2-Methyl-1,3-benzothiazole (Alfa)

Sulphuric acid (Fisher Scientific)

Nitric Acid (Fisher Scientific)

To a 250 mL wide necked conical flask* was added 2-methyl-1,3-benzothiazole (11.66 g, 78 mmol) and concentrated sulphuric acid (46 mL).  The solution was transferred to an ice bath and with constant stirring a pre-cooled mixture of concentrated sulphuric acid (7 mL) and concentrated nitric acid (9.4 mL, 0.23 mol) was added dropwise via a dropping funnel. Upon total addition of the acidic mixture, the reaction was allowed to stir at room temperature for 3 hours. The reaction mixture was then poured over ice (approx. 500 g) which yielded a red precipitate.  Upon standing overnight, the pH was then adjusted to pH=8, via the slow addition of sodium hydroxide pellets** and the precipitate produced upon neutralisation was isolated by vacuum filtration and washed with deionised water (500 mL). The solid was recrystallised in a minimum amount of hot methanol to afford 6-nitro-2-methylbenzothiazole (13.04 g, 86%) as yellow/cream flake-like crystals.

*A conical flat bottomed flask fitted with a dropping funnel was used.  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.

** Universal indicator paper was used to monitor the change in pH to pH=8.

1H-NMR (300 MHz, DMSO-d6): δ 9.12 (d, J = 2.0 Hz, 1H, Ar-H), 8.31 (dd, J = 9.0, 2.0 Hz, 1H, Ar-H), 8.10 (d, J = 9.0 Hz, 1H, Ar-H), 2.89 (s, 3H, C-CH3). 13C-NMR (300 MHz, DMSO-d6): δ 175.09, 157.25, 144.54, 136.40, 122.77, 121.86, 119.60, 20.72. IR (ATR): 3066, 2995, 1601, 1569, 1503, 1434, 1329, 1268, 1174, 1117, 993, 903, 821, 749, 671. GC-MS (EI) m/z: 193.95 ([M-H]+). 

Demeter, O., Kormos, A., Koehler, C., Mezö, G., Németh, K., Kozma, E., Takács, L.B., Lemke, E.A., Kele, P. Bisazide Cyanine Dyes as Fluorogenic Probes for Bis-Cyclooctynylated Peptide Tags and as Fluorogenic Cross-Linkers of Cyclooctynylated Proteins (2017) Bioconjugate Chemistry, 28 (5), pp. 1552-1559.