Mechanisms a2 organic Flashcards
Optical isomerism mechanism (nucleophillic addition) aldehydes to hydroxynitriles
acidified kcn and h+ or acidified hcn. so– :CN- arrow to the delta positive carbon under the c=o bond. then arrow from middle of c=o bond to the oxygen. that makes :o- then join your cn at the bottom, put an arrow to a h+ floating around and then you form a hydroxyalkanenitrile.
carboxylic acids are weak acids, what do they disassociate to make
carboxylate ion and a h+. equilibrium lies to the left because it disassociates poorly.
what do acyl chlorides react with
water, alcohol, ammonia and primary amines
acyl chloride and water and observations
carboxylic acid +hcl. vigorous reaction, white misty fumes of hcl produced
acyl chloride and ammonia
produce amides. again vigorous, white misty fumes of hcl produced
acyl chloride and alcohol
esters, again hcl produced as well white misty fumes vig rec
acyl chloride and primary amines
produce n- substituted amides. and hcl. the h is the one thats substitued from the n. so its n substitued because it donates the hydrogen.
nhch3 +hcl for example when you react ch3nh2 with an acyl chloride.
what do acid anhydrides react with
the same as amines, water ammonia alcohol and primary amines. except these reactions are less vigorous and this is why acid anhydrides are used as opposed to acyl chlorides.
acid anhydride and water
2 carboxylic acids
acid anhydride and alcohol
ester and carboxylic acid
acid anhydride and primary amine
n substituted amide and carboxylic acid
the actual mechanism for reacting an acyl chloride with an alcohol. you know it already forms an ester and hcl from the simplified way. what mechanism is this
nucleophillic addition elimination
you have your acyl chloride and set out your alochol below it like this. R-O:: - –H on the other side and put it like a upside down L. (the o has 2 lone pairs o it)
arrow from o to c. then from c=o bond from c to o.
then this forms intermediate w c-cl on top o:- on the right and at the bottom the alcohol joined but w o+-r-r
then arrow from the o:- to the c to reform double bond. then arrow from c to cl to eliminate cl:-
then you have your semi ester w alcohol attached. then cl:- attacks hydrogen on alcohol and then arrow from h to o+ this eliminates h as well forming hcl. thats it thats your ester.
how is aspirin made
aspirin is an ester made by reacting ethanoic anhydride or ethanoic chloride with salicylic acid. makes aspirin and a carboxylic acid.
why use ethanoic anhydride in industry vs ethanoic chloride
safer as less corrosive, does not react as vigorously with water, does not produce the toxic hcl gas, it is cheaper. re
reactions of arenes what mechanism is it and why
they undergo electrophillic substitution reactions.
because, benzene has a high electron density as it has a delocalised ring of electrons, this is attractive to electrophiles.
Benzene is also stable so unlike traditional alkenes they do not undergo electrophillic addition reactions as this would disrupt the stable ring of electrons.
instead they undergo electrophillic substitution reactions where the hydrogen or a functional group are substituted for an electrophile
the two mechanisms of arenes
friedel crafts acylation and nitration reactions
fridel crafts acylation
in order to add onto the benzene what must the electrophile have
benzene is too stable and so is difficult to react, when an acyl group (RCO- ) is added onto a benzene it makes the structure weaker and more easier to modify to make useful products.
it must have a very strong positive charge, the acyl group isnt strong enough therefore we have to carry out a prep step
our prep step
we can use a halogen carrier eg alcl3 which will produce a much stronger electrophile with a much stronger positive charge. so in fridel crafts acylation we have to react an acyl chloride with AlCl3 to form a strongly postive electrophile.
alcl3 accepts a pair of electrons away from the acyl group, this forms a positive carbocation r-c (+)=o and Alcl4- (this will be reformed bc it is your catalyst so alcl3 will be back)
the actual mechanism
we react the electrophile with a benzene to make a less stable phenylketone under reflux and a dry ether solvent.
from benzene ring a arrow to the positive carbocation. this then disrupts the ring of delocalised electrons and it forms a positive charge in the benzene with a ring not extending beyond the adjacent carbons to the ketone. you also have your hydrogen c-h on that remember.
then you have your alcl4 structurally drawn next to it and arrow from the cl to the hydrogen as your alcl4- is attracted to the postively charged ring and cl breaks away and then from the c-h bond to inside of the benzene ring to reform the benzene ring.
that then forms your less stable phenylketone and hcl + AlCl3
nitration of benzene
useful as it allows us to make dyes for clothes and explosives. if we heat benzene with conc h2so4 and conc hno3 then we form nitrobenzene. but we have to make a poweful electrophile first.
the prep step
hno3+ h2so4–> h2no3+ +hso4-
the h2no3+ decomposes to form the electrophile
hno3+–>No2+ + h2o
We know use the nitronium ion and react this with benzene to form nitrobenzene
the mechanism
pretty much same as friedels acylation. arrow from ring to that, then you have your o2n and h off the same carbon. the ring is halved with a positive charge in the middle. from the c-h bond an arrow moves back into the ring to reform it. that forms your nitrobenzene +h+
The h+ reacts with the hso4- in the prep step and that reforms your h2so4 catalyst.
important about nitration and its uses
a temp below 55 degrees will ensure a single No2 subsitution, above this will result in multiple substitutions.
dyes and pharmaceuticals can be made by reducing nitrobenzenes to aromatic amines. (benzene with nh2 attached)
explosives- made from nitrobenzene
reduction of nitrobenzene (reducing agents for nitrobenzene to aromatic amines- benzene w nh2 attached)
reacted with sn and conc hcl. so sn or hcl
when you reduce nitrobenzene how many hydrogens do you need
3h2 or 6h to make the aromatic amine nh2 and 2h2o
how to make aliphatic amines pros and cons
haloalkane and excess ammonia. nucleophillic substitution.
reducing nitriles (nickel or pt catalyst and h2 gas- catalytic hydrogenation)
or use a strong reducing agent eg LiAlH4 and dilute acid dissolved in dry ether
pros cons
impure, lone pairs of electrons can form sec tert quat amines.
this forms primary amines. and this reac is also more expensive, nitrogen can act as a nucleophile.
catalytic hydr= cheapest, high temp and high pressure, pure product
using LiAlH4= more expensive as it is more exp.
reacting haloalkanes w excess ammonia
nucleophillic sub reaction mechanism. ammonia is a nucleophile that attacks the positive carbon on the c-hx and then arrow to the halogen. this eliminates the cl:- and instead we have the nh3 attached on the end. and then draw it out properly with n+-h-h. then another ammonia molecule’s lone pair attacks the hydrogen on the nh3 and then that moves up to the n+
that forms your primary amine and nh4+cl- (ammonium chloride salt)
the primary amine can still act as a nucleophile though. and can react with the haloalkane to form other types
reducing nitriles- catalytic hydrogenation to make primary amines
h2 gas and nickel or platinum catalyst, high temp and pressure pure product made. cheapest way
r-ch2-cn +2h2–>r-ch2-ch2-nh2
Reducing nitriles w LiAlH4 to make primary amines
strong reducing agent and dilute acid. more expensive, reducing agent dissolved in a dry ether.
R-ch2-cn + 4(H) —> R-ch2-ch2-nh2
making aromatic amines
made by reducing nitro compounds eg nitrobenzene to form phenylamines. used to make dye stuff and pharmaceuticals
reduction and we use 6h or 3h2.
how does reducing nitro compounds work
we react it with 6(h) we use tin and conc hcl. —-> so they go above and below the arrow (we heat nitrobenzene under reflux with conc hcl and tin to form a phenyl ammonium salt. eg c6h5nnh3cl
then what
when you have your c6h5nh3cl react this with naoh so alkali. this will then give you your phenyl amine c6h5nh2 +nacl+ h2o.
this is done at room temp bc it goes from less stable to more stable.
so in conclusion, tin conc hcl and then naoh to form the phenyl amine from the phenyl ammonium salt
reduction of a ketone or aldehyde with nahbh4
add 2(h) so the first h is a h:- and that attacks the c=o carbonyl group and then that forms o:- and then arrow from the lone on the o towards another h, but this time h+ to form a hydroxy. so you form your primary or secondary alcohol depending on your aldehyde or ketone
carboxylic acids and sodium carbonate and hydrogencarbonate
ch3cooh+ nahco3–> ch3cooNa +h2o+ co2
ch3cooh + Na2Co3–> 2ch3cooNa +h2o +co2
esterification
carboxylic acids and alochols/ acid anhydrides in prescence of strong acid catalyst eg sulfuric acid. this is for cooh oh esterification forming a carboxylic acid and water.
for acid anhydrie it forms an ester and a carboxylic acid
ester hydrolysis
using h2o, can be sped up by using an acid or a base
acid hydrolysis
dilute acid eg hcl. ester+h2o–> (h+) on top of arrow carboxylic acid and alcohol.
this reaction is reversible so not as high atom
economy
conducted under reflux
base hydrolysis
uses a base eg naoh under reflux.
this forms a carboxylate ion and alcohol bc we have oh- reacting not water
coo- + alcohol.
if we use naoh we make coona which is a soap (carboxylate salt) and this is saponification
making soap with hydrolysing animal fats and vegetable oils with sodium hydroxide
this uses animal fats to make soap
glycerol+ fat reacts w 3naoh–> glycerol and your sodium salt which is your soap. 3the bits on the end, coo-na+
vegetable oils
can be converted into biodiesel by reacting oils with methanol and using koh as the catalyst
oil+ 3methanol–> glycerol+ methyl ester
methyl esters can be used for biodiesel
