(CN)CH3 in high yield, whereas internal acetylenes afford a mixture of regioisomers. 

Hydrocyanic acid may be prepared in various ways by passing electric sparks through a mixture of acetylene and nitrogen,... 

From Acetylene.—The second synthesis of hydrocyanic acid supporting this same constitution is from acetylene by reaction with nitrogen under the influence of an electrical discharge. The nitrogen would split the acetylene molecule at the triple linkage of the two carbons leaving each hydrogen linked to carbon in the hydrocyanic acid. 

Many other addition reactions of olefins, dienes, and acetylenes are known, which are catalyzed by metal carbonyls including Ni(CO)4, Fe(CO)5, and Co2(CO)8 and by carbonyl derivatives such as hydrocarbonyls or phosphine-substituted carbonyls. Among these are the hydro-carboxylation, hydroesterification, and hydrocyanation of olefins the synthesis of hydroquiniones from acetylenes, carbon monoxide, and water ... 

The addition [44] of hydrocyanic acid to acetylene (eq. (20)) in a solution of copper chloride in aqueous hydrochloric acid gives good yields and, prior to the time when the synthesis of acrylonitrile by ammonoxidation [45] from propene became technically feasible, was the major preparation process. This synthesis, too, has nowadays completely lost its importance. 

Alkynes are readily hydrocyanated in the presence of a homogeneous catalyst, especially a nickel-based catalyst system. However, zerovalent palladium compounds are reported to catalyze the reaction as well, but are less efficient [60], The reaction gives an easy access to the synthetically valuable a,P-un-saturated nitriles. The use of acetone cyanohydrin as a synthetic equivalent for the difficult-to-handle HCN provides an efficient alternative, but the substrate/ catalyst ratio has to be increased in comparison with the reaction with HCN. The regioselectivity of the reaction is controlled by steric, electronic, and chelative effects. Investigations were predominantly performed by changing the substituent pattern on the acetylenic substrate [61]. 

Derivation (1) Condensation of ethylene oxide with hydrocyanic acid followed by reaction with sulfuric acid at 320F (2) acetylene, carbon monoxide, and water, with nickel catalyst (3) propylene is vapor oxidized to acrolein, which is oxidized to acrylic acid at 300C with molybdenum-vanadium catalyst (4) hydrolysis of acrylonitrile. 

Familiar combinations include Y = H, X = olefin, acetylene, or diene Y = alkyl, X = CO Y = OH or OR, X = CO or olefin. Such reactions constitute important routes for addition to unsaturated molecules, and thus play a widespread role in catalytic reaction processes such as hydrogenation, hydrosilylation, and hydrocyanation of olefins, car-bonylation, etc. ... 

Dewar, who was then working with Kekule, also announced in 1870 pyridine may be written graphically as benzol in which nitrogen functions in place of the triatomic residue CH ". .. Thus as three molecules of acetylene condense and form benzol, so may two molecules of acetylene and one of hydrocyanic acid condense and form pyridine. (2C2H2 + HCN = C5H6N.) This was verified in Dewar s laboratory by Ramsay, who passed acetylene and hydrocyanic acid through a red-hot tube and obtained a trace of pyridine, identified only by its smell. 

The chemistry of vinylsilanes has also seen some interesting developments. A high level of regio- and stereo-selectivity is observed in the Pd(II)-catalysed addition of Me SiCN to terminal aryl acetylenes (ArCSCH) to give -(12 ) in good yield.Similarly vinylsilanes (128) and (129) have been obtained by a Ni(0)-catalysed hydrocyanation (Scheme 40) the regiocheraistry of addition of HCN is controlled by the bulk of the silyl residue. 

Although less studied, the hydrocyanation of alkynes in the presence of soluble transition metal complexes has also been reported. - The reactions conducted with nickel(O) catalysts occur with cis stereochemistry, high regioselectivity, and moderate-to-high yields. Again, both steric and electronic effects control the regioselectivity. These points are illustrated by the data in Equation 16.11. Terminal, straight-chain alkynes such as l-hex)me react to form predominantly the branched nitrile, whereas tert-butyl acetylene reacts to form mostly the terminal nitrile. Reactions conducted with DCN have shown that the addition occurs in a syn fashion. ... 

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