Structure & Functional Group Functional Group: Carboxylic acids contain a carbonyl attached to a hydroxyl group; this is called a carboxyl group Carboxyl group is defined by the double bond between carbon and oxygen R represents the carbon chain
Structure & Functional Group They are Brønsted-Lowry acids because they are proton (H+) donors which makes them more acidic than alcohol Acids with two or more carboxyl groups are called dicarboxylic, tricarboxylic, etc.
Quiz What functional group do carboxylic acids have? Why are carboxylic acids more acidic than alcohol? What is the difference between a carboxylic acid and a ketone?
Nomenclature Step 1: Identify longest carbon chain (gives you prefix) Begin at carbon that has the hydroxide and oxygen atoms bonded to it Step 2: Determine whether there are any double or triple bonds present
Nomenclature Step 3: Apply suffix –oic acid to the prefix determined by parent chain Step 4: Identify the presence of any branches (ethyl, methyl, propyl, etc.) Identify and record at which branch each meets the parent chain REMINDER: CARBOXYL GROUP ALWAYS TAKE PRESIDENCE WHEN NAMING A MOLECULE
Nomenclature Practice Name the following carboxylic acids:
Nomenclature Practice Draw the following carboxylic acids: 3-Methylbutanoic Acid 4-chloro-2-methyl-3-pentynoic acid
Properties Acidity Given by the name, Carboxylic acids are acidic. This is because of the transfer of the hydrogen ion present in the -COOH group, to a water molecule, ionizing the acid molecule
Properties Example 1: + ↔− + − (Above: Ethanoic acid, a weak acid) Carboxylic acids are relatively weak compared to other acids because they do not fully dissociate to produce H+ cations however are still the most acidic out of the organic functional groups.
Properties Solubility The hydrogen bonds, as well as the presence of a carbonyl group (-CO) both result in the molecules being polar, preforming similar solubility behaviour as alcohols. Carboxylic acids containing up to four carbon atoms will mix with water in any proportion, whereas larger hydrocarbon chains are more likely to be insoluble because they are more non-polar. However this means they can react with organic bases to produce organic salts.
Properties Melting/Boiling Point Carboxylic acids have higher boiling points than their parent alkanes due to the fact that the carboxyl group has increased intermolecular attractions from the high polarity of the molecule
Properties Example 2: Oxalic acid, similar to Ethanoic acid, has 2 carbon atoms and unlike Ethanoic acid, has 2 carboxyl groups. This increases the boiling point considerably because it is able to donate a proton twice, doubling the size of the molecule and increasing Vander Waal forces, therefore the boiling point. Oxalic acid (189◦C)
Uses Carboxylic acids are generally characterized by their distinctive smell or sour/tangy taste. They are found in citrus filled fruits such as apples, rhubarb, grapes and other fruits with high acidity Carboxylic acids are also produced when an alcohol is oxidized accordingly. This creates the double bond between the oxygen, creating the –COOH group. An example of this is when red wine is oxidized to make red wine vinegar, gaining the more sour taste.
Uses Carboxylic acids are also very useful when acting as precursors for producing other compounds due to the fact that they can undergo ionization, oxidization, react in neutralization reactions with alcohols and organic bases to form biological compounds.
Common Carboxylic Acids Citric AcidLactic AcidAscorbic acid (Vitamin C) Tartaric acid Formic acid (methanoic acid)
Quiz 2 True or False: Carboxylic acids are acidic because of condensation. Which Organic Family do Carboxylic acids have similar solubility as? True or False: Carboxylic acids have a high boiling point. What do alcohols undergo to produce Carboxylic acids?
Reactions Controlled Oxidization (Preparation) Conditions : Aqueous solutions Requires Catalyst: Usually K2Cr2O7 (Potassium dichromate (VI)) A carboxylic acid is formed from a controlled oxidation of an aldehyde Mild oxidation Aldehyde Further controlled oxidation Carboxylic Acid Functional group: carboxyl group (One additional O atom) Add an O to the H to make OH
Reactions Formation of an aldehyde: Formation of a carboxylic acid:
Reactions Example 2: Breathalyzer (Oxidation of ethanol to acetic acid) Ethanol + (O) Ethanal (Acetaldehyde) + (O) Acetic Acid
Reactions When measured volume of air containing ethanol passes through breathalyzer tube, ethanol is oxidized to acetaldehyde (ethanol) then to acetic acid. This process is accompanied by a reduction of the chromate ion to its Cr³ ⁺ oxidation state. The extent of the green colour down the breathalyzer tube provides a measure of the concentration of alcohol in the breath.