Although organic substances such as sugar, starch, alcohol, resins, oils, indigo, etc had been known from earliest times, very little progress in their chemistry was made until about the beginning of the eighteenth century. In 1675, Lemery published his famous Cours de Chymie, in which he divided compounds from natural sources into three classes: mineral, vegetable and animal. This classification was accepted very quickly, but it was Lavoisier who first showed in 1784, that all compounds obtained from vegetable and animal sources always contained at least carbon and hydrogen, and frequently, nitrogen and phosporus. Lavoisier, in spite of showing this close relationship between vegetable and animal products, still retained Lemery's classification. Lavoisier's analytical work, however, simulated further research in this direction, and resulted in much-improved technique, due to which Lemery's classification had to be modified. Lemery had based his classification on the origin of the compound , but it was now found (undoubtedly due to the improved analytical methods) that in a number of cases the same compound could be obtained from both vegetable and animal sources. Thus, no difference existed between these two classes of compounds, and hence it was no longer justifiable to consider them under separate headings. This led to the reclassification of substances into two groups: all those which could be obtained from vegetables or animals, i.e, substances that were produced by the living organism, were classified as organic; and all those substances which were not prepared from the living organism were classified as inorganic.
At this stage of the investigation of organic compounds it appeared that there were definite differences between organic and inorganic compounds, e.g., complexity of composition and the combustibility of the former. Berzelius(1815) thought that organic compounds were produced from their elements by laws different from those governing the formation of inorganic compounds. This then led him to believe that organic compounds were produced under the influence of a vital force, and that they could not be prepared artificially.
In 1828, Wohler converted ammonium cyanate into urea, a substance hitherto obtained only from animal sources. This synthesis weakened the distinction between organic and inorganic compounds, and this distinction was completely ended with the synthesis of acetic acid from its elements by Kolbe in 1845, and the synthesis of methane by Berthelot in 1856. A common belief appears to be that Wohler's synthesis had little effect on the vital-force theory because it did noy start with the elements. Wohler had prepared his ammonium cyanate from ammonia and cyanic acid, both of which were of animal origin. Partingtom (1960), however, les the student to that Priestley (1781) had obtained ammonia by reduction of nitric acid, which was synthesized from its elements by Cavendish (1785). Also, potassium cyanide was obtained by Scheele (1783) by passing nitrogen over a strongly heated mixture of potassium carbonate and carbon, and since one form of carbon used was graphite, this reaction was therefore carried out with inorganic materials. Since potassium cyanide is readily converted into potassium cyannate, Wohler's synthesis is one which starts from the elements.
Since the supposed differences between the two classes of compounds have been disproved, the terms organic and inorganic would appear to be no longer necessary. Nevertheless, they have been retained, but it should be appreciated that they have lost their original meaning. The retention of the terms organic and inorganic may be ascribed to several reasons:
(i) all so-called organic compounds contain carbon
(ii) the compounds of carbon are far more numerous (over 1000000) than the known compounds of all the other elements put together
(iii) carbon has the power to combine with other carbon atoms to form long chains. This property, known as catenation, is not shown to such an extent by any other element.
Hence organic chemistry is the chemistry of the carbon compounds.
This definition includes compounds such as carbon monoxide, carbon dioxide, carbonates, carbon disulphide, etc. Since these occur chiefly in the inorganic kingdom (original meaning), they are usually described in text-books of inorganic chemistry.
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