Platinum catalysts, sulfided reductive alkylation

The current work indicates that sulfided platinum catalysts are, in general, more active and selective than Pt, Pd, or sulfided Pd catalysts for reductive alkylation of primary amines with ketones. The choice of the catalyst preparation parameters, especially the support, plays a major role in determining the performance of the catalyst. Diamines, especially of lower molecular weight, tend to react with ketones even at room temperature to form heterocycles such as imidazolidine, diazepanes, and pyrimidines. Hence, a continuous reactor configuration that minimizes the contact between the amine and the ketone, along with a highly active catalyst is desired to obtain the dialkylated product. In general, sulfided Pt appears to be more suited for the reductive alkylation of ethylenediamine while unsulfided Pd or Pt may also be used if 1,3-diaminopropane is the amine. 

Platinum and rhodium sulfided catalysts are very effective for reductive alkylation. They are more resistant to poisoning than are nonsulfided catalysts, have little tendency to reduce the carbonyl to an alcohol, and are effective for avoidance of dehydrohalogenation in reductive alkylation of chloronitroaromatics and chloroanilines (14,15). Sulfided catalysts are very much less active than nonsulfided and require, for economical use, elevated temperatures and pressures (300-2(KX) psig, 50-l80 C). Most industrial reductive alkylations, regardless of catalyst, are used at elevated temperatures and pressures to maximize space-time yields and for most economical use of catalysts. 

These results illustrate the practicality of preparing trialkylamines by the reductive alkylation of dialkylamines with aliphatic ketones. Excellent yields are obtained, particularly with the more reactive and less hindered ketones, such as cyclohexanone and acetone, and with the less hindered secondary amines. Platinum sulfide, or other platinum metal sulfides, are the catalysts of choice when more hindered reagents require more severe operating conditions. 

Malz, Jr. and Greenfield studied the preparation of tertiary amines by reductive alkylation of aliphatic secondary amines with ketones, using platinum metals and their sulfides as catalysts.40 Excellent yields of tertiary amines were obtained with unhindered ketones, such as cyclohexanone and acetone, and relatively unhindered secondary amines. In this study, 5% Pd-C and various transition metal sulfides were compared in the reductive alkylation of dibutylamine with cyclohexanone. By using the reaction conditions suitable to each catalyst, excellent yields of tertiary amines were obtained, as shown in Table 6.5. Approximately 5-15% of the excess cyclohex-... 

The reductive alkylation of /V-alkylarylamines and diarylamine with ketones to give tertiary amines has been investigated by Greenfield and Malz, Jr.42 with platinum metal sulfides that had been shown to be excellent catalysts for the reductive alkylation of primary arylamines with ketones37 (see eq. 6.15). Good conversions to tertiary amines were obtained with relatively unhindered secondary arylamines and less hindered ketones. The relative ease in the reductive alkylation of diarylamines with ketones was in the following order cyclohexanone > acetone > ethyl methyl ketone > isoamyl methyl ketone > isobutyl methyl ketone. For example, 58% of diphenylamine was converted to iV-alkyldiphenylamine with cyclohexanone over rhodium sulfide at 150°C and 3.4-5.5 MPa H2 (eq. 6.19), while with isobutyl methyl ketone, a conversion of only 28% was obtained even at 235°C with in the same reaction time. 

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