Hydrogenation of Adiponitrile to Hexamethylenediamine

More recently, dihydrogen complexes have been patented for nitrile hydrogenation. For example, the complex Ru(7/2-H2)2(H)2(PCy3)2 (Fig. 3.6) catalyzes the hydrogenation of adiponitrile to hexamethylenediamine (HMD) in toluene at 90 °C, 70 bar H2 with TON 52, TOF 5 IT1 [68]. At intermediate conversions, the... 

Activated hollow spheres have been found to be advantageous for the hydrogenation of carbonyl compounds, nitriles, aromatics, and unsaturated C-C bounds. In the case of carbonyl conqrounds, promoters (e.g.. Mo and Cr) that exist as surface cations were found to be the most effective. In the case of nitriles, the use of promoters to stabilize the residual A1 content of the catalyst so that it can be used with base modifiers was found to be the most useful combination. An example of this was the improved performance of the LiOH treated Cr / Ni promoted Co hollow spheres for the hydrogenation of adiponitrile to hexamethylenediamine. Some reactions were found to be more sensitive to the type of promoter they require. In the case of l,4-dihydroxy-2-butyne, it was found that Mo worked satisfactory as a promoter while the Cr / Fe combination led to worse results. Nonetheless, for all of the reactions studied here it was found that the activate hollow spheres were more active than the activated tablets on both a volume and weight basis, thereby allowing increased flexibility in the use of promoters and other selectivity enhancing additives. 

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. 

The hydrogenation of functionalities in the carboxylic acid oxidation state can also be useful for small- or large-scale syntheses. For example, the hydrogenation of adiponitrile generates hexamethylenediamine that is one of the two monomers in the production of nylon. This reaction is conducted with a heterogeneous catalyst, but homogeneous catalysts for the reduction of nitriles to amines would be convenient for the conversion of nitriles to amines on a laboratory scale. The hydrogenation of esters to aldehydes would... 

Hexamethylenediamine (HMDA), a monomer for the synthesis of polyamide-6,6, is produced by catalytic hydrogenation of adiponitrile. Three processes, each based on a different reactant, produce the latter coimnercially. The original Du Pont process, still used in a few plants, starts with adipic acid made from cyclohexane adipic acid then reacts with ammonia to yield the dinitrile. This process has been replaced in many plants by the catalytic hydrocyanation of butadiene. A third route to adiponitrile is the electrolytic dimerization of acrylonitrile, the latter produced by the ammoxidation of propene. 

A process for the hydrogenation of adiponitrile and 6-aminocapronitrile to hexamethylenediamine in streams of depolymerized Nylon-6,6 or a blend of Nylon-6 and Nylon-6,6 has been described. Semi-batch and continuous hydrogenation reactions of depolymerized (ammonolysis) products were performed to study the efficacy of Raney Ni 2400 and Raney Co 2724 catalysts. The study showed signs of deactivation of Raney Ni 2400 even in the presence of caustic, whereas little or no deactivation of Raney Co 2724 was observed for the hydrogenation of the ammonolysis product. The hydrogenation products from the continuous run using Raney Co 2724 were subsequently distilled and the recycled hexamethylenediamine (HMD) monomer was polymerized with adipic acid. The properties of the polymer prepared from recycled HMD were found to be identical to that obtained from virgin HMD. 

Extraction and distillation is necessary to obtain pure adiponitrile. Even then the hexamethylenediamine made by hydrogenation of adiponitrile must also be distilled through seven columns to purify it before polymerization to nylon. Hexamethylenediamine is produced from adiponitrile by hydrogenation. 

Currently the global production of hexamethylenediamine exceeds 1.2 Mt/a and production (e.g. ICI, BASF and Rhone-Poulenc in Europe) is based on the hydrogenation of adiponitrile, largely obtained by catalytic addition of HCN to butadiene. Celanese produced hexamethylenediamine by reaction of ammonia with hexane-1,6-diol, coming from the hydrogenation of adipic acid. However, production by this method was abandoned in 1984. 

Figure 9 The hydrogenation of adiponitrile, an a,(n-dinitrile, to hexamethylenediamine via 6-aminohexanonitrile.

The main disadvantages of the present industrial process are the use of large amounts of ammonia as solvent and the degradation of the Raney nickel catalyst either by attrition or leaching (solubilization in liquid ammonia). Considerable efforts are currently being made to search for efficient and resistant catalysts for the gas phase hydrogenation of adiponitrile with high hexamethylenediamine selectivity. 

Another process to obtain hexamethylenediamine by hydrogenation has been developped by Toyo Rayon. Caprolactam and ammonia are contacted in the gas phase at 350°C to form aminocapronitrile in the presence of a phosphate catalyst. Aminocapronitrile is hydrogenated to give hexamethylenediamine in a process very simi-mar to that of the hydrogenation of adiponitrile. 

Adiponitrile is readily hydrogenated catalytically to hexamethylenediamine, which is an important starting material for the prodnction of nylons and other plastics. The electrochemical production of adiponitrile was started in the United States in 1965 at present its volume is about 200 kilotons per year. The reaction occurs at lead or cadmium cathodes with current densities of np to 200 mA/cm in phosphate buffer solutions of pH 8.5 to 9. Salts of tetrabntylammonium [N(C4H9)4] are added to the solution this cation is specihcally adsorbed on the cathode and displaces water molecules from the first solution layer at the snrface. Therefore, the concentration of proton donors is drastically rednced in the reaction zone, and the reaction follows the scheme of (15.36) rather than that of (15.35), which wonld yield propi-onitrile. 

Figure 3 Hydrogenation of recycled Nylon-6 and Nylon-6,6 ammonolysis feed in the presence of 5 g of Raney Co 2724 catalyst at a total pressure of 500 psig, and temperature of 85 to 90°C, at a feed flowrate of 12 ml/h. Hexamethylenediamine ( ), caprolactam (A), adiponitrile ( ), 6-...

Adiponitrile undergoes the typical nitrile reactions, eg, hydrolysis to adipamide and adipic acid and alcoholysis to substituted amides and esters. The most important industrial reaction is the catalytic hydrogenation to hexamethylenediamine. A variety of catalysts are used for this reduction including cobalt—nickel (46), cobalt manganese (47), cobalt boride (48), copper cobalt (49), and iron oxide (50), and Raney nickel (51). An extensive review on the hydrogenation of nitriles has been recendy published (10). 

Adipic acid so obtained is both a reactant for the production of nylon and the raw material source for hexamethylenediamine, the other reactant. The adipic acid first is converted to adiponitrile by ammonolysis and then to hexamethylenediamine by hydrogenation ... 

The hexamethylenediamine used with adipic acid to make nylon-6,6 is made by reduction of adiponitrile, prepared, in turn, by the addition of hydrogen cyanide to 1,3-... 

Nylon 6,6. Phenol is hydrogenated, or cyclohexane is cata-lytically oxidized with air, and the resulting cyclohexanol is oxidized to adipic acid. Dehydration of ammonium adipate then yields adiponitrile, which is hydrogenated to hexamethylenediamine. Equivalent amounts... 

Production of Adiponitrile. The production of adiponitrile by hydrodimerization of acrylonitrile is the only organic electrochemical process used commercially to produce a large volume of organic chemical. Throughout the world, a total of more than 100,000 metric tons per year of adiponitrile is produced by this process. Adiponitrile is hydrogenated to hexamethylenediamine which is one of the components of nylon 66. The success in this process gave a significant impact to nylon industry. 

Nylon 66 is a polymer manufactured by the condensation of adipic acid with hexamethylcnediamine, and in excess of I million ton year are manufactured in the USA atone. Adiponitrile is a convenient intermediate for the production of both hexamethylenediamine and adipic acid, the former by hydrogenation and the Latter by hydrolysis. In addition, acrylonitrile is available from the gas phase, catalytic oxy-amination of propylene. Hence, to complete the manufacture of nylon from propylene and ammonia, a procedure for the conversion of acrylonitrile to adiponitrile is required (Fig. 6.1). 

The manufacture of hexamethylenediamine is usually a two stage process. In the first stage, adiponitrile is produced, and in the second stage, adiponitrile is hydrogenated to hexamethylenediamine. Adiponitrile has been manufactured, in the main, from three feedstocks, and these will be described briefly in tixm. 

In a typical process adiponitrile is formed by the interaction of adipic acid and gaseous ammonia in the presence of a boron phosphate catalyst at 305-350°C. The adiponitrile is purified and then subjected to continuous hydrogenation at 130°C and 4000 Ibf/in (28 MPa) pressure in the presence of excess ammonia and a cobalt catalyst. By-products such as hexamethyleneimine are formed but the quantity produced is minimized by the use of excess ammonia. Pure hexamethylenediamine (boiling point 90-92°C at 14mmHg pressure, melting point 39°C) is obtained by distillation, Hexamethylenediamine is also prepared commercially from butadience. The butadiene feedstock is of relatively low cost but it does use substantial quantities of hydrogen cyanide. The process developed by Du Pont may be given schematically as ... 

Hexamethylenediamine is discussed in Chapter 10, Sections 1 and 8. It is produced from adiponitrile by hydrogenation. Adiponitrile comes from electrodimerization of acrylonitrile (32%) or from anti-Markovnikov addition of 2 moles of hydrogen cyanide to butadiene (68%). 

The manufacture of hexamethylenediamine [124-09-1], a key comonomer in nylon-6,6 production proceeds by a two-step HCN addition reaction to produce adiponitrile [111 -69-3], NCCH2CH2CH2CH2CN. The adiponitrile is then hydrogenated to produce the desired diamine. The other half of nylon-6,6, adipic acid (qv), can also be produced from butadiene by means of either of two similar routes involving the addition of CO. Reaction between the diamine and adipic acid [124-04-5] produces nylon-6,6. 

In a typical process, adipic acid is converted to the nitrile in the vapour phase by treatment with ammonia at 350—450°C using boron phosphate as catalyst. The adiponitrile is separated by distillation and then hydrogenated at 100-135°C and about 670 atmospheres. Hydrogenation is carried out in the presence of a supported cobalt catalyst and ammonia (which minimizes cyclization to hexamethyleneimine). Pure hexamethylenediamine is isolated by distillation under reduced pressure. 

Almost 250 million lb of butadiene are converted into raw materials for nylon manufacture. Butadiene reacts with hydrogen cyanide in a two-step process to give adiponitrile, which then is hydrogenated to produce hexamethylenediamine. It also can be reacted with carbon monoxide and methanol to give first a pentene ester and then the dimethyl ester of adipic acid. Hydrolysis of the ester then gives the free acid. 

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