Unit 2b The World of Carbon

1. Unit 2b The World of Carbon

2. Carboxylic acids • contain the carboxyl group, –COOH • name ends in –oic • usual rules of naming i.e. longest carbon chain must include –COOH; • number carbon atoms from end closest to –COOH; • branches assigned smallest number possible • e.g. • Uses: ethanoic acid – pickle food (vinegar), feedstock for paints; • benzoic acid – preservative and antioxidant in food • benzene-1,4-dicarboxylic acid – nylon production

3. Esters • contain the ester group, -COO- • made by a condensation reaction of an alcohol, –OH, with • an alkanoic acid –COOH giving an ester –COO- + water, H-OH • e.g. • first part of ester name from alcohol, second part from acid e.g. • pentanoic acid + butan-1-ol makes butyl pentanoate • the reverse reaction is hydrolysis • NaOH is often used for hydrolysis, rather than water

4. Uses of esters • smelly so useful as flavourings and in perfumes • solvents, e.g. in paints • making medicines

5. Percentage yield Percentage yield = actual yield x 100 theoretical yield

6. Polymers • very large molecules made from small monomers • Addition polymers: • made from unsaturated monomers (usually just the 1) • alkene monomer polyalkene product (only!) • alkenes made by cracking alkanes • polymers have carbon-to-carbon backbone –C-C-C-C- • e.g.

7. Condensation polymers: • made from monomers with 2 functional groups • (usually 2 monomers) • small molecule, usually water, made at same time • have O, and sometimes N, in backbone • polyesters, polyamides, methanal-based polymers

8. Polyesters • ester group –COO- • 1 monomer a diol, the other a diacid • repeating unit in brackets • linear structures, used for fibres • additional functional groups in monomers allow • cross-linking between chains; used for resins

9. Polyamides • amide group –CONH- • usually 1 monomer a diacid, the other a diamine • (protein monomers are amino acids) this polymer is nylon-6.6 as each monomer has 6 carbon atoms • hydrogen bonding between chains increases the • strength of the polymer

10. Methanal based thermosetting polymers • methanol made from synthesis gas (CO + H2) • and oxidised to methanal • examples are urea-methanal and Bakelite • electrical insulators • thermosetting polymers cannot be remoulded

11. Newer polymers Addition polymers Polyethyne – electrical conductor; used in high performance loudspeakers Poly(vinyl carbazole) – photoconductor; used in photocopiers Poly(ethenol) – water soluble; used in hospital laundry bags Poly(ethene) with carbonyl groups – photodegradable; used in packaging material Condensation polymers Kevlar – very strong; used in bullet-proof vests Biopol – biodegradable; high costs have stopped production

12. Natural Products • Fats and oils • good energy source • fats from animals; oils from plants and fish • esters; hydrolysis produces 1 mole glycerol: 3 moles fatty acids • fatty acids are straight-chain carboxylic acids, C4 to C24; • can be saturated or unsaturated • oils more unsaturated, more double bonds than fats. less • densely packed molecules so fewer van der waals interactions • hence lower melting points • hydrogenation of oils produces fats (vegetable oils margarine) • hydrolysis with NaOH produces soaps

13. Natural Products • Proteins • natural condensation polymers • polyamides ie contain many –CONH- groups • amino acid monomers e.g. • essential amino acids cannot be made by body, are obtained • through diet • digestion of proteins produces amino acids

14. Classifying proteins – 2 types fibrous: structural materials e.g. in skin, nails, hair globular proteins: involved in regulation of life processes e.g. enzymes, hormones. haemoglobin • Enzymes • specific, only catalyse on reaction • substrate fits enzyme on ‘lock and key’ principle • can be building up reactions, as well as breaking down • denatured by high temperature, shape irreversibly changed • optimum pH for activity e.g. pH 2 or pepsin, stomach enzyme