Chemistry of the Functional Group

Transcription

1 Name Lab Day Chemistry of the Functional Group Introduction: rganic molecules comprised only of carbon and hydrogen would be relatively unreactive and biologically unimportant. Inclusion of atoms of other elements in organic molecules or changes in the oxidation state increases the numbers and kinds of reactions of the compound. The biological activity of molecules is primarily a function of these changes. The inclusion of heteroatoms in the organic molecule does not produce an infinite number of related physical and chemical properties. The chemist has learned that compounds containing heteroatoms can be classified and organized into classes of compounds whose chemical properties are, to a large extent, determined by the heteroatom or oxidation state of the compound itself. The particular heteroatom or group of heteroatoms and the various oxidation states comprise the functional groups. rganic molecules are classified with respect to various functional groups contained in the molecule. Unsaturated Hydrocarbons: Carbon carbon double (alkenes) and triple (alkynes) are functional groups which undergo various addition reactions to produce saturated hydrocarbons or their derivatives. The reactivity of these functional reactions which characterize unsaturated molecules are the addition of bromine to unsaturated bonds and the oxidation of these bond by potassium permanganate. Bromine has a dark red color in non-polar solvents which disappears upon addition of an alkene or alkyne. An aqueous solution of potassium permanganate is a deep purple. Addition of an alkene or alkyne reduces the permanganate resulting in a dark brown or black precipitate of manganese dioxide. amber colorless H C C + KMn 4 C C + Mn 2 (s) purple H brown

2 2 Halides: Halogens in organic compounds are detected by the Beilstein flame test or by the formation of a silver halide precipitate when treated with alcoholic silver nitrate. Not all halides are susceptible to the silver nitrate test. The test reactivity is dependent upon: (1) the degree of branching on the carbon to which the halogen is bonded, (2) whether or not the carbon is sp or sp 2 hybridized, and (3) the type of halogen present. The rate of formation of the precipitate is a measure of the reactivity of the halide which generally follows the order, I > Br > Cl >> F. H 2 C Cl + AgN 3 C H + AgCl (s) Alcohols: Alcohols possess the functional group, H. This group is sensitive to the Lucas test reagent which is an acidified (HCl) solution of zinc chloride. Addition of an alcohol to the reagent results in the formation of an insoluble alkyl halide causing the solution to become turbid. The rate at which the alkyl halide is formed is dependent on the nature of the carbon to which the H is attached. Branching results in an increased rate, while hybridization other than sp 3 results in slowing the rate. HCl C H + ZnCl 2 C Cl + H 2 Acids and Bases: rganic molecules having the functional group, C H are classified as acids and those containing a nitrogen atom are classified as bases. Those acids and bases which are soluble in water yield the characteristic color change when the solution is tested with litmus paper. Insoluble acids react with dilute base (10% sodium bicarbonate) to yield a soluble salt and insoluble bases react with dilute acid to yield a soluble quartenary ammonium salt. C H + HC 3 C + H 2 C 3 N.. + H + N H +

3 3 Aldehydes and Ketones: Aldehydes and ketones possess an oxygen atom attached to a carbon with a higher oxidation number than alcohols. These compounds have similar, though not identical, properties and can be distinguished chemically. Both will react with 2,4 dinitrophenylhydrazine reagent to give a solid derivative. However, aldehydes may be readily oxidized to the acid, while ketones can not. R C H R C R' aldehyde ketone R C H + 2 Ag(NH 3 ) 2 H 2 Ag + R C NH NH 3 + H 2 _ R C H + 2 Cu H Cu 2 + R C + 3 H 2 Experimental: Unsaturated Hydrocarbons A. Bromine in methylene chloride (or dichloromethane). Place 2 ml of CH2Cl2 in a test tube and add 6 drops of the compound to be tested. To this solution, add 5% Br2 in CH2Cl2 drop-wise and record the results. A positive test is the disappearance of the red amber color. B. Potassium permanganate (Baeyer test). Place 2 ml of 95% ethyl alcohol (ethanol) in a test tube and add 6 drops of the compound to be tested. Add 5 drops of 2% KMn4 solution and record the results. A positive test is the disappearance of the purple color and the formation of a brown or black precipitate. Compound bservations Conclusions Br2 in CH2Cl2 KMn4 cyclohexane cyclohexene toluene oleic acid mineral oil

4 4 rganic Halides A. Beilstein flame test. Coil the end of a piece of copper wire into a loop and heat with a burner until the flame is no longer colored. Dip the cooled loop into a drop of material to be tested. Slowly bring the loop with the organic halide into the flame. A positive test is a flash of green flame as the compound is brought into the flame. Compound Structure bservation 2 bromopropane Br CH 3 CH CH 3 cyclohexane 1 chlorobutane CH 3 CH 2 CH 2 CH 2 Cl B. Silver nitrate. Place 2 ml of 2% alcoholic AgN3 in a test tube and add 2 drops of the compound to be tested. Note the time required for the reaction to occur. If nothing happens in 5 minutes, carefully heat in boiling water on a hot plate (the alcohol is flammable). Compound Structure Time bservations 2 bromopropane 2 chloropropane Br CH 3 CH CH 3 Cl CH 3 CH CH 3 1 chlorobutane CH 3 CH 2 CH 2 CH 2 Cl CH 3 tert-butyl chloride CH 3 C CH 3 Cl bromobenzene Br

5 5 Alcohols Lucas test. Place 10 drops of the compound in a test tube and add 5 ml of Lucas reagent. Shake the tube and then allow to stand for a few minutes. Note the time required to observe the appearance of a turbid (cloudy) solution. Compound Structure Time bservations 2 butanol H CH 3 CH CH 2 CH 3 1 butanol CH 3 CH 2 CH 2 CH 2 H CH 3 tert-butyl alcohol CH 3 C CH 3 H Acids and bases A. Carboxylic acids. To 2 ml of water in a test tube, add 3 drops (or a small pinch if a solid) of the compound. Shake the tube. If the material is soluble, test with litmus paper. If the material is insoluble, add 3 ml of 10% NaHC3. Compound Structure Solubility bservations propanoic acid acetone CH 3 CH 2 C H CH 3 C CH 3 benzoic acid C H

6 6 B. Amines. To 2 ml of water in a test tube add 6 drops (or a small pinch) of the compound. Shake the tube and the test the mixture with red litmus paper if the compound is soluble. If the compound is insoluble, add dilute HCl. Compound Structure Solubility bservations pyridine N acetanilide NH C CH 3 aniline NH 2 Aldehydes and ketones A. 2,4 dinitrophenylhydrazine (2,4 DNP). To 2 ml of 2,4 DNP reagent in a test tube, add 2 drops of the compound. A positive test is the formation of a yellow or orange precipitate. If no precipitate forms immediately, allow the tube to stand for 3 to 5 minutes. Compound Structure bservation propionaldehyde propionic acid CH 3 CH 2 C H CH 3 CH 2 C H 1 butanol CH 3 CH 2 CH 2 CH 2 H 3 pentanone CH 3 CH 2 C CH 2 CH 3 H H H H H H glucose H C C C C C C H H H H H

7 7 B. Benedict s test. Place 2 ml of Benedict s reagent in a test tube and heat just to boiling. Add 6 drops of the compound and heat the mixture in a boiling water bath for 1 minute. Allow the tube to stand. The formation of a cloudy greenish solution is a positive test. C. Tollen s test. Use a very clean test tube. Place 2 ml of Tollen s reagent in the clean test tube and add 2 drops of the compound. If no reaction occurs immediately, place the test tube in a beaker of warm water. A positive test is the formation of a silver mirror on the inside of the test tube or the formation of a black precipitate. Compound Structure Benedict s Tollen s H H H H H H glucose H C C C C C C H H H H H 3 pentanone propionaldehyde CH 3 CH 2 C CH 2 CH 3 CH 3 CH 2 C H Combustion Like most organic substances, hydrocarbons are combustible. The products of their complete combustion are carbon dioxide and water. Aromatic compounds do not burn completely and generally give off a sooty flame containing bits of unoxidized carbon. Place about 1 ml of the compounds below into separate evaporating dishes and (in the hood!) start them burning by bringing a lighted splint to the edge of the evaporating dishes. Note the characteristics of the flames. Compound Structure bservation n hexane CH 3 CH 2 CH 2 CH 2 CH 2 CH 3 1 hexene CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 toluene CH 3