4.2 Module 2: Polymers and Synthesis

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1 4.2 Module 2: Polymers ad Sythesis Amio Acids ad hirality Geeral structure of a α amio acid 2 2 The group ca be a variety of differet thigs depedig o what amio acid it is. The alpha i α amio acid meas both 2 ad groups are joied to the same. Zwitterios The o charge form of a amio acid ever occurs. The amio acid exists as a dipolar zwitterio. Amio acids are ofte solids The simplest amio acid is glycie, where the is a amig amio acids 2 You do ot eed to kow ay commo ames for the 20 2 essetial amio acids. We 2 2 should, however, be able to 2-amiobutaedioic acid ame give amio acids usig IUPA orgaic amig (2-)amioethaoic acid amio-3- hydroxypropaoic acid 3 The ioic iteractio betwee zwitterios explais the relatively high meltig poits of amio acids as opposed to the weaker hydroge bodig that would occur i the o charge form. A amio acid exists as a zwitterio at a p value called the isoelectric poit 2 - Zwitterio Some amio acids have a extra carboxylic acid or a amie group o the group. These are classed as acidic or basic (respectively) amio acids Aspartic acid ( 2 ) 4 2 Lycie (basic) 2 2,6-diamiohexaoic acid If the side group of a amio acid cotais a acidic of basic group the p value of the isoelectric poit will be differet A amie group o the group may make the isoelectric poit be p > 10 A carboxylic acid group o the group may make the isoelectric poit be p < 3 Acidity ad Basicity The amie group is basic ad the carboxylic acid group is acidic Species i Species i alkalie solutio eutral solutio igh p 3 2 Species i acidic solutio Low p Amio acids act as weak buffers ad will oly gradually chage p if small amouts of acid or alkali are added to the amio acids l l a a 2 The extra carboxylic acid or amie groups o the group will also react ad chage form i alkalie ad acid coditios Aspartic acid i high p Goalby chemrevise.org 1

2 Proteis Proteis are polymers made from combiatios of amio acids. The amio acids are liked by peptide liks, which are the amide fuctioal group. Dipeptides Dipeptides are simple combiatio molecules of two amio acids with oe amide (peptide) lik For ay two differet amio acids there are two possible combiatios of the amio acids i the dipeptide. S alaie leucie cysteie-methioie Give the ames of the amio acids be able to ame to a protei as doe above S a make or Importace of hydroge bodig i proteis The 3D arragemet of amio acids with the polypeptide chai i a corkscrew shape is held i place by ydroge bods betwee the of δ- δ group ad the of δ = δ- δ- : δ δ- δ δ- : δ- δ ydrolysis of di-peptides/proteis If proteis are heated with dilute acid or alkali they ca be hydrolysed ad split back i to their costituet amio acids ther reactios of amio acids 3 3 The compositio of the protei molecule may the be deduced by usig paper chromatography The carboxylic acid group ad amie group i amio acids ca udergo the usual reactios of these fuctioal groups met i earlier topics. Sometimes questios refer to these. e.g. Esterificatio reactio Goalby chemrevise.org 2

3 ptical Isomerism ptical isomerism occurs i carbo compouds with 4 differet groups of atoms attached to a carbo (called a asymmetric carbo). These four groups are arraged tetrahedrally aroud the carbo. A carbo atom that has four differet groups attached is called a chiral (asymmetric) carbo atom This causes two differet isomers that are ot superimposable to be formed. They are mirror images May aturally occurrig molecules cotai chiral atoms, but are usually foud i ature as a pure eatiomer ptical Activity All amio acids, except glycie, are chiral because there are four differet groups aroud the Two compouds that are optical isomers of each other are called eatiomers. ptical isomers have similar physical ad chemical properties, but they rotate plae polarised light i differet directios. e eatiomer rotates it i oe directio ad the other eatiomer rotates it by the same amout i the opposite directio. Differet systems of omeclature are is existece for optical isomers. D/L or /- are commoly used, but both have bee superseded by the more useful ad iformative /S system (this is ot o the syllabus for iformatio oly). e optical isomer will rotate light clockwise ()(called dextrorotatory). The other will rotate it aticlockwise(- )(called laevorotatory). ptical isomerism ad EIZ isomerism are differet types of stereoisomerism, which is defied as the same structural formula but a differet spatial arragemet of atoms -ve eatiomer Aticlockwise rotatio ve eatiomer clockwise rotatio Goalby chemrevise.org 3

4 4.2.2 Polyesters ad Polyamides There are two types of polymerisatio: additio ad codesatio Additio Polymerisatio A additio polymer forms whe usaturated moomers react to form a polymer Moomers cotai = bods Poly(alkees) are chemically iert due to the strog - ad - bods ad o-polar ature of the bods ad therefore are o-biodegradable. hai forms whe same basic uit is repeated over ad over. You should be able to draw the polymer repeatig uit for ay alkee It is best to first draw out e.g. For but-2-ee the moomer with groups 3 of atoms arraged aroud 3 3 the double bod odesatio Polymerisatio The two most commo types of codesatio polymers are polyesters ad polyamides which ivolve the formatio of a ester likage or a amide likage. I codesatio polymerisatio there are two differet moomers that add together ad a small molecule is usually give off as a side-product e.g. 2 or l. The moomers usually have the same fuctioal group o both eds of the molecule e.g. di-amie, di carboxylic acid, diol, diacyl chloride. Formig polyesters ad polyamide uses these reactios we met earlier i the course arboxylic Acid Alcohol Ester water Acyl chloride Alcohol Ester l arboxylic Acid Amie amide water Acyl chloride Amie amide l If we have the same fuctioal group o each ed of molecule we ca make polymers so we have the aalogous equatios: dicarboxylic acid diol poly(ester) water diacyl dichloride diol poly(ester) l dicarboxylic acid diamie poly(amide) water diacyl dichloride diamie poly(amide) l Usig the carboxylic acid to make the ester or amide would eed a acid catalyst ad would oly give a equilibrium mixture. The more reactive acyl chloride goes to completio ad does ot eed a catalyst but does produce hazardous l fumes. Terylee- a commo polyester Bezee-1,4-dicarboxylic acid 2 2 Ethae-1,2-diol Terylee fabric is used i clothig, tire cords The -1 here is because at each ed of the chai the ad are still preset ( 2 ) 3 l l Petaedioyl dichloride Bezee-1,4-diol ( 2 ) l Goalby chemrevise.org 4

5 ylo 6,6 - a commo polyamide ( ( 2 ) 4 2 ) 6 hexaedioic acid exae-1,6-diamie ( 2 ) 4 ( 2 ) 6 The 6,6 stads for 6 carbos i each of the moomers. Differet legth carbo chais produce differet polyamides Kevlar- a commo polyamide ote o classificatio for codesatio polymers If asked for type of polymer: It is polyamide or polyester Whereas type of polymerisatio is codesatio It is also possible for polyamides ad polyesters to form from oe moomer, if that moomer cotais both the fuctioal groups eeded to react hydroxypropaoic acid lactic acid 3 3 repeatig uits 3 3 repeatig uits poly(lactic acid) 3 hemical reactivity of codesatio polymers polyesters ad polyamides ca be broke dow by hydrolysis ad are, therefore, biodegradable The reactivity ca be explaied by the presece of polar bods which ca attract attackig species such as ucleophiles ad acids Polyesters ca be hydrolysed by acid ad alkali With l a polyester will be hydrolysed ad split up i to the origial dicarboxylic acid ad diol With a a polyester will be hydrolysed ad split up ito the diol ad dicarboxylic acid salt. Polyamides ca be hydrolysed by aqueous acids or alkalis. With l a polyamide will be hydrolysed ad split up i to the origial dicarboxylic acid ad diamie salt With a a polyamide will be hydrolysed ad split up ito the diamie ad dicarboxylic acid salt odesatio polymers may be photodegradable as the = bod absorbs radiatio. Goalby chemrevise.org 5

6 4.2.3 Sythesis poly(alkee) dihalogeoalkae K aqueous heat uder reflux u Sub diol high pressure catalyst alcohol alkee coc. 2 S 4 or coc. 3 P 4 Elimiatio, dehydratio Br 2, l 2 room temp EAdd K aqueous heat uder reflux usub Br, lroom temp EAdd alkae Br 2, l 2 UV light Fr Sub halogeoalkae ab 4 ed u Add If primary a 2 r 2 7 / heat ad distill partial ox aldehyde If secodary a 2 r 2 7 / heat oxidatio ketoe ab 4 ed u Add aboxylicacid 2 S 4 heat esterificatio Alcoholic 3 heat uder pressure usub 1 o amie (If primary) a 2 r 2 7 / heat uder reflux excess oxidisig aget xidatio Esters ad amides ca be hydrolysed by a ad acids carboxylic acid Alcohol 2 S 4 heat esterificatio ester Alcohol esterificatio Acid ahydride Goalby chemrevise.org 6

7 Aromatic sythetic routes 2 Electrophilic substitutio Br 2 coc itric acid coc sulphuric acid Electrophilic substitutio S ad l reductio 2 a 2 l <10 o catalyst FeBr 3 Br a Testig for fuctioal groups Fuctioal group eaget esult Alkee Bromie water ragecolour decolourises carboyl 2,4-DP rageprecipitate formed Aldehyde Tolles eaget Silver mirror formed arboxlicacid Sodiumcarboate Effervescece of 2 evolved 1 o 2 o alcohol ad aldehyde Sodiumdichromate ad sulphuric acid rageto gree colour chage haloalkae Warm withsilver itrate Slow formatioof white precipitate Goalby chemrevise.org 7

8 Drugs Makig Aspiri Aspiri Aspiri is made from 2- hydroxybezoic acid which cotais a pheol group. I the reactio the pheol group is tured ito a ester by reactig it with the reactive ethaoic ahydride hirality i pharmaceutical sythesis The sythesis of pharmaceuticals ofte requires the productio of a sigle optical isomer Drug actio ad optical isomers Drug actio may be determied by the stereochemistry of the molecule. Differet optical isomers may have very differet effects Molecules prepared sythetically i the laboratory ofte cotai a mixture of optical isomers, whereas molecules of the same compoud produced aturally by ezymes i livig systems will ofte be preset as oe optical isomer oly Thalidomide hiral carbo Ibuprofe e eatiomer of thalidomide causes birth defects i ubor childre whilst the other had useful sedative problems. Ufortuately it was give i a mixture of the two whe first used. Sythesis of a pharmaceutical that is a sigle optical isomer is more expesive because separatio of the sigle isomer is difficult. owever oe of the isomers may be more pharmacologically active ad oe of the isomers might have adverse side effects. Moder sythesis of a pharmaceutical with a sigle optical isomer is ofte carried out: (i) usig ezymes or bacteria which promote stereoselectivity, (ii) usig chemical chiral sythesis or chiral catalysts, (iii) usig atural chiral molecules, such as L-amio acids or sugars, as startig materials. Goalby chemrevise.org 8

9 rgaic techiques Distillatio I geeral used as separatio techique to separate a orgaic product from its reactig mixture. eed to collect the distillate of the approximate boilig poit rage of the desired liquid. thermometer lassic AS reactio usig distillatio eactio: primary alcohol aldehyde eaget: potassium dichromate (VI) solutio ad dilute sulphuric acid. oditios: use a limited amout of dichromate ad warm getly ad distil out the aldehyde as it forms [This prevets further oxidatio to the carboxylic acid] [] bservatio rage dichromate solutio chages to gree colour of r 3 ios eat Water out Liebig codeser Water i eflux eflux is used whe heatig orgaic reactio mixtures for log periods. The codeser prevets orgaic vapours from escapig by codesig them back to liquids. ever seal the ed of the codeser as the build up of gas pressure could cause the apparatus to explode. This is true of ay apparatus where volatile liquids are heated lassic AS reactio usig reflux eactio: primary alcohol carboxylic acid eaget: potassium dichromate(vi) solutio ad dilute sulphuric acid oditios: use a excess of dichromate, ad heat uder reflux: (distill off product after the reactio has fiished usig distillatio set up) [] bservatio rage dichromate solutio chages to gree colour of r 3 ios Ati-bumpig graules are added to the flask i both distillatio ad reflux to prevet vigorous, ueve boilig. Goalby chemrevise.org 9

10 Purifyig a orgaic liquid Put the distillate of impure product ito a separatig fuel wash product by addig either sodium hydrogecarboate solutio, shakig ad releasig the pressure from 2 produced. Saturated sodium chloride solutio Allow the layers to separate i the fuel, ad the ru ad discard the aqueous layer. u the orgaic layer ito a clea, dry coical flask ad add three spatula loads of dryig aget (ahydrous sodium sulphate) to dry the orgaic liquid. Sodium hydrogecarboate will eutralise ay remaiig reactat acid. Sodium chloride will help separate the orgaic layer from the aqueous layer The dryig aget should be isoluble i the orgaic liquid ot react with the orgaic liquid arefully decat the liquid ito the distillatio flask Distill to collect pure product Separatig fuel Purifyig a orgaic solid: ecrystallisatio Used for purifyig aspiri Step easo 1. Dissolve the impure compoud i a miimum volume of hot (ear boilig) solvet. A appropriate solvet is oe which will dissolve both compoud ad impurities whe hot ad oe i which the compoud itself does ot dissolve well whe cold. The miimum volume is used to obtai saturated solutio ad to eable crystallisatio o coolig 2. ot filter solutio through (fluted) filter paper quickly. This step will remove ay isoluble impurities ad heat will prevet crystals reformig durig filtratio 3. ool the filtered solutio by isertig beaker i ice rystals will reform but soluble impurities will remai i solutio form because they are preset i small quatities so solutio is ot saturated. Ice will icrease the yield of crystals 4. Suctio filtrate with a bucher flask to separate out crystals The water pump coected to the Bucher flask reduces the pressure ad speeds up the filtratio. 5 Wash the crystals with distilled water To remove soluble impurities 6. Dry the crystals betwee absorbet paper Loss of yield i this process rystals lost whe filterig or washig Some product stays i solutio after recrystallisatio other side reactios occurrig bucher flask Goalby chemrevise.org 10

11 Measurig meltig poit e way of testig for the degree of purity is to determie the meltig poit, or meltig rage, of the sample. If the sample is very pure the the meltig poit will be a sharp oe, at the same value as quoted i data books. If impurities are preset (ad this ca iclude solvet from the recrystallisatio process) the meltig poit will be lowered ad the sample will melt over a rage of several degrees elsius Meltig poit ca be measured i a electroic meltig poit machie or by usig a practical set up where the capillary tube is strapped to a thermometer immersed i some heatig oil. I both cases a small amout of the salt is put ito a capillary tube. Thermometer with capillary tube strapped to it cotaiig sample eatig oil- eeds to have boilig poit higher tha samples meltig poit ad low flammability omparig a experimetally determied meltig poit value with oe quoted i a data source will verify the degree of purity. eat Sometimes a error may occur if the temperature o the thermometer is ot the same as the temperature i the actual sample tube. Measurig boilig poit Purity of liquid ca be determied by measurig a boilig poit. This ca be doe i a distillatio set up or by simply boilig a tube of the sample i a heatig oil bath. Pressure should be oted as chagig pressure ca chage the boilig poit of a liquid Measurig boilig poit is ot the most accurate method of idetifyig a substace as several substaces may have the same boilig poit. To get a correct measure of boilig poit the thermometer should be above the level of the surface of the boilig liquid ad be measurig the temperature of the saturated vapour. Goalby chemrevise.org 11

4. Amines, Amides and Amino Acids

4. Amines, Amides and Amino Acids 4. Amies, Amides ad Amio Acids amig Amies These ed i amie. There is, however, rather cofusigly two ways of usig this suffix. The exam board ted to use the propylamie commo versio where the ame r propa-1-amie