ALCOHOLS, PHENOLS AND ETHERS J.V. DE GUZMAN DEPARTMENT OF CHEMICAL ENGINEERING, COLLEGE OF ENGINEERING UNIVERSITY OF THE PHILIPPINES, DILIMAN QUEZON CITY, PHILIPPINES DATE PERFORMED: FEBRUARY 27, 2015 INSTRUCTOR’S NAME: ALLAN KENNETH REGUNTON
ANSWERS TO QUESTIONS 1. Give the balance equations for all the reactions. a. Ethyl alcohol + Lucas Reagent ZnCl2
+ HCl No reaction (clear, colorless solution) b. Isopropyl Alcohol + Lucas Reagent ZnCl2
+ HCl
+ H2O (slow)
Insolule-cloudiness
c. Benzyl alcohol + Lucas Reagent ZnCl
+ HCl
2
+HO
Insolule-cloudiness 2
d. Tert-butyl alcohol + Lucas Reagent ZnCl 2
+ HCl e. Ethyl alcohol + KMnO4
Insolule-cloudiness
+ MnO4Balanced: CH3-CH2-OH + COH=O + H2O f. Isopropyl alcohol + KMnO4
2
+ MnO4-
2
+ H2O
+ MnO4MnO4-(aq)
(fast)
MnO2(s) +
+ MnO2(s) + 2H2O
+ MnO2(s) CH3-
g. Benzyl alcohol + KMnO4
+ MnO4h. Tert-butyl alcohol + KMnO4
+ MnO4i. Diethyl ether + KMnO4
+ MnO2(s) + H2O
No Reaction
+ MnO4j. Phenol + Bromine water
No Reaction
+ 3Br2 k. Phenol + KMnO4
+ 3HBr
+ MnO4l. Phenol + FeCl3 36 + FeCl3 + 3Clm. p-nitrophenol + FeCl3
3 + FeCl3 HCl n. p-bromophenol + FeCl3
3 + 3HCl
+ FeCl3
Fe
+ 6H+
6
Fe
3
Fe
+
3
3
o. β-naphthol + FeCl3
+ FeCl3 3
Fe
+ 3HCl
2. Why is Lucas Test applicable only to alcohols containing 5 or less carbons? Lucas test makes use of the solubility of the reagent for the reaction to happen. As such, this method applies only for alcohols that are soluble in the reagent in order for the chlorination reaction of the alcohol to occur. Lucas reagent is a solution of ZnCl 2 in HCl, as such; this polar solution dissolves only highly polar alcohols or those that have less number of non-polar groups. More than 5 carbons, the alcohol becomes more nonpolar, therefore, Lucas test is applicable only to alcohols with less than 5 or less carbons. 3. Why tertiary alcohols and ethers cannot undergo oxidation upon reaction with potassium permanganate? Oxidation of the alcohol depends on its relative stability. As the number of alkyl substituent of the carbon of which the hydroxide is bonded increases, the greater is the stability of the alcohol. Therefore, it can be arranged that tertiary alcohol>secondary alcohol>primary alcohol in terms of stability. Permanganate can oxidize primary alcohols into aldehyde then into carboxylic acids and secondary alcohols into ketones only. However, potassium permanganate cannot remove an electron from a tertiary alcohol to oxidize it because of its great stability. The same also applies for diethyl ether. The symmetric structure of diethyl ether gives stability to the molecule as such permanganate cannot withdraw an electron form it. 4. Correlate the structure of the phenolic compounds with the measured pH values. Given are the structure and corresponding pH values of phenolic compounds:
Picric acid (pH=3)
p-nitrophenol
Phenol (pH=5)
The relative acidity of phenolic compounds is dependent on electron withdrawing groups attach to the ring. As the electron withdrawing group increases, the benzene ring becomes more positively charged thereby making the compound more acidic. In phenol, there is only one electron (OH) withdrawing group and two for p-nitrophenol (-OH and –NO2) making nitrophenol more acidic than phenol. Picric acid has four electron withdrawing groups (-OH and 3(-NO2)) making it the strongest organic acid. This idea correlates with the obtained pH values of the phenolic compounds: picric acid > p-nitrophenol > phenol in terms of relative acidity. REFERENCES: [1]Pahlavan, L. Properties of Alcohol: structure, reactions and identification of alcohols. Southwest College Houston Community College. [Online]. 2014. Retrieved from: http://swc2.hccs.edu/pahlavan/2425L4.pdf (accessed March 3, 2015). [2]Pavia, D. L., Lampman, G. M., Kriz, G.S., Engel, R. Introduction to Organic Laboratory Techniques: A Microscale Approach. Part 3: Identification of Organic Substances-Experiment 53H: Alcohols. Saunders College Publishing: Orlando, 1995. pg 513. [3]Xiamen University. Oxidation of Alcohols. [Online]. 2002. Retrieved from: http://chem.xmu.edu.cn/teach/yjhx/chem/02en/chpt12_2.pdf (accessed March 3, 2015).
