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:

A systematic study of the degradation of dimethyl phthalate using a high-frequency ultrasonic process. A comprehensive study of the sonochemical degradation of dimethyl phthalate (DMP) was carried out using high-frequency ultrasonic processes. The effects of various operating parameters were investigated, including ultrasonic frequency, power density, initial DMP concentration, solution pH and the presence of hydrogen peroxide. In general, a frequency of 400kHz was the optimum for achieving the highest DMP degradation rate. The degradation rate was directly proportional to the power density and inversely related to the initial DMP concentration. It was interesting to find that faster removal rate was observed under weakly acidic condition, while hydrolysis effect dominated in extreme-basic condition. The addition of hydrogen peroxide can increase the radical generation to some extent. Furthermore, both hydroxylation of the aromatic ring and oxidation of the aliphatic chain appear to be the major mechanism of DMP degradation by sonolysis based on LC/ESI-MS analysis. Among the principle reaction intermediates identified, tri- and tetra-hydroxylated derivatives of DMP, as well as hydroxylated monomethyl phthalates and hydroxylated phthalic acid were reported for the first time in this study. Reaction pathways for DMP sonolysis are proposed based on the detected intermediates.
{"Chemical": ["dimethyl phthalate", "hydrogen peroxide", "DMP", "hydroxylated phthalic acid", "hydroxylated monomethyl phthalates"]}