1 Chapter 14 Carboxylic Acids, Esters, Amines, and Amides 14.1 Carboxylic Acids.
Carboxylic acids and esters Describe carboxylic acids as proton donors. Describe the reactions of...
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Transcript of Carboxylic acids and esters Describe carboxylic acids as proton donors. Describe the reactions of...
Carboxylic acids and esters
• Describe carboxylic acids as proton donors.
• Describe the reactions of carboxylic acids, typified by ethanoic acid:
a. with aqueous alkalis to form carboxylates (salts)b. with alcohols, in the presence of an acid catalyst, to
form esters
Candidates should be able to:
Structure of the Carboxylic acids
• Oxygen more electronegative than C and H
• Electrons in C=O and O-H bonds closer to the Oxygen
• The COH bond is easily broken to give C-O- and H+
General Formula CnH2n+1COOH
Naming carboxylic acids
1. COOH group is always Carbon 1
2. Give position and name any branches
3. Name number of carbons including COOH
4. Either
a. give position of C=C followed by en or
b. an
5. Functional group ending = oic acid
6. For SALTS Functional group ending = oate
Name CH3CH2CH(CH3)COOH
Position of branch = 2, type of branch = METHYL
Longest chain (including COOH carbon) = BUT
No C=C hence AN
Functional group ending = OIC ACID
Name = 2-METHYLBUTANOIC ACID
Name CH3CH2CHCHCH2COOH
Name CH3CH2CH2CH2COO- Na+
Hex-3-enoic acid
Sodium pentanoate
Formation of the Carboxylic acidsa. From Primary Alcohols (Oxidation)Addition of excess Acidified Potassium Dichromate / reflux RCH2OH + 2[O] RCOOH + H2O
b. From Aldehydes (Oxidation)Addition of excess Acidified Potassium Dichromate / reflux Addition of ammonical silver nitrate (Tollins) / warm
RCHO + [O] RCOOH
Carboxylic acids as acids
• Partially dissociate in water (Are weak acids)
RCOOH(aq)+ H2O(l) RCOO-(aq) + H3O+
(aq)
• React with alkalis to form a salt and water
RCOOH(aq)+NaOH(aq) RCOO-(aq)+ Na+
(aq)+ H2O(l)
• React with carbonates to form a salt, carbon dioxide and water
RCOOH(aq)+NaHCO3(aq) RCOO-(aq)+ Na+
(aq)+ H2O(l) + CO2(g)
• React with metals to form a salt and hydrogen
2RCOOH(aq)+ Mg(s) 2RCOO-(aq)+ Mg+2
(aq)+ H2(g)
Organic reactions
• React with alcohols in the presence of conc Sulphuric acid / Reflux to form ESTERS
RCOOH(l)+ R!OH (l) RCOOR!(l) + H2O
(l)
Carboxylic acids and esters
describe esterification of carboxylic acids with alcohols, in the presence of an acid catalyst
describe the hydrolysis of esters:(i) in hot aqueous acid to form carboxylic acids and alcohols,(ii) in hot aqueous alkali to form carboxylate salts and alcohols;
state the uses of esters in perfumes and flavourings;
describe a triglyceride as a triester of glycerol (propane-1,2,3-triol) and fatty acids;
compare the structures of saturated fats, unsaturated fats and fatty acids, including cis and trans isomers, from systematic names and shorthand formulae;
compare the link between trans fatty acids, the possible increase in ‘bad’ cholesterol and the resultant increased risk of coronary heart disease and strokes;
describe and explain the increased use of esters of fatty acids as biodiesel.
Candidates can
Naming esters
1. Carbon chain bonded to O is named as a branch
2. Carbon chain including C=O is named as a salt of a carboxylic acid (with C=O carbon 1)
3. Ester is named as branch salt name
Name CH3CH2CH(CH3)COOCH3
Chain beyond O is METHYL
In carbons beyond C=O
Position of branch = 2, type of branch = METHYL
Longest chain (including COOH carbon) = BUT
No C=C hence AN
Functional group ending = OATE
Name = METHYL 2-METHYLBUTANOATE
Name
CH3CH2CH2COOCH2CH3
CH3CH2CH2CH2OCOCH2CH2CH2CH3
CH3C(CH3)2CH2CH2COOCH2CH2CH3
Ethyl butanoate
Butylpentanoate
Propyl 4,4dimethyl pentanoate
Formation of esters1. The acid catalysed condensation reaction between an alcohol and a
carboxylic acid. The reaction mixture is heated under reflux
ROH + R!COOH ROOCR + H2O2. The reaction between an acid anhydride and an alcohol. The
reaction occurs readily at RT.
ROH + R!COOCOR ROOCR + RCOOH
Uses of the esters
• Flavourings
Most of low Bp so evaporate readily
Most have a sweet aroma
• Fragrances / perfumes
Most of low Bp so evaporate readily
Most have a sweet aroma
Chemical reactions• Can be hydrolysed to the corresponding alcohol / carboxylic
acid. Reflux the ester with 2M HCl. The alcohol can be removed by distillation.
RCOOR! + H2O RCOOH + R!OH
• Can be hydrolysed to the corresponding alcohol / carboxylate anion
Reflux the ester with 2M NaOH. The alcohol can be removed by distillation.
RCOOR! + NaOH RCOO- Na+ + R!OH
• The carboxylic acid can be formed by acidifying the carboxylate anion
RCOO- Na+ + HCl RCOOH + NaCl
Triglycerides• Glycerol and Fatty (long chain) acid
• Found in nature as Oils/fats (eg Olive oil)• Saturated and Unsaturated Fats (oils)
• NOTE Three different acids can bond to the glycerol
Fatty Acids• Saturated
• Unsaturated
• Cis/Trans unsaturated fatty acids
• NamingConvention = X:Y(a,b,c....) X= No of C, Y = No of C=C, a,b,c.... = position of C=C
Eg = 10,2 (3,5)
Fatty Acids
In Animal fat In Vegetable fat
SOLID at RT Liquids at RT
BAD FOR YOU BETTER FOR YOU
FOR margarine we need to convert poly unsaturated fats to mono unsaturated fats
HEAT with H2 and Ni catalyst
Health issues Fatty acids
Saturated and Unsaturated fatty acids1.Cis unsaturated fats help to lower levels of total cholesterol and LDL proteins in the blood They increase HDL particles which are able to remove cholesterol from the arteries and transport it back to the liver for excretion 2.Trans unsaturated or saturated fats increase levels of LDL proteins which leads to cholesterol build up in blood vessels which lead to blockage
NOTE TRANS UNSATURATED FATS ARE BAD FOR YOUIn converting poly unsaturated fats to mono unsaturated fats the C=C are often converted from cis trans
Biodiesel
• Fuels from triglycerides found in plants
Renewable energy sourcesBoth products of the reaction are useful so atom economy is high
‘Carbon neutral’ CO2 given out in burning equates to the CO2 taken in by the original plant
Fields are being converted into Biodiesel fields
rather than crop fields
Click here to see how Biodiesel is made