Some old potassium and sodium compounds

Long before sodium and potassium metals were isolated, many of their compounds were in common use. Among the most important of these were potash (potassium carbonate), cream of tartar, saltpeter, alum, common salt, Glaubers salt, and soda (sodium carbonate). Both potash and soda have been used since ancient times in the manufacture of glass. 

Boerhaave even stated in his Elements of Chemistry that all die vegetables which have grown on the earth since the beginning of the world to the present, and which have putrefied without bemg reduced to ash by the action of fire, and have been consumed in the course of time, have never yielded a single gram of fixed alkaline salt. On the contrary, they have been dispersed in volatile particles. . (7). 

In 1770 C. W. Scheele showed that the natural product cream of tartar is a salt with a vegetable alkaline base (potash) supersaturated with a vegetable acid (tartaric). When he dissolved cream of tartar [potassium acid tartrate] in boiling water and added powdered chalk to the solution, the lime combined with part of the tartaric acid and gave a copious white precipitate. On evaporating the supernatant liquid he obtained crystals of soluble tartar [normal potassium tartrate] (9, 10). 

Rouelle, A. S. Marggraf, and others showed experimentally that potash can be extracted from plants without the use of fire (11). In 1764 Marggraf, for example, prepared saltpeter by treating tartar with nitric acid. Since saltpeter was known to contain the vegetable alkali, the latter 

Maequer pointed out in his Dictionary of Chemistry (1778) that when plants are decomposed without combustion, acidic substances such as tartar and potassium acid oxalate are produced, that plants from which these acidic substances have been removed by extraction or distillation yield much less vegetable alkali than they otherwise would that by ignition tartar can be converted almost completely to this alkali (potassium carbonate) that the alkali in vegetable ash is therefore produced by the combustion of this acidic substance that decayed wood, in which the plant acids have been destroyed by fermentation, yields scarcely any alkali (as Boerhaave had observed) and that plants containing little or no acid yield on combustion little or no vegetable alkali (5). 

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The earliest method of this type was the old Marckwald synthesis (1] in which a suitable a-aminocarbonyl compound is cyclized with cyanate, thiocyanate or isothiocyanatc. More recent modifications have employed the acetals of the a-amino aldehyde or ketone or an a-amino acid ester. The two-carbon fragment can also be provided by cyanamide, a thioxamate, a carbodiimidc or an imidic ester. When cyanates, thiocyanates or isothiocyanates are used, the imidazolin-2-ones or -2-thiones (1) are formed initially, but they can be converted into 2-unsubstituted imidazoles quite readily by oxidative or dehydrogenative means (Scheme 4.1.1). The chief limitations of the method arc the difficulty of making some a-aminocarbonyls and the very limited range of 2 substituents which are possible in the eventual imidazole products. The method is nonetheless valuable and widely used, and typically condenses the hydrochloride of an a-amino aldehyde or ketone (or the acetals or ketals), or an a-amino-)6-ketoester with the salt of a cyanic or thiocyanic acid. Usually the aminocarbonyl hydrochloride is warmed in aqueous solution with one equivalent of sodium or potassium cyanate or thiocyanate. An alkyl or aryl isocyanate or isothiocyanate will give an A-substituted imidazole product (2), as will a substituted aminocarbonyl compound (Scheme 4.1.1) [2-4]. 

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