carboxylic acids and esters describe carboxylic acids as proton donors. describe the reactions of...

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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:

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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

Physical Properties

• BP

Hydrogen Bond

Physical Properties

• Solubility

Hydrogen Bond

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

Structure of the Esters

General Formula CnH2n+1COOCmH2m+1

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

Biodiesel FormationTransesterification

(Swap alcohol bits in ester)