Halogenoalkane Reactions and Mechanisms Flashcards
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
where would your curly arrows be if you were drawing this mechanisms
- one arrow would be going from the lone pair of electrons on the oxygen atom of the hydroxide ion to the electron deficient carbon atom
- the other arrow would be going from the bond between the carbon atom and the halogen to the halogen itself
what do both of those arrows indicate
- the first arrow shows the oxygen bonding to the carbon atom
- the second arrow shows the electrons in the C-X bond moving to the halogen
how would the mechanism of reaction 4 start off
- the nitrogen atom of the ammonia would donate a lone pair of electrons to the electron deficient carbon atom
- leading to the formation of a C-N bond
- at the same time the electrons in the C-X bond move to the X atom
- leading to that bond breaking
how would your curly arrows look like this first stage
- the same as the ones for reaction 2
- but instead you have formed a positively charged nitrogen ion bonded to 3 hydrogens and a carbon
what happens in the second step
- another ammonia molecule acts a base
- this removes a hydrogen atom from the ion formed in the first step
what ions do you have in the first and second step and how do they interact
- the ion in the first step is the negatively charged halogen ion
- the ion in the second step is the positively charged ammonia ion
- they both react to form an ammonium halide
what does the OH- ion act as if ethanol is the solvent that reaction 2 happens in
a base instead of a nucleophile
what does the OH- ion react with
the hydrogen atom attached to the carbon atom next to the carbon with the C-X bond
what would the equation be for the reaction between 2-bromopropane and ethanolic potassium hydroxide
CH3-CHBr-CH3 + KOH = CH2=CH-CH3 + H2O + KBr
what does this reaction with ethanol being the solvent therefore produce
an alkene with water and a salt
why is this reaction referred to as an elimination reaction
- because the H and X are removed from the halogenoalkane
- but are not replaced by other atoms
what is the difference between nitrile organic compounds and primary amine organic compounds
- nitriles contain the C-CN group
- primary amines contain the C-NH2 group
