as chem: halogenoalkanes and alkenes, quick q's

im not sure wat these mean, cos at the mo im writing notes on halogenoalkanes and alcohol

Halogenoalkane:

(iii) halogenoalkanes as synthetic intermediates in chemistry.

why are they synthetic intermediates and wat makes it useful?

outline the role of chemists in minimising damage to the environment by, for example, the development of alternatives to CFCs so that depletion of the ozone layer

r there any other roles for halogenoalkanes?

alkenes

outline the role of chemists in minimising damage to the environment by, for example, the removal of toxic waste products (such as HCl) during disposal by combustion of halogenated plastics (such as pvc)

how is HCL removed and r there any other roles?

appreicate the help :smile:

Reply 1

Ourkid

Hey, hope I can help you here.

(iii) halogenoalkanes as synthetic intermediates in chemistry.
why are they synthetic intermediates and wat makes it useful?

I think synthetic intermediates are 'subproducts' of reactions which are generally highly reactive and serve as routes to getting products which can be harder to obtain via a direct route (be that due to conditions required, catalysts, or just because the direct route produces a low yield). Hence the reason why they're called intermediates.

They're highly reactive because of the halogen, which (as you go towards flourine) increase in electronegativity. This makes them more reactive, due to the production of a dipole.

outline the role of chemists in minimising damage to the environment by, for example, the development of alternatives to CFCs so that depletion of the ozone layer

r there any other roles for halogenoalkanes?

The role of chemists in minimising damage is an important one, as CFC's react with ozone molecules in free radical chain reactions. The production of free radicals makes them very reactive, where the unpaired electron tries its hardest to react and pair up.

I think the sun provides the energy to break the initial R-H (H = halogen) bond, creating the free radical in the first place.

By creating alternatives that won't take part in these chain reactions means that less ozone molecules are destroyed, and essentially means we won't be fried.

alkenes

outline the role of chemists in minimising damage to the environment by, for example, the removal of toxic waste products (such as HCl) during disposal by combustion of halogenated plastics (such as pvc)

how is HCL removed and r there any other roles?

Ok, I don't know this one, but I'm going to have a stab in the dark and suggest bubbling hydrogen chloride gas through water, producing hydrochloric acid, and selling it for a profit.

Erm, hope I've helped. If anyone notices any mistakes I've made, please let me know :wink:

w00tt

Reply 2

Eau

HCl is usually neutralised using an organic base, such as pyridine. Any excess pyridine is easily removed.

Reply 3

Ourkid

is that for hydrogen chloride gas or hydrochloric acid?

Reply 4

Eau

w00tt

is that for hydrogen chloride gas or hydrochloric acid?

Hydrochloric acid in solution.

Reply 5

Ourkid

oh ok, I thought the question was asking for Hydrogen Chloride Gas, but i suppose if you weren't to sell it, you would continue and nuetralise it :smile:

Thanks for that.
w00tt

Reply 6

Claire is a pirate

w00tt

I think the sun provides the energy to break the initial R-H (H = halogen) bond, creating the free radical in the first place.

Sorry felt the need to give extra information...

The atom which takes place in the reaction is originally a diatomic chlorine molecule. This molecule comes from a series of reactions which occur on the ice caps called the "polar flux", this involves the cold temperatures of the poles causing the CFCs to sink and stay where they are for AGES due to like six month nights or something, whilst the CFCs are there they generally fall apart a bit and produce Cl-Cl molecules, come the warmer (relativly speaking) temperatures of the six months day/summer/whatever, the chlorine molecules get enough energy to rise up into the atmosphere, specifically the tropopause region where they undergo heterolytic fission (using UV light from the sun) to form free radicals which break down the ozone layer up there.

HURRAH FOR ENVIRONMENTAL SCIENCE AND CHEMISTRY OVERLAP!

Yeah, sorry too much information, I had an urge.