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CARBONATES

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Originally appearing in Volume V05, Page 309 of the 1911 Encyclopedia Britannica.
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CARBONATES . (I) The metallic carbonates are the salts of carbonic See also:

acid, H2CO3. Many are found as-minerals, the more important of such naturally occurring carbonates being See also:cerussite (See also:lead carbonate, PbCO3), See also:malachite and See also:azurite (both basic See also:copper carbonates), See also:calamine (See also:zinc carbonate, ZnCO3), See also:witherite (See also:barium carbonate, BaCO3), See also:strontianite (See also:strontium carbonate, SrCO3), See also:calcite (See also:calcium carbonate, CaCO3), See also:dolomite (calcium See also:magnesium carbonate, CaCO3•MgCO3), and See also:sodium carbonate, Na2CO3. Most metals See also:form carbonates (See also:aluminium and . See also:chromium are exceptions), the See also:alkali metals yielding both acid and normal carbonates of the types MHCO3 and M2CO3(M=one See also:atom of a monovalent See also:metal); whilst See also:bismuth, copper and magnesium appear only to form basic carbonates. The acid carbonates of the alkali metals can be prepared by saturating an aqueous See also:solution of the alkaline hydroxide with See also:carbon dioxide, Ni•OH+See also:CO2= MHCO3, and from these acid salts the normal salts may be obtained by See also:gentle See also:heating, carbon dioxide and See also:water being produced at the same See also:time, 2MHCO3 = M2CO3+H02+ CO2. Most other carbonates are formed by precipitation of salts of the metals by means of alkaline carbonates. All carbonates, except those of the alkali metals and of See also:thallium, are insoluble in water; and the See also:majority decompose when heated strongly, carbon dioxide being liberated and a See also:residue of an See also:oxide of the metal See also:left. The alkaline carbonates undergo only a very slight decomposition, even at a very See also:bright red See also:heat. The carbonates are decomposed by See also:mineral acids, with formation of the corresponding See also:salt of the acid, and liberation of carbon dioxide. Many carbonates which are insoluble in water dissolve in water containing carbon dioxide. The individual carbonates are described under the various metals. (2) The organic carbonates are the See also:esters of carbonic acid, H2CO3, and of the unknown ortho-carbonic acid, C(OH)4.

The acid esters of carbonic acid of the type HO•CO.OR are not known in the See also:

free See also:state, but J. B. See also:Dumas obtained barium methyl carbonate by the See also:action of carbon dioxide on baryta dissolved in methyl See also:alcohol (See also:Ann., 1840, 35, p. 283). See also:Potassium See also:ethyl carbonate, KO•CO.002H5, is obtained in the form of pearly scales when carbon dioxide is passed into an alcoholic solution of potassium ethylate, CO2+KOC2H5 = KO•CO.002H5. It is not very See also:stable, water decomposing it into alcohol and the alkaline carbonate. The normal esters may be prepared by the action of See also:silver carbonate on the alkyl iodides, or by the action of See also:alcohols on the chlorcarbonic esters. These normal esters are colourless, pleasant-smelling liquids, which are readily soluble in water. They show all the reactions of esters, being readily hydrolysed by See also:caustic alkalis, and reacting with See also:ammonia to produce carhamic esters and See also:urea. By heating with See also:phosphorus pentachloride an alkyl See also:group is eliminated and a chlorcarbonic ester formed. Dimethylcarbonate, CO(OCH3)2, is a colourless liquid, which boils at 90.6° C., and is prepared by heating the methyl ester of chlorcarbonic acid with lead oxide. Diethylcarbonate, CO(OC2H5)2, is a colourless liquid, which boils at 125.8° C.; its specific gravity is 0.978 (20°) [H.

See also:

Kopp]. When it is heated to 120° C. with sodium ethylate it decomposes into ethyl See also:ether and sodium ethyl carbonate (A. Geuther, Zeit. f. Chemie, 1868). Ortho-carbonic ester, C(OC2H5)4, is formed by the action of sodium ethylate on See also:chlorpicrin (H. Bassett, Ann., 1864, 132, p. 54), CC13NO2+4C H5ONa=C(OC,Hs)4+NaNO2-+-3NaCl.Itisanetherealsmelling liquid, which boils at 158-159° C., and has a specific gravity of 0.925. When heated with ammonia' it yields See also:guanidine, and on boiling with alcoholic potash it yields potassium carbonate. Chlorcarbonic ester, Cl CO.002H5, is formed by the addition of well-cooled See also:absolute alcohol to phosgene (carbonyl chloride). It is a pungent-smelling liquid, which fumes strongly on exposure to See also:air. It boils at 93.1 ° C., and has a specific gravity of 1.144 (15° C.). When heated with ammonia it yields See also:urethane.

Sodium See also:

amalgam converts it into formic acid; whilst with alcohol it yields the normal carbonic ester. It is easily broken down by many substances (aluminium chloride, zinc chloride, &c.) into ethyl chloride and carbon dioxide. Percarbonates.—Barium percarbonate, BaCO4, is obtained by passing an excess of carbon dioxide into water containing barium peroxide in suspension; it is fairly stable. and yields See also:hydrogen peroxide when treated with acids (E. See also:Merck, Abs. J.C.S., 1907, H. p. 859). Sodium percarbonates of the formulae Na2CO4, Na2C2O6, Na2CO5, NaHCO4 (two isomers) are obtained by the action of gaseous or solid carbon dioxide on the peroxides Na2Os, Na203, NaHOs (two isomers)in the presence of water at a See also:low temperature (R.Wolffenstein and E.Peltner, Ber., 1908, 41, pp. 275, 280). Potassium percarbonate, K2C206, is obtained in the See also:electrolysis of potassium carbonate at -10 to -15°.

End of Article: CARBONATES

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