Volume 4

Acid-Base Properties of Alcohols and Carboxylic Acids • Redox Reactions of Alcohols, Aldehydes, and Carboxylic Acids. What is Oxidation and Reduction in Organic Chemistry? • Esterification. Esters. Saponification. What Are Triglycerides? • Polyester • Ethers • Exercises
4.7.1. Acid-Base Properties of Alcohols and Carboxylic Acids. Alcohols are very weak acids. Methanol is roughly as acidic as water. The acidity of ethanol, propanol, and isopropanol is even lower.

The acidic character of alcohols is demonstrated by their reactions with highly reactive metals, such as sodium or potassium. Watch a demonstration of the reaction of methanol with sodium here. This reaction produces hydrogen gas and sodium methoxide, the sodium salt of methanol (Figure 4-98). Ethanol reacts with sodium similarly, albeit more slowly, to give sodium ethoxide, C2H5ONa. Less acidic propanol and isopropanol react with sodium even more sluggishly.
Figure 4-98. Reaction of methanol with sodium metal.

In contrast with most alcohols, phenol is much more acidic than water, roughly by a factor of 10,000. Yet phenol is still about 4,500 times weaker than H2CO3, a very weak acid (Volume 3). The order of acidity is:

H2CO3 > phenol > H2O ≈ CH3OH > C2H5OH and other alcohols

The degree of dissociation α of phenol in a 1M aqueous solution at room temperature is 0.001%, meaning that only 0.001% of all of the phenol molecules in that solution are dissociated. Nevertheless, because phenol is orders of magnitude more acidic than water, it reacts with strong alkali bases such as NaOH or KOH to give sodium or potassium phenoxide, respectively (Figure 4-99). Sodium phenoxide is used to manufacture aspirin.
Figure 4-99. Reaction of phenol with sodium hydroxide.

The C-H bond of the aldehyde (formyl) group is not acidic. Remember that well. In fact, some aldehydes (and also ketones) can function as proton donors, but it is not the H atom bonded to the carbonyl group (CO) that is the source of the acidity. Although the acid-base chemistry of aldehydes and ketones is of great importance for organic synthesis, such reactions are beyond the scope of our introductory course.

In general, carboxylic acids are stronger than weak inorganic acids such as H2CO3, but weaker than acids of medium strength. For example, one of the strongest monobasic carboxylic acids, formic acid, is approximately 50 times weaker than phosphoric acid, H3PO4 (1st dissociation). Benzoic and acetic acids are weaker than formic acid by a factor of 2.5 and 10, respectively. Like inorganic acids, carboxylic acids react with NaOH and other metal hydroxides to give the corresponding salt and water (Figure 4-100).
Figure 4-100. Neutralization of acetic and benzoic acids with alkali.

Strong mineral acids such as H2SO4 and HCl free up much weaker carboxylic acids from their salts. For example, glacial (anhydrous) acetic acid can be made from sodium acetate, CH3COONa, and sulfuric acid (Figure 4-101), as shown and explained in this video. Note that although the reaction is highly exothermic, additional external heat is needed to distill off the acetic acid product. The boiling point of acetic acid is 118 oC.
Figure 4-101. Formation of acetic acid from sodium acetate and sulfuric acid.

4.7.2. Redox Reactions of Alcohols, Aldehydes, and Carboxylic Acids. What is Oxidation and Reduction in Organic Chemistry? Being all organic compounds, alcohols, aldehydes, and carboxylic acids burn in air or pure oxygen. Watch this mesmerizing video demonstration of a flame test using methanol, which burns cleanly in air to produce CO2 and H2O, according to the equation below.

2 CH3OH + 3 O2 = 2 CO2 + 4 H2O

In this combustion reaction, methanol is exhaustively (fully) oxidized, which means that the products of the reaction cannot be oxidized any further. Under other conditions, however, methanol can be oxidized step-wise first to formaldehyde, then to formic acid, and finally to CO2 (Figure 4-102).
Figure 4-102. Step-wise oxidation of methanol.

All three processes shown in Figure 4-102 are identified as oxidation reactions because of an increase in the oxidation state of the carbon atom in each of the steps. The oxidation state of a carbon atom in an organic compound can be calculated by the same method as was used previously for inorganic substances (Volumes 2 and 3). To determine the oxidation states of the carbon for the molecules shown in Figure 4-102, we just need to remember that carbon is more electronegative than hydrogen but less electronegative than oxygen. The electronegativity values for H (2.1), C (2.5), and O (3.5) can be found in Figure 2-52 (Volume 2).

In CH3OH, the C atom is bonded to one O atom and three H atoms. The conceptual heterolytic cleavage of the C-O single bond induces a charge of +1 on the carbon. Breaking the three C-H bonds heterolytically would induce a charge of -3 on the carbon. The total, +1 – 3 = -2 is the oxidation state of the carbon atom in methanol. The oxidation states for the carbon atom in formaldehyde (CH2O), formic acid (HCOOH), and CO2 are calculated in the same manner. Note that heterolytic cleavage of the C=O double bond induces the charge of +2 on the carbon because a double bond is formed by two shared electron pairs, not one.

There is, however, a simpler and faster way to determine if an organic compound has been oxidized or reduced in a chemical transformation. Here is the rule.

If, as a result of a chemical reaction, an organic compound loses hydrogen atoms and/or gains oxygen atoms, that compound is oxidized. Conversely, if an organic compound gains hydrogen atoms and/or loses oxygen atoms in a chemical transformation, that compound is reduced.

As simple as that. Let us apply this rule to the redox transformations in Figure 4-102. When going from methanol, CH3OH, to formaldehyde, CH2O, no change takes place in the number of oxygen atoms in the molecule. However, two H atoms are lost. Therefore, this is oxidation. As formaldehyde, CH2O, is converted to formic acid, HCOOH, the number of H atoms does not change, but one oxygen atom is added, indicating oxidation. The final step is oxidation of formic acid via loss of two hydrogen atoms.

Alcohols can be oxidized to the corresponding aldehydes by a variety of methods. For example, ethanol is easily oxidized to acetaldehyde by O2 in the air in the presence of copper metal. If a piece of copper wire is heated in an open flame, the Cu surface turns black due to the formation of CuO. If then the still hot wire is immersed in ethanol, the original red color of Cu metal is restored and the characteristic "green apple" smell of acetaldehyde is given off (Figure 4-103).
Figure 4-103. Oxidation of ethanol with CuO.

This reaction can be performed catalytically in copper (Figure 4-104). Imagine one Cu atom. This Cu atom is oxidized by oxygen to CuO. The CuO then reacts with a molecule of ethanol to give one molecule of acetaldehyde, one molecule of water, and the same Cu atom that we started with. This Cu atom can be oxidized with oxygen again to give CuO, which would then oxidize another molecule of ethanol. The cycle then repeats itself until all of the ethanol has been oxidized using just the same single Cu atom. This is the beauty of catalysis.
Figure 4-104. Balanced overall equation for Cu-catalyzed oxidation of ethanol to acetaldehyde (top) and a simplified mechanism of the copper catalysis for this reaction (bottom).

The Cu-catalyzed air-oxidation reaction of ethanol is exothermic, with the heat produced being sufficient to make the process self-sustaining. Watch this reaction occur in this fascinating video demonstration. Note that the title of the video "Ethanol oxidation with Copper wire" is not entirely correct, as copper metal in the form of wire or any other form cannot oxidize anything. Copper metal can be only a reducer, not an oxidizer. The oxidizer is the oxygen of the air, and the copper wire is the oxidation catalyst.
Digression. Acetone can also be air-oxidized in the presence of copper as a catalyst, as shown here. Note that the heat produced in this reaction is sufficient to make the copper wire glow in the dark! The chemical transformations involved in this experiment are more complex than those taking place in the oxidation of ethanol and other simple alcohols.
So, alcohols can be oxidized to aldehydes. Aldehydes, in turn, can be further oxidized to carboxylic acids. Metal ions like Ag+ and Cu2+ easily oxidize aldehydes under basic conditions (Figures 4-105 and 4-106).
Figure 4-105. Oxidation of acetaldehyde with Ag+.
igure 4-106. Oxidation of acetaldehyde with Cu2+.

Both reactions exhibit easily recognizable visual changes as they occur. The silver metal formed in the reaction (Figure 4-105) forms a silver mirror on the inner walls of the glass reactor used, as is shown in this video. That is why this reaction is often called the silver mirror test for aldehydes.

Another video shows how in the reaction with Cu(OH)2 (Figure 4-106) the blue color of the divalent copper changes to the brownish-yellow color of copper (I) oxide. In both cases, the reduction of the Ag(I) to Ag(0) (silver metal) and of the Cu(II) to Cu(I) occurs as the aldehyde is oxidized to the carboxylic acid.

The chemical equations in Figures 4-105 and 4-106 are simplified. First, the Ag(I) used for the reduction is in the form of its ammonia complex, [Ag(NH3)2]+, prepared from AgNO3 and aqueous ammonia, often in the presence of NaOH or KOH. Such solutions of [Ag(NH3)2]+ are called Tollens' reagent after the German chemist Bernhard Christian Gottfried Tollens (1841-1918) who developed it.

Second, both reactions occur under basic conditions and therefore produce a salt of the carboxylic acid rather than the acid itself. We simplify the equations in order to stay focused on the key point, which is: aldehydes can be oxidized to carboxylic acids.

Besides Cu(II) and Ag(I), there are many other reagents that oxidize aldehydes to carboxylic acids. Some aldehydes are quite readily oxidized with just air. For instance, if pure liquid benzaldehyde is poured into a shallow dish and left in air at room temperature, white crystals of benzoic will be produced within an hour or so (Figure 4-107).
Figure 4-107. Oxidation of benzaldehyde in air.

The reverse, reduction processes from a carboxylic acid all the way to the corresponding hydrocarbon are also possible (Figure 4-108). Aldehydes are reduced to alcohols more easily than carboxylic acids are reduced to aldehydes. Consequently, it is challenging to stop a reduction reaction of a carboxylic acid at the step of the formation of the corresponding aldehyde: once the aldehyde is produced, it is reduced to the alcohol right away.
Figure 4-108. Step-wise reduction of a carboxylic acid to the corresponding alcohol via aldehyde.

There are only a few methods to reduce and aldehyde (or a ketone) to the corresponding hydrocarbon in one step. One is the Clemmensen reduction, named after the discoverer of this reaction, Erik Christian Clemmensen (1876-1941), a Danish-American chemist. The Clemmensen reduction employs simple conditions and readily available inexpensive reagents, Zn metal and hydrochloric acid (Figure 4-109).
Figure 4-109. The Clemmensen reduction of benzaldehyde and acetone.

If you are confused which oxidation and reduction reactions of alcohols, aldehydes, and carboxylic acids are more facile and which ones are harder to perform, we can try to fix that. All you need is:

- to know the oxidation sequence alcohol → aldehyde → carboxylic acid and the reduction sequence back, carboxylic acid → aldehyde → alcohol; and

- to remember that of all of these redox reactions, there is only one that requires a very strong reagent, the reduction of a carboxylic acid to an aldehyde (Figure 4-110).

Using simple logic, we can conclude that reducing a carboxylic acid to the corresponding aldehyde is challenging because once formed, the aldehyde will be quickly reduced to the alcohol with the powerful reducing agent used.
Figure 4-110. Redox interconversions of alcohols, aldehydes, and carboxylic acids.

There is one compound that occupies a special place in the redox chemistry of alcohols, aldehydes, and carboxylic acids. This compound is formic acid, which can and does behave as both a carboxylic acid and an aldehyde. Figure 4-111 shows the double functionality of formic acid.
Figure 4-111. The double functionality of formic acid as a carboxylic acid (red) and as an aldehyde (blue).

Unsurprisingly, formic acid can undergo transformations that are characteristic of only aldehydes and that no other carboxylic acid can undergo. One such transformation is the silver mirror reaction (Figure 4-105). Formic acid readily reacts with Tollens' reagent to give rise to carbonic acid, which quickly decomposes to CO2 and H2O (Figure 4-112). That is why the oxidation of formic acid with Ag+ is characterized not only by silver mirror deposition on the walls of the reactor, but also by the formation of CO2 that bubbles off as the reaction occurs.
Figure 4-112. Oxidation of formic acid with Ag+.

4.7.3. Esterification. Esters. Saponification. What Are Triglycerides? A characteristic and important chemical transformation of oxygen-containing organic compounds is esterification, the reaction of a carboxylic acid with an alcohol to give an ester (Figure 4-113).
Figure 4-113. Esterification reaction of acetic acid with methanol to give methyl acetate, an ester.

Esters are derivatives of carboxylic acids, in which the H atom of the COOH group has been replaced with a carbon substituent R. This substituent R can be any organic group, such as methyl, ethyl, or phenyl. To name an ester, the group R from the parent alcohol is named first, followed by the name of the anion of the parent carboxylic acid. Figure 4-114 illustrates how ester names are derived from the names of the parent alcohol and carboxylic acid.
Figure 4-114. Examples of esters with names.

Although there are many interesting facts about esters, perhaps the most widely known one is that the vast majority of esters have very pleasant fruity smells. Different esters produced from different combinations of alcohols and carboxylic acids have different aromas (Figure 4-115). Naturally occurring in fruits and vegetables, many nontoxic carboxylic acid esters are extensively used in the food, drink, and fragrance industries. If you are interested in learning more about ester smells, explore the Table of Esters and Their Smells.
Figure 4-115. Examples of esters with fruity smells (source).

There are some interesting and important features of the esterification reaction, one example of which is shown in Figure 4-113.

- First, did you notice that Figure 4-113 suggests that in the formation of the ester, the OH group comes from the acid and the H from the alcohol? Don't you find it strange, since carboxylic acids are much more acidic than alcohols? There is no mistake in Figure 4-113 that is based on the results of an isotopic labeling experiment. In this experiment, the oxygen atom of the alcohol used for the reaction was not the regular isotope 16O, but the rare heavier isotope 18O whose natural abundance is only 0.2%. After the reaction, it was found that the 18O isotope ended up exclusively in the ester and not in the water (Figure 4-116). This experiment was crucial in the elucidation of the mechanism of the esterification reaction, which you may learn from a more advanced organic chemistry course.
Figure 4-116. The 18O isotope labeling experiment showing that in the esterification reaction the OH comes from the acid and the H from the alcohol, not the other way around.

- Second, the esterification reaction does not occur by simply mixing and heating a mixture of an alcohol and a carboxylic acid. To take place, the reaction needs a catalyst, a small amount of a strong acid. Usually, H2SO4 is used.

- Third, the esterification reaction is reversible, which means that the ester is both formed and hydrolyzed in the reaction (Figure 4-117). In many cases, the equilibrium is shifted 60-70% to the right. Consequently, the amount of an ester that can be made in, and isolated from, the reaction cannot exceed 60-70%. To increase the yield of the ester, the equilibrium needs to be shited further to the right. Le Chatelier's principle suggests that one way of doing that is to somehow remove the water co-produced in the esterification as it occurs. This is usually achieved by distilling off the water product during the reaction. For that, a Dean-Stark apparatus is employed, a remarkably simple yet efficient, smartly conceived and elegantly designed piece of glassware.
Figure 4-117. Reversibility of the esterification reaction: the ester is both formed and hydrolyzed.

Sometimes there is a need to hydrolyze an ester back to the carboxylic acid and alcohol. To shift the equilibrium (Figure 4-117) to the left, more water should be added to the system. However, achieving full conversion of an ester to the parent carboxylic acid and alcohol can still be challenging due to the reversibility of the reaction. The best way to efficiently and fully hydrolyze an ester is to use basic rather than acidic conditions. Unlike acidic hydrolysis of esters, their alkaline hydrolysis is irreversible, producing the alcohol and a salt of the carboxylic acid (Figure 4-118).
Figure 4-118. Alakline (basic) hydrolysis of an ester.

Alkaline hydrolysis of esters is often called saponification. The name saponification comes from the Latin sapo, which means soap. Why soap? What does soap have to do with hydrolysis of esters?

The very making of soap is a reaction of alkaline hydrolysis of esters. These esters are plant oils and animal fats. Yes, fats and oils are esters of glycerol and long-chain carboxylic acids, so-called fatty acids. The carbon chain of a fatty acid is straight (unbranched), varying from 8 to 26 carbon atoms in length. This chain can contain one, two, and even more C=C double bonds or no double bonds whatsoever. A molecule of an oil or fat can derive from more than one fatty acid, but the alcohol component is invariably the same, glycerol, which is a triol (tribasic alcohol). That is why fats and oils are called triglycerides.

A triglyceride molecule is often a glycerol ester of two or three different fatty acids. There are some exceptions such as stearin, the triglyceride derived from only one fatty acid, stearic, C17H35CO2H (Figure 4-119). Stearin occurs in both animals and plants.
Figure 4-119. Structure of stearin with the glycerol moiety in blue and stearic acid moieties in red.

The alkaline hydrolysis (saponification) of stearin produces glycerol and a salt of stearic acid, soap (Figure 4-120). In real life, it is not necessarily pure stearin that is used in soap-making, but rather naturally occurring mixtures of various triglycerides.
Figure 4-120. Saponification of stearin to glycerol and sodium stearate (soap).
Digression. The mechanism of action of soap is described in the previous section (Figure 4-93). But who invented soap? We do not know. All we know is that soap-like materials were already produced and used in Babylon as early as 2800 BC. There is a reason to believe that soap was first discovered hundreds of thousands or maybe even over a million years before that, when our remote ancestors started using fire for cooking. Fats and oils must have dripped down onto the hot wood ashes during the open fire cooking. As the wood ashes, which are alkaline, came in contact with triglycerides of the dripping fat at the high temperatures, saponification occurred to produce fatty acid salts. The slippery feel on the skin of wet hands from the cooled ashes containing the just formed soap and the cleaning effect of those ashes must have been noticed pretty quickly.
4.7.4. Polyester. Imagine carrying out esterification of a dibasic carboxylic acid with a diol. Then a polymer will be produced, a polyester, as shown in Figure 4-121. We have already encountered one polymer in this course, polyethylene. Please refresh your memory on polyethylene and how it is made. Now, apart from the very different molecules involved in the formation of the two polymers, polyethylene and polyester, can you see any big difference between the two polymerization reactions leading to these polymers?
Figure 4-121. Formation of polyester from a dibasic carboxylic acid and a diol.

The key difference is that in the formation of polyethylene from ethylene, only the polymer is formed. In contrast, the formation of polyester, also a polymer, is accompanied by the co-production of small molecules (water). Reactions that give rise to a polymer as the only product are called polymerization reactions. Those leading to a polymer as a result of small molecules (such as water) splitting out in the process are called polycondensation reactions.

A broad variety of polyesters can be made using different carboxylic acids and diols. By far the most important polyester is polyethylene terephthalate (PET), synthesized from ethylene glycol and terephthalic acid (Figure 4-122).
Figure 4-122. Formation of polyethylene terephthalate (PET) polyester from terephthalic acid and ethylene glycol.

PET is manufactured on an exceptionally large scale. The world capacity for PET is nearly 5 million tons annually to meet the demand from many industries. Applications of PET are diverse, including in the production of plastic bottles, textiles and fabrics, various food packaging materials, carriers for magnetic and adhesive tapes, composite materials and fiber plastics, and, more recently, in plastics for 3D printing and thin film solar cells. PET is recyclable and, in fact, fleece fabrics have been, and continue to be, made of used plastic bottles. However, the sad fact is that making PET is cheaper than recycling it. As a result, huge amounts of used plastics end up being dumped in landfills, contaminating the environment. It is extremely unfortunate that many companies prefer going cheap to make more money, while carelessly neglecting environmental issues.

4.7.5. Ethers. Imagine an ester and, in your mind's eye, pull out the carbonyl group (CO) and reconnect the C and O atoms that were bonded to it (Figure 4-123). The resultant molecule is an ether.
Figure 4-123. Conceptual formation of an ether from an ester.

Note that the transformation shown in Figure 4-123 is purely conceptual and is presented exclusively for illustrative purposes. (It was recently found that such a chemical reaction can be performed, albeit only for aromatic esters). Some examples of ethers and their names are given in Figure 4-124.
Figure 4-124. Selected ethers with names.

It is self-explanatory from Figure 4-124 that to name an ether having two identical substituents on the central oxygen atom, we just name the substituent with (or even without) a prefix di, followed by "ether". If the two organic groups on the O atom are different, then both should be named as separate words, followed by "ether".

The most common ether is diethyl ether, or ethyl ether, or just ether. Diethyl ether has been known for hundreds of years. It is a colorless, very volatile liquid that boils at about 35 oC and has a characteristic "medical" smell that I personally would not identify as unpleasant. Diethyl ether is one of the two oldest-known general anesthetics (do you remember the other one? Chloroform!) and is a very good one due to its low toxicity. Also, ether is an excellent solvent, especially for some particular types of reactions. Yet, ether is no longer used for anesthesia, and the modern chemical industry avoids ether as the plague. The reason for that is the exceptionally high flammability of ether, which poses the extreme risk of fire.

Ether can be made by the reaction of ethanol with sulfuric acid (Figure 4-125). As a matter of fact, the old name of ether was "sweet oil of vitriol" because the standard method to make it was by heating a mixture of ethanol and sulfuric acid, which back then was called "oil of vitriol".
Figure 4-125. Synthesis of diethyl ether from ethanol and concentrated sulfuric acid.

The reaction of ethanol to give ether is a dehydration reaction, meaning that water is lost from the starting material during the transformation. This dehydration is intermolecular. The prefix inter ("between" in Latin) indicates that the water is produced from two molecules of ethanol. In the preparation of ethyl ether from ethyl alcohol in the presence of H2SO4 (Figure 4-125), it is critical to maintain the temperature of the reaction mixture below 150 oC, as otherwise intramolecular dehydration of ethanol to ethylene will occur (Figure 4-126). The prefix intra ("inside" in Latin) indicates that the H and OH that form a molecule of water in the reaction come from within the same molecule of ethanol.
Figure 4-126. Intramolecular dehydration of ethanol with concentrated H2SO4 above 150 oC.

A very important general method to make ethers, which is broadly used today, was developed by the famous Scottish-English organic chemist Alexander William Williamson (1824-1904) almost 170 years ago. Williamson was appointed professor at University College, London, in 1849, when he was only 25 years old. The following year he discovered the synthesis of ethers, which bears his name. The Williamson ether synthesis is the reaction of a sodium or potassium alkoxide with a haloalkane, as exemplified by Figure 4-127.
Figure 4-127. The Williamson synthesis of diethyl ether from sodium ethoxide and bromoethane.

An ether featuring a C-H bond next to the central oxygen atom slowly reacts with oxygen if stored exposed to the air. The reaction involves the insertion of a molecule of O2 into a C-H bond adjacent to the oxygen atom of an ether to give rise to an ether hydroperoxide (Figure 4-128).
igure 4-128. Slow reaction of diisopropyl ether with oxygen of the air to give hydroperoxide.

At room temperature, the reaction of an ether with O2 is quite sluggish, occurring on the order of weeks and even months. While most ethers are liquids, their hydroperoxides are solids that gradually precipitate out in the form of white crystals as the oxidation slowly takes place.

Ether hydroperoxides are diabolically insidious explosive substances. The danger of ether hydroperoxides stems from their extreme shock- and friction-sensitivity. A solid ether hydroperoxide may detonate on gentle tap or just touch with a spatula. Breaking or crushing a crystal of an ether hydroperoxide is virtually guaranteed to prompt an explosion.

Diisopropyl ether reacts with O2 particularly readily (Figure 4-128). Diethyl ether also forms a hydroperoxide, albeit more slowly. If you ever happen to see a bottle marked or labeled "Diethyl Ether" or "Diisopropyl Ether" containing white crystals in a liquid, make no mistake — you are looking at an extreme explosion hazard. Do not touch the bottle and immediately alert the owner of the threat. To avoid the formation of dangerous hydroperoxides, peroxidizable ethers should be stored protected from the air.
Digression. Once an ether scared me to the bone. Back then I was doing research in a North American university. The building we worked in was old and we were all to move to a brand new, state of the art chemistry building that had just been erected. At one point, as we prepared for the move packing our glassware, chemicals, and other stuff, a 1st year PhD student approached me. His eyes were wide with fear. He asked me to follow him and when I saw what he wanted me to see I got petrified. Underneath the lab benchtop, deep in the back of a wooden storage cabinet was an old bottle full of large white crystals immersed in a small amount of a liquid. By appearance, the bottle must have been at least 20 years old. The label on the bottle said Diisopropyl Ether. I felt shivers down my spine right away.

Startled and scared, I starred at that bottle full of those sinister looking white crystals. I knew it was a bomb, quite powerful and vastly more dangerous than any military munitions, due to the extreme shock sensitivity of the hydroperoxide. We called the federal special service that dealt with explosives. Within 20 minutes a crew of experts arrived, looking like astronauts in their helmets and special suits and gloves. The entire building was evacuated and fenced right away. The Department reopened four days later after the bottle had been transferred to the back yard of the building, covered with sandbags, and set off using a remote control device. I was also told that, originally the explosives experts had considered driving the bottle on a specially designed truck for carrying super-sensitive explosive materials at 10 miles per hour to their special facility outside of town. They were going to do that around 3:00 in the morning when the number of cars on the roads and highways would be minimal. For 3 days, they carefully watched the traffic between 2:00 and 4:00 a.m., just to arrive at the conclusion that even during those hours there were enough vehicles on the roads to make the transportation too risky an affair. As a result, the decision was finally made to destroy the bottle in the back yard of the Chemistry Department building.
4.7.6. Exercises.

1. As an acid, phenol is stronger than water, methanol, and ethanol, but weaker than even weak inorganic acids such as H2CO3 and H2S. What will happen if CO2 is bubbled through a solution of sodium phenoxide? Answer

2. Write chemical equations for oxidation of methanol and phenol to the corresponding aldehyde. Answer

3. Would you consider the addition of water to ethylene to give ethanol as an oxidation or reduction reaction of ethylene? Answer

4. Sodium metal (1 g) was dissolved in 100 mL of ethanol. What is the mass percentage concentration of the resultant sodium ethoxide solution? The density of ethanol is 0.79 g/mL. Assume zero solubility of H2 in ethanol. Answer

5. The OH group of phenol strongly activates the C-H bonds in the ortho and para positions of the ring toward substitution reactions. While benzene itself is brominated with Br2 only in the presence of a catalyst to give bromobenzene, the reaction of phenol with bromine in water quickly produces 2,4,6-tribromophenol in the absence of any catalyst:
Using only mental calculations, determine how much Br2 is needed to make 2,4,6-triboromophenol from 47 grams of phenol. (a) 120 g; (b) 240 g; (c) 80 g; (d) 160 g. Answer

6. How would you make methyl ethyl ether using the following chemicals: methane, ethylene, bromine, phosphoric acid, water, and sodium? Answer

7. Reducing carboxylic acids to the corresponding aldehydes is (a) easy; (b) not easy, but can be done with Tollens' reagent; (c) easy using the Clemmensen reduction reaction; (d) very challenging because the strong reductants needed to reduce carboxylic acids reduce aldehydes to alcohols even more easily; (e) somewhat challenging, but can be performed using Cu2O in a reaction that is the reverse of the oxidation of aldehydes to acids with Cu(OH)2 under basic conditions. Answer

8. Esterification is catalyzed by (a) strong acids; (b) strong bases; (c) either an acid or a base; (d) occurs without a catalyst. Answer

9. Hydrolysis of esters is (a) irreversible in the presence of an acid; (b) reversible in the presence of an acid; (c) irreversible in the presence of a base; (d) reversible in the presence of a base. Answer

10. What is the difference between polymerization and polycondensation? [Answer: See 4.7.4]

11. Write a chemical scheme for polycondensation of terephthalic acid with ethylene glycol. [Answer: See 4.7.4]

12. Diethyl ether is seldom used as a solvent in industry because (a) of its very low boiling point; (b) it produces explosive hydroperoxides on storage in air; (c) it is highly flammable; (d) it is too expensive to make in large quantities. Answer

13. A sample of PET polyester has a molecular weight of 4,800 a.m.u. What is the degree of polymerization n? Answer

14. What is soap? How is soap made? What is the mechanism of action of soap? [Answer: See 4.7.3 and 4.6.4]

15. Draw chemical structures of rubbing alcohol and methyl ethyl ether. Are these two isomers? Answer

16. Medical doctors often use the terms "bad triglycerides" and "good triglycerides" when analyzing blood test data. What are those good and bad triglycerides? Answer

17. Of the ethers shown below, identify those that can form dangerous hydroperoxides on storage in air.

18. In his article entitled "A Sobering Experience with lsopropyl Ether Peroxide", Irwin B. Douglass writes:

"In sorting through some bottles of chemicals in a basement storeroom recently we found two 2½-L glass-stoppered bottles labeled Isopropyl Ether – Student Preparation. Although no date was on the labels, we knew that the bottles had been there for more than twenty years.

"Both bottles were nearly a third full of camphor-like crystalline solid beneath the liquid upper layer. Having heard of the tendency for isopropyl ether to form a peroxide, we suspected that the solid might be dangerous although it looked harmless enough. The bottles were taken to the dispensing stockroom, and the supernatant liquid poured down the drain. Water was added but the solid proved to be insoluble. The bottles with their contained water and solid were allowed to stand around several weeks awaiting disposal.

"As part of a general stockroom cleanup the bottles were finally loaded into a box along with sundry containers of sodium scraps and unlabeled chemicals and taken by the writer and the stockroom keeper to the dump, located in a marshy area, at the edge of town. Still aware that the white solid might be dangerous we tossed one bottle as far as possible out into the bog and the second after it in the hope that both would be broken. Failing in this attempt, we threw stones at the bottles to break them. When the first stone struck, there was s. violent explosion which blasted mud and debris over the surrounding landscape. Fortunately, neither the writer nor his assistant were hit by flying glass."

What would you do and NOT do if you were in Dr. Douglass's shoes? Answer

19. Describe in your own words the criteria used in organic chemistry to determine if an organic compound has been oxidized or reduced in a chemical reaction. [Answer: See 4.7.2]

20. Acetic acid is (a) more acidic than phenol, methanol, and ethanol; (b) more acidic than carbonic acid but less acidic than phosphoric and nitric acids; (c) more acidic than methanol but less acidic than phenol; (d) more acidic than phenol but less acidic than carbonic acid. Answer

21. Would you expect phenol to react with metallic sodium? Answer

22. The correct order of acidity is (a) H2SO4 > H3PO4 > H2CO3 > CH3COOH > C6H5OH (phenol) > CH3OH; (b) H2SO4 > H3PO4 > CH3COOH > H2CO3 > H2O > C6H5OH (phenol) > CH3OH; (c) H2SO4 > CH3COOH > H3PO4 > H2CO3 > H2O ≈ CH3OH > C6H5OH (phenol); (d) H2SO4 > H3PO4 > CH3COOH > H2CO3 > C6H5OH (phenol) > CH3OH ≈ H2O. Answer

23. Write equations/schemes for the following reactions: (a) Cu-catalyzed oxidation of 1-propanol to propanal with O2; (b) oxidation of benzaldehyde with Cu(OH)2; (c) oxidation of 3-methylbutanal with Ag+; (d) oxidation of formic acid with Ag+; (e) the Clemmensen reduction of methyl ethyl ketone; (f) esterification of benzoic acid with methanol; (g) esterification of acetic acid with 1-butanol; (h) hydrolysis of ethyl benzoate with aqueous NaOH; (i) hydrolysis of ethylene glycol diacetate with aqueous KOH.

24. Esterfication is a reversible reaction. What is the standard method to shift the esterification equilibrium toward the ester product? Answer

25. Write a chemical equation for the Williamson reaction between iodomethane and potassium ethoxide. Answer