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Level 3: Organics Part II Amides Acid Chlorides Amino Acids Polymers Author: J R Reid Amides - Introduction Amides look very much like a cross between amines and carboxylic acids There are two types of amides; primary and secondary. We will look at these in more detail on the next page All (except methanamide) are solid at room temperature They have no smell (unlike amines) They are weak bases compared to amines Amides can be found in nature as Urea (a component of urine and an important fertiliser) H3C C O NH2 Amides - Continued There are three types of amines: primary, secondary and tertiary. Unfortunately we use these words slightly differently than we do with alcohols: Identify the trend… Secondary Primary O H3C C NH2 H 3C NH CH3 C O We only need to name primary amides this year. The names of amides has the suffix “–amide” e.g. ethanamide, octanamide…etc Amides – Reactions Making amides Acid chlorides and concentrated ammonia H3C C Cl + H3C NH3 C NH2 + HCl O O Esters and concentrated ammonia H3C C O CH3 + H3C NH3 C + NH2 H3C OH O O Hydrolysis Amides can be hydrolysed (they can break up water) in acid and alkaline conditions: H3C C NH2 + H3O + H3C O H3C C O C + OH + NH4 O NH2 + - HO H3C - C O O + NH3 Acid Chlorides Introduction (Acyl Chorides) As we have seen earlier acid chlorides can be used to make amides They are very similar in structure to carboxylic acids except the –OH is replaced by a –Cl They are very reactive and acidic organic compounds Their names end in the suffixes –oyl chloride e.g. propanoyl chloride H3 C C Cl O Acid Chloride Introduction II Acid chlorides are strongly polar. This a low melting point, but they don’t dissolve in water (see why on the next page) They are so reactive that they even react with water vapour in the air to give a fuming appearance (the production of HCl gas) Production – Acid chlorides don’t survive long in nature, so they have to be made in the lab: Acid chlorides are made by the nucleophilic substitution of carboxylic acids with PCl5, SOCl2, and PCl3 e.g. H3C C O OH + PCl 5 H3C C O Cl + POCl3 + HCl Acid Chlorides - Reactions Reactions of acid chlorides: Hydrolysis – acid chlorides can break water apart H 3C C Cl + H 2O H 3C C + OH HCl O O Condensation – (esterification) H3C C O Cl + H3C OH H3C C O CH3 + O Amide production – as we saw earlier HCl Amino Acids Amino acids are the building blocks of all proteins. There are many different amino acids but they all have two things in common: R H2N Amino – they have an amine group attached somewhere to their structure Acid – they also have a carboxylic acid group Amino acids can be linked together into long chains called polypeptides (or proteins). The bonds between two amino acids is called a peptide bond A peptide bond is a bond formed between the carboxylic acid group and a neighbouring amine group bond (releasing water as a byproduct) C C H O OH R R H 2N C C H O OH H R H 2N + H2N C C OH O R C C NH C C H O H O OH Other Polymers Polymers are made up of small units (monomers) that are linked together into long, repeating chains. We saw on the previous page one example: The monomer is an amino acid. When linked together it forms a chain, a polymer called a polypeptide There are a number of different types of polymers. Chemists have grouped some together based on how they are made: Addition polymers – these link together with no byproducts. This is normally because to the breaking of a double bond Condensation polymers – these produce a by-product (normally water) when the monomers link together Polymers II Addition polymers Examples of addition polymers are: Polythene (many ethenes), poly vinyl chloride (PVC), polypropylene and polystyrene Polythene is made by linking together many ethene molecules: H H C + C H H H H H H C H + C H C + C H H H H C H H H H H H H H H C C C C C C C C H H H H H H H H H C H H Condensation polymers Examples of condensation polymers include: Polyesters, polypeptides (proteins), polyamides and polysaccharides (many sugars) See the next page for examples of these polymers Polymers - Examples Polyester A polyester is created by reacting carboxylic acids and alcohols together. In order to create long chains of them the chemicals need to be ‘double ended.’ The two ended alcohol is called a ‘dialcohol’, and the two ended carboxylic acid is called a ‘dicarboxylic acid’ CH HO C CH C O CH C CH C OH + HO CH2 CH2 OH C C C O O CH H O CH CH C O CH2 CH2 O H O CH Polyamide A polyamide is a sort of long chain secondary amide. These are created from double ended amines (diamines) and carboxylic acids (dicarboxylic acids) reacting H N H R N H H + HO C O R C O OH H N H R N C H O R C O H Polysaccharides – another polymer Sugars such as glucose can be turned into polymers for food storage. If we link many glucose molecules we create the chemical we know as starch Simple sugars (monosaccharides) bonded in pairs are called disaccharides. An example of this is sucrose (cane sugar) H C C H H OH C OH O H C H C + OH H C H O C C H H OH C OH OH H2COH H C H2COH H2COH H2COH O H C H C + OH H H C H C OH OH H C O H C C O H H OH C H C OH OH H2COH O C H C H C OH OH H2COH O H H C H C OH OH H C O H C C O H H C H C OH OH H C O H