(9) Derivatives of COOH Flashcards
What are the two derivatives of carboxylic acids?
Esters and acyl chlorides
What is an ester and how is it formed?
(COO-)formed from condensation reaction between carboxylic acid and alcohol
R - C = O
l
O - C - R
What are acyl chlorides and now are they formed?
(-COCI )formed when carboxylic acid reacts with PCI5. OH in COOH replaced with CI
Describe observations when COOH reacts w/ PCI.5
- Heat released
- white solid appears
-Misty fumes ( HCI )
How do you name an ester
-Part from carboxylic acid; no. of carbons-oate
- Part from alcohol; no. of carbons-yl
Alcohol first then carboxylic acid
How to name acyl chlorides
written no. of carbons-oyl chloride
smells of esters
neutral liquids; pleasant, fruity odour
esters solubility in water
- very small esters are soluble in water as C=O is polar so can form H-bonds with water
- larger chain esters solubility decreases as C=O looses influence
what type of intermolecular bonds do esters have
permanent dipole-dipole attractions and van der Waals
why are the bpt of esters lower than acids
cannot form H-bonds
bpt trend in esters as chain increases
-inc. no. of electrons
-greater van der Waals
-more emergy required to break forces between molecules
-bpt inc.
two ways esters can be formed
- alcohol and a carboxylic acid
- alcohol and acyl chloride
describe reaction between alcohol and carboxylic acid to form an ester
-H from OH alcohol and OH from COOH forms water
-remainder of alcohol and carboxylic acid form ester
state how an ester is collected during preparation
-reaction mixture heated gently in distillation
-larger esters reflux required
why is conc sulfuric acid added to alcohol and carboxylic acid reaction mixture to form ester
it acts as a catalyst and dehydrating agent (removes water therefore equilibrium favouors RHS
describe reaction between alcohol and an acyl chloride to form an ester
-H form OH alcohol and Cl form COCl forms water
-remainder of alcohol and acyl chloride form ester
why does the reaction of acyl chloride and alcohol produce a higher yield of ester without need for conc acid or heating?
-it is a complete reaction (not in equilibrium)
disadvantage of forming ester with alcohol and acyl chloride
- misty acidic fumes of HCl
- must be under anhydrous conditions
why must you open tap form time to time while shaking reaction mixture with sodium carbonate solution
to release pressure
how to tell which layer is aqueous layer in separating funnel when forming an ester
add water and whichever layer increases in volume is aqueous
why is mixture shaken with sodium carbonate solution when preparing an ester
to remove acidic impurities, neutralises conc sulfuric acid catalyst
what is the use of anti bumping granules
to promote smooth boiling
why is anhydrous calcium chloride added when preparing an ester
drying agent, to remove water impurities from ester
what are lipids
naturally occurring esters of carboxylic acid
use of lipids
source of energy in animal diets and play vital roles in cell membranes and nervous system
lipids solubility
soluble in organic solvents but insoluble in water (means dont interfere with reactions in cytoplasm of cell)
main group of lipids
fats and oils
how to distinguish between fat and oil physically
fats = solids
oils = liquid
how are fats and oils formed
the reaction between propane-1,2,3-triol with long chain carbojxylic acids
common fatty acids
- stearic acid (C.17H.35COOH) — octadecanoic acid
- oleic acid (C.17H.33COOH) — (9Z)-octadec-9-enoic acid
how do fatty acids vary
-length of carbon chain
-saturated or unsaturated
difference between saturated and unsaturated fatty acids
s = each carbon is C-C
u = one or more C=C
propane-1,2,3-triol + one/two/three fatty acids →
fat/oil + mono-/di-/triester
(most fats are triesters/triglycerides)
fatty acid forumla
O
ll
C—R
l
OH
what are fatty acids called when they contain just one C=C/two or more C=C
one C=C → mono unsaturated
Two or more C=C → polyunsaturated
Describe the mpt of fats with mainly saturated fatty acids
- more effective van der waals between fat molecules → greater energy required to break forces
- Higher mpt→ likely to be solid at room temp.
Describe mpt of a fat with a large proportion of unsaturation
- Weaker vdW between fat molecules→less energy needed to break forces
- lower melting point → liquid at room temp.
What is transesterification
The process of swapping an alkyl group in an ester for a different alkyl group,
Changes intermolecular forces between the molecules
What can a transesterification reaction between fats/oils and methanol be use for?
To produce biodiesel or margarine
What is a biodiesel?
A renewable fuel made from veg oils such as rapeseed, palm and soybean oils.
Can be used in normal diesel engines to power cars and buses
What can occur after transesterification?
-Hydrogenation → Transesterification in this case
Changes carboxylate groups within same fat molecule ( intramolecular exchange) or between fat molecules ( intermolecular exchange
Conditions needed for transesterification to occur?
At 400k in presence of an alkali (usually NaOH), glycerol and a catalyst
How can unsaturated oil be hardened?
Hydrogenating it in presence of finely divided nickel at 180°
What does hydrogenation do?
Results in an increase of vdw between molecules which raises mpt of liquid oil making it a solid fat
why would we not want to remove all C=C in unsaturated fats
there are possible health benefits
describe the effects on health by eating saturated fats
- provides energy and insulation
-can raise levels of cholesterol in blood which can lead to coronary heart disease or stroke
describe the effect on eating polyunsaturated fats
- can have a beneficial effect on heart when eaten in moderation or to replace saturated or trans fats
- reduces bad cholesterol levels and increases HDL levels which reduces coronary heart disease
large esters in fats/oils + conc NaOH solution
—> glycerol and sodium salt* of fatty acid
*sodium salts are important ingredients in soap (why alkaline hydrolysis of fats is called saponification)
acyl chlorides + water
(describe observations and type of reaction as well)
carboxylic acid + hydrogen chloride gas
(fizzing, misty fumes of HCl)
(hydrolysis reaction)
