Experiment 3 Chemical Properties of Aliphatic and Aromatic Alcohols

Transcription

1 Experiment 3 Chemical Properties of Aliphatic and Aromatic Alcohols In the first part of this experiment you will learn the difference between 1 o, 2 o and 3 o alcohols and aromatic alcohols with respect to their redox reactivity with the strong oxidizing reagent sodium dichromate. This can be easily demonstrated by noting a color change when the Cr in the +6 oxidation state of the orange colored dichromate ion, Cr 2 O 7 2-, is reduced to the green colored chromium (III), Cr 3+, ion. Simultaneously, an appropriate alcohol is oxidized to either an aldehyde (and subsequently to a carboxylic acid) or a ketone. Of course, if there is no redox reaction there will be no observed color change. In general the following unbalanced reaction describes the redox reaction: Alcohol + 2- Cr 2 O 7 carboxylic acid (or ketone) + Cr 3+ (colorless) (orange) (colorless) (green) In the second part of this experiment the chemical properties not displayed by the aliphatic alcohols will be examined. Here we will compare the solubility, acid/base properties and the reactivity with iron (III) chloride (ferric chloride) of a similar sized aliphatic alcohol with that of the aromatic alcohol phenol. Procedure: Part 1: Obtain ~5 ml of acidic dichromate solution (prepared previously by mixing 3 ml of a 5% sodium dichromate and 1 ml of concentrated sulfuric acid) and place ~ 1 ml (~20 drops) into four separate, clean, dry small test tubes and note the color. Caution: the dichromate solution can potentially burn your skin or make holes in your clothes. If you spill any of this reagent report the spill immediately to your instructor so that if may be cleaned up in an appropriate manner. To the separate test tubes add ~0.5 ml (~10 drops) of ethyl alcohol, isopropyl alcohol, t-butyl alcohol, or aqueous phenol. Mix by finger flicking the test tubes. Observe and record the

2 colors of the resultant solutions. Dispose of the solutions in the special waste container for dichromate waste. Part 2: Solubility: Using a spatula or forceps, place ~ a pea sized amount of solid phenol crystals into two separate, clean, dry small test tubes. To one add 1 ml (~20 drops) of distilled water and to the other add 1 ml (~20 drops) of 3M NaOH (sodium hydroxide). Swirl the test tubes equally and note the relative speed with which the crystals dissolve. Record your observations. Repeat this procedure using 1 ml (20 drops) of cyclopentanol instead of the phenol. In this case you are adding a liquid to a liquid, thus solubility is noted by a single homogenous solution and insolubility by two layers. Record your observations and dispose of these solutions as indicated by your instructor. Part 3: Acid/base Properties: Place 1 ml (~20 drops) of distilled water, ethyl alcohol and aqueous phenol into three separate, clean, dry test tubes. To each sample add one drop of Universal Indicator solution and observe the color. Compare the solution s color to the reference Universal Indicator color card and estimate the solution s ph. Record your observations and dispose of these solutions as indicated by your instructor. Part 4: Reactivity with Iron (III) chloride (FeCl 3 ): Obtain and observe the color of the iron (III) chloride solution. Place 1 ml (~20 drops) of distilled water, cyclopentanol and aqueous phenol into three separate, clean, dry test tubes. To each sample add one drop of the iron (III) chloride solution. Mix by finger flicking the test tubes. Observe and record the colors of the resultant solutions and dispose of these solutions as indicated by your instructor.

3 Experiment 3 Report Name Part 1: 1. a. Draw condensed structural formulas of ethyl alcohol, isopropyl alcohol, t-butyl alcohol, and phenol. b. Classify each of the preceding alcohols as 1 o, 2 o, 3 o, or aromatic. 2. What is the function of the acid solution of sodium dichromate? 3. a. What did you observe when the sodium dichromate solution was added to ethyl alcohol? b. What did you observe when the sodium dichromate solution was added to isopropyl alcohol? c. What did you observe when the sodium dichromate solution was added to t-butyl alcohol? d. What did you observe when the sodium dichromate solution was added to the phenol solution? 4. Draw condensed structural formulas for the organic products of the above reactions that occur. If no reaction occurs, write NR.

4 Part 2: 1. a. Did the phenol crystals dissolve better in water or in the NaOH solution? b. Did the cyclopentanol dissolve better in water or in the NaOH solution? c. Based on the different behaviors of phenol and cyclopentanol, what generalization can you make about the solubility of similar sized aliphatic and aromatic alcohols? d. Write a full chemical equation for the chemical reaction that occurred when NaOH was added to phenol. e. Write a net ionic equation for the chemical reaction that occurred when NaOH was added to phenol. Part 3: Based on the Universal Indicator Color Chart, what is the approximate ph of: a. the distilled water? b. the ethyl alcohol? c. the aqueous phenol? 3. Write a full chemical equation for the chemical reaction that occurs when phenol is placed in water that explains the observed ph. Is phenol an acid or a base? Part 4:. Can ferric chloride be used to distinguish aromatic alcohols from aliphatic alcohols? Explain.

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