Butadiene, reaction with hydrogen cyanide

Hydrocyanation of 1,3-butadiene to a mixture of pentenenitriles and 2-methyl-3-butenenitrile (and, in a second step, their reaction with hydrogen cyanide to produce adiponitrile) has received special attention because of its commercial application. ... 

The commercial diamines used for nylon manufacture are usually best made by hydrogenation of the corresponding dinitriles. Hexamethylene-diamine is made by hydrogenation of the adiponitrile. Adiponitrile is now commercially produced by several methods. In the oldest method, ammonium adipate was catalytically dehydrated to the dinitrile. In a method developed since World War II, butadiene is treated with chlorine to produce mixture of dichlorobutenes. Reaction with hydrogen cyanide in the prewnce of cuprous halides yields l,4-dicyanobutene-2 exclusively. Hy-dn enation produces adiponitrile. 

REPPE PROCESS. Any of several processes involving reaction of acetylene (1) with formaldehyde to produce 2-butync-l,4-diol which can be converted to butadiene (2) with formaldehyde under different conditions to produce propargyl alcohol and, form this, allyl alcohol (3) with hydrogen cyanide to yield acrylonitrile (4) with alcohols to give vinyl ethers (5) with amines or phenols to give vinyl derivatives (6) with carbon monoxide and alcohols to give esters of acrylic acid (7) by polymerization to produce cyclooctatetraene and (8) with phenols to make resins. The use of catalysis, pressures up to 30 atm, and special techniques to avoid or contain explosions are important factors in these processes. 

Derivation (1) Reaction of adipic acid and ammonia (catalytic vapor phase) to yield adiponitrile, followed by liquid-phase catalytic hydrogenation. (2) Chlorination of butadiene followed by reaction with sodium cyanide (cuprous chloride catalyst) to 1,4-dicyanobutylene and hydrogenation. 

Hexamethylenediamine (HMDA) is a precursor for nylon 6/6. There are numerous routes to HMDA, but all of the commercial processes involve the synthesis of adiponitrile and the subsequent hydrogenation of adiponitrile to HMDA. The dominant process is the reaction of hydrogen cyanide with 1,3 butadiene to form adiponitrile followed by hydrogenation of adiponitrile to hexamethylene diamine. 

Copper-catalyzed monoaddition of hydrogen cyanide to conjugated alkenes proceeded very conveniently with 1,3-butadiene, but not with its methyl-substituted derivatives. The most efficient catalytic system consisted of cupric bromide associated to trichloroacetic acid, in acetonitrile at 79 °C. Under these conditions, 1,3-butadiene was converted mainly to (Z )-l-cyano-2-butene, in 68% yield. A few percents of (Z)-l-cyano-2-butene and 3-cyano-1-butene (3% and 4%, respectively) were also observed. Polymerization of the olefinic products was almost absent. The very high regioselectivity in favor of 1,4-addition of hydrogen cyanide contrasted markedly with the very low regioselectivity of acetic acid addition (vide supra). Methyl substituents on 1,3-butadiene decreased significantly the efficiency of the reaction. With isoprene and piperylene, the mononitrile yields were reduced... 

Hydrogen cyanide can be added across olefins in the presence of Ni, Co, or Pd complexes (Scheme 56) (123). Conversion of butadiene to adiponitrile is a commercial process at DuPont Co. The reaction appears to occur via oxidative addition of hydrogen cyanide to a low-valence metal, olefin insertion to the metal-hydrogen bond, and reductive elimination of the nitrile product. The overall reaction proceeds with cis... 

Hydrogen cyanide smoothly adds to butadiene (BD) in the presence of zero-valent nickel catalysts to give (3PN) and (2M3BN) [1,4- and 1,2-addition products, respectively, Eq. (7)]. A variety of Ni[P(OR)3]4 (R = alkyl or aryl) complexes are suitable as catalysts. The reaction may be carried out neat or in a variety of aromatic or nitrile solvents at temperatures from 50-120°C. Whereas in many olefin hydrocyanations it is desirable to keep the HCN concentration very low to protect the nickel from degradation, with butadiene HCN may be added batchwise as long as the HCN concentration is kept near the butadiene concentration. In the case of batch reactions one must be cautious because of possible temperature rises of 50°C or more over a period of a few minutes. Under typical batch conditions, when Ni[P(OEt)3]4, butadiene, and HCN are allowed to react in a ratio of 0.03 1.0 1.0 at 100°C for 8 hr, a 65% conversion to 3PN and 2M3BN (1.5 1) is observed (7). 

Cases in which allyl radicals display sufficient reactivity to participate successfully in radical chain reactions include the addition of bromotrichloromethane to butadiene the reaction of cyclopentadiene with tosyl cyanide, the addition of thiols , stannanes " and hydrogen halides . All these reactions follow the simple two-step radical chain mechanism depicted in Scheme 1, and the low reactivity of the intermediate allyl radicals can be compensated by using the trapping agent in excess or even as the solvent. In chain reactions with three or more chain-carrying radicals, this compensation is not possible anymore, because the concentration of the reaction partners has to be chosen such that the selectivity requirements for all intermediate radicals are satisfied. Complex radical chain reactions with polyenes as one of the reactants are therefore not known. 

The hydrogenation of 1,3-butadiene, in contrast, yields a mixture of the isomeric butenes with product distributions highly depending on reaction conditions (nature of solvent, cyanide cobalt ratio) 134-136... 

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