UNIT 4 A2 ORGANIC CHEMISTRY MECHANISMS AND REAGENTS.

ALDEHYDES & KETONES Identified by Tollens reagent Fehling’s Solution Aldehydes are oxidised to carboxylic acids. Therefore, the Tollens’ and Fehling’s must be reduced. Tollens’ Reagent Sodium hydroxide, aqueous silver nitrate this produces a precipitate. Ammonia is then added to make aqueous [Ag(NH 3 ) 2 ] + This is reduced to silver when an aldehyde is added. Fehling’s Solution This is a blue solution containing Cu 2+ ions. When aldehydes are added and heated, these ions are reduced to cooper (I) oxide Cu 2 O, producing a brick-red ppt. AQA A2 text book, p64

ALCOHOLS FROM ALDEHYDES & KETONES ALDEHYDE KETONE PRIMARY ALCOHOL SECONDARY ALCOHOL Lithium tetrahydridoaluminate LiAlH 4 Sodium tetrahydridoborate NaBH 4 [H] Mechanism Nucleophilic addition The reducing agents produce the H - ion (the nucleophile). The carbonyl bond is polar, due to oxygen being more electronegative. First Step is the hydride ion being attracted to the ƍ + carbon. Second step, the product of first step gains a proton. AQA A2 text book, p66

HYDROXYNITRILES FROM ALDEHYDES & KETONES Mechanism Similar to making alcohols! Nucleophilic addition The reducing agents produce the CN - ion (the nucleophile). The carbonyl bond is polar, due to oxygen being more electronegative. First Step is the cyanide ion being attracted to the ƍ + carbon. Second step, the product of first step gains a proton from the solvent or hydrogen cyanide. ALDEHYDE KETONE HYDROXYNITRILE HCN KCN/H 2 SO 4 AQA A2 text book, p68

HYDROLYSIS OF THE NITRILE GROUP AQA A2 text book, p69 The nitrile is hydrolysed in acidic conditions, producing a carboxylic group. HYDROXYNITRILE H 2 O/ H + CARBOXYLIC ACID AMMONIUM

ESTERS FROM CARBOXYLIC ACIDS & ALCOHOLS CARBOXYLIC ACID ALCOHOLS ESTER WATER H 2 SO 4 or HCl cat, reflux AQA A2 text book, p71 No need for Mechanism But you do need to be able to draw and name ester. OH from carboxylic acid and H from OH in alcohol bond to produce water. First part of name comes from the alcohol, second from the carboxylic acid.

ESTER HYDROLYSIS AQA A2 text book, p74 ESTER WATER CARBOXYLIC ACID ALCOHOLS Acid Catalysed Hydrolysis Reverse of esterification. Dilute sulfuric acid or hydrochloric acid. Heat under reflux. Base-Catalysed Hydrolysis Form a salt Dilute strong base, sodium hydroxide. Heat under reflux. This method is quicker than acid catalysed. ESTER SODIUM HYDROXIDE ALCOHOLS SODIUM CARBOXYLATE Heat with excess dilute acid to produce carboxylic acid

VEGETABLE OILS & ANIMAL FATS Alkyl chain in Vegetable oils are unsaturated.Alkyl chain in Animal fats are saturated. TRIACYLGLYCEROLS or TRIGLYCERIDES (three “esters”) TRIESTERS AQA A2 text book, p74-75 TRIACYGLYCEROL No need for Mechanism Hydrolysed by heating with aqueous sodium hydroxide or potassium hydroxide. Produces glycerol (propane-1,2,3-triol) and sodium/potassium salt. SODIUM HYDROXIDE PROPANE-1,2,3-TRIOL SODIUM CARBOXYLATE Three molesThree moles produced

BIODIESEL No need for Mechanism Base catalysed Transesterification. Heating vegetable oil with methanol and sodium hydroxide. Produces methyl esters with long chains and propane-1,2,3-triol. TRIACYGLYCEROL SODIUM HYDROXIDE PROPANE-1,2,3-TRIOL METHYL ESTER AQA A2 text book, p75 METHANOL Three moles

ACYL CHLORIDES Mechanism Nucleophilic Substitution reactions. (two steps addition + elimination) Greater ƍ + on carbon due to Cl and O bond. 1 st Step (addition) nucleophile attacks carbon ƍ +. Pair of electrons in C=O is transferred to oxygen. 2 nd Step (elimination) lone pair of electrons on oxygen forms C=O, chlorine is eliminated. Hydrogen attached to oxygen atom breaks. AQA A2 text book, p76-81 ACYL CHLORIDE ESTER N-SUBSTITUTED AMIDE CARBOXYLIC ACID AMIDE water alcohol Primary amine ammonia Hydrogen chloride, HCl is the secondary product.

ACID ANHYDRIDE Mechanism Same as acyl chlorides. Secondary product is a carboxylic acid. Preferred in synthesis, cheaper, less violent reactions, no fumes of HCl ACID ANYDRIDE ESTER N-SUBSTITUTED AMIDE CARBOXYLIC ACID AMIDE water alcohol Primary amine ammonia Synthesis Dehydrate a carboxylic acid (P 4 O 10 cat) AQA A2 text book, p76-81

NITRO COMPOUNDS FROM BENZENE Mechanism Generate the nitronium ion. Nitric acid and sulfuric acid. Protonation of nitric acid, then protonated nitric acid breaks down. Electrophilic substitution(addition then elimination). Electrophile is attracted to the delocalized electron. C-H bond breaks and restores the stable delocalized electron structure. BENZENE UNSTABLE POSITIVELY CHARGED INTERMEDIATE NITROBENZENE Temperature should be kept at 50 o C. Further substitution occurs at 100 o C (1,3-dinitrobenzene). AQA A2 text book, p90-91

ICE DYES & DIAZONIUM SALTS PHENYLAMINEDIAZONIUM SALT Sodium nitrate(III), HCl Ice bath (chilled) Ice Dyes No need for mechanism but need to be able to draw compounds. Sodium chloride and water is also formed. AQA A2 text book, p92-93 Coupling Reaction (azo dyes) No need for mechanism but you need to be able to draw compounds. Diazonium salt reacts with phenylamine or other aromatic compounds to produce azo dyes. HCl is also produced. WATER SODIUM CHLORIDE

TRINITROTOLUENE, TNT No need for mechanism but need to be able to draw compounds. METHYLBENZENE2-METHYL-1,3,5-TRINITROBENZENE conc. HNO 3 conc. H 2 SO 4 AQA A2 text book, p93

FIEDEL-CRAFTS ACYLATION Mechanism Generate the electrophile. Aluminium chloride and acyl chloride. Electrophilic substitution(addition then elimination). Electrophile is attracted to the delocalized electron. C-H bond breaks and restores the stable delocalized electron structure. Aluminium chloride is regenerated whren [AlCl 4 ] - reacts with H +. BENZENE UNSTABLE POSITIVELY CHARGED INTERMEDIATE PHENYLETHANONE HYDROGEN CHLORIDE AQA A2 text book, p94

MAKING ALIPHATIC AMINES Mechanism If you can do this you can describe Amine acting as a nucleophile Amine acting as a base How to make secondary, tertiary amines and quarternary ammonium salts From Haloalkanes Excess ammonia reacting with primary haloalkanes. AMMONIA HALOALKANE AMMONIUM SALT HALIDE ION AMINE AMMONIUM HALIDE nucleophile NH 3 base NH 3 From Nitrile Amine can be made by reducing nitrile NITRILE AMINE LiAlH 4 H 2 /Ni AQA A2 text book, p [H]

MAKING AROMATIC AMINES Reduction of aromatic nitro compounds NITROBENZENE AMINE conc.HCl/Sn or conc. HCl/Fe 6[H] WATER AQA A2 text book, p101 NH 3 + INTERMEDIATE NaOH

ZWITTERIONS Acting as a Base Accepting protons. Acting as an Acid Donating protons. AMINO ACID H+H+ OH - AQA A2 text book, p HClSALT WATER NaOH SALT NITROGEN IS PROTONATED NEGATIVE CHARGE ON OXYGEN With Acid With Base

PROTEINS FROM AMINO ACIDS AQA A2 text book, p110 Amino group reacting with carboxylic group of another amino acid. PEPTIDE LINK Each link produces one water molecule. Condensation reaction. Can form ploymers (amino acids) AMINO ACID DIPEPTIDE WATER

AMINO ACIDS FROM PROTEINS Hydrolysis of peptide link. DIPEPTIDE AMINO ACID Heat Water 6 moldm -3 HCl for 24 hours AQA A2 text book, p112

ADDITION POLYMERS Mechanism Addition polymerisation Involves one functional groups. Carbon, carbon double bond. Need to be able to identify repeating units Taught in AS Chemistry Unit 2. AQA A2 text book, p AQA AS text book, p ALKENE POLY(ALKENE) Monomer Polymer

POLYESTERS Mechanism Condensation polymerisation Involves two functional groups. Polyesters are formed from a dicarboxylic acid and a diol. Carboxyl group forms an ester link with the hydroxy group. Need to identify ester link. Identify the repeating units. AQA A2 text book, p DICARBOXYLIC ACID DIOL POLYESTER WATER

POLYAMIDES Mechanism Condensation polymerisation Involves two functional groups. Polyamide are formed from a dicarboxylic acid and a diamines. Hydroxyl group from dicarboxylic acid reacts with hydrogen attached to nitrogen of polyamide. Forms an amide link. Need to identify amide link. Identify the repeating units. DICARBOXYLIC ACID DIAMINE POLYAMIDE WATER AQA A2 text book, p Questions on Nylon often appear on exams.

BIODEGRADABLE POLYMERS Esters and amides can be hydrolysed by water, acids, alkalis and enzymes. This is the same for polyesters and polyamides. Break ester link or amide link! AQA A2 text book, p POLYAMIDE DICARBOXYLIC ACIDDIAMINE DICARBOXYLIC ACIDDIAMINE SODIUM SALT OF DICARBOXYLIC ACID DIAMINE Water NaOH ACID With polyesters the secondary product is a diol. You need to be able to identify repeating units.