Alcohols, Carboxylic acids and Esters

Alcohols, Carboxylic acids and EstersAlcoholsWhat Are Alcohols?

Alcohols are organic chemical compounds which form a homologous series. They are compounds in which one or more hydrogen atoms in an alkane (saturated hydrocarbon) are replaced by hydroxyl (OH) groups.

The hydroxyl group (OH) is the part of the molecule that is responsible for the characteristic reactions and chemical properties of the alcohol. This is otherwise known as the 'functional group'

EthanolEthanol is an alcohol, which as we know, is a member of the homologous series.

Ethanol can be represented in a number of different forms: C2H5OH CH3CH2OH

Facts about Ethanol!Ethanol can:Dissolve in water to form a neutral solution.React with sodium to from hydrogen.Burn in air.Be used as fuels and solvents, and is the main alcohol in alcoholic drinks!Ethanol can be oxidised to ethanoic acid (by chemical oxidising agents or microbial action).

So what does Ethanol look like?The molecular structure of ethanol looks like this:

The OH part of Ethanol is sometimes referred to as the functional group!MethanolMethanol is another alcohol, which as we know, is also a member of the homologous series. Methanol can be represented as a formula:CH3OH

MethanolThe molecular structure of methanol look like this:

The OH part of methanol is sometimes referred to as the functional group!Facts about MethanolMethanol can:Dissolve in water to form a neutral solution.React with sodium to from hydrogen.Burn in air.Be used as fuels and solvents, and is the main alcohol in alcoholic drinks!

The Manufacture of EthanolCan you recall the properties and uses of ethanol?Properties: volatile liquid (evaporates quickly at room temperature, colourless, burns readily in air with a blue flame, good solvent

Uses: biofuels, solvents, feedstock for synthesis, cleaner etc

How do we make ethanol?Think about home brewing/winemaking? What process do we use?Fermentation is a key process for obtaining ethanol. It is relatively cheap and requires wheat or beet sugar.The process involves the anaerobic respiration of yeast at temperatures between 20 and 40C and at pH 7.

Conditions for fermentationWhy is temperature important?Outside an optimum temperature the yeast does not work (high temperatures kill the yeast).Why do you think pH is important?Outside an optimum pH the yeast does not work (extremes of pH kill the yeast).Why do you think it is important to shut out oxygen?To make ethanol the yeast must respire anaerobically (without oxygen).What effect will increasing ethanol concentration have on the yeast?Eventually the ethanol concentration will be too high for the fermentation to continue. This means only a dilute solution can be made.

How do we obtain a concentrated solution?Ethanol has a different boiling point to water. We can therefore separate water and ethanol using distillation.

Other methods of obtaining ethanolFor homework research the different methods of obtaining ethanol including fermentation. You might also come across a method using algae!

Produce a minimum of 1 page in your class book or e-mail a word processed sheet.

Plenary Balancing chemical equations Glucose (a simple sugar) is created in the plant by photosynthesis.Can you balance the following equation for photosynthesis?

__CO2 + ___ H2O C6H12O6 + __ O2

6 CO2 + 6 H2O C6H12O6 + 6 O2

Plenary part 2During ethanol fermentation, glucose is decomposed into ethanol and carbon dioxide.

Can you balance this equation?C6H12O6 __ CH3CH2OH+ __CO2

C6H12O6 2 CH3CH2OH+ 2 CO2

Plenary part 3During combustion ethanol reacts with oxygen to produce carbon dioxide, water, and heat:

Can you balance this equation?CH3CH2OH + __ O2 __ CO2 + __ H2O

CH3CH2OH + 3 O2 2 CO2 + 3 H2O

Carboxylic acidA carboxylic acid is an organic acid that contains one or more carboxyl groups. They usually have higher boiling points than water and are usually quite weak acids. These longer chain acids tend to be rather soluble in less-polar solvents such as ethers and alcohols.

Ethanoic AcidEthanoic acid can be found in your kitchen, any ideas? Yes, its vinegar! Ethanoic acid is one of the simplest carboxylic acids.

The COOH part of ethanoic acid is sometimes referred to as the functional group!Facts about Carboxylic acidsCarboxylic acids:Dissolve in water to produce acidic solutions.React with carbonates to produce carbon dioxide.React with alcohols in the presence of an acid catalyst to produce esters. Do not ionise completely when dissolved in water and so are weak acids.Aqueous solutions of weak acids have a higher pH value than aqueous solutions of stronger acids with the same concentration.

EstersEsters are chemical compounds made by condensing acids with alcohols. Esters with low molecular weight are commonly used as fragrances and found in essential oils and pheromones.

Making an EsterEthyl ethanoate is synthesized in industry mainly via the classic Fischer esterification reaction of ethanol and acetic acid. This mixture converts to the ester in about 65% yield at room temperature: CH3CH2OH + CH3COOH CH3COOCH2CH3 + H2O

The reaction can be accelerated by acid catalysis and the equilibrium can be shifted to the right by removal of water. It is also prepared in industry using the Tishchenko reaction, by combining two equivalents of acetaldehyde in the presence of an alkoxide catalyst: 2 CH3CHO CH3COOCH2CH3

What do esters look like?-Ethyl ethanoate-Ethyl ethanoate is the organic compound with the formula CH3COOCH2CH3. This colourless liquid has a characteristic sweet smell and is used in glues, nail polish removers, decaffeinating tea and coffee, and cigarettes.

The COO part of ethyl ethanoate is sometimes referred to as the functional group!