Halogenoalkane Reactions and Mechanisms
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what are the four substitution reactions we need to know
• reaction 1 - RX + H20 = ROH • reaction 2 - RX + KOH = ROH • reaction 3 - RX + KCN = RCN • reaction 4 - RX + NH3 = RNH2
what are the conditions for the four reaction
• reaction 1 = warm • reaction 2 = heating under reflux • reaction 3 = heating under reflux • reaction 4 = heat in a sealed tube
what type of reaction is reaction 1
a hydrolysis reaction
what does the reaction between a halogenoalkane and aqueous potassium hydroxide make
an alcohol
what is the attacking nucleophile in the reaction
the OH- ion from KOH
what would the structural formula and ionic structural formula for the reaction between 1-chloropropane and potassium hydroxide making propan-1-ol be
• CH3-CH2-CH2Cl + KOH = CH3-CH2-CH2OH + KCl - CH3-CH2-CH2Cl + OH- = CH3-CH2-CH2OH + Cl-
what is the advantage of writing out the ionic equation
it clearly shows the nucleophile
for reaction 3, what does heating a halogenoalkane with potassium cyanide dissolved in ethanol, under a reflux, make
nitriles
what is the attacking nucleophile
the CN- ion`
what would the structural formula for the reaction between bromoethane and potassium cyanide be
• CH3-CH2Br + KCN = CH3-CH2CN + KBr
what would the name of the produced organic product be and why
• propanentrile - because it now contains an extra carbon atom
how are primary amines made
• by heating a halogenoalkane with ammonia solution in a heated tube • it is reaction 4
what is the attacking nucleophile
the NH3 molecule
what is the structural formula for the reaction between 1-iodopropane and ammonia as well as the products name
• CH3-CH2-CH2l + NH3 = CH3-CH2-CH2NH2 + HI - propylamine
what actually happens during reaction 4 before it is complete
• the organic product is a base - this means that it would react with the inorganic acid HI to from a salt
what would a more accurate equation of the reaction then be
CH3-CH2-CH2I + NH3 = CH3-CH2-CH2NH3+ + I-
if a salt is produced as well rather than just the primary amine, how do you produce a high yield of amine
• use ammonia in excess - some of this excess reacts in a second step to produce the amine
what is the ionic equation for this second step
CH3-CH2-CH2HN3+ I- + 2NH3 = CH3-CH2-CH2NH2 + NH4+ I-
therefore, what are the final products
propylamine and ammonium iodide
if the attacking species of a substitution reaction is nucleophile, what is the full name of the reaction
nucleophilic substitution
what is the main mechanism of reaction 2 between a halogenoalkane and aqueous potassium hydroxide
• the oxygen on the hydroxide ion donates a lone pair of electrons to the electron deficient carbon atom bonded to the halogen • the electronegativity of the halogen causes the C-X bond to break, resulting in the hydroxide ion bonding with the carbocation to make an alcohol
why is the carbon atom electron deficient in the first place
• because the halogen atom is electronegative • this means that the shared electron moves towards the halogen more, making the carbon atom partially positively charged • hence why the negative hydroxide ion is attracted to it
what bonds are formed and broken at the same time
• a C-O bond forms - at the same time the C-X bond is broken
what is this kind of bond breaking called
heterolytic fission