Wohler

Urea (the diamide of carbonic acid) can be prepared by the historic method of Wohler. When an aqueous solution of ammonium cyanate is allowed to stand, the cyanate undergoes molecular rearrangement to urea, and an equilibrium mixture containing about 93% of urea is thus formed. Urea is... 

Mono-substituted and unsymmetrical di-substituted ureas may be prepared by a modification of Wohler s urea synthesis, salts of primary or secondary amines being used instead of the ammonium salt for interaction with potassium cyanate. Thus when an aqueous solution containing both aniline hydrochloride and potassium cyanate is heated, aniline cyanate is first formed, and then C,HjNH,HCl -h KCNO = C,H6NHj,HCNO -h KCl C,HsNH HCNO = C.H NHCONH, by the usual molecular rearrangement is converted into monophenyburea. 

Wohler s classical synthesis of urea from ammonium cyanate may be carried out by evaporating solutions of sodium cyanate and ammonium sulphate ... 

Gr. beryllos, beryl also called Glucinium or Glucinum, Gr. glykys, sweet) Discovered as the oxide by Vauquelin in beryl and in emeralds in 1798. The metal was isolated in 1828 by Wohler and by Bussy independently by the action of potassium on beryllium chloride. 

Wohler is generally credited with having isolated the metal in 1827, although an impure form was prepared by Oersted two years earlier. In 1807, Davy proposed the name aluminum for the metal, undiscovered at that time, and later agreed to change it to aluminum. Shortly thereafter, the name aluminum was adopted to conform with the "ium" ending of most elements, and this spelling is now in use elsewhere in the world. 

It is recovered commercially from monazite sand, which contains about 3%, and from bastnasite, which contains about 0.2%. Wohler obtained the impure element in 1828 by reduction of the anhydrous chloride with potassium. The metal is now produced commercially by reduction of the fluoride with calcium metal. It can also be prepared by other techniques. 

The article Wohler and the Vital Force in the March 1957 issue of the ioc/rna/of Chemical Education (pp 141-142) describes how Wohler s experiment af fected the doctrine of vital ism A more recent account of the significance of Woh ler s work appears in the September 1996 issue of the same journal (pp 883-886)... 

What particularly seemed to excite Wohler and his mentor Berzelius about this experiment had very little to do with vitalism Berzelius was interested m cases m which two clearly different materials had the same elemental composition and he invented the term isomerism to define it The fact that an inorganic compound (ammonium cyanate) of molecular formula CH4N2O could be transformed into an organic compound (urea) of the same molecular formula had an important bearing on the concept of isomerism... 

In the introduction we noted that both Berzelius and Wohler were fascinated by the fact that two different compounds with different properties ammonium cyanate and urea pos sessed exactly the same molecular formula CH4N2O Berzelius had studied examples of similar phenomena earlier and invented the word isomer to describe different compounds that have the same molecular formula... 

The possibility of the existence of organosilicone compounds was first predicted by Dumas in 1840, and in 1857 Buff and Wohler found the substance now known to be trichlorosilane by passing hydrochloric acid gas over a heated mixture of silicone and carbon. In 1863 Friedel and Crafts prepared tetraethylsilane by reacting zinc diethyl with silicon tetrachloride. 

Cotarnine, This base, first obtained by Wohler, is... 

This German stamp depicts a molecular model of urea and was issued in 1982 to commemorate the hundredth anniversary of Wohler s death. The computer graphic that opened this introductory chapter is also a model of urea. 

The vitalist theory of Berzelius challenged by F. Wohler faged 28) who synthesized urea, (NH2)2CO. from NHaiOCN),... 

The hydroxyl derivative of X-CN is cyanic acid HO-CN it cannot be prepared pure due to rapid decomposition but it is probably present to the extent of about 3% when its tautomer, isocyanic acid (HNCO) is prepared from sodium cyanate and HCI. HNCO rapidly trimerizes to cyanuric acid (Fig. 8.25) from which it can be regenerated by pyrolysis. It is a fairly strong acid (Ka 1.2 x 10 at 0°) freezing at —86.8° and boiling at 23.5°C. Thermolysis of urea is an alternative route to HNCO and (HNCO)3 the reverse reaction, involving the isomerization of ammonium cyanate, is the clas.sic synthesis of urea by F. Wohler (1828) ... 

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