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 C n H 2n+1 COOH

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 CH 3 CH 2 CH(CH 3 )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 CH 3 CH 2 CHCHCH 2 COOH Name CH 3 CH 2 CH 2 CH 2 COO - Na + Hex-3-enoic acid Sodium pentanoate

Physical Properties BP Hydrogen Bond

Physical Properties Solubility Hydrogen Bond

Formation of the Carboxylic acids a.From Primary Alcohols (Oxidation) Addition of excess Acidified Potassium Dichromate / reflux RCH 2 OH + 2[O]  RCOOH + H 2 O 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) + H 2 O (l) RCOO - (aq) + H 3 O + (aq ) React with alkalis to form a salt and water RCOOH (aq) +NaOH (aq)  RCOO - (aq) + Na + (aq) + H 2 O (l) React with carbonates to form a salt, carbon dioxide and water RCOOH (aq) +NaHCO 3(aq)  RCOO - (aq) + Na + (aq) + H 2 O (l) + CO 2(g) React with metals to form a salt and hydrogen 2RCOOH (aq) + Mg (s)  2RCOO - (aq) + Mg +2 (aq) + H 2(g)

Organic reactions React with alcohols in the presence of conc Sulphuric acid / Reflux to form ESTERS RCOOH (l) + R ! OH (l) RCOOR ! (l) + H 2 O (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 C n H 2n+1 COOC m H 2m+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 CH 3 CH 2 CH(CH 3 )COOCH 3 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 CH 3 CH 2 CH 2 COOCH 2 CH 3 CH 3 CH 2 CH 2 CH 2 OCOCH 2 CH 2 CH 2 CH 3 CH 3 C(CH 3 ) 2 CH 2 CH 2 COOCH 2 CH 2 CH 3 Ethyl butanoate Butylpentanoate Propyl 4,4dimethyl pentanoate

Formation of esters 1.The acid catalysed condensation reaction between an alcohol and a carboxylic acid. The reaction mixture is heated under reflux ROH + R ! COOH  ROOCR + H 2 O 2.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 ! + H 2 O  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 Naming Convention = 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 fatIn Vegetable fat SOLID at RTLiquids at RT BAD FOR YOUBETTER FOR YOU FOR margarine we need to convert poly unsaturated fats to mono unsaturated fats HEAT with H 2 and Ni catalyst

Health issues Fatty acids Saturated and Unsaturated fatty acids 1.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 YOU In 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 sources Both products of the reaction are useful so atom economy is high ‘Carbon neutral’ CO 2 given out in burning equates to the CO 2 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 Formation Transesterification (Swap alcohol bits in ester)