CXVII.—The constitution of carbamides. Part XI. The mechanism of the synthesis of urea from ammonium carbamate. The preparation of certain mixed tri-substituted carbamates and dithiocarbamates
Journal of the Chemical Society Transactions
IN 1868 Basarov ( J . pr. Chern., [ii], 1, 283; Journ. Chem. Soc., 21, 194) obctaineld urea by the! action of he'at on ammolnium csasbamats under pressure. The change, which is suppmed to1 be obviously explaineld by the simple1 equation is always considered t o representl the1 ootnversa of the ultimate hydrolysis of urea t o ammoaium carbonatel, and foil-this relason this synthesis is commonly cited as elvide~nce pur excellence in favour of the1 deiwlptivei " carbaniide " cclnfiguration.++ To
... tisfy this view, it has been assumeld, without any proolf, that water is elliminakld from the group *O*NH" the produotion of urea beling thus analogous t o the formation od aaeltamide from ammonium acetate, or of olxamidei from ammonium oxalab. As a mattsr of fact, the mechanism of the formation of urea in this relaction is of quite a, cliffelrant order, since i t is nothing more than a moldifioation of Wohler's synthesis, namely, the production of urea from ammonia and cyanic acid (HNZCO) as the1 relsult of the fodlowing series od change6 : (HO*CN t HN:CO) + H20 ; (3) NH, + HN:CO + HN:C<& YH* . So far as ammoaium oarbarnab is concerned, the fact that urea and a,mmoaium uyanate were found in the p r d u d after vaporising the1 salt tlhrolugh a glass tnbe heiated t'o incipient, reldness is not final proof tchat cyanio acid was produced as shown a<bove, since Mixter ( A m e r . Chem. J., 1882, 4, 35) obtaineld urea from ca,rbon * It may be of interest, t o record that Kolbe, in presenting Basarov's paper to the Society, opens with the words : " From the conviction that urea is not carbamide "-a remark which, the author is equally convinced, has been fully justified.