Imidazolines Subject

The broader subject of the interaction of stable carbenes with main-group compounds has recently been reviewed. Accordingly, the following discussion focuses on metallic elements of the s and p blocks. Dimeric NHC-alkali adducts have been characterized for lithium, sodium, and potassium. For imidazolin-2-ylidenes, alkoxy-bridged lithium dimer 20 and a lithium-cyclopentadienyl derivative 21 have been reported. For tetrahydropyrimid-2-ylidenes, amido-bridged dimers 22 have been characterized for lithium, sodium, and potassium. Since one of the synthetic approaches to stable NHCs involves the deprotonation of imidazolium cations with alkali metal bases, the interactions of alkali metal cations with NHCs are considered to be important for understanding the solution behavior of NHCs. 

The 3-alkyl, benzyl and phenyl derivatives of l-(2-hydroxy-4-bromophenyl)-3-methyl-4-imidazolin-2-one have been studied by solid-state C CPMAS NMR. The differences in chemical shifts A = 5(liquid) — 8(solid) are significant for aromatic carbons C3 ( — 2.9 ppm), C4 (3.6 ppm) and C5 (—3.9 ppm) and C7 (—1.5 ppm), which are adjacent to N1-C4, and are subject to the largest changes of the environment during reorientation of the imidazolin-2-one moiety. 

Interestingly, when lower temperature and energy microwave is used, loss of water does not occur, and die imidazolin-pyridinium salt forms. When this intermediate is subjected to the hydrolysis conditions, a Dimroth-type rearrangement is proposed to occur which leads to the alkyl substituent that was at die 1-position of the imidazole ring to now be on the 2-amino-substituent as shown. 

Heine also demonstrated that the rearrangement can occur on differentially acylated aziridines to give rise to different heterocycles such as imidazolines (11), imidazolones (13), and complex heterocycles such as 15. Futhermore, this reaction has been the subject of reviews by Heine and others. 

Compatibility Corrosion inhibitors can undergo reactions with components of the environment. Amines react with HjS. Unsaturated fatty acids and derivatives thereof (imidazolines) are subject to vulcanization in the presence of elemental sulfur or oxygen in combination with HjS. Polyfunctional acids react with polyfunctional amines to form gels or solids. Such considerations are important, since production or process streams are often treated with more than one chemical (oil and gas production processing, transport and refining, cooling water circuits— the examples are endless). 

The first step is the synthesis of dihromosilane LSiBr2 by the treatment of imidazolin-2-iminato lithium LiL with Cp SiBr3. The dihromosilane is afterward subjected to reduction to yield the iminosilylene. 

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