chapter 28

• Why is C-C bond formation important?

  Allows the length of the carbon chain to increase.
• How are nitriles formed from haloalkanes?

  Haloalkanes are heated with a cyanide salt in ethanol under reflux, increasing the length of the carbon chain, e.g.:

  CH3-Cl + KCN -> CH3-CN + KCl

  -This reaction involves a nucleophilic substitution mechanism

  -If water is present, a substitution of -OH tends to occur instead
• How are nitriles formed from aldehydes and ketones?

  Aldehydes and ketones react with hydrogen cyanide in a nucleophilic addition reaction, producing a hydroxynitrile, e.g.:

  CH3-CO-CH3 + HCN -> CH3-C(OH)(CN)-CH3

  -Since hydrogen cyanide is extremely poisonous, a mixture of sodium cyanide and sulfuric acid is used

  
• How are carboxylic acids formed from nitriles?

  Nitriles undergo acid hydrolysis via heating with dilute aqueous acid, e.g.:

  CH3-CN + 2H2O + HCl -> CH3-COOH + NH4Cl
• What is filtration under reduced pressure?

  A technique for separating a solid product from a solvent or liquid reaction mixture.
• What is a Buchner flask?

  A conical flask with a quickfit connection off the side.

  
• What is a Buchner funnel?

  A porous funnel used with filter paper during vacuum filtration.

  
• How is filtration under reduced pressure carried out?

  -Pressure tubing connects vacuum outlet/filter pump to the Buchner flask

  -Buchner funnel is fit to Buchner flask such that it is tight

  -The vacuum pump or tap to which the filter pump is attached is switched on

  -Suction is tested

  -Filter paper is wet with solvent and placed inside Buchner funnel

  -The reaction mixture is slowly poured from a beaker into the filter paper's centre

  -The beaker with the solvent is rinsed so that all of the crystals collect in the Buchner funnel

  -The crystals are rinsed with more solvent and are left under suction to dry
• What is recrystallization?


  The process in which a crystalline material (solute) dissolves in a hot solvent and then returns to a solid again by crystallization in a cooled solvent.

  -impurities typically will not crystallize if the process is conducted carefully
• How is recrystallisation carried out?

  -Chosen solvent is poured into conical flask

  -Solvent is warmed in a water bath if flammable

  -Solvent is warmed over a Bunsen if water

  -The impure sample is poured into a second conical flask or beaker

  -The minimum volume of hot solvent to dissolve the solid is slowly added to the impure sample

  -Once the solid has dissolved, the solution is cooled

  -Crystals of the desired product should form in the conical flask or beaker

  -When no more crystals form, they are filtered under reduced pressure to obtain a dry crystalline solid
• What is melting point determination?

  Chemists determine the melting point of solids to identify whether a solid compound is pure. A pure sample usually has a very sharp melting range within one or two degrees.

  The melting range is the difference between the temperature when the sample starts to melt and when it is done.

  The solid contains impurities if it melts over a wide range of temperatures; impure samples normally have a lower melting point than a pure sample.
• How is a melting point tube prepared?

  -A dry, free flowing sample is collected

  -One end of a glass capillary tube is held in a hot flame or Bunsen burner

  -The tube is rotated in the flame until the end is sealed

  -The tube is allowed to cool and is then filled with crystals to about 3cm depth

  -This is done by pushing the open end through the sample
• How is the melting point of a sample determined using an electrical heater?

  -A melting point tube containing a sample is placed into the sample hole and a 0-300C thermometer is placed into the thermometer hole of the apparatus

  -Using the rapid heating setting the sample is heated under observation through the magnifying window

  -The melting point is recorded once the solid is seen to melt

  -The melting point apparatus is allowed to cool

  -A second sample is prepared in a new capillary tube and the experiment is repeated

  -As the melting point is approached, the heating setting is turned to low

  -The temperature is raised slowly whilst observing the sample

  -An accurate melting point determination can then be obtained
• How is the melting point of a sample determined using an oil bath or Thiele tube?

  -The oil bath or Thiele tube are set up

  -The capillary tube containing the sample is attached to a thermometer with a rubber band

  -The thermometer is inserted through a hole in the cork when using a Thiele tube or it is clamped when using an oil bath

  -A micro-burner slowly heats the Thiele tube or oil bath side arm whilst the solid is observed

  -When the solid starts to melt the heat is removed and the temperature at which all the solid has melted is recorded

  -The oil is heated slowly approaching the melting point

  -The experiment is repeated to determine an accurate value
• How is a primary alcohol esterified?

  It is reacted with a carboxylic acid in the presence of H2SO4, e.g.:

  CH3-OH + HCOOH -> HCOO-CH3 + H2O
• How is a primary alcohol oxidised into an aldehyde?

  It is distilled with acidified potassium dichromate, e.g.:

  CH3-OH + [O] -> HCOH + H2O
• How is a primary alcohol formed into a haloalkane?

  It is reacted with sodium halide in the presence of H2SO4, e.g.:

  CH3-OH + NaCl -> CH3-Cl + NaOH

  -Nucleophilic substitution
• How is a primary alcohol dehydrated into an alkene?

  It is catalysed by H2SO4, e.g.:

  CH3-CH2-OH -> CH2=CH2 + H2O
• How is an alkene hydrated into an alchol?

  It is reacted with water in the presence of H3PO4, e.g.:

  CH2=CH2 + H2O -> CH3-CH2-OH

  -Electrophilic addition
• How is an alkene formed into a haloalkane?

  It is reacted with hydrogen halide, e.g.:

  CH2=CH2 + HBr -> CH3-CH2Br

  -Electrophilic addition
• How is a haloalkane formed into an amine?

  It is reacted with excess ammonia in ethanol, e.g.:

  CH3-Cl + NH3 -> (CH3-NH3+)Cl-

  -Nucleophilic substitution

  It is then reacted with an alkali, e.g.:

  (CH3-NH3+)Cl- + NaOH -> CH3-NH2 + NaCl + H2O
• How is a haloalkane formed into a primary alcohol?

  It is reacted with an alkali, e.g.:

  CH3-Cl + NaOH -> CH3-OH + NaCl

  -Nucleophilic substitution
• How is a nitrile reduced to form an amine?

  It is reacted with H2 in the presence of a nickel catalyst, e.g.:

  CH3-CN + 2H2 -> CH3-CH2-NH2
• How is an aldehyde reduced to form a primary alcohol?

  It is reacted with water and NaBH4, e.g.:

  HCOH + 2[H] -> CH3-OH
• How is an aldehyde formed into a carboxylic acid?

  It is reacted with acidified potassium dichromate under reflux, e.g.:

  HCOH + [O] -> HCOOH
• How is a carboxylic acid formed into an acyl chloride?

  It is reacted with SOCl2, e.g.:

  HCOOH + SOCl2 -> HCOCl + SO2 + HCl
• How is an acyl chloride esterified with an alcohol?

  It is reacted with an alcohol, e.g.:

  HCOCl + H3C-OH -> HCOOCH3 + HCl
• How is an acyl chloride formed into a carboxylic acid?

  It is reacted with water, e.g.:

  HCOCl + H2O -> HCOOH + HCl
• How is an acyl chloride formed into a primary amide?

  It is reacted with ammonia, e.g.:

  HCOCl + NH3 -> HCONH2 + HCl
• How is an acyl chloride formed into a secondary amide?

  It is reacted with a primary amide, e.g.:

  HCOCl + CH3-NH2 -> HCONH-CH3 + HCl
• How is an ester hydrolised with an acid?

  It is reacted with water in the presence of an acid, e.g.:

  HCOOCH3 + H2O -> HCOOH + CH3-OH
• How is an ester hydrolised with an alkali?

  It reacts with an alkali, e.g.:

  HCOOCH3 + NaOH -> (HCOO-)Na+ + CH3-OH
• How is benzene alkylated?

  It reacts with an alkyl-chloride in the presence of AlCl3, e.g.:

  C6H6 + CH3-Cl -> C6H5-CH3 + HCl

  -Electrophilic substitution
• How is benzene acylated?

  It reacts with an acyl-chloride in the presence of AlCl3, e.g.:

  C6H6 + HCOCl -> C6H5-CHO + HCl

  -Electrophilic substitution
• How is benzene nitrated?

  It reacts with HNO3 in the presence of H2SO4, e.g.:

  C6H6 + HNO3 -> C6H5-NO2 + H2O

  -Electrophilic substitution
• How is benzene brominated?

  It reacts with Br2 in the presence of FeBr3, e.g.:

  C6H6 + Br2 -> C6H5Br + HBr

  -Electrophilic substitution
• How is benzene chlorinated?

  It reacts with Cl2 in the presence of AlCl3, e.g.:

  C6H6 + Cl2 -> C6H5Cl + HCl

  -Electrophilic substitution
• How is nitrobenzene reduced to phenylamine?

  It reacts with HCl in the presence of Sn, e.g.:

  C6H5-NO2 + 6[H] -> C6H5-NH2 + 2H2O
• How is benzoic acid reduced?

  It reacts with NaBH4, e.g.:

  C6H5-CHO + 2[H] -> C6H5-CH2-OH
• How is phenol nitrated?

  It reacts with HNO3, e.g.:

  C6H5-OH + HNO3 -> C6H4(OH)(NO2) + H2O

  -Electrophilic substitution