| 摘要 |
1. A process for purifying crude piperidines of the formula I where R<1> to R<4> are C1-C6-alkyl, R<1> and R<2> and/or R<3> and R<4> together are a CH2-chain of 2 to 5 carbons, which comprises, in a first step, removing high-boiling substances and, if present, water from the crude piperidines by distillation, in a second step, adding from 0.01 to 5 % by weight, based on the product of the first step, of a reducing agent, and, in a third step, isolating the piperidines by distillation. 2. A process as claimed in claim 1, wherein substituents R<1>, R<2>, R<3> and R<4> are C1-C3-alkyl 3. A process as claimed in claim 1 or 2, wherein the reducing agent is a compound of the formula MXH4-m-Ym, where M is an alkali metal,or NR4, where each R is an identical or different C1-C4-alkyl, or one equivalent of an alkaline earth metal or one equivalent of zinc, X is boron or aluminum, Y is H or CN, and m is 0 or 1. 4. A process as claimed in any one of claims 1 to 3, wherein from 0.001 to 0.02 % by weight, based on the piperidines, of a reducing agent is added to the piperidines I isolated by distillation in the third step. |
