Synthesis and Chemical Reactivity of Imidazolidines

Imidazolidine is a five-membered, saturated, nonplanar, nonaromatic heterocycle with two nitrogen atoms at the  1,3-positions. It is also referred to as methylene-bridged ethylenediamine or cyclic aminal and acts as a sec.amine.

Synthesis

Imidazolidines have been prepared in three steps. The initial step is the condensation of ethylenediamine with  aldehyde in dry benzene, which gave N,N′dibenzylideneethane-1,2-diamine and was reduced in the second step  with sodium borohydride in ethanol to N,N′-dibenzylethylenediamine. The substituted diamine on condensation  with aryl aldehyde in the final step afforded 1,3-dibenzyl-2-arylimidazolidine.

When one of the amino groups of ethylenediamine is in the form of a secondary amine. It also undergoes cyclocondensation with an aldehyde to build imidazolidine in 70% yields.

Ethylenediamine on reaction with cyanobromide underwent a substitution–cyclization reaction to form  2-iminoimidazolidine.

A mixture of triethoxymethane and glycine derivatives was refluxed in acetic anhydride for 2 h and cooled.  The resulting solid was filtered, purified, and characterized as 3-(4-hydroxyphenyl-2-(1H-imidazolidin-4-one-3-yl) propanoic acid.

It has been prepared by refluxing a mixture of ethylenediamine with ethyl trifluoromethylacetoacetate in xylene  with a Dean-Stark trap for 1 h and left standing overnight. The crystalline material was separated through decantation  of xylene. The crystalline material obtained was identified as 1,2,3,4-tetrahydro-7-trifluoromethyl-1,4-diazepin-5-one. The decanted xylene was evaporated and residual oil was fractionated in vacuo. On standing, the fraction collected at 77–78°C at 0.2 mm of pressure was solidified and crystallized from CCl4  and yielded 25%.

Imidazolidine-2-thiones have been prepared by the acid-catalyzed cyclocondensation of N,N′-diarylthiourea  and glyoxal in refluxing acetonitrile and afforded 1,3-diaryl-4,5-dihydroxyimidazolidine-2-thiones.

Imidazolin-2-ones have been prepared by heating ethylenediamine with urea in 75% yields.

Diethyl oxalate on condensation with urea yielded imidazolidine-2,4,5-trione.

Chemical Reactivity

Imidazolidines are found in both solid and liquid states depending on the substituent present. They are readily  soluble in organic solvents but insoluble in water. 

Imidazolidines are prone to hydrolyze with 10% aqueous HCl or H2 SO4  to the corresponding diamine and aldehyde but are unaffected with 10% aqueous sodium hydroxide. 1,3-Dibenzyl-2-phenylimidazolidine is easily hydrolyzed to 1,2-bis(benzylamino)ethane and benzaldehyde.

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