1-methylpiperidine

Thirty-one grams (0.33 mole) of a-picoline and 3 g. of Raney nickel catalyst [Org. Syntheses, 21, 15 (1941)] are treated with hydrogen with agitation at a pressure of 2200-4400 lb. and a temperature of 200°. Absorption of hydrogen is complete in 35-40 minutes, and the catalyst is removed by filtration from the cooled product. Distillation of the product gives 30 g. (90%) of 2-methylpiperidine boiling at 117-1197740 mm. 

One hundred grams of concentrated sulfuric acid is added to a mixture of 25 g. (0.182 mole) of p-nitrotoluene, 38 g. (0.354 mole) of 

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Figure 17 Mass spectra of (1) 3-methylpiperidine and (2) 3-methyipyridine (Reproduced with permission from...

Methyl-1 -phenylethyl)-4-(2-propynyloxy)benzene, 3754 /V-(3-Methylpheny) )-2-nitrobenzimidyl chloride, 3634 Methylphosphine, 0495 f 1-Methylpiperidine, 2517 f 2-Methylpiperidine, 2518 f 3-Methylpiperidine, 2519 f 4-Methylpiperidine, 2520... 

The condensation product (in the following indicated as the dimer1) of 3-methylpiperidine and the partially hydrogenated MGN in Figure 2 (in the following indicated as the iminonitnle ) was identified by GC/MS in the reaction product mixture, where its relative concentration easily reached 25 %. The formation of this dimer was taken as a sign for unwanted intermolecular condensations. 

The higher dehydrogenation activity keeps the 3-methylpiperidine concentration on the metal surface at lower levels thus suppressing the condensation reaction leading to the dimer. The increased (de)hydrogenation activity at higher dispersion can be explained in different ways. The rate of a structure insensitive reaction can be linearly correlated to the number of active sites thus to the dispersion. On the other hand metal particles with different shapes and dimensions could interact with molecules in the gas phase in a different way or could display different resistance against deposition of coke precursors. 

Increasing the total pressure while keeping the H2/MGN ratio constant, has a positive influence on MGN conversion as well (Figure 6a). At the same time however the increased hydrogen partial pressure shifts die equilibrium between p-picoline and 3-methylpiperidine to the side of this latter. The dimer selectivity seems to be independent of the total pressure as shown in Figure 6b. 

These results can be explained by the kinedk network indicated in Figure 1 in which competitive adsorption of hydrogen MGN, 3-methylpiperidine and irmnonitrile on the metal surface plays an important role. The iminonitrile can either be further... 

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