Properties of Alcohols
They all contain an O-H functional group, and this allows hydrogen bonds between molecules.
Volatility and boiling point
The hydrigen bond are very strong intermolecular forces, and result in alcohols have much higher boiling points, and much lower volatility.
The polarity of the O-H bond means that alcohols are soluble as they form hydrogen bonds with water molecules.
Solubility decreases and chain length increases. This is because hydrocarbon chains are non polar, and do not form hydrogen bonds,
Classification of alcohols
Just one carbon chain (alkyl group) attached to the carbon the OH is bonded too e.g. butan-1-ol
Two alkyls groups attached to the carbon OH is bonded too e.g. propan-2-ol
Three alkyl groups e/g. 2-methylbutan-2-ol
Oxidation of alcohols
Only primary and secondary alcohols can be oxidised. This usally uses potassium dichromate as an oxidising agent.
Primary alcohols can be oxidised, firstly, to aldehydes.
CH3CH2CHOH + (O) > CH3CH2CH=O + H20
They must be distilled out of the colution, to avoud further oxidation.
Carboxylic acids are made by reflux of primary alcohols (aldehydes.)
CH3CH2CHOH +2(O) > CH3CH2COOH +H20
Secondary alcohols are oxidised to make ketones.
CH3CH(OH)CH3 +(O) > CH3C=OCH2CH3 +H20
Tertairy alcohols are resistant to oxidation.
Esterification and dehydration of alcohols
Esterification is when a alcohol becomes an ester.
You need to combine an alcohol witha carboxylic acid and a sulphuric acid catalyst.
The OH of the carboxylic group, and the H of the hydroxyl grouo of the alcohol combine to make water, leaving an oxygen link e.g. an ester.
Esters are used as adhesives and solvents. They are also used as falvours and fragrances.
Orange smell= octyl ethanoate.
Banana smell = pentyl ethanoate.
HOW TO DO IT
- add 1cm3 of COOH acid and 1cm3 of alcohol.
- add a few drops of acid.
- place in a water bath at 80 degrees celcius.
- pour into beacker of cold water.
- floating oil is the ester.
An example of a elimination reaction. It uses concentrated phosphoric or sulphuric acid.
The alcohol is heated for around 40 minutes under reflux.
It can also work with cyclic alcohols.
Reactivity results from the difference in electronegativity between carbon and halogens.
The halogens are more electronegative, and pull electron pair towards them, and results in a polar bond.
The electron-deficient carbon atom attracts nucleophiles such as H2O, NH3 and OH-.
Halogenoalkanes react in substitution reactions, in which the nucleophile replaces the halogen.
reactions of halogenoalkanes: Alkanes
Alkanes- radical substitution
Initiation: Cl2>> 2Cl*
Propagation:1)Cl* + CH4 >>>> CH3* + HCl
2) CH3* + Cl2>>> CH3Cl + Cl*
Termination: 1) Cl*+ Cl* >> Cl2 2) Cl* + CH3* >> CH3Cl 3) CH3* + CH3>> C2H6
C2H4 + Cl2 >>> C2H4Cl2
The double bond in an alkene is an area of electron density, and repels electrons in the chlorine molecule. A dipole is created and the molecule splits by heterolytic fission. The double bond breaks creating a halogenoalkane cation. The chloride ion, with two electrons, quickly attaches to the cation.
C2H5Cl + NaOH >>> C2H5OH + NaCl
The carbon-chloride bond is polar, with the carbon positive. This attracts the OH- ions, and the carbon-chloride bond breaks heterolytically (electrons from the bond going to the chlorine atom.)