Preparation method of beta-lactamase inhibitor intermediate chiral impurity

The invention discloses a method for preparing chiral impurities of beta-lactamase inhibitor intermediates, which comprises the following steps of: taking crystallization mother liquor for preparing (2S, 5R)-5-(benzyloxy amino)-piperidine-2-ethyl formate oxalate or crystallization mother liquor for preparing (2R, 5S)-5-(benzyloxy amino)-piperidine-2-ethyl formate oxalate as extraction raw materials, and extracting the chiral impurities in a solvent to obtain the chiral impurities of the beta-lactamase inhibitor intermediates. (2S, 5S)-5-(benzyloxy amino)-piperidine-2-ethyl formate sulfate or (2R, 5R)-5-(benzyloxy amino)-piperidine-2-ethyl formate sulfate is separated out through a method for selectively splitting and salifying sulfuric acid, and then high-purity diastereoisomer (2S, 5S)-5-(benzyloxy amino)-piperidine-2-ethyl formate oxalate or (2R, 5R)-5-(benzyloxy amino)-piperidine-2-ethyl formate oxalate is prepared through the processes of dissociation, oxalic acid salifying crystallization and the like. T