Organic chem - alcohols Flashcards
Explain why pentan-2-ol has a higher boiling point than pent-1-ene
-pentan-2-ol has hydrogen bonding whereas pent-1-ene only has van der waals
-Hydrogen bonding is stronger than Van der waals
-this means that it requires more energy to overcome
explain why propanone has a lower boiling point than propan-2-ol
-propanone has permanent dipole and van der waal intermoleculer forces of attraction whereas propan-2-ol has all 3 including hydrogen bonding so requires a lot of energy….
state the two reagents required to oxidise ethanol
sulfuric acid and acidified potassium dichromate (VI)
state the formula of the reacting anion and cation
Cr2O72-
H+
propan-1-ol can be oxidised. Which compound cannot be produced by the oxidation of this alcohol
CH3COCCH3
which compound produces (CH3)2CHCOCH3 when oxidised
3-methylbutan-2-ol
Ethanedioic acid is formed by the oxidation of ethane-1,2-diol (HOCH2CH2OH) .
State a suitable reagent and condition
reagent = acidified potassium dichromate (IV)
condition = reflux
which is the correct equation for the oxidation of 1-pehnylethanol
C6H5CH(OH)CH3 + [O] –> C6H5COCH3 + H2O
Suggest what would happen if the thermometer was too high
-boiling point recorded will be inaccurate - if the temp is high it does not read the temp of gaseous vapour
explain why the water should enter the condenser at the bottom and not the top
-ensures condensor is fully filled w water so organic product is fully condensed
explain 3 problems in the apparatus above
-no anti-bumping granules to create smaller bubbles
-open system w no thermometer to prevent gases escaping + allow connection of alcohol
-movement of water should be reversed to ensure complete condensation
alcohols
-alcohols are a homologous series of organic compounds with the general formula CnH2n+1OH and names ending in –ol
-The functional group of alcohols is the hydroxyl group (OH)
intermolecular forces present in alcohols
Intermolecular forces present in alcohols
-permanent dipole-permanent dipole (C-O)
-van der waals (present in all molecules)
-hydrogen bonding (O-H)
boiling point of alcohols
-alcohols have higher overall boiling point due to their hydrogen bonding which is the strongest intermolecular force so therefore requires more energy to overcome
aldehydes, ketones and carboxylic acids
Aldehyde = CHO = name ends in al
Ketone = COC = name ends in one
Carboxylic acid = COOH = name ends in oic acid
solubility
-ketones are soluble in water because they can form hydrogen bonds with molecules of water
-However, ketones are unable to form hydrogen bonds between eachother because they don’t have a delta positive hydrogen
combustion of alcohols
-alcohols burn in a plentiful supply of air with a clean (No soot) pale blue flame
-Methanol and Ethanol are both common fuels
e.g complete combustion of propanol –> C3H8O + 9/2O2 –> 3CO2 + 4H2O
primary, tertiary, secondary
-Alcohols can be described as primary, secondary or tertiary
Primary = only 1 R (alkyl group) attached
Secondary = 2 R groups attached
Tertiary = three R groups attached
e.g Secondary if 2 alkyl groups attached to the central carbon atom
potassium dichromate
Alcohols can be classified as primary, secondary or tertiary and can react with potassium dichromate (VI) (K2Cr2O7) in different ways dependent on the type of alcohol
-All three types of alcohol can be reacted with oxidising agents to produce different products
products of primary, secondary and tertiary alcohols reacting with acidified potassium dichromate (oxidised)
Primary alcohols –> aldehyde –> carboxylic acid
Secondary alcohols –> ketone
Tertiary alcohols –> cannot be oxidised so no reaction
oxidising equations
RCH2OH + [O] –> RCHO + H2O (alcohol –> aldehyde + water)
RCHO + [O] –> RCOOH (aldehyde –> carboxylic acid)
= RCH2OH + 2[O] –> RCOOH + H2O
distinguishing between types of alcohol
-Acidified potassium dichromate is orange in its usual conditions but will undergo a colour change when it is reduced
-orange –> green (Cr2O7^2- –> Cr3+)
-Cr2O72- + 14H+ + 6e- –> 2Cr3+ + 7H2O
-during the oxidation of a primary and secondary alcohol K2Cr2O7 will change from orange to green
-there is no colour change for a tertiary alcohol as it cannot be oxidised
oxidation of a primary alcohol
-distillation is used when making aldehydes to allow the aldehyde to be collected preventing further oxidation
-when being distilled to an aldehyde excess alcohol is added to prevent further oxidation
disitllation apparatus
-When distilling an alcohol the equipment must be set up carefully
Thermometer cannot be too high (must be at intersection by condenser)
Bung must be sealed around thermometer to prevent gas escaping
Water must go into the bottom and out the top of the cooling jacket
Product cannot be sealed as this could cause an explosion
anti bumping granules
-antibumping granules or small pieces of porcelain are added to prevent violent uncontrolled boiling
-Adding sulfuric acid slowly to the reacting mixture will also help prevent uncontrolled boiling bc reaction is exothermic
identify reagent P (distillation exam question)
H2SO4 (sulfuric acid)
state the chemical change that causes the solution in the flask to appear green at the end of the reaction
dichromate is reduced from Cr2O7^2- to Cr3+
give one reason why using a water bath is better than direct heating with a bunsen burner
alcohol is flammable or allows temperature to be controlled
state the purpose of the condenser
condenses volatile reactants so they are not lost / has complete oxidation
what is the purpose of adding anhydrous solid calcium chloride
-acts as a drying agent to remove excess water
Complete when turns clear from cloudy
oxidation of primary alcohols
-in order to oxidise the aldehyde further into a carboxylic acid, the primary alcohol is heated further and a reflux condenser is used
why is the condenser needed when the alcohol is heated under reflux
the chemicals (alcohol and ketone) are so volatile so would escape. Vapours condense to liquid and drip back down so ensures complete oxidation
drying agents
-drying agents can be used to remove excess water to purify the impure product
Examples of drying agents:
-anhydrous magnesium sulfate
-anhydrous sodium sulfate
-anhydrous calcium chloride
Method –> add drying agent to mixture, leave then filter
Observation –> cloudy to clear
dehydration of alcohol
-alcohols react with acids to undergo a dehydration reaction. The mechanism is elimination (alcohol –> alkene)
1) lone pair on OH –> H+ ion
2) CH2 bond to OH+2
3) H to CH2+
4) alkene double bond
which alcohol when dehydrated forms a mixture of alkenes
pentan-2-ol
which compound produces (CH3)2CHCOCH3 when oxidsied
3-methylbutan-2-ol
which pair of reagents does not produce ethanol
CH3COOCH3 and NaOH
which compound can be dehydrated to form an alkene
CH3CH2OH (alcohol)
give a reason why CO2 absorbs infrared radiation
C=O bonds vibrate at the same frequency as infrared radiation
Pent-1-ene is formed by the elimination of water from pentan-2-ol
state the reagent and condition for this reaction
reagent = concentrated sulfuric acid
condition = hot
ehtanedoic acid is formed by the oxidation of ethane-1,2-diol
state a suitable reagent and condition
acidified potassium dichromate (VI)
reflux
identify a suitable catalyst for the conversion of ethanol into ethene
concentrated phosphoric acid
state the class of alcohols which ethanol belongs to
primary
nucleophilles (negative)
-all nucleophilles have a lone pair of electrons which is attracted to an electron deficient carbon atom
-donates lone pair of electrons to form covalent bond
haloalkanes
-covalent bond between carbon and halogen atom is a polar bond due to difference in electronegativity
-polarity determines how haloalkanes react (they react with nucelophilles)
conditions for hydrolysis of haloalkanes
-ethanol solvent
-heat under reflux
formula for acidified potassium dichromate
K2Cr2O7
aqueous hydroxide ions
nucelophillic subsitution
reflux
Reflux: continuous boiling and condensing of a reaction mixture.
The production of a carboxylic acid from a primary alcohol using acidified potassium dichromate. The production of an ester from an alcohol and acid in the presence of an acid catalyst.
bond angles in alcohol
All the H-C-H bonds and C- C-O are 109.5o
(tetrahedral
shape), because there are 4
bonding pairs of electrons
repelling to a position of
minimum repulsion.
The H-O- C bond is 104.5o
(bent line
shape), because there are 2 bonding
pairs of electrons and 2 lone pairs
repelling to a position of minimum
repulsion. Lone pairs repel more than
bonding pairs so the bond angle is
reduced.
key points from specification
-alcohols are produced industrially by hydration of alkenes in the presence of an acid catalyst
-ethanol is produced industrially by fermentation of glucose and is then used a biofuel through fractional distillation
formula for phosphoric acid
H3PO4
name the mechanism for the reaction of concentrated sulfuric acid with propene to show the formation of the major product
electrophillic addition
how to turn alkenes into alcohols
1) fractional distillation of crude oil
2) cracking of alkanes to make ethene
3) hydration reaction (alkene + water + phosphoric acid catalyst –> alcohol)
state the conditions for direct hydration reaction
state 2 advantages and 2 disadvantages of fermenation compared to hydration method
-high temperature and phosophoric acid catalyst required
Advantages –> renewable resources, fewer steps
Disdvantages –> slower and lower atom economy
“the fact that bioethanol is carbon-neutral outweighs the environmental disadvantages of producing bioethanol”
Evaluate
-photosynthesis –> 6CO2 + 6H2O –> C6H12O6 + 6O2
-bioethanol produced via fermentation –> C6H12O6 –> 2C2H5OH + 2CO2
-combustion of ethanol –> 2C2H5OH + 6O2 –> 4CO2 + 6H2O
-CO2 released in cutting of trees
-loss of biodiversity
-CO2 released in transportation
alcohol –> alkene (dehydration)
ELIMINATION
Reagents: Concentrated sulfuric or phosphoric acids
Conditions: warm (under reflux)
Role of reagent: dehydrating agent/catalyst
Type of reaction: acid catalysed elimination
conditions for fermentation
The conditions needed are: *Yeast *No air *temperatures 30 –40oC
define biofuel
a fuel produced by plants
alcohol production
-Ethanol is manufactured by reacting ethene with steam (H2O (g))
-The catalyst used for this reaction is solid silicon dioxide coated with phosphoric acid
g Ethene + steam –> ethanol
steps for alkenes –> alcohols
(hydration reaction)
1) dipole is formed in the OH bond of the acid as it nears the alkene
2) A lone pair is donated from the double bond to hydrogen of the acid
3) The OH bond is broken in the acid and a carbocation is formed in the alkene
4) The lone pair on the O of the acid attacks the carbocation
5) The intermediate product is formed based on the stability of the carbocation
dehydration of alcohols to form alkenes
-there are 2 reactions which can lead to the dehydration of an alcohol
1) Passing the reactant over aluminum oxide (Al2O3) –> alcohol –> alkene + water
2) Heating it will an excess of concentrated acid catalyst (H2SO4) –> oxidation/elimination of alcohol
production of alcohols (2)
-fermentation
-alcohol has been produced by fermentation of sugars for thousands of years
-sugar from fruit or grains such as wheat are mixed with yeast and water which produces ethanol and other compounds
–the product is a mixture of water and 15% ethanol by volume
-No more alcohol can be produced bc the yeast is denatured by the alcohol
equation for fermentation
Glucose –> ethanol + carbon dioxide
C6H12O6 –> 2C2H5OH + 2CO2
hydration of alkanes
-Raw material –> crude oil
-Steps to turn into alcohol –> fractional distillation –> cracking to make ethene –> hydration reaction
-Fast rate of reaction
-continious process
-300 degrees, 60-70atm, phosphoric acid catalyst
-95% purity
-Advantages –> efficient, fast, high purity, 100% atom economy
-Disadvantages –>*high technology equipment needed (expensive initial costs) *ethene is non-renewable resource (will become more expensive when raw materials run out) *high energy costs for pumping to produce high pressures
Fermentation conditions
-Raw material –> plant materials (sugars)
-Steps to turn into alcohol –> break down complex sugars –> fermentation
-slow rate of reaction
-batch process
-low temperature (35 degrees), 100kpa
-15% purity
-Advantages –> fewer steps, renewable resouces, less energy required so cheaper
-Disadvantages –> *batch process which is slow and gives high production costs *ethanol made is not pure and needs purifying by fractional distillation *depletes land used for growing food crops
state the purpose of the small glass beads
prevent bumping
state a simple chemical test that distinguishes propan-1ol from propanoic acid
sodium carbonate
propanoic acid = effervescence
propan-1-ol = no reaction
describe a test tube reaction on the product to show that cyclohexanol has been dehydrated (alcohol –> alkene)
bromine water
colour change from orange to colourless
give a property of anhydrous calcium chloride other than its ability as a drying agent
doesnt dissolve in cyclohexene
ethanoic acid
CH3COOH
bond angle of alcohol
109.5 but varies
are alcohols soluble in water
alcohols are soluble in water as oxygen can form hydrogen bonds
-but longer chain alcohols = less soluble
2 ways of ethanol production
fractional distillation -> cracking -> hydration
photosynthesis –> fermentation –> distillation
explain one disadvanatage for carrying out fermentation at higher temperatures
more energy required
