Oximes conversion

Figure 3. Effect of temperature on cyclohexanone oxime conversion and products selectivity.

Effect of time on stream on oxime conversion and product selectivity was studied over CeMAPO-36 at 200 °C and 4.4 h"1 WHSV. The results are depicted in Fig. 5. Although the conversion decreased with increase of time on stream, the decrease was only 7% for 6 h time on stream. This observation elucidates that the reaction occurs over Lewis acid sites particularly the formation of coke. In addition, higher WHSV (4.4 h 1) is also the main cause for suppression of coke formation. The yield of caprolactum decreased with increase in time on stream. The selectivity of caprolactum did not show... 

Fig-1, (a) oxime conversion, (+ ) ceprolactam selectivity and ( ) caprolactam yield with time using 0.1 g boria on alumina catalyst at a reaction temperature of 300 C. 

The effect of temperature on the conversion, selectivity and yield after 3 hours on stream is shown in figure 2. In each case a catalyst mass of 0.1g boria on alumina catalyst was tested. With increasing reaction temperature the oxime conversion increased, however, maxima in lactam selectivity and yield were observed at a reaction temperature of 300 C. At higher temperatures excessive coking and side reactions were thought to occur,... 

Fig.4. (a) Oxime conversion, (b) Caproiactam selectivity, (c) Caproiactam Yield using 0.2g (.) boria on alumina, M regenerated boria on alumina and (+) alumina catalyst at 300 C for 30 hours. 

For a preparative synthesis of 4,5,6,7-tetrahydroindole (1), the following conditions have been recommended (86ZOR489) 110°C, 3 hr, the oxime 116/KOH/vinyl chloride molar ratio 1 6 5, yield 46% based on the oxime consumed with oxime conversion of 75%. 

With 1,2-dibromoethane (run 4) under comparable conditions (run 2), somewhat poorer results are achieved with the same total yield (about 30%), the crude product contains nearly 40% of the starting oxime. As in the reaction with free acetylene (see Section II.C.l), the substitution of KOH by NaOH and LiOH (run 5,6) makes the process completely selective, but leads to a sharp drop in the yield of products and in the oxime conversion. 

Touaux, B., Texier-Boullet, F., and Hamelin, 1.1998. Synthesis of oximes, conversion to nitrile oxides and their subsequent 1,3-dipolar cycloaddition reactions under microwave irradiation and solvent-free reaction conditions. Heteroatom Chemistry, 9 351-54. 

Figure 4. Effect of diluent on cyclohexanone oxime conversion and lactam selectivity over H-BEA. Temp. 623 K, oxime/diluent/N2 molar ratio 1/9/5.9 and W/F of 80 g cat h moloxime time on stream of 6 h.

Figure 5. Change in cyclohexanone oxime conversion and lactam selectivity with time on stream in the vapor phase Beckmann rearrangement over 12-MR zeolites. Diluent (a) methanol, (b) 1-hexanol. (X) H-BEA, (A) H-LTL, (V) H-OFF-ERI, ( ) H-USY (Si02/Al203 = 62), (O) H-MOR, (O) H-MTW 623 K, oxime/diluent/N, molar ratio of 1/9/5.9 and W/F of 80 g cat h mol oxime [41].

Sato et al found that over highly siliceous ZSM-5 the selectivity for s-caprolac-tam was increased by use of CO2 as carrier gas [18,20]. Catalytic performance also improved greatly when methanol was co-fed with oxime [56]. Up to a methanol/ oxime ratio of unity lactam selectivity increased and then leveled off. Oxime conversion was little changed up to the ratio of unity and decreased beyond this value. It has been claimed [65] that addition of methanol and a small amount of H2O to cyclohexanone oxime resulted in long catalyst life. 

In the absence of a boundary layer and internal and external diffusional influences, the cyclohexanone oxime conversion follows the requirements of Bassett-Habgood kinetic treatment [20] for first order reaction processes in which the rate determining step is the suiiface reaction ... 

The results in Table 2 show that a relationship exists between siurface acidity and catalytic activity (kKox)> Thus, AP catalytic activity follows the same sequence as it surface acidity AP-B > AP-P > AP-A. Besides, the experimental data in Table 2 clearly show how the catalytic activity of AP can be modified by the incorporation of TiOj. The most striking feature of the activity studies is that among the tested AFTi catalysts, those obtained in propylene oxide and with lower TiOj content showed higher activity for cyclohexanone oxime conversion than did the other acid catalysts. Thus, APTi-P-31 catalyst exhibits an increase in activity about twice higher than that for the starting AP-P catalyst. 

Oxime conversion (Xqx) and product selectivities (S), at Xqx SO mol%, in the rearrangement of cyclohexanone oxime to e-caprolactam over AP and APTi catalysts... 

Moreover, poisoning with pyridine (Table 4) slightly decreases Xox values while S afr i mained almost unchanged. Furthermore, the addition of carbon disulfide or 1-butanethiol produce a decrease in the oxime conversion as well as in the S afr values (Table 4). In this sense, previous results [8] show that cyclohexanone oxime also rearranges to a great extent when a solution of oxime in neat pyridine is used as the reactant. 

Thus, the reaction network of die cyclohexanone oxime conversion is complex due to the simultaneous intervention of a large number of reactions. An outline of catalyzed reactions was presented in Figure 2. The first step would imply the chemisorption of the oxime on the catalyst, and then either a rearrangement reaction could take place or a firagmentation process which would lead to the intermediate I (6-cyanopentyl carbenium ion) being unstable. This in its turn could evolve to a more stable structure such as II. 

However, another approach to find the suitable catalyst for the conversion of cyclohexanone oxime to caprolactam in order to completely eliminate the salt formation has been reported by Sumitomo, of Japan. They reported the use of a solid high-silica zeolite catalyst (ZSM-5) for the gas-phase rearrangement of cyclohexanone oxime at 350 °C. Caprolactam is produced with 95% selectivity at 100% oxime conversion. 

Fig. 3.32 Effect of B2O3 content. (1) Oxime conversion of impregnation BjOs-SiOj, (2) oxime conversion of vapor decomposition B203-Si02, (3) lactam selectivity of impregnation B20s-Si02, (4) lactam selectivity of vapor decomposition B20 -Si02 reaction temperture, 423 K.

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