Benign and high-yielding, large-scale synthesis of diphenylphosphinodithioic acid and related compounds

Diphenylphosphinodithioic acid (6b) and its triethyl ammonium salt (6a) were prepared by two new synthetic pathways, each employing cheap and readily available starting materials. These facile one-pot reactions were conducted on a kilogram scale and produced the desired products in high yield and quality, thereby surpassing all previously known routes. The synthesis of triethyl ammonium salts of 6H-dibenzo[c,e][1,2]oxaphosphinine-6-thiolate 6-sulfide (3a) was also further improved.