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Unit 2.8 - Organic chemistry - alcohols and halogenoalkanes

Revision - IUPAC system for naming organic compounds
You should remember from unit 1 that there is a set of rules, set by IUPAC, for classifying and
naming organic compounds. As we will be studying further organic chemistry in this unit now is a
good time to remind yourself of those rules:


                 Number of
                                      Position of functional groups in the chain
     Prefix      Carbons in
                   chain
                                     1. The 'parent' chain is the ___________ possible chain
      meth-
                                     2. The carbon with the functional group attached is given
      eth-
                                       a ____________.
      prop-
                                     3. Numbering starts from the end of the chain that gives
                                       the carbon being considered the ____________ number.
      but-

      pent-
                                             Alkyl groups

      hex-
                                                                          methyl

      hept-
                                     1. Position in chain is               ethyl
                                       indicated by
       oct-
                                       ___________ possible               propyl
                                       number.
      dec-

                                     2. If more than 1 side chain is attached then the name
     dodec-
                                       of the compound includes the side groups in
                                       _________________ order, regardless of which
      eicos-                           carbon atom they are found on.



Try these examples:




                                                      4-methylpent-1-ene             E-hex-2-ene

1. Alcohols

Introduction
Ethanol is the compound generally referred to as alcohol and found in
alcoholic drinks. It is most commonly produced through the action of yeast
on natural sugars otherwise known as fermentation. Many other alcohols do exist; in chemistry
‘alcohol’ refers to the homologous series of molecules containing the hydroxyl (- OH) functional
group. The reactivity of alcohols is based on the hydroxyl group. They are industrially important as
raw materials in the synthesis of other compounds and as solvents.


Naming
Naming alcohols is relatively simple - the name of the alkyl group containing the ______________
number of carbons is used and the suffix ______ is added. Here are some examples:


      Name                        Displayed formula                          Skeletal formula

     Methanol



      Ethanol



    Propan-1-ol




________pentan-2-
       ol




Primary, secondary or tertiary?
There are three main types of alcohol - primary , secondary and tertiary ; they are defined by the
number of alkyl (- C) groups attached to the carbon with the hydroxyl (-OH) group:


Primary alcohols




      Ethanol
Primary alcohols have the general structure RCH2OH. There are two hydrogens and one alkyl
group attached to the same carbon as the hydroxyl group
Secondary alcohols




    Propan-2-ol
Secondary alcohols have the general structure RR1CHOH. There is one hydrogen and two
__________ groups attached to the same carbon as the hydroxyl group
Tertiary alcohols




 2-methylpropan-2-ol
Tertiary alcohols…



NB These differences in structure are very important as they affect the way that the alcohol
reacts!




Reactions of Alcohols - combustion, reduction, oxidation and substitution


a. Combustion
     Alcohols burn readily in air or even more readily in pure oxygen. Many burn with an almost
     unperceivable blue flame. Combustion of alcohols produces carbon dioxide and _________
                             CH3CH2OH(l) + ___O2(g) → ___CO2(g) + ___H2O(l)
                         CH3CH2CH2CH2OH(l) + ___O2(g) → ___CO2(g) + ___H2O(l)


b. Reaction with sodium
      •   Sodium reacts vigorously with water to produce _________________ and ____________.
          The sodium is less dense than water so it floats, fizzes and moves around. Water acts as
          an acid in this reaction by losing a proton
      •   The reaction with alcohols is _________vigorous and the sodium _________ in the ethanol
          as it is _________ dense than the alcohol
                            2Na(s) + 2CH3CH2OH(l) → 2CH3CH2O-Na+(alc) + H2(g)
                                                     sodium ethoxide
      •   The products are _________________ and ___________, the reaction is less vigorous
          because ethanol is a _____________ acid than water
c. Oxidation
      Oxidation reactions are a useful test to find out if an alcohol is primary, secondary or tertiary
      as they each give different products. Common oxidising agents such as acidified
      potassium dichromate(VI) and potassium manganate(VII) can be used…


       •   Primary alcohols - Are readily oxidised to form aldehydes, which then rapidly oxidise to
           form carboxylic acids:



                                                          + H2O


             Propan-1-ol                     Propanal                         Propanoic acid
           Primary alcohol                   Aldehyde                         Carboxylic acid*


       *The most common product of this oxidation is the carboxylic acid; however, the aldehyde can
       be separated during the reaction


       •   Secondary alcohols - Are readily oxidised to form ketones with no further oxidation
           occurring:




                         Propan-2-ol                     Propanone

                     Secondary alcohol                     Ketone



       •   Tertiary alcohols - Are not oxidised by any of the common oxidising reactions, there is
           simply no reaction



                                                 Oxidation as a test for primary, secondary or
                                                 tertiary
                                                 Add acidified potassium dichromate (VI)
                                                 Primary -
                                                 Secondary -
                                                 Tertiary -


     Chromium(III) compounds are dark green
Distillation - separating the products of oxidation
                                                       • Distillation can be used to prepare a ketone
                                                        from a secondary alcohol:
 Compound               Boiling temp (°C)
 Butanone                        80
 Butan-2-ol                      95
 Only the ketone will be collected if the
 temperature is kept between 80 °C & 94
 °C

                                                              • Or to separate the products of
                                                              oxidation of a
                                                               primary alcohol:
                                                        Compound           Boiling temp
                                                                           (°C)
                                                        Ethanol                      78
                                                        Ethanal                      21
                                                        Ethanoic acid               118
                                                        The aldehyde can be collected between
                                                        21 °C & 70 °C
Reflux - preparing carboxylic acids from primary alcohols
Heating under reflux ensures that the oxidation reaction is completed



                                         Any aldehyde or unreacted primary alcohol
                                         evaporates, condenses here in the
                                         _______________ and falls back into the
                                         reaction vessel where it can it oxidised



                                       The oxidation reaction takes place here. First the aldehyde
                                       is produced then, after further oxidation, the
                                       ________________. Heat causes the products to
                                       _____________.




d. Substitution to form halogenoalkanes
Alcohols react with phosphorous(V) chloride (PCl5) to produce a chloroalkane and hydrogen chloride
gas…
                             CH3CH2OH(l) + PCl5(s) → CH3CH2Cl(l) + HCl(g)


NB this reaction can be used as a test for alcohols - if you add PCl5 to an unknown liquid the
production of HCl gas is evidence for the presence of an -OH group.



Preparation - halogenoalkanes from alcohols
e.g. the preparation of 1-bromobutane from butan-1-ol…
Step 1 - Sodium bromide reacts with conc. sulphuric to produce hydrogen bromide
             NaBr(s) + H2SO4(l) → NaHSO4 + HBr(g)
      Step 2 - Hydrogen bromide reacts with alcohol to produce 1-bromobutane
             CH3CH2CH2CH2OH(l) + HBr(g) → CH3CH2CH2CH2Br(l) + H2O9(l)
     Step 3 - The products are distilled to yield a mixture, which separates into 2 layers -
aqueous
           and organic, a separating funnel is used to collect the organic layer
      Step 4 - The aqueous layer is discarded and the organic layer is redistilled to produce 1-
             bromobutane, which has a boiling temperature of 102 °C




2. Halogenoalkanes


Introduction
Halogenoalkanes are saturated hydrocarbons with one or several halogen functional groups. The
halogens are found in group ___ and consist of __________, ___________, __________ and
____________.


                                  Uses of halogenoalkanes                               (p214-
                                  p217)
                                  Until 1986 chlorofluorocarbons (CFCs) were routinely used as
                                  refrigerants in fridges and freezer and propellants in aerosols;
                                  however, it was discovered that they undergo radical reactions
                                  when exposed to UV radiation high in the atmosphere, which lead
                                  to the removal of ozone (O 3 ) from the ozone layer…
                                        CCl2F2 → •CClF2 + Cl•
                                        Cl• + O3 → ClO• + O2
                                        ClO• + O3 → Cl• + 2O2       Net reaction: 2O 3 → 3O 2
As the ozone layer protects us from harmful UV radiation, the international community chose to ban
the use if CFCs. Unfortunately many CFCs are very unreactive and will persist in the atmosphere for
hundreds of years.


Naming
Naming halogenoalkanes is relatively simple and follows the IUPAC convention…
      •   Prefix with fluoro, chloro, ____________ or _____________ depending on the halogen
      •   More than one halogen group can be indicated by adding di, tri or tetra
      •   Numbers are used to indicate the position of the halogen group in the chain
_________________        __________________         __________________        __________________




Primary, secondary or tertiary?
Just like alcohols, halogenoalkanes can be either primary, secondary or tertiary depending on the
number of alkyl groups attached to the carbon with the halogen group…


Primary halogenoalkanes




    Chloroethane
Primary halogenoalkanes have the general structure RCH2X. There are two hydrogens and one
alkyl group attached to the same carbon as the halogen group
Secondary halogenoalkanes




  2-chloropropane
Secondary halogenoalkanes have the general structure RR1CHX. There is one hydrogen and two
__________ groups attached to the same carbon as the halogen group
Tertiary halogenoalkanes




2-bromo-2-methylpropane
Tertiary halogenoalkanes…



Primary, secondary and tertiary halogenoalkanes react very differently. Luckily there is a test, which
can be used to identify which is present using silver nitrate solution. We will cover the test in the
reactions section under hydrolysis.




Reactions - hydrolysis, elimination and substitution
As mentioned on the previous page, the position of the halogen in the hydrocarbon chain affects
reactivity, as does the type of halogen present…
                                                         Bond              Average bond energy
                                                                                 (kJmol -1 )
  C-X bonds become ______________ down the       C-F                                467
                                                 C-Cl                               346
  group, meaning that fluorocarbons are very     C-Br                               290
  _______________ and iodocarbons are            C-I                                228
  relatively ______________
a. Hydrolysis - ‘splitting with water’
Halogenoalkanes react with water or hydroxide (OH - ) ions in a reaction known as hydrolysis. The
products are an alcohol and a hydrogen halide :          RX + H2O → ROH + HX
                                                         RX + OH- → ROH + X-
e.g.   CH3Cl + H2O → _____ + _____
       CH3CH2CH2Br + H2O → _____________ + _____


NB Reactivity depends on the H-X bond strength as shown in the table above. Fluorocarbons are the
least likely to undergo hydrolysis


Test for primary, secondary or tertiary - silver nitrate
                                                        Procedure
                                                                 •   Add 1 cm3 of silver nitrate and 1
                                                                     cm3 ethanol (__________) to each
                                                                     tube and warm
                                                                 • Add 5 drops of the different
                                                                   halogenoalkanes and observe
                                                                 Explanation
                                                                 •   Halogenoalkanes react with water
                                                                     to form an _____________ and
 1-bromobutane        2-bromobutane        2-bromo-2-
                                                                     some _____________ ions
                                           methylbutane
                                                                 •   Silver nitrate (AgNO3) reacts with
       Primary
                                                                     the halide ions to form an insoluble
                                                                     _______________
                                                                 •   Rate of reaction:
                                                                 _________ > _________ > _________
b. Reaction with potassium hydroxide
Potassium hydroxide (KOH) can react with halogenoalkanes in one of two ways depending on
whether it is dissolved in water or ethanol :


Conditions                         Type of reaction                      Product
i) Reflux heating with aqueous
                                              Substitution                            Alcohol
KOH (dissolved in _________)
ii) Reflux heating with
alcoholic KOH (dissolved in                    Elimination                            Alkene
__________)

For example:
      i) CH3CHBrCH3(l)     +       KOH(aq)     →    ____________         +   ______
      2-bromopropane           aqueous KOH
      ii) CH3CHBrCH3(l)    +       KOH(alc)    →    ____________         +   ______
        2-bromopropane         alcoholic KOH


c. Reaction with alcoholic ammonia
There is a ________ pair of electrons on the ____________ atom of
ammonia (NH3), this means it can act as a nucleophile and replace
the halogen atom in a halogenoalkane:


      i) CH3CH2I + NH3 → CH3CH2NH2 + HI
                               ethylamine


Ethylamine also has a lone pair of electrons on nitrogen so it can react further with iodoethane and
there is a chain reaction*:


      ii) CH3CH2I + CH3CH2NH2 → (CH3CH2)2NH + HI
      iii) CH3CH2I + (CH3CH2)2NH → (CH3CH2)3N +HI
      iv) CH3CH2I + (CH3CH2)3N → (CH 3 CH 2 ) 4 N + I -
                                   tetraethylammonium iodide
*Skeletal formulae for the amine products reactions i-iv respectively:
Spider diagram of A-level organic chemistry reactions


Task -     Produce your own spider diagrams to represent the reactions of alcohols and
           halogenoalkanes that we have covered. Be sure to include:
                    • Reactants
                    • Conditions
                    • Products

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Unit 2 8 Alcohols And Halogenoalkanes Notes

  • 1. Unit 2.8 - Organic chemistry - alcohols and halogenoalkanes Revision - IUPAC system for naming organic compounds You should remember from unit 1 that there is a set of rules, set by IUPAC, for classifying and naming organic compounds. As we will be studying further organic chemistry in this unit now is a good time to remind yourself of those rules: Number of Position of functional groups in the chain Prefix Carbons in chain 1. The 'parent' chain is the ___________ possible chain meth- 2. The carbon with the functional group attached is given eth- a ____________. prop- 3. Numbering starts from the end of the chain that gives the carbon being considered the ____________ number. but- pent- Alkyl groups hex- methyl hept- 1. Position in chain is ethyl indicated by oct- ___________ possible propyl number. dec- 2. If more than 1 side chain is attached then the name dodec- of the compound includes the side groups in _________________ order, regardless of which eicos- carbon atom they are found on. Try these examples: 4-methylpent-1-ene E-hex-2-ene 1. Alcohols Introduction Ethanol is the compound generally referred to as alcohol and found in alcoholic drinks. It is most commonly produced through the action of yeast
  • 2. on natural sugars otherwise known as fermentation. Many other alcohols do exist; in chemistry ‘alcohol’ refers to the homologous series of molecules containing the hydroxyl (- OH) functional group. The reactivity of alcohols is based on the hydroxyl group. They are industrially important as raw materials in the synthesis of other compounds and as solvents. Naming Naming alcohols is relatively simple - the name of the alkyl group containing the ______________ number of carbons is used and the suffix ______ is added. Here are some examples: Name Displayed formula Skeletal formula Methanol Ethanol Propan-1-ol ________pentan-2- ol Primary, secondary or tertiary? There are three main types of alcohol - primary , secondary and tertiary ; they are defined by the number of alkyl (- C) groups attached to the carbon with the hydroxyl (-OH) group: Primary alcohols Ethanol Primary alcohols have the general structure RCH2OH. There are two hydrogens and one alkyl group attached to the same carbon as the hydroxyl group
  • 3. Secondary alcohols Propan-2-ol Secondary alcohols have the general structure RR1CHOH. There is one hydrogen and two __________ groups attached to the same carbon as the hydroxyl group Tertiary alcohols 2-methylpropan-2-ol Tertiary alcohols… NB These differences in structure are very important as they affect the way that the alcohol reacts! Reactions of Alcohols - combustion, reduction, oxidation and substitution a. Combustion Alcohols burn readily in air or even more readily in pure oxygen. Many burn with an almost unperceivable blue flame. Combustion of alcohols produces carbon dioxide and _________ CH3CH2OH(l) + ___O2(g) → ___CO2(g) + ___H2O(l) CH3CH2CH2CH2OH(l) + ___O2(g) → ___CO2(g) + ___H2O(l) b. Reaction with sodium • Sodium reacts vigorously with water to produce _________________ and ____________. The sodium is less dense than water so it floats, fizzes and moves around. Water acts as an acid in this reaction by losing a proton • The reaction with alcohols is _________vigorous and the sodium _________ in the ethanol as it is _________ dense than the alcohol 2Na(s) + 2CH3CH2OH(l) → 2CH3CH2O-Na+(alc) + H2(g) sodium ethoxide • The products are _________________ and ___________, the reaction is less vigorous because ethanol is a _____________ acid than water
  • 4. c. Oxidation Oxidation reactions are a useful test to find out if an alcohol is primary, secondary or tertiary as they each give different products. Common oxidising agents such as acidified potassium dichromate(VI) and potassium manganate(VII) can be used… • Primary alcohols - Are readily oxidised to form aldehydes, which then rapidly oxidise to form carboxylic acids: + H2O Propan-1-ol Propanal Propanoic acid Primary alcohol Aldehyde Carboxylic acid* *The most common product of this oxidation is the carboxylic acid; however, the aldehyde can be separated during the reaction • Secondary alcohols - Are readily oxidised to form ketones with no further oxidation occurring: Propan-2-ol Propanone Secondary alcohol Ketone • Tertiary alcohols - Are not oxidised by any of the common oxidising reactions, there is simply no reaction Oxidation as a test for primary, secondary or tertiary Add acidified potassium dichromate (VI) Primary - Secondary - Tertiary - Chromium(III) compounds are dark green
  • 5. Distillation - separating the products of oxidation • Distillation can be used to prepare a ketone from a secondary alcohol: Compound Boiling temp (°C) Butanone 80 Butan-2-ol 95 Only the ketone will be collected if the temperature is kept between 80 °C & 94 °C • Or to separate the products of oxidation of a primary alcohol: Compound Boiling temp (°C) Ethanol 78 Ethanal 21 Ethanoic acid 118 The aldehyde can be collected between 21 °C & 70 °C Reflux - preparing carboxylic acids from primary alcohols Heating under reflux ensures that the oxidation reaction is completed Any aldehyde or unreacted primary alcohol evaporates, condenses here in the _______________ and falls back into the reaction vessel where it can it oxidised The oxidation reaction takes place here. First the aldehyde is produced then, after further oxidation, the ________________. Heat causes the products to _____________. d. Substitution to form halogenoalkanes Alcohols react with phosphorous(V) chloride (PCl5) to produce a chloroalkane and hydrogen chloride gas… CH3CH2OH(l) + PCl5(s) → CH3CH2Cl(l) + HCl(g) NB this reaction can be used as a test for alcohols - if you add PCl5 to an unknown liquid the production of HCl gas is evidence for the presence of an -OH group. Preparation - halogenoalkanes from alcohols e.g. the preparation of 1-bromobutane from butan-1-ol…
  • 6. Step 1 - Sodium bromide reacts with conc. sulphuric to produce hydrogen bromide NaBr(s) + H2SO4(l) → NaHSO4 + HBr(g) Step 2 - Hydrogen bromide reacts with alcohol to produce 1-bromobutane CH3CH2CH2CH2OH(l) + HBr(g) → CH3CH2CH2CH2Br(l) + H2O9(l) Step 3 - The products are distilled to yield a mixture, which separates into 2 layers - aqueous and organic, a separating funnel is used to collect the organic layer Step 4 - The aqueous layer is discarded and the organic layer is redistilled to produce 1- bromobutane, which has a boiling temperature of 102 °C 2. Halogenoalkanes Introduction Halogenoalkanes are saturated hydrocarbons with one or several halogen functional groups. The halogens are found in group ___ and consist of __________, ___________, __________ and ____________. Uses of halogenoalkanes (p214- p217) Until 1986 chlorofluorocarbons (CFCs) were routinely used as refrigerants in fridges and freezer and propellants in aerosols; however, it was discovered that they undergo radical reactions when exposed to UV radiation high in the atmosphere, which lead to the removal of ozone (O 3 ) from the ozone layer… CCl2F2 → •CClF2 + Cl• Cl• + O3 → ClO• + O2 ClO• + O3 → Cl• + 2O2 Net reaction: 2O 3 → 3O 2 As the ozone layer protects us from harmful UV radiation, the international community chose to ban the use if CFCs. Unfortunately many CFCs are very unreactive and will persist in the atmosphere for hundreds of years. Naming Naming halogenoalkanes is relatively simple and follows the IUPAC convention… • Prefix with fluoro, chloro, ____________ or _____________ depending on the halogen • More than one halogen group can be indicated by adding di, tri or tetra • Numbers are used to indicate the position of the halogen group in the chain
  • 7. _________________ __________________ __________________ __________________ Primary, secondary or tertiary? Just like alcohols, halogenoalkanes can be either primary, secondary or tertiary depending on the number of alkyl groups attached to the carbon with the halogen group… Primary halogenoalkanes Chloroethane Primary halogenoalkanes have the general structure RCH2X. There are two hydrogens and one alkyl group attached to the same carbon as the halogen group Secondary halogenoalkanes 2-chloropropane Secondary halogenoalkanes have the general structure RR1CHX. There is one hydrogen and two __________ groups attached to the same carbon as the halogen group Tertiary halogenoalkanes 2-bromo-2-methylpropane Tertiary halogenoalkanes… Primary, secondary and tertiary halogenoalkanes react very differently. Luckily there is a test, which
  • 8. can be used to identify which is present using silver nitrate solution. We will cover the test in the reactions section under hydrolysis. Reactions - hydrolysis, elimination and substitution As mentioned on the previous page, the position of the halogen in the hydrocarbon chain affects reactivity, as does the type of halogen present… Bond Average bond energy (kJmol -1 ) C-X bonds become ______________ down the C-F 467 C-Cl 346 group, meaning that fluorocarbons are very C-Br 290 _______________ and iodocarbons are C-I 228 relatively ______________ a. Hydrolysis - ‘splitting with water’ Halogenoalkanes react with water or hydroxide (OH - ) ions in a reaction known as hydrolysis. The products are an alcohol and a hydrogen halide : RX + H2O → ROH + HX RX + OH- → ROH + X- e.g. CH3Cl + H2O → _____ + _____ CH3CH2CH2Br + H2O → _____________ + _____ NB Reactivity depends on the H-X bond strength as shown in the table above. Fluorocarbons are the least likely to undergo hydrolysis Test for primary, secondary or tertiary - silver nitrate Procedure • Add 1 cm3 of silver nitrate and 1 cm3 ethanol (__________) to each tube and warm • Add 5 drops of the different halogenoalkanes and observe Explanation • Halogenoalkanes react with water to form an _____________ and 1-bromobutane 2-bromobutane 2-bromo-2- some _____________ ions methylbutane • Silver nitrate (AgNO3) reacts with Primary the halide ions to form an insoluble _______________ • Rate of reaction: _________ > _________ > _________
  • 9. b. Reaction with potassium hydroxide Potassium hydroxide (KOH) can react with halogenoalkanes in one of two ways depending on whether it is dissolved in water or ethanol : Conditions Type of reaction Product i) Reflux heating with aqueous Substitution Alcohol KOH (dissolved in _________) ii) Reflux heating with alcoholic KOH (dissolved in Elimination Alkene __________) For example: i) CH3CHBrCH3(l) + KOH(aq) → ____________ + ______ 2-bromopropane aqueous KOH ii) CH3CHBrCH3(l) + KOH(alc) → ____________ + ______ 2-bromopropane alcoholic KOH c. Reaction with alcoholic ammonia There is a ________ pair of electrons on the ____________ atom of ammonia (NH3), this means it can act as a nucleophile and replace the halogen atom in a halogenoalkane: i) CH3CH2I + NH3 → CH3CH2NH2 + HI ethylamine Ethylamine also has a lone pair of electrons on nitrogen so it can react further with iodoethane and there is a chain reaction*: ii) CH3CH2I + CH3CH2NH2 → (CH3CH2)2NH + HI iii) CH3CH2I + (CH3CH2)2NH → (CH3CH2)3N +HI iv) CH3CH2I + (CH3CH2)3N → (CH 3 CH 2 ) 4 N + I - tetraethylammonium iodide *Skeletal formulae for the amine products reactions i-iv respectively:
  • 10. Spider diagram of A-level organic chemistry reactions Task - Produce your own spider diagrams to represent the reactions of alcohols and halogenoalkanes that we have covered. Be sure to include: • Reactants • Conditions • Products