Objectives: To observe the solubility of alcohols relative to their chemical structure, to perform chemical tests to distinguish primary, secondary and tertiary alcohols, and a color test for phenol. Introduction The general formula of an alcohol is ROH in which the R is an aliphatic hydrocarbon group. Alcohols may be looked upon as derivatives of water, HOH. One hydrogen of water is substituted by an alkyl group, R. Like water, alcohols show hydrogen bonding. As the chain of the R group increases the hydrocarbon character of the compound overshadows the polar character of the OH group. Consequently, the solubility and boiling point of an alcohol are affected by the length of the carbon chain and the shape of the molecule. The short chain alcohols are soluble in water, whereas the longer chain alcohols are insoluble in water. In general a molecule which is more compact (i.e., more branched) will be more soluble in water and will have a lower boiling point than the straight chain isomer. Phenols are aromatic alcohols, in which R is an aromatic ring. This experiment will demonstrate some of the properties of alcohols and phenols. Although alkyl alcohols have an -OH group, they do not ionize in water, whereas phenols ionize like acids (donating a proton to water). The -OH group of alkyl alcohols can be positioned on different carbon atoms of the carbon chain and are classified as primary (1°), secondary (2°), or tertiary (3°) alcohols depending on whether the -OH group is attached to a carbon with 1, 2 or 3 other carbon atoms attached to it. These different alcohols react differently with Lucas reagent and with Bordwell-Wellman reagent; hence these reagents can be used for identifying the class of alcohol. The relative acidity of phenols can be used to characterize this class of alcohols relative to the alkyl alcohols. This property will be exploited in the identification of phenol.
Materials Test tubes, Bordwell-Wellman reagent, n-butyl alcohol (1-butanol), secondary-butyl alcohol (2butanol), tertiary-butyl alcohol (2-methyl-2-propanol), glycerol, ferric chloride solution, Lucas reagent, phenol (3% solution), 10% sodium hydroxide solution, acetone, unknown.
Notice: Each student must have his/her own unknown and be sure to record the number of your unknown on the report sheet. If you work in pairs, each pair must have 2 unknowns. Keep the tubes containing your unknown at your bench until you finish all parts of the lab. 19
Part A. Solubility To test the solubility in water of alcohols, add several (10) drops of alcohol to about 2 mL water, shake the test tube vigorously [Use a cork to stopper the test tube; do not use your thumb] and notice if two layers form. If two layers form, the liquids are immiscible, hence, insoluble or of only limited solubility. You should make sure you mix viscous alcohols (such as glycerol) well because they may not dissolve immediately. Procedure 1. 2. Place 2 ml of water into each of 5 small test tubes. To one test tube add 10 drops of n-butyl alcohol (1-butanol). To a second test tube add 10 drops of sec-butyl alcohol (2-butanol). To a third test tube add 10 drops t-butyl alcohol (2-methyl-2-propanol), and to a fourth test tube add 10 drops glycerol, to a fifth test tube add 10 drops of your unknown. If you are working in pairs, you should have a sixth test tube with the second unknown. Stir each mixture by holding the top of the tube and tapping the bottom with your finger. Note whether these substances are soluble in water. You may have to stir the viscous glycerol sample vigorously. Record your observation on the Report Sheet, Table 1. You may dispose of these solutions in the sink and flush with water. Part B. Lucas Test for Primary, Secondary and Tertiary Alcohols. The Lucas reagent is a solution of zinc chloride in concentrated HCl. This solution must be made freshly to get proper results. The test depends on a difference in the...