Transcript 06_reactions

Organic Chemistry
Reactions
Reactions
Hydrolysis of a polysaccharide
polysaccharide + water → disaccharide
Example: 2(C6H10O5)n + nH2O → nC12H22O11
Hydrolysis of a disaccharide
disaccharide + water → monosaccharide
Example: C12H22O11 + H2O → 2C6H12O6
Reactions
Fermentation of glucose
C6H12O6 → 2C2H5OH + 2CO2
Special conditions for fermentation:
• optimum temperature range between 20°C and 30°C
• little or no oxygen present
• enzymes (catalyst) e.g. in yeast
Reactions
Oxidation of a primary alcohol
primary alcohol + oxidising agent → aldehyde
(there will be more reactants and products depending on the oxidising agent)
Note: if the aldehyde is not immediately removed it will be further oxidised
to a carboxylic acid
Example: ethanol + acidified dichromate → ethanal + chromium ions
CH3CH2OH + Cr2O72- + 12H+ → CH3CHO + 2Cr3+ + 7H2O
(For definitions of primary and secondary alcohols, see notes, Subtopic 5.2)
Reactions
Oxidation of a secondary alcohol
secondary alcohol + oxidising agent → ketone
(there will be more reactants and products depending on the oxidising agent)
Example: propan-2-ol + acidified dichromate → propanone + chromium ions
CH3CH(OH)CH3 + Cr2O72- + 12H+ → CH3COCH3 + 2Cr3+ + 7H2O
(For definitions of primary and secondary alcohols, see notes, Subtopic 5.2)
Reactions
Oxidation of an aldehyde under acidic conditions
aldehyde + oxidising agent + H+ → carboxylic acid
(there will be more reactants or products depending on the oxidising agent)
Example: ethanal + acidified dichromate → ethanoic acid + chromium ions
CH3CHO + Cr2O72- + 12H+ → CH3COOH + 2Cr3+ + 6H2O
Reactions
Oxidation of an aldehyde by Tollens’ reagent
aldehyde + Tollens’ reagent → carboxylate anion + silver metal + ammonia
(there will be more reactants or products depending on half-reactions)
Example: methanal + Tollens’ reagent → methanoic acid + silver + ammonia
CH2O + Ag(NH3)2+ + H2O → CHOOH + Ag + 2NH3 + 2H+
Since an obvious silver ‘mirror’ forms on the flask if a reaction occurs, this is
commonly used to test whether a substance is a ketone or an aldehyde.
A ketone cannot be oxidised, so no silver mirror would form.
Tollens’ reagent is ammoniacal silver nitrate solution, Ag(NH3)2NO3 (aq)
Usually we wouldn’t write the nitrate, since it is a spectator.
And many more…
See “Organic_reactiontypes” in the Notes folder for a
full list. Some are detailed further in other notes files
or the textbook.