Lead cyanate

Wohler (1828) synthesized urea (an organic compound found in human urine) from lead cyanate and ammonium hydroxide, neither of which are found in living matter. 

Silicon tetraisocyanate is prepared from silicon tetrachloride and silver cyanate or lead cyanate. ... 

Until the mid-eighteenth century, scientists believed organic compounds came only from live plants and animals. They reasoned that organisms possessed a vital force that enabled them to produce organic compounds. The first serious blow to this theory of vitalism, which marked the beginning of modern organic chemistry, occurred when Friedrich Wohler (1800-1882) synthesized urea from the two inorganic substances lead cyanate and ammonium hydroxide ... 

Silicon tetraisocyanate and methylsilicon isocyanates, of the type (CH3) Si(NCO)4 (n = 1, 2, or 3), were first prepared in 75 to 90% yields by treating silicon(IV) chloride or the appropriate methylchlorosilane with silver isocyanate in anhydrous benzene. Forbes and Anderson report that much smaller yields are obtained when lead cyanate is used instead of silver isocyanate. The following procedure, however, when performed with lead cyanate, produces 52 to 71% yields of the silicon isocyanates. Comments on the use of less expensive lead cyanate are therefore included along with the silver isocyanate method of preparation. 

Lead cyanate is similarly prepared from 1987 g. (6.0 mols) of lead nitrate and 973 g. (12.0 mols) of potassium cyanate. 

High yields of the silicon isocyanates are obtained when freshly prepared silver isocyanate or lead cyanate is employed. When the silver or lead salt is several weeks old, or is dried in an oven, the yields of silicon isocyanates are about 20% lower. 

A 10% excess of silver isocyanate or lead cyanate has repeatedly been found to give the highest yields of product. A 25% excess produces no greater yield. Stoichiometric amounts produce slightly lower yields. On the other hand, a 10% excess of silicon(lV) chloride results in only a 40% yield of silicon tetraisocyanate. ... 

When freshly prepared lead cyanate (642 g. 2.2 mols 10% theoretical excess) is employed in the above procedure instead of silver isocyanate, the reaction is only slightly exothermic. The silicon(IV) chloride can therefore be added at a fairly rapid rate after the reaction has been initiated by heating to 35 to 40". The mixture is then refluxed with vigorous stirring for 3 hours. After the benzene is distilled, the 3ueld of silicon tetraisocyanate is 121 g. [61.8% based on silicon(IV) chloride]. 

Because trimethylsilicon isocyanate boils at 91 , making its separation from benzene somewhat difficult, this isocyanate is more readily prepared by using the same volume of xylene instead of benzene. With this modification, the yield of trimethylsilicon isocyanate is 91% from silver isocyanate, or 71% from lead cyanate. Anal. Calcd. for (CH3)3SiNCO N, 12.2 Si, 24.4. Found (by checkers) N, 11.8 Si, 23.6. 

Only during 17 and 18 centuries, important foundations were laid in many fields of biology. The 19 century observed the development of very crucial concepts, which include the cell theory by Schleiden and Schwaim, Mendel s study of inheritance and Darwin s theory of evolution. The real push to biochemistry was given in 1828 when total s)mthesis of urea from lead cyanate and ammonia was successfully achieved by Wohler who thus initiated the synthesis of organic compound from inorganic compound. Louis Pasteur,... 

NATURE POSSESSED A CERTAIN VITAL FORCE AND THAT ONLY LIVING THINGS COULD PRODUCE ORGANIC COMPOUNDS. ThIS ROMANTIC NOTION WAS DISPROVED IN 1828 BY pRIEDRICH WOHLER, A GERMAN CHEMIST WHO PREPARED UREA, AN ORGANIC COMPOUND, FROM THE REACTION BETWEEN THE INORGANIC COMPOUNDS LEAD CYANATE AND AQUEOUS AMMONIA ... 

In 1828 Wohler attempted to synthesize ammonium cyanate via the treatment of silver cyanate with aqueous ammonium chloride. The reaction produced a white crystalline solid that did not possess the properties of ammonium cyanate. Wohler then attempted to synthesize ammonium cyanate using lead cyanate and ammonium hydroxide. This produced the same white powder, but with fewer contaminants so that it could be analyzed. Upon analysis this white powder proved to have the composition and properties of urea, a compound that had been isolated from urine. 

Lead cyanate may be prepared by treating NCO with Ba to remove any C03 , then adding Pb " to the filtrate. The lead cyanate precipitated is comparatively stable and serves well for the preparation of HNCO. 

Carbon compounds are called organic because it was originally thought that they could be produced only from living organisms. In 1828, Friedrich Wbhler proved this idea to be false when he converted the inorganic salt lead cyanate into urea, an organic product of protein metabolism in mammals (Real Life 1-1). 

The synthesis was the result of an attempt to prepare ammonium cyanate by the action of ammonium chloride on silver cyanate, or ammonium hydroxide on lead cyanate. In each reaction a crystalline product was obtained which was identical with urea, previously found only in urine. The mechanism of the synthesis has been explained by Werner. Cyanic acid, HOCN, readily changes into its isomer, iso- or keto-oyanic acid, HN CO, which unites with ammonia directly to form urea. 

---