Colour by Design Flashcards
what is the formula for benzene?
C6H6
if Kekule’s structure for benzene was correct there should be…
3 bonds with the C-C length bond and 3 bonds with the C=C length bond
why was Kekules structure wrong?
all the C-C bonds in benzene are the same length
explain the structure of the delocalised model of benzene
the carbons are arranged in a ring
each carbon donates an electron from its p orbital. the p orbitals combine to form a ring of delocalised electrons
ethene + bromine is an example of what kind of reaction?
electrophilic addition
in the reaction ethene + bromine what is produced?
1,2- di bromoethane
why is benzene stable?
the electrons in the delocalised ring can get further away from each other so the negative charge is more spread out
when you warm benzene with concentrated nitric and sulfuric acid you get….
nitrobenzene
halogen carriers help to make good….
electrophiles
how do halogen carriers help to make electrophiles with polar molecules?
halogen carrier accepts a lone pair of electrons from the polar molecule containing a halogen. the lone pair of electrons pulls away the polarisation in electrophile increases, sometimes a carbocation forms
what is a carbocation?
an organic ion with a positively charged carbon atom
halogen carriers can be put an alkyl group on…
benzene
how can methylbenzene be made?
- carbocation formed from chloroalkane and AlCl3
- then the carbocation reacts with benzene via electrophilic substitution
- the halogen carrier gets regenerated when AlCl4- reacts with the H+ ion comes off the benzene
what type of reaction is the method to put an alkyl group on a benzene ring?
friedel-crafts alkylation
the general reaction when an alkyl group is put on a benzene is…
C6H6 + RCl –> C6H5R + HCl
catalyst - AlCl3
reflux
what conditions are needed to put an alkyl group on a benzene?
reflux
halogen carriers help halogens….
substitute onto a benzene ring
how do halogen carriers help halogens substitute into the benzene ring?
- halogen carriers polarise halogen molecules
- the +vely charges end of the halogen acts as an electrophile and reacts with the benzene ring
- electrophilic substitution reaction
what type of reaction is halogen substituting onto a benzene ring?
electrophilic substitution
halogen carriers can put acyl groups…
on benzene
what is the method for substituting a acyl group on a benzene?
- acylium ion is formed from acyl chloride and AlCl3
- the acylium ion acts as the electrophile and goes to react with benzene
- AlCl3 then gets regenerated
when an acyl group is substituted for a H atom on benzene what conditions are needed?
reflux
azo dyes are man made dyes that contain the azo group. the azo group is….
-N=N-
in azo dyes the azo group links…
two aromatic groups
why does delocalisation extend across the whole dye molecule?
it contains two aromatic groups making it very stable. the azo group becomes part of the delocalised electron system
what type of reaction makes an azo dye?
a coupling reaction
what are the 2 steps to making an azo dye?
- react phenylamine with nitrous acid to make a diazonium salt
- make the azo dye by coupling the diazonium salt with phenol
how is a diazonium salt made?
- HNO2 is made in situ from sodium nitrate and HCl
- HNO2 reacts with phenylamine and HCl to form benzenediazonium chloride.
it must be done below 5 degrees
when a diazonium salt is made why does it have to be carried out below 5 degrees?
to prevents a phenol forming instead
how is an azo dye made by coupling the diazonium salt with a phenol?
- phenol dissolved in NaOH to make sodium phenoxide solution
- stand it in ice and add chilled diazonium salt
- the azo dye precipitates out of the solution immediately
what does colourfast mean?
a dye cant wash out too easily or fade in the light
which part of a dye binds to the fabric?
its functional group
dyes that contain the amine group bind best to what material?
cotton rayon and linen
why do dyes with amine groups bond to cotton, rayon and nylon best?
NH2 form H bonds with OH groups. there are many OH groups groups in these materials.
are dyes with the functional group NH2 bound to the material strong? why?
no
hydrogen bonds aren’t strong enough
dyes that contain acidic groups bind best to what materials?
wool, silk and nylon
how do dyes with acidic groups join to wool, silk and nylon?
the acidic group binds to the -NH- links in fibres. the H+ ions move from dye to fibre molecule and ionic interactions hold them together
dyes that contain ionic salt groups bind best to what materials?
wool, silk and nylon
how do dyes with ionic salt groups bind to wool, silk and nylon?
bind with the -NH- links. the salt groups dissociate in when you dissolve the dye in water then acid is added to provide H+ to the NH links so slat groups will bind
the most permanent type of dye is….
fibre reactive dyes
why are fibre reactive dyes the most permanent type of dye?
they have a functional group that will react with the OH or NH group in the fibre, forming strong covalent bonds
what part of a dye molecule gives the dye its colour?
the chromophore
when light hits a chromophore how is light seen?
certain wavelengths are absorbed by electrons in the chromophore. visible wavelengths not absorbed will be seen as a particular colour
how does modifying the chromophore change the colour of a molecule?
it will change the frequency of light it absorbs
when functional groups conatining O and N are added to the chromophore why does the molecules colour change?
the lone pair of electrons becomes part of the delocalised system responsible for absorbing light
what groups are sometimes added to dyes to make them more water soluble?
ionic groups
how does light appear colored?
when electrons absorb light energy (UV or visible light) they are excited to higher energy levels. if the energy gap between filled and empty shells corresponds to frequencies of visible light then the molecule appears coloured. the colour will be complementary to the light absorbed
how do you make a aldehyde from a primary alcohol?
gently heat alcohol with potassium dichromate and distil the aldehyde out