1. Field of the Invention:
The present invention relates to a process for the production of polyalkylpiperidylamines.
2. Description of the Prior Art:
Polyalkylpiperidylamines should properly be called dimers due to the number of piperidine units they contain. They are distinguished from piperidylamines, which contain only one piperidine unit (monomer) or more than four piperidine units (polymer). Polyalkylpiperidylamines are valuable intermediates, especially for the synthesis of plastic additives.
Currently, polyalkylpiperidylamines are prepared by the reductive amination of polyalkyl-4-piperidones. For example, the process of GB-PS No. 834 290 involves the reaction of 2,2,6,6-tetramethyl-4-piperidone with dialkylaminoalkylamines in the presence of a platinum/activated carbon catalyst and hydrogen to form 2,2,6,6-tetramethylpiperidine substituted at the 4-position.
DE-OS No. 23 49 962 describes the reductive amination of 1-benzyl-2,2,6,6-tetramethyl-4-piperidone with butylamine in methyl alcohol on a platinum catalyst.
In another example of a reductive amination technique, DE-OS No. 26 11 208 discloses the reductive amination of 2,2,6,6-tetraalkyl-4-piperidone with alkylenediamines on platinum catalysts and the subsequent reaction of the resulting dimer polyalkylpiperidylamines with difunctional compounds, which contain halogen and/or epoxy groups, to form polymeric polyalkylpiperidylamines.
DE-OS No. 26 21 870 describes the reductive amination of 2,2,6,6-tetramethyl-4-piperidone in the presence of a Raney nickel catalyst.
Additionally, DE-OS No. 30 07 996 discloses reductive amination of 2,2,6,6-tetramethyl-4-piperidone with mono- or di-amines on cobalt and nickel catalysts. It is also recommended that the reaction water formed during condensation be removed by azeotropic distillation before commencing hydrogenation.
All of the above-described processes suffer from at least one serious disadvantage. For example, in the first three processes described above, the use of expensive noble metal catalysts is disadvantageous, as these catalysts cannot be regenerated without loss. Raney catalysts, which are used in the fourth process described above, are essentially best suited for batch processes. Reuse of the catalysts is complicated and use in a continuous process requires considerable expense.
Moreover, as the last described process illustrates, it is advantageous in the reductive amination of 2,2,6,6-tetramethyl-4-piperidone that the reaction water be removed from the reaction mixture as quickly as possible. The reason for this is the ease with which 2,2,6,6-tetramethyl-4-piperidone is hydrolyzed, particularly at higher temperatures. This tendency has lead to yield losses.
An alternative approach to the production of polyalkylpiperidylamines is set forth in DE-OS No. 26 11 208. This approach entails the reaction of 4-aminopolyalkyl-piperidines with dihalide compounds in the presence of alkali compounds to neutralize the nascent hydrogen halides. Although high polyalkylpiperidylamine yields are attained, the use of alkali compounds and the accumulation of considerable amounts of salts are a considerable disadvantage. Also, because of the high water solubility of polyalkylpiperidylamines, considerable product losses occur in separation from the reaction mixture.
Finally, the present inventors attempted to produce dimer polyalkylpiperidylamines by the hydrogenating alkylation of diamines with polyalkylpiperidimes hydroxylated in the 4-position and found the results to be unsatisfactory. It was found that under the reaction conditions, the diamines react with one another. For example, when ethylenediamine was used, piperazine was obtained, and when hexamethylenediamine was used, azacycloheptane was obtained. Thus, a breakthrough with the process of hydrogenating alkylation of amines, as described in Houben-Weyl, Vol. XI/1, P. 126 ff, appears most unlikely.
Therefore, a need clearly continues to exist for a process for the production of polyalkylpiperidylamines which produces satisfactory yields of the product, and which does not entail the use of expensive noble metal catalysts, Raney catalysts or alkali compounds.