Carbylamine reaction: Difference between revisions
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{{Short description|Method of synthesizing an isocyanide}} |
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The '''Carbylamine reaction''' is a [[chemical test]] for detection of primary [[amine]]s. In this reaction, the analyte is heated with alcoholic [[potassium hydroxide]] and chloroform. If a primary amine is present, the isocyanide is formed. |
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The '''carbylamine reaction''' (also known as the '''Hoffmann isocyanide synthesis''') is the synthesis of an isocyanide by the reaction of a [[primary amine]], [[chloroform]], and base. The conversion involves the intermediacy of [[dichlorocarbene]]. |
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Illustrative is the synthesis of [[tert-Butyl isocyanide|''tert''-butyl isocyanide]] from [[Tert-Butylamine|''tert''-butylamine]] in the presence of [[catalytic]] amount of the [[phase transfer catalyst]] [[benzyltriethylammonium chloride]].<ref>{{cite journal|author1=G. W. Gokel|author2=R. P. Widera|author3=W. P. Weber| title = Phase-transfer Hofmann Carbylamine Reaction: tert-Butyl Isocyanide|journal=Organic Syntheses| volume=55|doi=10.15227/orgsyn.055.0096| pages = 232| year = 1988}}</ref> |
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For example, the reaction with ethylamine: |
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:Me<sub>3</sub>CNH<sub>2</sub> + CHCl<sub>3</sub> + 3 NaOH → Me<sub>3</sub>CNC + 3 NaCl + 3 H<sub>2</sub>O |
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Similar reactions have been reported for aniline. It is used to prepare secondary amines. |
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[[Image:Carbylamine.png|500px|The carbylamine reaction with ethyl amine]] |
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==Test for primary amines== |
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The reaction with aniline: |
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As it is only effective for primary amines, the carbylamine reaction can be used as a [[chemical test]] for their presence. In this context, the reaction is also known as '''Saytzeff's isocyanide test'''.<ref>[http://www.books-about-california.com/Pages/Experimental_Organic_Chemistry/Ex_Organic_Chem_Chap_09.html Carbylamine reaction]</ref> In this reaction, the analyte is heated with alcoholic [[potassium hydroxide]] and chloroform. If a primary amine is present, the [[isocyanide]] (carbylamine) is formed, as indicated by a foul odour. The carbylamine test does not give a positive reaction with secondary and tertiary amines. |
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==Mechanism== |
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[[Image:Carbylamine2.PNG|500px|The carbylamine reaction with aniline]] |
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The mechanism involves the addition of amine to dichlorocarbene, a reactive intermediate generated by the [[dehydrohalogenation]] of chloroform. Two successive base-mediated dehydrochlorination steps result in formation of the isocyanide. |
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[[File:Carbylamine mechanism.png|center|frameless|400x400px]] |
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The carbylamine test does not give a positive reaction with secondary and tertiary amines. |
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== See also == |
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[http://www.books-about-california.com/Pages/Experimental_Organic_Chemistry/Ex_Organic_Chem_Chap_09.html Carbylamine reaction] |
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* [[Isodiazomethane]] |
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* [[Carbene]] |
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==References== |
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{{Reflist}} |
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{{Organic reactions}} |
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[[Category:Organic reactions]] |
[[Category:Organic reactions]] |
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[[Category:Chemical tests]] |
[[Category:Chemical tests]] |
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Latest revision as of 20:57, 28 February 2024
The carbylamine reaction (also known as the Hoffmann isocyanide synthesis) is the synthesis of an isocyanide by the reaction of a primary amine, chloroform, and base. The conversion involves the intermediacy of dichlorocarbene.
Illustrative is the synthesis of tert-butyl isocyanide from tert-butylamine in the presence of catalytic amount of the phase transfer catalyst benzyltriethylammonium chloride.[1]
- Me3CNH2 + CHCl3 + 3 NaOH → Me3CNC + 3 NaCl + 3 H2O
Similar reactions have been reported for aniline. It is used to prepare secondary amines.
Test for primary amines
[edit]As it is only effective for primary amines, the carbylamine reaction can be used as a chemical test for their presence. In this context, the reaction is also known as Saytzeff's isocyanide test.[2] In this reaction, the analyte is heated with alcoholic potassium hydroxide and chloroform. If a primary amine is present, the isocyanide (carbylamine) is formed, as indicated by a foul odour. The carbylamine test does not give a positive reaction with secondary and tertiary amines.
Mechanism
[edit]The mechanism involves the addition of amine to dichlorocarbene, a reactive intermediate generated by the dehydrohalogenation of chloroform. Two successive base-mediated dehydrochlorination steps result in formation of the isocyanide.
See also
[edit]References
[edit]- ^ G. W. Gokel; R. P. Widera; W. P. Weber (1988). "Phase-transfer Hofmann Carbylamine Reaction: tert-Butyl Isocyanide". Organic Syntheses. 55: 232. doi:10.15227/orgsyn.055.0096.
- ^ Carbylamine reaction