QUALITATIVE TESTS FOR ELEMENTS IN ORGANIC COMPOUNDS

Carbon and hydrogen• Detected qualitatively by a heating a mixture

(glucose) with dry CuO in a test tube.• The glucose is oxidized forming CO2 and H2O.• The presence of CO2 is indicated by the

formation of a white ppt. of calcium carbonate when gaseous products are passed through a solution of lime water.

• The presence of water is indicated by the formation of droplets of water in the cooler end of the hard glass tube.

Oxygen• The presence of oxygen may be determined

either with the use of ferrox paper or the compound iron (III) hexathiocyanatoferrate(III).

• In the presence of oxygen contaning compounds, the complex FeCNS++ gives a deep red colored solution as it distributed between the filter paper and the test compound.

• Solutions of compounds which do not contain oxygen remain colorless.

• Iron (III) ammonium sulfate and potassium thiocyanate react to form iron (III) hexathiocyanatoferrate(III). This compound dissolves in the presence of oxygen-containing compounds to give a red to reddish-purple color.

• 2Fe(NH4)(SO4)2 + 6 KSCN Iron (III) ammonium sulfate potassium thiocyanate

Fe[Fe(SCN)6] + 3 K2SO4 + (NH4)2SO4 iron (III) hexathiocyanatoferrate(III)

Nitrogen, Halogens and Sulfur

• Difficult to detect for organic compounds due to its non-polar nature. They do not ionize in solution to give ions.

• Necessary to convert these elements into inorganic ions before making qualitative tests.

• The conversion is done through fusion with metallic sodium, w/c decomposes the organic compound forming soluble salts.

• Organic compound [C] [H][O][N][X][S] + N fusion NaCN, NaOH, NaX and Na2S

The resulting organic compounds are tested qualitatively for the presence of N, S and halogens.

NITROGEN• Detected by the formation of Prussian blue

after the sodium fusion.• Nitrogen in cyanide form is converted to

sodium ferrocyanide, which produces Prussian blue (ferric ferrocyanide, Fe4[Fe(CN)6]3 with ferric chloride in acid solution.

• Nitrogen in the form of amino nitrogen (-NH2), heating with soda lime (a mixture of fused NaOH and CaO) will liberate ammonia gas, which is tested with moist red litmus paper.

Sulfur• Detected by the production of brownish-black

lead sulfide.• With sodium nitroprusside, the sulfide ion

produces a red-violet color, which fades somewhat readily.

Halogens

• Detected by Beilstein test.• Organic halogen imparts a green color to the

flame when burned upon the surface of a copper wire. The copper oxide formed from the copper wire reacts with the halogens to form the cuprous halide, which burns with a green flame.