Alcohols

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Alcohols:

Properties of Alcohols:

- General formula of CnH(2n+1)OH

- The bond between the O-H is 109.5 (tetrahedral) due to the electron repulsion of the lone pairs on oxygen

- Hydrogen bonding forms between the -OH groups of different molecules, therefore giving alcohols high melting and boiling points compared to alkanes of a similar Mr. 

e.g: 

(http://www.chemhume.co.uk/ASCHEM/Unit%202/Ch11%20Alcohols/images/hydrogen_bonding_ethanol_water.jpg)

Ethanol production:

There are 2 main methods that are used to produce ethanol and other alcohols industrially. These are by Hydration or Fermentation. 

1. Hydration of Alkenes:

This method is used to produce PURE ethanol from alkenes (obtained from the cracking of heavy fractions of crude oil) for industrial purposes. 

Typically, ethene is hydrated into ethanol using the general formula:

(http://www.slcc-science.org/chem/giddings/chem2320/images/acid-catalyzed-hydration-of-alkenes.gif) 

whereby the conditions are as follows: 

- Alkene reacted with steam at 300 degrees celcius 

- Pressure of 60atm 

- Presence of a concentrated phosphoric acid catalyst (H3PO4) 

Hydration Mechanism: 

(INSERT MECHANISM)

- alternatively on pg. 230 of CGP textbook

This process is: 

- Non-renewable

- Fast

- Continuous 

- Produces 5% yield which allows the recycling of unreacted ethene gas to produce a 95% yield of Ethanol (PURE)

2. Fermentation of Glucose

This method is used to produce impure ethanol (up to 20%), however this can be concentrated using fractional distillation to produce alcoholic drinks, however may be used industrially in the future when there are low supplies of crude oil for hydration.

The reaction follows the equation:

(http://philschatz.com/chemistry-book/resources/CNX_Chem_20_02_ferment_img.jpg)

whereby the conditions are as follows: 

- Sealed container - Anerobic conditions (no oxygen) - As any oxygen will react with the ethanol to produce ethanoic acid (Vinegar) 

- 30-40 degrees celcius, this is when the reaction is fastest, At lower temperatures, the rate of the reaction will decrease whilst at higher temperatures the enzymes in yeast will denature. 

- Yeast catalyst 

This process is: 

- Renewable (from sugars) 

- Slow

- Batch process 

- Produces 15% ethanol as after this point the yeast dies

Inorder to increase the concentration of ethanol, fractional distillation can be used: 

(http://3.bp.blogspot.com/-3jnoTQ6hYfA/Tra_x_QgQQI/AAAAAAAAAAc/2ks_TzxH5NE/s1600/fraction.jpg)

Notes:

- The reaction mixture is filtered and then distilled to remove the plant matter etc. 

- Anti-bumping grannules may be used to prevent over boiling by equalling out the boiling. 

- Ethanol has a boiling point of 78 degrees which is lower than that of water so it moves up the collumn and distills into the beaker. 

The ethanol produced from fermentation could be considered as a bio fuel. 

Biofuels are: Renewable fuels

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