organic compund

Question

Which of the following compounds CANNOT be produced directly from ethene?
A. CO2
B. ethanol
C. ethyl ethanoate
D. 1,2dibromoethane

please explain why ethanol can be produced directly from ethene?
also,explain what is catalytic dehydration

Answer 1

C. of course.
A: burning ethene in oxygen produces CO2. burning in air may produce carbon monoxide or soot (incomplete combustion). (however, WHO would make CO2in this way?)
B: passing ethene into conc. sulphuric acid followed by heating in water yields ethanol. ethene (CH2=CH2) ------ [ethyl hydrogensulphate (CH3CH2OSO3H)](not important step) ------- ethanol (CH3CH2OH)
D: i wonder why they say that it is hydrogenation. in fact, it is an addition reaction with halogen. simply adding bromine (in organc solvents) yields the product----saturated, but with no extra hydrogen.

C: yes...first produce ethanol from ethene (see B), then heat with conc. sulphuric acid and ethanoic acid (it may be produced by oxidation of ethanol by acidified potassium dichromate). ethene ------ ethanol ------- ethyl ethanoate (CH3COOCH2CH3)

2006-10-31 19:37:50 補充：
"catalytic dehydration" is a term meaning removal of water molecules from a compound by passing it through a (usually hot) catalyst.

2006-10-31 19:38:02 補充：
for example, ethanol produces ethene when allowed to pass through strongly heated pieces of broken porecelein (hope i have not spell it wrong). CH3CH2OH --------- CH2=CH2OR passing ethanol into conc. sulphuric acid will do.

Answer 2

The answer is C but I have a different explanation to the poster above:
Ethyl ethanoate has to be be made from ethanol via oxidation with potassium permanganate or Cr(II) catalysts. And ethanol is made from ethene first (see below).
Ethanol can be made directly from ethene via addition of H2O through a process called Hydration. The double bond gets protonated to give a carbocation, which then one unit of H2O is added. Then via deprotonation of the H2O unit to give the final product as ethanol.
1,2-dibromoethane is made via E2 electrophilic addition.
CO2(g) can be made from ethene via combustion with O2(g) to give CO2(g) and H2O(g) (water vapour) - extremely explosive!
I also think it's catalytic hydrogenation. This is where the double bond reacts with H2(g) that is absorbed onto the surface of palladium catalysts on activated charcol (written as Pd/C most of the time). The alkene is then attached to the surface of the catalyst with H2 units already, which are the delivered to the alkene double bond to give the hydrogenated compound ethane (with a single bond).
Hope that makes sense


2006-11-01 00:52:35 補充：
Catalytic dehydration can also be done with metalic catalysts...expensive though

Answer 3

答案： C

ethene + sulphuric acid --) ethyl hydrogensulphate ( in COLD condition)

ethyl hydrogensulphate + water --) ethanol + sulphuric acid ( in HEAT condition)


CH2=CH2 + H--OSO3H --) CH3--CH2(OSO3H) ( in COLD condition)

CH3--CH2(OSO3H) + H2O --) CH3CH2OH + H2SO4 ( in HEAT condition)


你係唔係問錯？alkene 果個應該係 catalytic hydrogenation，唔係 catalytic dehydration

catalytic hydrogenation is used to convert liquid vegetable oils to semi-soild fats in making margarine and soild cooking fats

e,g.

CH2=CH2 + H2 --) CH3CH3 ( Pt, Pd or Ni catalyst, HEAT)