Module 6.1 Flashcards
(134 cards)
1
Q
What is Benzene
A
Benzene is a naturall occuring aromatic compound , which is a very stable planar ring structure with delocalised electrons .
2
Q
What is a model
A
a model is a simplified version that allows us to make predictions and understand observations more easily .
3
Q
what is the empirical formula and moleucular formula of benzene
A
-emprical formula is CH .
-It has the molecular formula C6H6 .
4
Q
what state is benzene in
A
It is liquid at room temperature and is a key ingredient added to gasoline as it increases the efficencey of the car engine .
5
Q
What is kekule’s model of benzene (1)
-Check page 122 on figure 1
A
Friedrick Kekule , was a German chemist who in 1865 suggested that benzene was a six membered rign with ALTERNATING SINGLE ND DOUBLE BONDS , between the carbon atoms .
6
Q
kekule’s model of benzene (2)
A
He discovered that when one group was added to benzene , onl one isomer was ever made ; but hwen two groups were added , they were always three structural isomers produced . He used this experimental evidence , about hte types of isomers produced when benzene reacted , this supported his theory .
7
Q
what is the first problem with the kekule model
A
unlike alkenes benzene is resistant to addition reactions .
8
Q
what is the second problem with the kekule model .
A
enthalpy of hydrogenation of benzene shows that benzene is much more stable than was predicted .
9
Q
what is the third problem with the kekule model
A
all six carbon bonds in benzene are the same length .
10
Q
why does benzene tend to undergo substitution of a hydrogen atom rather than addition reactions? why was this unexpected
A
using the kekule model , you would expect benzene to undergo similar reactions to alkenees .
-ethene will readily undergo addition reactions but benzene tends to undergo substiution of a hdygrogen atom rather than addition reactions .
-kekule tried to explain this by saying the double and single bonds changed position in a very fast equilibrium . check f2 .
11
Q
what is hydrogenaiton
A
hdyorgenation is the addition of hdyrogen to an unsaturated chemical .
12
Q
the enthalpy change for the complete hydrogenation of cyclohexene (this was expected for benzene as well )
A
using bond enthalpy data , we can calculate the hdyrogenaion of cylohexene , and cyclo1,3,5 hexatriene .
-cyclohexatriene is the kekule model of benzene .
13
Q
what is the enthalpy change of hydrogenation of benzene
A
it is actually -208kjmol , which shows it is 152kjmol more energetically stable than predicted .
14
Q
check figure 3 and figure 4 on page 123
A
…
15
Q
what are the bond lengths of kekules structrue and what techniqque was used to show this .
This evdience disporved kekule’s strucutre as all six bonds are the same length .
A
-Xry diffraction techniques were used , and they have shown all six crbon bonds in benzene is 0.140 nm , which are between c-c single bonds 0.14nm and c=c double bond at 0.135 nm .
-Kekule’s structure suggests that there should be three shorer c=c double bonds and three longer c-c single bonds .
This evdience disporved kekule’s strucutre as all six bonds are the same length .
16
Q
it is now thought that beznene has a delocalised electron strucutre . EXPLAIN
-DOES NOT SUPPORT KEKULE;S STRUCTURE
A
in the delocalised strucuture , each of the si crbon atoms donate one electron from its p-orbital . These electrons combine to form a ring of delocalised electrons above and below the plane of the moleucle .
-THe electrons in the rings are said to be delocalised as theya re bale to move freely within the ring and do not belong to a single atom . Therefore , UNLIKE kekule;s strucutures ,a ll bonds in this ring are identical so are the same length .
17
Q
so how many kjmol is benzne due to the delocalised electrons
A
about 152jkmol-1 . MOre stable than expected when using the kekule model . Beause so much energy is needed to disrupt this decoalisation benzene is ver stable and resistant to addition reaction .
18
Q
what structure can u use when representing benzene
A
kekule or delocalised strcture .
19
Q
what is a substiution reaction
A
where a group or atom is exchanged for another group or atom in a chemical reaction
20
Q
benzene derivative
A
a benzene ring that has undergone a substiution reaction .
21
Q
what happens when benzene undergoes substiution reactions
A
as benzene has delocalised electrons it is energetically more stable than initially calculated so it rarely undergoes addition reactions but it will undergoo substituion reacions ..
-In these reactions , a hdyrogen atom is substituted for a different group and a benzene derivative is formed .
22
Q
subtitute - chlorine atom
-what is the formula
-what is the naming prefix
A
-cl
-chloro
23
Q
subtitute - bromine tom
-what is the formula
-what is the naming prefix
A
-br
-bromo
24
Q
subtitute - nitro functional group
-what is the formula
-what is the naming prefix
A
-no2
-nitro
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subtitute - alkyl chains
-what is the formula
-what is the naming prefix
e.g - ch3
-e.g methyl
26
what is a single substiuted benzene derivative
check f1 on page 124
when one hdyorgen is replaced by another group a single substiution reaction has occurred . this compound can be named (check module 4 )
-STEM - the longest chain ofcarbon atom is the aromati ring and has the stem benzene .
PREFIX 0 ther eis one ethyl group on the ring so there is no need to nmber , SO , the prefix is ethyl , the name of this compound is ethylbenzene .
27
what is a double substituted benzene derivative
two hydorgen toms on different carbon atoms of benzene can be replaed by two groups . If the groups are different , the name is written as a prefix in alphabetical order .
-One group will be added first an dbe given carbon number 1 , the second group will then be given a number to state which carbon atom it is on , with respect to the first substituted group . When naming double substituted benzene dreivatives , the SMALLEST POSSIBLE NUMBERS SHOULD BE USED .
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SKIM OVER page 125
...
29
what are multiple substitutions
-further hydorgen atoms , on the aromatic ring can be subsituted . This may take a number of stages in an organic syntsynthesisheiss. For example , benzene can rect to make methylbenzene and then two nitro functiona groups can substitute a further two hydrogen atom .
-TO show there is more than one of the same functional group prefixes such as di and tri are used .
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what is an electrophilic substitution
it is a substitution reaction where an electrophile is attracted to an electron-rich atom or part of a molmoleculeeucle and a new covalent bond is formed by the electrophile accepting an electron pair .
31
what is a reaction mechanism
it is a model with steps to explain and predict a chemical reactin .
32
recap what makes benzene ring stable
electrons are delocalidelocadelocalizedlizedsed on the benzene ring . This makes the structure stable and unlikely to undergo additional reactins . As the ring , is so electron-dense it is susceptible to electrophilic attack and a hydrogen atom can be substituted by another group.
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electrophilic substitution (1)
-electrons above and below the plane of atoms in the benzene ring attract an electrophile .
-electrophile accepts a pair of pi electrons from the delocalised ring and make a covalent bond . This is the slowest step and known as the rate-detrminign step Find out more abt this in 5.1.4
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electrophilic subsitiuion (2)
-figure 1 - page 126
- a reactive intermediate is formed where the deloclaied electrons have been disrupted
-the unstable intermediae releases an H+ ion and the stable product is formed . This is a very fast ste[ .
-THIS REACTION MECHANISM can be summarised using curly arrows - where X+ represents a general electrophile .
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p.g127 nitration of benzene
this is an electrophilic substiution reaction where a hydorgen atom is exchanged for a nitrogroup (-NO2) . FOor the nitration of benzene the reagent iis CONCENTRATED NITRIC ACID , with concenrated sulfuric acid as a catalyst .
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nitration of benzene (3)
-what is added to generate the 2=no2+ electrophile
sulfuric acid is regenerated after the nitration and is thereofre a catalkyst . THe steps of the mechanism is shown below .
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nitration of benzene (2)
-how is the reaction set up
- write the balanced equation
-initially the concentrated nitric acid and concentrated sulfuric acid are mixed together ina flask held in an ice bath .
-The benzene is added and a reflux condenser is set up , keeping the mixture at 50 degrees to prevent further subsittiuion reactions occuring .
38
halogenation of benzene - does it happen directly why/why not
benzene does not directly react with halogen as the aromatic ring is too stable . A halogen carrier such as iron 9which forms an iron halide in situ 0 , iron halides or aluminium halides are used . The halogen carrier will generate a positive halogen ion .
39
halogenation carriers that can be used for chlorination
ALCL3 , FECL3 , or Fe
40
halogenation carriers for bromination
ALBR3 , FEBR3 OR FE
41
bromine can react with iron bromide (III)to form what ?
a positive bromine ion that can act as electrophile . This can be represented by the following balanced chemical equation .
-check sheet ofr equation .
42
bromine reacting with iron bromie - bromine i egenrated in situ , so what happens next
it can then attack the benzene ring and electrophilic substituion occurs ;
-the halogen carrir is a catalyst and regenerated at the end of the halogenation as the relesed H+ , from the benzene rng forms HBr . the follwoign balanced chemiccl equation illustraed this ;
check equation .
43
what is a friedel crafts reaction
it is a substitution reaction where hydrogen is exchanged for an alkul or acyl chain .
44
why is benzene not as reactive as alkenes even thoguh it is aromatic compounds and they are unsaturated
-in 4.1.8 we saw that ethene is the simplest alkene has a pi bond between the two carbon atoms , this is a region of high electron denisty and will readily undergo addition reactions to become saturated .
45
what does shaking etehene with bromine do
it causes decolourisation as the coloured bromine is used to form the colourless 1,2dibromoethane .
-check sheet f1 128 for bonding ethene .
46
if cyclohexene is mixed with bromine water what happens
an addition reaction occurs . the first part of the mechanism is the bromine moleucle having an induced diple due to the interaction of the pi bond of the cyclohexene
47
what happens when benzene is haken with bromine water and why is this suprising
this suprisiing result occurs even thought the electrons in benzene are delocalised in pi bonds . So benzene must have a lower electron density between the crbon atoms than alkene .
48
why is a hdyorgen carrier useful
when non-polar molecules like bromine approach the benzene ring , there is not enough electron densit betweent he carbon atoms to induce a diple and start the reaction . This is also the case when attempting to substitute alkl halides like haloalkanes . Byusing a halogen carrier a stronger electrophile can be generated and alkylation can occur .
49
how did friedel crafts come about
in paris during the 19th century , french chemist charles friedel worked with ajmes cradt to develop a technique for aromatic electrophilic subsitions where hdyorgen is subsititued for an alkyl chain
50
how does friedel crafts work
this occurs by breaking C-H bonds and forming a C0C bond and this is called allkylation . It is very difficult to add alkyl groups to benzene and this was a signifiant breakthrough in organic syntheisis . In all these reactings a strong LEWIS ACID (which acceps a apir of electrons see 5.1.9 is ussed as a catalsyst .
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52
friedel crafts reaction - haloalkanes like chloromethane are mixed with a halogen carrier such as iron (iII) chlochlorideroide , what happens
the halogen carrier acts as a catalysts and is regenerated at the end of the reaction .
-A reactive carbocation is made which undergoes electrophilic subsituion with the benzenne ring .
53
figure 3 shows he general mechanisms in gigure 3 shows a chloroalkane undergoing a friedel crafts reaction , what is r
R is an alkyl group , This reaction will occur at room temperture .
54
multiple subsitiutions are likel so therefore what is likel to be made . hwo can these things then be separated
multiple substisubstitutionsutions are likleh and therefore a mixture of prodcuts is amde . The products can be separated using fractional distillation or chromatogrpahy. THe actual yiel of a singl-susbstsingle-substituteditued porduct can be imporimprovedved by adding excess benzene .
55
whhy is the mixture of products caused
the mixture of products is causes as each successive subsitituion makes the delocalised pi eelctrons more nucleophilic and therefore more susceptible to eelctrophilic attack . This increase in reactivit is due to the alkyl chin donaitng electrons to the aromatic ring .
56
what is an acyl chloride
an acyl chloride has the funcitonal group RCOCL , and is very reactive . This can be used in a Friedel crafts reaction as the halogen carrier to substiute jjus one hydrogen atom . As the carbonyl group withdraws electrons from the aromaic rings , a less reactive ketone is made . So , only one substitution can occur .
-This reaction is clled acylation . The reaction mixture is held at about 60 degrees for 30 mins udner reflux for the reaction to occur .
57
Meaning of phenols check f1
are a class of aromatic compounds wheere a hydroxyl goup is directly attaches to a aromatic ring .
PHENOL IS THE FIRST MEMBER OF A YPE OF AROMATIC COMPOUNDS WHERE A HYDROXYL GROUP (-OH) is atatched dirctly to an aroamtic ring .
58
what happens if the hydroxyl group is attached to an alkyl chain on the aromatic ring check f2
then the compound is no longer a phenol derivative . It would be described as an aromatic alcohol .
59
phenol is a weak acid meaning what
it partialy dissociates in water . The chemical equilibrium cna be shown in a blanced chemical reaction .
-As a weak acid , phenol will react with strong base , to form salt and water . You can find out more aout reactions of weak acids in topic 5.1.10 , a balanced chemicl equaiton illlustrates the eaction between phenol and sodium hydroxide check sheet for equaion .
60
why is phenol a weak acid
-it is a weak acid because it reacts with strong bases such as NaOH .
-HOwever , it is a weak acid becasue it does not react with carbonates . Phenol will not react with weak bases such as sodium carbonate .
61
reactivity of phenol
-phenol is more reactive than benzene . This is due to the p-orbital electron from the oxygen of the hydroxyl group adding to the delocalise electrons of the aromatic ring .
-So the pi system of the aromatic ring becomes MORE NUCLEOPHILIC . tHE ICNREASE IN ELECTRON density allows the aromaic ring in phenol to be more susceptible ot electrophilic attrak as it can induce a dipole in non-polar moelcules .
62
why is the aromatic ring in phenol omre electron dense
so it can induce a dipole in the non-polar bromine molucle . So phenol can undergo direct halogenation unlike benzene .
63
what is the directing effect
is how a functional group attached directly to an aromatic ring affects which carbon atoms are more likely to undergo substiution .
64
phenol will readily undergo electrophilic substiutions with what
a vareity of reagents without the presence of a catalyst . This enhanced reactivity is due to extra electrons from the oxygen on the hydroxyl group being donated to the pi systems of the aromatic ring .
65
will pheno undergo bromination
-what is the products if it does
phenol will undergo a triple subsiituion reaction wiht bromine water at room temperature . The balanced chemical equaiton for this reaction is shown in this equaiton .
-The resulting product is a white precipiate of 2,4,6 tribromophenol which smells of antiseptic .
66
phenol's reaction with niric acid (1)
phenol will undergo a single substiutiion reaction with dilute nitric acid (HNO3) at room remperature . This reaction forms a mixtrue of 2-nitrophenol and 4-nitrophenol . The balanced chemical equaiton for this reaction is shown
-p.g 132
67
phenol nitration (2)
-unlike nitration with benzene , this reaction does not require concenraed nitric acid or sulfuric cid catalyst .
-however , if concenrated nitric aid is used , a triple substitution occurs forming 246 trinitrophenol .
68
why may substiution reactions can be more fvourable for certain carbon atoms whn a functional group is directly attached to the aromatic rings .
-In pehnol the hydorxl group pushed additional electrons into the pi system . This makes substiuion reactions many occur on the 2 and 4 positions of the aromatic ring .
-The hydroxyl group activates these carbon atoms so that thier rate of substiution is faster than the other positions .
-This is known as a 2 and 4 directign effect . This effect is more pronounced in aromatic compounds with an NH2 , group directly attached to the aromatic ring .
69
what happens when a no2 groups are directly attached to the aromatic ring , what happens
a 3 directing effect is seen . THe nitro group withdrws electron from the pi system and the rate of substiution highest on the third carbon atom .
70
what is important about a reaction pathway in organic syntheiss
it is important that a reaction pathway can be designed to maximise the desired product . By considering the electron donating or withdrawing effects of a directl attached functionl group , predictions can be made as to the position in which substiution will take place .
71
what is a nucleophile /
it is a species attracted to an electron-deficient part of a molecule ,w here it donates a pair of electrons to make a new covalent bond ..
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difference between a ketone and a aldehyde
a carbonyl functional group is c=0 . If the functional group is on the end of the carbon atom , an aldehyde is formed ; if he carbonl is not at the end of a carbon chain , then a ketone is formed . Each class of compounds has different properties .
73
aldehdyes undergoing oxidiation to form what
a carboxylic acid
74
what are the regaents for oxidation of aldehyde
potassium dichromate K2CR207 and sulfuric acid H2SO4 . Reganets rect in situ to form the oxidising species
--CR2O72- and H+
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look on page 134 , for balanced iconic equaiton for the oxidiaion of ethanal to ethanoic acid
...
76
how are oxidising agents summaraised as check 134
what is the process , what colouor changes are we gonna see for oxidation of aldehydes
in the lab , the reaction mixture is gently heated under reflux . As the reaction proceeds , a colour change is observed from orang e to green , due to he oxidation state of the chromium changing .
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nucleophilic addiiton reactions on carbonyl compounds (1)
-carbonyl compounds have a dipole in the c=o funcional group .
-This makes them susceptible to he nucelophilic attack on the delta positive carbon atom .
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nucleophilic addition reactions of carbonyl compounds (2)
a nuclephile donates a lone pair of electrons to the electron-deficient carbon .
-Simultaneously the pi bond in the c=o , breaks and a reactive intermediate is formed . The exra electron pair is quickly donated to the neighbouring hydrogen to form an alcohol group and the stable porduct .
79
how can nucleophilic addition reactions can be modelled in a general mechanism
check figrue 3 on pge 135
where r is an alkyl group or hydrogen , H-A is a small molecule like H20 , OR HCN and Nu- is a nucleophile .
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what is sodium tetrahydriodoborate (III)
Sodium tetrahydridoborate (III0 is more commonly known as sodium borohydriide and has the formula NaBH4 . It is a reducing agent used commonly used in organic synthesis . This compound is made of a BH4- ion , which acts as a source of hydride ions , H- .
-The hydride ion , is he species that is invovled in the electrophilic addiiton and reduction of carbonyl compounds to alcohols .
81
The reducing agent can be summarised as (H) , the simplified balanced chemical equation for the reduction of pentan-2-one
check equation
82
wha is hydrogen cyanide
-other sources of cyanide is NaCN
hdorgen cyanide is a weka acid that will partially ionise in solution a cyanide nucleophile with a negative charge on the carbon atom is formed the balanced chemical euation for hte reaction is on p.g 135 .
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CAN CYANIDE REACT DIRECTLY with carbonyl compounds
no , but when the reaction is acidified , the carbonyl functional group becomes more reactive as polarity of the c=o bond is increased .
84
how can hydorgen cyanide reacition be summarised , check page 135
the reaction can be summarised as a mechanism in the second step , the hdyogren could also be obtined froma nother small moeleucle in the reaction mixture such as ethanol .
-Adiition of cyanide allows furhter arbon atoms to be added to the organic moleucle . In this reaction , a h dyeoxynitrile is fomred which is an important chemical used in many industrial processes .
85
why do aldehydes and ketones react differenlty
as they have c=o functional groups in different places on their carbon chain . This results in them having differnt chemical properties . THeir different reactions wih the same reganes can be used to disitinguish them between these classes of carbonyl compounds .
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how to test for a carbonyl funcitonal group
BRADY;S REAGENT , is an orange transparent mixture of methanol , sulfuric acid and a solution of 2,4DNP . When this is added to an aldehdye or ketone a yellow/orange precipitate of a 2,4DNP derivative is seen .
-No recipitatio is observed with a carboxylic acid or an ester despite these compounds also having the c=o bond .
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indetifying a specific aldehyde or ketone (1)
after a positivity brady's reagent test , fruther procesing of the precipitate allows the specific aldehdye or ketone to be identied .
-the 2,4 dinitrophenylhdyraozne derivative precipite can be collected by filtiriation and purified using recrystallisation . After drying , the accurte melting point of the pure porduct can then be measured through experiment .
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identifying aldehyde or ketone (2)
-the aldehyde or ketone can be identified by compring the melting point of the 2,4 DNp hydrzone derivative ppt with a database .
-The database is a list of accurately measured melting points of the 2,4 dnhyrazone deriviatives listed against the aldehdye or ketone that made it .
89
identifiyig a specific aldehdye or ketone
although every pure chemical has a specific melting and boiling point that would allow identifiation , this is experiemntally difficult for simialr ketones .
-Ketones with a similar chain length have very similar boiling points making it challenging to experimentall distingush between them . However , 2,4 DNPhydrazone derivatives have very different melting points .
90
tollen's reagent is a two stge process explin
tollen's reagent is also called ammoniacal silver nitrae , is a colourlcess chemicl that is made in a two stage process .
1.sodim hdyroxide solution is dded to silver nitrate solution until a prown ppt formed .
2.d ilut ammonaia is added drop-wise until the brown ppl redissovles .
91
how is tollen's regent ca be used to disitnguish between n aldehyde a ketone .
-it is a weak oxidisng agent and can react with the carbonl funcitonal group in an aldehyde but not a ketone . when tollen's ragent is added to a etone there is no reaction . This is because ketones cannot be oxidised further . When tollen;s reagent is added to an aldehyde a silver mirror is observed .
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what happens when aldehdye react wiht tollens reagent
a redo reaction occurs . the silver ions are reduced and he aldehyde fucntional group is oxidies .
-the balanced ionic equaiton for the oxidation of the silver ions is i the sheet .
93
oxidation of an aldehdye usinjg tollen's reagent (20
THIS REACTION causes silver metal o be ppted out and htis is observed as a silver mirror effect on the isnide of the reaciton vessel .
-simultaneously the aldehyde funcitonal group is oxidies ot a cabroxylic acid
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what is a base
a chemical that will react with an acid .
95
strucutre of methanoic acid
HCOOH
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96
97
Strucutre of ethanoic cid
CH3COOH
98
Strcture of propanoic acid
CH3CH2COOH
99
Butanoic acid
CH3CH2CH2COOH
100
Solubility of caboxylic acids
small carboxylic acids like those listen above are very soluble in polar solvents like water . This is because hdyrogen bonds can be formed betweent he carboxlic acid functional group and water .
-As the hydrocarbon chain of a carboxlic acid increases in size , the solubility decreases This is because only the polar carboxylic acid functional group can form hdyorgen bonds with the water . sO , AS MORE OF THE MOELCULE BECOMES NON-POLAR THEN SOLUBILITYW ILL DECREASE .
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CHEMICAL Properties of carboxylic acids
carboxylic acids are weak acids , as they partially ionise in solution releasing the H+ ion , fromt he carboxylic acid group forming a carboxylate ion . So this class of compounds will undergo typical acid reactions .
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102
what reeactions will happen faster , carboxylic acid or strong acid
carboxylic acid reactions will haappen at a slower rate than with a strong acid as the pH is higher nd therefore the cocnenration of H+ will be lower .
103
reactions wth metals
carboxlic acids will react with metals above hydrogen in the reactivity series to make hdyorgen and a metal salt . The name of the salt is generated from the acid . THe suffix of he acid changes from oic acid to oate . check page 139
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reaction with metl oxdies
metal oxides react with acids and theorefroe can be classified as abses . Carboxylic acids will react with metal oxides to make water and a metal salt .
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reaction with metal hdyroxidies
group1 metal hdyroxides are soluble bases that realease OH- . Carboxylic acids will react with emtal hdyroxides to make water and a metal salt .
106
reaction with metal carboantes
metl carbonates are also bases , carboxylic acids will react with metal carboantes to make wter carbondioxide and a metal salt .
-Group1 metal can also form meal hdyrogencabronaes his is where he carbonic acid H2CO3 , has had onl one proton exhcnaged for a metal ion to form the metal hdyrogencarbonate where MHCO3 where m is a group1 metal .
-ACIDS WILL ALSO react with this class o compound to form a salt water and arbon dioxide
107
what functional group do esters contain
esters contian the functional group R-COO-R where R and R are alkyl groups that may be the same or different . This class of compounds are cabroxlic acid derivtives ehre the H of the acid group has been replaced with an alkyl chain .
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physical properties of esters
ESTER ARE FOUND FREQUENTLY IN NATURE AND HAVE A Pungent smell . Syntheic esters have many uses inclduing solvennts rtifical fruit flavourings and perfumes .
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naming esters - how to do it
-to nam en ester look at the structure of the ester - paritcualrly the ester funcitonl group . The first part of the name is the alkul chin with carbon atom bonded to only one oxygen atom . TH esecond part of the name is the alkyl chain containig the c=o carbon atom followed by h suffix oate .
-chekc oage 140 for table
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how to prepare small ester
add an alcohol and a carboxlic acid are heated gently in the presence of a sulfuric acid catalsyt .
-esterifiicaiton is a reversible reaction and ha s a low rate of reaction . F2 shows the strcutural formula chemical equaiton for an esterification reaction to make thyl ethanoate chec f2
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how canesters be separated during reaction
as the ester is volatile with the lowest boiling point of the chemicals it can be separated fromt he reaction mixture using distillation . The separation has to happen quickl to prevent the reverse reaction occuring .
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how to prepare large ester
the reaction mixture will need to be heted under reflux until ewuilibrium has been established .The ester can be separated using frctional distillation .
-This method of preparation of an ester is not suitable of rphenol or its derivatives as the rate of reaction is so slow .
114
how do acid anhydride react will alcochol
an acid anhydride is an acid derivative that is more reactive than a similar carboxylic acid . It is made by the removal of moleucle water from two carboxylic acid moleucles .
115
acid anhydrides will react with alcohols including phenols and its derivatives to make an ester , describe this this method of ester production
this porduction of ester production is not reversible and therfore has a yield thann using a carboxlic acid . The rae of rection is still slow but cnan be increased byg ently warming the reaction mixture f4 shows the formaiton of methyl ehtanoate usingan acid anhydride .
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what is a hydrolysis
hdyrolysis is a chemical reaction where water breaks down another product . Esters can undergo hydrolysis to form an alcohol it is the reverse reaction of esterification . By varying the condition seither carboxylic cids or carboxlte alts re formed s the other product .
117
wha happens when esters are reluxed with a catalst of hot aquous acids
such as dilute sufluric acid or dilute hdyrochloric acid the ester ill decompose reversibly inot an alcohol and a carboxylic acid . THe following equation illustrates the hdyrolyis of propyle htoanote .
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alkaline coniditons ndiitons reactuion of naoh with ester fo rexample
alkaline chemicals are bases react wih cids that can dissolve in water . when an ester is refluxed with a hot aqueous alkali such as potssium hdyroxide or sodium hdyrocide , it will decompose into n alacohol nd cabroxylate salt . This reaction is not reversible .
-Alkaline hdyrolysis of esters is used to make soaps therefore it is also clled SAPONIFICTION . the follwoign ewuaiton illustrates the saponficiaiton of ethyl propanoate .
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what are acyl chlorides
acyl chlorides contain the functional group R-COCL where R is an alkyl group .
This class of compounds are carboxylic acid derivtives where he -OH , of the acid group has been replaced with a chlorine atom ,
-the name of of this class of compounds comes from the hdyrcarbon chanin RCO , which was once known as an acyl group .
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what are sall acyl chlorides like
small acyl chlorides are fuming (a visual gas or vapour being released ) colourless liquids . They are very reactive with chlorine aom being substituted for other groups.
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check structure of acyl chloride propanl chloride
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122
check strcutre of acyl chloride butanoyl chloride
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123
check strucuture of acyl chloride - pentanoyl chloride
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124
how is the acyl chloride separated
using distillation . The balanced chemical reaction shows the formaiton of ethanoyl chloride .
125
how to make an acyl chloride
the OH group on a carboxlic acid must be substituted for a chlorine atom .
-One method is to use SOCL2 , which is liquid at room emperature and redily reacts with a carboxylic acid to make the desired product .
PRODUCTS - sulfur dioxdie and hydrogen chloride gases are also made .
126
how do acyl chlorids form esters
-they react with alxohols to make an ester . This is the method of ester production is not reversible and therefore has a HIGHER YIELD , than using a caroxyclic acid .
-The balanced chemical reactions shows he formation of an ester ethyl ethanoate from an acyl chloride .
127
how can alcohols make esters
they can react with carboxlic acids to make esters . Like alcohols , phenols have an oh group but they do not rect easily with carboxylic acids .
-Therefore ,t o amke an ester from phenols , the acyl chloride method mut be used . HOwever , the reaction is also violent and produces corrosive fumes of HCL
127
what happens when a small acyl chlorides are added to water
like ethanoyl chlroide , when it is added to water , it quickl hydrolyses to produces a carboxlic acid . This is a very exothermic reaction and misty gumes of HCL are igven off .
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what happens when an acyl chloride recacts with a primary amide - e.g ammonia
a primary amide is produced . To prepre ethanamide ,e htanol chloride is added to a concnetrated ammonia solution . This quickly produces a mixture of solid ammonium chloride and ethamide observed as whie smoe . SOme of the producs remain in a colourless solutions .
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when an acyl chloride reacts with a primary amide what happens
the product is a secondary amide , where the nitrogen has one hydogen atom atom directly bonded to it . The nitorgen atom also has two organic groups attached and is often called a N-substituted amide
-A white solid compounds , of N-ethylethamide , can be made from ethanoyl chloride and a cold cocnentrated solution of ethylamine .
