O-Cresol (Sigma Aldrich), ≥ 99%, C85700
Thiophenol (sigma Aldrich) ≥99%, 240249
Formaldehyde Solution 37% (Sigma Aldrich), 15512
Trifluoroacetic acid (SD fine Chemicals Ltd), 98%, 40508L05

To the solution of thiophenol (100 mg, 1.0 mmol) in 0.1% TFA in water (5 mL) was added formaldehyde (80 µl, 3 equiv.). The resulting reaction mixture was then refluxed at 80 °C for 10 min. The ortho-cresol (108 mg, 1.1 mmol) was then added and reaction mixture was further stirred at 80 °C for 4 h. The reaction mixture was purified by silica gel column chromatography using EtOAc: hexane as mobile phase to yield pair of products, one with para-substituted o-cresols 1a (55%) and other with ortho-/para-disubstituted o-cresols 1b (28%).

• This work provides green and efficient protocol for coupling of various thiophenols with formaldehyde and phenols in water.
• Reaction proceeds through in situ formation of thiophenylmethylium cation intermediate

2-Methyl-4-((phenylthio)methyl)phenol (1a): white solid, m.p: 68-70°C
¹H NMR: (CDCl₃, 400 MHz): δ 7.31-7.29 (m, 2H), 7.26-7.22 (m, 2H), 7.18-7.14 (m, 1H), 7.04 (s, 1H), 6.98  (d, J = 8.0 Hz, 1H), 6.65 (d, J = 8.0 Hz, 1H), 5.0 (s, 1H), 4.03 (s, 2H), 2.18 (s, 3H).
¹³C NMR: (CDCl₃, 100 MHz): δ 153.1, 136.7, 131.7, 129.6, 129.3, 128.9, 127.6, 126.3, 124.2, 115.1, 38.5, 15.9
IR (CHCl₃): 3847, 3350, 3058, 2921, 2850, 2351, 2284, 1600, 1585, 1501, 1479, 1436, 1384, 1368, 1298, 1265, 1245,
1201, 1151, 1114, 1089, 1070, 1042, 1024  cm^-1

2-Methyl-4,6-bis((phenylthio)methyl)phenol (1b): light brown solid  m.p : 97-99°c
¹H NMR: (CDCl₃, 400 MHz): δ 7.34-7.31 (m, 2H), 7.27-7.17 (m, 8H), 6.97 (s, 1H), 6.84 (s, 1H), 5.95 (s, 1H), 4.11 (s, 2H), 3.96 (s, 2H), 2.21 (s, 3H).
¹³C NMR: (CDCl₃, 100 MHz): δ 152.2, 136.7, 134.5, 131.0, 130.7, 129.6, 129.0, 128.9, 128.8, 128.7, 127.1, 126.2, 125.4, 122.0, 38.4, 36.0, 15.9.
IR (CHCl₃): 3445, 2921, 2852, 1619, 1480, 1438, 1019 cm^-1.