carboxylic acids and derivatives

How do esters form?

Carboxylic acids and alcohols react in the presence of an acid catalyst (H2SO4).

Vegetable oils and animal fats are esters of …

propane-1,2,3-triol (glycerol)

Vegetable oils and animal fats can be hydrolysed in alkaline conditions to give …

Soap (long-chain carboxylic acids) and glycerol

What is biodiesel?

A mixture of methyl esters of long chain carboxylic acids.

A mixture of fatty acids made from methyl esters and can be made from rapeseed oil.

How is biodiesel produced?

By reacting vegetable oils with methanol in the presence of a catalyst.

Alkyl chlorides and acid anhydrides under what reactions?

Nucleophilic addition- elimination

Carboxylic acids are weak acids (partially dissociate) and they react with carbonates to form …

CO2 as acid + carbonate gives salt + water + carbon dioxide

Acid + base gives …

Salt + water

Carboxylic acids dissociate to form …

A H+ ions and a carboxylate ion

Carbonate

CO3 2-

Sodium hydrogen carbonate

NaHCO3

Alcohol + acid anhydride »

Ester + carboxylic acid

How? One part of the acid anhydride which is R-C=O-O with the R group form alcohol forms the ester. The acid anhydride has an R-C=O left over and that joins with the OH from alcohol to form a carboxylic acid.

Esterification ( in equilibrium)

The carboxylic acid reacts with alcohol. The R-C=O stays and from the alcohol everything else joins from the O part of the OH. Leave the H out. The H forms water with the left over OH from the carboxylic acid.

Esters can be hydrolysed. What does that mean?

Split using water.

How can an ester being hydrolysed be sped up?

Using an acid and a base … acid hydrolysis and base hydrolysis.

The addition of more water shifts the equilibrium to the right so more product can be formed.

Acid hydrolysis.

Use dilute acid to spilt an ester into a carboxylic acid and an alcohol. Example of acids: sulfuric or hydrochloric acid and the reaction is conducted under reflux.

Ester + H2O »« with H+ above line → carboxylic acid + alcohol

Base hydrolysis

Use dilute base to split an ester into a carboxylate ion and an alcohol. Base used : Sodium hydroxide a the reaction is conducted under reflux.

You have the ester + OH- »« carboxylate ions + alcohol

When we react glycerol (alcohol) and fatty acids (carboxylic acid) we produce an ester…

The ester makes fats and oils.

Glycerol (propane-1,2,3-triol) is reacted with long chain fatty acids. These long chain fatty acids can be saturated (single bonds) or unsaturated (double bonds).

Saturated fatty acid … /\/\/\/\/\/\COOH

Unsaturated fatty acid … \/\/\=/\/\COOH

And if more than 1 double bond ], they’re called polyunsaturated fatty acids.

Oil ester is formed when the alcohol is connected to the side with COOH and the /\/\=/\ after. Vegetable oil.

Fat ester has the alcohol with /\/\/\COOH. Animal fats.

Vegetable oils

They have unsaturated hydrocarbon chains that are not straight, which means the chains can’t pack together closely. Therefore, lower van der waals forces and lower melting points. Liquid at room temp.

Can have cis trans / E/Z isomerism

Animal fats

They have saturated hydrocarbon chains that are straight and more uniform than oils, which means the chain can pack together closely hence they have much higher van der waals and higher melting points. Solid at room temp.

Animal fats and vegetable oils can be hydrolysed by heating them with … the product is ….

Sodium hydroxide. SOAP!

Fat + sodium hydroxide »

Glycerol and soap (sodium salt)

How can vegetable oils be converted into biodiesel?

By reacting oils with methanol and a KOH catalyst.

3x methanol and 3 x methyl ester that forms.

One glycerol is also formed.

Acyl chlorides functional group?

-COCl

Name? Add -oyl chloride on the end like ethanol chloride

C=O -Cl

What do Acyl chlorides react with?

Water, ammonia, alcohol and primary amines.

• In each reaction, the Cl is substituted for either an oxygen or nitrogen.

• White misty fumes of HCl gas is formed.

Acyl chlorides reaction with … produces …

• Water - Carboxylic Acid

• Ammonia - Amides (ethanamide)

• Alcohol - Ester (all of alcohol is added on apart from H)

• Primary Amines - N-Substituted amides (all of primary amine is added on apart from 1x H)

Difference between amines and amides

Amides has C=O and NH2 and amines just have the NH2

What is an acid anhydride?

A molecule made from 2 carboxylic acids that are the same.

So when you name them, look at the first carboxylic acid… ethanoic acid…. But adjust the name to make it ethanoic anhydride.

Acid anhydrides reaction with … produces … and carboxylic acids

• Water - 2 x carboxylic acids (separate)

• Ammonia - amides + carb acid

• Alcohol - esters + carb acid

• Primary amines- N- substituted amides and carb acid

Nucleophilic addition - elimination

• Acyl chlorides gave a string §+ on the carbon which can be attacked from nucleophiles

• Oxygen and chlorine atoms are electronegative

• In C=O, the bond breaks … a lair of electrons from the double bond are transferred to the oxygen. Forms :O- and the electrons from that reform the double bond again.

• The alcohol has a + charge when bonded.

• The C-Cl bond then breaks … the molecule is called an intermediate

• But the lone pair on that chlorine attracts the H from the alcohol.

• The electrons in the OH bond move to the oxygen, the positive charge is neutralised.

Aspirin

• It’s an ester

• Made from reacting ethanoic anhydride/ ethanoyl chloride and salicylic.

• Salicylic acid … benzene with an OH and next to it has a COOH.

Positives of using ethanoic anhydride instead of ethanoyl chloride

Safer as it’s less corrosive. Cheaper. Safer as doesn’t produce HCl gas. Safer as it doesn’t react vigorously with water.

Reflux

A technique used when you want to heat volatile liquids.

Using a round bottom flask and a Liebig condenser.

Heating done by a water bath or electric heater (mantle).

Distillation

Separating substances with different boiling points.

Filtration

Used to separate solids from liquids.

A Buchner funnel and filter paper. Vacuum.

The vacuum creates a reduced pressure in the flask and pulls the liquid through. The solid will be left in the Buchner flask. The solid can be recrystallised to purify further.