The invention relates to a method for preparing
mercaptoacetic acid. The method comprises the following steps: (1) adding monochloro
acetic acid,
sodium chloroacetate and
carbon disulfide into a reactor, stirring, dripping an alkali solution, and separating the
oil phase from the water phase after the reaction is completed; (2) recycling unreacted
carbon disulfide from the separated
oil phase mixture for circulation, acidifying the residual mixture into a weak acid solution, adding an
organic solvent to extract for 2-3 times, combining organic phases, washing with a
salt solution and water, and separating the
oil phase and the water phase; and (3) distilling the separated oil phase, and recycling the
organic solvent, thereby obtaining residues, that is, the
mercaptoacetic acid. As
carbon disulfide is adopted to react with alkali to generate sulfydryl, the sulfydryl is further reacted with
sodium chloroacetate to generate
sodium thioglycollate, and a proper amount of acids,
organic solvent and alkali solution are added, the
raw material cost is low, and a small amount of reagents are used; as the excessive carbon disulfide can be recycled and circulated, the
utilization rate is high, and the method is a clean production process; the
reaction conditions are gentle, the reaction time is short, no high temperature or
high pressure is needed, and the equipment investment is low.