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Preparation of 1° Amines: Hofmann and Curtius Rearrangement Overview

Preparation of 1° Amines: Hofmann and Curtius Rearrangement Overview

In the presence of an aqueous base and a halogen, primary amides can lose the carbonyl (as carbon dioxide) and undergo rearrangement to form primary amines. This reaction, called the Hofmann rearrangement, can produce primary amines (aryl and alkyl) in high yields without contamination by secondary and tertiary amines.

Diazonium Group Substitution: –OH and –H

Diazonium Group Substitution: –OH and –H

Nitrous acid, a weak acid, is prepared in situ via the reaction of sodium nitrite with a strong acid under cold conditions. This nitrous acid prepared in situ reacts with primary arylamines to form arenediazonium salts. Such reactions are known as diazotization reactions. As shown in Figure 1, the formation of arenediazonium salts begins with the decomposition of nitrous acid in an acidic solution to give nitrosonium ions.

Preparation of 1° Amines: Hofmann and Curtius Rearrangement Mechanism

Preparation of 1° Amines: Hofmann and Curtius Rearrangement Mechanism

The Hofmann and Curtius rearrangement reactions can be applied to synthesize primary amines from carboxylic acid derivatives such as amides and acyl azides. In the Hofmann rearrangement, a primary amide undergoes deprotonation in the presence of a base, followed by halogenation to generate an N-haloamide. A second proton abstraction produces a stabilized anionic species, which rearranges to an isocyanate intermediate via an alkyl group migration from the carbonyl carbon to the neighboring...

Structural Isomerism

Structural Isomerism

Isomerism in Complexes
Isomers are different chemical species that have the same chemical formula. Structural isomerism of coordination compounds can be divided into two subcategories, the linkage isomers and coordination-sphere isomers.
Linkage isomers occur when the coordination compound contains a ligand that can bind to the transition metal center through two different atoms. For example, the CN− ligand can bind through the carbon atom or through the nitrogen atom. Similarly, SCN− can...

Structure of Amines

Structure of Amines

The hybridized nitrogen atom in amines possesses a lone pair of electrons and is bound to three substituents with a bond angle of around 108°, which is less than the tetrahedral angle of 109.5°. However, the C–N–H bond angle is slightly larger at 112°, with a carbon–nitrogen bond length of 147 pm. This carbon–nitrogen bond length of of amines is longer than the carbon–oxygen bond of alcohols (143 pm) but shorter than alkanes’ carbon–carbon bond (154 pm). These aspects are...

Nomenclature of Aryl and Heterocyclic Amines

Nomenclature of Aryl and Heterocyclic Amines

The simplest aromatic amine is phenylamine, which contains an –NH2 functionality directly attached to an aromatic ring. The name aniline is designated for this skeleton. As shown in Figure 1, the common names of the functionalized anilines involve prefixes ortho-, meta-, and para- to indicate the substitution position. Different functionalized aniline derivatives also have notable trivial names.

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Updated: Mar 15, 2026

Regioselective O-Glycosylation of Nucleosides via the Temporary 2',3'-Diol Protection by a Boronic Ester for the Synthesis of Disaccharide Nucleosides

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Published on: July 26, 2018

Concomitant polymorphs of 1,3-bis(3-fluorophenyl)urea.

Christina A Capacci-Daniel¹, Jeffery A Bertke¹, Shoaleh Dehghan¹

¹Department of Chemistry, Georgetown University, 37th & O St. NW, Washington, DC 20057, USA.

Acta Crystallographica. Section C, Structural Chemistry

|September 3, 2016

Summary

Crystal engineering studies reveal two polymorphs of 1,3-bis(3-fluorophenyl)urea. One form shows typical antiparallel urea chains, while the other exhibits a rare parallel chain orientation.

Keywords:

Hirshfeld surface analysis crystal structure diphenylurea fluorine hydrogen-bonding motifs polymorph

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Synthesis of pH Dependent Pyrazole, Imidazole, and Isoindolone Dipyrrinone Fluorophores using a Claisen-Schmidt Condensation Approach

Synthesis of pH Dependent Pyrazole, Imidazole, and Isoindolone Dipyrrinone Fluorophores using a Claisen-Schmidt Condensation Approach

Published on: June 10, 2021

Area of Science:

Crystal engineering
Supramolecular chemistry
Materials science

Background:

Hydrogen bonding in urea functionalities is a key structural motif in crystal engineering.
Diphenylureas commonly exhibit antiparallel hydrogen-bonded chains in their crystalline structures.

Purpose of the Study:

To investigate the polymorphic behavior of 1,3-bis(3-fluorophenyl)urea during crystallization.
To characterize the different crystal structures and hydrogen bonding arrangements formed.

Main Methods:

Crystallization of 1,3-bis(3-fluorophenyl)urea from various solvents.
X-ray diffraction analysis to determine crystal structures.
Analysis of hydrogen bonding patterns and molecular packing.

Main Results:

Crystallization yielded mixtures of at least two polymorphs.
The monoclinic polymorph features one-dimensional antiparallel urea chains, consistent with typical diphenylureas.
The orthorhombic polymorph displays one-dimensional parallel urea chains, a rare orientation for symmetrically substituted diphenylureas.

Conclusions:

1,3-bis(3-fluorophenyl)urea exhibits complex polymorphic behavior.
The study highlights the formation of a rarely observed parallel hydrogen-bonded chain motif in the orthorhombic polymorph.
This finding contributes to the understanding of crystal structure control in urea derivatives.