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Demethylation of 2-​methoxy-9H-thioxanthen-​9-​one; 2-Hydroxy-9H-thioxanthen-​9-​one

SyntheticPage 868
DOI: 10.1039/SP868
Submitted Nov 13, 2018, published Nov 14, 2018
Robert Smith (, Mariyah Sajjad (), Mark Wainwright (, Robin W.R. van den Kieboom ()
A contribution from Smith Group

			Reaction Scheme: <IMG src="/images/empty.gif">Demethylation of <SPAN id=csm1542205824667 class="csm-chemical-name csm-not-validated" title=2-​methoxy-9H-thioxanthen-​9-​one grpid="1">2-​methoxy-<EM>9H</EM>-thioxanthen-​9-​one</SPAN><IMG src="/images/empty.gif">

Chemicals Used

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

Hydrobromic acid (Sigma Aldrich)

Glacial Acetic Acid (Fisher Scientific)


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's 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.


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

Supplementary Information

1H - 31696-67-0.pdf
1H1H COSY - 31696-67-0.pdf
13C - 31696-67-0.pdf
13C vs 135DEPT - 31696-67-0.pdf
135DEPT - 31696-67-0.pdf

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Keywords: alcohols, aromatics/arenes, demethylation, ethers, ketones, thiol

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