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Formation of benzyl azide from benzyl bromide; Benzyl azide

SyntheticPage 408
DOI: 10.1039/SP408
Submitted May 06, 2010, published May 06, 2010
Suzanne Elizabeth Howson (s.e.howson@warwick.ac.uk), Peter Scott (peter.scott@warwick.ac.uk)
A contribution from Scott group, Warwick University


			Reaction Scheme: Formation of <span id="csm1276782412706" class="csm-chemical-name" title="benzyl azide">benzyl azide</span> from <span id="csm1276782310388" class="csm-chemical-name" title="benzyl bromide">benzyl bromide</span>

Chemicals Used

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%.

Author's Comments

Suitable precautions should be taken in the synthesis of organic azides as they are all potentially explosive, and particularly so where the C/N ratio or similar calculation indicates that this is likely. While you should do your own research on this, the following references may be useful:

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
http://dx.doi.org/10.1021/ol062557a (General Procedure for the synthesis of azides)

Supplementary Information

Click to open Interactive 1H NMR
Click to open Interactive 13C NMR
1H NMR (1H Benzyl Azide.jcamp)
13C NMR (13C benzyl azide.jcamp)

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Get structure file (.cdx, .sk2, .mol)

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

Post new comment
  • Registered user Brandon FindlayJul 13 2012 7:44PMModification

    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.

    • Guest utbiotechMar 21 2013 11:45AMre

      good point, what about the yield?

      • Guest AntApr 24 2013 2:06PMre

        Using that ratio of acetone:water, with 30cc DCM and two extractions of distilled H2O (2 x 10cc) then the again with brine (2 x 10cc), got a yield of 67%. There's a source floating around that claims 100% (http://www.rsc.org/suppdata/cc/b8/b822994e/b822994e.pdf) though they use much less starting material (60mmol for us vs 2.5mmol for them)

    • Guest pavanDec 13 2013 9:57AM

      ofcourse work up is looks easier but better to remove excess azide by water work up before going for distillation..

    • 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?

      • Registered user Peter ScottMar 23 2017 10:02AM

        While this is not a forum for advice on reactions you may wish to consider that bromide is a better leaving group than chloride, so if loss of halide is rate-limiting, the reaction with chloride will be slower. You must ensure that a full and competent risk assessment is carried out in your chemistry, particularly when hazardous substances such as azides are being used and formed.

  • Guest SamAug 8 2014 7:07PMquestion

    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.

    • Registered user Peter ScottAug 11 2014 6:31PM

      There is no HBr generated in the stoichiometric reaction here. The co-product is NaBr

  • Guest NickSep 23 2014 5:57PMComment

    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.

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