Unit 2b The World of Carbon

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

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

Uses of esters

• smelly so useful as flavourings and in perfumes

• solvents, e.g. in paints

• making medicines

Percentage yieldPercentage yield = actual yield x 100

theoretical yield

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.

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

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

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

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

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

Natural ProductsFats and oils

• good energy source

• fats from animals; oils from plants and fish

• esters; hydrolysis produces 1 mole glycerol: 3 moles fatty acids

• hydrolysis with NaOH produces soaps

• 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)

Natural ProductsProteins

• 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

Classifying proteins – 2 typesfibrous: 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