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A2 chemistry 5.4.2

Edexcel chemistry - nitrogen compounds

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 Aromatic weakest, lone pair partially withdrawn into benzene ring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
Created by: 11043



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