Provided is a preparation of a thioether-based polythiol in a high purity using a metal monosulfide for the incorporation of a thioether group, wherein the content of such components as a metal polysulfide present in the metal monosulfide is controlled to a predetermined level or lower. As a result, an optical lens of high quality with a high refractive index can be produced using the polythiol.

Provided is a preparation of a thioether-based polythiol in a high purity using a metal monosulfide for the incorporation of a thioether group, wherein the content of such components as a metal polysulfide present in the metal monosulfide is controlled to a predetermined level or lower. As a result, an optical lens of high quality with a high refractive index can be produced using the polythiol.

A method for producing 3-mercaptopropionic acid and methods using same for producing a carbonic acid ester compound having a mercapto group and a thiourethane-based optical material. The present invention improves a process during the production of 3-mercaptopropionic acid, significantly increases yield, and reduces the temperature and time during vacuum distillation, thereby preventing the destruction of a product and significantly increasing productivity. The present invention allows high-purity 3-mercaptopropionic acid having an excellent color to be finally yielded; accordingly, by using same, a high-purity carbonic acid ester compound having an excellent color and a mercapto group can be inexpensively obtained. A thiourethane-based polymeric composition and a thiourethane-based optical material obtained by polymerizing same can likewise be inexpensively obtained by using said carbonic acid ester compound. Such carbonic acid ester compound can be used for the production of inexpensive thiourethane optical lenses; consequently, inexpensive optical lenses having an excellent color can be obtained.

A method for producing 3-mercaptopropionic acid and methods using same for producing a carbonic acid ester compound having a mercapto group and a thiourethane-based optical material. The present invention improves a process during the production of 3-mercaptopropionic acid, significantly increases yield, and reduces the temperature and time during vacuum distillation, thereby preventing the destruction of a product and significantly increasing productivity. The present invention allows high-purity 3-mercaptopropionic acid having an excellent color to be finally yielded; accordingly, by using same, a high-purity carbonic acid ester compound having an excellent color and a mercapto group can be inexpensively obtained. A thiourethane-based polymeric composition and a thiourethane-based optical material obtained by polymerizing same can likewise be inexpensively obtained by using said carbonic acid ester compound. Such carbonic acid ester compound can be used for the production of inexpensive thiourethane optical lenses; consequently, inexpensive optical lenses having an excellent color can be obtained.

A compound, which is 1-(1,3-bis(methylthio)propoxy)-3-(methylthio)propan-1-ol, a composition containing the compound, a method for the preparation thereof, a method for preparing 3-methylthiopropionaldehyde by reacting 1-(1,3-bis(methylthio)propoxy)-3-(methylthio)propan-1-ol with acrolein, and also to the use of 1-(1,3-bis(methylthio)propoxy)-3-(methylthio)propan-1-ol or compositions containing the compound for the storage and/or transport of 3-methylthiopropionaldehyde and/or methyl mercaptan.

A compound, which is 1-(1,3-bis(methylthio)propoxy)-3-(methylthio)propan-1-ol, a composition containing the compound, a method for the preparation thereof, a method for preparing 3-methylthiopropionaldehyde by reacting 1-(1,3-bis(methylthio)propoxy)-3-(methylthio)propan-1-ol with acrolein, and also to the use of 1-(1,3-bis(methylthio)propoxy)-3-(methylthio)propan-1-ol or compositions containing the compound for the storage and/or transport of 3-methylthiopropionaldehyde and/or methyl mercaptan.

A compound, which is 1-(1,3-bis(methylthio)propoxy)-3-(methylthio)propan-1-ol, a composition containing the compound, a method for the preparation thereof, a method for preparing 3-methylthiopropionaldehyde by reacting 1-(1,3-bis(methylthio)propoxy)-3-(methylthio)propan-1-ol with acrolein, and also to the use of 1-(1,3-bis(methylthio)propoxy)-3-(methylthio)propan-1-ol or compositions containing the compound for the storage and/or transport of 3-methylthiopropionaldehyde and/or methyl mercaptan.

Methods for using sulfur-containing compounds comprising short chain aliphatic ester or amide moieties as solvents and compositions comprising these compounds are provided.

Methods for using sulfur-containing compounds comprising short chain aliphatic ester or amide moieties as solvents and compositions comprising these compounds are provided.

The invention relates to a method for crystallizing D,L-methionine from aqueous solutions and/or suspensions containing D,L-methionine and D,L-methionine ammonium salts, having a Met content of 70-180 g/kg, an NH.sub.4.sub.+ content of 1-5 g/kg, in the presence of a crystallization additive, which comprises a nonionic or anionic surfactant or a mixture of various nonionic or anionic surfactants, in which the temperature of the solution and/or suspension is lowered directly or stepwise from T.sub.1=85-110 C. to T.sub.2=30-50 C., so that D,L-methionine precipitates as a solid.