17. Organic II (CARBOXYLIC)

Boiling point of carboxylic acids is greater than other carbonyls due to the hydrogen bonding between the acid molecules (compared to only permanent dipole -permanent dipole intermolecular forces between carbonyls molecules)

Smaller carboxylic acids are but as carbon chain increases solubility decreases Some smaller carboxylic acids can also form dimers

Weak acids, meaning they partially disassociate into carboxylate ions and H+ –> The C=O group pulls electrons away from the OH group so H is more delta positive so it can behave as a proton donor

Acid constant dissociation - more disassociated the acid, the more acidic it is and the larger the Ka value Units for Ka are moldm-3 The more stable the carboxylate anion, the further to the right the equilibrium and the LARGER the Ka value of the carboxylic acid

Longer alkyl chains have a positive inductive effect, donating electron density towards the carboxylate ion. This destabilises the negatively charged conjugate base. A less stable conjugate base means the acid is less willing to lose H⁺. Therefore, the equilibrium lies further to the left and the acid has a lower Ka.

Oxidation of a primary alcohol - reflux Oxidation on an aldehyde - reflux Hydrolysis of an ester - acid/ alkali conditions Hydrolysis of a nitrile - acid/ alkali conditions

Forms a carboxylic acid AND an ammonium ion CH3CH2CN + 2H2O + H+ –> CH3CH2COOH + NH4+

Forms a carboxylate salt and ammonia CH3CH2CN + H2O + OH- –> CH3CH2COO- + NH3

Wash it with acid to protonate the carboxylate ion to get the carboxylic acid

1) With LiAIH4 in dry ether 2) With Na2CO3/ NaHCO3/NaOH 3) With PCL5 4) With an alcohol and sulfuric acid catalyst 5) With UV light

In dry ether Carboxylic acid is reduced straight to a primary alcohol RCOOH + 4[H] –> RCH2OH + H20

2RCOOH + 2Na —> 2RCOO-Na+ + H2 RCOOH + sodium carbonate/ sodium hydrogen carbonate/ –> RCOO-Na+ + CO2 + H2O. You would observe effervescence. Reacting Na2CO3/ NaHCO3 and producing bubbles of CO2 is a classic test for carboxylic acids RCOOH + sodium hydroxide –> RCOO-Na+ + H2O

Makes an acyl chloride (eg: ethanoyl chloride) RCOOH + PCl5 –> RCOCl + POCL3 + HCL –> steamy fumes of HCL produced which will turn damp blue litmus paper red RCOCl is then separated by distillation from reaction mixture Condition: anydrous as acyl chloride reacts vigorously with water

Need sulphuric acid catalyst and reflux Carboxylic acid + alcohol ⇌ ester + H2O Note equilibrium - reaction does not go to completion

Forms a chlorocarboxylic acid COOH doesn’t change, you are just substituting a hydrogen with a chlorine RCH2COOH + Cl2 –> RCHClCOOH + HCl

Volatile liquids at room room temperature Soluble in ORGANIC solutions but they react with water to form carboxylic acids so they are not typically used in AQUEOUS solution

ROCl + alcohol –> Ester + HCL

Forms primary amide + ammonium chloride Ammonium chloride appears as a white cloud You need excess NH3 ROCl + 2NH3 –> RCONH2 + NH3+Cl-

1) With water –> VERY reactive with water. They revert back to carboxylic acids and hydrochloric acid 2) With alcohols 3) With concentrated ammonia 4) With amines

Using an acyl chloride is easier as you don’t need an acid catalyst and its not a reversible reaction so you get a higher yield of ester. You also don’t need to reflux as reaction occurs at room temperature

Excess amine Forms an alkyl ammonium salt which is a secondary amide RCOCl + RNH2 –> RCONHR +HCL

Acyl chloride + water —> carboxylic acid + HCl Vigorous reaction - evolution of misty white fumes (hydrogen chloride)