4. Amines, Amides and Amino Acids

Size: px

Start display at page:

Download "4. Amines, Amides and Amino Acids"

Peter Cross
6 years ago
Views:

1 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 stem eds i -yl propylamie. The IUPA versio of the same chemical is propa-1-amie. (This is used i the same way as amig alcohols) If there is aother priority fuctioal group as well as the amie group the the prefix amio is used. -amiopropaoic acid. If the amie is secodary ad has two alkyl groups attached to the itroge, the each chai is amed ad the smaller alkyl group is preceded by a which plays the same role as a umber i positioig a side alkyl chai I the commo amig versio if the chai legths are the same a is ot used - methylpropylamie (commo ame) - methylpropa-1-amie (IUPA ame) Diethylamie (commo ame- does ot use if chais are same legth) -ethylethaamie (IUPA ame does still use ) If a tertiary amie similar rules apply, ad each alkyl side group is give a,dimethylpropylamie (commo ame),dimethylpropa-1-amie (IUPA ame) ()6 hexae-1,6-diamie It could also be amed 1,6-diamiohexae Amides Add amideto the stem ame ethaamide Secodary ad tertiary amides are amed differetly to show the two (or three) carbo chais. The smaller alkyl group is preceded by a which plays the same role as a umber i positioig a side alkyl chai -methylpropaamide,-dimethylpropaamide,,-trimethylpropaamide 1

2 δ Properties of Amies Amies have a characteristic fishy smell δ+ - δ + δ - Small amies ca form hydroge bods with water ad therefore ca dissolve readily i water. Base Properties δ+ δ+ Primary aliphatic amies act as Brosted-Lowry Bases because the loe pair of electros o the itroge is readily available for formig a dative covalet bod with a + ad so acceptig a proto. Primary aliphatic amies are stroger bases tha ammoia as the alkyl groups are electro releasig ad push electros towards the itroge atom ad so make it a stroger base (aq) 4 + (aq) + - (aq) + (l) Secodary amies are stroger bases tha primary amies because they have more alkyl groups that are substituted oto the atom i place of atoms. Therefore more electro desity is pushed oto the atom (as the iductive effect of alkyl groups is greater tha that of atoms). e might expect usig the same tred that tertiary amie would be the strogest amie base but the tred does ot hold. The tertiary amies ad correspodig ammoium salts are less soluble i water ad this makes them less strog bases tha the secodary amies. (This poit will ot be examied) Base stregth of aromatic amies Primary aromatic amies such as Pheylamie do ot form basic solutios because the loe pair of electros o the itroge delocalise with the rig of electros i the bezee rig. This meas the is less able to accept protos. Reactios with acids pheylamie Amies as bases react with acids to form ammoium salts. + - (aq) +l (aq) l (aq) Methylamie methylammoium chloride + - (aq) + S 4 (aq) ( ) S 4 (aq) The ioic salts formed i this reactio meas that the compouds are soluble i the acid. e.g. Pheylamie is ot very soluble i water but pheylammoium chloride is soluble Additio of a to a ammoium salt will covert it back to the amie These ioic salts will be solid crystals, if the water is evaporated, because of the strog ioic iteractios. Makig a basic buffer from a amie Basic buffers ca be made from combiig a weak base with a salt of that weak base e.g. Ammoia ad ammoium chloride Methylamie ad methylammoium chloride Ethylamie ad ethylammoium chloride Formatio of complex ios The loe pair of electros o the itroge eable amies to act as ligads ad form dative covalet bods ito trasitio metal ios to form coloured complex ios. 4 + u( ) 6 + [u( ) 4 ( ) ] + +4 This is a similar ligad exchage reactio to the oe where ammoia acts as the ligad 4 + u( ) + [u( ) ( ) ] light blue solutio 4 deep blue solutio

3 : Reactio of primary Amies with halogeoalkaes formig secodary amies Amies will react with halogeoalkaes i a similar way to the reactio of ammoia with halogeoalkaes via a ucleophilic substitutio reactio + Br + Br Br + - Br + + Br : Diethylamie The secodary amie formed ca also the react with more halogeoalkae to form a tertiary amie ad subsequetly o to what is called a quaterary ammoium salt Where RX is the haloalkae R R RX RX RX : R : R : R + R R R R R Reactio with primary amies with acyl chlorides hage i fuctioal group: acyl chloride Reaget: primary amie oditios: room temp. secodary amide Rl + l + R + + l l - -methylethaamide Paracetamol is made by the reactio of a aromatic amie with a acyl chloride to produce a amide l Paracetamol

4 Reducig itroarees to aromatic amies The itro group o a aree ca be reduced a amie group as follows Reaget: S ad l or Fe ad l oditios: eatig Mechaism:reductio + 6[] + itrobezee pheylamie The pheylamie formed i this reactio is best separated from the reactio mixture by steam distillatio. As the reactio is carried out i l the salt + l - will be formed. 6 5 Reactig this salt with a will give pheylamie. Sythesis of azo dyes Step 1: reactio of a aromatic amie with itrous acid at <10, formig a diazoium io, a + l <10 o + itrous acid is geerated i situ from a /l. Below 0 o the temperature is too low ad the reactio would be too slow l l diazoium io + If the diazoium io is allowed to heat above 10 o it reacts with water to form pheol ad gas Step : couplig of diazoium io with a pheol uder alkalie coditios; a l l 4-hydroxyazobezee Azo dyes are used for dyes, pigmets ad colourigs 4

5 Polymers 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 hai forms whe same basic uit is repeated over ad over. Poly(alkees) are chemically iert due to the strog - ad - bods ad o-polar ature of the bods ad therefore are o-biodegradable. You should be able to draw the polymer repeatig uit for ay alkee e.g. For but--ee e.g. For propeamide It is best to first draw out the moomer with groups of atoms arraged aroud the double bod poly(propeamide) Poly(etheol) The additio polymer poly(etheol) has good solubility i water because it ca form may strog hydroge bods with water. The makes it a useful polymer for uses such as soluble laudry bags adliquid deterget capsules. poly(etheol) 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. 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 arboxylic Acid + Amie amide + water Acyl chloride + Alcohol Ester + l 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 5

6 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 + Ethae-1,-diol Bezee-1,4-dicarboxylic acid Terylee fabric is used i clothig, tire cords + -1 The -1 here is because at each ed of the chai the ad are still preset ( ) + l l Petaedioyl dichloride Bezee-1,4-diol ( ) + -1 l ylo 6,6 - a commo polyamide ()4 + ()6 ()4 () hexaedioic acid exae-1,6-diamie 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 () () () () l repeatig uits repeatig uits 6

7 : 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 Itermolecular bodig betwee codesatio polymers chais Polyesters have permaet dipole bodig betwee the δ+ = δ- groups i the differet chais i additio to the Lodo forces betwee the chais. Polyamides (ad proteis) have hydroge bodig betwee the loe pairs o oxyge i δ+ = δ- groups ad the i the δ- δ+ groups i the differet chais. There are also Permaet dipole-permaet dipole forces because the polar = bod ad polar - bod There are also Lodo forces which are large because there are may electros i the molecule Polyamides will therefore have higher meltig poits tha polyesters. :δ- δ- δ+ δ+ δ+ δ- δ+ δ- δ+ δ- δ- δ+ : δ- δ- δ+ δ+ Amio Acids Geeral structure of a amio acid The simplest amio acid is glycie, where the R is a R The R group ca be a variety of differet thigs depedig o what amio acid it is. amig amio acids You do ot eed to kow ay commo ames for the 0 essetial amio acids. We should, however, be able to ame give amio acids usig IUPA orgaic amig (-)amioethaoic acid -amiobutaedioic acid -amio-- hydroxypropaoic acid Some amio acids have a extra carboxylic acid or a amie group o the R group. These are classed as acidic or basic (respectively) amio acids ()4 Aspartic acid Lycie (basic),6-diamiohexaoic acid 7

8 Zwitterios The o charge form of a amio acid ever occurs. R R The amio acid exists as a dipolar zwitterio. + - Amio acids are ofte solids 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. Zwitterio Acidity ad Basicity The amie group is basic ad the carboxylic acid group is acidic. R - R + R Species i Species i Species i alkalie solutio eutral solutio acidic solutio igh p 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 + + The extra carboxylic acid or amie groups o the R group will also react ad chage form i alkalie ad acid coditios - - Aspartic acid i high p hromatography of Amio Acids A mixture of amio acids ca be separated by chromatography ad idetified from the amout they have moved. R f value = distace moved by amio acid distace moved by the solvet Each amio acid has its ow R f value. ompare a ukow amio acid s Rf value with kow values i a data book to idetify the amio acid Method Take chromatography paper ad draw a pecil lie 1.5cm from bottom. With a capillary tube put a small drop of amio acid o pecil lie Roll up paper ad stad it i a large beaker. The solvet i the beaker should be below the pecil lie. Allow to stad for 0 mis ad mark fial solvet level Spray paper with ihydri ad put i ove If ihydri is sprayed o a amio acid ad the heated for 10 miutes the red to blue spots appear. This is doe because amio acids are trasparet ad caot be see. ptical Activity All amio acids, except glycie, are chiral because ptical isomers have similar physical ad chemical properties, but they rotate there are four differet groups plae polarised light i aroud the They rotate plae polarised light. differet directios.

9 8

10 : Proteis Proteis are polymers made from combiatios of amio acids. The amio acids are liked by peptide liks, which are the amide fuctioal group. S S R R R 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. + a make or Importace of hydroge bodig i proteis The D 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+ R δ+ R δ- δ- δ+ R R ydrolysis of di-peptides/proteis If proteis are heated with dilute acid or alkali they ca be The compositio of the protei hydrolysed ad split back i to their costituet amio acids. molecule may the be deduced by usig paper chromatography ther reactios of amio acids 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

N Goalby chemrevise.org

N Goalby chemrevise.org 21. olymers There are two types of polymerisatio additio ad codesatio Additio olymerisatio A additio polymer forms whe usaturated moomers react to form a polymer Moomers cotai = bods oly(alkees) are chemically