You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Chemical"].

Please return the output as a JSON object of the format: {"Chemical": ["Arsenic", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

Improved preparation of methyl bis(2,2,2-trifluoroethoxy)-bromophosphonoacetate for the stereoselective synthesis of (E)-α-bromoacrylates. We have established an efficient method for preparing methyl bis(2,2,2-trifluoroethoxy)bromophosphonoacetate, which we developed for the stereoselective synthesis of (E)-α-bromoacrylates. This improved method enables the reagent to be prepared reproducibly in one step from methyl bis(2,2,2-trifluoroethoxy)phosphonoacetate.
{"Chemical": ["methyl bis(2,2,2-trifluoroethoxy)bromophosphonoacetate", "methyl bis(2,2,2-trifluoroethoxy)-bromophosphonoacetate", "methyl bis(2,2,2-trifluoroethoxy)phosphonoacetate", "(E)-\u03b1-bromoacrylates"]}