Utilization of phosphorus pentasulfide in thionylations using phase transfer catalysis
View Patent ↗A method is disclosed for the preparation of benzo[b]thiophenecarbodithioic esters of the formula: wherein R is alkyl, R 1 is hydrogen, halogen, or alkyl, R 2 , R 3 , R 4 , and R 5 are independently selected from the group consisting of hydrogen, halogen, alkyl, alkoxy, alkylthio, trifluoromethyl, cyano, and aryl, wherein said method comprises reacting an equivalent of an S-thiol ester of the formula: with one-third of an equivalent of P 2 S 5 , 2 equivalents of at least one alkali metal carbonate, about 2.5 mole percent of a phase transfer catalyst, and a catalytic amount of water in hot toluene.
1. A method for the preparation of benzo[b]thiophenecarbodithioic esters of the formula:
wherein R is alkyl, R 1 is hydrogen, halogen, or alkyl, R 2 , R 3 , R 4 , and R 5 are independently selected from the group consisting of hydrogen, halogen, alkyl, alkoxy, alkylthio, trifluoromethyl, cyano, and aryl,
wherein said method comprises reacting an equivalent of an S-thiol ester of the formula:
with one-third of an equivalent of P 2 S 5 , 2 equivalents of at least one alkali metal carbonate, about 2.5 mole percent of a phase transfer catalyst, and a catalytic amount of water in hot toluene.
2. The method of claim 1 wherein R is methyl or ethyl and R 1 R 2 , R 3 , R 4 , and R 5 are independently selected from the group consisting of hydrogen, chlorine, C 1 -C 4 alkyl, and trifluoromethyl.
3. The method of claim 2 wherein R 1 R 2 , R 3 , R 4 , and R 5 are hydrogen.
4. The method of claim 3 wherein R is ethyl.
5. The method of claim 1 wherein the alkali metal carbonate is potassium carbonate or cesium carbonate.
6. The method of claim 5 wherein the alkali metal carbonate is potassium carbonate.
7. The method of claim 1 wherein the phase transfer catalyst is benzyltriethylammonium chloride or tetrabutylammonium bromide.
8. The method of claim 7 wherein the phase transfer catalyst is benzyltriethylammonium chloride.
9. The method of claim 7 wherein the phase transfer catalyst is tetrabutylammonium bromide.
10. The method of claim 1 wherein R is ethyl, R 1 , R 2 , R 3 , R 4 , and R 5 are hydrogen, the alkali metal carbonate is potassium carbonate, and the phase transfer catalyst is benzyltriethylammonium chloride.