Organic - 3.5 Alcohols Flashcards
What are the physical properties of alcohol?
1) Greater boiling point than alkanes with similar Mr due to presence of hydrogen bonding between alcohol molecules.
2) VDW forces and hydrogen bonding present between alcohol molecules.
What are the three classifications of alcohols?
Primary (1R Group)
Secondary (2 R Groups)
Tertiary (3 R Groups)
This depends on the position of the -OH group in the carbon chain
Where is the R group located in a primary alcohol?
The -OH group is positioned at the end of the chain
Where is the R group located in a secondary alcohol?
The -OH group is positioned along the length of the chain.
Where is the R group located in a tertiary alcohol?
The -OH group is positioned at a branch in the chain.
What are primary alcohols oxidised to?
Aldehydes then carboxylic acids
What are secondary alcohols oxidised to?
Ketones and then do not undergo further oxidation
Why are tertiary alcohols not easily oxidised?
They do not have two hydrogen atoms directly attached to the carbon that is bonded to the -O-H group.
They can be oxidised using hot concentrated nitric acid because the breaking of the strong C-C bond is required.
What are the conditions for oxidising a primary alcohol?
1) Oxidising agent in excess (acidified potassium or sodium dichromate)
2) Refluxed gently
3) Carboxylic acid can be removed from the mixture in the reaction vessel by distillation.
4) To produce the aldehyde, the primary alcohol must be in excess and the product distilled off immediately. This is to ensure the oxidation is only partial and the carboxylic acid is not formed.
What are the conditions for oxidising a secondary alcohol?
Must be Refluxed gently with an excess of the oxidising agent (acidified potassium or sodium dichromate) to produce a ketone.
What are the tests for aldehydes and ketones?
The silver mirror test (Tollens reagent). When tollens reagent is warmed gently in the presence of an aldehyde the aldehyde is oxidised to a carboxylic acid and the silver ions in the tollens reagent are reduced to silver atoms. Ketones will not react with tollens reagent and the mixture remains colourless and the silver mirror does not form.
Fehling’s solution is also used as it is a mild oxidising agent, when warmed gently with an aldehyde, the blue colour gradually disappears and an orange-red precipitate of copper oxide forms. The solution remains blue when warmed with a ketone.
What is the test for aldehydes and ketones?
When warmed gently with an aldehyde fehlings solution blue colour disappears and an orange red precipitate forms. When reacting with a ketone, the solution remains blue
In what type of reaction is water removed from an alcohol?
In an elimination reaction where a molecule of water is eliminated from an alcohol to produce an alkene. (can also be called a dehydration reaction as water is removed)
How is alcohol produced by fermentation?
Fermentation occurs when yeast and bacteria convert sugars to alcohols, acids and various gases such as carbon dioxide and methane. By fermentation, yeast converts sugars such as glucose to ethanol and carbon dioxide.
What are the conditions for the production of alcohol by fermentation?
1) In the presence of yeast (yeast provides the enzymes which convert sugars into methanol).
2) In the absence of air (anaerobic conditions).
3) AT temperatures of 35 degrees.
4) In a neutral aqueous solution
What are the conditions for the production of alcohol by the hydration of ethene?
1) Catalyst of concentrated phosphoric acid absorbed on a solid silica surface.
2) 60 atm pressure.
3) 600K temperature.
4) Excess ethane to give a high yield.
