Ammonium Phosphorodithioate: A Mild, Easily Handled, Efficient, and Air-Stable Reagent for the Conversion of Amides into Thioamides

Abstract

A simple, efficient, and new method has been developed for the synthesis of thioamides from amides. As described below, the reaction of a variety of aromatic and aliphatic amides in the presence of ammonium phosphorodithioate as an efficient reagent proceeded effectively to afford the corresponding thioamides in high yields. This method is easy, rapid, and high-yielding for the synthesis of thioamides from amides using an easily handled reagent.

Key words

thioamides - amides - phosphorodithioates - thionation

References and Notes

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17

The amide (5 mmol) was added to a mixture of O,O-diethyl ammonium phosphorodithioate salt (10 mmol, 2.03 g)^¹6a and toluene (5 mL), and the reaction mixture was stirred for 4-10 h at reflux. After stirring for a known period (Table  [²] ), the mixture was evaporated under reduced pressure. The resulting mixture was subjected to column chromatography on silica gel with EtOAc-n-hexane (1:9), and evaporation of the solvent under reduced pressure gave pure products in 70-91% yields. All products gave satisfactory spectral data in accord with the assigned structures and literature reports.^{9-¹6,¹8-²²}
Thiobenzamide (2a)
^¹H NMR (400 MHz, CDCl₃): δ = 7.29 (br, 1 H, NH₂), 7.43 (t, 2 H, J = 8.0 Hz), 7.54 (t, 1 H, J = 8.0 Hz), 7.89 (d, 2 H, J = 8.0 Hz), 7.90 (br, 1 H, NH₂). ^¹³C NMR (100.65 MHz, CDCl₃): δ = 126.9, 128.5, 132.1, 139.2, 202.2.
2-Chlorothiobenzamide (2b)
^¹H NMR (400 MHz, CDCl₃): δ = 7.35 (br, 1 H, NH₂), 7.28-7.48 (m, 3 H), 7.62 (d, 1 H, J = 8.0 Hz), 8.45 (br, 1 H, NH₂). ^¹³C NMR (100.65 MHz, CDCl₃): δ = 127.1, 128.2, 130.1, 130.2, 131.0, 140.4, 201.5.
3-Chlorothiobenzamide (2c)
^¹H NMR (400 MHz, CDCl₃): δ = 7.29 (br, 1 H, NH₂), 7.37 (t, 1 H, J = 8.0 Hz), 7.50 (d, 1 H, J = 8.0 Hz), 7.72 (d, 1 H, J = 8.0 Hz), 7.88 (s, 1 H), 7.92 (br, 1 H, NH₂). ^¹³C NMR (100.65 MHz, CDCl₃): δ = 124.8, 127.3, 131.9, 134.6, 140.8, 201.1.
N -Phenylthiobenzamide (2d)
^¹H NMR (400 MHz, CDCl₃): δ = 7.23-7.90 (m, 10 H), 9.03 (br, 1 H, NH). ^¹³C NMR (100.65 MHz, CDCl₃): δ = 123.6, 126.7, 127.0, 128.7, 129.1, 131.3, 138.9, 143.3, 198.3.
N -(2-Ethylphenyl)thiobenzamide (2e)
^¹H NMR (400 MHz, CDCl₃): δ = 1.29 (t, 3 H, J = 7.6 Hz), 2.71 (q, 2 H, J = 7.6 Hz), 7.23-7.45 (m, 3 H), 7.47 (t, 2 H, J = 7.6 Hz), 7.57 (t, 2 H, J = 7.2 Hz), 7.93 (d, 2 H, J = 7.2 Hz), 8.87 (br, 1 H, NH). ^¹³C NMR (100.65 MHz, CDCl₃): δ = 14.4, 24.5, 126.8, 127.4, 128.5, 128.7, 129.2, 131.5, 137.0, 139.8, 142.2, 200.0.
N -(4-Methoxyphenyl)thiobenzamide (2f)
^¹H NMR (400 MHz, CDCl₃): δ = 3.88 (s, 3 H), 7.01 (d, 2 H, J = 7.2 Hz), 7.45 (t, 2 H, J = 7.6 Hz), 7.53 (t, 1 H, J = 7.2 Hz), 7.66 (d, 2 H, J = 7.2 Hz), 7.89 (d, 2 H, J = 7.2 Hz), 8.97 (br, 1 H, NH). ^¹³C NMR (100.65 MHz, CDCl₃): δ = 55.5, 114.2, 125.6, 126.7, 128.7, 129.2, 131.3, 131.9, 143.0, 158.2, 198.2.
N -(4-Bromophenyl)thiobenzamide (2g)
^¹H NMR (400 MHz, CDCl₃): δ = 7.40-7.65 (m, 5 H), 7.74 (d, 2 H, J = 7.2 Hz), 7.87 (d, 2 H, J = 7.2 Hz), 8.98 (br, 1 H, NH). ^¹³C NMR (100.65 MHz, CDCl₃): δ = 119.9, 125.1, 128.8, 129.2, 131.5, 132.2, 137.9, 198.0.
N -Cyclohexylthiobenzamide (2h)
^¹H NMR (400 MHz, CDCl₃): δ = 1.19-1.60 (m, 5 H), 1.62-1.85 (m, 3 H), 2.17-2.25 (m, 2 H), 4.48-4.61 (m, 1 H), 7.36 (t, 2 H, J = 7.6 Hz), 7.44 (t, 1 H, J = 7.2 Hz), 7.54 (br, 1 H, NH), 7.70 (d, 2 H, J = 7.2 Hz). ^¹³C NMR (100.65 MHz, CDCl₃): δ = 24.7, 25.5, 31.6, 55.0, 126.7, 128.4, 130.9, 142.3, 197.6.
2-Chloro- N -cyclohexylthiobenzamide (2i)
^¹H NMR (400 MHz, CDCl₃): δ = 1.19-1.60 (m, 5 H), 1.62-1.85 (m, 3 H), 2.17-2.25 (m, 2 H), 4.48-4.62 (m, 1 H), 7.27-7.40 (m, 3 H, NH), 7.50-7.40 (m, 1 H), 7.57-7.62 (m, 1 H). ^¹³C NMR (100.65 MHz, CDCl₃): δ = 24.6, 25.5, 31.3, 54.8, 127.0, 128.3, 129.9, 130.1, 130.3, 142.2, 195.5.
N,N- Dimethylthiobenzamide (2j)
^¹H NMR (400 MHz, CDCl₃): δ = 3.03 (s, 3 H), 3.47 (s, 3 H), 7.15-7.29 (m, 5 H). ^¹³C NMR (100.65 MHz, CDCl₃): δ = 43.2, 44.2, 125.7, 128.3, 128.5, 143.3, 200.7.
4-Methyl- N , N- dimethylthiobenzamide (2k)
^¹H NMR (400 MHz, CDCl₃): δ = 2.34 (s, 3 H), 3.16 (s, 3 H), 3.57 (s, 3 H), 7.13 (d, 2 H, J = 8.0 Hz), 7.20 (d, 2 H, J = 8.0 Hz). ^¹³C NMR (100.65 MHz, CDCl₃): δ = 21.3, 43.4, 44.3, 125.9, 128.9, 138.7, 140.6, 201.4.
4-Chloro- N , N- dimethylthiobenzamide (2l)
CAS No. 15563-46. ^¹H NMR (400 MHz, CDCl₃): δ = 3.19 (s, 3 H), 3.60 (s, 3 H), 7.26 (d, 2 H, J = 8.4 Hz), 7.34 (d, 2 H, J = 8.4 Hz). ^¹³C NMR (100.65 MHz, CDCl₃): δ = 43.3, 44.2, 127.3, 128.6, 134.6, 141.6, 199.8.
3-Methyl- N , N- dimethylthiobenzamide (2m)
^¹H NMR (400 MHz, CDCl₃): δ = 2.34 (s, 3 H), 3.14 (s, 3 H), 3.57 (s, 3 H), 7.05 (d, 1 H, J = 7.6 Hz), 7.12 (d, 2 H, J = 6.0 Hz), 7.22 (d, 1 H, J = 8.0 Hz). ^¹³C NMR (100.65 MHz, CDCl₃): δ = 21.4, 43.2, 44.2, 122.6, 126.3, 128.2, 129.3, 138.1, 143.4, 201.4.
Thioacetamide (2n)
CAS No. 62-55-5. ^¹H NMR (400 MHz, CDCl₃): δ = 3.34 (s, 3 H), 8.90-9.20 (br, 2 H, NH₂). ^¹³C NMR (100.65 MHz, CDCl₃): δ = 31.0, 206.1.