Caprolactam synthesis

In 1979, Olah [47] reported a one step conversion of alicyclic ketones into lactams by means of hydroxylamine O-sulfonic acid and formic acid under reflux for a few hours. More recently this reaction has been realized under solvent-free conditions with Si02 as inorganic support and focused irradiation, as exemplified in Scheme 8.29 for caprolactam synthesis. 

In addition to the epoxidation of olefins, zeolitic materials have been studied for other fine chemical transformations. Table 12.21 indexes the zeolites used for oxidative dehydrogenation of propane, direct hydroxylation of benzene to phenol and e-caprolactam synthesis. A recent review summarizes other reactions for which there is not enough space in the table [138, 139]. 

A similar mechanism has been proposed for photonitrosylations, with the difference that the reaction of the alkyl radical with NOC1 (Eq. 5) is not competitive (absence of chain reaction) and that the rate of reaction 6 cannot prevent dismutation (Eq. 4) and subsequent radical polymerization of unsaturated hydrocarbons (e.g., cyclohexene in the case of caprolactam synthesis). 

Photonitrosylations show an extremely high tendency for filming, and the difficulties in implementing the caprolactam synthesis on an industrial scale are also linked to reactor designs not taking into account the competitive secondary reactions leading to polymerized material. 

Tetrahydroindole (1) was isolated by extraction of the reaction mixture with organic solvents (Et20, benzene) and purified by distillation or recrystallization. This process for preparing 4,5,6,7-tetrahydroindole is simple enough, industrially feasible, safe, and based on the cheap and accessible raw materials. Cyclohexanone oxime is an inexpensive large-scale commercial product (caprolactam synthesis intermediate), vinyl chloride being one of the cheapest commercial vinyl compounds. 

Of special interest for petrochemical and organic synthesis is the implementation of thermodynamically hindered reactions, among which incomplete benzene hydrogenation or incomplete cyclohexene and cyclohexadiene dehydrogenation should be mentioned. Cost-effective methods of cyclohexene production would stimulate the creation of new processes of phenol, cyclohexanol, cyclohexene oxide, pyrocatechol synthesis, cyclohexadiene application in synthetic rubber production, and a possibility for designing caprolactam synthesis from cyclohexene and cyclohexadiene via combined epoxidation. At present, the most... 

Micotoxic 3H- and 4H-azepines, synthesis of 90JHC107. C-Substituted e-caprolactams, synthesis using desulfurization of thieno-annelated caprolactams 88MI17 90MI13. 

The polyamide made from caprolactam is technically an addition polymer by the above definition, while the product made from the amino acid would be a condensation polymer. Actually, only the caprolactam synthesis is used commercially, and the product (polycaprolaclam = nyIon-6) is called a condensation polymer because all polyamides are so classified. 

Note that in all textbooks of green chemistry the new Sumitomo process of caprolactam synthesis is given as an example, because it eliminates ammonium sulfate generation, while, usually, the DSM route is not considered. In reality, ammonium sulfate generation is only one aspect of the impact on the environment. 

There are other processes for caprolactam synthesis, however, a thorough discussion of this subject is beyond the scope of this book. 

FIGURE 9.23. Sumitomo process combined ammoximation and vapor phase Beckmann rearrangement for caprolactam synthesis. 

FIGURE 9.24. Overall reaction of current process for caprolactam synthesis. 

In 1938, Schlack had carried caprolactam synthesis in the laboratory to the kilogram scale [2l]. Subsequently a large-scale continuous process was developed by H. Hopff and G. Wiest at Ludwigshafen, and by J. Giesen and F. Korn at Leuna. Key to the successful operation was control of the exothermic Beckmann rearrangement. This was accomplished by separate, continuous addition of moist, molten oxime and concentrated sulfuric acid... 

Figure 15.2. Comparison of the classical (black arrows) and green (green arrows) approaches to e-caprolactam synthesis. In the ammoximation step 2.8 kg/kg ammonium sulfate is co-produced, and is comprised of the salt produced during hydroxylamine sulfate preparation (Raschig process) and cyclohexanone oxime synthesis.

---