Process for depolymerizing polysulfides and the preparation of bis-mercapto-diethers
View Patent ↗The invention related to a process for the preparation of a bismercaptodiether by reacting a polysulfide with a monothiol in the presence of a base and to a process for the depolymerization of a polysulfide by reacting said polysulfide with a monothiol in the presence of a base. These processes enable the preparation of bismercaptodiethers without inorganic salt formation.
1. A process for the preparation of a bismercaptodiether of the formula
HS—R 1 —O—C(R 2 )H—O—R 1 —SH
wherein R 1 is a linear, branched, or cyclic alkylene group with 1 to 6 carbon atoms, or an arylene group and R 2 is hydrogen, a linear, branched, or cyclic alkyl group with 1 to 6 carbon atoms, or an aryl group; R 1 and R 2 may be optionally substituted with heteroatoms,
by reacting a polysulfide with the following repeating unit:
—[S—R 1 —O—C(R 2 )H—O—R 1 —S]—
wherein R 1 and R 2 are as described above,
with a monothiol of the formula
R 4 —SH
wherein R 4 is a linear or branched alkyl, aryl, or alkaryl group, optionally substituted with heteroatoms, in the presence of a base.
2. The process according to claim 1 wherein said polysulfide has the following structure:
R 3 —S—[S—R 1 —O—C(R 2 )H—O—R 1 —S] n —S—R 3
wherein each R 3 is independently selected from —SH and —OH terminated alkyl, etheralkyl, aryl, and alkaryl groups having 1 to 6 carbon atoms, and n ranges from 1 to 100.
3. The process according to claim 2 wherein R 3 is an OH-terminated alkyl, etheralkyl, aryl, or alkaryl group with 1 to 6 carbon atoms.
4. The process according to claim 3 wherein R 3 is —CH 2 CH 2 OH.
5. The process according to claim 1 wherein said polysulfide is a network consisting for at least 90 wt % of said repeating units.
6. The process according to claim 1 wherein R 2 is hydrogen.
7. The process according to claim 1 wherein R 1 is —CH 2 CH 2 —.
8. The process according to claim 1 wherein R 4 is a hydroxy-terminated alkyl group.
9. The process according to claim 1 wherein the bismercaptodiether is separated from the reaction mixture during the reaction.
10. The process according to claim 9 wherein the bismercaptodiether is separated from the reaction mixture during the reaction by way of extraction.
11. The process according to claim 10 wherein the process is conducted as a multi-stage counter-current extraction process.
12. The process according to claim 11 wherein the multi-stage counter-current extraction process is operated continuously.
13. The process according to claim 11 wherein the number of stages is at least 4.
14. The process according to claim 1 wherein the reaction is performed in the presence of water.
15. Process for the preparation of a polysulfide comprising the steps of (i) preparing a bismercaptodiether according to the process of claim 1 and (ii) polymerizing this bismercaptodiether to form a polysulfide.