1,2-Bis(p-phenyl-thiocarbamic Acid-S-benzothiazol-2-yl-ester)ethane and 1-(o-Phenyl-thiocarbamic Acid-S-benzothiazol-2-yl-ester)-2-(p-phenyl-thiocarbamic Acid-S-benzothiazol-2-yl-ester)ethane

The experimental procedure follows the general synthesis of blocked isocyanates [1,2]. A solution of mercaptobenzothiazole (MBT) was obtained by mixing 23 g (0.1373 mol) with 250 mL 1,2-dichloroethane (DCE) and 50 mL acetone, then heating gradually to 35-50°C for 0.5 h until the mixture became homogeneous. A solution of 1,2-bis(p-isocyanato-phenyl)ethane (4,4'-dibenzyl diisocyanate) [3,4] (17 g, 0.0644 mol) in 100 mL DCE was added to this mixture under stirring during 0.25 h and then 0.2 g diazabicyclo[2.2.2]octane (DABCO) also was added. The mixture was stirred at 68-72°C for 6 - 8 h. After cooling, the light yellow solid was isolated by filtration, washed with DCE and acetone (to remove the excess of MBT) and dried at 90-100°C (22.5 g, 57.73% yield).

The synthesis of the nonsymmetrical isomer is described as follows. To a solution of MBT (5 g, 0.029895 mol) in 100 mL DCE and 15 mL acetone, 1-(o-isocyanato-phenyl)-2-(p-isocyanato-phenyl)ethane (2,4'-dibenzyl diisocyanate) (3.42 mL, 3.8 g, 0.01439 mol) and 0.1 g DABCO was added. The mixture was stirred for 10 h at 70-72°C. After cooling, the solid product was isolated by filtration, washed several times with acetone and dried (3 g, 34.84% yield).

1,2-Bis(p-phenyl-thiocarbamic acid-S-benzothiazol-2-yl-ester)ethane 

Thermal behavior: M.p. >328°C (decomposition), (thermo-optical method)

IR (KBr, cm^-1): 3320 m (NH), 3030 mw (C-H), 2945 mw (CH₂), 2850 mw (CH₂), 1720-1700 m (NHCOS), 1670-1650 m (CONH), 1600 ms (p-Ar), 1550 s, 1530 s, 1510 s (SCONH), 1500 m (sh, p-Ar), 1410 m (C-S, MBT), 1320 m (MBT, p-Ar), 1240 ms (C-S, C-O), 1200 m (sh, C-N, C-O), 1080 m (C-O, C-N), 835 m (p-Ar), 750 mw (C-N, MBT), 660 mw (C-S).

¹H NMR (60 MHz, d, DMSO-d₆, 80°C): 8.95, 8.2 (NH, 2H), 7.2, 7.08, 6.95, 6.8 (m, Ar, 16H), 3.62 (s, CH₂-Ar, 4H) ppm.

Elemental analysis: Calculated for: C₃₀H₂₂N₄O₂S₄: C%= 60.18; H%= 3.37; N%= 9.36; S%= 21.42. Found: C%= 60.58; H%= 3.73; N%= 9.87.

1-(o-phenyl-thiocarbamic acid-S-benzothiazol-2-yl-ester)-2-(p-phenyl-thiocarbamic acid-S-benzothiazol-2-yl-ester)ethane 

Thermal behavior: M.p.> 228°C (decomposition), (thermo-optical method).

IR (KBr, cm^-1): 3300 ms (NH), 3040 w (C-H), 2940 w (CH₂), 2865 w (CH₂), 1700 m (sh, NHCOS), 1680-1655 ms (CONH), 1610-1590 ms (Ar), 1550 s, 1515 s (SCONH), 1500 ms (sh, Ar), 1450 ms, 1410 m (C-S, MBT), 1330-1300 m (MBT), 1260-1240 ms (C-S, C-O), 1180 m (sh, C-N, C-O), 1090 mw (C-O), 830 mw (p-Ar), 760 m (o-Ar, NNCOS), 700 w, 670 w (C-S).

¹H NMR (60 MHz, d, DMSO-d₆, 60°C): 8.56, 8.2, 7.95 (t, NH, 2H), 7.65, 7.45, 7.3, 7.2, 7.07, 6.95, 6.85 (m, Ar, 16H), 3.56 (m, CH₂-Ar, 4H) ppm.

Elemental analysis: Calculated for: C₃₀H₂₂N₄O₂S₄: C%= 60.18; H%= 3.37; N%= 9.36; S%= 21.42. Found: C%= 60.47; H%= 3.85; N%= 9.65.