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Esters

SCH4U
by

Nayera El-Sawah

on 9 April 2013

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Transcript of Esters

Constituents: Alcohol + Carboxylic Acid Properties What are esters? carboxylic acid derivatives
COOH -> H is replaced by a hydrocarbon
characterized by a carbonyl group bonded to an O atom Esters By Jiakai, Mary Lynn, Nayera & Sebastian General Formula Hydrolysis Reactions COO = ester bond O C R OR' Esterification condensation reaction
requires heat and a strong acid catalyst O C R OH R' + OH O C R OR' + OH H carboxylic acid alcohol ester water H SO 2 4 (aq) Formation of Esters: Esterification Naming Acid-Catalyzed Hydrolysis reverse of esterification
conversion of ester into parent carboxylic acid and alcohol O C R OH R' + OH O C R OR' + OH H carboxylic acid alcohol ester water H SO 2 4 (aq) Base Hydrolysis: Saponification forms important ingredient of soap
sodium salt of parent carboxylic acid O C R R' + Na OH ester sodium hydroxide O + (aq) + - (aq) O C R O - Na + (aq) R' OH + + sodium salt of acid alcohol 1 2 3 1 Where You Would Find Esters In Nature In Industry most fats are triesters
glycerol (alcohol) + 3 fatty acids (carboxylic acids)
small “simple” esters are responsible for pleasant fragrances and flavours of many flowers and fruits
pheromones and essential oils widely used in the food industry as flavourings
soaps (saponification)
anesthetics (benzocaine and procaine)
cosmetics (i.e. jojoba esters)
polyesters polymer: large molecule whose structure repeats throughout its length
can be formed by condensation reactions between dicarboxylic acids and diols
i.e. ethylene glycol
very stable and strong
does not absorb moisture
used in the manufacturing of many products
clothing
furnishings
industrial fabrics
computer and recording tapes
electrical insulation Polyesters R C O O - polar nonpolar Solubility Polarity Odour Physical State Boiling/Melting Point small esters have boiling points similar to those of aldehydes and ketones with the same number of C atoms
no H-bonds
BP and MP not as high as an acid with the same number of C atoms molecule type boiling point (°C) CH COOCH CH
(ethyl acetate) ester carboxylic acid 77.1 163.5 2 2 3 CH CH CH COOH
(butanoic acid) 2 2 3 more polar than ethers but less than alcohols
dipole-dipole interactions + van der Waals forces
hydrogen bond acceptors
not donors like their parent alcohols and carboxylic acids small esters are soluble in water
solubility decreases with increase in molecular weight of esters
soluble in organic solvents – themselves are good organic solvents All esters have a strong fruity smell ester formula solubility
(g/100g of water) ethyl methanoate ethyl ethanoate ethyl propanoate 10.5 8.7 1.7 HCOOHCH CH CH COOHCH CH CH CH COOHCH CH 2 3 3 3 2 3 2 3 2 esters of lower molecular weights are colourless volatile liquids
higher esters are colourless waxy solids Acidic Nature Esters are neutral to litmus tests 1. Locate the O bonded to 2 C atoms (has 2 single bonds). 2. Number the C atoms out from the O atom. 3. Name both sides of the esters using an Alkyl Alkane format.
alkyl group -> C atoms furthest from the carbonyl group
-> alcohol derivative
alkane -> C atoms bonded to the central C in the carbonyl
-> carboxylic acid
alkyl and the alkane are separated by a space
NOTE: esters are named in the direction opposite to the way the formula is written Side closest to central carbon in carbonyl (Alkane)Carbon Count: 3 -> ∴ Propane Side furthest from central carbon in carbonyl (Alkyl)
Carbon count: 1 -> ∴ Methyl 4. Change the name of the alkane to "alkanoate". Propane -> Propanoate ∴ methyl propanoate Special Cases of Naming ethanoate -> acetate methyl ethanoate -> methyl acetate 1-chloromethyl acetate methyl 1-chloroacetate propyl 2-methylbutanoate ethyl
2-phenylbutanoate pentyl propanoate Alternative Mechanism of Esterification can be made from reactions between alcohols and acyl chlorides
organic compound with functional group COCl R' OH O C R Cl H Cl O C R OR' + + alcohol acyl chloride ester Which ester would the following 2 reactants produce? 1-propanol 2-methyl butanoic acid + propyl 2-methylbutanoate CH CH CH COOCH CH CH CH 3 2 2 2 3 Which ester would the following 2 reactants produce? CH COOH CH CH CHCH acetic acid 2-butanol 3 3 2 3 + CH COOCHCH CH 1-methylpropyl acetate 3 3 2 Which 2 reactants would produce the following ester? Which 2 reactants would produce the following ester? CH COOCH CHCH CH CH nonyl hexanoate Interesting Fact Although esters are responsible for pleasant “fruit” tastes and odours, they are not widely used in high-quality perfumes, more often in the cheap “eau de toilettes”
Why?
1. The quality of the scents compared to higher end essential oil perfumes.
2. The hydrolytic reactivity of esters.
esters hydrolyze under basic or acidic conditions
unstable in the presence of sweat (slightly acidic)
sweat will catalyze ester hydrolysis to the corresponding carboxylic acid and alcohol.
organic acids have unpleasant smells Interesting Fact Boiling point of an ester can be used to check its purity before we use it in food flavourings.
a pure compound has a fixed boiling point at a fixed pressure
ester would have a range of boiling points if it was impure carboxylic acid alcohol methyl 3-methylpentanoate OH CH 1-nonol hexanoic acid + CH 3 3 2 2 2 2-methylpentyl acetate 3 acetic acid 2-methyl-1-pentanol CH COOH CH CHCH CH CH 3 OH CH 3 2 2 2 Legend carbon oxygen hydrogen CHL p. 66 #11,12
p. 67 # 13
p. 68 # 1,2 Interesting Fact esterification is similar to the neutralization reactions resulting in salt formation
considered "organic salts"
formerly called ethereal salts
not actually salts since they aren't ionized in solution 3 3 3
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