Caprolactam Production schemes

A few caprolactam containing PILs were successfully used as solvents and catalysts for the Beckmann rearrangement of cyclohexanone to produce caprolactam. Unusually, the caprolactam product is the same as the neutral form of the cation in the PIL, shown in Scheme 15. The caprolactam BF4 PIL under optimized conditions led to yields of 93% with 89% selectivity. In comparison, under the same conditions, [HMIm]BF4 only had yields of 44% with 33% selectivity, showing the particular suitability of the caprolactam containing PILs for this reaction. Other anions were trialed with the caprolactam cation with good performance, though the BF4 anion gave the best results. ... 

However, recent research agrees that the main route of thermal degradation of PA-6 is the formation of caprolactam with yields as high as 85% - the presence of oligomeric products with nitrile and vinyl chain ends, which are formed as a result of depolymerisation, has been confirmed 890179 [a.l7, a.ll4j. The increase of reaction order of the overall decomposition of PA-6 above 420 C is correlated with the formation of by-products. Especially, the formation of the cyclic dimer seems to be a second-order reaction, which is responsible for the increase of the overall reaction order. The observed first-order reaction of E-caprolactam formation (Table 3) is consistent with the mechanism of cfs-elimination suggested, whereby the ds-elimination proceeds via a six-membered intermediate product (Scheme 12) [a.ll4] Table 3 [a.ll5] provides kinetic data. 

In analogy, Ugi et al. reported on a lactam formation by running a one-pot three components reaction the condensation of L-lysine 7, isobutyraldehyde and methyl isocyanide led to the corresponding a-amino-c-caprolactam 9, but the yield was not given. The authors presumed either a nucleophilic substitution of the ester 8 as the primary Ugi product by the amino function of the side chain or, alternatively, the nucleophilic attack of the NH2-group on an intermediately formed 0-acylamide and a subsequent rearrangement (Scheme 1) [4]. 

Sticking with nylon production, high-silica pentasil zeolites are used by Sumitomo to overcome environmental issues associated with the conversion of cyclohexanone oxime to caprolactam (Chapter 1, Scheme 1.4). 

Currently, cyclohexanone oxime is synthesized starting from cyclohexanone and hy-droxylamine (Route A, Scheme 30) or by photonitrosation of cyclohexane with NOCl (PNC process. Route B, Scheme 30). Of these approaches. Route A is most often employed and accounts for about 70% of the total production of e-caprolactam worldwide. However, this method has several drawbacks. ... 

Note also that nylon-6 was listed in Table 2-2 as the product of the ringopening polymerization of the cyclic monomer caprolactam. So here is an example of the same polymer that can be made from (at least) two different monomers by two different mechanisms. This illustrates the complexity of our classification and nomenclature schemes, because polycaprolactam,... 

In contrast, exocyclic vinylic groups migrate readily. ( )-a-Benzylidenecyclohexanone oxime (20) formed a stable, crystalline addition product (21) upon tosylation in pyridine dilute acidolysis gave the caprolactam derivative (22) in high overall yield (Scheme 3). ... 

For some years Foray s enzymatic process for L-lysine (L-Lys, 41) was competitive compared with fermentation. This chemoenzymatic L-Lys production was established with a capacity of 5000-10000 t/y. The key intermediate is a-amino-e-caprolactam (ACL), produced from cyclohexanone in a modified Beckmann rearrangement. The enantiospecific hydrolysis forming L-Lys is based on two enzymes L-ACL-hydrolase opens the ring of ACL to L-Lys and in the presence of the ACL-racemase the d-ACL is racemized. Incubating d,l-ACL with cells of Cryptococcus laurentii having l-ACL lactamase activity together with cells of Achromobacter obae with ACL-racemase activity, L-Lys could be obtained in a yield of nearly 100% (Scheme 24) [102]. 

The catalytic effect of e-caprolactam in the production of benzoyl chloride from phosgene and benzoic acid has been explained in terms of the following scheme [1495] ... 

In conclusion, a correct analysis of the sustainability in caprolactam manufacture should consider the full scheme of production and the alternatives, including the critical steps to be further developed. 

Phenol is a material of major commercial importance. One of its earliest uses was as a disinfectant (carbolic acid). Earlier in the twentieth century, it became important as a feedstock for resins such as Bakelite , and in the latter part of the century it also became very important as a precursor for caprolactone and caprolactam and hence polyester and polyamide manufacture. The two major methods for phenol production nowadays are by the catalytic oxidation of benzoic acid and catalytic decomposition of cumene hydroperoxide (Scheme 4.55). 

Cyclic amides can also be hydrolyzed in a highly selective fashion using enzymes. A well known example in this respect is the biocatalytic production of L-lysine from d,l-a-amino- -caprolactam (d,l-ACL) I45"47 . This process is based on the combination of two enzymatic reactions the enzymatic enantiospecific hydrolysis of L-a-amino-s-caprolactam to L-lysine and the simultaneous racemization of the residual D-a-amino-s-caprolactam (Scheme 12.2-10). 

Cyclohexanone, 2-cyclohexen-l-one, 5-hexenenitrile, and hexanenitrile are commonly observed by-products in the Beckmann rearrangement of cyclohexanone oxime. Aniline and 2-methylpyridine are also occasionally formed. An outline of the reaction scheme is shown in Figure 7. From the selectivity change with time with AIPO4 as catalyst, it was found that e-caprolactam, cyclohexanone, and... 

Hydrolytic polymerization of caprolactam is the most important commercial process for the production of nylon 6. The following synthetic scheme outlines hydrolytic polymerization of caprolactam ... 

Union Carbide Corp. developed a process using cyclohexanone as a principal intermediate and used this process commercially in 1966. According to the following reaction scheme, cyclohexanone is oxidized to caprolactone with peracetic acid, which is obtained by the reaction of acetaldehyde and hydrogen peroxide. The caprolactone is then converted to caprolactam by reaction with ammonia at high temperature and high pressure (process 5, Figure 2.11). The only by-product is acetic acid the amount of acetic acid obtained is about 1 kg/kg of product [123]. 

Addition reactions proceed typically at unsaturated bonds such as C=C, C=0, C=N, C=N or carbon-carbon triple bonds. A molecule is added to the substrate and the product forms without release of any another molecule. With all substrates becoming part of the product, the atom economy of addition reactions is very favorable. Because today s chemical technology is largely based on unsaturated base chemicals obtained in the steam cracker process (e.g., ethylene, propylene, butenes, benzene, see Chapter 6.6), addition reactions are of the highest relevance in the whole petrochemistry. Scheme 2.2.2 shows as one important example, namely, the addition of hydrogen to benzene to form cyclohexane, a key intermediate in the production of, for example, adipinic acid or caprolactam (nylon). 

Rearrangement or isomerization reactions proceed typically at carbocations or other electron-deficient positions of a molecule. In rearrangement reactions the substrate stabilizes itself by rearranging its structure without changing the number and type of its atoms. Thus, rearrangement reactions proceed without addition/release of molecules other than substrate and product. Rearrangement reactions of technical importance are the isomerization of linear alkanes to branched alkanes (important to increase the quality of fuels) and the rearrangement of cyclohexanone oxime to e-caprolactam (Scheme 2.2.4). 

Among the industrially produced lactams, e-caprolactam has by far the highest production capacity due to its important role as monomer in the polyamide business. There exist several synthetic routes to produce e-caprolactam. The most important one starts from benzene (Scheme 5.3.7). Benzene is hydrogenated in a first step to cyclohexane, followed by oxidation of the latter to a mixture of cyclohexanone and cydohexanol. This mixture is then reacted with NH2OH to give cyclohexanone oxime, which is converted under add catalysis in a so-called Beckmann rearrangement reaction to e-caprolactam. Alternative routes try to avoid the oxime intermediate (UCC peracetic add process via e-caprolactone), try to avoid the cydohexanone intermediate (e.g., DuPont process converting cydohexane directly into the oxime intermediate by reaction with nitric add), or start from toluene (Snia-Viscosa process). 

Scheme 5.3.7 Production route to E-caprolactam via Beckmann-rearrangement of cyclohexanone oxime.

Scheme 1.20 Development of industrial methods for production of caprolactame...

The rearrangement step is most efficiently performed by the original solid catalyst based on Si/Al zeolite and coded as ZSM-5, discovered by the research team of Sumitomo Co. (Scheme 1.20c) [17, 18]. It catalyzes the rearrangement to caprolactame with 95 % selectivity and 100 % yield, without side products. 

Caprolactam scaffold represents a bioactive moiety in many drugs [99]. Fox and coworkers have described the synthesis of 3-(acylamino)azepan-2-one derivatives as stable broad-spectrum chemokine inhibitors resistant to metabolism in vivo [100]. Azepan-2-ones are also reported as valuable inhibitors of metallic proteinase [101]. The synthesis of N-alkyl-2-(2-oxoazepan-l-yl)-2-arylacetamide derivatives is carried out by a three-component Ugi reaction in water. The reaction of 6-aminohexanoic acid 133, aromatic aldehydes 51, and isocyanide derivatives 134 in water under reflux without any catalyst affords N-alkyl-2-(2-oxoazepan-l-yl)-2-arylacetamides 135 (Scheme 45) [102]. The first step of the reaction leads to the formation of imines 136 by the reaction of 6-aminohexanoic acid 133 and aldehydes 51 (Scheme 46). The nucleophilic attack of the isocyanide 134 on protonated imine 137 leads to the formation of nitrilium carboxylate intermediate 138, which xmdergoes cyclization through attack of carboxylate on nytrilium carbon to give an intermediate cyclic product 139. The latter product undergoes a Mumm rearrangement to yield the final product 135 via the intermediate 140. 

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