Nylon monomer intermediates

The development of new reaction paths to nylon monomer intermediates is an active industrial research area. Millions of kilograms of these monomers are produced each year and even small fractional improvements can have large economic impact. 

The results of the study indicated several new research directions which the research and development teams are now pursuing. 

ACS Symposium Series American Chemical Society Washington, DC, 1977. 

The ability of programs like REACT to generate reasonable and potentially Interesting reaction paths depends on the number and quality of reactions In the data base. A strong commitment to reaction doctimentatlon needs to be Initiated within a company If the conq uter program Is going to be useful. The spe-ical reactions known to the company as well as reactions reported In the open literature need to be considered. 

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Levulinic acid can be used in various heterogeneous and homogeneous catalytic reactions to provide monomer intermediates for polymers such as caprolactam, nylon and polyesters. 

Since adipic acid has been produced in commercial quantities for almost 50 years, it is not surprising that many variations and improvements have been made to the basic cyclohexane process. In general, however, the commercially important processes stiU employ two major reaction stages. The first reaction stage is the production of the intermediates cyclohexanone [108-94-1] and cyclohexanol [108-93-0], usuaHy abbreviated as KA, KA oil, ol-one, or anone-anol. The KA (ketone, alcohol), after separation from unreacted cyclohexane (which is recycled) and reaction by-products, is then converted to adipic acid by oxidation with nitric acid. An important alternative to this use of KA is its use as an intermediate in the manufacture of caprolactam, the monomer for production of nylon-6 [25038-54-4]. The latter use of KA predominates by a substantial margin on a worldwide basis, but not in the United States. 

Ammonium sulfate is also recovered as a by-product in large amounts during the coking of coal, nickel refining, and organic monomer synthesis, particularly during production of caprolactam (qv). About four metric tons of ammonium sulfate are produced per ton of caprolactam which is an intermediate in the production of nylon. 

Caprolactam [105-60-2] (2-oxohexamethyleiiiiriiQe, liexaliydro-2J -a2epin-2-one) is one of the most widely used chemical intermediates. However, almost all of the aimual production of 3.0 x 10 t is consumed as the monomer for nylon-6 fibers and plastics (see Fibers survey Polyamides, plastics). Cyclohexanone, which is the most common organic precursor of caprolactam, is made from benzene by either phenol hydrogenation or cyclohexane oxidation (see Cyclohexanoland cyclohexanone). Reaction with ammonia-derived hydroxjlamine forms cyclohexanone oxime, which undergoes molecular rearrangement to the seven-membered ring S-caprolactam. 

Butadiene is by far the most important monomer for synthetic rubber production. It can be polymerized to polybutadiene or copolymerized with styrene to styrene-butadiene rubber (SBR). Butadiene is an important intermediate for the synthesis of many chemicals such as hexa-methylenediamine and adipic acid. Both are monomers for producing nylon. Chloroprene is another butadiene derivative for the synthesis of neoprene rubber. 

KA oil is used to produce caprolactam, the monomer for nylon 6. Caprolactam is also produced from toluene through the intermediate formation of cyclohexane carboxylic acid. 

Uses Manufacture of ethylbenzene (preparation of styrene monomer), dodecylbenzene (for detergents), cyclohexane (for nylon), nitrobenzene, aniline, maleic anhydride, biphenyl, benzene hexachloride, benzene sulfonic acid, phenol, dichlorobenzenes, insecticides, pesticides, fumigants, explosives, aviation fuel, flavors, perfume, medicine, dyes, and many other organic chemicals paints, coatings, plastics and resins food processing photographic chemicals nylon intermediates paint removers rubber cement antiknock gasoline solvent for fats, waxes, resins, inks, oils, paints, plastics, and rubber. 

Conversion of polymers and biomass to chemical intermediates and monomers by using subcritical and supercritical water as the reaction solvent is probable. Reactions of cellulose in supercritical water are rapid (< 50 ms) and proceed to 100% conversion with no char formation. This shows a remarkable increase in hydrolysis products and lower pyrolysis products when compared with reactions in subcritical water. There is a jump in the reaction rate of cellulose at the critical temperature of water. If the methods used for cellulose are applied to synthetic polymers, such as PET, nylon or others, high liquid yields can be achieved although the reactions require about 10 min for complete conversion. The reason is the heterogeneous nature of the reaction system (Arai, 1998). 

Caprolactam or (hexahydroazepin-2-one) is, without doubt, the most important azepine derivative. This seven-membered lactam is produced in vast quantities as an intermediate for the manufacture of nylon 6 (B-75MI51601, B-70MI51601). Polymerization, which is carried out at high temperatures with water as the initiator or at low temperatures with a strong base (e.g. NaH), proceeds by attack at the caprolactam carbonyl by the amino function of the open-chain monomer, e -aminohexanoic acid. 

Acrylonitrile is a monomer used in high volume principally in the manufacture of acrylic fibres, resins (acrylonitrile-butadiene-styrene, styrene-acrylonitrile and others) and nitrile rubbers (butadiene-acrylonitrile). Other important uses are as an intermediate in the preparation of adiponitrile (for nylon 6/6) and acrylamide and, in the past, as a fumigant. Occupational exposures to acrylonitrile occur in its production and use in the preparation of fibres, resins and other products. It is present in cigarette smoke and has been detected rarely and at low levels in ambient air and water. 

Some of the monomers commonly used to prepare the nylon resins are shown in Ihe accompanying table. Both petrochemical and vegetable products provide the source materials that are transformed into the reactive intermediates. Tile table correctly suggests that there is a wider choice in diacids than in diamines. The most important commercial polyamide resins are nylons-66 and -6. Other commercial nylons include 610, 612, 11, and 12. 

The Beckmann rearrangement of cyclic oximes results in lactams. This is exemplified in Figure 11.38 with the generation of e-caprolactam, the monomer of nylon-6. The nitrilium ion intermediate cannot adopt the preferred linear structure because it is embedded in a seven-membered ring. Therefore, in this case the intermediate might better be described as the resonance hybride of the resonance forms A (C=N+ triple bond) and B (C+=N double bond). The C,N multiple bond in this intermediate resembles the bond between the two C atoms in benzyne that do not carry H atoms. 

The benzene-derived petrochemicals in Figure 4.15 are intermediate feedstocks for styrenic and phenolic plastics. In the styrenics chain, ethylbenzene is dehydrogenated to styrene, to be used as polystyrene monomer or as a copolymer with acrylonitrile and butadiene. In the phenolics chain, cumene is an intermediate for making phenol. Bisphenol A is the condensation product of two moles of phenol and acetone. Phenol and Bisphenol A are used to manufacture resins and polycarbonates. Phenol and cyclohexane are the starting materials for the manufacture of nylon 6. 

This type of reaction is now of major industrial importance because it constitutes a straiglitforward synthesis of nitriles. Wlien it is applied to a diolefm, such as butadiene, it leads to the formation of dinitriles, which are precursors of valuable monomers for the preparation of polymers (butadiene leads to adipo-nilrile. a nylon-b, fvprecursor). Du Font developed the first commercial process using butadiene and HCN for adiponitrile synthesis from butadiene, but this process does nut proceed through a hydrocyanation reaction it is. in fact, a copper-catalyzed halogenation reaction followed by a cyanaikm reaction (tquaiion (16)) of the chlorinated intermediate (Fquation (17)). 

Nylon-6 will undergo re-equilibration with the cyclic monomer as well as with larger cyclics at elevated temperature. This is the reverse of the polymerization process, which occurs at 200 °C and takes place through an intermediate carboxy-terminated hydrolysis fragment that undergoes intramolecular (or intermolecular) reaction to generate the cyclic monomer s-caprolactam as shown below in Scheme 1.63. 

Raney catalysts are used in a broad range of industrial hydrogenations. These include reductions of nitriles and dinitriles (e.g. for nylon intermediates), aldehydes (e.g. for sorbitol or alkane diols), olefins and alkynes (e.g. for monomer purification) and aromatic nitro compounds (e.g. for urethane intermediates). 

Primary aliphatic diamines are very important intermediates in polymer industry. Tetramethylene diamine is a monomer for polyamide 4,6. Hexame-thylene diamine is used in two main industrial productions. Copolymerisation with adipic add gives rise to nylon 6,6. Reaction with phosgene leads to isocyanates which are monomers for painting industry. Methylpenta-methylene diamine is a monomer for thermoplastics (DU PONT s DYTEK). 

Another reaction commercialized by EniChem is the ammoximation of ketones, particularly the conversion of cyclohexanone to cyclohexanone oxime (47). This latter compound is an intermediate in the manufacturing of caprolactam, the monomer for Nylon 6. This reaction, outlined in Figure 10.13, proceeds with both high conversion and selectivity for the oxime product. Again, TS-1 is uniquely active for this reaction compared to other catalysts, and TS-1 can catalyze this reaction on a variety of substrates. It is believed that in all cases the hydroxylamine is first formed, followed by reaction with the ketone. TS-1 is currently used commercially by EniChem to produce 12,000 ton per year of cyclohexanone oxime. 

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