Chapter 26 quizlet

• What can aldehydes be oxidised to?

  carboxylic acids
• Conditions for oxidation of aldehydes

  Acidified potassium dichromate, heat under reflux
• Can ketones be oxidised?

  No, as there is no H on the carbon
• Method of distinguishing between ketones and aldehydes

  Oxidise them - aldehyde will oxidise, ketone will not
• What is a nucleophile?

  An electron pair donor
• Why can aldehydes and ketones undergo nucleophilic addition?

  The nature of the C=O causes a dipole across the bond, so nucleophile is attracted to the positive dipole
• How can aldehydes and ketones be reduced?

  Reaction with NaBH4(aq) and warm gently
• What are aldehydes reduced into?

  primary alcohols
• What are ketones reduced into?

  secondary alcohols
• Describe the mechanism for reduction of a ketone/aldehyde

  Nucleophilic addition:

  - H- ion ( from NaBH4) donates pair of electrons to positive dipole on carbon atom, creating a C-H bond.

  - C=O bond splits to form a negative charge on the oxygen.

  - positive dipole on hydrogen from water molecule attracts the oxygen, forming C-OH, leaving an OH- ion.
• Why is reaction of carbonyls with HCN useful?

  Adds carbon atoms to the chain
• Conditions for reaction of carbonyl with HCN

  Sodium cyanide and H2SO4
• Why is cyanide dangerous?

  Colourless, poisonous and boils at just above room temperature
• Describe nucleophilic addition between carbonyl and HCN

  - negative CN ion is attracted to positive carbon dipole, forming C-CN

  - C=O bond breaks, forming negative O-

  - O- is attracted to H+ ion, forming alcohol group
• What can be used to detect carbonyls?

  2,4 - DNP
• Observation of 2,4 - DNP with carbonyls


  Forms orange crystals
• How can structure of specific carbonyls be found after reaction with DNP?

  Further analysis of the crystals produced ( e.g. compare melting point to known values)
• How to distinguish between Aldehydes and Ketones?

  Add Tollens reagent and place in a water bath at 50°C
• Observations of carbonyls + Tollens

  Aldehydes - silver mirror is produced

  Ketone - no reaction
• How does Tollen's reagent work?

  Tollens reagent is a colourless solution of silver nitrate dissolved in aqueous ammonia. It contains silver ions, which act as an oxidising agent in the presence of ammonia. In the reaction, the silver ions are reduce to silver, and aldehyde is oxidised to a carboxylic acid.
• Equations for Tollen's reagent

  Ag+ + e- -> Ag(s)

  
  

  R-COH + [O] -> R-COOH
• What are carboxylic acids commonly used for?

  Starting materials or intermediates in the formation of more useful compounds
• Why are carboxylic acids soluble in water?


  Polar C=O and O-H bonds allowing them to form hydrogen bonds
• Which carboxylic acids are soluble in water?

  Methanoic acid to Butanoic acid
• Why are longer chain carboxylic acids not soluble

  The longer the non-polar chain is, the greater the effect on the polar part, reducing strength.
• Why are carboxylic acids classed as a weak acid?

  The partially dissociate
• What is used in reactions to show partial dissociation?

  Reversible reaction symbol
• What type of salts do carboxylic acids form when reacting with metals or bases?

  Carboxylates
• Observations for COOH + metal ( or metal base ) in a redox reaction

  Metal disappears, effervescence given off
• Organic product produced when propanoic acid reacts with Magnesium


  (CH3CH2COO-)2Mg+2
• What is the test for carboxylic acid group?

  Effervescence when reacted with metal carbonate
• Why does the test for COOH work?

  COOH is the only common organic compound that can react with metal carbonates
• What are derivatives of carboxylic acids?

  Esters, acyl chlorides, acid anhydrides, amides - all have an acyl group, attached to an electronegative atom or group of atoms
• What is esterification?


  a reaction of alcohol with an acid to produce an ester and water
• Conditions for esterification


  conc H2SO4 catalyst
• How to name esters

  Alcohol = Alkyl

  COOH = R - oate
• What is hydrolysis of esters?

  Addition of water to esters, to break them down
• What is acid hydrolysis of esters? Equation?

  reverse of esterification: Ester is heated under reflux with dilute acid catalyst

  
  

  Ester + water <-> carboxylic acid + alcohol
• What is saponification?


  Alkali hydrolysis of ester - ester is heated under reflux with aqueous OH- ions, forming a carboxylate and an alcohol
• How can acyl chlorides be produced? Equation?

  Reacting COOH with thionyl chloride, SoCl2

  
  

  R-COOH + SoCl2 -> Acyl chloride + SO2 + HCl