Acyl Compounds

EXERCISE 9

Acyl Compounds, Soaps and Detergents EXERCISE 9Acyl Compounds

carboxylic acidacid halideesteracid anhydrideamideNucleophilic Acyl Substitutionnucleophilic addition to the carbonyl group is less likely in acyl compounds than in aldehydes and ketones. The characteristic reaction of acyl compounds is nucleophilic acyl substitutionreaction begin with the addition of a nucleophile to a polar C=O bond to give a tetrahedral intermediate. The intermediate formed from a carboxylic acid derivative expels a leaving group to give a new carbonyl compound

Nucleophilic Acyl Substitution---SIMPLIFIED VIEWaddition ofnucleophileelimination ofleaving groupmost arent this simple, protontransfers are usually requiredcarbonyl groupforms again4Solubility of Carboxylic AcidsSampleH2O10% NaOH10% NaHCO3acetic acid+benzoic acid-++sodium benzoate+phenol-+_Solubility of Carboxylic Acidsacetic acidfully miscible with watercapable of hydrogen bondingacetic acid dissociates in waterCH3COOH(aq) + H2O(l) CH3COO-(aq) + H3O+(aq)

Solubility of Carboxylic Acidsbenzoic acidsolubility in water at 25 C: 3.4 g/Lhas large hydrophobic aromatic ring that limits solubility in water

Solubility of Carboxylic Acidssodium benzoatesoluble in water because of ion-dipole interaction

Acidity of carboxylic acids and phenols

benzoic acidpKa = 4.19carbonic acidpKa = 6.00phenolpKa = 9.89Increasing acidity: lower pKa value, more acidicAcidity of carboxylic acids and phenolscarboxylic acids react with NaOH and NaHCO3 to give sodium carboxylate

carboxylic acids dissociate to give carboxylate ion in which the negative charge is delocalized over two equivalent oxygen atoms

Acidity of carboxylic acids and phenolsanything that stabilizes the conjugate base of an acid will necessarily make that acid stronger and shift the equilibrium to the right. Both the carboxyl group and the carboxylate anion are stabilized by resonance, but the stabilization of the carboxylate is greater compared to the carboxylic acidcarboxylate ion is therefore stabilized by resonance

Hydrolysis of Acyl CompoundsSampleWithout heatingWith heatingLitmus testacetyl chloride+acidicacetic anhydride+acidicethyl benzoate-+neutralbenzamide-+neutralHydrolysis of Acyl Compounds

H2OCl-

H2OHydrolysis of Acyl Compounds

H2O

H2ONH2-Hydrolysis of Acyl Compounds

Hydrolysis of Acyl CompoundsReactivity trendsLeaving group abilityweak bases are better leaving groups than strong bases reactivity of acyl compounds towards nucleophiles decreases as the basicity of the leaving group increasesHydrolysis of Acyl CompoundsSampleConjugate Base/ Leaving GrouppKaCl--74.7615.9

Hydrolysis of Acyl CompoundsSampleConjugate Base/ Leaving GrouppKaNH2-

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chloride and carboxylate are good leaving groups because they are weak bases and they are stable in solution alkoxides and amide are poor leaving groups since they are strong bases heating the mixture gives a drastic condition which forces the reaction to proceedHydrolysis of Acyl CompoundsResonancewhen a nucleophile attacks a acyl compound and a tetrahedral intermediate is formed, the energetically favorable resonance effect is lost, making it least reactive towards nucleophilic acyl substitutionSoaps and DetergentsTriacylglycerols / triglycerides esters of long-chain carboxylic acids and glycerolscarboxylic acids attached to glycerol may be identical or differentundergo same reactions as low molecular mass esters Soaps and DetergentsSaponificationfrom Latin sapo meaning soaphydrolysis of an ester such as triglycerides when the reaction is carried out under alkaline conditions, producing a mixture of soaps and glycerolssoaps salt from the acid-base reaction between an ester and a strong base such as NaOH and KOHSoaps and Detergents

Saponification reactiontriglyceridesodium salts of fatty acids or soapsglycerol22SOAP MAKING

Saponification is the process of making soap from fat. The chemical reaction for this is shown in the slide. 3 C19H37O2 + 3 NaOH -----> 3 C18H35O21- Na1+ + C3H8O3 glyceryl tristearate (fat) sodium hydroxide sodium stearate (soap) glycerin

Read Chem Matters Soap Making

Soaps and Detergents

triglyceride of lauric acidsodium laureateglycerolSoaps and DetergentsDetergentscleaning agents characterized by the presence of the sulfate groupcomes from a strong acid (sulfonic acid) and a strong basesame amphiphatic structure as soap

Soaps and Detergents

H2SO4lauryl alcohol

NaOHlauryl hydrogen sulfate

Comparison of Soaps and DetergentsSoap DetergentHydrolysisRed to blueNeutralReaction with acidFormation of precipitateClear solutionReaction with soft waterClear solutionClear solutionReaction with hard waterFormation of precipitateClear solutionEmulsifying action++Comparison of Soaps and DetergentsHydrolysissoaps undergo a hydrolysis reaction in water. As a result, soap solutions tend to be alkaline. detergent solutions are neutralComparison of Soaps and DetergentsHydrolysis

H2OOH-soap

H2O+ OH-detergentComparison of Soaps and DetergentsReaction with an acidsoaps are water soluble, but the fatty acids themselves are not. A soap can be converted into the fatty acid by means of a reaction with a strong acid.acidification of detergents produces acids which are often water soluble29Comparison of Soaps and DetergentsReaction with acid

H+

H+soapdetergentwater -solublewater - insolubleComparison of Soaps and DetergentsReaction with hard watersodium ion in soap is replaced by either magnesium or calcium ions to form insoluble precipitates (scum)detergents form water-soluble salts with calcium and magnesium ionsComparison of Soaps and DetergentsReaction with hard waterSoap

Ca2+Ca2+2Mg2+Mg2+2calcium and magnesium carborxylates are water insolubleComparison of Soaps and DetergentsReaction with hard waterDetergentCa2+Ca2+2Mg2+Mg2+2

Comparison of Soaps and DetergentsEmulsifying actionsoaps and detergents form micelles in waterthe nonpolar region of the soap/detergent interacts with the grease film while the polar region interacts with water molecules, forming a emulsion

Emulsifying/cleaning action of SoapWhen a dirty cloth is put is put in water containing soap than the hydrocarbon ends of the soap molecule in the micelle attach to the oil or grease particles present on the surface of dirty cloth. In this way the soap micelles entraps the oily particles by using the hydrocarbon ends. The ionic ends of the soap molecules remain attached to the water when the dirty cloth is agitated in soap solution. The oily particles presents on its surface gets dispersed in the water due to which the cloth gets clean.