Photonitrosation process

Of the other routes the photonitrosation process involving nitrosyl chloride is in use in Japan. This avoids, at the expense of complicated purification processes, the high yields of ammonium sulphate unavoidably produced in the route involving the Beckmann rearrangement. 

The role of aromatic photonitration and photonitrosation processes in natural waters is still not clearly understood. It is, however, very interesting to report that nitration and nitrosation of monolinuron have been observed upon photolysis of nitrate and nitrite at environmental concentration levels [144], Studies on the environmental importance of such reactions will indeed benefit from the use of HPLC-MS-MS techniques for both process studies and field analysis, as they allow much lower detection limits to be reached when compared with traditional HPLC techniques. In the case of process studies, it would be very interesting to determine the extent at which the pathways observed for the photonitration and photonitrosation of aromatic compounds at fairly high concentration levels can be extrapolated to environmental conditions. 

With the advent of petrochemistry, BASF gradually replaced phenol by cyclohexane as the starting material. Development of a new continuous caprolactam process based on cyclohexane was started by BASF in 1950, and a full-scale plant went on stream in 1960 [20]. Similar processes based on cyclohexane were developed by DSM, Bayer and Inventa. A number of alternative processes were developed by other companies (Fig. 3). To name only some of them the cumene/phenol based process of Allied (on stream in 1958), the photonitrosation process of Toyo Rayon (1962), the toluene based Snia process (1964), and DuPont s nitrocyclohexane process (in operation from 1961 to 1966). 

Toray. The photonitrosation of cyclohexane or PNC process results in the direct conversion of cyclohexane to cyclohexanone oxime hydrochloride by reaction with nitrosyl chloride in the presence of uv light (15) (see Photochemical technology). Beckmann rearrangement of the cyclohexanone oxime hydrochloride in oleum results in the evolution of HCl, which is recycled to form NOCl by reaction with nitrosylsulfuric acid. The latter is produced by conventional absorption of NO from ammonia oxidation in oleum. Neutralization of the rearrangement mass with ammonia yields 1.7 kg ammonium sulfate per kilogram of caprolactam. Purification is by vacuum distillation. The novel chemistry is as follows ... 

Future developments are expected not only to yield a greater understanding of the mechanisms of many photochemical reactions, but also to provide a means for the adaptation of these reactions to large-scale industrial syntheses. A glimpse of the latter is seen in the production of e-caprolactam (Nylon 6 monomer) by the Toyo Rayon Company using the photonitrosation of cyclohexane. In this process nitrosyl chloride is cleaved by light and the following sequence of reactions takes place ... 

PNC [Photonitrosation of cyclohexane] A photochemical process for making caprolactam (a precursor for nylon) from cyclohexane, nitrosyl chloride, and hydrogen chloride. The first photochemical product is cyclohexanone oxime ... 

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. ... 

About 90% of the caprolactam is produced by the conventional cyclohexanone process. Cyclohexanone is obtained by catalytic oxidation of cyclohexane with air, or by hydrogenation of phenol and dehydrogenation of the cyclohexanol byproduct. The conversion of cyclohexanone to cyclohexanone oxime followed by Beckmann rearrangement gives caprolactam. About 10% of caprolactam is produced by photonitrosation of cyclohexane or by nitrosation of cyclohexanecarboxylic acid in the presence of sulfuric acid264. 

Photonitrosation of cyclohexane with nitrosyl chloride (PNC process) [112,113] (process 2, Figure 2.11)... 

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