Why does fruit smell so good? Esters Why does fruit smell so good?

Esters in fruits Smell Reactants needed Ester Banana or pear Propan-1-ol + ethanoic acid Pineapple 1-pentanol + ethanoic acid Peach Phenylmethanol + ethanoic acid Rasberry 2-methylpropan-1-ol + methanoic acid Apple Pentyl pentanoate Orange Octyl ethanoate Fruits contain mixtures of esters that give a distinct smell that is unique to the fruit.

Where does the bridging oxygen come from? How can isotopic labelling of oxygen be used to check? The bridging oxygen comes from the alcohol

Properties of esters Predict Boiling and melting point Solubility in water Smell Volatility VdW bonding and dipole-dipole interactions mean they have low mpts. and bpts. There is no hydrogen bonding, therefore they are insoluble in water and other polar solvents (non-polar) Distinct feature - they smell pleasant They are volatile compounds.

How doe we get naturally occurring esters? + Type of reaction? + 3 H2O Type of reaction? Water is leaving so it is condensation. Type of compound?

What else are esters used for? Key question What else are esters used for?

Reactions of esters CH3COOCH2CH3 + H2O CH3COOCH2CH3 + NaOH CH2OOCR1 CHOOCR2 + CH3OH CH2OOCR3 Predict the products. Suggest a name for the reaction. Explain the chemistry!

Reactions of esters CH3COOCH2CH3 + H2O Esters can be split up using boiling water But even more effectively with the use of an acid Therefore, this reaction is called acid hydrolysis Predict the products. Suggest a name for the reaction. Explain the chemistry!

Reactions of esters CH3COOCH2CH3 + NaOH Esters can also be split up using boiling KOH (aq) This is even more efficient. Suggest why. Therefore, this reaction is called base hydrolysis Predict the products. Suggest a name for the reaction. Explain the chemistry!

SAPONIFICATION Why fats and ash??

Soya bean & corn oil Olive oil Animal fats Fatty acids form esters that are found in fats and oils. These are common fatty acids. Oleic acid – Olive oil Stearic acid – Animal fat Linoleic acid – Soya bean and corn oil Animal fats

A2427 26/05/2018 Saturated fat

Monounsaturated fat

Polyunsaturated fat

Hydrolysis of esters When an ester is heated with an alkali, it is hydrolysed to.....? CH3CH2COOCH2CH3 + NaOH

Soap! Glycerol Hydrolysis of esters + 3 KOH When an ester is boiled with an alkali.....? Hydrolysis – because reverse of condensation as glycerol is formed. Also, OH is added. Name of soap molecule / salt of COOH acid: potassium octadecanaoic acid + Soap! propane-1,2,3-triol Glycerol

The reaction propane-1,2,3-triol sodium octadecanoate Glycerol – used in cosmetics, in food and glue, also used in wine adding sweetness and viscosity! Glycerol also has many uses. With its three O-H bonds, it can form hydrogen bonds easily and therefore attracts water

Reactions of esters CH2OOCR1 CH3OOCR1 CH2OH CHOOCR2 + 3 CH3OH CH3OOCR2 + CHOH CH2OOCR3 CH3OOCR3 CH2OH This reaction is called transesterification. It produces bio-diesel! Consider, the advantages. Predict the products. Suggest a name for the reaction. Explain the chemistry!

Biodiesel formation catalysed by: react with: by-product: %yield: Conditions: Source: main product:

Biodiesel formation catalysed by: NaOH Methyl esters of long-chain fatty acids (triglycerides react with: Alcohol by-product: Glycerol reversible %yield: 98% Conditions: Low temp. (50◦C) & pressure Source: Vegetable oils: soya bean and rapeseed oils. Also, waste vegetable oils and discarded animal fats main product: New ester - biodiesel

Why bio-diesel? Mixed with ____________ (___% biodiesel and ____% petrodiesel, which can be used in __________ ________ N____________ B_____________ C________ burning than petrodiesel G__________ is a useful chemical Saves ___________ ______ R_____________ sources

Why bio-diesel? Mixed with petro-diesel (20% biodiesel and 80% petro-diesel, which can be used in diesel engines Non-toxic Biodegradable Cleaner burning than petro-diesel Glycerol is a useful chemical Saves crude oil Renewable sources

How could polyethylene terephthalate (PET) polymer be made? Polyesters How could polyethylene terephthalate (PET) polymer be made?

strong acid or specific enzyme 26/05/2018 Polyesters diacid diol diacid diol strong acid or specific enzyme - H2O

strong acid or specific enzyme 26/05/2018 Polyesters strong acid or specific enzyme

Use of polyesters

HW 1. Read up on and summarise HSW Soaps and detergents (including cleaning action of soap) HSW Biodiesel HSW Margarine and low-fat spreads HSW – Polyesters everyday and biological esters 2. Test corrections