Copper protective agent

A method of preparing a copper protective agent, comprising steps of:

• a step S1 of adding N-butyl lithium into a tetrahydrofuran solution having a halogenated hydrocarbon dropwise at −78° C. under protection of an inert gas, to form a reaction system;
• a step S2 of adding sulfur powders into the reaction system, and gradually increasing a temperature of the reaction system to the room temperature, wherein the sulfur powders and the reaction system react at the room temperature;
• a step S3 of extracting the reaction system with an organic solvent to obtain a crude product;
• and
• a step S4 of purifying the crude product by a column chromatography or a distillation technique to obtain a purified copper protective agent;
• wherein the copper protective agent is represented by a general formula (GI):
• HS—R(GI);
• and
• wherein R is a linear or branched alkyl group having 1 to 20 carbon atoms.