Qualitative Analysis of Organic Compounds

PURPOSE STATEMENT

The aim of qualitative analysis in organic chemistry was to identify the unknown organic liquid and its structure. To determine unidentified sample of organic liquid, its chemical and physical characteristics were analyzed by performing laboratory tests like solubility test, NMR analysis, density test, Refractive test, boiling point test and potassium permanganate test. The results obtained aided in inferring the name and chemical structure of the unknown organic liquid.

                  During the experiment, various organic compounds were identified, for instance, alkynes, alkyl halides, alkenes, and dienes.  Therefore, physical properties of the samples are not sufficient to qualitatively identify the unknown organic liquid. For instance, unsaturated organic compounds like dienes, alkenes, and alkynes test positive in the solubility test while the alkyl halide tests negative thus hence there is a need for other tests.

                  One of the suitable chemical tests for characterization of organic compounds which exhibit same physical characteristics is the Potassium permanganate test. The test is employing to determine unsaturated organic compounds. For the test of alkenes in potassium permanganate, they require various drops to change the color of potassium from purple to colorless while for dienes and the alkynes just need half the amount of the drops required by the alkenes. Another crucial test is the spectroscopic analysis which can be IR spectroscopy, NMR spectroscopy or UV spectroscopy. The tests aid in identifying the functional groups of a compound like the existence of double bonds and their positions in the carbon chain, the structure of the compound. This experiment helps learners to acquire chemical skills in inferring diverse organic compounds. Not only the skills acquired in this experiment aid only in the identification of organic compounds for academic purposes but it is applied to various processing industries. 

CHEMICAL REACTIONS

For potassium permanganate test, ethene was used to represent the reaction of the possible unknown liquid. Manganate (VII) ions oxidized the ethene to   ethane-1, 2-diol while in the process it was reduced to manganate (II) ions as shown: 

In alkaline condition, Manganate (VII) ions oxidized ethene to ethane-1,2-diol and reduced to manganate(VI) ions when then changed to solid manganese(IV) oxide which was dark brown in color as outlined in the equation. 

The unknown liquid (as represented by ethene) reacted with concentrated sulfuric to produce alkyl hydrogen sulfate as indicated below: 

H₂SO₄+ ethene → (alkyl hydrogen sulfate) H-OSO₃H →    (alcohol) H-OH 

RESULTS

The results found indicated that the unknown liquid #3 recorded NMR of, the average density of 0.6822g/ml; the refractive index of 1.41.

OBSERVATIONS               

The purple color of  freshly prepared 1% potassium permanganate(in acidic condition) in test tube disappeared(the color became colorless) after addition of 30 drops of hexane and this happened too to the unknown organic liquid after  addition of 27 drops of it.

                  When prepared potassium permanganate in alkaline condition, hexane was added to it its purple color to dark green and then dark brown precipitate after 30 drops of hexane. This was true with the unknown liquid after addition of 27 drops. The unknown liquid dissolved in sulfuric acid and there was the liberation of heat.

DISCUSSION

The presence of double bond in the hexane and probably in the unknown led to the formation of the alkyl hydrogen sulfate as a result of protonation of the double bond

                      The color change of potassium permanganate  when hexane and the unknown liquid were added from purple to colorless in both acidic and alkaline conditions indicated  that the unknown liquid contained a double bond and not aromatic. 

                      The unknown liquid dissolved in concentrated sulfuric acid (tested positive for solubility test) hence ruled out possibility unknown# 3 to be alkyl halide.  Therefore, the unknown was unsaturated compound (alkene, diene or alkyne). From the experimental data, the unknown had a refractive index of 1.41, the average density of 0.6822g/ml which is close to the refractive index of 3-hyxyne which has a refractive index of 1.4115 and density of 0.724g/ml(obtained from literature). In all reactions of unknown liquid performed, the reactions were faster as compared to the reaction of the hexane hence there was a possibility of the presence of the triple in the structure of the unknown liquid. From the data analyzed, the unknown organic liquid is likely to be alkyne (3-hyxyne).

                      During the experiment, there were no major challenges as every step to carry out the experiment was easier to follow. Although there were some issues of contamination of the compounds and chemical used and this might resulted in some errors which in turn affected the final results.

                  The organic qualitative analysis is very important in the life of chemists and scientists as it enable them to identify organic compounds by carrying out various tests both physical and chemical to certain the specific characteristics of a given compound and even their functional groups.

                  At the end of the experiment, one can possibly say that the unknown organic liquid was a 3-hyxyne, however, further chemical tests are required to qualitatively certain the possibility of the unknown to be 3-hyxyne. Hence, by performing thorough advanced chemical tests like UV spectroscopy, IR spectroscopy, and NMR spectroscopy, one will be in a position to justify the finding of this experiment.