2-Nitro-9H-thioxanthen-​9-​one (prepared in house using similar methodology to the compound in Synthetic Page 847)

Glacial acetic acid (Fisher Scientific)

Anhydrous tin(II) chloride (Sigma Aldrich)

Concentrated hydrochloric acid (Fisher Scientific)

Sodium hydroxide (Sigma Aldrich)

To a round-bottomed flask was added 2-nitro-9H-thioxanthen-​9-​one (1.00 g, 3.81 mmol) and acetic acid, (14 mL) and the suspension was allowed to stir for 5 minutes. To the reaction mixture was added a solution of anhydrous tin(II) chloride, 4.20g, (22.15 mmol) dissolved in concentrated hydrochloric acid (6mL).  The reaction mixture was heated to 100°C for 3 hours.*  Upon cooling a dark yellow solid was isolated by vacuum filtration on a Buchner funnel and then transferred to a conical flask.  To the conical flask was added an aqueous solution of 2.5M sodium hydroxide (50 mL)** and the suspension was heated to boiling for 15 minutes.  Upon cooling, the crude solid was isolated by vacuum filtration on a Buchner funnel and washed with acetic acid (20 mL).  The compound was recrystallized from propan-2-ol to yield 2-amino-thioxanthen-9-one (0.56 g, 63%) as bright-orange needles.

*A round-bottomed flask fitted with a reflux condenser was used which fitted snugly into a metal heating block.  A thermocouple was used to control the temperature and the reaction was open to the air (no inert gasses were required).  Stirring was accomplished using a stirring bar, which was controlled from the hot plate.  The whole reaction was accomplished in the open air without the need of dry/inert conditions.  It should also be noted that the reaction mixture remained as a suspension for the whole of the reaction time.

**pH was not monitored.

¹H NMR (400 MHz, DMSO-d₆) δ 8.47 – 8.43 (m, 1H, Ar-H), 7.77 (dd, J = 8.1, 0.7 Hz, 1H, Ar-H), 7.73 – 7.65 (m, 2H, Ar-H), 7.55 – 7.48 (m, 2H, Ar-H), 7.10 (dd, J = 8.6, 2.7 Hz, 1H, Ar-H), 5.69 (s, 2H, NH_²).  ¹³C NMR (101 MHz, DMSO) δ 179.17, 148.56, 137.64, 132.66, 129.83, 129.51, 128.38, 127.58, 126.87, 126.41, 122.49, 121.69, 111.31. FTIR (cm^-1): 3430.36, 3339.29, 1600.84, 1584.48, 1457.32, 1435.73, 1343.17, 1319.80, 1162.72, 1077.75, 819.36, 733.68 GC/MS: m/z 227 [M+].

F.G. Mann and J.H. Turnbull, Xanthones and Thioxanthones Part I, Cambridge University Chemical Laboratory, Cambridge, 1950.