Carbonylation of amines with carbon dioxide under atmospheric conditions

Bis[(S)-(−)-α-methylbenzyl]thiourea

“…Our recent interest in the application of guanidines as ligands for transition metals has lead us to isolate a number of different thiourea compounds as intermediates in their synthesis (Bailey, Blake, Kryszczuk, Parsons & Reed, 1995). We report here the crystal structure of one of these, namely, enantiomerically pure bis[(S)-(-)-a-methylbenzyl]thiourea, (1), which was synthesized via standard procedures from (S)-(-)-a-methylbenzylamine and carbon disulfide (Yamazaki, Higashi & Iguchi, 1974 The crystal structure is composed of discrete molecules of (1) (Fig. 1), the bond lengths and angles (Table 1) being quite typical for acyclic thiourea compounds in the Cambridge Structural Database (Allen & Kennard, 1993;Fletcher, McMeeking & Parkin, © 1997 International Union of Crystallography Printed in Great Britain -all rights reserved Compound (1) should thus be properly regarded as a resonance hybrid of C:N-containing canonical forms, with only a relatively small contribution from the C:Sbonded form frequently used to represent thiourea compounds (see scheme below).…”

Carbon dioxide: a renewable feedstock for the synthesis of fine and bulk chemicals

“…However, these methylating reagents are relatively expensive and are currently produced via similar hazardous routes of phosgenation or oxidative carbonylation. Hence, an idea of direct synthesis of 1,3-disubstituted ureas from amines and CO 2 come forward (Scheme 17) [217][218][219][220][221][222]. Different catalysts, such as RuCl 3 $H 2 O/Bu 3 P and Ph 3 SbO/P 4 S 10 [223] have been reported for 1,3-disubstituted urea synthesis from CO 2 .…”

“…In these reactions water is formed as the only by-product. As these reactions are reversible, the addition of dehydrating agents such as POCl 3 , propargyl alcohols [224], Me 3 NSO 3 [221], diorganophosphites [225], and carbodiimide [219] is required to increase the yield of the target product. Vos and coworkers prepared symmetrical and unsymmetrical urea derivatives in good yields from CO 2 and amines using Cs + base catalysts and N-methylpyrrolidone as the solvent without a dehydrating agent [217].…”

Co(acac)3/BMMImCl as a base-free catalyst system for clean syntheses of N,N′-disubstituted ureas from amines and CO2

“…and strong bases (i.e., NEt 3 , DBU, etc.) is worse [20][21][22][23]. Thus, the development of effective catalysts for the syntheses of N,N′-disubstituted ureas with CO 2 as the carbonyl source is highly desirable.…”