Alcohols Alcohols formed when a hydrogen in an alkane has been replaced by –OH, hydroxyl group. General formula C n H 2n+1 OH. Physical Properties The presence of the –OH group means molecules can hydrogen bond to each other, therefore the intermolecular forces are stronger than in alkanes and as a result the mpt and bpt are higher than in the corresponding alkanes. The solubility in water of alcohols is due to the presence of the –OH group, lower members of the groups are soluble however as the molecules get larger, solubility decreases. Alcohols can be classified based on the position of the –OH group in the molecule. Reactions of alcohols 1. Oxidation Primary alcohols → aldehydes → carboxylic acids Secondary alcohol→ ketones Tertiary alcohols → resists oxidation KMnO 4 /H + or K 2 Cr 2 O 7 /H + can be used to oxidise primary and secondary alcohols. They are reducing agents and therefore give the expected
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AlcoholsAlcohols formed when a hydrogen in an alkane has been replaced by OH, hydroxyl group.General formula CnH2n+1OH.Physical Properties
The presence of the OH group means molecules can hydrogen bond to each other, therefore the intermolecular forces are stronger than in alkanes and as a result the mpt and bpt are higher than in the corresponding alkanes.The solubility in water of alcohols is due to the presence of the OH group, lower members of the groups are soluble however as the molecules get larger, solubility decreases.Alcohols can be classified based on the position of the OH group in the molecule.
Reactions of alcohols1. Oxidation
Primary alcohols aldehydes carboxylic acids Secondary alcohol ketones
Tertiary alcohols resists oxidationKMnO4/H+ or K2Cr2O7/H+ can be used to oxidise primary and secondary alcohols. They are reducing agents and therefore give the expected colour changes with these oxidizing agents. There is no colour change with tertiary alcohols.
AldehydeCarboxylic acid
XS alcoholXS oxidizing agent
Distill off aldehyde as it formsReflux to keep aldehyde in mixture
2. Esterification
Alcohol + acid ester + water
Write an equation for the formation of a) ethyl butanoate.b) propyl methanoate3. Iodoform Reaction
Used to identify alcohols with a particular structure.
When alcohols with this structure are heated with I2 in NaOH, yellow crystals of iodoform are formed.This test can therefore be used to distinguish between alcohols with this structure and those without. Circle the following alcohols which will give a positive iodoform test?
4. Reactions with metals Alcohols and reactive metals form alkoxide salts and hydrogen. Draw the structural formula below the name of the compound. 2CH3CH2OH + 2Na 2CH3CH2O-Na+ + H2
Ethanol
sodium ethoxide
2CH3CH2CH2OH + Ca (CH3CH2CH2O)2Ca2+ + H2
Propan-1-ol calcium propoxide
Complete the equation for the reaction of phenylmethanol with barium.
5. Reaction with Concentrated H2SO4This results in dehydration reactions either within the molecule (alkene formation) or between molecules (ether formation), water is a second product in both reactions.
Write a balanced equation for the following reaction.
6. Reaction with halogenating agents
-SOCl2
sulphur dichloride oxide
-PCl5
phosphorous pentachloride
These convert the alcohol to a chloroalkane. The reaction with PCl5 is violent with copious fumes of HCl(g) evolved. SOCl2 also produces white fumes of HCl(g) and also SO2. These reactions can be used to show an OH group is present in an unknown (once other groups like -COOH which give the same observation have been eliminated as possibilities).Watch PCl5 react with an alcohol and an acid https://www.youtube.com/watch?v=AryisNZQCssSee some of the above reactions in this animation http://www.youtube.com/watch?v=YI-os7Py8SMhttp://www.chemguide.co.uk/organicprops/alcoholmenu.html#top, November 22nd, 2014
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