Module 08 Applications of Functional Groups PDF

Module 08 Applications of Functional Groups Polymers, Soaps and Lipids  Contents of the lecture Polymers Introduction and nomenclature Types of polymers Soaps and detergents Structural similarities and differences Function of soaps Lipids Classification sche...

Module 08 Applications of Functional Groups Polymers, Soaps and Lipids  Contents of the lecture Polymers Introduction and nomenclature Types of polymers Soaps and detergents Structural similarities and differences Function of soaps Lipids Classification scheme Examples  Prior knowledge Alkene functional groups do addition reactions ✓Alkene + something → one product Ester functional groups ✓Carboxylic acid + alcohol → ester + water Esterification is a reversible reaction  Prior knowledge Solubility ✓Dissolving in water requires that the molecules be polar and (preferably) capable of hydrogen bonding ✓Hydrocarbons are non-polar molecules that cannot dissolve in water because they cannot form hydrogen bonds ✓The ratio of polar to non-polar parts of a molecule can affect its solubility in water  Polymers Focus on synthetic polymers  Polymers: introduction ✓Polymers (poly = many, meros = parts) are long chain molecules made by linking monomers by different chemical reactions ✓Molecular weight of a polymer varies from 10,000 to 1,000,000 grams per mole ✓Polymer architecture is diverse - structures can be linear, branches, combs, ladders, stars and cross-linked comb ladder star  Polymers: introduction Do you hear ‘polymer’ and think of ‘plastic’? Plastics ✓Polymers which can be shaped when hot and retain that shape when they are cooled ✓Thermoplastics Polymers which can be melted and become fluid enough to be poured into moulds Can be reheated, reshaped as necessary (recyclable) ✓Thermosetting plastics Can be moulded when first prepared, but once cooled, harden irreversibly and cannot be remoulded (not recyclable)  Polymers: structure Structure of a polymer is shown by putting brackets around the repeating unit and using a subscript ✓A repeating unit is smallest molecular fragment that contains all non-repeating structural features of the chain ✓Subscript indicates the average degree of polymerisation (shows how many times there is a repeat unit) Part of extended chain O CH2 CH2 O CH2 CH2 O CH2 Repeating unit CH2 CH2 O n  Polymers: nomenclature Most commonly, the polymer is named by putting the prefix “poly-” in front of the monomer’s name CH2 Polystyrene CH2 CH2 CH n n Polyethylene When a complex monomer is used, the monomer’s name is in brackets CH2 CH Poly(vinyl chloride) or PVC n Cl  Polymers: formation reactions There are two general ways to form synthetic polymers: ✓Condensation reaction ✓Addition reaction Condensation reaction ✓Reaction between two functional groups that produces H2O e.g. carboxylic acid + alcohol → ester + water e.g. carboxylic acid + amine → amide + water Addition reaction ✓Reaction of alkene functional groups, adding together in long chains without releasing any other products  Polymers: condensation Condensation polymerisation requires di-functional monomer molecules ✓Di-functional means having two functional groups HO O A-A di-functional monomer C CH2 C O OH O HO CH2 C A-B di-functional monomer OH Condensation reactions can happen in two ways: ✓Self-condensation of A-B monomers to give (-A-B-)n polymers (uncommon) ✓A-A reacting with B-B to give (-A-A-B-B-)n polymers (common)  Polymers: condensation A-A monomers reacting with B-B monomers ✓Each monomer has two functional groups of the same kind ✓The product has general formula (-A-A-B-B-)n ✓This example is formation of a polyester O O n n HO CH2 CH2 OH C C HO (CH2) 4 OH hexanedioic acid 1,2-ethanediol (adipic acid) (ethylene glycol) O O C C + nH 2O (CH2) 4 OCH2CH2O n poly(ethylene adip ate)  Polymers: condensation A-A monomers reacting with B-B monomers ✓Again, each monomer has two of the same functional groups ✓The product has general formula (-A-A-B-B-)n ✓This example is formation of a polyamide O O n n H 2N (CH2) 6 NH2 C C HO (CH2) 4 OH hexanedioic acid 1,6-hexaned iamine (adipic acid) (hexamethyl enediamine) O O C C + nH 2O (CH2) 4 NH (CH2) 6 NH n Nylon 66 (a polyamide)  Polymers: condensation Here are two more examples of other well-known polymers that are formed by the condensation process Kevlar - a polyaromatic amide that’s lightweight and very strong O O C C NH NH n Dacron (Mylar) - a polyester, much stronger than Nylon 66 because of the aromatic group O O C C O CH2 CH2 O n  Example question Draw the starting materials required to produce this polymer. O O C C NH NH n  Polymers: condensation These two monomers will react to form a polymer HO O CH2 CH2 HO CH OH C (CH2)3 C O OH CH3 pentanedioic acid 2-methyl-1,3-propanediol ✓What type of condensation polymer will it form? ✓What is the structure of the repeating unit?  Polymers: condensation HO O CH2 CH2 HO CH OH C (CH2)3 C O OH CH3 pentanedioic acid 2-methyl-1,3-propanediol  Polymers: addition Addition polymerisation involves the joining together of monomer units without loss of atoms. Example: polyethylene formation ✓Monomer is an alkene, polymer is an alkane ✓Proceeds via radical mechanism ✓Requires a catalyst catalyst n H 2C CH2 CH2 CH2 n ethylene polyethylene  Polymers: addition Addition polymerisation happens by a 3-step process Initiation ✓Forms the radical ‘initiator’ species, often a catalyst ✓A radical is a species with an unpaired electron – very reactive Propagation ✓Initiator (radical species) reacts with a monomer unit, producing part of the polymer chain and another radical. ✓The new radical produced can then go on and react with another monomer unit, forming more of the chain and another radical... Termination ✓Radicals are “terminated” by different processes and the polymer chain stops growing  Polymers: addition Lots of small alkene monomers will undergo addition polymerisation to form polyalkanes General addition reaction equation catalyst n X X ✓When X is –H, gives polyethylene ✓When X is –CH3, gives polypropylene ✓When X is – C6H5, (benzene ring) gives polystyrene  Polymers: addition Can you draw the structure of the monomer? CH2 CH CH2 n CCl2 n poly(1,1-dichloroethylene) one part of 'glad wrap' CH2 C polystyrene n CF2 CH3 O C CF2 n CH3 poly(tetrafluoroethylene) poly(methyl methacrylate) Teflon coating Plexiglass (methyl 2-methylprop-2-enoate) Polymers: addition Cl CH2 CH2 Cl Styrene 1,1-dichloroethylene F F CH3 H2C O F F H3C O Tetrafluoroethylene Methyl methacrylate Soaps and Detergents  Soaps: introduction Saponification (soap-forming) reactions are some of the oldest organic reactions known ✓Ancient Egyptians used animal fats and wood ash (KOH) ✓Modern saponification uses concentrated NaOH solution mixed with triglyceride (type of lipid) ✓Products formed are glycerol and fatty acid salts (soap) O O C R1 H 2C OH R 1COO Na H 2C O HC O C R2 + 3 NaOH HC OH + R 2COO Na O H 2C H 2C OH R 3COO Na O C R3  Soaps: introduction Triglycerides (fats) have ester functional groups Concentrated NaOH solution breaks the ester bond – the reaction is called hydrolysis Hydrolysis of esters produces alcohol and carboxylic acid ✓Because the reaction is in basic solution, the carboxylic acid is in the form of the carboxylate ion (RCOO−) and the sodium ions are attracted to the negatively-charged end ✓The actual fatty acid salts produced depends on the R groups that were bonded by the ester bonds in the triglyceride  Soaps: structure A soap molecule has two parts: ✓a hydrophilic (water-loving) head ✓a hydrophobic (water-fearing) tail O C O The hydrophilic end will dissolve easily in aqueous solution (i.e. in the washing water) but the hydrophobic end is not soluble in aqueous solution.  Soaps: hard water “Hard” water ✓Has a relatively high concentration of Ca2+, Mg2+ or Fe3+ Soaps do not function in hard water because the ions form insoluble salts with the soap The solid salt is often grey, sticky and unpleasant ✓Also called ‘soap scum’  Detergents Synthetic detergents are an alternative to soaps ✓Detergents don’t form insoluble salts in hard water Detergent molecules have similar structure to soap: ✓A hydrophobic tail – the long carbon chain ✓A hydrophilic head – benzene sulfonate ion functional group SO3 Na Note the difference in the functional group in a detergent compared to a soap molecule  Another common detergent/surfactant ✓Sodium dodecyl sulfate also known as lauryl sulfate or SDS. ✓Check out your shampoos and you will find it listed in the ingredients.  Soaps, detergents and cleaning The molecules will arrange themselves so all the hydrophobic tails point in towards each other (micelle), and the hydrophilic heads interact with the water Most ‘dirt’ is non-polar, and will be encapsulated by the micelle, surrounded by hydrophobic tails Lipids  Lipids: introduction Lipids are a group of compounds with different compositions and structures, but they have the same solubility: ✓Insoluble in water ✓Soluble in non-polar solvents Members of the lipid family include: ✓Triglycerides (fats and oils) ✓Fatty acids (long-chain carboxylic acids) ✓Fat-soluble vitamins ✓Prostaglandins ✓Steroids and hormones  Lipids: functions The various roles of lipids in the body are determined by their chemical structure. Energy storage ✓Triglycerides (also called fats and oils) Cell membranes ✓Phospholipid layers form the outer layer of a cell, allowing some species to pass through (e.g. ions) Emulsifying agents ✓Bile salts are steroids that dissolve fats and transport them around the body Metabolism regulation ✓Hormones are steroids that control biological processes  Lipids: classification The lipid family contains so many different members, we need to have a classification system Saponifiable vs. non-saponifiable lipids ✓Lipids that contain an ester functional group can be hydrolysed in basic conditions (e.g. NaOH solution). O O R1 C + OH R1 C + R2 OH O R2 O ✓Other lipids that can’t be hydrolysed are non-saponifiable  Lipids: classification lipids Can undergo hydrolysis Cannot undergo hydrolysis saponifiable Non-saponifiable waxes triglycerides phospholipids prostaglandins steroids  Saponifiable lipids – all have an ester group wax tryglyceride phospholipid  Non-saponifiable lipids prostaglandin steroid  Fatty acids ✓Fatty acids are long-chain carboxylic acids and are the building blocks for many lipids ✓They are produced when a triglyceride (or a wax or phospholipid) is hydrolysed with base. ✓Fatty acids (and fatty acid salts) have polar heads and non-polar tails, so they are both hydrophilic and hydrophobic O O C R1 H2C O CH2 OH R1 COO HC O C R2 + 3OH CH OH + R2 COO O H2C CH2 OH R3 COO O C R3 triglyceride (fat, oil) glycerol fatty acid salts  Fatty acids Fatty acids behave like soaps ✓They form micelles in aqueous solution with their non-polar tails pointed inward, and their polar heads pointed towards water ✓Fatty acids are useful for transporting insoluble lipids in blood. General features of fatty acids ✓Straight carbon chains (no branches) ✓10-22 carbons in length, usually an even number ✓Saturated or unsaturated, depends on triglyceride came from ✓In unsaturated fatty acids, the cis isomer is most common  Fatty acids Humans can synthesise all but two of the important fatty acids in their bodies Linoleic acid and linolenic acid are called essential fatty acids because they must be consumed ✓These essential fatty acids are used to make hormones that control blood clotting, inflammation response etc ✓Examples of polyunsaturated fatty acids (PUFA)  Linoleic and linolenic acids CH3-(CH2)4-(CH=CHCH2)2-(CH2)6-COOH PUFA 18:2 n-6 Omega 6 a w Linoleic acid CH3-CH2-(CH=CHCH2)3-(CH2)6-COOH PUFA 18:3 n-3 Omega 3 Linolenic acid  Fatty acids Melting Physical properties Carbon Atoms/ Common Point MP and BP Double Bonds* Name (°C) increase with Saturated Fatty Acids chain length due to 12:0 Lauric acid 44 more dispersion forces 14:0 Myristic acid 58 16:0 Palmitic acid 63 MP and BP 18:0 Stearic acid 70 decrease as chains 20:0 Arachidic acid 77 get more Unsaturated Fatty Acids unsaturated 16:1 Palmitoleic acid 1 (have more 18:1 Oleic acid 16 C=C bonds) 18:2 Linoleic acid -5 18:3 Linolenic acid -11 20:4 Arachidonic acid -49 Structure with increasing no. double bonds  Triglycerides, fats and oils Triglycerides are also called tri-acyl-glycerols They are ‘tri-esters’ of glycerol (three ester bonds) Glycerol + 3 fatty acids Triglyceride + water O CH2 OH R1 COOH O C R1 H2C O CH OH + R2 COOH + 3H2O HC O C R2 CH2 OH R3 COOH O H2C O C R3  Triglycerides Most fats and oils are triglycerides ✓Most fats are from animals (solids at room temperature) while oils are from plants (liquids at room temperature) ✓Generally, ‘fats’ have saturated fatty acid components, while ‘oils’ have unsaturated fatty acid components. Triglyceride reactions ✓Hydrolysis – reaction in acidic solution, will form glycerol and three fatty acid chains ✓Saponification – reaction in basic solution, will form glycerol and three fatty acid salts (soaps) ✓Hydrogenation – reaction with H2/catalyst, changes unsaturated chains into saturated chains  Triglycerides Hydrogenation ✓This is also called ‘hardening’ ✓Unsaturated vegetable oils are selectively hydrogenated to turn alkene groups into alkanes ✓With careful control, oils with specific consistency, MP and BP can be created ✓Most of these are sold as kitchen products or used in manufacture of foods (usually snacks, chocolate bars etc) ✓On the label as “hydrogenated vegetable oil” ✓If all the C=C bonds are hydrogenated, not chemically different to an animal fat, it just doesn’t come from an animal  Triglycerides in the body When a fatty food such as cheese is eaten, it is first emulsified into small droplets by bile salts (a type of lipid) Lipase, an enzyme, helps to break the ester bonds ✓The 3 fatty acids are separated from the glycerol Fatty acids are transported to cells ✓Mitochondria are small organelles inside cells ✓Mitochondria use the fatty acids in metabolic processes to provide energy, use the atoms to make protein molecules etc  Bile salts ✓ Salts of cholic acid, lithocholic acid etc ✓ Act like detergents, having both hydrophobic and hydrophilic ends the can solubilise the non-polar fats  What kind of lipid is lithocholic acid? Saponifiable or non-saponifiable?  Waxes Waxes are closely related to triglycerides, but they don’t have the glycerol backbone High molecular weight esters A fatty acid reacts with long-chain alcohol to make a wax Structure of carnauba wax, extracted from Brazilian palm tree Waxes are ✓Saponifiable or non-saponifiable? ✓Soluble in water?  Phospholipids Phospholipids are also called phosphoglycerides O Main function = cell membrane structure O C R1 H2C O HC O C R2 O General structure H2C ✓Glycerol backbone O P O R3 ✓2 fatty acid chains O ✓1 phosphate group ✓1 aminoalcohol linked to phosphate group (in this case, R3) ✓Bond between glycerol’s OH group and phosphoric acid group is called a “phosphate ester”  Phospholipids OH Aminoalcohols Choline H3C N + CH3 Lecithins HO CH3 + Ethanolamine NH3 Cephalins HO O Serine + - Cephalins H3N O  Phospholipids One very common phospholipid is “lecithin” (proper name phosphatidylcholine) ✓The ‘phospho’ end of the molecule is quite polar and very hydrophilic. The other side chains are hydrophobic ✓Lecithin acts as an emulsifying agent, used in margarine and chocolate to blend oil and water, gives a smooth texture O O C (CH2)16 CH3 H2C O HC O C (CH2)7CH=CHCH2CH=CH(CH2)4CH3 O H2C O P O CH2CH2-N(CH3)3 O  Phospholipids Phospholipids are mostly used to form cell membranes and small structures within cells In aqueous solution, complex lipids form a lipid bilayer (a back-to- back arrangement of lipid layers) ✓Polar heads are in contact with the aqueous environment ✓Non-polar tails are buried within the bilayer ✓Major force driving the formation of lipid bilayers is hydrophobic interaction ✓Arrangement of hydrocarbon tails in the interior can be rigid (if many saturated fatty acid chains) or floppy (if there are many unsaturated fatty acid chains)  Phospholipids O Lipid bilayer, key component of cell H2C O C O (CH2)16 CH3 membranes. HC O C (CH2)7CH=CHCH2CH=CH(CH2)4CH3 Fluid like to impart flexibility H2C O Stiffening reagents, e.g. cholesterol, O P O CH2CH2-N(CH3)3 to impart some rigidity O Non-polar polar  Antifungal drugs Human cell membranes use cholesterol to increase rigidity of the lipid bilayer fungal cell membranes use ergosterol. cholesterol ergosterol  Antifungal agent – Amphotericin B Selective for ergosterol, and binds with it, disrupting the normal function of the cells. https://pdfs.semanticscholar.org/553d/7045ec23817ff1c72633adf15e3d507b9838.pdf  Sphingolipids A type of complex lipid that doesn’t contain a glycerol backbone but has sphingosine instead It also has a phosphate ester group that is saponifiable CH3(CH2)12CH=CH CH OH O General structure HC NH C (CH2)7CH=CH(CH2)7CH3 ✓ Sphingosine O ✓ Fatty acid H2C O P O CH2CH2N(CH3)3 ✓ Phosphate group O This sphingolipid is called sphingomyelin, found in the brain and nervous tissue.  Sphingolipids Glycolipids Another sphingolipid Contain monosaccharides  Steroids Steroids have two broad functions ✓chemical messengers / signalling compounds / hormones transported in the bloodstream ✓Control lipid membrane fluidity All steroids have a basic four ring structure Where have we seen this structure before? Is a steroid saponifiable or non-saponifiable?  Steroids Cholesterol is the most abundant steroid in the body, and the most important one HO Cholesterol is part of all cell membranes, a precursor for bile salts, male and female sex hormones, vitamin D, etc Is cholesterol water soluble? How does it travel in the bloodstream?  Lipoproteins ✓Lipids form complexes with proteins (lipoproteins) ✓Different classes of lipoprotein carry different types of fats (phospholipid, triglycerides, cholesterol) ✓Low density lipoproteins (LDLs) carry fat around the entire body within the bloodstream ✓High density lipoproteins (HDLs) collect fat from cells and tissues and return it to the liver  Steroids Androgens – male sex hormones ✓Synthesised in the testes ✓Responsible for male secondary sex characteristics OH O O HO testosterone androsterone  Steroids Estrogens – female sex hormones ✓Synthesised in the ovaries ✓Responsible for female secondary sex characteristics and regulating the menstrual cycle O C CH3 OH O HO progesterone estradiol  Prostaglandins Prostaglandins have in common a 20-carbon skeleton including a cyclopentane ring ✓Made in the body from arachidonic acid ✓Arachidonic acid is manufactured in the body from the essential fatty acid, linoleic acid. ✓Prostaglandins have hormone-like effects, and are produced “on site” or “locally” at sites of tissue damage, infection, inflammation etc 1 7 5 3 9 COOH 8 6 4 2 10 12 14 16 18 20 11 13 15 17 19  Summary - polymers Polymers can be formed by condensation or addition reactions ✓Condensation – formation of polyester or polyamide, makes a water molecule too ✓Addition – formation of alkane by breaking alkene. No loss of atoms (i.e. no by-product e.g. water produced)  Summary – soaps, detergents Soaps are formed from triglycerides (fats, oils) ✓Functional group is carboxylate ion ✓Unable to function in hard water Detergents are formed synthetically ✓Functional group is aromatic sulfonate ion ✓Able to function in hard water Soaps, detergents have hydrophilic and hydrophobic parts ✓Cleaning dirt away means forming a micelle with hydrophobic tails pointing inwards and hydrophilic heads pointing towards polar solvent  Summary - lipids Fatty acids are the building blocks of most lipids ✓Can be saturated or unsaturated ✓Two essential fatty acids, rest made in the body Lipids are broken into categories ✓Saponifiable (contain ester functional group) ✓Non-saponifiable (does not contain ester functional grp) Triglyercides are tri-esters of glycerol ✓3 fatty acids react with alcohol functional groups on glycerol to make triglycerides ✓Animal fats and vegetable oils ✓Undergo hydrolysis, saponification and hydrogenation  Summary - lipids Waxes are simply long-chain esters ✓Not easily hydrolysed, good for protective coatings Phospholipids are triglycerides where one fatty acid has been replaced by a “phosphoric acid and aminoalcohol” group ✓Good emulsifying agents ✓Form cell membranes by arranging themselves in bilayers, hydrophobic tails pointed towards the middle Sphingolipids ✓The glycerol backbone is has been replaced by a long-chain aminoalcohol called sphingosine  Summary - lipids Steroids are lipids with a characteristic four ring structure ✓Function as emulsifying agents and hormones, and are present in the cell wall Prostaglandins ✓20-carbon ‘folded over’ structure of prostanoic acid ✓Have hormone-like effects in the body ✓Must be synthesised from essential fatty acids You aren’t expected to know individual molecules, just recognise the main features and functional groups Saponifiable vs. non-saponifiable Triglycerides, waxes, phospholipids, steroids, prostaglandins