They contains the Carbonyl Functional Group- COOH
Their systematic names all end with -oic acid. They are formed from the oxidation of primary alcohols to aldehydes then carboxylic acids.
Reactions: 1. Acid- Base Reactions: carboxylic acids partially dissociate in aq. solution to form oxonium ions (H30-) [OR H+ IONS] and carboxylate ions (RCOO-). They react with bases to form salts. Acid + Base --> Salt + Water
2. Esterification Reactions: Carboxylic Acid + Alcohol --> Ester + Water when heated under reflux with a strong acid catalyst eg, concentrated sulfuric acid.
Tests for Carboxylic Acids: Carbonate + Acid --> Salt + Water + Carbon Dioxide. Common chemicals used for tests are sodium carbonate and sodium hydrogencarbonate.
Derivatives: Ester (COO)
Acyl Chloride (COCl)
Acid Anhydride (COO-COO)
The OH Group in Alcohols, Phenols and Carboxylic A
Alcohols: -OH group is attached to an aliphatic carbon chain.
Phenols: There is 1 or more -OH groups attached directly to a benzene ring.
Test for Phenols: Use neutral iron (lll) chloride solution. A purple complex will be formed.
Acidic Properties of alcohols, phenols and carboxylic acids:
- All are weak acids
- React with water producing oxonium ions.
- ethanol < water < phenol < carboxylic acids.
- Strength is explained by comparing stability of the anion. (R-O-)
- Phenoxide and Carboxylate ions are more stable than hydroxide and ethoxide ions because the negative charge on the ion can be delocalised across several atoms.
- Carboxylic acids and phenols react with NaOH to form their sodium salts.
- Only carboxylic acids react with Na2CO3.
- Alcohols do not react with either.
Made by heating under reflux with a concentrated acid catalyst (conc. sulfuric/ hydrochloric acid) with the reaction Alcohol + Carboxylic Acid <--> Ester + Water. This is ESTERIFICATION and a CONDENSATION REACTION. The reverse reaction is called ESTER HYDROLYSIS and dilute acid is used.
Phenol + Acid Anhydride <--> Ester (Anhydrous conditions, heated under reflux)
Phenol + Acyl Chlorides <--> Ester (Anhydrous conditions, at room temperature)
When phenols are used, ethanoic acid is often used. This is ETHANOYLATION. Ethanoic Anhydride and Ethanoyl Chloride are Ethanoylating Agents, and belong the the functional group ACYLATING AGENTS.
Esters end in -oate and have the COO functional group. They have a sweet, fruity smell.
Naming Esters: Two parts- the first part is from the alcohol/ phenol and the second is from the carboxylic acid/ acid derivative.
Ester Hydrolysis: Can be carried out with an acid or alkaline catalyst, Alkaline is preferred as the reaction goes to completion. (Produces a carboxylate salt)
% atom economy = RFM of useful product ÷ RFM of reactants used x 100
Reaction Types in order of Decreasing Atom Economy:
Rearrangement and Addition- 100% atom economy, no atoms formed or removed.
Substitution- the larger the Mr of the leaving group/ replacing group, the lower the atom economy.
Elimination- Removing a group from a molecule, so will always be less than 100%.
Aldehydes and Ketones
Aldehydes and Ketones both contain the carbonyl group- C=O.
Aldehydes: end in -al and have the functional group COH. Ketones end in -one.
Preparation: Oxidation of alcohol. For an aldehyde, oxidation of a primary alcohol with potassium dichromate (VI) solution (H+/Cr2O72-), which causes the colour change from orange to green. Excess acid is used, and the aldehyde is distilled off when formed (in situ).
For a ketone, a secondary alcohol is used, the same oxidising agent is used with the same colour change seen.
Reactions: OXIDATION: Only aldehydes can be further oxidised to carboxylic acids due to the hydrogen atom on the carbonyl group. Aldehydes can be reacted with Fehlings Solution and it will be oxidised to a carboxylic acid and the blue copper ions are reduced to copper oxide which forms a orange/ brown precipitate.
REDUCTION: Carbonyl compounds are reduced back to the alcohol with sodium tetrahydridoborate (NaBH4)
ADDITION: Both undergo nucleophilic addition reactions with HCN with a present alkali. This produces a Hydroxynitrile or a Cyanohydrin. It produces a new C-C bond.
Acid- Base Reactions
Acids- proton donors, turn litmus red, liberate CO2 from carbonates.
Bases- proton acceptors, dissolves in water to produce hydroxide ions.
Proton Transfer: Acids donate H+ ions to water to become oxonium ions (H3O+).
Acid Base Pairs: HA(aq) <------à H+(aq)+ A-(aq). In this equation the HA is the conjugate acid and the A- is the conjugate base. The HA donates a proton to the A-. This is a conjugate acid- base pair. Substances that act like an acid and a base are called amphoteric eg. water
Stengths: stong acids have weak conjugate bases etc.
Indicators:Acid base indicators eg. methyl red or phenolphthalein are weak acids. The conjugate acid and conjugate base are different colours.
The Molecular Ion (M+) is produced when a molecule loses one electron. This ion is unstable and can break up leading to FRAGMENTATION. Only the positive ions formed in fragmentation pass through the mass spectrometer to the detector.
Typical Mass Spectrum
- x axis has the mass to charge ratio (m/z)
- y axis shows intensity
- every line represents a + ion. The molecular ion is NOT always the peak.
- Identify the M+ peak, usually the highest peak. This gives RFM of the compound.
- List masses of major peaks then find difference between it and the M+ peak.
- Identify isotope peaks.
THE LARGEST PEAK IS THE BASE PEAK.