carbonyl compounds

• Aldehydes and ketones are carbonyl compounds containing a C=O group.
• Aldehydes and ketones can be prepared from the oxidation of primary and secondary alcohols respectively.
• The oxidising agents used to prepare aldehydes and ketones from alcohols include acidi ed potassium dichromate (K Cr O) and acidi ed potassium manganate (KMnO).
• When the alcohols are oxidised, the orange dichromate ions (Cr O) are reduced to green Cr ions.
• When the alcohols are oxidised, the purple manganate ions (MnO) are reduced to colourless Mn ions.
• The oxidising agents change colour when they oxidise an alcohol and get reduced themselves.
• To make an aldehyde, warm primary alcohol is slowly added to the oxidising agent.
• The formed aldehyde has a lower boiling point than the alcohol and can therefore be distilled off as soon as it forms.
• The aldehyde is then condensed into a liquid and collected.
• Aldehydes are formed from the oxidation of primary alcohols.
• In the alkaline conditions, the carboxylic acid will become a carboxylate ion and form a salt.
• The Ag ions in Tollens’ reagent are oxidising agents, oxidising the aldehyde to a carboxylic acid and getting reduced themselves to silver atoms.
• Ketones cannot be oxidised and therefore give a negative test when warmed with Tollens’ reagent.
• The Ag atoms form a silver ‘mirror’ on the inside of the tube.
• When warmed with an aldehyde, the aldehyde is oxidised to a carboxylic acid and the Ag ions are reduced to Ag atoms.
• The carbonyl group -C=O, in aldehydes and ketones is polarised.
• Hydroxynitriles are nitriles containing a hydroxy, -OH, group.
• The actual negative charge on the cyanide ion is on the carbon atom and not on the nitrogen atom.
• Aldehydes are reduced to primary alcohols and ketones are reduced to secondary alcohols.
• In step 2, the negatively charged oxygen atom in the reactive intermediate quickly reacts with aqueous H (either from HCN, water or dilute acid) to form 2-hydroxynitrile +.
• The carbonyl carbon is therefore susceptible to attack by a nucleophile, such as the cyanide ion.
• The cyanide ion, CN, acts as a nucleophile and adds across the C-O bond.
• The nucleophilic addition of hydrogen cyanide to carbonyl compounds is a two-step process.
• Aldehydes and ketones can undergo nucleophilic addition with hydrogen cyanide, HCN.
• The oxygen atom is more electronegative than carbon drawing electron density towards itself, leaving the carbon atom slightly positively charged and the oxygen atom slightly negatively charged.
• Aldehydes and ketones react with HCN, KCN as catalyst and heat to produce hydroxynitriles.
• Aldehydes and ketones can be reduced by reducing agents such as NaBH or LiAlH.
• The nucleophilic addition of HCN to an aldehyde or ketone increases the length of the carbon chain by one carbon atom.
• In step 1, the cyanide ion attacks the carbonyl carbon to form a negatively charged intermediate.
• To make a ketone, warm secondary alcohol is slowly added to the oxidising agent.
• Since the formed ketone cannot be further oxidised it does not need to be distilled off straightaway after it has been formed.
• Ketones are formed from the oxidation of secondary alcohols.
• If the aldehyde formed is not distilled off, further re-reducing with excess oxidising agent will oxidise the aldehyde to a carboxylic acid.
• When warmed with an aldehyde, the aldehyde is oxidised to a carboxylic acid and the Cu ions are reduced to Cu ions.
• The carboxylate ion (-COO) will form a salt with a positively charged metal ion such as sodium (-COO Na).
• The product formed when 2,4-DNPH is added to a solution that contains an aldehyde or ketone is a deep-orange precipitate which can be purified by recrystallisation.
• 2,4-dinitrophenylhydrazine (also known as 2,4-DNPH) is a reagent which detects the presence of carbonyl compounds (compounds with -C=O group).
• A condensation reaction is a reaction in which two molecules join together and a small molecule (such as H2O or HCl) is eliminated.
• Fehling’s solution is an alkaline solution containing copper(II) ions which act as the oxidising agent.
• The carbonyl group of aldehydes and ketones undergoes a condensation reaction with 2,4-dinitrophenylhydrazine.