|Named after||Gustave Louis Blanc|
|Reaction type||Substitution reaction|
|Organic Chemistry Portal|
The Blanc chloromethylation (also called the Blanc reaction) is the chemical reaction of aromatic rings with formaldehyde and hydrogen chloride catalyzed by zinc chloride or other Lewis acid to form chloromethyl arenes. The reaction was discovered by Gustave Louis Blanc (1872-1927) in 1923. The reaction is performed with care as, like most chloromethylation reactions, it produces highly carcinogenic bis(chloromethyl) ether as a by-product.
The reaction is carried out under acidic conditions and with a ZnCl2 catalyst. These conditions protonate the formaldehyde carbonyl making the carbon much more electrophilic. The aldehyde is then attacked by the aromatic pi-electrons, followed by rearomatization of the aromatic ring. The benzyl alcohol thus formed is quickly converted to the chloride under the reaction conditions.
Although the reaction is an efficient means of introducing a chloromethyl group, the production of small amounts of highly carcinogenic bis(chloromethyl) ether is a disadvantage.
Chloromethylation of thiols can be effected with concentrated HCl and formaldehyde:
- ArSH + CH2O + HCl → ArSCH2Cl + H2O
Chloromethylation can also be effected using chloromethyl methyl ether:
- ArH + CH3OCH2Cl → ArCH2Cl + CH3OH
- Gustave Louis Blanc Bull. Soc. Chim. France 1923, 33, 313
- Whitmore, F. C.; Ginsburg, Abram; Rueggeberg, Walter; Tharp, I.; Nottorf, H.; Cannon, M.; Carnahan, F.; Cryder, D.; FLeming, G.; Goldberg, G.; Haggard, H.; Herr, C.; Hoover, T.; Lovell, H.; Mraz, R.; Noll, C.; Oakwood, T.; Patterson, H.; Van Strien, R.; Walter, R.; Zook, H.; Wagner, R.; Weisgerber, C.; Wilkins, J. (May 1946). "Production of Benzyl Chloride by Chloromethylation of Benzene. Laboratory and Pilot Plant Studies". Industrial & Engineering Chemistry. 38 (5): 478–485. doi:10.1021/ie50437a013.
- Belen'kii, Leonid I; Vol'kenshtein, Yu B; Karmanova, I B (30 September 1977). "New Data on the Chloromethylation of Aromatic and Heteroaromatic Compounds". Russian Chemical Reviews. 46 (9): 891–903. Bibcode:1977RuCRv..46..891B. doi:10.1070/RC1977v046n09ABEH002180.
- D. Enders, S. Von Berg, B. Jandeleit (2002). "Diethyl [(Phenylsulfonyl)methyl]phosphonate". Org. Synth. 78: 169. doi:10.15227/orgsyn.078.0169.
- François Dardel and Thomas V. Arden "Ion Exchangers" in Ullmann's Encyclopedia of Industrial Chemistry, 2008, Wiley-VCH, Weinheim. doi:10.1002/14356007.a14_393.pub2
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