Chapter 14 - Alcohols Flashcards
the OH group?
the hydroxyl group, is responsible for both the physical and chemical properties of alcohols
methanol uses?
- high performance fuel bc of its efficient combustion
- an important chemical feedstock - the starting material in many industrial syntheses
ethanol uses?
primarily in alcoholic drinks and as a fuel, solvent, and a feedstock
when there are two OH groups?
- suffix is -diol
- -diol does not start with a vowel so the alkane chain name is not shortened e.g. not butan instead of butane
alcohols vs alkanes physical properties?
- when alcohols and alkanes of the same number of C atoms are compared,
- alcohols are less volatile, have higher melting points, greater water solubility than the corresponding alkane
- the differences become much smaller as the C chain length inc
bonds in alkanes vs bonds in alcohols?
- alkanes have non polar bonds as C&H have similar electroneg, so molecules = non polar
- sp induced dipole forces, weak
- alcohols have polar O-H bond, so mols r polar
- Hydrogen bonds, much stronger
influence of OH group?
as the hydrocarbon chain length inc, the influence of the OH group becomes relatively smaller, solubility decreases
e.g.s of primary alcohols?
methanol and ethanol
what is a primary alcohol?
the OH group is attached to a C that is attached to 1 alkyl group
when alcohols are oxidised, why is there a colour change from orange to green?
-the orange solution containing dichromate (VI) ions is reduced to a green solution containing chromium (III) ions :
C2O7 2- -> Cr3+
when preparing carboxylic acids (full ox)?
excess acidified potassium dichromate is used which ensures that all of the alcohol is oxidised
when preparing an aldehyde ? is used, but when preparing a carboxylic acid ? is used
- aldehyde: use distillation to remove the aldehyde from the reaction mixture
- carboxylic acid: reflux
what colour change will happen when acidified potassium dichromate is added to a tertiaty alcohol?
stays orange
are alcohols saturated or unsaturated?
sat (single bonds only)
general formula?
CnH2n+1OH
Properties of alcohols?
- gradation in physical properties - BP ⬆ w C chain length
- have similar chemical properties
Classed as ?
Primary, Secondary, tertiary
Trend in BP?
- As chain length ⬆, the molecules get longer, there are more SA contact points, so stronger induced dipole forces, so stronger + more induced dipole forces means more energy required to overcome & BP ⬆
SOLUBILITY?
- Soluble in polar solvents - ‘LIKE DISSOLVES LIKE’
- The OH gr is polar, H2O mols r polar
- alcs can form H bonds w H2O mols
vs. alkanes?
- higher BP than alkanes - alchols can form H bonds, e.g. propanol has higher BP than propane
- Less Volatile - As BP are ⬆ than alkanes, less volatile
what does volatile mean?
the tendency of a substance to evaporate
?
thru Ox, alcohols lose atoms of H - lost from OH and the H opposite the OH
why can tertiary alc not be ox?
OH present, but no H bonded to the C that’s bonded to the OH
Alcohols can b combusted as ?
a fuel source
what happens in dehydration of an alcohol?
- an elimination reaction
- H2O lost
- alkene forms bc a π bond forms between the adjacent C atoms
2 ways to make ethanol?
- Industrial production
- fermentation
Industrial production?
= hydration of ethene
Reagents/ Conditions: Ethene is passed over a phosphoric acid catalyst along w steam at 330 degrees C (has to be over 100) + under high pressure
hydration of ethene to form ethanol equation?
ethene + water -> (phosphoric acid catalyst on arrow) ethanol
- C2H4(g) + H2O (g) -> C2H5OH(l)
+s of industrial production of ethanol?
+ the hydration of ethene is a much faster reaction producing a high conc of ethanol
+ continous process
+ unreacted ethene and H2O recycled
+ 100% atom economy
+ High % conversion to C2H5Oh >95%, catalyst reusable
-s of industrial production of ethanol?
- requires conditions that take a lot of energy to sustain
- uses a non renewable starting materual - oil
fermentation?
Reagents/ Conditions: yeast, air kept out of fermentation vessels to prevent Ox of the ethanol to ethanoic acid - anaerobic
- temp carefully controlled, too low = slow R, too high = yeast enzymes won’t work effectively - 35 degrees used
fermentation equation?
- anaerobic respiration
- C6H12O6 -> (yeast on arrow) 2C2H5OH(aq) +2CO2(g
+s of fermentation?
+ uses renewable starting materials
+ low energy costs
-s of fermenatation?
- batch process, labour intensive, produces a low conc impure sol o ethanol
- alc needs separating
- 15% alcohol (yeast denatures)
what is the filtrate?
the liquid that passes thru the filter paper
what is the residue?
the bit left over in the filter paper
what are antibumping granules?
little pieces of an unreactive material that allow the mixture to boil evenly
distillation flask can be either?
round or peark shaped
what does the adaptor do?
‘T shaped’ - connects distillation flask to condensor
what does the test tube do?
collect distillate
why can you collect the ethanol when the distillation flask is heated to 80 degrees?
- the ethanol will evaporate
- as the H bonda and induced dipole forces between the ethanol molecules are weaker than the H bonds between H2O molecules
- so the bonds between ethanol molecules break at a lower temp as less energy required
what is the distillate?
the liquid that collects
making ethanol by fermentation what is the residue, filtrate/
residue = yeast - too large to pass thru filter paper filtrate = ethanol + H2O + dissolved glucose
what happens when you ignite the distillate/
burns with an almost invisible blue flame suggesting its ethanol as H2O and glucose are NOT flammable, must be ethanol if it burns
what can distillation be used to do?
seperate the most volatile liquids from a mixture
what does volatile mean?
a substance w a low BP that easily changes to a gas
in a distillation flask where does the water go and out and where does it come in?
water out at top, in at bottom
why must the water go in at the bottom of the flask and come out at the top?
so the outer wall of the condenser can completely fill w water so the vapours can condense
if fermentation was carried out under reflux (upwards appartus instead of reflux) what would happen?
- the mixture would boil but no seperation of the alcohol would take place. No liquids would evaportae -> when the liquids evaporate , the vapours move up into the condenser and change back into iquids which drip down into the flask
what does heating under reflux allow?
liquids to be heated for a long period of tim w/o any loss due to evap
why are many organic chemicals heated under reflux?
- organic chemicals are all volatile
- w/o refluxing, they would evaporate when we heated them to react
Hydrogen bond definition?
the strongest type of IMF. A permanent dipole force forms between delta + H on one molecule and the lone pair of e-s on the delta - O or delta - N or delta - F of a neighbouring molecule
distillation flask definition?
a round or pear shaped glass container that contains the mixture of chemicals
filtrate definition?
the liquid that passes thru the filter paper, it contains dissolved chemicals
anti-bumping granules definition?
an unevenly shaped piece of solif added to make liquids boil more calmly
Distillate definition?
the liquid that has been condensed from a vapour and collected
IMF definition?
a weak force of attraction between molecules
distillation definition?
heating a liquid to evaporate it, then cooling the vapour in a condenser & collecting it - a sep tech.
reflux definition?
continual boiling and condensing of liquids to ensure the reaction takes place w/o loss of the liquids due to evaporation
volatile definition?
a liquid w a low BP that readily changes into a gas
compare and explain the solubility of pentan-1-ol and methanol in H2O?
- both soluble as both form H bonds to H2O
- the short C chain in Methanol will not prevent methanol molecules from bonding to H2O molecules so methanol will be soluble in H2O
- the non polar C chain in Pentanol will bond to other C5H11 chains by induced dipole forces. The Pentanol molecules will stay bonded to each other and not mix w H2O
reactions: combustion?
- alcohols burn releasing energy
- Reagent: O2
- e.g. C2H5OH (l) + 3O2(g) -> 2CO2(g) + 3H2O(l)
- this reaction is exothermic, releasing a large quan. of energy in the form of heat
- as the no. of C atoms in the chain ⬆, the quan of heat released per mole also ⬆
- plentiful supply of O2 needed
reactions: reaction w Na forming H2(g) and a salt e.g. sodium ethoxide (this is the chemical test for an alcohol)
ethanol + sodium -> sodium ethoxide + hydrogen
R: Na (s)
Equation for propanol: CH3CH2CH2OH(l) + Na(s) -> CH3CH2CH2ONa(aq) + 1/2 H2(g)
-> sodium propoxide is formed (an ionic salt)
the slow release of H2 is used as a test for OH
reactions: dehydration of an alcohol to form an alkene?
- isomers possible
- conditions: acid catalyst (conc H2SO4or H3PO4), heat under reflux
- reagent: none
- cycloalkenes can also be formed from the dehydration of cycloalcohols
- H2O AND ALKENE FORMED
distillation vs reflux position?
condenser in the vertical position is known as the reflux position and when condenser is sideways = distillation position
reactions: substitution of the OH group for a halogen, forming a haloalkane?
- the alc is heated under reflux w H2SO4 & a Na or K halide. These reagents form the H halide.
- OH group is swapped for a halogen
- R: NaBr + H2SO4
c: Under reflux
reactions: substitution of the OH group for a halogen, forming a haloalkane - equations?
NaBr(s) + H2SO4(aq) -> NaHSO4 (aq) + HBr(aq)
HBr + CH3CH2CH2OH -> CH3CH2CH2CH2Br +H2O- the H halide reacts w the alc
the OH group should have its own what in a skeletal formula?
LINE, can’t just write it on the last C
reactions: substitution of the OH group for a halogen, forming a haloalkane -overall equation?
CH3CH2CH2CH2OH + NaBr + H2SO4 -> CH3CH2CH3CH2Br + H2O + NaHSO4
when can dehydration give 2 possible products?
when there is 2 ways of removing a molecule of water - where the molecule is removed bond determines the position of the C=C
What are the reagents and conditions used for Ox of alcs?
- acidified Potassium or Sodium Dichromate (H2SO4 & K2CR2O7) which changes colour from orange -> green during reaction +Ox agent [O], conditions vary depending on class
Ox of a primary alc?
- can be either mild or full
- mild under distillation & forms an aldehyde - al ending
- full under reflux and forms carboxylic acid - oic acid
- water is always formed - mild Ox needs 1[O] and full needs 2[O]
aldehyde FG?
CHO
CA FG?
COOH
Ox of a 2ndry alc?
- under reflux
- ketone formed - none ending
What is the difference between ketone and aldehyde?
Aldehyde C=O is on the end of the mol and is bonded to a H, Ketone is not bonded to a H and is the middle
Ox rememver?
2 H’s have to be lost from same C + react w {O} to form the water
