In alcohols, the polar hydroxyl group and its ability to hydrogen bond make small alcohols completely miscible with water. As the nonpolar alkyl chain of the alcohol gets larger, it is harder and harder for the polar –OH to provide enough interaction with water to get the entire nonpolar “tail” into solution.The same thing is going on with carboxylic acids; the carboxyl group is very polar and can hydrogen bond with water. As the molar mass increases, the nonpolar hydrocarbon “tail” is harder and harder for the carboxyl group to get into solution.
Note that “complete solubility” means the same thing as “miscible.”The graph applies only to straight-chain carboxylic acids with no multiple bonds.The carboxylic acids with one through four carbons are completely soluble in water. These are methanoic acid, ethanoic acid, propanoic acid, and butanoic acid.At 5 carbons and beyond, the solubility drops off rapidly; hexadecanoic acid, with a 16-carbon chain, is insoluble in water.
Many cream and lotion bottles say, “with alpha-hydroxy!” You may be remembering that, when we have an –OH on a compound that is not an alcohol, the –OH substituent is called hydroxy-. In non-IUPAC nomenclature, the carbon next to the carboxyl carbon is called the alpha carbon. [The carbon two over from the carboxyl carbon is called the beta carbon.] A carboxylic acid with a hydroxyl group on the alpha carbon is called an alpha hydroxy acid. So, when a product claims it contains “alpha hydroxy,” it is claiming to have a molecule-less substituent. The correct term is “alpha hydroxy acid.”
We have been using BioBags for quite some time, and they work just fine and are not prohibitively expensive, especially if you consider the environmental cost of regular plastic bags.
For pentyl butanoate: Begin with butanol and oxidize it to butanoic acid. React butanoic acid with pentanol and a trace of acid to produce pentyl butanoate.For octyl ethanoate:Begin with ethanol and oxidize it to ethanoic acid. React ethanoic acid with octanol and a trace of acid to produce octyl ethanoate.
1. ethanoic acid and propanol2. potassium hexanoate and propanol3. sodium pentanoate and methanol4. hexanoic acid and 2-pentanol
Old fashioned soap was made from animal fat and lye, the equivalent of triglycerides and strong base shown in this slide. A triglyceride is a molecule with three esters attached.Each of these three esters detaches in the presence of base to form a carboxylic acid salt. The other product is glycerol, properly called 1,2,3-propanetriol according to IUPAC rules. The salts of carboxylic acids act as soaps.
1. Carboxylic acids The carboxyl group consists of carbonyl and hydroxyl groups attached to the same carbon. carbonyl + hydroxyl = carboxyl An aliphatic or aromatic group can be attached to the carboxyl group.
1. Carboxylic acids The acyl group is a carboxyl group with either a hydroxyl or alkoxy group. If R is a hydroxyl group, the compound is a carboxylic acid. If R is an alkoxy group, the compound is an ester.
1. Carboxylic acids: boiling points Intermolecular forces are strong in carboxylic acids due to the high polarity of the carboxyl group; the presence of hydrogen- bonding between carboxylic acid molecules.
1. Carboxylic acids: boiling points When two hydrogen bonds form between two carboxylic acid molecules, the result is a dimer. Dimer formation can cause carboxylic acids to seem to have double their actual molecular mass.
1. Carboxylic acids: boiling points Compare molecules with similar molar masses and different functional groups:
1. Carboxylic acids: boiling points Boiling point (oC) vs. number of carbons for acids, alcohols, aldehydes, and alkanes.
1. Carboxylic acids: solubility Lower molecular weight carboxylic acids are very soluble in water. Vinegar is a solution of ethanoic acid. Solubility falls off as molecular weight increases. Why? Hexadecanoic acid is insoluble in water.
1. Carboxylic acids: solubility Solubility (g acid/g H2O) vs. number of carbons for saturated, unbranched- chain carboxylic acids.
1. Carboxylic acids: nomenclature Determine the parent compound from the longest chain that includes the carboxyl carbon. Number the chain so that the carboxyl carbon is carbon 1. Replace the –e ending with –oic acid. Assign numbers to any remaining substituents.
1. Carboxylic acids: nomenclature Additional notes: If two carboxyl groups are present use –dioic acid. For cycloalkanes, add carboxylic acid to the name of the cycloalkane. For aromatic acids, the simplest acid is benzoic acid. If the acid group is attached to the aromatic ring, name after benzoic acid. If the acid group is not attached to the aromatic ring, name after the longest chain, with a –phenyl substituent.
1. Carboxylic acids: nomenclature Name the following compounds: pencast
1. Carboxylic acids: nomenclature Draw structures for the following compounds: 2,5-dimethylhexanoic acid 3-bromo-5-chlorooctanoic acid pencast 2,2-dimethylbutanedioic acid 3-methylcyclohexanecarboxylic acid 2,4-dichlorobenzoic acid 3-phenylpentanoic acid
1. Carboxylic acids Is “alpha-hydroxy” an actual substance? glycolic acid lactic acid tartaric acid
1. Carboxylic acids The last paragraph in the inset box on pages 460-461 of your textbook states: "For the time being, biodegradable plastics cannot outcompete their nonbiodegradable counterparts. Future research and development will be required to reduce the cost of commercial production and fulfill the promise of an environmentally friendly garbage bag.” This statement gives the impression that there are no biodegradable plastics available to consumers at a reasonable cost. Compostable plastic bags
1. Carboxylic acids: reactions Preparation is by complete oxidation of primary alcohols or oxidation of aldehydes. 1o alcohol aldehyde carboxylic acid
1. Carboxylic acids: reactions Carboxylic acids are proton donors and therefore react as acids. Carboxylic acids are weak acids, dissociating only slightly in solution. >95% <5%
1. Carboxylic acids: reactions When a strong base is added to a carboxylic (weak) acid, water and salt are formed. Although the carboxylic acid isn’t initially completely dissociated, as H+ is removed by reaction with OH-, more acid dissociates. Remember le Chatelier’s principle? When product (H+) is removed, the equilibrium shifts to make more product (and less undissociated acid).
1. Carboxylic acids: reactions Acid-base reactioncarboxylic acid + strong base carboxylic acid salt + water
1. Carboxylic acids: reactions Naming salts of carboxylic acids Name the carboxylic acid. Replace the –ic acid ending with –ate. Precede this name with the name of the cation. Name the salts formed in the following reactions: ethanoic acid + KOH benzoic acid + LiOH hexanoic acid + NaOH pencast
1. Carboxylic acids: reactions Esterification is the formation of water and an ester from a carboxylic acid and an alcohol. More about this in the next section…
2. Esters Esters are carboxylic acid derivatives, in which the acidic -H of the acid has been replaced by an alkyl or aryl group – R. carboxylic acid ester derivative
2. Esters: properties Esters are slightly polar; boil at about the same temperature as corresponding aldehydes and ketones; are somewhat soluble in water when they are small. have pleasant aromas.
2. Esters: nomenclature Recall nomenclature of salts of carboxylic acids. Name the carboxylic acid. Replace the –ic acid ending with –ate. Precede this name with the name of the cation. Esters are named in the same way, except the alkyl or aryl portion of the alcohol is used in place of the cation name. Name the carboxylic acid. Replace the –ic acid ending with –ate. Precede this name with the name of the alkyl or aryl portion of the alcohol.
2. Esters: nomenclature Name the following esters. pencast
2. Esters: nomenclature Draw the structures of the following esters. propyl ethanoate octyl decanoate methyl methanoate 2-methylpropyl propanoate pencast 3-methylbutyl ethanoate phenyl pentanoate
2. Esters: reactions Preparation of esters is by reaction of a carboxylic acid and an alcohol to produce an ester and water. This is a dehydration reaction. [water is lost] Heat and a trace of acid catalyst (H+) are required. The reaction produces an equilibrium mixture. heat
2. Esters: reactions Show the esterification reaction that would produce butyl propanoate. pencast
2. Esters: reactions Esters can be synthesized starting from alcohols only. An alcohol can be oxidized to an aldehyde, and further oxidized to a carboxylic acid. This carboxylic acid can undergo an esterification reaction with another alcohol. Name the required alcohols and show the necessary reactions to produce pentyl butanoate (apricots). octyl ethanoate (oranges). pencast
2. Esters: reactions Hydrolysis (hydration) of esters, when it is acid-catalyzed, is the reverse of the esterification reaction. H2O ester carboxylic acid alcohol
2. Esters: reactions Hydrolysis of esters, when it is base-catalyzed, is called saponification. ester carboxylic acid salt alcohol
2. Esters: reactions The carboxylic acid that forms when the ester breaks up reacts immediately with the base, forming the carboxylate anion, associated with the cation of the base.
2. Esters: reactions What are the products of the following reactions? + H2O pencast + H2O + H2O + H2O
2. Esters: saponification (salts of carboxylic acids) + +
2. Esters: saponification A soap (carboxylic acid salt) has a nonpolar end that dissolves in nonpolar fats and oils, and a polar end that dissolves in water. forms groups of soap molecules called micelles that dissolve in water and are washed away.
EXTRA CREDIT QUESTION Radioactive isotopes of an element behave chemically in exactly the same manner as the nonradioactive isotopes. As a result, they can be used as tracers to investigate the details of chemical reactions. A scientist is curious about the origin of the bridging oxygen atom in an ester molecule. She has chosen to use the radioactive isotope 18O to study the following reaction: Design experiments using 18O that will demonstrate whether the oxygen in the water molecule came from the –OH of the alcohol or the –OH of the carboxylic acid. Post your answer in the Journal for this module with tag = XC.
3. Acid chlorides and acid anhydrides Acid chlorides are carboxylic acid derivatives in which the hydroxyl group, -OH, has been replaced by –Cl. Naming Name the corresponding carboxylic acid. Replace the -oic acid ending with –oyl chloride.
3. Acid chlorides and acid anhydrides Name the following acid chlorides. pencast Draw structures for the following acid chlorides. heptanoyl chloride 2-hydroxypropanoyl chloride
3. Acid chlorides and acid anhydrides Preparation of acid chlorides PCl3 or + PCl5 or + inorganic products SOCl2 The reagents PCl3, PCl5, and SOCl2 are inorganic acid chlorides
3. Acid chlorides and acid anhydrides PCl3, PCl5, and SOCl2 replace the hydroxyl group on the acid with a chloride, by the following mechanism!
3. Acid chlorides and acid anhydrides Write an equation for the reaction of benzoic acid with SOCl2 and name the organic product. pencast SOCl2 benzoyl chloride
3. Acid chlorides and acid anhydrides Acid anhydrides are two carboxylic acid molecules with a water molecule removed. + H2O
3. Acid chlorides and acid anhydrides Acid anhydrides with identical acyl groups are symmetrical. Symmetrical acid anhydrides are named after the acid from which they are made, with the acid ending replaced with anhydride. The molecule above, made from two molecules of ethanoic acid, is called ethanoic anhydride.
3. Acid chlorides and acid anhydrides Unsymmetrical anhydrides have two different acyl groups. Unsymmetrical anhydrides are named using both parent carboxylic acid names, in alphabetical order, followed by the word anhydride. The molecule above is called butanoic ethanoic anhydride.
3. Acid chlorides and acid anhydrides Name the following acid anhydrides. pencast
3. Acid chlorides and acid anhydrides Acid anhydrides can be prepared from an acid chloride and a carboxylate anion. Direct reaction of the two parent carboxylic acids is usually not possible. acid chloride carboxylate anion acid anhydride
3. Acid chlorides and acid anhydrides Write equations for the synthesis of butanoic anhydride, beginning with butanoic acid. pencast
3. Acid chlorides and acid anhydrides Acid anhydrides react with water, if it is present, to produce two carboxylic acids. + H2O
3. Acid chlorides and acid anhydrides What are the products of the hydrolysis of ethanoic anhydride? pencast ethanoic methanoic anhydride?
3. Acid chlorides and acid anhydrides An acid anhydride can also react with an alcohol, in a reaction analogous to hydrolysis. Hydrolysis: products are two carboxylic acids. Reaction with alcohol: products are an ester and an acid.