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The Royal Society of Chemistry"

Formation of benzyl azide from benzyl bromide

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Submitted: May 6, 2010, published: May 6, 2010

Authors

Peter Scott (peter.scott@warwick.ac.uk)

Suzanne Elizabeth Howson (s.e.howson@warwick.ac.uk)

A contribution from 

Reaction Scheme

Chemicals

Benzyl bromide
Dimethyl sulfoxide (DMSO)
Sodium azide
Water (distilled)
Diethyl ether
Sodium sulfate

Procedure

Benzyl bromide (2.0 ml, 16.84 mmol, 1.0 eq.) was dissolved in DMSO (40 ml). Sodium azide (1.64 g, 25.26 mmol, 1.5 eq.) was added as a solid and the reaction was stirred overnight at ambient temperature. Water (75 ml) was added slowly (exothermic) before extracting the product into diethyl ether (3 × 150 ml). The combined diethyl ether layers were washed with brine (2 × 150 ml), dried over sodium sulfate and the solvent removed to leave a clear oil. Yield = 1.63 g, 12.24 mmol, 73%.

Data

1H NMR (400 MHz, 298 K, CDCl3) 7.42-7.32 (5H, m, Ph), 4.35 (2H, s, CH2).

 13C{1H} NMR (100 MHz, 298 K, CDCl3) 135.4 (Ph), 128.9 (Ph), 128.3 (Ph), 128.2 (Ph), 54.8 (CH2).

 MS (EI/CI) m/z 105.1 [M-2N]+.

 IR cm-1: 2090 s, 1497 w, 1455 m, 1253 m, 876 w, 735 m, 696 s.

 Elemental Analysis found (Calculated for C7H7N3) % C 63.53 (63.14), H 5.72 (5.30), N 31.34 (31.56).

Lead Reference

E. J. O'Neil, K. M. DiVittorio and B. D. Smith, Org. Lett., 2007, 9, 199-202 (General Procedure for the synthesis of azides)

Keywords

alkyl/alkenyl/aryl halides, Azide, nucleophilic, substitution

Comments

Modification
I've had good results with 4:1 acetone:water as the solvent. The workup is a little simpler, as the acetone can be removed on a rotovap prior to extraction with diethyl ether.
By Brandon Findlay on July 13, 2012
re
good point, what about the yield?
By utbiotech on March 21, 2013
ofcourse work up is looks easier but better to remove excess azide by water work up before going for distillation..
By pavan on December 13, 2013
more than 48 hours needed for completion of the reaction
So I try this with benzyl chloride instead and it took more than 48 hours for the reaction to go to completion. Any suggestion to make it goes faster? Also what is the reason for such slowly reaction compare to bromide?
By David on March 22, 2017
question
I want to conduct a similar reaction on my brominated polymer. Want to find out if this reaction is carried out in a closed round bottom flask? If so how can I release the HBr by product that forms. Thank You.
By Sam on August 8, 2014
There is no HBr generated in the stoichiometric reaction here. The co-product is NaBr
By Peter Scott on August 11, 2014
Comment
Having made a lot of organic azides in my PhD, I fully recommend this procedure. Small organic azides are potentially explosive, so you really don't want to be heating them much/at all. The extraction into Et2O in this procedure is perfect, because it's so easy to remove on a rotavap with little/no heating.
By Nick on September 23, 2014
recommended
By utbiotech on November 24, 2015