Microscale – Preparation of 9-bromoanthracene

Objective

To acquaint students with the free-radical halogenation reactions, in particular a bromination using N-bromosuccinimide (NBS).

Synthesis of 9-bromoanthracene
Synthesis of 9-bromoanthracene

Background

N-bromosuccinimide (NBS) is used as a highly specific bromination agent both in free-radical substitutions and in electrophilic additions of unsaturated systems, because releases small quantities of bromine.

Anthracene can be brominated at position 9 by a radical process. The reaction begins with Br2 formation from NBS. Light or other initiating agents can produce Br·, which attacks anthracene at position 9 to give a 9-anthracenyl radical and HBr. HBr reacts with new molecules of NBS to produce more new Br2 molecules and succinimide. Bromine reacts with the formed 9-anthracenyl radical to give the substitution product and a new bromine radical, which promotes the reaction (propagation step).

Microscale experimental procedure

In a 25 ml Erlenmeyer prepare a solution of 200 mg of I2 in 10 ml of CCl4. Cap the flask containing the mixture with a septum and store in the fume hood for the next step. Mix 50 mg of anthracene (0.28 mmol) 50 mg and NBS (0.28 mmol) with 0.4 ml of CCl4 in a conic vial with a spin vane. With a Pasteur pipette, add 1 drop of the I2/CCl4 solution. Fix a water-jacketed condenser with a dry tube and reflux for 1 h. A brownish color will appear and a solid will form, corresponding to succinimide. After reflux, cool the mixture to r.t. Filter the succinimide under vacuum with a Hirsch funnel, and then wash the solid with cold CCl4 (2 × 1 ml). Transfer the organic solution to a tared 10 ml round-bottom flask, and eliminate the solvent under vacuum (rotary evaporator) to get a greenish yellow solid corresponding to 9-bromoanthracene. Once the solid is dry, weigh and calculate the yield. Purify the final product by recrystallization in a Craig tube in 95% EtOH (m.p. = 101-103 ºC).

Physico-chemical properties

This table collects data for the molecular weight (Mw), melting point (M.p.) boiling point (B.p.) and density of the reactives and compounds used in this laboratory experiment.

Name Mw (g/mol) M.p. (ºC) B.p. (ºC) Density (g/ml)
Anthracene178.23210-215340 -
Br2159.817.258.8 -
CCl4153.82-2376-771.594
EtOH46.07-114.178.50.790
HBr80.91-87-672.140
Iodine I2253.811131844.930
Succinimide99.09123-125285-290 -
9-(Hydroxymethyl)anthracene208.26162-164 - -
9-Bromoanthracene257.1397-103 - -

GHS pictograms

Hazard pictograms form part of the international Globally Harmonized System of Classification and Labelling of Chemicals (GHS) and are collected in the followinf Table for the chemical compounds used in this experiment.

Name GHS
Anthracene ghs07  Warning Toxic cat. 4 Irritant cat. 2 or 3 Lower systemic health hazards pictogram ghs09  Warning (for cat. 1) (for cat. 2 no signal word) Environmental hazard pictogram
Br2 ghs06  Danger Toxic cat. 1–3 pictogram ghs05  Danger Warning Corrosive cat. 1 pictogram ghs09  Warning (for cat. 1) (for cat. 2 no signal word) Environmental hazard pictogram
CCl4 ghs08  Danger Warning Systemic health hazards pictogram ghs06  Danger Toxic cat. 1–3 pictogram
EtOH ghs02  Danger Warning Flammable pictogram
HBr ghs05  Danger Warning Corrosive cat. 1 pictogram ghs07  Warning Toxic cat. 4 Irritant cat. 2 or 3 Lower systemic health hazards pictogram ghs04  Warning Compressed gas pictogram
Iodine I2 ghs07  Warning Toxic cat. 4 Irritant cat. 2 or 3 Lower systemic health hazards pictogram ghs09  Warning (for cat. 1) (for cat. 2 no signal word) Environmental hazard pictogram
Succinimide Non-hazardous
9-(Hydroxymethyl)anthracene Non-hazardous
9-Bromoanthracene Non-hazardous

International Chemical Identifier

The IUPAC InChI key identifiers for the main compounds used in this experiment are provided to facilitate the nomenclature and formulation of chemical compounds and the search for information on the Internet for these compounds.

AnthraceneMWPLVEDNUUSJAV-UHFFFAOYSA-N
Br2GDTBXPJZTBHREO-UHFFFAOYSA-N
CCl4VZGDMQKNWNREIO-UHFFFAOYSA-N
EtOHLFQSCWFLJHTTHZ-UHFFFAOYSA-N
HBrCPELXLSAUQHCOX-UHFFFAOYSA-N
Iodine I2PNDPGZBMCMUPRI-UHFFFAOYSA-N
SuccinimideKZNICNPSHKQLFF-UHFFFAOYSA-N
9-(Hydroxymethyl)anthraceneJCJNNHDZTLRSGN-UHFFFAOYSA-N
9-BromoanthraceneZIRVQSRSPDUEOJ-UHFFFAOYSA-N

References

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