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A2 chemistry 5.4.2
Edexcel chemistry - nitrogen compounds
| Question | Answer |
|---|---|
| What are the physical properties of amines? | Characteristic fish-like smell (particularly large amines), high boiling points (London forces, hydrogen bonding), small amines are miscible with water (H bonding, London forces) |
| Are amines basic or alkaline, why + evidence? | Basic: lewis base (N is lone pair donor) and BL base (proton acceptor). REacts with water to form: RNH3+ + OH- (resulting solution is alkaline). Reacts with acids to form alkylammonium salt |
| What determines base strength? | Amount of electron density on N atom, how delta negative it is, more delta negative = accepts H+ more easily = stronger base. 3 strongest, +ve inductive effect, 3 alkyl groups. Aromatic weakest, lone pair partially withdrawn into benzene ring |
| Describe the formation of complexes between Cu2+ ions and amines | CuSO4 contains blue [Cu(H2O)6]2+. Small amount of amine: deprotonation, amine acts as BL base, blue ppt [Cu(H2O)4(OH)2]. Excess amine: ligand exchange, amine acts as lewis base, ppt dissolves to form a deep blue solution [Cu(RNH2)4(H2O)2]2+ |
| Which type of amines are more likely to form complexes? | - small amines> large amines - too much steric hindrance for large amines. - tertiary > primary - stronger base, N is more delta negative |
| Describe reaction of amines with halogenoalkanes | Amine/ Nh3 + halogenoalkane -> higher degree amine + HX, as long as HX doesn't protonate product further substitution occurs WITH A STRONGER NUCLEOPHILE, all Hs are successively replaced by R group -> 4ary amine salt, conc NH3, ethanol, heat in sealed tub |
| What is the final product more likely to be with excess halogenoalkane or excess Nh3? | Excess halogenoalkane: quaternary amine salts. Excess NH3: lower degree amines |
| Draw products of reaction between chloroethane and 2-aminopropane | C2H5 group added at 3 locations |
| Describe the reaction of amines with acyl chlorides | Forms N-substituted amide + alkylammonium chloride, H on N replaced by RC=O group, no further substitution |
| Draw mechanism/ equation for ethanoyl chloride + 2-aminobutane | Ethanoyl chloride + 2-aminobutane -> N-(2-butyl)ethanamide + butylammonium chloride |
| Draw structure of paracetamol + reactants | Ethanoyl chloride, 4-hydroxyphenylamine, forms N-(4-hydroxyphenyl)ethanamide + HCl |
| How can amines be produced from carboxylic acids, why are the conditions important + yield lower than acyl chlorides? | Carboxylic acid + amine -> N-sub amide + H2O, above 100 degrees. Below 100: acid-base reaction, carboxylate ion + alkylammonium salt. C-O bond weaker than C-Cl bond so lower yield |
| How can amines be prepared? | NH3 + halogenoalkanes (complex mixture hard to separate), reduction of amides/ nitriles with LiAlH4 (dry ether -> aqueous acid) or H2/Ni catalyst |
| What are the physical properties of phenylamine? | More soluble in HCl and organic solvents than water, high boiling point (H bonding, London forces) |
| How do the properties of phenylamine differ to benzene? | In neutral solutions, benzene ring is activated (interact, withdraw, density, susceptible) - bromination only requires bromine water + milder conditions. NH2 group: doesn't undergo nitration (deactivation) or friedel crafts (nucleophilic substitution) |
| How does phenylamine differ in reactivity to aliphatic amines? | N is less delta negative as lone pair interacts with π bonds, withdrawn, less accessible - weaker nucleophile, weaker base |
| Write equation for phenylamine + H2O | C6H5NH2 + H2O -> C6H5NH3+ + OH-, weak base, low Kb |
| Write equation for phenylamine + H2SO4 | 2C6H5NH2 + H2SO4 -> [C6H5NH3+]2 SO42- ... or: C6H5NH2 + H2SO4 -> C6H5NH3+ HSO4- |
| How does phenylamine react with halogenoalkanes? | Nucleophilic substitution forms secondary amine + HX, as long as HX doesn't protonate amine product then further substitution occurs, HX + phenylamine -> phenylammonium salt |
| Write equation for phenylamine + chloropropane | C6H5NH2 + C3H7Cl -> C6H5NHC3H7 (N-propyl phenylamine)+ HCl. HCl + C6H5NH2 -> C6H5NH3+Cl- (phenylammonium chloride) |
| How does phenylamine react with acyl chlorides? | Nucleophilic substitution forms a N-phenyl amide + HCl, H atom on amine N replaced by RC=O group, no further substitution, HCl + phenylamine -> phenylammonium chloride |
| How is phenylamine synthesised + isolated? | Heat nitrobenzene, Sn, conc HCl under reflux (produces phenylammonium ion), cool to RT adding EXCESS NaOH (forms phenylamine), isolate phenylamine (steam distillation, separating funnel, dry with drying agent e.g. anhydrous CaCl2 |
| Write the equation for this reaction | C6H5NO2 + 6[H] -> C6H5NH2 + 2H2O |
| What is the function of the tin? | Tin provides electrons for the reduction of nitrobenzene as it is easily oxidised |
| How do you test for phenylamine? | Add excess HCl and NaNO2, then phenol and NaOH in ice (0-10 degrees) - positive test is yellow/ orange ppt, azo dye |
| How is benzene diazonium chloride produced? | Phenylamine + HNO2, unstable, formed in situ from NaNO2 and excess HCl, 0-10 degrees c |
| Why is the temperature of this reaction so important | 0-10 degrees c. Too low = too slow, too high = benzenediazonium chloride decomposes and reacts with water to form phenol |
| How are azo dyes formed + chemical equation? | Benzenediazonium chloride + phenol + NaOH. C6H5N2+Cl- + C6H5OH + NaOH -> C6H5NNC6H5OH + NaCl + H2O. Nitrogen coupling reaction, electrophilic substitution, diazonium ion is strong electrophile as N is positively charged and an electrophile. Yellow ppt |
| What are azo dyes? | Dyes made by reacting benzenediazonium chloride with phenol and NaOH. Yellow/ orange ppt. Azo group: -N=N-. Conjugated, chromophores, absorb visible light. Hydrogen bond with fabric so good dyes |
| Draw amide functional group | RCONH2 /R'R'' |
| How can amides be formed? | * acyl chloride + NH3 -> amide + NH4Cl (WHITE SMOKE). * acyl chloride + amine -> N-sub amide + alkylammonium chloride. * carboxylic acid + amine -> N-sub amide + H2O ABOVE 100 DEGREES |
| Which of these reactions produces the lowest yield and why? | carboxylic acid + amine. 1) if below 100 degree c, neutralisation reaction. 2) still likely to undergo neutralisation reaction. 3) C-O bond stronger than C-Cl bond, OH is less readily lost |
| How can amides be hydrolysed? | Heat under reflux with aqueous acid: hydrolysed into carboxylic acid and ammonium salt. Heat under reflux with aqueous alkali: hydrolysed into carboxylate ion and NH3 |
| How can amides be converted to amines? | Reduction with LiAlH4 (dry ether, aqueous acid) or H2/ Ni catalyst. RCONH2 + 4[H] -> RCH2NH2 + H2O |
| How do polyamides form? | Condensation polymerisation - diamine + diacyl chloride / dicarboxylic acid -> polyamide + HCl/H2O, amide bonds |
| Define condensation polymer | Formed when monomers join together while eliminating a simple molecule |
| How are polyesters generically formed, and give a specific example + its uses | Diacyl chloride/ dicarboxylic acid + diol -> polyester +HCl/H2O. PET: benzene-1,4-dicarboxylic acid +ethan-1,2-diol -> PET + (2n-1)H2O. Plastic bottles: shatterproof, doesn't allow dissolves CO2 to escape |
| How are polyamides generically formed? | Diacyl chloride/ dicarboxylic acid + diamine -> polyamide + HCl/H2O |
| What reactants are needed to produce nylon-6,6, what are its properties + uses? | Hexanedioic acid + 1,6-diaminohexane -> nylon-6,6 + (2n-1) H2O, derived from benzene. Properties: polymer chains hydrogen bond, high melting point, high electrical resistance. Uses: tights, carpets, machine pieces, electrical switches |
| What reactants are needed to produce kevlar, what are its properties + uses? | benzene-1,4-dicarbonyl chloride + 1,4-diaminobenzene -> Kevlar + (2n-1)HCl. Properties: fire resistant, high strength:weight ratio, high tensile strength. Uses: fire proof clothing, bullet proof vests, aircraft parts |
| Define addition polymer | Monomers contain C=C bonds, π bond in 1 monomer breaks and it forms a sigma bond with another monomer, FREE RADICAL ADDITION! |
| What reactant is needed to form polypropenamide, what are its properties + uses? | Propenamide, cross-linking between chains by hydrogen bonding produces a gel that can absorb water + swell, uses: disposable nappies, soft contact lenses |
| How is polyethenol formed and why? | Ethenol is very unstable + turns into ethanal isomer. Ethenyl ethanoate -> poly(ethenyl ethanoate) -> poly(ethenol) by transesterification with methanol |
| Why is polyethenol water soluble at what affects its solubility? | Hydroxyl group on alternate carbon atoms, small monomer, many hydrogen bonds with water. Depends on how many ester groups are replaced by H from methanol |
| What are the uses of polyethenol? | Hospital laundry bags, coating for liquitabs (capsules containing liquid detergent) |
| What tends to be more biodegradable: addition or condensation polymers? | Condensation tend to have polar bonds, sites for nucleophilic attack, may be broken down in acid/ alkali. Addition hydrocarbons, no polar bonds, resistant to acids, alkalis, C-H bonds are strong, persist in landfill sites |
| What is a zwitterion? | Amino acids predominantly exist as zwitterions: COOH group of 1 amino acid protonates NH2 group of adjacent amino acid, forming COO- and NH3+, molecule doesn't have an overall charge |
| Why are amino acids solid at RT? | Positively and negatively charged ends of zwitterions attract each other by ionic bonds |
| Write equation for zwiterrion + HCl | +H3NCHRCOO- + HCl -> +H3NCHRCOOH Cl- SALT! |
| Write equation for amino acid + NaOH | H2NCHRCOOH + NaOH -> H2NCHRCOO- Na+ + H2O SALT + WATER |
| How can amino acids form esters? | Alcohol reacts with carboxylic acid group, conc. H2SO4 ensures COOH group is protonated |
| Describe the properties of amino acids as primary amines | HIGH PH to ensure NH2 group isn't protonated (no lone pair). Amino acid + halogenoalkane -> secondary amine, further substitution. Amino acid + acyl chloride -> N-sub amide + HCl, HCl + amino acid -> salt |
| How do separate amino acids? | Thin layer chromatography, stationary phase is Al2O3/silica gel on glass/plastic plate. Dissolve unknown AA in solvent, add spot, add spots of known amino acids, dip in eluent, rises by capillary action, spray with ninhydrin/heat, oxidises, purple |
| How do you identify amino acids? | Calculate Rf values then compare to databook, unique to amino acids. Compare distances travelled by known and unknown amino acids |
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