Demethylation of 2-methoxy-9H-thioxanthen-9-one

SyntheticPage 868

DOI:

10.1039/SP868

Submitted: November 13, 2018, published: November 14, 2018

Authors

Mariyah Sajjad

Mark Wainwright (M.Wainwright@ljmu.ac.uk)

Robert Smith (rbsmith@uclan.ac.uk)

Robin W.R. van den Kieboom

A contribution from

Smith Group

Chemicals

2-Methoxy-9H-thioxanthen-9-one (prepared in house, see Synthetic Page 847)

Hydrobromic acid (Sigma Aldrich)

Glacial Acetic Acid (Fisher Scientific)

Procedure

To a quick fit round bottomed flask charged 2-methoxy-9H-thioxanthen-9-one (2.42 g, 10 mmol), concentrated hydrobromic acid (20 mL) and glacial acetic acid (20 mL) and the reaction mixture was heated to reflux for 6h with constant stirring.* Upon cooling the reaction mixture was poured over ice (200 g) and distilled water (300 mL) was added slowly with vigorous stirring. The yellow precipitate produced was isolated and dried at the vacuum pump to yield 2-hydroxy-9H-thioxanthen-9-one (2.02g, 89%) as a yellow solid.

Author Comments

* A quick fit round bottomed flask and reflux condenser was used, which fitted snugly into a metal heating block. A thermocouple was used to control the temperature and 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.

Data

¹H NMR (400 MHz, DMSO-d₆) δ 8.43 (d, J = 7.9 Hz, 1H), 7.84 (d, J = 2.7 Hz, 1H), 7.80 – 7.68 (m, 2H), 7.68 – 7.63 (m, 1H), 7.53 (t, J = 7.5 Hz, 1H), 7.26 (dd, J = 8.7, 2.8 Hz, 1H). ¹³C NMR (101 MHz, DMSO) δ 179.04, 156.90, 137.43, 133.07, 130.05, 129.51, 128.46, 128.19, 126.94, 126.82, 126.60, 123.17, 113.67. LCMS m/z: 229 [M+]

Lead Reference

Casimero, C., McConville, A., John-Joe, F., Lawrence, C.L., Taylor, C.M., Smith, R.B., Davis J. Sensor systems for bacterial reactors: A new flavin-phenol composite film for the in situ voltammetric measurement of pH (2018) Analytica Chimica Acta, (2018), 1027, pp. 1-8